April 30, 2024 • 50 mins
Daniel and Katie bushwack their way between theories of gravity and electromagnetism, looking for the elusive connection.
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Speaker 1 (00:08):
Hey, Daniel, have you guys figured out how to make
quantum mechanics and gravity work together?
Speaker 2 (00:12):
Yet? Oh?
Speaker 3 (00:13):
Hit me hard with a nasty question right off the bat.
Huh well, unfortunately we haven't figured it out yet.
Speaker 1 (00:19):
Well what have you guys been working on and how
long have you been working on it?
Speaker 4 (00:22):
Like decades?
Speaker 3 (00:24):
More than one hundred years? Actually?
Speaker 1 (00:26):
Uh? Well, and I thought I was a little bit
behind on my deadlines.
Speaker 4 (00:30):
So you know how long you think it's going to take?
Speaker 1 (00:33):
Another weekend? Another thousand years? Can I get it in
by monday?
Speaker 3 (00:40):
You know? The only progress we've really made is coming
up with some long, confusing names for.
Speaker 1 (00:44):
It, like Mississippi or quantum gravity.
Speaker 3 (00:49):
No, that would be much too clear.
Speaker 1 (00:51):
Okay, like gravito, quantum field, hydrodynamically.
Speaker 3 (00:56):
I think you should be a physicist, Katie. You have
the knack for it.
Speaker 1 (01:00):
I know how to throw a ball and look at
it go up and come down, So I'm already halfway there.
Speaker 3 (01:20):
Hi. I'm Daniel. I'm a particle physicist and a professor
at UC Irvine, and I desperately want to know the
underlying rules of the universe.
Speaker 1 (01:28):
I am Katie Golden. I am not a particle physicist.
I host a podcast about animals, but that doesn't mean
that I couldn't maybe try to smash quantum mechanics and
gravity together if you give me a government grant.
Speaker 3 (01:44):
I think everybody who's not a particle physicist should introduce
themselves that way. Hi, I'm Sally. I'm not a particle physicist.
Speaker 4 (01:50):
I think that makes the most sense.
Speaker 3 (01:54):
In that case, I should start off by listing all
the things that I'm not every time I introduce myself
to somebody. I'm not an Olympic gymnast. I'm not a
Wall Street trader dot dot.
Speaker 4 (02:03):
I am not a hot dog eating champion.
Speaker 3 (02:05):
Yet we can all aspire to stuff well. Welcome to
the podcast Daniel and Jorge Explain the Universe, a production
of iHeartRadio in which we aspire to be particle physicists.
We all want to understand the way the universe works.
We all want to figure it out, to zoom down
to the tiniest little bits of the universe, the basic
(02:27):
building blocks and the rules that tertangle them, and zoom
out from that picture to understand how it all comes
together to make our amazing hour Bonkers are wonderful, our
delicious universe.
Speaker 1 (02:37):
Yeah, like a nice stew of concepts all mingled up
in the stars.
Speaker 4 (02:43):
So yeah, I mean it is interesting.
Speaker 1 (02:45):
Because I think we've talked a little bit on the
times that I've been on the show about quantum mechanics.
We've talked about gravity, We've talked about sort of this
distinction between the physics involved in the really tiny and
the really huge, and how it's a bit of a
puzzle to fit those together.
Speaker 3 (03:04):
Yeah, the basic strategy of physics has always been to
zoom down to the littlest bits of the universe to
try to understand them, and then hope that we can carefully,
one step at a time, zoom out and figure out
how those things come together to make our world. You know,
how electrons and protons come together to make atoms, and
atoms come together to make molecules, and molecules come together
(03:27):
to make proteins, and proteins come together to make steak
and ice cream and all the delicious things that you eat.
That's sort of like reductionist approach. We zoom down and
then one at a time step back up to understand
our world. Has long been the approach we wanted to
take to understand the universe, and that's worked for lots
of stuff, like the way we understand ice cream and
blueberries and steak and goats and all that stuff. But
(03:48):
you're right, Katie, there's one big thing that it hasn't
been able to explain, maybe the biggest, most important thing
that shapes our universe, and that's gravity. How everything seems
to attract itself or how things flow through space time.
We still don't understand how that bubbles up from the
tiniest little bits of.
Speaker 1 (04:05):
The universe because gravity is sort of, I guess, like
a big force that we observe. So like you know,
you feel gravity on a planet. Maybe you and I
have our own gravitational pull, but it's much weaker than
a planet, so we're not going to notice it. But
is gravity something you can really measure much when you
(04:25):
get really small, like say you're looking at particles, Like
does a particle have its own gravity? Or can you
even measure gravity of say like a neutron or a
proton or an electron.
Speaker 3 (04:37):
Yeah, that's exactly the puzzle. On a theoretical sense. We
don't know how to stitch these two things together, and
we'll talk about that more during this podcast. But even
more frustrating in experimental sense, we can't even see what
the universe does. Basically, the job of physics is to
explain what is the universe doing, what's happening out there,
and why does it make sense? And the first step
(04:59):
there is to see what's happening in the universe. And
so the first thing you want to do if you
want to explain the gravity of little particles, the quantum
mechanical understanding of gravity is to see gravity operating on
little particles. That's basically what you're asking. And the challenge
there is that gravity is so dang weak compared to
the other forces of electromagnetism, even the weak force and
(05:20):
definitely the strong force, Gravity is like a bajillion zillion
quintillion times weaker, which is why, for example, like a
simple fridge magnet can overpower the gravity of the Earth
and hold your recipe against your fridge or your pictures
of your kids and their cousins. It's not hard to
overcome the gravity of an entire planet with a tiny
(05:40):
little bit of electromagnetism. And so when you're looking at
a tiny particle, a proton or a neutron, its gravity
is basically zero. It's so hard to measure. The smallest
thing we've ever measured the gravity of is something like
on the order of a gram, you know, which means
it has like ten to twenty particles in it. We
are nowhere close to being able to see gravity operate
(06:04):
on particles so that we can then try to explain
how it all works.
Speaker 1 (06:08):
That seems kind of hard because like science is mostly
about say, either direct observation or setting up an experiment.
Speaker 4 (06:17):
So if you can't even see it happening.
Speaker 1 (06:20):
Or figure out how to observe it in particles, how
can you ever figure out how it works on such
a small scale.
Speaker 3 (06:27):
Yeah, great question. Well one is you don't give up.
Speaker 4 (06:30):
Oh I was I was gonna go for Just give up, never.
Speaker 3 (06:37):
Give up, never give it. People are doing these incredible experiments.
It's really an amazing accomplishment to figure out how to
test gravity on the smaller and smaller things. And there's
this history getting all the way back to like Cavendish
torsion experiments of lead balls a weigh a few pounds,
down to smaller objects and smaller objects, and very recently
down to stuff like smaller than a raisin, you know,
(06:59):
a few grains of sand of material, and I really
want to underscore that there's a special scientific skill there.
It's not like mathematics or genius insight into philosophy. It's
experimental bravura, you know. It's what Jorge might call engineering.
It's like figuring out how to make your experimental system
so quiet and so clean and so pristine that you
(07:20):
can force the universe to reveal one of its secrets.
It's a really special skill in science. And so those
folks are working hard and drilling down. But yeah, they're
like twenty orders of magnitude away from figuring it out,
so it's going to be a while. The other thing is,
you could, you know, try to visit a black hole.
Inside a black hole. We think that gravity and quant
mechanics are both relevant because obviously there's strong gravity, but
(07:42):
also things are squished really really small at the singularity
inside the black hole. Of course, that's inside the black
hole beyond the event horizon. So we still haven't figured
out how to probe that.
Speaker 1 (07:54):
Yeah, we've talked about this. It is not in the
budget to go to a black just yet.
Speaker 3 (08:01):
No, so instead you might want to make your own
black hole and then study the patterns of its hawking
radiation to try to get some clues as to what
might be inside of it. But nobody succeeded in making
a black hole yet, and if they did, it might
destroy the Earth, and so there are some questions there.
So while the experimental side is super tooper frustrating, we
can try to make some progress on the theoretical side, thinking
(08:24):
deeply about the universe, eating special mushrooms and having insights
about you know, connections and mathematical symmetries between these two ideas,
to look for links, to look for connections, to look
for ways to fit them together in our minds that
might give us some new clues as to how to
bridge these two fundamental pillars of modern physics.
Speaker 1 (08:44):
Now, do you get university funding for mushroom tripping in
the sake of theoretical physics.
Speaker 3 (08:52):
If you can convince the funding agency that it's essential
for your research to make progress, then ya, I'll bet you.
And so today on the podcast, we'll be exploring one
of those potential directions to bring gravity and quantum mechanics
together to try to fit these two genius insights about
the way the universe works into one mega inside and
(09:13):
today in the podcast, we're asking the question what is
gravito electro magnetism? Boy? Is that a mouthful? I feel
like this must have been named by some German person. Yeah,
every time they come up with a name for something,
they just like stick a bunch of words together into
one super long word instead of.
Speaker 4 (09:33):
Coming up with a new word.
Speaker 1 (09:34):
It's use the words you already have, but stick them
all together.
Speaker 3 (09:40):
Imagine if you came up with new ice cream flavors
that way, cookies and cream all one word.
Speaker 4 (09:45):
Wait it isn't already.
Speaker 3 (09:48):
No, No, I think that's exactly how they figured it out.
Speaker 1 (09:51):
Like, I think it's interesting that I don't think I've
ever seen a question before of the audience where people
are just like, I can't even comprehend the name of this.
Speaker 3 (10:00):
That's right, And so this was maybe a little bit
unfair to drop this on the listeners, But what the heck.
I think it's fun to ask the guys questions about
things you never heard about. So thanks very much to
everybody who volunteers for this audience participation segment of the
podcast and is caught aware by by very technical physics
questions without an opportunity to prepare We really appreciate you
(10:20):
being gained for this. If you would like to play
for future episodes of the podcast, please write to me
two questions at Danielanthorge dot com. So before you hear
these answers, think about it for a minute. What do
you think gravito electromagnetism could be. Here's what some listeners
had to say as.
Speaker 2 (10:38):
The electrochage put off by strong gravity. Maybe I don't
know how you combine gravity and electromagnetism, but it sounds
like some kind of combo of the two. So maybe
it's the way in which electromagnetic fields are affected by gravity.
Speaker 3 (11:03):
Or vice versa. I'm going to guess that gravito electromagnetism is.
Speaker 1 (11:10):
The impact that gravity has on the electromagnetic force. I
wonder what insane clown posse has to say about gravito electromagnetism,
and if they know how it works?
Speaker 4 (11:25):
Does that call back too old?
Speaker 1 (11:27):
Now?
Speaker 4 (11:27):
Am I old?
Speaker 3 (11:30):
I'm not going to comment on it. I will say
that I am approaching fifty and so I've embraced being
fifty by calling myself fifty before I even got there.
And my kids think it's weird that I round myself
with to fifty, but I love it.
Speaker 4 (11:45):
I do that too.
Speaker 1 (11:46):
I round up so I'm not so shocked when it happens.
Speaker 3 (11:49):
Exactly. That's what I was thinking. And then my daughter
asked me. She said, well, does that mean when you
turn fifty one you're gonna round yourself up to one hundred?
Speaker 4 (11:57):
Why not?
