February 9, 2023 • 48 mins
Daniel and Jorge talk about how close photons and protons can get to the speed of light, and what's stopping them!
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Speaker 1 (00:02):
Yeah, or hey, do you find yourself speeding up or
slowing down as we get older? Kind of both both?
How's that possible? Well, I'm faster at falling asleep on
the couch, that's true. I'm faster at finding a place
to sit down as soon as I get somewhere, But
(00:22):
I'm getting slower at the same time that time seems
to go faster. Do you think there's like a maximum
speed to that if we live to be like nine
years old, like Yoda with the years just passed by
in a blink. Well, first of all, I definitely want
to be Yoda. I don't want to look like Yoda
when I'm Somebody needs to tell Yoda about sunscreen. Although
my ears are getting bigger, but my light serious skills
(00:44):
are getting worse. As long as you can still do
those flips, well you know what he said. He said,
do or do not? There is no try. Hi am
(01:07):
or Handma cartoonists and the creator of PhD comics. Hi,
I'm Daniel. I'm a particle physicist and a professor at
U C Irvine, and I don't think I will ever
do a backflip in my whole life. Oh, I feel
bad for you. You've never done a backflip or a
front flip except underwater. I've done one underwater, but you know,
not like standing on the ground. And I feel like
I've sort of passed the age where you could like
(01:28):
learn to do that in the future. I still do backflips.
You can do a standing backflip. Yeah, that's amazing. I
think we have to see a video of that. Yeah. Well,
usually do it at those trampoline places. Yeah. I can
do backflips while skydiving. Yeah. Have you skydive? Actually have
jumped out of an airplane once? Did you do a backflip?
(01:50):
We did all sorts of crazy maneuvers, but I had
somebody strapped to my back, so it's sort of like
a double backflip. You had someone strapped to your back,
or someone had you strapped through their front. It was
basically like Baby Buern skydiving. Welcome to our podcast Daniel
and Jorge Explain the Universe, a production of My Heart
Radio in which our goal is to make your brain
and do backflips as you understand the incredible beauty and
(02:12):
mystery of our universe. We seek to dive into all
of the crazy mysteries about how things work unraveled the
explanations that humanity has discovered for what's actually out there
in the universe and what rules it is following. We
talk about all of that on the podcast and make
sure we can explain all of it to you. That's right.
It is a vast universe moving slowly and fast at
(02:35):
the same time, and we are here to help you
do those mental gymnastics to put it all inside of
your brain. We hope that you get that feeling of
satisfaction when you land that triple backflip of understanding quantum
mechanics and general relativity in squeezing all that into your brain.
Do you think we usually stick de landing on the podcast.
I think we usually stick something somewhere at the wall.
(02:56):
Usually we just throw back points at the wall and
and I hope something sticks. Thank God for good editors.
But it is a wonderful and interesting universe with all
kinds of rules in it. It seems that kind of
govern how things can happen, what things can do, what
particles and energy and forces and waves can do out there.
That gives us this interesting and very complex universe that
(03:17):
we live in, and a very human thing to do
when understanding the universe is to try to figure out
what are the rules, What are the laws, what are
the limits, what are the things that we are not
allowed to do. It's like we're still children pushing up
against the boundaries, trying to understand what's allowed and what's not.
And now we're translating that to understanding what things in
the universe can do. What is a particle allowed to
(03:40):
do when it whizzes around a black hole? How fast
can it go when it rides the shock wave from
a supernova? Wait? Are we trying to figure out the
rules so we can break them or so we can
avoid getting into trouble? What does that mean? To get
into trouble? As the universe gonna punish us if we
go faster than the speed of light. No dessert for
a week, we might get a time out from the universe.
(04:00):
No screen time for a few millennium go over the
black hole and have your time dilated. No. I think
we are trying to break the rules because that helps
us understand what the rules are. I mean, if you
think that there's a hard and past rule in physics
and then you break it, then you discover the universe
is different from the way you thought it was. And
that's exactly the process of science. That's what we are
hoping to do, right, to pull back the veil of
(04:21):
our ignorance and understand how the universe actually is. But wait,
if you break a rule, then it wasn't really a rule,
was it. No, it wasn't a rule. But then you
try to figure out what the new rule is, what
the real rule is. We hope we think that the
universe does follow some set of rules, and that we
can approximate or learn those rules over time. Well, the
(04:41):
universe definitely rules, and there are lots of amazing things
to consider and discover, including those rules themselves. It seems
like the universe does kind of have limits about what
you can and can't do in it. It certainly does.
There are things that happen in the universe and things
that just don't ever happen, And something we do a
lot in science is take to that and wonder like,
why is it a muon doesn't ever decay directly to
(05:05):
an electron? Why is it that the universe is made
of these particles and never those kinds of particles? And
we think that all of these things are clues that
there are reasons for the universe to do one thing
and never some other thing, And we're trying to uncover
those rules and deduce from them what the underlying mechanics
are of the workings of the universe. Daniel wonder if
that's a philosophically impossible task. I mean, isn't it impossible
(05:29):
to prove a negative which means you can never prove
that a rule can't be broken, which means you can
never prove that something is a rule that's certainly true.
And a great example of that is a deep question
about the nature of matter, like is matter itself stable?
We are made of protons. We think that protons might
live forever, but we don't know because we've never seen
a proton fall apart. Like you put a proton out
(05:51):
into empty space, we don't know how long they last.
We've watched a bunch of protons for a bunch of
years and none of them fell apart. That doesn't mean
that eventually one day they might all fall apart. We
can't prove that they won't, so we should just give up. Man,
you can never prove anything, you know. What we can
do is make statistical limits. We can say we're very
confident that the lifetime of a proton is longer than
(06:12):
the current age of the universe. We don't know if
it's infinity or if it's just very, very long, but
that doesn't mean we don't know anything. We certainly know
that the lifetime of our proton is not ten minutes
or one minute, right, or we wouldn't even be here.
So we can certainly learn things about the universe, even
if we can never know for sure what those rules are.
(06:33):
I am nine certain that is unsatisfactory and welcome to philosophy.
But the universe does seem to have sort of rules
that things seem to fall on. One of them. Maybe
the biggest one that affects our everyday live is the
speed of light that let me you all the time,
Like when you're going to the post office and stuff,
you're like, oh, I wish I could drive there faster.
But this dang speed of light. Yeah, I mean it
(06:54):
affects everything, right, It means there's a speed limit to
how fast things can happen. Because it doesn't just apply
to the life, It applies to everything in the universe. Right, Yeah,
that's true. It probably applies to the people listen to
this podcast because it limits how fast that download can happen.
You write, everything in the universe, all information, and all matter,
is limited to the speed of light. That means if
(07:16):
you want to download all of the Explain the Universe
back catalog and it's seven point twenty one gigabytes or whatever,
it's gonna take a while because information takes time to transit.
I wonder how many people out there cursing the speed
of light because they can't hear our voices fast enough.
One maybe or zero. I think that our voices arrive
at just the right speed. We're like wizards in the
(07:39):
Lord of the Rings. We arrived precisely when we intended
to arrive. Yeah, that's true. Although maybe people are out
there listening to us at like two x speed, and
so we already are breaking the rules. I wonder if
anyone puts this at speed of light, plate this podcast
is finished as soon as you started it. Yeah, maybe
before it started. Maybe people are out there listening to
(08:00):
us at half speed because we're going too quickly, or
maybe somebody's playing us at negative speed, which would reveal
some interesting and deep secrets about the universe. If you
play the podcast backwards, you actually hear the rules of
the antimatter universe, the anti rules of the antimatter universe,
which means what you should do, which maybe should be
any religion. I forgot what this podcast is supposed to
(08:21):
be about. Now it's about anti religion. I think we
kind of went a little off key there. It's about
the speed of light and the speed of things in
the universe. Because it's easy to be a very basic
principle in the universe, right the information, light particles, they
don't seem to be able to go faster than a
very specific number out there in the universe. Yeah, this
is a discovery made just about a hundred and twenty
(08:42):
years ago that the universe does seem to have a
speed limit. No matter how fast you're going, you throw
that baseball out of your spaceship, it will never go
faster than a certain speed. No light, no photon, no particle,
nothing in the universe, no information even seems can transfer
from one place in the universe to another faster than
this stubborn speed limit. It's fascinating, and it's forced us
(09:04):
to rethink the nature of space and time and simultaneity
and all sorts of crazy stuff. Or at least, that's
what it seems like. We haven't seen anything move faster
than the speed of light. But you gotta wonder if
maybe there are exceptions to that rule I made. There
are special situations or circumstances in which that could happen,
and so do they. On the podcast, we'll be asking
(09:26):
the question, what's the fastest that a charged particle can go? Now?
Charges is like a particle that's had a lot of coffee,
or it's just pumped up with excitement, or just the
plane of electromagnetic charge. I can't speak to the emotions
of these particles or their caffeine intake, certainly not. And
(09:49):
I think, like a molecule, caffeine is probably much much
bigger than an electron. So I don't even know how
that would work. How do electrons zip coffee? Right, there's
a philosophy question for you without an answer. Maybe if
the electron is part of the caffeine molecule technically, then
it would be supercharged. Yeah, that's right. Our electrons that
are part of caffeine, do they have a different experience
(10:10):
than electrons that are part of something heavy and slow? Yeah?
I guess it depends on whether they like coffee or not.
Are they part of a latte molecule or expressing molecule.
I think they probably have a lot of fun. But
back to the question at hand. It's interesting that there
is an overall speed limit to the universe, something that
nothing can ever exceed. But practically speaking, there are also
other limits to how fast particles can go, especially if
(10:32):
they have other attributes to them, mass or charge, and
in this case we're thinking about the old fashioned electromagnetic charge,
and so this is an interesting question, and as usually,
we were wondering how many people out there had thought
about this, whether charge particles have a different speed limit
than non charged particles. So thank you very much to
everybody out there who answers these questions on the podcast.
(10:53):
It's a lot of fun for us to hear what
you are thinking. And if you would like to share
your thoughts on the podcast, please don't be shy right
to us. Two questions at Daniel and Jorge dot com.
Just think about it for a second. How fast do
you think charge particles can go? Here's what people had
to say. My quick answer it will be like ninety
(11:13):
nine point nine of speed of light. But does just
a guess with speed of light minus plunks, constant multiply
something that makes units consistent. As far as I know,
the maximum speed would be the speed of light. And
it's only particles that have mass that cannot achieve speed
(11:35):
of light, so I think that would be the speed
of light. I suppose my answer depends on whether or
not charge particles have mass, and I'm honestly not sure
if they do or not. If they are masthless, my
I would guess that they travel at the speed of light.
But if they do have mass and their mass is
non zero, I would say they travel at a significant
fraction of the speed of light, maybe upwards of speed
of light. Uh. The fastest charge particle could move in space,
(11:58):
I would think would be the speed of light, if
not the speed of light. All right, everyone seemed to
have the speed of light as the limit, or at
least ninety nine a lot of nine in these answers.
