October 22, 2019 • 36 mins
The distance between stars is massive. Can we build a warp drive to allow us to travel between the stars faster?
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Speaker 1 (00:08):
Traveling to the stars always seems so exciting in the movies.
At least it involves lots of dramatic wooshing noises. There's
some strengths of light, exotic planets to visit, probably dramatic
meetings with aliens. You also noticed in those movies everybody
is always well rested. They walk everywhere with a purpose,
and they're wearing a well fitting uniform, and everybody seems
(00:31):
to be in great shape. I don't know about you,
but that's not like any travel experience that I've ever had. Realistically,
a trip to the stars is more likely to involve
tired people eating junk food and shopping at duty free stores.
It probably resembles the experience of a cruise ship more
than a trip on the Star Trek Enterprise. So load
(00:51):
up on the buffet because we're going to Alpha Centauri. Hi.
I'm Daniel. I'm a particle physicist, and you're listening to
(01:15):
the podcast Daniel and Jorge Explain the Universe, brought to
you by My Heart Radio. Jorge is still away. He's
my friend and collaborator and usual co host of this podcast,
in which we zoom all around the universe and try
to find interesting, amazing facts and talk to you about
them and explain them to you so that you really
understand them, so they're not just words that you hear
(01:37):
coming out of your mouth to try to impress your friends,
but actual concepts in your mind you can manipulate and
talk about with intelligence. And today we're gonna do more
than just zoom around the universe. We're going to talk
about how we're going to zoom around the universe. And
if you're like me, you like looking up at the
stars and imagining what it's like to be over there.
What would it be like to orbit that other star?
(01:59):
Are there planning it over there? Could you put your
foot on them? And I think there's a natural human
desire to explore, to see other parts of the world
and other parts of the universe. Well, the problem is
that the universe is big, frustratingly big, stubbornly huge. Like
the nearest star, the closest one to our sun, is
(02:20):
four point two light years away. It's called Proximus Centauri.
That's a huge distance by any measure. If you use kilometers,
which is sort of absurd, you've got a number like
forty trillion kilometers. It's sort of like we're on a
little island in the middle of nowhere. If anybody out
there has been to like Tahiti or a tiny little
dot in the Pacific Ocean, you know, the feeling of
(02:42):
standing on an island and being surrounded by water and
feeling like maybe there's nothing else out there. That's sort
of the way I feel standing on Earth, where in
an ocean of space, and everything else out there is
super duper far away. These distances, they're sort of hard
to grasp. You know. Let's talk about how long would
it take to get there. Well, if you travel on
(03:03):
speeds that are familiar here on Earth, like if you
traveled at the speed of a car, then going forty
trillion kilometers would take you about forty five million years.
Even if you travel at the speed of an airplane,
it would take you five million years. Now, nobody's actually
gonna drive to Alpha Centauri or even fly an airplane.
You can imagine some technology that might take you there
(03:25):
in a spaceship at a respectable fraction in the speed
of light, maybe five percent or ten percent. Even those
kind of ships would take hundreds of years to get
to Alpha Centauri. And who wants to board a ship
knowing that they're going to die on it, And who
wants to have kids on a ship knowing that those
kids will probably never set foot on land, any land,
(03:45):
on any planet. This kind of structure, of course, is
called a colony ship, where you have generations upon generations
of humanity living on board, and then eventually one day
some some group of people generations down the road, get
to actually land on that planet. That would work. That's
one way to explore the universe. But I want more.
I'm greedy, and I want to walk on those other
(04:06):
planets myself. But even if you traveled like at the
speed of light, it would still take you four years
to get to proximates centauri. That's a long time to
spend eating junk food and shopping duty free, And so
it makes you wonder is there any way to get
there faster? So today on the podcast, we're asking the
question can we build a warp drive to travel the universe?
(04:35):
I want to take a step back and talk about
how we travel the universe and sort of the size
of our horizons. You know, a hundred years ago or
five hundred years ago, things on the other side of
the Earth seemed unreachable. To travel to China, for example,
would take months or years. It's not the kind of
thing you could do in an afternoon or even a week. Now,
of course, because we have better technology for transportation, it's
(04:59):
not a big deal to go to the other side
of the planet. You can go there, you can come
back a couple of days later. So the scope about
the universe that we can explore has expanded and has
expanded because our technology has improved. And so the thing
to understand is that it's not actually distances that are important.