Speaker 3 (11:58):
Yeah, I thought, you know, for the sake of consistence,
I guess I have to.
Speaker 1 (12:01):
I mean, you know, then you could be the oldest
person on earth, even before you start getting a pension.
Speaker 3 (12:07):
That's true. I'm just hoping to get some of those
compliments like wow, Daniel, you look good for it. All right,
But back to the topic of quantum mechanics and gravity.
We see people are struggling to understand what this word means.
But there is a sense there that it's about some
relationship between gravity and electromagnetism. Maybe gravity is caused by electromagnetism,
(12:29):
or maybe you get electric charges from gravity. There's some
fun ideas in there.
Speaker 4 (12:33):
It does sound like a little scammy.
Speaker 1 (12:37):
It sounds like something where someone's trying to sell something
to me, because it's just so many technical sounding words
all smashed together. It's like, yeah, I kind of want
to know what it is. The only thing I can
think of like these listeners is just that it's like
kind of trying to smoosh the concepts of gravity and
electromagnetism together, but I kind of want to know more
(12:59):
specifically what that is and how that works.
Speaker 3 (13:03):
Yeah, and so delay the groundwork. I think we need
to spell out a little bit of detail about like
why this problem is hard. Why is it difficult to
bring gravity and electromagnetism, or gravity and quantum mechanical theories
of forces together in general, And so we should probably
start with those quantum mechanical theories. And you know, we
talked about electromagnetism because it's one of the fundamental forces
(13:27):
that we know about in the universe. And all of
these fundamental forces are quantum mechanical, meaning that we have
a theory of quantum mechanics that describes particles and how
they move through space or how they exist and how
they have probabilities to exist. And those quantum mechanical theories,
those Shroninger equations and the lagrongins and the Hamiltonians, all
(13:47):
those mathematical structures are quantum mechanical and they describe the forces.
So we have electromagnetism, we have the weak force, and
we have the strong force. All these things can be
described using a quant maicaanical theory. It means we know
how to calculate what happens when one particle pushes or
pulls on another particle using one of these forces. Like
(14:08):
when two electrons are coming near each other, they repel
each other, and they use these forces to do so.
They use electromagnetism, And you can think about that quantum mechanically,
either as one electron has a big electromagnetic field and
that's pushing on the other electron, or if you prefer
the particle picture, you can imagine that the two electrons
are exchanging photons. They're tossing photons back and forth, and
(14:31):
that's how they're pushing on each other. But either way,
we have a nice quantum mechanical picture from the ground up,
from the littlest bits of these three fundamental forces electromagnetism,
the weak force, and the strong force.
Speaker 1 (14:43):
So is gravity even weaker than the weak force?
Speaker 3 (14:48):
Gravity is like ten to the thirty times weaker than
the weak force. It's almost unimaginably weak. It's so much
weaker than the other forces that it's a big puzzle
in physics. Like in physics we look for patterns and clues.
We expect things that are similar in nature to all
operate in under similar principles and have similar numbers. So
(15:09):
if you want a lump gravity in as one of
the forces, then you got to answer the question why
is it so much weaker than the other forces? Not
by a factor of ten, not by a factor of
one hundred, not by a million, but ten with thirty
zeros behind it. That's a big deal.
Speaker 1 (15:25):
And so like the difference between electromagnetism, the weak force,
and strong force like is not nearly as big as
the difference between all those three and gravity.
Speaker 3 (15:37):
Yeah, exactly. The strong force is like ten times more
powerful than electromagnetism, which is like one hundred times more
powerful than the weak force, which is like a gajillion
billion of jillion times more valuation.
Speaker 1 (15:49):
To hang on, that doesn't even sound like a number, Okay,
but I get it. So gravity is so incredibly weak
it doesn't even seem like it's in the same category
as these other things. It's like comparing like a blue
whale to an ant.
Speaker 3 (16:03):
Yeah, that's exactly right now, fundamentally, that's not a problem.
Like it's possible that you could have for forces in
the universe and one of them is just much weaker.
There are ways that you can do that. It's not
an insurmountable issue. It's strange and it would make you
ask like why is that and to look for explanations,
but mathematically it doesn't prevent us from describing it. That's
(16:25):
not the challenge with gravity. If you sit down and
try to describe gravity using some kinds of maths similar
to the way we describe electromagnetism and the weak force
and strong force, to come up with like a quantum
theory of gravity that describes it as a force. Then
you start to build in gravitational fields and you can
think about the quantized ripples in those fields as particles.
(16:46):
In this case, it would be the graviton. So when
two planets come near each other and pull on each other,
the quantum picture of gravity would have them exchanging gravitons
the way two electrons are like exchange photon. So you
can start to go down that road mathematically and things
seem okay. You just like dial the force way way
(17:06):
down to make it super duper weak, but then you
run into a lot of mathematical problems actually making that
theory work.
Speaker 1 (17:13):
How do you check your math in a situation like this,
Like what are the kinds of mathematical problems that you
run into? And how do you know that they're problems?
Speaker 3 (17:22):
Yeah? Great question. The way that you know that your
theory is working or not working is that you try
to use it and you see if it gives reasonable results.
Like if you ask, I want to push these two
particles together, I want to calculate the probability of various outcomes.
I want to know the particles are going to bounce
off each other, or if they're going to scatter off
at this angle or at that angle. So you try
to calculate things. You try to make predictions in physics.
(17:45):
For your predictions to be reasonable, there's some limits. There's
some restrictions, like your predictions can't have probabilities greater than one.
If you ask, like is my electron going to go
left or right? And your theory says you have one
hundred and seventy five percent chance of its going left,
And you're like, hm, well that's that seems wrong. That
can't r right.
Speaker 1 (18:03):
So when my gym teacher told me to give it
my one hundred and ten percent. Like, that's not right,
that's physically impossible.
Speaker 4 (18:11):
That's right, my all.
Speaker 3 (18:14):
Your gym teacher is violating the fundamental rules.
Speaker 4 (18:17):
Of physicals call them up right now.
Speaker 3 (18:18):
Or maybe your gym teacher is a quantum gravity theorist,
because that's exactly what happens when we try to make
a quantum gravity theory. Gravitons are really tricky because they
don't just transmit gravity. They have energy themselves, which means
they also couple to gravity. They feel gravity, they emit gravity.
So like when you emit a photon, photons don't feel electromagnetism,
(18:42):
they don't bounce off of other photons, they don't emit
other photons. Right, Photons don't feel electric charges because they
are neutral. They don't have a charge themselves, so they
will like fly right through an electric field. But a
graviton has energy, and gravity is felt by everything with energy,
So graviton feel gravity, which means they emit more gravitons,
(19:03):
and those gravitons emit more gravitons, and pretty soon you
have an infinite number of gravitons, and you start to
get nonsense answers out of your theory.
Speaker 1 (19:11):
When you say a graviton, right, I'm thinking of a
particle sort of like a photon. But photons we've actually measured, right,
We've actually been able to sort of get physical evidence
of their existence. Like, do we have like physical evidence
of the existence of gravitons as like an existing thing
(19:32):
other than just knowing that gravity exists.
Speaker 3 (19:35):
We do not have any evidence of gravitons. We have
a very successful theory of gravity. It's Einstein's theory of
general relativity that describes how space and time bend around
masses and that affects how things move, and that's very,
very precise, but that describes gravity as not a force.
It's like a bending in space and time. We're going
to switch over and try to think about gravity as
(19:56):
a force instead of bending in space and time. Then
you need these gravitons, and nobody's ever seen them. The
reason they're so hard to see is precisely because gravity
is so weak, Like electromagnetism is a pretty strong force.
Electrons are radiating photons all the time. It's not a
rare thing to happen in the universe. But gravitons are
more rare because gravity is so weak, and they're much
(20:18):
harder to see because gravity is so weak, so the
impact of like one graviton would be very very hard
to detect. So we don't know that gravitons are real,
but they are a necessary part of a theory of
quantum gravity that tries to make gravity look like a
force and fitted it into this quantum mechanical framework. So far,
and nobody's even been able to make the math work
(20:40):
to have like a consistent theory that we could even
go out and test in experiments.
Speaker 1 (20:45):
So we can't make the math work. We can't even
find any evidence that gravitons exist. Things are looking pretty good,
pretty good so far. Maybe we should take a quick break.
I will look around see if I've got any gravitons
just kind of lying around, you never know, And then
when we get back, maybe we can take another crack
(21:06):
at this and see if there's any anything that actually
where the math you carry the ones and it all works.
Speaker 4 (21:13):
Out all right. So bad news.
Speaker 1 (21:28):
Daniel couldn't find any gravitons, not a single one. I'm
also out of milk, so things aren't looking so good
here do you have any good news for me in
our effort to smoosh together quantum mechanics and general relativity.
Speaker 3 (21:45):
I didn't figure it out in the last couple of minutes,
but you know, a lot of clever people have been
thinking about this and trying to find some connections between
gravity and electromagnetism, or between electromagnetism and gravity, sort of
going both directions, trying to make gravity look more like
electromagnetism and the theoretical side, or giving up on that
and trying to make electromagnetism look more like gravity. So
(22:08):
we don't have any experimental results to guide us, but
we can still think deeply about the structure of these
theories and try to make some theoretical progress in our minds.
Magic mushrooms or no.
Speaker 1 (22:20):
All right, so we're in the mindscape. What are we
doing in order to solve the hurdle of the math
not mathing in this idea, because it sounds like we
were sort of trying to think of planets as like
scaled up particles and gravity as like a force between them,
as if they're giant particles, and that didn't really work. Like,
(22:43):
is there another approach that you could use or is
there a way to like fine tune that approach such
that it actually does work.
Speaker 3 (22:50):
Yeah, So the short answer is there isn't a great approach,
but that doesn't mean we can't make progress. And I
think people should understand that. In theoretical physics, it's not
like you sit down one day and come up with
the whole theory movies. You're entering like a mathematical jungle.
You're not sure if there is a path through, and
it takes exploration. Exploration is not just something we do
(23:11):
in experimental physics or in experimental biology. We're like walking
through a literal jungle looking for new kinds of frogs.
In theoretical physics, you can also explore. You can just
like try stuff and say, well, I'm going to go
in this direction and see if it works out, kind
of like when you're trying a proof in tenth grade
geometry and you're like, well, I'm not sure this is
gonna get me where I need to go, but I'm
gonna play around with these angles. And so in theoretical physics,
(23:34):
people are trying something that has a long tradition dating
all the way back to like Maxwell James Clerk, Maxwell
in the eighteen hundreds was looking at theories of electricity
and theories of magnetism, and he tried something cool. He said, well,
let me write down the equations for electricity and write
down the equations for magnetism and try to smooth them
together and make them look as much like each other
(23:55):
as possible. And when he did that, he realized, oh,
my gosh, these basically have the same equations. And not
only that, but you can click the equations together because
sometimes electric field cause magnetic field and vice versa to
make one bigger picture. So we had this great insight,
which is where we got the theory of electromagnetism. So
now people are trying to do something similar. They're saying,
(24:16):
let's look at the equations for electromagnetism and the equations
for gravity and see if we can find relationships. Are
they like a mirror image of each other? Can we
somehow find patterns there and then use that to guide
us through this intellectual jungle to a theory that combines
gravity and electromagnetism into one big theory.