I give it a nine out of ten for that
vault attempt. Yeah, most people seem on board the idea
(12:20):
that the speed of light is the speed limit, but
that massive particles can't reach the speed of light. So
people definitely know there's a limit to things, and that
limit is less for things that have mass, and so
the question is discharge also give them a different speed limit. Well,
let's dig into this topic generally speaking, Daniel, what is
the speed limit that the universe seems to have so
(12:42):
special relativity? Einstein's description of space and time and motion
and how all those things interact tells us that the
speed limit is the speed of light in a vacuum,
which is about three hundred million meters per second, which
is first of all, a very very fast number. It's huge, right,
three hundred million meters in a second is an extraordinary
(13:05):
distance to traverse in just one second. And on the
other hand, it's very very slow because things in the
universe are far apart. So even if you can fly
three millions in a second, it can still take you
years to get to the next star, thousands of years
to get across the galaxy, and millions of years to
get to other galaxies. Yeah, although I wassuming you don't
(13:26):
want to go that far, it is pretty much instantaneous, right,
if you're not the traveling type or want to go
to another galaxy or planet, it's pretty much instantaneous, right,
at least to our brains. Yeah, it's pretty much instantaneous.
You know, light takes about a nanosecond to go afoot,
So if you're looking at something like your computer screen,
it's about a foot away, you're seeing the computer screen
(13:49):
as it looked a nanosecond ago. But you know, the
human eye also can't really distinguish things that happen faster
than like a thirty milliseconds. So for all extents and
purpose is it's instantaneous on the sort of scale of
things that we live in, right, But I guess it
is interesting this idea that there's nothing instantaneous kind of
in the universe, right that the even light or pretty
(14:10):
much anything just information in general, things, events, the actual
existence of things can't sort of move faster in this
universe than the speed of light. Yeah, it makes our
universe local. It means that you can only be influenced
by things around you. And what we mean by around
you depends on that speed of light. If the speed
of light was much much faster than things that could
(14:33):
influence you, things that we would say are local would
be things that are also further away. If the speed
of light was much much slower than the universe would
be sort of more local. You could only be influenced
by things that were closer to you. We talked in
the podcast several times about this concept of a light cone,
the sort of cone of things in your past that
can influence you. Things that are nearby can influence you
(14:53):
fairly recently. Things that are really really far away can
only influence you from the past. Things that happen in
like Andromeda right now can't affect us, and that can
be good news. Right If aliens are building a death
ray and shooting get at us, then it won't arrive
here for quite a little while. Yeah, I feel like
it's a very philosophical question too, and an impact just
on the very nature of existence. Like a giant pink
(15:15):
unicorn suddenly appeared on top of Jupiter. To us, that
wouldn't really exist until several minutes later, right, because that
information would take some time to get to us. As opposed,
it depends on what you mean by exists. We wouldn't
know it existed, We couldn't prove that it existed, So
in that sense, it wouldn't be real in the way
that it wouldn't appear in our experiments, right, But to
(15:36):
somebody else on Jupiter, they would be able to see it, right, Yeah,
that's what I mean that for us, it wouldn't exist,
right Yeah, in the same way that if the Sun disappeared,
we wouldn't notice for eight minutes because it takes that
long for light from the Sun to reach here. So
the universe as we see it is not the universe
as it is right now. And more deeply, relativity says
(15:57):
that there is no sort of universal definition of right now,
that time and the universe depends on where you are
and how fast you are going. This sort of requires
us to give up this concept that there is a
universe that's marching forward in time uniformly, sort of an
ancient Newtonian view, right. And so it's called the speed
of light, but it should actually be called the speed
(16:19):
of anything in the universe. We just call it the
speed of light because basically light is the only thing
we know that can go at that speed, or the
first thing we knew that could go at that speed. Yeah,
it really should be called the speed of everything, or
maybe the speed of anything. But it's the sort of
maximum speed limit of any kind of information, any field.
For example, in the universe, when it wiggles, information can't
(16:40):
move through that field faster than the speed of light,
and so that limit applies to every field, including the
electromagnetic field, for which photons are a ripple in that field,
and because they have no mass, they can move at
that maximum speed. It's true for any massless ripple in
a field. So, for example, we think that gravitational waves
travel at the feed of light as well, because those
(17:01):
ripples in the gravitational field, or equivalently, ripples in the
curvature of space, so we think those also move at
the speed of light. And if there are other particles
out there we haven't discovered that are massless, they would
also move at the speed of light. Are there other
particles we've discovered that are massless gluons, which are the
particles that helped transmit the strong force. They are also massless,
(17:22):
so they move at the speed of light. But gluons
are weird because they interact very strongly with themselves, and
so you never sort of see a gluon by itself.
They conform weird states like glue balls, but those have
energy inside of them, so they have mass, So the
glue balls don't move at the speed of light, even
if individual gluons do. Interesting, so photons are the only
(17:43):
particles that we know of that can move at the
speed of light. Well, I think gluons count is moving
at the speed of light, even though they don't go
very far. Gravitational waves aren't a particle. If gravity is
quantized and made of gravitons, then those are probably massless
and would move at the speed of light. But we
don't know if gravitons exist. Yeah, so, so technically photons
are the only particle we know of. What do you
(18:03):
have against gluhons? You know, then you say a little
while ago that they don't quite you don't never see
them move with the speed of light. Yeah, you can't
like shoot a gluon across the universe and have a
travel like a photon. But you know a gluon which
is exchanged between two quarks, that does happen at the
speed of light. The speed of information of the strong
force is the speed of light. All right, Well, photons
(18:24):
and gluons, I guess they they're stuck together in that category.
But again, maybe give us an into the sense. What
does it mean to move at the speed of light?
What is it like? It's a fun question. What is
it like to move at the speed of light. You
would like to be able to put yourself in that
frame and say, I'm moving along with a photon. What
is the photon? See? It's not something you can really
(18:44):
do because photons don't have a frame. Like if a
spaceship is flying by the Earth, you can put yourself
in this frame where the spaceship is at rest and say, okay,
I'm moving with the spaceship. What do I see? I
see the same thing as the spaceship. You can't do
that with a photon because the photon is never at rest.
There's no like frame you can put yourself in to
say I'm moving with the photon. Photons always move at
(19:06):
the speed of light relative to anybody, So no matter
where you are in the universe and how fast you're going,
that photon is zipping away from you at the speed
of light, and so you can't sort of like put
yourself in the point of view of a photon. M mmm.
So there's sort of like pure motion, right, because they
don't have mass, so they don't have a substance to them,
so all of their energy is in their speed. Yeah,
(19:27):
all of their energy is in their speed exactly. They
are just motioned. There's nothing to them, Like if you
could catch up with a photon, it was sort of
disappear in a puff of motionlessness. You know, they are
only motion, but it's it's like a wiggle in the
like a kinetic field. Right, Yeah, it's the motion of
that field. But isn't it a wiggle like a little perturbation. Yeah,
(19:49):
pure kinetic energy. Right, And people right in they're confused
about that because they say, well, it's energy, and energy
is mc squared, So doesn't that mean the photon has mass? Right?
And the wrinkle there is that equals mc squared only
applies to particles at rest, because the m there applies
to its rest mass. There's another term there which we
don't often talk about. The full equation is like E
(20:10):
squared equals M squared c to the fourth plus p
squared c square. There's a term there for momentum, and
so for a particle that has mass and momentum, there
are two terms there. There's the mass term and the
momentum term. Photons don't have any mass, so they just
have the momentum term. The equation for photon is E
equals pc momentum times the speed of light. So photons
(20:33):
are really weird because they don't have mass, but they
do have momentum, so they can like push things. Right,
that's how solar sales work. Right. They catch sunlight and
they transfer that momentum to motion, and that's how you
can sail out of the solar system. So photons do
have momentum and they go at the speed of light,
but there are a couple of caveats to that, maybe
(20:55):
not just for photons, but for everything else. Let's dig
into the ways that the rules that don't apply. But first,
let's take a quick break. All right, we're talking about
(21:16):
the speed limit of the universe and how it applies
to a charged particle, because I guess the charged particle
is a little bit different. Yeah, particles that have charge
also have mass, and the rules for massive particles and
for charge particles are a little bit different than the
rules for massless chargeless photons. Yeah, we've been talking about
(21:37):
how the speed limit applies to photons, which I guess
it does, but it almost only applies to photons and
I guess gluons. But it limits how fast photons can go.
But there are caveats to that rule. Right, it's not
necessarily the case that photons go at the speed of light. Yeah,
there are caveats to that rule. When we say that
photons always travel at the speed of light, when we mean,
(22:00):
but we don't often say, is that that's true in
your local inertial frame. If space is not curved, basically
the playground of special relativity, operate in flat space and
have things whizzing around near each other, that's what you're
going to observe. But if space is curved or expanding,
or things are really really far away from you, then
(22:21):
you can no longer apply those rules, and things start
to get really weird. It seems like a very limiting
caveat I mean local flat space. That's almost never true.
And if you're there, then you're bending space, which means
it doesn't apply to that's true, although you're not that massive,
and so you don't really bend space. Oh thanks, I've
(22:42):
been working out, and no matter how curved the universe is,
you can always find a locally flat approximation to it. Right,
space is always flat. In a local approximation, you can
always put a tangent on some surface and say, oh,
in this vicinity, I can assume I'm in flats space,
and that's sort of the issue is that special relativity
(23:02):
applies in our local vicinity where we can assume things
are flat, but then over larger distances we can't really
make that assumption, and that's why things break down. Well,
I guess the question is how do they break down
when when space is not flat, when it's a little
curved or a lot curve, does like go faster than
the speed of light or slower than the speed of light.
The space is curved between you and another galaxy, then
(23:24):
you have two different frames. You have your frame, you
have the frame in that galaxy, and how you translate
velocity from one frame to another is a little bit arbitrary.
You can do it in lots of different ways because
space is curved between you. We talked about this once
in the podcast. That has to do with like comparing
whether two vectors are parallel and comparing their length, and
(23:46):
if space is curved between two points, then how you
move that vector over that space depends on the path
that you've taken. So it's sort of not well defined
in the sense that there's like many ways that you
could do it and get different and service so you
can't really compare velocities in two different frames, if this
curvature or expansion between them. Yeah, it gets really tricky
(24:09):
and complicated, and we spend a whole hour talking about this.
I remember, but I guess what's the takeaway? There are
many ways to compute the velocity of a photo going
from between here and another galaxy. But do some of
these solutions tell you that this light is moving faster
or slower than the speed of light? Or do they
all tell you it's moving slower than the speed of light?
Some of them tell you that those photons are moving
faster than the speed of light, and some of them
(24:30):
tell you that the photons are moving slower than the
speed of light. So there's an infinite number of ways
that you could do this, compare velocities in one galaxy
to another because there are different reference frames. There's also
sort of a standard way that we do it, which
is that we just try to like extrapolate our frame
out to the end of the universe, even though we
know that doesn't really work. And those galaxies are moving
away from us faster than the speed of light, so
(24:51):
things seem to be breaking that speed of light limit.