Speaker 1 (24:35):
So for someone just theoretically who does not have a
grasp of what theoretical math would look like, and when
you say equations, like what that is?
Speaker 4 (24:46):
Like are we.
Speaker 1 (24:47):
Talking about like you have five equations that you have
to memorize to understand gravity? Like are there hundreds of equations?
And when you're trying to like smash together equations, you know,
is it sort of like a brilliant mind where you
just see floating numbers kind of going together and doing
things like what in terms that someone like me who
(25:11):
math is trying to calculate a tip?
Speaker 4 (25:14):
How does that work?
Speaker 3 (25:15):
Yeah, that's a great question, and we could start off
pretty simply. You know, people are probably familiar with Newton's
law of gravity. That just says that the force between
two objects is proportional to the two masses divided by
the distance between them squared, and then you multiply that
whole thing by a constant big G Newton's constant. So
(25:35):
Newton's equation for the force between two objects is like
gmm over R squared. All right, So that's Newton's theory
of gravity. Then we can look over at electromagnetism. We
can say, what's the equation for the force between two
particles that have charge? Like remember our question was like
what happens when two electrons come near each other. Can
we calculate that well, Kulham's law tells us that the
(25:58):
force between two parts particles goes like the charge of
the two particles divided by the distance squared between them,
all multiplied by a constant in this case K. So
you look at these two equations, you notice instantly, like HM,
these have kind of similar structures. On the top of
the equation is the charge of the two objects. Where
(26:18):
gravity the charge would be the mass, and for electromagnetism
the charge is obviously the electric charge. And both of
them get weaker as the distance grows by the same
power you get twice as far apart. Gravity and electromagnetism
both get four times weaker. You go ten times further away,
the force of gravity and electromagnetism both go down by
(26:39):
a power of one hundred. So they have very similar
structures there already. That's encouraging.
Speaker 1 (26:44):
But if it was just as simple as finding sort
of some of these equations that seem to look kind
of similar and match them together, like it seems like
we would have already figured this out. So what is
the scale of the complexity, Like, why have it we've
been able to find just like a bunch of these
equations that kind of look similar and seem to have
(27:05):
the same general structure and have them work together.
Speaker 3 (27:08):
Yeah. Well, one issue, of course, is that we know
that Newton's theory of gravity is not the right theory.
Speaker 4 (27:13):
Whoops.
Speaker 3 (27:15):
When Newton was a very clever man, and he has
a very nice theory which mostly works but not.
Speaker 4 (27:20):
Quite irresponsible with apples too.
Speaker 3 (27:24):
Einstein's theory of gravity is not just a reimagining. It's
not just saying, look, the story is wrong. It's not
a force between objects, it's a bending of space and time.
It also gives different predictions, like, for example, Newton says
that the force just depends on the mass. It doesn't
depend on whether the object is spinning or not. So
according to Newton, if you're in orbit around the Earth,
(27:47):
whether the Earth is spinning or if it stopped spinning
or spinning the other way makes no difference for gravity.
Einstein says, Nope, that's not true. If the Earth is spinning,
that has more energy, and since gravity is linked to
energy of all kinds, not just mass, that changes the
gravitational force on the object in a complicated way. So
(28:07):
Einstein's equations are much more complicated than Newton's. He doesn't
just have like one simple force equation. He's got a
really complicated tensor equation, where a tensor it's just like
a matrix. It's like an array in computer programming, you know,
a way to keep track of a bunch of numbers
all at once. So he has more complicated equations. And
so you can't just say, look, Newton's law and kulums
(28:27):
are similar. You got to dig deep into Einstein's rules
for gravity.
Speaker 1 (28:31):
So how do we know Einstein is right and Newton
is wrong. It can't just be that Einstein's got cooler
hair or more complex equations.
Speaker 3 (28:40):
Well, Einstein and Newton make different predictions, and famously Einstein's
predictions were right. Einstein predicted stuff about how light bends
around the Sun during an eclipse, and he predicted stuff
about how mercury orbits the Sun and the angle of
the eclipse of mercury, how that twists as mercury is
orbiting the Sun. All these little difference between Newton and
(29:00):
Einstein add up and a few special cases, so we
know that Einstein's theory was right. So then people took
this on. They're like Okay, well, can I take Einstein's
equations and try to make them look like electromagnetism. Like
we were able to take Newton's law and make it
look like Kulam's law. Can we take Einstein's gravity and
make it look like electromagnetism? And people have actually succeeded
(29:23):
in doing this. There are these Gravita electromagnetic equations when
if you write them down, you get equations that look
very similar to Maxwell's equations for electromagnetism. Maxwell has four equations,
and I won't get into the math with you. You know,
there's a there's like a divergence and a curl for
electricity and magnetism and indie gravita electromagnetic equations. There are
(29:46):
also four equations and have a very similar structure to
Maxwell's equations. You should look them up and write them
side by side. They look very very similar. It's eerie,
it's spooky. It's like the universe is saying, oh, look,
you found the pattern. It's over here in the gravity
world and in the electromagnetic world.
Speaker 1 (30:03):
This does feel like a conspiracy theorist sort of aligning
charts and with a corkboard and yarn and trying to
make these connections. But yeah, I mean, I'm looking at
this and you know, I don't know a look of
complex math, but it yes, they look very similar.
Speaker 4 (30:20):
But if we've.
Speaker 1 (30:21):
Found this, right, it doesn't mean that we've figured out
how they interlock. Like we found some similarities, some equations
that seem to match, but the bigger picture has not
yet become clear.
Speaker 3 (30:33):
Yeah, that's right, and I hear you setting me up
to deliver the bad news of why this is going
to work. But first there's a little bit more good, okay,
which I think is a fun insight into how this works.
The thing about Einstein's equations for gravity, as we were
saying before, is that it gives you more than just
like a straightforce between two objects. Spinning objects can create
like torque and drag in space time itself, which gives
(30:56):
all sorts of weird forces, like if you are orbiting
the Earth and the Earth is spinning, then there's some
frame dragging effects there. Check out our whole episode about
that if you want more details. But effectively, it gives
like a twist on things that are orbiting the Earth.
So according to Einstein's gravity, it's not just a force
between two objects. There are more subtle effects there. And
(31:17):
the really cool thing is that in the gravito electromagnetic equations,
the ones where you take Einstein's gravity and try to
convert them to look like electromagnetism, you can see this emerge.
And in those equations you have what they call a
gravito electric field, which is sort of like the straight
up Newtonian version, plus this gravito magnetic field. So basically,
(31:40):
to explain all of Einstein's gravity you break it up
into two pieces, this analogy to the electric field and
this analogy to the magnetic field. And it goes even
deeper than that, because it's not just notation. It's not
just like, hey, let's write this down in a cute
way that looks sort of similar. There really is a
conceptual connection there because an electromagnetic the way you get
(32:01):
magnetic fields is you take electric fields and you wiggle
them like currents of electrons give you magnetic fields. So
it's like velocity dependent, right. Well, the cool thing about
the gravitomagnetic field, this other component of these equations you
have to add on to be able to describe Einstein's
gravity with equations that look like electromagnetism is that they
(32:22):
create velocity dependent acceleration in just the same way. For example,
those spinning masses. When the Earth is spinning, that's an
acceleration because any sort of rotation is an acceleration, and
that gives an acceleration. On satellites, it gives a twist,
it gives a pull. So when you force gravity into
this structure that looks like electromagnetism, you learn some things
(32:45):
about gravity. It like sorts it in your mind in
a way that actually gives you a little bit of insight.
And that's a good sign. When you're bushwhacking your way
through the theoretical jungle trying to make connections between things.
You don't have to force things into categories. When they
sort of naturally fall into those categories and reveals something
deep about the nature of that force or the nature
of the phenomenon, it's a sign that you might be
(33:07):
on the right track. So that's the good news that
there really is something satisfying about making gravity look like
the equations of electromagnetism. It's not just like hacking it
up into bits and shoving it in boxes.
Speaker 1 (33:20):
It's not just using the same colored gelpins to write
the equation.
Speaker 3 (33:25):
Exactly.
Speaker 1 (33:26):
That sounds very promising, right, that sounds like a very
like promising path. And the fact that there's this wiggle
connection where wiggling or velocity movement for gravity like creates
this this field is very interesting.
Speaker 4 (33:42):
I just I feel a butt is common.
Speaker 3 (33:44):
There is a big butt, A.
Speaker 1 (33:45):
Man, I knew I like big butts, and I cannot lie.
Speaker 3 (33:52):
Now that's a reference.
Speaker 4 (33:53):
I hope everybody hopefully Stelia.
Speaker 3 (33:55):
The other brothers can't deny. Well, the thing that the
other brothers can deny is that this works in difficult situations.
Like we said that you could take Einstein's rules and
you can express them in mathematical equations that look like electromagnetism.
But there was a butt there I left off, And
the butt is This only works if gravity is kind
(34:16):
of weak, like when the curvature of space time is
not very strong, when you're like far from any intense mass,
when you're far away from a black hole, for example,
or even from the Sun, then this works pretty well.
But when the curvature of space time gets more intense,
this breaks down. Like the equations are just too complicated,
too intense. We have no way to fit them into
(34:37):
these boxes to make them look like electromagnetism. In order
to do that, to take the complicated Tensor equations of
general relativity and to make them look like electromagnetism, you
have to make a bunch of assumptions, and one of
those assumptions is gravity is pretty weak. So basically what's
happened here is you've avoided the hard problem. You know,
the hard problem of making quantum gravity work was figuring
(34:59):
out what happened when gravitons amid other gravitons amid other gravitons. Basically,
when gravity gets very very strong and it can no
longer be neglected, and that's exactly the situation that gravito
electromagnetism doesn't know how to answer. So it's some progress
in the sense of like, hmm, you found some cool
connections between these theories, but only in the easy parts,
(35:20):
not in the hard parts at all. When you get
to the hard part of gravity being very strong and
every graviton is emitting ten other gravitons, then this breaks
down and it doesn't help us at all. So it's
like an interesting island of understanding, but it doesn't make
any progress on the really hard part of the problem
of describing gravity as a quantum theory when gravity is
(35:40):
very very strong.
Speaker 1 (35:41):
But could it be revealing something about gravity still, like
maybe that there is a significant difference between a strong
or large amount of gravity, like the gravity of the
Sun versus the Earth. If there is some kind of
fundamental difference between like weak levels of gravity and strong
levels of gravity, that seems like that could itself be
(36:05):
an interesting kind of finding, even if it still doesn't
solve the bigger question of how to merge those concepts.
Speaker 3 (36:12):
Yeah, exactly, And that was the point I was trying
to make earlier that even intermedia progress is progress. You
don't have to know if this is going to fundamentally
solve the question of quantum mechanical gravity for it to
be cool that you figured something out, that you've made
some headway, you found some island of understanding whether it
actually connects to the mainland and reveals all the deep
secrets we don't know yet. But that doesn't mean it's
(36:33):
not worth doing and not worth exploring. Right, we've made
it to this stage where we've been able to accomplish
this connection between electromagnetism and gravity. It might be that
hunting around and digging around and poking in various directions.
Lets us build from this right that we can go
from here to figure out how to describe strong gravity.
Nobody knows how to do that yet, but this is
(36:54):
like another avenue of attack. This gives us another way
to think about it. At least it might be a
total dead end or might be the wave of the future.
We haven't figured that out yet. It's on the forefront
of knowledge.
Speaker 4 (37:05):
I mean, let's go with not being a dead end.
Speaker 1 (37:09):
We'll take a quick break and try to keep up
the optimism that this is actually going towards finding a
fundamental answer that'll change everyone's lives. And we're probably not
going to figure it out in the ad break, but
you know, we'll think about it. So we are back.
(37:40):
We have not yet solved how to weave together electromagnetism
and general relativity or gravity, but there has been some
interesting progress that has been made that is perhaps instructive
and perhaps interesting. So we had that issue that these
(38:02):
equations when gravity is weak, they seem to kind of align,
like you have the equations associated with general relativity and
then Maxwell's equations that looked similar then when gravity got
strong like the sun or a black hole, that kind
of broke down. It no longer worked in that way.
(38:23):
So is there another sort of angle of attack that
is being explored.
Speaker 3 (38:28):
Yeah, people are trying so many different things at once,
and you know, this is the way we make progress.
You push your way through the jungle. Maybe you make
it all the way through. Maybe you run into somebody
else coming from the other direction right, and you can
join you two efforts. And so that's what's happening is
a bunch of people are working on trying to make
gravity look like electromagnetism. So that's the gravito electromagnetic approach
(38:50):
that we just talked about. But some people are working
in the other direction. They're saying, let's not make gravity
look like electromagnetism, let's make electromagnetism look like gravity. Einstein's
big idea was let's not think of gravity as a force,
let's think of it as the curvature of space time.
And so people are wondering, like, can we extend that idea?
(39:11):
Can we also do that for electromagnetism. Remember that the
way Einstein did this is he said, look, it feels
like there's a force between you and the Earth. Newton's
description of gravity as a force is compelling because when
you throw a ball in the air, it falls to
the Earth and it looks like it's getting pulled on. Right,
we have this experience of gravity as a force. But
(39:32):
he said that it's not actually a force. That's something
of an illusion. What's happening when you toss a ball
is that you're releasing it into free fall. Space itself
is curved in the vicinity of mass, so there's a
natural path for objects to follow in curved space time.
So the ball naturally falls towards the center of the Earth.
So Newton's picture is there's a force pulling on the ball,
(39:55):
and then it hits the Earth and it stops it
because the Earth is balancing that force of gravity. Einstein's
picture is different. Einstein says, when the ball is in
the air, it's in freefall. There is no force on
the ball at all. It's just following the motion of
space and time. And then the Earth stops it because
the Earth itself is providing a force. It's accelerating against
(40:15):
that natural motion of space time.
Speaker 1 (40:17):
Yeah, and I think you've told me this is actually measurable, right,
that there is acceleration acting when you are standing on
the floor.
Speaker 3 (40:27):
Exactly, if you jump off a building instead of the ball,
and you take a scale with you, and as you're
falling through the air, hurtling towards the earth, you stand
on the scale, what are you going to measure? You're
going to measure nothing, right. You have no weight, and
that's because you're in freefall. There's no acceleration there. You're
not measuring anything. If you're standing on the surface of
the Earth and you stand on the scale, then you
measure your weight. That's where there's a force, right, So
(40:50):
there really is no force on you when you are
in freefall. There's a force on you when you're standing
on the surface of the earth. That's the Earth pushing
up against that natural motion. So the explanation is that
there is no force there. There's just a curvature of
space and time. And we couldn't see that curvature, and
that's why it looks to us like there is a force.
Speaker 1 (41:10):
Having this as the theory about gravity, like, how do
you then fit the quantum forces into this framework, right,
because like that seems fundamentally different. Those are forces, they're
pulling or pushing against each other. How does that fit
into this kind of idea of gravity being like the
shape of existence, which sounds it's hard for me to
(41:32):
kind of think about that, right, like the shape of
the universe, the shape of the fabric of the universe,
and then we're just kind of falling along it.
Speaker 4 (41:40):
And then you have these particles.
Speaker 1 (41:42):
Have we observed anything in particles that could sort of
fit within that framework.
Speaker 3 (41:48):
So we haven't observed anything yet, but there are some
theoretical ideas. The idea is to say, well, maybe electromagnetism
also isn't the force. Maybe it just looks like a
force and it's actually the result of a second kind
of curvature. So we have like first kind of curvature
is Einstein's curvature of space time that gives us the
apparent force of gravity. If space can also be curved
(42:11):
in another way, and that curvature gives us the appearance
of the force of electromagnetism. And in order to have
curvature in another way, you need more dimensions of space
and time. The idea is, like einstein space is three
plus one dimensions. You start with one dimension, which is
a line you draw a second dimension, which is perpendicular
(42:32):
to that. Now you have like a plane. You can
add a third dimension which is perpendicular to both of
the first two, and that gives you like three D
space right where each of those three lines are perpendicular
to each other. And that's it. There's no more room
to add another line perpendicular to all three.
Speaker 4 (42:49):
Right, because space, Yeah, it doesn't work.
Speaker 3 (42:53):
It's sort of crazy in mind bending. And I remember
as like an eight year old trying to imagine that's
fourth dimension but not being able to do it. But
we do think of time as sort of a fourth dimension.
How those three change. So Einstein space is four dimensional,
but we can extend it by adding another dimension of
space and having that curvature be in that additional dimension,
(43:14):
that fifth dimension. And you might ask, well, I can't
see that dimension. I can't imagine where that dimension would be.
How does that even work? Yeah, And this fifth dimension
is sort of similar to the way we think about time,
or like time we think about as the fourth dimension.
Imagine three dimensional space and then imagine that changing through time. Right,
save your full three dimensional space, But now you have
(43:34):
like another axis along which that three dimensional space is
changing so to imagine another dimension of space itself. Imagine
three dimensional space and then imagine a bunch of copies
of it. And this new dimension is not like the
original three. Instead of going on forever, it's like a
little loop. It's more like in polar coordinates, how you
have an angle and the angle can't go from zero
(43:57):
to infinity, just goes from zero to three hundred and
sixty degrees and it goes back to zero again. Right,
Imagine a new dimension of space that's sort of similar.
It has a maximum length, it's a circle instead of
an infinite line. Take three D space and sort of
move it around this circle. That's how we imagine a
universe with four spatial dimensions, the first three that are normal,
(44:18):
and then this weird rolled up dimension.
Speaker 1 (44:20):
Is it like when your Windows computer crashes and you're
dragging like your cursor or a window around, and then
there's a bunch of little copies of that that all
get stacked up and messed up.
Speaker 4 (44:32):
Is that what we're talking about here exactly?
Speaker 3 (44:37):
Or like when you win solitaire and the cards all
stack on top of each other. It's difficult to imagine
because we're used to three D space and we think
in three dimensions, and so squeezing that fourth dimension into
your brain is really a challenge. But mathematically it allows
something very cool. It allows you to have another kind
of curvature. A curvature in this new dimension might be
(44:58):
able to explain what we see as the force of electromagnetism.
So in this case, not just the curvature, but the
whole dimension would be basically invisible to us. This is
an ancient idea in physics. It goes all the way
back to nineteen nineteen. The guy Theodor Cluza came up
with this, just after Einstein came up with his idea
of relativity, and then a few years later a guy
(45:20):
named Oscar Klein turned it into a quantum theory in
nineteen twenty six. And try to calculate the size of
this new fifth dimension and figured out how to be
like twenty times the plank length, which means it's like
super duper tiny. It's like ten to the minus thirty
five meters long. So this seemed really exciting.
Speaker 1 (45:39):
I have so many questions just about that, like what
do you mean calculating the size of a dimension right?
Speaker 3 (45:46):
Like, remember that this new dimension is not infinite, we
think that you can go as far as you want
in X or and y, R and z. But this
new dimension is a loop, which means it has a length.
Now there's a maximum distance in this dimension. It's unlike
the other ones in a really weird way, and that
means that you can calculate, like, well, how big could
it be? What is the radius of curvature? What is
(46:08):
the length around this dimension? So it's very different in
a really counterintuitive way. And then Einstein got to work
on it, and he was like, all right, this is exciting.
Speaker 4 (46:18):
I trust him more than I trust me to think
about it.
Speaker 3 (46:21):
He thought, maybe this is exciting. Maybe I can make
this work. Maybe I can explain all of electromagnetism using
curvature in this new fifth dimension. And yeah, he died
before he found and people had been working on it
for a long time and nobody's been able to crack it.
There are some versions of this theory which sort of work,
but they all predict that we would have seen a
bunch of new particles. They predict that electrons would like
(46:44):
vibrate in this other dimension, and they would vibrate in
different ways, so you would see like different versions of
the electron the way like a string can vibrate, but
it can vibrate like one mode or two modes, or
three modes or four modes. Electrons could vibrate in this
other demands in various ways, and you would see like
heavier and heavier versions of the electron, where the heavy
(47:05):
ones are like vibrating in this new dimension with more energy,
which gives them effectively more mass. But we haven't seen
any heavy electrons, or any heavy muons, or any heavy
versions of these other particles at all. People thought for
a while, oh, maybe the muon is a heavy version
of the electron, and that's actually like, you know, something
vibrating in this new dimension. But that doesn't quite work
(47:25):
out because the electron and the muon feel the weak
force a little bit differently. So the bottom line is
it's an exciting direction theoretically to try to make electromagnetism
work in this clusive cline theory, but it's made predictions
that haven't been born out in the data, and so
it's not so promising.
Speaker 1 (47:44):
Well, we need to make a time machine go back
in time, and then ask Einstein, first of all, how
to make a time machine so that in the future
we can go back in time and talk to them
and then present them with all of this information.
Speaker 4 (48:00):
Or maybe, uh, there will be a.
Speaker 1 (48:02):
New kind of Einstein, or collectively instead of one super genius,
just a bunch of very smart people working together figuring
this out exactly.
Speaker 3 (48:14):
But it's promising. It's exciting that people are trying to
push their way through the theoretical jungle. You know, until
we figure out how to make a black hole here
on Earth, or we've come up with some clever quantum
gravity experiment that lets us see particles feeling gravity and
understand whether they're like bending space time probabilistically, or whether
gravity collapses their wave functions, or what's going on, we
(48:36):
can only make progress theoretically. That means trying to find
mathematical relationships between these theories, either making electromagnetism look more
like gravity or make gravity look more like electromagnetism. So far,
both paths have been sort of stuck in the jungle.
But maybe one day people will find a connection between
them and will all be illuminated.
Speaker 1 (48:57):
That is beautiful, but you do also keep breezing past
this plan to make up a black hole on Earth.
Speaker 4 (49:03):
That's feel sangerous.
Speaker 3 (49:04):
To me, it is very dangerous, but also potentially we
could learn a lot about the universe, so you know,
may be worth a risk.
Speaker 4 (49:11):
Yeah, ultimate knowledge right before oblivion. Sign me up.
Speaker 3 (49:18):
Sounds good. We'll stay tuned for more hints about potential
ultimate knowledge about the universe, just before you get sucked
into oblivion. Thanks so very much Katie for joining me
on this journey of theoretical understanding, and thanks to everybody
for tuning in. Tune in next time for more science
(49:39):
and curiosity. Come find us on social media where we
answer questions and post videos. We're on Twitter, Discord, Instant,
and now TikTok. Thanks for listening, and remember that Daniel
and Jorge Explain the Universe is a production of iHeartRadio.