Because you've done this thing of extending your inertial frame
out to the end of the universe, which you're not
technically allowed to do. The other way you can look
at it is to say they have their frame, we
have our frame, and space is expanding between those frames.
So nothing's breaking the speed of light limit. It's just
that space itself is growing and in its own frame,
(25:11):
everything is moving less than the speed of light. That's
what I mean when I say there's like different ways
you could assign that velocity. They're all sort of reasonable
and give you different answers. So there are those important capiats,
But in your local inertial frame, like your the laboratory,
the measurements you're going to actually make, you're never going
to observe anything going faster than the speed of light.
M M, I see. So even the local bending of
(25:32):
space can only slow down the speed of light. Is
that what you're saying? Like, if I'm orbiting a black hole,
for example, and space has really warped around me and
I run those experiments, what what would I see there?
I think you're breaking the assumption because we're talking about
a local flat frame, and if you're near a black hole,
then you're definitely not in a local, flat frame. So
I would say that if your space is pretty local
and pretty flat, you're always going to see photons moving
(25:55):
at the speed of light. So there's one caveat we
haven't talked about yet. But if you are near a
black hole or something else than spaces bendy and crazy
and the velocities get insane, and you could see photons
moving at zero velocity. For example, as a photon climbs
out of the gravity well or tries to climb out
of the gravity well of a black hole, to you,
it appears to go at zero velocity. Right, photons are
(26:17):
contained within a black hole. How could they do that
if they were moving at the speed of light Because
the bending nous of space there makes all these velocities
a little wonky to calculate. But would you ever see
it go faster? Probably not right. That only happens when
you have space expanding. Yeah, I believe that's true. The
bending of space can only effectively slow down the speed
(26:39):
of light that you observe. In order things to appear
to go fasten the speed of light, you need space
to expand rather than to curve. Well, there's another caveat
to this also is that the space has to be empty. Yes,
that's right. The limit that we talk about is the
speed of light in a vacuum, as if there's nothing
out there in space for these photons to interact with.
But we know that light slows down as it passes
(26:59):
through material hills or at the index of refraction tells
you the speed of light through that material. So light
traveling through glass goes slower than light traveling through a vacuum,
Like traveling through air goes a little bit slower than
light traveling through a vacuum. And that's not because somehow
the air molecules or the glass molecules like effect the
space that the light travels in. It's because light keeps
(27:21):
running into things, right, like trying to move through a
crowded room. The float that keeps bumping into the air
and glass molecules and then getting re emitted on the
other side. But it still has to sort of something
has to happen when they bump. The speed that we're
talking about here is basically the average speed from one
side of the material to the other side of the material.
You can think about it as the light sort of
zig zagging between molecules or atoms that it's interacting with
(27:44):
each of those zigs or each of those zags, it's
still moving at the speed of light. Of photon is
always moving at the speed of light, but it sort
of gets absorbed. It takes time to get re emitted,
and so that sort of slows it down. It's like
if you send your teenager on an errand to the
store and they stop and chat at their friends house
every block, it's can take them a lot longer to
get there, even if they're driving at top speed between
(28:05):
all of their friends houses. That's an interesting neighborhood you
live in where your teenagers is driving and stopping to
talk to their friends at the same time. Hopefully they
are being the speed limit there. Fortunately, I don't have
teenagers who can drive yet, so maybe my analogies will
improve when I have some data. So it's if space
is empty and it's not bend deep or distorted or expanding,
(28:29):
then light goes at the speed of light. But now
what about particles that are not light? Pretty much everything
else besides gluons. What if a particle, for example, has mass. Yes,
so photons can go with the speed of light if
they're in a vacuum and not near a black hole,
for example. But electrons, particles with mass, they can never
actually reach the speed of light. Oh yeah, is there
(28:50):
a particular reason for that. It's sort of interesting and philosophical.
It's not like there's a lower speed limit for electrons.
It's not like electrons can only go speed of light
and they're always pegg there. It's just that they ask
emp tonically can approach the speed of light, So there's
no actual limit there. They just get closer and closer
and closer to the speed of light as you add
more energy, but they never actually get to the speed
(29:14):
of light. Yeah, that's weird. So you're saying that it's
a speed limit, not because like if I just create
an electron or a proton or a cord going at
the speed of light, maybe can that can happen. It's
just that for any electron or a particle with mass
that starts address I can, I can never get it
to the speed of light. A particle with mass moving
(29:34):
at the speed of light would have infinite kinetic energy.
So if you could create a particle with infinite kinetic energy,
then yes, it would be moving at the speed of light. Otherwise,
taking a particle and getting it to the speed of
light would require giving it infinite kinetic energy. And the
key concept, of course is that these particles have mass.
So why is it that having master means that you
require infinite energy to get to the speed of light,
(29:55):
whereas a photon with a non infinite energy can move
at the speed of light it and the key concept there,
of course, is the mass of the particle. Mass is
this property of particles like resist changes to their motion.
So you have an electron, it's gonna stay at rest
unless you give it a push, and it's going to
stay at certain velocity unless you give it a push.
And mass is that ability to resist changes in motion.
(30:18):
So it takes energy to speed it up. So you
give the electron to push, it speeds up as it
gets faster and faster, though it takes bigger pushes more
energy to take it up the next level and speed.
It's not a linear relationship, right, And that's just kind
of how the universe is, right, Like, that's just what
mass is. It's not like they have mass and therefore
(30:38):
they're hard to push the more you go. It's like
the definition of mass is the fact that some particles
gets harder and harder to push. Yeah, I think it's
important to understand what things we understand and what things
we just like observe and define. Right. We have observed
that things that have internal energy in them have this
property of inertia. An electron has some internal energy to it,
(31:00):
protons have some internal energy to it, the mass of
the corks and then also the mass of the binding
energy between the corks. Anything with internal energy seems to
have this property of inertia, of resisting changes to its motions.
So yeah, sort of a deep philosophical mystery why that is,
Why do we live in the universe that way and
not some other way? But it's something that we've observed
in the universe and try to describe in our theories,
(31:21):
and those theories are very effective when we test them
out in nature, So that's why we believe they are true,
even if we don't know why the universe is this
way and not some other way. Yeah, it's a massive issue.
And how is this related to the Higgs boson and
the Higgs field, because I know everyone talks about how
the Higgs field is what gives particles mass. Is this
inertial mass that's related to the speed of light, related
(31:43):
to the Higgs field and Higgs boson. So most generally
mass is just internal stored energy of some kind, and
most of the mass in your body doesn't come from
the mass of the particles of your body. So for example,
you're mostly protons and neutrons, and those protons have massive
from their corks, but they also have mass from how
those corks are bound together. So the internal stored energy
(32:06):
the proton is mostly the energy of those particles bound together.
A little bit of the mass of the proton does
come from the mass of those particles, like the corks
that are inside the proton, and those corks they get
their inertial mass from the Higgs boson, but again it's
internal stored energy. The corks themselves, like the true theoretical object,
is massless, but as the cork moves through the universe,
(32:28):
it interacts with this Higgs field and it creates this
like effective cork, this object which is moving differently because
of its interactions with the Higgs field in such a
way that it moves as if it had mass. So
it is inertial mass that we're talking about, and some
of the inertial mass in the universe comes from the
Higgs boson, but not all of it, right, In fact,
most of it doesn't come from the Higgs field and
(32:48):
Higgs boson. Most of it just comes from this fact
of the universe that things with energy are are hard
to move in the universe and impossible to get moving
at the speed of light. Yeah, exact, you often hear
their frame that as things approach the speed of light,
they get more massive, as if like an electron is
getting as heavy as a car for example, if it
(33:09):
goes near the speed of light. And as some sort
of an old fashioned idea that is trying to convey
to you this concept that as something approaches the speed
of light, it takes more energy to move it up
in velocity than it did when it was moving slower.
We don't really think about things literally gaining mass. It's
just that it takes a bigger push to notch them
up to the next level of velocity. Right, Although it's
(33:30):
kind of true, right, I mean, the idea is that
mass is the resistance to movement or to increasing your movement.
Then yeah, as it gets harder, because the universe, as
it gets harder, technically it is sort of gaining mass, right,
It doesn't really hang together though, Like if you want
to use that mass and F equals m A, it
doesn't really work because then that mass is like weirdly
(33:51):
directionally dependent, because if you're moving along the x axis
for example, now you have like a lot of mass
along the x axis, but you don't have that mass
along the y axis, right, Like turnting can give you
a push along the y axis with a certain force
and you get one acceleration, but if they give you
a push along the x axis with that same force,
they get a different acceleration. The more general way to
(34:12):
think about it is just in terms of momentum. This
this equation for relativistic momentum which includes this factor. So
we just leave mass as the rest mass of an object,
like how massive would it be if it was at rest,
and this extra resistance to accelerating at high speeds. We
fold that into the definition of momentum, which then helps
fix up F equals I may, which in the end
(34:33):
is just F equals the derivative of momentum with respect
to time. So this is whole topic of relativistic kinematics,
which I think we dug into in another episode. Yeah,
I think what you're trying to say is that an
electron looks less massive depending on which angle you're looking
at it, Like the electron has a good angle and
a bad angle. I think the concept of relativistic mass
(34:53):
things actually getting heavier as you get to higher mass,
doesn't really hang together if you try to propagate it
through all the equations. But it's sort of an old
fashioned way of thinking about things. All right, that's how
mass effects how fast you can go in the universe.
Now let's talk about how other things might affect how
fast you can move through the universe, including whether space
is empty or not. So let's get into that. But
(35:14):
first let's take another quick break. All Right, we're asking
the question what is the fastest that a charge particle
or pretty much any particle can go, right, because there
(35:35):
are a lot of caveats to this idea that nothing
can move faster than the speed of light. One of
those caveats was that space had to be empty. But
what happens if space is not empty? Yeah, we talked
about photons moving through glass, photons moving through water, but
you might imagine, well, what about space between here and Andromeda?
For example? That's mostly empty, right, Or what about the
space outside of Earth in our solar system that's mostly empty? Right?
(35:58):
Photons surely spend most of their time whizzing around basically
at the speed of light. What turns out, space is
almost never empty. The space in our solar system is
filled with particles from the Sun. The Sun pumps out
a solar wind of protons and electrons and other stuff
that's always blowing through the Solar system. So photons traveling
through our solar system are constantly running into these protons
(36:19):
and these electrons and interacting with them. Really interesting. So
you're saying, like the space between us and the Sun
is not perfectly clear. There's all kinds of stuff in it,
which means that the speed of light in our solar
system is slower than the speed of light, a tiny, tiny,
tiny little bit slower. This is very dilute. Is like
not very many protons per cubic meter, you know, between
(36:39):
us and Jupiter, for example, but there are some. And
so if you're talking technically, like our photons that bounce
off Jupiter and then come back to Earth, are those
moving at the speed of light? Technically they're moving at
a little bit less than the speed of light. And
that's also true for photons from Andromeda, for example, because
the space between us and other galaxies is also not empty, right, yeah,
(37:01):
because there's a lot of stuff in between us and
and Drama. Not. Even though it's hard to see what
the naked eye, you probably imagine the university these clusters
of stars grouped into galaxies, and that's basically where everything is.