For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts,
or wherever you like listen to your favorite shows.
Hey, Daniel, have you guys figured out how to make
quantum mechanics and gravity work together?
Speaker 2 (00:12):
Yet? Oh?
Speaker 3 (00:13):
Hit me hard with a nasty question right off the bat.
Huh well, unfortunately we haven't figured it out yet.
Speaker 1 (00:19):
Well what have you guys been working on and how
long have you been working on it?
Speaker 4 (00:22):
Like decades?
Speaker 3 (00:24):
More than one hundred years? Actually?
Speaker 1 (00:26):
Uh? Well, and I thought I was a little bit
behind on my deadlines.
Speaker 4 (00:30):
So you know how long you think it's going to take?
Speaker 1 (00:33):
Another weekend? Another thousand years? Can I get it in
by monday?
Speaker 3 (00:40):
You know? The only progress we've really made is coming
up with some long, confusing names for.
Speaker 1 (00:44):
It, like Mississippi or quantum gravity.
Speaker 3 (00:49):
No, that would be much too clear.
Speaker 1 (00:51):
Okay, like gravito, quantum field, hydrodynamically.
Speaker 3 (00:56):
I think you should be a physicist, Katie. You have
the knack for it.
Speaker 1 (01:00):
I know how to throw a ball and look at
it go up and come down, So I'm already halfway there.
Speaker 3 (01:20):
Hi. I'm Daniel. I'm a particle physicist and a professor
at UC Irvine, and I desperately want to know the
underlying rules of the universe.
Speaker 1 (01:28):
I am Katie Golden. I am not a particle physicist.
I host a podcast about animals, but that doesn't mean
that I couldn't maybe try to smash quantum mechanics and
gravity together if you give me a government grant.
Speaker 3 (01:44):
I think everybody who's not a particle physicist should introduce
themselves that way. Hi, I'm Sally. I'm not a particle physicist.
Speaker 4 (01:50):
I think that makes the most sense.
Speaker 3 (01:54):
In that case, I should start off by listing all
the things that I'm not every time I introduce myself
to somebody. I'm not an Olympic gymnast. I'm not a
Wall Street trader dot dot.
Speaker 4 (02:03):
I am not a hot dog eating champion.
Speaker 3 (02:05):
Yet we can all aspire to stuff well. Welcome to
the podcast Daniel and Jorge Explain the Universe, a production
of iHeartRadio in which we aspire to be particle physicists.
We all want to understand the way the universe works.
We all want to figure it out, to zoom down
to the tiniest little bits of the universe, the basic
(02:27):
building blocks and the rules that tertangle them, and zoom
out from that picture to understand how it all comes
together to make our amazing hour Bonkers are wonderful, our
delicious universe.
Speaker 1 (02:37):
Yeah, like a nice stew of concepts all mingled up
in the stars.
Speaker 4 (02:43):
So yeah, I mean it is interesting.
Speaker 1 (02:45):
Because I think we've talked a little bit on the
times that I've been on the show about quantum mechanics.
We've talked about gravity, We've talked about sort of this
distinction between the physics involved in the really tiny and
the really huge, and how it's a bit of a
puzzle to fit those together.
Speaker 3 (03:04):
Yeah, the basic strategy of physics has always been to
zoom down to the littlest bits of the universe to
try to understand them, and then hope that we can carefully,
one step at a time, zoom out and figure out
how those things come together to make our world. You know,
how electrons and protons come together to make atoms, and
atoms come together to make molecules, and molecules come together
(03:27):
to make proteins, and proteins come together to make steak
and ice cream and all the delicious things that you eat.
That's sort of like reductionist approach. We zoom down and
then one at a time step back up to understand
our world. Has long been the approach we wanted to
take to understand the universe, and that's worked for lots
of stuff, like the way we understand ice cream and
blueberries and steak and goats and all that stuff. But
(03:48):
you're right, Katie, there's one big thing that it hasn't
been able to explain, maybe the biggest, most important thing
that shapes our universe, and that's gravity. How everything seems
to attract itself or how things flow through space time.
We still don't understand how that bubbles up from the
tiniest little bits of.
Speaker 1 (04:05):
The universe because gravity is sort of, I guess, like
a big force that we observe. So like you know,
you feel gravity on a planet. Maybe you and I
have our own gravitational pull, but it's much weaker than
a planet, so we're not going to notice it. But
is gravity something you can really measure much when you
(04:25):
get really small, like say you're looking at particles, Like
does a particle have its own gravity? Or can you
even measure gravity of say like a neutron or a
proton or an electron.
Speaker 3 (04:37):
Yeah, that's exactly the puzzle. On a theoretical sense. We
don't know how to stitch these two things together, and
we'll talk about that more during this podcast. But even
more frustrating in experimental sense, we can't even see what
the universe does. Basically, the job of physics is to
explain what is the universe doing, what's happening out there,
and why does it make sense? And the first step
(04:59):
there is to see what's happening in the universe. And
so the first thing you want to do if you
want to explain the gravity of little particles, the quantum
mechanical understanding of gravity is to see gravity operating on
little particles. That's basically what you're asking. And the challenge
there is that gravity is so dang weak compared to
the other forces of electromagnetism, even the weak force and
(05:20):
definitely the strong force, Gravity is like a bajillion zillion
quintillion times weaker, which is why, for example, like a
simple fridge magnet can overpower the gravity of the Earth
and hold your recipe against your fridge or your pictures
of your kids and their cousins. It's not hard to
overcome the gravity of an entire planet with a tiny
(05:40):
little bit of electromagnetism. And so when you're looking at
a tiny particle, a proton or a neutron, its gravity
is basically zero. It's so hard to measure. The smallest
thing we've ever measured the gravity of is something like
on the order of a gram, you know, which means
it has like ten to twenty particles in it. We
are nowhere close to being able to see gravity operate
(06:04):
on particles so that we can then try to explain
how it all works.
Speaker 1 (06:08):
That seems kind of hard because like science is mostly
about say, either direct observation or setting up an experiment.
Speaker 4 (06:17):
So if you can't even see it happening.
Speaker 1 (06:20):
Or figure out how to observe it in particles, how
can you ever figure out how it works on such
a small scale.
Speaker 3 (06:27):
Yeah, great question. Well one is you don't give up.
Speaker 4 (06:30):
Oh I was I was gonna go for Just give up, never.
Speaker 3 (06:37):
Give up, never give it. People are doing these incredible experiments.
It's really an amazing accomplishment to figure out how to
test gravity on the smaller and smaller things. And there's
this history getting all the way back to like Cavendish
torsion experiments of lead balls a weigh a few pounds,
down to smaller objects and smaller objects, and very recently
down to stuff like smaller than a raisin, you know,
(06:59):
a few grains of sand of material, and I really
want to underscore that there's a special scientific skill there.
It's not like mathematics or genius insight into philosophy. It's
experimental bravura, you know. It's what Jorge might call engineering.
It's like figuring out how to make your experimental system
so quiet and so clean and so pristine that you
(07:20):
can force the universe to reveal one of its secrets.
It's a really special skill in science. And so those
folks are working hard and drilling down. But yeah, they're
like twenty orders of magnitude away from figuring it out,
so it's going to be a while. The other thing is,
you could, you know, try to visit a black hole.
Inside a black hole. We think that gravity and quant
mechanics are both relevant because obviously there's strong gravity, but
(07:42):
also things are squished really really small at the singularity
inside the black hole. Of course, that's inside the black
hole beyond the event horizon. So we still haven't figured
out how to probe that.
Speaker 1 (07:54):
Yeah, we've talked about this. It is not in the
budget to go to a black just yet.
Speaker 3 (08:01):
No, so instead you might want to make your own
black hole and then study the patterns of its hawking
radiation to try to get some clues as to what
might be inside of it. But nobody succeeded in making
a black hole yet, and if they did, it might
destroy the Earth, and so there are some questions there.
So while the experimental side is super tooper frustrating, we
can try to make some progress on the theoretical side, thinking
(08:24):
deeply about the universe, eating special mushrooms and having insights
about you know, connections and mathematical symmetries between these two ideas,
to look for links, to look for connections, to look
for ways to fit them together in our minds that
might give us some new clues as to how to
bridge these two fundamental pillars of modern physics.
Speaker 1 (08:44):
Now, do you get university funding for mushroom tripping in
the sake of theoretical physics.
Speaker 3 (08:52):
If you can convince the funding agency that it's essential
for your research to make progress, then ya, I'll bet you.
And so today on the podcast, we'll be exploring one
of those potential directions to bring gravity and quantum mechanics
together to try to fit these two genius insights about
the way the universe works into one mega inside and
(09:13):
today in the podcast, we're asking the question what is
gravito electro magnetism? Boy? Is that a mouthful? I feel
like this must have been named by some German person. Yeah,
every time they come up with a name for something,
they just like stick a bunch of words together into
one super long word instead of.
Speaker 4 (09:33):
Coming up with a new word.
Speaker 1 (09:34):
It's use the words you already have, but stick them
all together.
Speaker 3 (09:40):
Imagine if you came up with new ice cream flavors
that way, cookies and cream all one word.
Speaker 4 (09:45):
Wait it isn't already.
Speaker 3 (09:48):
No, No, I think that's exactly how they figured it out.
Speaker 1 (09:51):
Like, I think it's interesting that I don't think I've
ever seen a question before of the audience where people
are just like, I can't even comprehend the name of this.
Speaker 3 (10:00):
That's right, And so this was maybe a little bit
unfair to drop this on the listeners, But what the heck.
I think it's fun to ask the guys questions about
things you never heard about. So thanks very much to
everybody who volunteers for this audience participation segment of the
podcast and is caught aware by by very technical physics
questions without an opportunity to prepare We really appreciate you
(10:20):
being gained for this. If you would like to play
for future episodes of the podcast, please write to me
two questions at Danielanthorge dot com. So before you hear
these answers, think about it for a minute. What do
you think gravito electromagnetism could be. Here's what some listeners
had to say as.
Speaker 2 (10:38):
The electrochage put off by strong gravity. Maybe I don't
know how you combine gravity and electromagnetism, but it sounds
like some kind of combo of the two. So maybe
it's the way in which electromagnetic fields are affected by gravity.
Speaker 3 (11:03):
Or vice versa. I'm going to guess that gravito electromagnetism is.
Speaker 1 (11:10):
The impact that gravity has on the electromagnetic force. I
wonder what insane clown posse has to say about gravito electromagnetism,
and if they know how it works?
Speaker 4 (11:25):
Does that call back too old?
Speaker 1 (11:27):
Now?
Speaker 4 (11:27):
Am I old?
Speaker 3 (11:30):
I'm not going to comment on it. I will say
that I am approaching fifty and so I've embraced being
fifty by calling myself fifty before I even got there.
And my kids think it's weird that I round myself
with to fifty, but I love it.
Speaker 4 (11:45):
I do that too.
Speaker 1 (11:46):
I round up so I'm not so shocked when it happens.
Speaker 3 (11:49):
Exactly. That's what I was thinking. And then my daughter
asked me. She said, well, does that mean when you
turn fifty one you're gonna round yourself up to one hundred?
Speaker 4 (11:57):
Why not?
Speaker 3 (11:58):
Yeah, I thought, you know, for the sake of consistence,
I guess I have to.
Speaker 1 (12:01):
I mean, you know, then you could be the oldest
person on earth, even before you start getting a pension.
Speaker 3 (12:07):
That's true. I'm just hoping to get some of those
compliments like wow, Daniel, you look good for it. All right,
But back to the topic of quantum mechanics and gravity.
We see people are struggling to understand what this word means.
But there is a sense there that it's about some
relationship between gravity and electromagnetism. Maybe gravity is caused by electromagnetism,
(12:29):
or maybe you get electric charges from gravity. There's some
fun ideas in there.
Speaker 4 (12:33):
It does sound like a little scammy.
Speaker 1 (12:37):
It sounds like something where someone's trying to sell something
to me, because it's just so many technical sounding words
all smashed together. It's like, yeah, I kind of want
to know what it is. The only thing I can
think of like these listeners is just that it's like
kind of trying to smoosh the concepts of gravity and
electromagnetism together, but I kind of want to know more
(12:59):
specifically what that is and how that works.
Speaker 3 (13:03):
Yeah, and so delay the groundwork. I think we need
to spell out a little bit of detail about like
why this problem is hard. Why is it difficult to
bring gravity and electromagnetism, or gravity and quantum mechanical theories
of forces together in general, And so we should probably
start with those quantum mechanical theories. And you know, we
talked about electromagnetism because it's one of the fundamental forces
(13:27):
that we know about in the universe. And all of
these fundamental forces are quantum mechanical, meaning that we have
a theory of quantum mechanics that describes particles and how
they move through space or how they exist and how
they have probabilities to exist. And those quantum mechanical theories,
those Shroninger equations and the lagrongins and the Hamiltonians, all
(13:47):
those mathematical structures are quantum mechanical and they describe the forces.
So we have electromagnetism, we have the weak force, and
we have the strong force. All these things can be
described using a quant maicaanical theory. It means we know
how to calculate what happens when one particle pushes or
pulls on another particle using one of these forces. Like
(14:08):
when two electrons are coming near each other, they repel
each other, and they use these forces to do so.
They use electromagnetism, And you can think about that quantum mechanically,
either as one electron has a big electromagnetic field and
that's pushing on the other electron, or if you prefer
the particle picture, you can imagine that the two electrons
are exchanging photons. They're tossing photons back and forth, and
(14:31):
that's how they're pushing on each other. But either way,
we have a nice quantum mechanical picture from the ground up,
from the littlest bits of these three fundamental forces electromagnetism,
the weak force, and the strong force.
Speaker 1 (14:43):
So is gravity even weaker than the weak force?
Speaker 3 (14:48):
Gravity is like ten to the thirty times weaker than
the weak force. It's almost unimaginably weak. It's so much
weaker than the other forces that it's a big puzzle
in physics. Like in physics we look for patterns and clues.
We expect things that are similar in nature to all
operate in under similar principles and have similar numbers. So
(15:09):
if you want a lump gravity in as one of
the forces, then you got to answer the question why
is it so much weaker than the other forces? Not
by a factor of ten, not by a factor of
one hundred, not by a million, but ten with thirty
zeros behind it. That's a big deal.
Speaker 1 (15:25):
And so like the difference between electromagnetism, the weak force,
and strong force like is not nearly as big as
the difference between all those three and gravity.
Speaker 3 (15:37):
Yeah, exactly. The strong force is like ten times more
powerful than electromagnetism, which is like one hundred times more
powerful than the weak force, which is like a gajillion
billion of jillion times more valuation.
Speaker 1 (15:49):
To hang on, that doesn't even sound like a number, Okay,
but I get it. So gravity is so incredibly weak
it doesn't even seem like it's in the same category
as these other things. It's like comparing like a blue
whale to an ant.
Speaker 3 (16:03):
Yeah, that's exactly right now, fundamentally, that's not a problem.
Like it's possible that you could have for forces in
the universe and one of them is just much weaker.
There are ways that you can do that. It's not
an insurmountable issue. It's strange and it would make you
ask like why is that and to look for explanations,
but mathematically it doesn't prevent us from describing it. That's
(16:25):
not the challenge with gravity. If you sit down and
try to describe gravity using some kinds of maths similar
to the way we describe electromagnetism and the weak force
and strong force, to come up with like a quantum
theory of gravity that describes it as a force. Then
you start to build in gravitational fields and you can
think about the quantized ripples in those fields as particles.
(16:46):
In this case, it would be the graviton. So when
two planets come near each other and pull on each other,
the quantum picture of gravity would have them exchanging gravitons
the way two electrons are like exchange photon. So you
can start to go down that road mathematically and things
seem okay. You just like dial the force way way
(17:06):
down to make it super duper weak, but then you
run into a lot of mathematical problems actually making that
theory work.
Speaker 1 (17:13):
How do you check your math in a situation like this,
Like what are the kinds of mathematical problems that you
run into? And how do you know that they're problems?
Speaker 3 (17:22):
Yeah? Great question. The way that you know that your
theory is working or not working is that you try
to use it and you see if it gives reasonable results.
Like if you ask, I want to push these two
particles together, I want to calculate the probability of various outcomes.
I want to know the particles are going to bounce
off each other, or if they're going to scatter off
at this angle or at that angle. So you try
to calculate things. You try to make predictions in physics.
(17:45):
For your predictions to be reasonable, there's some limits. There's
some restrictions, like your predictions can't have probabilities greater than one.
If you ask, like is my electron going to go
left or right? And your theory says you have one
hundred and seventy five percent chance of its going left,
And you're like, hm, well that's that seems wrong. That
can't r right.
Speaker 1 (18:03):
So when my gym teacher told me to give it
my one hundred and ten percent. Like, that's not right,
that's physically impossible.
Speaker 4 (18:11):
That's right, my all.
Speaker 3 (18:14):
Your gym teacher is violating the fundamental rules.
Speaker 4 (18:17):
Of physicals call them up right now.
Speaker 3 (18:18):
Or maybe your gym teacher is a quantum gravity theorist,
because that's exactly what happens when we try to make
a quantum gravity theory. Gravitons are really tricky because they
don't just transmit gravity. They have energy themselves, which means
they also couple to gravity. They feel gravity, they emit gravity.
So like when you emit a photon, photons don't feel electromagnetism,
(18:42):
they don't bounce off of other photons, they don't emit
other photons. Right, Photons don't feel electric charges because they
are neutral. They don't have a charge themselves, so they
will like fly right through an electric field. But a
graviton has energy, and gravity is felt by everything with energy,
So graviton feel gravity, which means they emit more gravitons,
(19:03):
and those gravitons emit more gravitons, and pretty soon you
have an infinite number of gravitons, and you start to
get nonsense answers out of your theory.
Speaker 1 (19:11):
When you say a graviton, right, I'm thinking of a
particle sort of like a photon. But photons we've actually measured, right,
We've actually been able to sort of get physical evidence
of their existence. Like, do we have like physical evidence
of the existence of gravitons as like an existing thing
(19:32):
other than just knowing that gravity exists.
Speaker 3 (19:35):
We do not have any evidence of gravitons. We have
a very successful theory of gravity. It's Einstein's theory of
general relativity that describes how space and time bend around
masses and that affects how things move, and that's very,
very precise, but that describes gravity as not a force.
It's like a bending in space and time. We're going
to switch over and try to think about gravity as
(19:56):
a force instead of bending in space and time. Then
you need these gravitons, and nobody's ever seen them. The
reason they're so hard to see is precisely because gravity
is so weak, Like electromagnetism is a pretty strong force.
Electrons are radiating photons all the time. It's not a
rare thing to happen in the universe. But gravitons are
more rare because gravity is so weak, and they're much
(20:18):
harder to see because gravity is so weak, so the
impact of like one graviton would be very very hard
to detect. So we don't know that gravitons are real,
but they are a necessary part of a theory of
quantum gravity that tries to make gravity look like a
force and fitted it into this quantum mechanical framework. So far,
and nobody's even been able to make the math work
(20:40):
to have like a consistent theory that we could even
go out and test in experiments.
Speaker 1 (20:45):
So we can't make the math work. We can't even
find any evidence that gravitons exist. Things are looking pretty good,
pretty good so far. Maybe we should take a quick break.
I will look around see if I've got any gravitons
just kind of lying around, you never know, And then
when we get back, maybe we can take another crack
(21:06):
at this and see if there's any anything that actually
where the math you carry the ones and it all works.
Speaker 4 (21:13):
Out all right. So bad news.
Speaker 1 (21:28):
Daniel couldn't find any gravitons, not a single one. I'm
also out of milk, so things aren't looking so good
here do you have any good news for me in
our effort to smoosh together quantum mechanics and general relativity.
Speaker 3 (21:45):
I didn't figure it out in the last couple of minutes,
but you know, a lot of clever people have been
thinking about this and trying to find some connections between
gravity and electromagnetism, or between electromagnetism and gravity, sort of
going both directions, trying to make gravity look more like
electromagnetism and the theoretical side, or giving up on that
and trying to make electromagnetism look more like gravity. So
(22:08):
we don't have any experimental results to guide us, but
we can still think deeply about the structure of these
theories and try to make some theoretical progress in our minds.
Magic mushrooms or no.
Speaker 1 (22:20):
All right, so we're in the mindscape. What are we
doing in order to solve the hurdle of the math
not mathing in this idea, because it sounds like we
were sort of trying to think of planets as like
scaled up particles and gravity as like a force between them,
as if they're giant particles, and that didn't really work. Like,
(22:43):
is there another approach that you could use or is
there a way to like fine tune that approach such
that it actually does work.
Speaker 3 (22:50):
Yeah, So the short answer is there isn't a great approach,
but that doesn't mean we can't make progress. And I
think people should understand that. In theoretical physics, it's not
like you sit down one day and come up with
the whole theory movies. You're entering like a mathematical jungle.
You're not sure if there is a path through, and
it takes exploration. Exploration is not just something we do
(23:11):
in experimental physics or in experimental biology. We're like walking
through a literal jungle looking for new kinds of frogs.
In theoretical physics, you can also explore. You can just
like try stuff and say, well, I'm going to go
in this direction and see if it works out, kind
of like when you're trying a proof in tenth grade
geometry and you're like, well, I'm not sure this is
gonna get me where I need to go, but I'm
gonna play around with these angles. And so in theoretical physics,
(23:34):
people are trying something that has a long tradition dating
all the way back to like Maxwell James Clerk, Maxwell
in the eighteen hundreds was looking at theories of electricity
and theories of magnetism, and he tried something cool. He said, well,
let me write down the equations for electricity and write
down the equations for magnetism and try to smooth them
together and make them look as much like each other
(23:55):
as possible. And when he did that, he realized, oh,
my gosh, these basically have the same equations. And not
only that, but you can click the equations together because
sometimes electric field cause magnetic field and vice versa to
make one bigger picture. So we had this great insight,
which is where we got the theory of electromagnetism. So
now people are trying to do something similar. They're saying,
(24:16):
let's look at the equations for electromagnetism and the equations
for gravity and see if we can find relationships. Are
they like a mirror image of each other? Can we
somehow find patterns there and then use that to guide
us through this intellectual jungle to a theory that combines
gravity and electromagnetism into one big theory.
Speaker 1 (24:35):
So for someone just theoretically who does not have a
grasp of what theoretical math would look like, and when
you say equations, like what that is?