But don't forget that the universe is mostly gas, right.
Stars are a tiny fraction in the universe, So really
you should be thinking about the gas in those galaxies,
and it's also gas between the galaxies. Think of the
(37:24):
universe not as a bunch of dots of stars clustered
into galaxies, but like a cosmic web of gas filaments,
and where those filaments overlap and intersect, then you have
these deep pools that form stars and visible light and
all that cool stuff. But between the galaxies there are
these very long tendrils of gas between Us and Andromeda,
for example, a huge amount of gas. They estimate like
(37:45):
a significant fraction of all the matter in the universe
are kind of matter is actually between galaxies, not in galaxies. Yeah,
like of the matter in the universe is basically small, right, Yeah,
they call this the warm hot intergalactic medium. I'm not
even gonna talk about why they call it warm hot.
(38:08):
But the acronym for it is w H I M,
which you know, they didn't choose on a whim, but
they did because it spells out whim. It's just a
whimsical name, you know, for something that's warm hot. Now,
why do they call it warm hot because it's not
cool warm. They call it warm hot because it's sort
of between warm and hot. And remember, if you were
out there in space, you would freeze your tissue off.
(38:29):
But these particles are fairly high speed, and so we
say that they have a fairly high temperature. This intergalactic
plasma can actually be fairly hot on a temperature scale,
even though it's very very dilute, so it doesn't contain
a lot of heat. But because of the speed of
the particles, they say it's fairly hot, not fast enough
to call it actually hot, not slow enough to call
(38:49):
it is warm. So it's sort of like warm too hot,
So they call it warm hot. It's not a whim
or a hymn, it's a whim. It should be W
T H I M, but then it'll be like with them,
I get the lukewarm intergalactic medium, wouldn't really fly there, No,
I suppose not, And so that slows down photons that
are moving through the universe between galaxies. So when you're
(39:12):
looking up at the night sky and know that all
the photons that are traveling towards you were traveling a
little bit less than the speed of light, even the
ones coming from other galaxies. But wait, wait, wait, isn't
the space between our galaxies also expanding? So space everywhere
is expanding, right, and the expansion happens simultaneously at every
point in space at the same rate for things are
(39:32):
near each other. However, that's a pretty small effect. And
also things that near each other have gravity, so the
gravity and Dromeda is actually pulling it towards us faster
than space is expanding between us. So you can basically
ignore the expansion of space when you're thinking about photons
from Andromeda, because they're like in our local gravitational bubble, right,
But it's it's still expanding, which is speeding up the
(39:53):
speed of light a little bit. But you're saying that
the effect of the whimsical gas in between is slowing
it down more than the expand sin is speeding it up. Yes,
so the expansion would be moving and Dromeda away from us,
but gravity is holding Andromeda in place, sort of the
same way that gravity holds the Earth around the Sun.
You're right there, the photons from Andromeda are moving through
expanding space. Because they're moving towards us, that would actually
(40:13):
be slowing down their effective speed. Okay, now let's talk
about charge particles. We know that particles with mass have
extra limitation with respect to the speed of light, and
we know that space is not empty. Does having a
charge affect you more than having mass? Like, does it
somehow give you a boost through this plasma or does
it slowly down more? Well, interestingly, there are no particles
(40:37):
that have charge and don't have mass. Right so the
photon has no charge and no mass. But if you're
a charge particle number one, that means that you have
mass like the electron and the corks. All the particles
that have charged also have mass, So that right away
means if you have charge, you can't go at the
speed of light. Really wouldn't that make you think they're
somehow related? Yeah, it's a really fascinating clue and one
(40:57):
that we just don't understand at all. Possible that one
day in the future we will discover a massless charged particle,
but none exists currently in our universe that we know about. Well,
gluons have charged, they just don't have electromagnetic charge, right,
that's right. They have color charge charged for the strong force. Yeah,
that's a really good point. And we do sometimes discover
(41:18):
new categories of particles, like the Higgs boson was a
particle like no particle we had seen before. It's the
first scale or particle that we've ever found before, a
particle without any spin. And so it's possible to discover
new categories of particles that we haven't seen before in
the universe, or we might discover that that's impossible for
some reason we haven't learned yet. But the higgs boson
(41:39):
has massed to it, right, it interacts with itself, but
it does the higgs boson have charge. The higgs boson
doesn't have electric charge. No, But it was interesting because
it also doesn't have quantum spin like all the other
particles do. So the higgs boson does have mass but
no charge. The higgs boson has mass but no charge.
But we don't have any particles that have charge but
no mass. Oh, it seems so if you have charge,
(42:01):
then you usually have mass. That's the pattern so far.
We don't know if that's a hard and fast rule
or just sort of like a coincidence or electromagnetic charge.
I should say, right, yes, exactly, electromagnetic charge. So now,
if you're a proton flying through space on an electron
flying through space, you obviously can't move at the speed
of light just because you have mass. So if you're
(42:21):
charged particle, that also means you have mass, which means
you can't travel at the speed of light. How does
the charge affect your motion? Does it make you go
faster or slower through this plasma in the universe? Well? Both.
First of all, it allows you to go really fast
because having a charge means that you can get accelerated
by cosmic electric fields or magnetic fields. For example, you
can be near a black hole or a pulsar, which
(42:42):
have very very strong magnetic fields and you can gain
huge acceleration. And so it allows you to sort of
like tap into cosmic accelerators to get to really really
high energies. But then on the flip side, it also
slows you down because particles that have charge interact with photons,
and the unit verse is filled with photons, if photons
(43:02):
left over from the Big Bang, from the cosmic microwave
background radiation that's everywhere in the universe, and so charge
particles flying through the universe interact with those photons, which
constantly sap their energy. Mm I think you're saying that.
You know, if you have charge, that means that you
can be pulled by something that has the opposite charge
(43:23):
ahead of you, right, But it could also maybe slow
you down if the thing is behind you. Absolutely could.
You have magnetic fields and electric fields from cosmic objects
can accelerate or decelerate these particles. But also just the
whole universe is filled with a fog. If you're an
electron and you're flying through the universe, there really is
no empty space. You see photons everywhere and they're all
interacting with you. And there's this effect that if a
(43:44):
particle is moving really really really really really fast, then
it tends to interact with this cosmic microwave background photons
in a way that SAPs its energy and turns it
into other particles. And so there's basically like an effective
limit to how fast a charge particle can move through
the universe because of its interaction with the cosmic microwave
background radiation. Meaning like, if I'm a proton flying through
(44:07):
space and uh I hit a photon head on, it's
going to slow me down, right, because the photon has momentum. Right,
You're gonna interact with that photon, and some of your
energy is going to get used up to create a
new particle, like a delta particle or some other low
mass particle, and then you can go fly off in
another direction, but you've lost some of that energy. What
if the photon hits you from behind, when did it
(44:27):
push you? Yeah, that's possible, and photons move faster than protons,
so they can catch up to a proton and give
it a little push. But the overall effect from a
proton like flying through this fob of photons, is that
it gets slowed down. It's like compressing the space in
front of it. You mean, like, there's an average speed
of all the photons in the universe, and if you're
(44:47):
going faster than that average speed, then you'll hit the
photons kind of like bugs in your windshield. I'm not
sure how to calculate the average speed of a photon.
But think about like the number of directions that a
photon could hit you. In. Most of the those ways
it would slow you down. In only a few ways
they would speed you up because you're you're moving in
a certain direction relative to the maybe the average direction
(45:08):
of all the photons. Yeah, that's right. And also, as
you move really fast through space, you tend to contract
the space in front of you, which increases the density
of the photons in front of you that you're hitting.
So there's a special relativistic effect there also, And what
this means is that really really high energy particles gets
slowed down. So we have cosmic accelerators out there, the
centers of galaxies and pulsars whatever, spewing out super high
(45:31):
energy charged particles, but then they basically screeched to a halt.
It's really really hard to have charged particles a crazy
high energy in the universe because the universe is kind
of like sticky for those charged particles. And that means
something really cool. It means that if you see one
of these particles, it can't have come from very far
away because very very high energy particles can't go very
(45:51):
far at our universe, they're sort of local, or they
started off with a super duper duper crazy amount of
energy to start with. Yeah, exactly, they would have to
have double bonkers energy if they come from really far away.
So you're saying that the whole universe is filled with
a little bit of light pollution, which kind of slows
everything down, makes it even harder to go at the
speed of light. And as time goes on, that light pollution,
(46:14):
the cosmic microwave background radiation is cooling, and so this
effect is fading because the universe is expanding, that light
is cooling, it's getting more and more dilute. So as
time goes on, the universe gets like less sticky for
charge particles, which means that these charged particles, these protons
coming out of cosmic accelerators can go faster and faster
as time goes on, or further and further at their
(46:36):
top speed. You mean like this light pollution of the
universe is kind of dissipating in a way. Yeah, precisely.
The fog is clearing very very slowly, Isn't the universe
also filled with like quantum vacuum energy, like particles popping
in and out. All space has quantum fields in it,
and those quantum fields can never relax down to zero,
so there's always some energy and space. We think that's
(46:59):
very very small. We also think that might be what's
causing the expansion of the universe. It's not something that
we understand very well. So then, if something is flying
through space, does it interact with those that vacuum quantum
fields particles popping up? It doesn't necessarily slow it down,
It just gives it inertia. So interacting with the Higgs
field is how the particle gets mass. It doesn't have
(47:20):
to slow it down. So it's possible to interact with
these quantum fields without slowing down. All right. Well, then
now to wrap it up and to answer the question
we set out to answer at the beginning, Daniel, what's
the fastest that a charge particle can go? Super duper
duper duper duper fast, but not actually the speed of
light and not for very far in the universe? You mean,
po Yeah, there's no actual limit, right, These particles can
(47:45):
keep approaching the speed of light but never actually get there.
And for charge particles, they just can't do it for
very far. So even if I did a perfect backflip
at the Olympics. You would only give me a nine.
I would give you a warm hot score. Yes, our right. Well,
another reminder that the universe has these strange rules. If
you think about them, they're kind of strange. But that's
(48:07):
kind of the job that we as humans have is
to figure out what are the rules and when can
you break them? And that's the job of us experimentalists
to go out there and actually try to break the
rules of the universe. All right, Well, we hope you
enjoyed that. Thanks for joining us, See you next time.