Speaker 4 (24:46):
Like are we.
Speaker 1 (24:47):
Talking about like you have five equations that you have
to memorize to understand gravity? Like are there hundreds of equations?
And when you're trying to like smash together equations, you know,
is it sort of like a brilliant mind where you
just see floating numbers kind of going together and doing
things like what in terms that someone like me who
(25:11):
math is trying to calculate a tip?
Speaker 4 (25:14):
How does that work?
Speaker 3 (25:15):
Yeah, that's a great question, and we could start off
pretty simply. You know, people are probably familiar with Newton's
law of gravity. That just says that the force between
two objects is proportional to the two masses divided by
the distance between them squared, and then you multiply that
whole thing by a constant big G Newton's constant. So
(25:35):
Newton's equation for the force between two objects is like
gmm over R squared. All right, So that's Newton's theory
of gravity. Then we can look over at electromagnetism. We
can say, what's the equation for the force between two
particles that have charge? Like remember our question was like
what happens when two electrons come near each other. Can
we calculate that well, Kulham's law tells us that the
(25:58):
force between two parts particles goes like the charge of
the two particles divided by the distance squared between them,
all multiplied by a constant in this case K. So
you look at these two equations, you notice instantly, like HM,
these have kind of similar structures. On the top of
the equation is the charge of the two objects. Where
(26:18):
gravity the charge would be the mass, and for electromagnetism
the charge is obviously the electric charge. And both of
them get weaker as the distance grows by the same
power you get twice as far apart. Gravity and electromagnetism
both get four times weaker. You go ten times further away,
the force of gravity and electromagnetism both go down by
(26:39):
a power of one hundred. So they have very similar
structures there already. That's encouraging.
Speaker 1 (26:44):
But if it was just as simple as finding sort
of some of these equations that seem to look kind
of similar and match them together, like it seems like
we would have already figured this out. So what is
the scale of the complexity, Like, why have it we've
been able to find just like a bunch of these
equations that kind of look similar and seem to have
(27:05):
the same general structure and have them work together.
Speaker 3 (27:08):
Yeah. Well, one issue, of course, is that we know
that Newton's theory of gravity is not the right theory.
Speaker 4 (27:13):
Whoops.
Speaker 3 (27:15):
When Newton was a very clever man, and he has
a very nice theory which mostly works but not.
Speaker 4 (27:20):
Quite irresponsible with apples too.
Speaker 3 (27:24):
Einstein's theory of gravity is not just a reimagining. It's
not just saying, look, the story is wrong. It's not
a force between objects, it's a bending of space and time.
It also gives different predictions, like, for example, Newton says
that the force just depends on the mass. It doesn't
depend on whether the object is spinning or not. So
according to Newton, if you're in orbit around the Earth,
(27:47):
whether the Earth is spinning or if it stopped spinning
or spinning the other way makes no difference for gravity.
Einstein says, Nope, that's not true. If the Earth is spinning,
that has more energy, and since gravity is linked to
energy of all kinds, not just mass, that changes the
gravitational force on the object in a complicated way. So
(28:07):
Einstein's equations are much more complicated than Newton's. He doesn't
just have like one simple force equation. He's got a
really complicated tensor equation, where a tensor it's just like
a matrix. It's like an array in computer programming, you know,
a way to keep track of a bunch of numbers
all at once. So he has more complicated equations. And
so you can't just say, look, Newton's law and kulums
(28:27):
are similar. You got to dig deep into Einstein's rules
for gravity.
Speaker 1 (28:31):
So how do we know Einstein is right and Newton
is wrong. It can't just be that Einstein's got cooler
hair or more complex equations.
Speaker 3 (28:40):
Well, Einstein and Newton make different predictions, and famously Einstein's
predictions were right. Einstein predicted stuff about how light bends
around the Sun during an eclipse, and he predicted stuff
about how mercury orbits the Sun and the angle of
the eclipse of mercury, how that twists as mercury is
orbiting the Sun. All these little difference between Newton and
(29:00):
Einstein add up and a few special cases, so we
know that Einstein's theory was right. So then people took
this on. They're like Okay, well, can I take Einstein's
equations and try to make them look like electromagnetism. Like
we were able to take Newton's law and make it
look like Kulam's law. Can we take Einstein's gravity and
make it look like electromagnetism? And people have actually succeeded
(29:23):
in doing this. There are these Gravita electromagnetic equations when
if you write them down, you get equations that look
very similar to Maxwell's equations for electromagnetism. Maxwell has four equations,
and I won't get into the math with you. You know,
there's a there's like a divergence and a curl for
electricity and magnetism and indie gravita electromagnetic equations. There are
(29:46):
also four equations and have a very similar structure to
Maxwell's equations. You should look them up and write them
side by side. They look very very similar. It's eerie,
it's spooky. It's like the universe is saying, oh, look,
you found the pattern. It's over here in the gravity
world and in the electromagnetic world.
Speaker 1 (30:03):
This does feel like a conspiracy theorist sort of aligning
charts and with a corkboard and yarn and trying to
make these connections. But yeah, I mean, I'm looking at
this and you know, I don't know a look of
complex math, but it yes, they look very similar.
Speaker 4 (30:20):
But if we've.
Speaker 1 (30:21):
Found this, right, it doesn't mean that we've figured out
how they interlock. Like we found some similarities, some equations
that seem to match, but the bigger picture has not
yet become clear.
Speaker 3 (30:33):
Yeah, that's right, and I hear you setting me up
to deliver the bad news of why this is going
to work. But first there's a little bit more good, okay,
which I think is a fun insight into how this works.
The thing about Einstein's equations for gravity, as we were
saying before, is that it gives you more than just
like a straightforce between two objects. Spinning objects can create
like torque and drag in space time itself, which gives
(30:56):
all sorts of weird forces, like if you are orbiting
the Earth and the Earth is spinning, then there's some
frame dragging effects there. Check out our whole episode about
that if you want more details. But effectively, it gives
like a twist on things that are orbiting the Earth.
So according to Einstein's gravity, it's not just a force
between two objects. There are more subtle effects there. And
(31:17):
the really cool thing is that in the gravito electromagnetic equations,
the ones where you take Einstein's gravity and try to
convert them to look like electromagnetism, you can see this emerge.
And in those equations you have what they call a
gravito electric field, which is sort of like the straight
up Newtonian version, plus this gravito magnetic field. So basically,
(31:40):
to explain all of Einstein's gravity you break it up
into two pieces, this analogy to the electric field and
this analogy to the magnetic field. And it goes even
deeper than that, because it's not just notation. It's not
just like, hey, let's write this down in a cute
way that looks sort of similar. There really is a
conceptual connection there because an electromagnetic the way you get
(32:01):
magnetic fields is you take electric fields and you wiggle
them like currents of electrons give you magnetic fields. So
it's like velocity dependent, right. Well, the cool thing about
the gravitomagnetic field, this other component of these equations you
have to add on to be able to describe Einstein's
gravity with equations that look like electromagnetism is that they
(32:22):
create velocity dependent acceleration in just the same way. For example,
those spinning masses. When the Earth is spinning, that's an
acceleration because any sort of rotation is an acceleration, and
that gives an acceleration. On satellites, it gives a twist,
it gives a pull. So when you force gravity into
this structure that looks like electromagnetism, you learn some things
(32:45):
about gravity. It like sorts it in your mind in
a way that actually gives you a little bit of insight.
And that's a good sign. When you're bushwhacking your way
through the theoretical jungle trying to make connections between things.
You don't have to force things into categories. When they
sort of naturally fall into those categories and reveals something
deep about the nature of that force or the nature
of the phenomenon, it's a sign that you might be
(33:07):
on the right track. So that's the good news that
there really is something satisfying about making gravity look like
the equations of electromagnetism. It's not just like hacking it
up into bits and shoving it in boxes.
Speaker 1 (33:20):
It's not just using the same colored gelpins to write
the equation.
Speaker 3 (33:25):
Exactly.
Speaker 1 (33:26):
That sounds very promising, right, that sounds like a very
like promising path. And the fact that there's this wiggle
connection where wiggling or velocity movement for gravity like creates
this this field is very interesting.
Speaker 4 (33:42):
I just I feel a butt is common.
Speaker 3 (33:44):
There is a big butt, A.
Speaker 1 (33:45):
Man, I knew I like big butts, and I cannot lie.
Speaker 3 (33:52):
Now that's a reference.
Speaker 4 (33:53):
I hope everybody hopefully Stelia.
Speaker 3 (33:55):
The other brothers can't deny. Well, the thing that the
other brothers can deny is that this works in difficult situations.
Like we said that you could take Einstein's rules and
you can express them in mathematical equations that look like electromagnetism.
But there was a butt there I left off, And
the butt is This only works if gravity is kind
(34:16):
of weak, like when the curvature of space time is
not very strong, when you're like far from any intense mass,
when you're far away from a black hole, for example,
or even from the Sun, then this works pretty well.
But when the curvature of space time gets more intense,
this breaks down. Like the equations are just too complicated,
too intense. We have no way to fit them into
(34:37):
these boxes to make them look like electromagnetism. In order
to do that, to take the complicated Tensor equations of
general relativity and to make them look like electromagnetism, you
have to make a bunch of assumptions, and one of
those assumptions is gravity is pretty weak. So basically what's
happened here is you've avoided the hard problem. You know,
the hard problem of making quantum gravity work was figuring
(34:59):
out what happened when gravitons amid other gravitons amid other gravitons. Basically,
when gravity gets very very strong and it can no
longer be neglected, and that's exactly the situation that gravito
electromagnetism doesn't know how to answer. So it's some progress
in the sense of like, hmm, you found some cool
connections between these theories, but only in the easy parts,
(35:20):
not in the hard parts at all. When you get
to the hard part of gravity being very strong and
every graviton is emitting ten other gravitons, then this breaks
down and it doesn't help us at all. So it's
like an interesting island of understanding, but it doesn't make
any progress on the really hard part of the problem
of describing gravity as a quantum theory when gravity is
(35:40):
very very strong.
Speaker 1 (35:41):
But could it be revealing something about gravity still, like
maybe that there is a significant difference between a strong
or large amount of gravity, like the gravity of the
Sun versus the Earth. If there is some kind of
fundamental difference between like weak levels of gravity and strong
levels of gravity, that seems like that could itself be
(36:05):
an interesting kind of finding, even if it still doesn't
solve the bigger question of how to merge those concepts.
Speaker 3 (36:12):
Yeah, exactly, And that was the point I was trying
to make earlier that even intermedia progress is progress. You
don't have to know if this is going to fundamentally
solve the question of quantum mechanical gravity for it to
be cool that you figured something out, that you've made
some headway, you found some island of understanding whether it
actually connects to the mainland and reveals all the deep
secrets we don't know yet. But that doesn't mean it's
(36:33):
not worth doing and not worth exploring. Right, we've made
it to this stage where we've been able to accomplish
this connection between electromagnetism and gravity. It might be that
hunting around and digging around and poking in various directions.
Lets us build from this right that we can go
from here to figure out how to describe strong gravity.
Nobody knows how to do that yet, but this is
(36:54):
like another avenue of attack. This gives us another way
to think about it. At least it might be a
total dead end or might be the wave of the future.
We haven't figured that out yet. It's on the forefront
of knowledge.
Speaker 4 (37:05):
I mean, let's go with not being a dead end.