(48:30):
Thanks for listening, and remember that Daniel and Jorge explain
the Universe is a production of I Heart Radio. For
more podcast from my heart Radio, visit the i heart
Radio app, Apple Podcasts, or wherever you listen to your
favorite shows. Yeah,
Yeah, or hey, do you find yourself speeding up or
slowing down as we get older? Kind of both both?
How's that possible? Well, I'm faster at falling asleep on
the couch, that's true. I'm faster at finding a place
to sit down as soon as I get somewhere, But
(00:22):
I'm getting slower at the same time that time seems
to go faster. Do you think there's like a maximum
speed to that if we live to be like nine
years old, like Yoda with the years just passed by
in a blink. Well, first of all, I definitely want
to be Yoda. I don't want to look like Yoda
when I'm Somebody needs to tell Yoda about sunscreen. Although
my ears are getting bigger, but my light serious skills
(00:44):
are getting worse. As long as you can still do
those flips, well you know what he said. He said,
do or do not? There is no try. Hi am
(01:07):
or Handma cartoonists and the creator of PhD comics. Hi,
I'm Daniel. I'm a particle physicist and a professor at
U C Irvine, and I don't think I will ever
do a backflip in my whole life. Oh, I feel
bad for you. You've never done a backflip or a
front flip except underwater. I've done one underwater, but you know,
not like standing on the ground. And I feel like
I've sort of passed the age where you could like
(01:28):
learn to do that in the future. I still do backflips.
You can do a standing backflip. Yeah, that's amazing. I
think we have to see a video of that. Yeah. Well,
usually do it at those trampoline places. Yeah. I can
do backflips while skydiving. Yeah. Have you skydive? Actually have
jumped out of an airplane once? Did you do a backflip?
(01:50):
We did all sorts of crazy maneuvers, but I had
somebody strapped to my back, so it's sort of like
a double backflip. You had someone strapped to your back,
or someone had you strapped through their front. It was
basically like Baby Buern skydiving. Welcome to our podcast Daniel
and Jorge Explain the Universe, a production of My Heart
Radio in which our goal is to make your brain
and do backflips as you understand the incredible beauty and
(02:12):
mystery of our universe. We seek to dive into all
of the crazy mysteries about how things work unraveled the
explanations that humanity has discovered for what's actually out there
in the universe and what rules it is following. We
talk about all of that on the podcast and make
sure we can explain all of it to you. That's right.
It is a vast universe moving slowly and fast at
(02:35):
the same time, and we are here to help you
do those mental gymnastics to put it all inside of
your brain. We hope that you get that feeling of
satisfaction when you land that triple backflip of understanding quantum
mechanics and general relativity in squeezing all that into your brain.
Do you think we usually stick de landing on the podcast.
I think we usually stick something somewhere at the wall.
(02:56):
Usually we just throw back points at the wall and
and I hope something sticks. Thank God for good editors.
But it is a wonderful and interesting universe with all
kinds of rules in it. It seems that kind of
govern how things can happen, what things can do, what
particles and energy and forces and waves can do out there.
That gives us this interesting and very complex universe that
(03:17):
we live in, and a very human thing to do
when understanding the universe is to try to figure out
what are the rules, What are the laws, what are
the limits, what are the things that we are not
allowed to do. It's like we're still children pushing up
against the boundaries, trying to understand what's allowed and what's not.
And now we're translating that to understanding what things in
the universe can do. What is a particle allowed to
(03:40):
do when it whizzes around a black hole? How fast
can it go when it rides the shock wave from
a supernova? Wait? Are we trying to figure out the
rules so we can break them or so we can
avoid getting into trouble? What does that mean? To get
into trouble? As the universe gonna punish us if we
go faster than the speed of light. No dessert for
a week, we might get a time out from the universe.
(04:00):
No screen time for a few millennium go over the
black hole and have your time dilated. No. I think
we are trying to break the rules because that helps
us understand what the rules are. I mean, if you
think that there's a hard and past rule in physics
and then you break it, then you discover the universe
is different from the way you thought it was. And
that's exactly the process of science. That's what we are
hoping to do, right, to pull back the veil of
(04:21):
our ignorance and understand how the universe actually is. But wait,
if you break a rule, then it wasn't really a rule,
was it. No, it wasn't a rule. But then you
try to figure out what the new rule is, what
the real rule is. We hope we think that the
universe does follow some set of rules, and that we
can approximate or learn those rules over time. Well, the
(04:41):
universe definitely rules, and there are lots of amazing things
to consider and discover, including those rules themselves. It seems
like the universe does kind of have limits about what
you can and can't do in it. It certainly does.
There are things that happen in the universe and things
that just don't ever happen, And something we do a
lot in science is take to that and wonder like,
why is it a muon doesn't ever decay directly to
(05:05):
an electron? Why is it that the universe is made
of these particles and never those kinds of particles? And
we think that all of these things are clues that
there are reasons for the universe to do one thing
and never some other thing, And we're trying to uncover
those rules and deduce from them what the underlying mechanics
are of the workings of the universe. Daniel wonder if
that's a philosophically impossible task. I mean, isn't it impossible
(05:29):
to prove a negative which means you can never prove
that a rule can't be broken, which means you can
never prove that something is a rule that's certainly true.
And a great example of that is a deep question
about the nature of matter, like is matter itself stable?
We are made of protons. We think that protons might
live forever, but we don't know because we've never seen
a proton fall apart. Like you put a proton out
(05:51):
into empty space, we don't know how long they last.
We've watched a bunch of protons for a bunch of
years and none of them fell apart. That doesn't mean
that eventually one day they might all fall apart. We
can't prove that they won't, so we should just give up. Man,
you can never prove anything, you know. What we can
do is make statistical limits. We can say we're very
confident that the lifetime of a proton is longer than
(06:12):
the current age of the universe. We don't know if
it's infinity or if it's just very, very long, but
that doesn't mean we don't know anything. We certainly know
that the lifetime of our proton is not ten minutes
or one minute, right, or we wouldn't even be here.
So we can certainly learn things about the universe, even
if we can never know for sure what those rules are.
(06:33):
I am nine certain that is unsatisfactory and welcome to philosophy.
But the universe does seem to have sort of rules
that things seem to fall on. One of them. Maybe
the biggest one that affects our everyday live is the
speed of light that let me you all the time,
Like when you're going to the post office and stuff,
you're like, oh, I wish I could drive there faster.
But this dang speed of light. Yeah, I mean it
(06:54):
affects everything, right, It means there's a speed limit to
how fast things can happen. Because it doesn't just apply
to the life, It applies to everything in the universe. Right, Yeah,
that's true. It probably applies to the people listen to
this podcast because it limits how fast that download can happen.
You write, everything in the universe, all information, and all matter,
is limited to the speed of light. That means if
(07:16):
you want to download all of the Explain the Universe
back catalog and it's seven point twenty one gigabytes or whatever,
it's gonna take a while because information takes time to transit.
I wonder how many people out there cursing the speed
of light because they can't hear our voices fast enough.
One maybe or zero. I think that our voices arrive
at just the right speed. We're like wizards in the
(07:39):
Lord of the Rings. We arrived precisely when we intended
to arrive. Yeah, that's true. Although maybe people are out
there listening to us at like two x speed, and
so we already are breaking the rules. I wonder if
anyone puts this at speed of light, plate this podcast
is finished as soon as you started it. Yeah, maybe
before it started. Maybe people are out there listening to
(08:00):
us at half speed because we're going too quickly, or
maybe somebody's playing us at negative speed, which would reveal
some interesting and deep secrets about the universe. If you
play the podcast backwards, you actually hear the rules of
the antimatter universe, the anti rules of the antimatter universe,
which means what you should do, which maybe should be
any religion. I forgot what this podcast is supposed to
(08:21):
be about. Now it's about anti religion. I think we
kind of went a little off key there. It's about
the speed of light and the speed of things in
the universe. Because it's easy to be a very basic
principle in the universe, right the information, light particles, they
don't seem to be able to go faster than a
very specific number out there in the universe. Yeah, this
is a discovery made just about a hundred and twenty
(08:42):
years ago that the universe does seem to have a
speed limit. No matter how fast you're going, you throw
that baseball out of your spaceship, it will never go
faster than a certain speed. No light, no photon, no particle,
nothing in the universe, no information even seems can transfer
from one place in the universe to another faster than
this stubborn speed limit. It's fascinating, and it's forced us
(09:04):
to rethink the nature of space and time and simultaneity
and all sorts of crazy stuff. Or at least, that's
what it seems like. We haven't seen anything move faster
than the speed of light. But you gotta wonder if
maybe there are exceptions to that rule I made. There
are special situations or circumstances in which that could happen,
and so do they. On the podcast, we'll be asking
(09:26):
the question, what's the fastest that a charged particle can go? Now?
Charges is like a particle that's had a lot of coffee,
or it's just pumped up with excitement, or just the
plane of electromagnetic charge. I can't speak to the emotions
of these particles or their caffeine intake, certainly not. And
(09:49):
I think, like a molecule, caffeine is probably much much
bigger than an electron. So I don't even know how
that would work. How do electrons zip coffee? Right, there's
a philosophy question for you without an answer. Maybe if
the electron is part of the caffeine molecule technically, then
it would be supercharged. Yeah, that's right. Our electrons that
are part of caffeine, do they have a different experience
(10:10):
than electrons that are part of something heavy and slow? Yeah?
I guess it depends on whether they like coffee or not.
Are they part of a latte molecule or expressing molecule.
I think they probably have a lot of fun. But
back to the question at hand. It's interesting that there
is an overall speed limit to the universe, something that
nothing can ever exceed. But practically speaking, there are also
other limits to how fast particles can go, especially if
(10:32):
they have other attributes to them, mass or charge, and
in this case we're thinking about the old fashioned electromagnetic charge,
and so this is an interesting question, and as usually,
we were wondering how many people out there had thought
about this, whether charge particles have a different speed limit
than non charged particles. So thank you very much to
everybody out there who answers these questions on the podcast.
(10:53):
It's a lot of fun for us to hear what
you are thinking. And if you would like to share
your thoughts on the podcast, please don't be shy right
to us. Two questions at Daniel and Jorge dot com.
Just think about it for a second. How fast do
you think charge particles can go? Here's what people had
to say. My quick answer it will be like ninety
(11:13):
nine point nine of speed of light. But does just
a guess with speed of light minus plunks, constant multiply
something that makes units consistent. As far as I know,
the maximum speed would be the speed of light. And
it's only particles that have mass that cannot achieve speed
(11:35):
of light, so I think that would be the speed
of light. I suppose my answer depends on whether or
not charge particles have mass, and I'm honestly not sure
if they do or not. If they are masthless, my
I would guess that they travel at the speed of light.
But if they do have mass and their mass is
non zero, I would say they travel at a significant
fraction of the speed of light, maybe upwards of speed
of light. Uh. The fastest charge particle could move in space,
(11:58):
I would think would be the speed of light, if
not the speed of light. All right, everyone seemed to
have the speed of light as the limit, or at
least ninety nine a lot of nine in these answers.
I give it a nine out of ten for that
vault attempt. Yeah, most people seem on board the idea
(12:20):
that the speed of light is the speed limit, but
that massive particles can't reach the speed of light. So
people definitely know there's a limit to things, and that
limit is less for things that have mass, and so
the question is discharge also give them a different speed limit. Well,
let's dig into this topic generally speaking, Daniel, what is
the speed limit that the universe seems to have so
(12:42):
special relativity? Einstein's description of space and time and motion
and how all those things interact tells us that the
speed limit is the speed of light in a vacuum,
which is about three hundred million meters per second, which
is first of all, a very very fast number. It's huge, right,
three hundred million meters in a second is an extraordinary
(13:05):
distance to traverse in just one second. And on the
other hand, it's very very slow because things in the
universe are far apart. So even if you can fly
three millions in a second, it can still take you
years to get to the next star, thousands of years
to get across the galaxy, and millions of years to
get to other galaxies. Yeah, although I wassuming you don't
(13:26):
want to go that far, it is pretty much instantaneous, right,
if you're not the traveling type or want to go
to another galaxy or planet, it's pretty much instantaneous, right,
at least to our brains. Yeah, it's pretty much instantaneous.
You know, light takes about a nanosecond to go afoot,
So if you're looking at something like your computer screen,
it's about a foot away, you're seeing the computer screen
(13:49):
as it looked a nanosecond ago. But you know, the
human eye also can't really distinguish things that happen faster
than like a thirty milliseconds. So for all extents and
purpose is it's instantaneous on the sort of scale of
things that we live in, right, But I guess it
is interesting this idea that there's nothing instantaneous kind of
in the universe, right that the even light or pretty
(14:10):
much anything just information in general, things, events, the actual
existence of things can't sort of move faster in this
universe than the speed of light. Yeah, it makes our
universe local. It means that you can only be influenced
by things around you. And what we mean by around
you depends on that speed of light. If the speed
of light was much much faster than things that could
(14:33):
influence you, things that we would say are local would
be things that are also further away. If the speed
of light was much much slower than the universe would
be sort of more local. You could only be influenced
by things that were closer to you. We talked in
the podcast several times about this concept of a light cone,
the sort of cone of things in your past that
can influence you. Things that are nearby can influence you
(14:53):
fairly recently. Things that are really really far away can
only influence you from the past. Things that happen in
like Andromeda right now can't affect us, and that can
be good news. Right If aliens are building a death
ray and shooting get at us, then it won't arrive
here for quite a little while. Yeah, I feel like
it's a very philosophical question too, and an impact just
on the very nature of existence. Like a giant pink
(15:15):
unicorn suddenly appeared on top of Jupiter. To us, that
wouldn't really exist until several minutes later, right, because that
information would take some time to get to us. As opposed,
it depends on what you mean by exists. We wouldn't
know it existed, We couldn't prove that it existed, So
in that sense, it wouldn't be real in the way
that it wouldn't appear in our experiments, right, But to
(15:36):
somebody else on Jupiter, they would be able to see it, right, Yeah,
that's what I mean that for us, it wouldn't exist,
right Yeah, in the same way that if the Sun disappeared,
we wouldn't notice for eight minutes because it takes that
long for light from the Sun to reach here. So
the universe as we see it is not the universe
as it is right now. And more deeply, relativity says
(15:57):
that there is no sort of universal definition of right now,
that time and the universe depends on where you are
and how fast you are going. This sort of requires
us to give up this concept that there is a
universe that's marching forward in time uniformly, sort of an
ancient Newtonian view, right. And so it's called the speed
of light, but it should actually be called the speed
(16:19):
of anything in the universe. We just call it the
speed of light because basically light is the only thing
we know that can go at that speed, or the
first thing we knew that could go at that speed. Yeah,
it really should be called the speed of everything, or
maybe the speed of anything. But it's the sort of
maximum speed limit of any kind of information, any field.
For example, in the universe, when it wiggles, information can't
(16:40):
move through that field faster than the speed of light,
and so that limit applies to every field, including the
electromagnetic field, for which photons are a ripple in that field,
and because they have no mass, they can move at
that maximum speed. It's true for any massless ripple in
a field. So, for example, we think that gravitational waves
travel at the feed of light as well, because those
(17:01):
ripples in the gravitational field, or equivalently, ripples in the
curvature of space, so we think those also move at
the speed of light. And if there are other particles
out there we haven't discovered that are massless, they would
also move at the speed of light. Are there other
particles we've discovered that are massless gluons, which are the
particles that helped transmit the strong force. They are also massless,
(17:22):
so they move at the speed of light. But gluons
are weird because they interact very strongly with themselves, and
so you never sort of see a gluon by itself.
They conform weird states like glue balls, but those have
energy inside of them, so they have mass, So the
glue balls don't move at the speed of light, even
if individual gluons do. Interesting, so photons are the only
(17:43):
particles that we know of that can move at the
speed of light. Well, I think gluons count is moving
at the speed of light, even though they don't go
very far. Gravitational waves aren't a particle. If gravity is
quantized and made of gravitons, then those are probably massless
and would move at the speed of light. But we
don't know if gravitons exist. Yeah, so, so technically photons
are the only particle we know of. What do you
(18:03):
have against gluhons? You know, then you say a little
while ago that they don't quite you don't never see
them move with the speed of light. Yeah, you can't
like shoot a gluon across the universe and have a
travel like a photon. But you know a gluon which
is exchanged between two quarks, that does happen at the
speed of light. The speed of information of the strong
force is the speed of light. All right, Well, photons
(18:24):
and gluons, I guess they they're stuck together in that category.
But again, maybe give us an into the sense. What
does it mean to move at the speed of light?
What is it like? It's a fun question. What is
it like to move at the speed of light. You
would like to be able to put yourself in that
frame and say, I'm moving along with a photon. What
is the photon? See? It's not something you can really
(18:44):
do because photons don't have a frame. Like if a
spaceship is flying by the Earth, you can put yourself
in this frame where the spaceship is at rest and say, okay,
I'm moving with the spaceship. What do I see? I
see the same thing as the spaceship. You can't do
that with a photon because the photon is never at rest.
There's no like frame you can put yourself in to
say I'm moving with the photon. Photons always move at
(19:06):
the speed of light relative to anybody, So no matter
where you are in the universe and how fast you're going,
that photon is zipping away from you at the speed
of light, and so you can't sort of like put
yourself in the point of view of a photon. M mmm.
So there's sort of like pure motion, right, because they
don't have mass, so they don't have a substance to them,
so all of their energy is in their speed. Yeah,
(19:27):
all of their energy is in their speed exactly. They
are just motioned. There's nothing to them, Like if you
could catch up with a photon, it was sort of
disappear in a puff of motionlessness. You know, they are
only motion, but it's it's like a wiggle in the
like a kinetic field. Right, Yeah, it's the motion of
that field. But isn't it a wiggle like a little perturbation. Yeah,
(19:49):
pure kinetic energy. Right, And people right in they're confused
about that because they say, well, it's energy, and energy
is mc squared, So doesn't that mean the photon has mass? Right?
And the wrinkle there is that equals mc squared only
applies to particles at rest, because the m there applies
to its rest mass. There's another term there which we
don't often talk about. The full equation is like E
(20:10):
squared equals M squared c to the fourth plus p
squared c square. There's a term there for momentum, and
so for a particle that has mass and momentum, there
are two terms there. There's the mass term and the
momentum term. Photons don't have any mass, so they just
have the momentum term. The equation for photon is E
equals pc momentum times the speed of light. So photons
(20:33):
are really weird because they don't have mass, but they
do have momentum, so they can like push things. Right,
that's how solar sales work. Right. They catch sunlight and
they transfer that momentum to motion, and that's how you
can sail out of the solar system. So photons do
have momentum and they go at the speed of light,
but there are a couple of caveats to that, maybe
(20:55):
not just for photons, but for everything else. Let's dig
into the ways that the rules that don't apply. But first,
let's take a quick break. All right, we're talking about
(21:16):
the speed limit of the universe and how it applies
to a charged particle, because I guess the charged particle
is a little bit different. Yeah, particles that have charge
also have mass, and the rules for massive particles and
for charge particles are a little bit different than the
rules for massless chargeless photons. Yeah, we've been talking about
(21:37):
how the speed limit applies to photons, which I guess
it does, but it almost only applies to photons and
I guess gluons. But it limits how fast photons can go.
But there are caveats to that rule. Right, it's not
necessarily the case that photons go at the speed of light. Yeah,
there are caveats to that rule. When we say that
photons always travel at the speed of light, when we mean,
(22:00):
but we don't often say, is that that's true in
your local inertial frame. If space is not curved, basically
the playground of special relativity, operate in flat space and
have things whizzing around near each other, that's what you're
going to observe. But if space is curved or expanding,
or things are really really far away from you, then
(22:21):
you can no longer apply those rules, and things start
to get really weird. It seems like a very limiting
caveat I mean local flat space. That's almost never true.
And if you're there, then you're bending space, which means
it doesn't apply to that's true, although you're not that massive,
and so you don't really bend space. Oh thanks, I've
(22:42):
been working out, and no matter how curved the universe is,
you can always find a locally flat approximation to it. Right,
space is always flat. In a local approximation, you can
always put a tangent on some surface and say, oh,
in this vicinity, I can assume I'm in flats space,
and that's sort of the issue is that special relativity
(23:02):
applies in our local vicinity where we can assume things
are flat, but then over larger distances we can't really
make that assumption, and that's why things break down. Well,
I guess the question is how do they break down
when when space is not flat, when it's a little
curved or a lot curve, does like go faster than
the speed of light or slower than the speed of light.
The space is curved between you and another galaxy, then
(23:24):
you have two different frames. You have your frame, you
have the frame in that galaxy, and how you translate
velocity from one frame to another is a little bit arbitrary.
You can do it in lots of different ways because
space is curved between you. We talked about this once
in the podcast. That has to do with like comparing
whether two vectors are parallel and comparing their length, and
(23:46):
if space is curved between two points, then how you
move that vector over that space depends on the path
that you've taken. So it's sort of not well defined
in the sense that there's like many ways that you
could do it and get different and service so you
can't really compare velocities in two different frames, if this
curvature or expansion between them. Yeah, it gets really tricky
(24:09):
and complicated, and we spend a whole hour talking about this.
I remember, but I guess what's the takeaway? There are
many ways to compute the velocity of a photo going
from between here and another galaxy. But do some of
these solutions tell you that this light is moving faster
or slower than the speed of light? Or do they
all tell you it's moving slower than the speed of light?
Some of them tell you that those photons are moving
faster than the speed of light, and some of them
(24:30):
tell you that the photons are moving slower than the
speed of light. So there's an infinite number of ways
that you could do this, compare velocities in one galaxy
to another because there are different reference frames. There's also
sort of a standard way that we do it, which
is that we just try to like extrapolate our frame
out to the end of the universe, even though we
know that doesn't really work. And those galaxies are moving
away from us faster than the speed of light, so
(24:51):
things seem to be breaking that speed of light limit.