Speaker 1 (37:09):
We'll take a quick break and try to keep up
the optimism that this is actually going towards finding a
fundamental answer that'll change everyone's lives. And we're probably not
going to figure it out in the ad break, but
you know, we'll think about it. So we are back.
(37:40):
We have not yet solved how to weave together electromagnetism
and general relativity or gravity, but there has been some
interesting progress that has been made that is perhaps instructive
and perhaps interesting. So we had that issue that these
(38:02):
equations when gravity is weak, they seem to kind of align,
like you have the equations associated with general relativity and
then Maxwell's equations that looked similar then when gravity got
strong like the sun or a black hole, that kind
of broke down. It no longer worked in that way.
(38:23):
So is there another sort of angle of attack that
is being explored.
Speaker 3 (38:28):
Yeah, people are trying so many different things at once,
and you know, this is the way we make progress.
You push your way through the jungle. Maybe you make
it all the way through. Maybe you run into somebody
else coming from the other direction right, and you can
join you two efforts. And so that's what's happening is
a bunch of people are working on trying to make
gravity look like electromagnetism. So that's the gravito electromagnetic approach
(38:50):
that we just talked about. But some people are working
in the other direction. They're saying, let's not make gravity
look like electromagnetism, let's make electromagnetism look like gravity. Einstein's
big idea was let's not think of gravity as a force,
let's think of it as the curvature of space time.
And so people are wondering, like, can we extend that idea?
(39:11):
Can we also do that for electromagnetism. Remember that the
way Einstein did this is he said, look, it feels
like there's a force between you and the Earth. Newton's
description of gravity as a force is compelling because when
you throw a ball in the air, it falls to
the Earth and it looks like it's getting pulled on. Right,
we have this experience of gravity as a force. But
(39:32):
he said that it's not actually a force. That's something
of an illusion. What's happening when you toss a ball
is that you're releasing it into free fall. Space itself
is curved in the vicinity of mass, so there's a
natural path for objects to follow in curved space time.
So the ball naturally falls towards the center of the Earth.
So Newton's picture is there's a force pulling on the ball,
(39:55):
and then it hits the Earth and it stops it
because the Earth is balancing that force of gravity. Einstein's
picture is different. Einstein says, when the ball is in
the air, it's in freefall. There is no force on
the ball at all. It's just following the motion of
space and time. And then the Earth stops it because
the Earth itself is providing a force. It's accelerating against
(40:15):
that natural motion of space time.
Speaker 1 (40:17):
Yeah, and I think you've told me this is actually measurable, right,
that there is acceleration acting when you are standing on
the floor.
Speaker 3 (40:27):
Exactly, if you jump off a building instead of the ball,
and you take a scale with you, and as you're
falling through the air, hurtling towards the earth, you stand
on the scale, what are you going to measure? You're
going to measure nothing, right. You have no weight, and
that's because you're in freefall. There's no acceleration there. You're
not measuring anything. If you're standing on the surface of
the Earth and you stand on the scale, then you
measure your weight. That's where there's a force, right, So
(40:50):
there really is no force on you when you are
in freefall. There's a force on you when you're standing
on the surface of the earth. That's the Earth pushing
up against that natural motion. So the explanation is that
there is no force there. There's just a curvature of
space and time. And we couldn't see that curvature, and
that's why it looks to us like there is a force.
Speaker 1 (41:10):
Having this as the theory about gravity, like, how do
you then fit the quantum forces into this framework, right,
because like that seems fundamentally different. Those are forces, they're
pulling or pushing against each other. How does that fit
into this kind of idea of gravity being like the
shape of existence, which sounds it's hard for me to
(41:32):
kind of think about that, right, like the shape of
the universe, the shape of the fabric of the universe,
and then we're just kind of falling along it.
Speaker 4 (41:40):
And then you have these particles.
Speaker 1 (41:42):
Have we observed anything in particles that could sort of
fit within that framework.
Speaker 3 (41:48):
So we haven't observed anything yet, but there are some
theoretical ideas. The idea is to say, well, maybe electromagnetism
also isn't the force. Maybe it just looks like a
force and it's actually the result of a second kind
of curvature. So we have like first kind of curvature
is Einstein's curvature of space time that gives us the
apparent force of gravity. If space can also be curved
(42:11):
in another way, and that curvature gives us the appearance
of the force of electromagnetism. And in order to have
curvature in another way, you need more dimensions of space
and time. The idea is, like einstein space is three
plus one dimensions. You start with one dimension, which is
a line you draw a second dimension, which is perpendicular
(42:32):
to that. Now you have like a plane. You can
add a third dimension which is perpendicular to both of
the first two, and that gives you like three D
space right where each of those three lines are perpendicular
to each other. And that's it. There's no more room
to add another line perpendicular to all three.
Speaker 4 (42:49):
Right, because space, Yeah, it doesn't work.
Speaker 3 (42:53):
It's sort of crazy in mind bending. And I remember
as like an eight year old trying to imagine that's
fourth dimension but not being able to do it. But
we do think of time as sort of a fourth dimension.
How those three change. So Einstein space is four dimensional,
but we can extend it by adding another dimension of
space and having that curvature be in that additional dimension,
(43:14):
that fifth dimension. And you might ask, well, I can't
see that dimension. I can't imagine where that dimension would be.
How does that even work? Yeah, And this fifth dimension
is sort of similar to the way we think about time,
or like time we think about as the fourth dimension.
Imagine three dimensional space and then imagine that changing through time. Right,
save your full three dimensional space, But now you have
(43:34):
like another axis along which that three dimensional space is
changing so to imagine another dimension of space itself. Imagine
three dimensional space and then imagine a bunch of copies
of it. And this new dimension is not like the
original three. Instead of going on forever, it's like a
little loop. It's more like in polar coordinates, how you
have an angle and the angle can't go from zero
(43:57):
to infinity, just goes from zero to three hundred and
sixty degrees and it goes back to zero again. Right,
Imagine a new dimension of space that's sort of similar.
It has a maximum length, it's a circle instead of
an infinite line. Take three D space and sort of
move it around this circle. That's how we imagine a
universe with four spatial dimensions, the first three that are normal,
(44:18):
and then this weird rolled up dimension.
Speaker 1 (44:20):
Is it like when your Windows computer crashes and you're
dragging like your cursor or a window around, and then
there's a bunch of little copies of that that all
get stacked up and messed up.
Speaker 4 (44:32):
Is that what we're talking about here exactly?
Speaker 3 (44:37):
Or like when you win solitaire and the cards all
stack on top of each other. It's difficult to imagine
because we're used to three D space and we think
in three dimensions, and so squeezing that fourth dimension into
your brain is really a challenge. But mathematically it allows
something very cool. It allows you to have another kind
of curvature. A curvature in this new dimension might be
(44:58):
able to explain what we see as the force of electromagnetism.
So in this case, not just the curvature, but the
whole dimension would be basically invisible to us. This is
an ancient idea in physics. It goes all the way
back to nineteen nineteen. The guy Theodor Cluza came up
with this, just after Einstein came up with his idea
of relativity, and then a few years later a guy
(45:20):
named Oscar Klein turned it into a quantum theory in
nineteen twenty six. And try to calculate the size of
this new fifth dimension and figured out how to be
like twenty times the plank length, which means it's like
super duper tiny. It's like ten to the minus thirty
five meters long. So this seemed really exciting.
Speaker 1 (45:39):
I have so many questions just about that, like what
do you mean calculating the size of a dimension right?
Speaker 3 (45:46):
Like, remember that this new dimension is not infinite, we
think that you can go as far as you want
in X or and y, R and z. But this
new dimension is a loop, which means it has a length.
Now there's a maximum distance in this dimension. It's unlike
the other ones in a really weird way, and that
means that you can calculate, like, well, how big could
it be? What is the radius of curvature? What is
(46:08):
the length around this dimension? So it's very different in
a really counterintuitive way. And then Einstein got to work
on it, and he was like, all right, this is exciting.
Speaker 4 (46:18):
I trust him more than I trust me to think
about it.
Speaker 3 (46:21):
He thought, maybe this is exciting. Maybe I can make
this work. Maybe I can explain all of electromagnetism using
curvature in this new fifth dimension. And yeah, he died
before he found and people had been working on it
for a long time and nobody's been able to crack it.
There are some versions of this theory which sort of work,
but they all predict that we would have seen a
bunch of new particles. They predict that electrons would like
(46:44):
vibrate in this other dimension, and they would vibrate in
different ways, so you would see like different versions of
the electron the way like a string can vibrate, but
it can vibrate like one mode or two modes, or
three modes or four modes. Electrons could vibrate in this
other demands in various ways, and you would see like
heavier and heavier versions of the electron, where the heavy
(47:05):
ones are like vibrating in this new dimension with more energy,
which gives them effectively more mass. But we haven't seen
any heavy electrons, or any heavy muons, or any heavy
versions of these other particles at all. People thought for
a while, oh, maybe the muon is a heavy version
of the electron, and that's actually like, you know, something
vibrating in this new dimension. But that doesn't quite work
(47:25):
out because the electron and the muon feel the weak
force a little bit differently. So the bottom line is
it's an exciting direction theoretically to try to make electromagnetism
work in this clusive cline theory, but it's made predictions
that haven't been born out in the data, and so
it's not so promising.
Speaker 1 (47:44):
Well, we need to make a time machine go back
in time, and then ask Einstein, first of all, how
to make a time machine so that in the future
we can go back in time and talk to them
and then present them with all of this information.
Speaker 4 (48:00):
Or maybe, uh, there will be a.
Speaker 1 (48:02):
New kind of Einstein, or collectively instead of one super genius,
just a bunch of very smart people working together figuring
this out exactly.
Speaker 3 (48:14):
But it's promising. It's exciting that people are trying to
push their way through the theoretical jungle. You know, until
we figure out how to make a black hole here
on Earth, or we've come up with some clever quantum
gravity experiment that lets us see particles feeling gravity and
understand whether they're like bending space time probabilistically, or whether
gravity collapses their wave functions, or what's going on, we
(48:36):
can only make progress theoretically. That means trying to find
mathematical relationships between these theories, either making electromagnetism look more
like gravity or make gravity look more like electromagnetism. So far,
both paths have been sort of stuck in the jungle.
But maybe one day people will find a connection between
them and will all be illuminated.
Speaker 1 (48:57):
That is beautiful, but you do also keep breezing past
this plan to make up a black hole on Earth.
Speaker 4 (49:03):
That's feel sangerous.
Speaker 3 (49:04):
To me, it is very dangerous, but also potentially we
could learn a lot about the universe, so you know,
may be worth a risk.
Speaker 4 (49:11):
Yeah, ultimate knowledge right before oblivion. Sign me up.
Speaker 3 (49:18):
Sounds good. We'll stay tuned for more hints about potential
ultimate knowledge about the universe, just before you get sucked
into oblivion. Thanks so very much Katie for joining me
on this journey of theoretical understanding, and thanks to everybody
for tuning in. Tune in next time for more science
(49:39):
and curiosity. Come find us on social media where we
answer questions and post videos. We're on Twitter, Discord, Instant,
and now TikTok. Thanks for listening, and remember that Daniel
and Jorge Explain the Universe is a production of iHeartRadio.
For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts,
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Hosts And Creators
Daniel Whiteson
Jorge Cham
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