Because you've done this thing of extending your inertial frame
out to the end of the universe, which you're not
technically allowed to do. The other way you can look
at it is to say they have their frame, we
have our frame, and space is expanding between those frames.
So nothing's breaking the speed of light limit. It's just
that space itself is growing and in its own frame,
(25:11):
everything is moving less than the speed of light. That's
what I mean when I say there's like different ways
you could assign that velocity. They're all sort of reasonable
and give you different answers. So there are those important capiats,
But in your local inertial frame, like your the laboratory,
the measurements you're going to actually make, you're never going
to observe anything going faster than the speed of light.
M M, I see. So even the local bending of
(25:32):
space can only slow down the speed of light. Is
that what you're saying? Like, if I'm orbiting a black hole,
for example, and space has really warped around me and
I run those experiments, what what would I see there?
I think you're breaking the assumption because we're talking about
a local flat frame, and if you're near a black hole,
then you're definitely not in a local, flat frame. So
I would say that if your space is pretty local
and pretty flat, you're always going to see photons moving
(25:55):
at the speed of light. So there's one caveat we
haven't talked about yet. But if you are near a
black hole or something else than spaces bendy and crazy
and the velocities get insane, and you could see photons
moving at zero velocity. For example, as a photon climbs
out of the gravity well or tries to climb out
of the gravity well of a black hole, to you,
it appears to go at zero velocity. Right, photons are
(26:17):
contained within a black hole. How could they do that
if they were moving at the speed of light Because
the bending nous of space there makes all these velocities
a little wonky to calculate. But would you ever see
it go faster? Probably not right. That only happens when
you have space expanding. Yeah, I believe that's true. The
bending of space can only effectively slow down the speed
(26:39):
of light that you observe. In order things to appear
to go fasten the speed of light, you need space
to expand rather than to curve. Well, there's another caveat
to this also is that the space has to be empty. Yes,
that's right. The limit that we talk about is the
speed of light in a vacuum, as if there's nothing
out there in space for these photons to interact with.
But we know that light slows down as it passes
(26:59):
through material hills or at the index of refraction tells
you the speed of light through that material. So light
traveling through glass goes slower than light traveling through a vacuum,
Like traveling through air goes a little bit slower than
light traveling through a vacuum. And that's not because somehow
the air molecules or the glass molecules like effect the
space that the light travels in. It's because light keeps
(27:21):
running into things, right, like trying to move through a
crowded room. The float that keeps bumping into the air
and glass molecules and then getting re emitted on the
other side. But it still has to sort of something
has to happen when they bump. The speed that we're
talking about here is basically the average speed from one
side of the material to the other side of the material.
You can think about it as the light sort of
zig zagging between molecules or atoms that it's interacting with
(27:44):
each of those zigs or each of those zags, it's
still moving at the speed of light. Of photon is
always moving at the speed of light, but it sort
of gets absorbed. It takes time to get re emitted,
and so that sort of slows it down. It's like
if you send your teenager on an errand to the
store and they stop and chat at their friends house
every block, it's can take them a lot longer to
get there, even if they're driving at top speed between
(28:05):
all of their friends houses. That's an interesting neighborhood you
live in where your teenagers is driving and stopping to
talk to their friends at the same time. Hopefully they
are being the speed limit there. Fortunately, I don't have
teenagers who can drive yet, so maybe my analogies will
improve when I have some data. So it's if space
is empty and it's not bend deep or distorted or expanding,
(28:29):
then light goes at the speed of light. But now
what about particles that are not light? Pretty much everything
else besides gluons. What if a particle, for example, has mass. Yes,
so photons can go with the speed of light if
they're in a vacuum and not near a black hole,
for example. But electrons, particles with mass, they can never
actually reach the speed of light. Oh yeah, is there
(28:50):
a particular reason for that. It's sort of interesting and philosophical.
It's not like there's a lower speed limit for electrons.
It's not like electrons can only go speed of light
and they're always pegg there. It's just that they ask
emp tonically can approach the speed of light, So there's
no actual limit there. They just get closer and closer
and closer to the speed of light as you add
more energy, but they never actually get to the speed
(29:14):
of light. Yeah, that's weird. So you're saying that it's
a speed limit, not because like if I just create
an electron or a proton or a cord going at
the speed of light, maybe can that can happen. It's
just that for any electron or a particle with mass
that starts address I can, I can never get it
to the speed of light. A particle with mass moving
(29:34):
at the speed of light would have infinite kinetic energy.
So if you could create a particle with infinite kinetic energy,
then yes, it would be moving at the speed of light. Otherwise,
taking a particle and getting it to the speed of
light would require giving it infinite kinetic energy. And the
key concept, of course is that these particles have mass.
So why is it that having master means that you
require infinite energy to get to the speed of light,
(29:55):
whereas a photon with a non infinite energy can move
at the speed of light it and the key concept there,
of course, is the mass of the particle. Mass is
this property of particles like resist changes to their motion.
So you have an electron, it's gonna stay at rest
unless you give it a push, and it's going to
stay at certain velocity unless you give it a push.
And mass is that ability to resist changes in motion.
(30:18):
So it takes energy to speed it up. So you
give the electron to push, it speeds up as it
gets faster and faster, though it takes bigger pushes more
energy to take it up the next level and speed.
It's not a linear relationship, right, And that's just kind
of how the universe is, right, Like, that's just what
mass is. It's not like they have mass and therefore
(30:38):
they're hard to push the more you go. It's like
the definition of mass is the fact that some particles
gets harder and harder to push. Yeah, I think it's
important to understand what things we understand and what things
we just like observe and define. Right. We have observed
that things that have internal energy in them have this
property of inertia. An electron has some internal energy to it,
(31:00):
protons have some internal energy to it, the mass of
the corks and then also the mass of the binding
energy between the corks. Anything with internal energy seems to
have this property of inertia, of resisting changes to its motions.
So yeah, sort of a deep philosophical mystery why that is,
Why do we live in the universe that way and
not some other way? But it's something that we've observed
in the universe and try to describe in our theories,
(31:21):
and those theories are very effective when we test them
out in nature, So that's why we believe they are true,
even if we don't know why the universe is this
way and not some other way. Yeah, it's a massive issue.
And how is this related to the Higgs boson and
the Higgs field, because I know everyone talks about how
the Higgs field is what gives particles mass. Is this
inertial mass that's related to the speed of light, related
(31:43):
to the Higgs field and Higgs boson. So most generally
mass is just internal stored energy of some kind, and
most of the mass in your body doesn't come from
the mass of the particles of your body. So for example,
you're mostly protons and neutrons, and those protons have massive
from their corks, but they also have mass from how
those corks are bound together. So the internal stored energy
(32:06):
the proton is mostly the energy of those particles bound together.
A little bit of the mass of the proton does
come from the mass of those particles, like the corks
that are inside the proton, and those corks they get
their inertial mass from the Higgs boson, but again it's
internal stored energy. The corks themselves, like the true theoretical object,
is massless, but as the cork moves through the universe,
(32:28):
it interacts with this Higgs field and it creates this
like effective cork, this object which is moving differently because
of its interactions with the Higgs field in such a
way that it moves as if it had mass. So
it is inertial mass that we're talking about, and some
of the inertial mass in the universe comes from the
Higgs boson, but not all of it, right, In fact,
most of it doesn't come from the Higgs field and
(32:48):
Higgs boson. Most of it just comes from this fact
of the universe that things with energy are are hard
to move in the universe and impossible to get moving
at the speed of light. Yeah, exact, you often hear
their frame that as things approach the speed of light,
they get more massive, as if like an electron is
getting as heavy as a car for example, if it
(33:09):
goes near the speed of light. And as some sort
of an old fashioned idea that is trying to convey
to you this concept that as something approaches the speed
of light, it takes more energy to move it up
in velocity than it did when it was moving slower.
We don't really think about things literally gaining mass. It's
just that it takes a bigger push to notch them
up to the next level of velocity. Right, Although it's
(33:30):
kind of true, right, I mean, the idea is that
mass is the resistance to movement or to increasing your movement.
Then yeah, as it gets harder, because the universe, as
it gets harder, technically it is sort of gaining mass, right,
It doesn't really hang together though, Like if you want
to use that mass and F equals m A, it
doesn't really work because then that mass is like weirdly
(33:51):
directionally dependent, because if you're moving along the x axis
for example, now you have like a lot of mass
along the x axis, but you don't have that mass
along the y axis, right, Like turnting can give you
a push along the y axis with a certain force
and you get one acceleration, but if they give you
a push along the x axis with that same force,
they get a different acceleration. The more general way to
(34:12):
think about it is just in terms of momentum. This
this equation for relativistic momentum which includes this factor. So
we just leave mass as the rest mass of an object,
like how massive would it be if it was at rest,
and this extra resistance to accelerating at high speeds. We
fold that into the definition of momentum, which then helps
fix up F equals I may, which in the end
(34:33):
is just F equals the derivative of momentum with respect
to time. So this is whole topic of relativistic kinematics,
which I think we dug into in another episode. Yeah,
I think what you're trying to say is that an
electron looks less massive depending on which angle you're looking
at it, Like the electron has a good angle and
a bad angle. I think the concept of relativistic mass
(34:53):
things actually getting heavier as you get to higher mass,
doesn't really hang together if you try to propagate it
through all the equations. But it's sort of an old
fashioned way of thinking about things. All right, that's how
mass effects how fast you can go in the universe.
Now let's talk about how other things might affect how
fast you can move through the universe, including whether space
is empty or not. So let's get into that. But
(35:14):
first let's take another quick break. All Right, we're asking
the question what is the fastest that a charge particle
or pretty much any particle can go, right, because there
(35:35):
are a lot of caveats to this idea that nothing
can move faster than the speed of light. One of
those caveats was that space had to be empty. But
what happens if space is not empty? Yeah, we talked
about photons moving through glass, photons moving through water, but
you might imagine, well, what about space between here and Andromeda?
For example? That's mostly empty, right, Or what about the
space outside of Earth in our solar system that's mostly empty? Right?
(35:58):
Photons surely spend most of their time whizzing around basically
at the speed of light. What turns out, space is
almost never empty. The space in our solar system is
filled with particles from the Sun. The Sun pumps out
a solar wind of protons and electrons and other stuff
that's always blowing through the Solar system. So photons traveling
through our solar system are constantly running into these protons
(36:19):
and these electrons and interacting with them. Really interesting. So
you're saying, like the space between us and the Sun
is not perfectly clear. There's all kinds of stuff in it,
which means that the speed of light in our solar
system is slower than the speed of light, a tiny, tiny,
tiny little bit slower. This is very dilute. Is like
not very many protons per cubic meter, you know, between
(36:39):
us and Jupiter, for example, but there are some. And
so if you're talking technically, like our photons that bounce
off Jupiter and then come back to Earth, are those
moving at the speed of light? Technically they're moving at
a little bit less than the speed of light. And
that's also true for photons from Andromeda, for example, because
the space between us and other galaxies is also not empty, right, yeah,
(37:01):
because there's a lot of stuff in between us and
and Drama. Not. Even though it's hard to see what
the naked eye, you probably imagine the university these clusters
of stars grouped into galaxies, and that's basically where everything is.
But don't forget that the universe is mostly gas, right.
Stars are a tiny fraction in the universe, So really
you should be thinking about the gas in those galaxies,
and it's also gas between the galaxies. Think of the
(37:24):
universe not as a bunch of dots of stars clustered
into galaxies, but like a cosmic web of gas filaments,
and where those filaments overlap and intersect, then you have
these deep pools that form stars and visible light and
all that cool stuff. But between the galaxies there are
these very long tendrils of gas between Us and Andromeda,
for example, a huge amount of gas. They estimate like
(37:45):
a significant fraction of all the matter in the universe
are kind of matter is actually between galaxies, not in galaxies. Yeah,
like of the matter in the universe is basically small, right, Yeah,
they call this the warm hot intergalactic medium. I'm not
even gonna talk about why they call it warm hot.
(38:08):
But the acronym for it is w H I M,
which you know, they didn't choose on a whim, but
they did because it spells out whim. It's just a
whimsical name, you know, for something that's warm hot. Now,
why do they call it warm hot because it's not
cool warm. They call it warm hot because it's sort
of between warm and hot. And remember, if you were
out there in space, you would freeze your tissue off.
(38:29):
But these particles are fairly high speed, and so we
say that they have a fairly high temperature. This intergalactic
plasma can actually be fairly hot on a temperature scale,
even though it's very very dilute, so it doesn't contain
a lot of heat. But because of the speed of
the particles, they say it's fairly hot, not fast enough
to call it actually hot, not slow enough to call
(38:49):
it is warm. So it's sort of like warm too hot,
So they call it warm hot. It's not a whim
or a hymn, it's a whim. It should be W
T H I M, but then it'll be like with them,
I get the lukewarm intergalactic medium, wouldn't really fly there, No,
I suppose not, And so that slows down photons that
are moving through the universe between galaxies. So when you're
(39:12):
looking up at the night sky and know that all
the photons that are traveling towards you were traveling a
little bit less than the speed of light, even the
ones coming from other galaxies. But wait, wait, wait, isn't
the space between our galaxies also expanding? So space everywhere
is expanding, right, and the expansion happens simultaneously at every
point in space at the same rate for things are
(39:32):
near each other. However, that's a pretty small effect. And
also things that near each other have gravity, so the
gravity and Dromeda is actually pulling it towards us faster
than space is expanding between us. So you can basically
ignore the expansion of space when you're thinking about photons
from Andromeda, because they're like in our local gravitational bubble, right,
But it's it's still expanding, which is speeding up the
(39:53):
speed of light a little bit. But you're saying that
the effect of the whimsical gas in between is slowing
it down more than the expand sin is speeding it up. Yes,
so the expansion would be moving and Dromeda away from us,
but gravity is holding Andromeda in place, sort of the
same way that gravity holds the Earth around the Sun.
You're right there, the photons from Andromeda are moving through
expanding space. Because they're moving towards us, that would actually
(40:13):
be slowing down their effective speed. Okay, now let's talk
about charge particles. We know that particles with mass have
extra limitation with respect to the speed of light, and
we know that space is not empty. Does having a
charge affect you more than having mass? Like, does it
somehow give you a boost through this plasma or does
it slowly down more? Well, interestingly, there are no particles
(40:37):
that have charge and don't have mass. Right so the
photon has no charge and no mass. But if you're
a charge particle number one, that means that you have
mass like the electron and the corks. All the particles
that have charged also have mass, So that right away
means if you have charge, you can't go at the
speed of light. Really wouldn't that make you think they're
somehow related? Yeah, it's a really fascinating clue and one
(40:57):
that we just don't understand at all. Possible that one
day in the future we will discover a massless charged particle,
but none exists currently in our universe that we know about. Well,
gluons have charged, they just don't have electromagnetic charge, right,
that's right. They have color charge charged for the strong force. Yeah,
that's a really good point. And we do sometimes discover
(41:18):
new categories of particles, like the Higgs boson was a
particle like no particle we had seen before. It's the
first scale or particle that we've ever found before, a
particle without any spin. And so it's possible to discover
new categories of particles that we haven't seen before in
the universe, or we might discover that that's impossible for
some reason we haven't learned yet. But the higgs boson
(41:39):
has massed to it, right, it interacts with itself, but
it does the higgs boson have charge. The higgs boson
doesn't have electric charge. No, But it was interesting because
it also doesn't have quantum spin like all the other
particles do. So the higgs boson does have mass but
no charge. The higgs boson has mass but no charge.
But we don't have any particles that have charge but
no mass. Oh, it seems so if you have charge,
(42:01):
then you usually have mass. That's the pattern so far.
We don't know if that's a hard and fast rule
or just sort of like a coincidence or electromagnetic charge.
I should say, right, yes, exactly, electromagnetic charge. So now,
if you're a proton flying through space on an electron
flying through space, you obviously can't move at the speed
of light just because you have mass. So if you're
(42:21):
charged particle, that also means you have mass, which means
you can't travel at the speed of light. How does
the charge affect your motion? Does it make you go
faster or slower through this plasma in the universe? Well? Both.
First of all, it allows you to go really fast
because having a charge means that you can get accelerated
by cosmic electric fields or magnetic fields. For example, you
can be near a black hole or a pulsar, which
(42:42):
have very very strong magnetic fields and you can gain
huge acceleration. And so it allows you to sort of
like tap into cosmic accelerators to get to really really
high energies. But then on the flip side, it also
slows you down because particles that have charge interact with photons,
and the unit verse is filled with photons, if photons
(43:02):
left over from the Big Bang, from the cosmic microwave
background radiation that's everywhere in the universe, and so charge
particles flying through the universe interact with those photons, which
constantly sap their energy. Mm I think you're saying that.
You know, if you have charge, that means that you
can be pulled by something that has the opposite charge
(43:23):
ahead of you, right, But it could also maybe slow
you down if the thing is behind you. Absolutely could.
You have magnetic fields and electric fields from cosmic objects
can accelerate or decelerate these particles. But also just the
whole universe is filled with a fog. If you're an
electron and you're flying through the universe, there really is
no empty space. You see photons everywhere and they're all
interacting with you. And there's this effect that if a
(43:44):
particle is moving really really really really really fast, then
it tends to interact with this cosmic microwave background photons
in a way that SAPs its energy and turns it
into other particles. And so there's basically like an effective
limit to how fast a charge particle can move through
the universe because of its interaction with the cosmic microwave
background radiation. Meaning like, if I'm a proton flying through
(44:07):
space and uh I hit a photon head on, it's
going to slow me down, right, because the photon has momentum. Right,
You're gonna interact with that photon, and some of your
energy is going to get used up to create a
new particle, like a delta particle or some other low
mass particle, and then you can go fly off in
another direction, but you've lost some of that energy. What
if the photon hits you from behind, when did it
(44:27):
push you? Yeah, that's possible, and photons move faster than protons,
so they can catch up to a proton and give
it a little push. But the overall effect from a
proton like flying through this fob of photons, is that
it gets slowed down. It's like compressing the space in
front of it. You mean, like, there's an average speed
of all the photons in the universe, and if you're
(44:47):
going faster than that average speed, then you'll hit the
photons kind of like bugs in your windshield. I'm not
sure how to calculate the average speed of a photon.
But think about like the number of directions that a
photon could hit you. In. Most of the those ways
it would slow you down. In only a few ways
they would speed you up because you're you're moving in
a certain direction relative to the maybe the average direction
(45:08):
of all the photons. Yeah, that's right. And also, as
you move really fast through space, you tend to contract
the space in front of you, which increases the density
of the photons in front of you that you're hitting.
So there's a special relativistic effect there also, And what
this means is that really really high energy particles gets
slowed down. So we have cosmic accelerators out there, the
centers of galaxies and pulsars whatever, spewing out super high
(45:31):
energy charged particles, but then they basically screeched to a halt.
It's really really hard to have charged particles a crazy
high energy in the universe because the universe is kind
of like sticky for those charged particles. And that means
something really cool. It means that if you see one
of these particles, it can't have come from very far
away because very very high energy particles can't go very
(45:51):
far at our universe, they're sort of local, or they
started off with a super duper duper crazy amount of
energy to start with. Yeah, exactly, they would have to
have double bonkers energy if they come from really far away.
So you're saying that the whole universe is filled with
a little bit of light pollution, which kind of slows
everything down, makes it even harder to go at the
speed of light. And as time goes on, that light pollution,
(46:14):
the cosmic microwave background radiation is cooling, and so this
effect is fading because the universe is expanding, that light
is cooling, it's getting more and more dilute. So as
time goes on, the universe gets like less sticky for
charge particles, which means that these charged particles, these protons
coming out of cosmic accelerators can go faster and faster
as time goes on, or further and further at their
(46:36):
top speed. You mean like this light pollution of the
universe is kind of dissipating in a way. Yeah, precisely.
The fog is clearing very very slowly, Isn't the universe
also filled with like quantum vacuum energy, like particles popping
in and out. All space has quantum fields in it,
and those quantum fields can never relax down to zero,
so there's always some energy and space. We think that's
(46:59):
very very small. We also think that might be what's
causing the expansion of the universe. It's not something that
we understand very well. So then, if something is flying
through space, does it interact with those that vacuum quantum
fields particles popping up? It doesn't necessarily slow it down,
It just gives it inertia. So interacting with the Higgs
field is how the particle gets mass. It doesn't have
(47:20):
to slow it down. So it's possible to interact with
these quantum fields without slowing down. All right. Well, then
now to wrap it up and to answer the question
we set out to answer at the beginning, Daniel, what's
the fastest that a charge particle can go? Super duper
duper duper duper fast, but not actually the speed of
light and not for very far in the universe? You mean,
po Yeah, there's no actual limit, right, These particles can
(47:45):
keep approaching the speed of light but never actually get there.
And for charge particles, they just can't do it for
very far. So even if I did a perfect backflip
at the Olympics. You would only give me a nine.
I would give you a warm hot score. Yes, our right. Well,
another reminder that the universe has these strange rules. If
you think about them, they're kind of strange. But that's
(48:07):
kind of the job that we as humans have is
to figure out what are the rules and when can
you break them? And that's the job of us experimentalists
to go out there and actually try to break the
rules of the universe. All right, Well, we hope you
enjoyed that. Thanks for joining us, See you next time.
(48:30):
Thanks for listening, and remember that Daniel and Jorge explain
the Universe is a production of I Heart Radio. For
more podcast from my heart Radio, visit the i heart
Radio app, Apple Podcasts, or wherever you listen to your
favorite shows. Yeah,
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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