The number, the actual number of kilometers between you and
(05:20):
and another location, isn't the thing that determines whether or
not it's in sort of your sphere of explorability. What
determines that is the maximum speed you can travel. Back
when the fastest thing you can do is ride a horse,
then going across country was a huge endeavor, not something
you can do in days of weeks. Going to the
(05:40):
other side of the planet in less than months or
years was impossible. Now, of course, the top speed we
can travel is much much higher. We have airplanes who
can go hundreds of kilometers per hour, and so our
sphere of explorability now encompasses essentially the entire Earth, And
if you talk to old people who remember the day
when when those kind of technologies weren't wide the available
(06:00):
to them, the world seems to have suddenly gotten smaller.
So you might wonder, like, can science just continue? Can
science deliver and engine that brings the stars into our
sphere of explorability so that you'll be talking one day
to your great great grandkids about how amazing it is
that you can go to Alpha Centauri and and come
(06:21):
back in the same afternoon. That's the question we're focusing
on today. Is it possible for science to bring those
stars into our grasp. So before we dig into the question,
I of course walked around campus that you see Irvine,
and I asked people if they thought that a warp
drive is possible. How much faith did they have in
science or do they think that we have them already.
(06:42):
Before you hear these answers, think to yourself, do you
believe a warp drive is possible now or in the future.
Here's what people that you see Irhune had to say,
I honestly don't know enough about that to even answer it.
I don't know what a warp drive is yes, you
think like possible in the few you're possible today, uh future,
(07:02):
you know, I think so. I remember seeing a guide
that proved that it was possible, but you would have
to use a lot of energy, and it was changing
to spacetime ahead and afterwards maybe like today or in
the future or in the future today. Probably not at
(07:25):
the most point, I think it can well certainly not now.
So if all the questions I've ever asked people on
the street, this is the one that maybe got the
broadest set of responses. You have people saying I don't
know what a warp drive is. You have people saying
very confidently, yeah, I'm pretty sure we'll figure it out,
to people saying I think people could build them today.
It's crazy. And let me clarify again what I mean
(07:48):
by a warp drive. I mean an engine that could
take a spaceship from here to somewhere else faster than
light could get there. That's the goal. We don't want
to travel just close to the speed of light, because
even that would take us years and years to get anywhere.
The nearest stars for light years away, but other stars,
many more stars that we would love to visit in
our galaxy are hundreds or thousands of light years away.
(08:11):
Remember that our galaxy is a hundred thousand light years
across and the next galaxy is millions of light years away.
So if we want to explore the universe, if we
want to find alien life, if we want to see
crazy things that would never happen in our neighborhood of
the universe, after all, that's what's so amazing about traveling,
then we need to develop some sort of technology that
(08:33):
lets us get to places faster than lightwood get there.
And that's the question we're going to dig into today.
But first, let's take a quick break. We're back and
(08:54):
we're talking about whether we can build an engine we
could put in a starship that would take us somewhere
faster than light would get there. So the naturally, the
first question you might ask is can we travel faster
than light? And here physics is pretty specific. Physics says no,
nothing can move through space faster than light moves through space.
(09:15):
And there's already a little clue there, there's a little wrinkle,
a little loophole you might want to try to take
advantage of. Nothing moves through space faster than light moves
through that space those of you either who know something
about physics and particle physics might have heard of Churenkoff light.
For example, when a muan moves really fast through ice,
(09:35):
it can emit this special kind of radiation of blue
glow called turank Off light, and it does that because
it's moving faster than the light moves through the ice. Right,
So muans can go through ice faster than light goes
through ice, and they produced this turank Off radiation sort
of for the same reason that a plane produces a
sonic boom. The muans are traveling faster than the light
(09:58):
they make, and so the light they catch up to
the light they make and they're adding to it creates
this wake, right, So it's sort of like alluminal bloom,
not a sonic boom. But that doesn't mean that you
could travel through space faster than light can travel through space.
It just means that in some materials, some particles can
travel through that material faster than light travels through that material.
(10:21):
But the speed of light in a vacuum is still
the absolute top speed anything can move through space. It
just so happens that ice slows light down more than
it slows down muance. For example, so you get this
special little loophole. But loopholes are a key. We want
to pay very careful attention to exactly what the laws
of physics say so we can try to exploit them later.
(10:45):
But back to traveling faster than the speed of light.
You've probably heard me say it and learned it in
lots of other places. Is impossible to travel faster than
the speed of light, and not just because it would
require you to have infinite mass or anything else, but
just because the universe does not out according to special relativity.
There is no way to get faster than the speed
of light. In fact, you can't even travel at the
(11:07):
speed of light if you have any mass at all.
Only massless things like photons and gravitons can travel at
the speed of light. So unless you have a way
to transform your spaceship into light and beam it over there,
you can't even travel at the speed of light. And
you might ask, okay, but that's the way we think today,
that's today's physics idea of the way the universe works.
(11:29):
Isn't it possible that we're wrong? And that's a good point,
And I'm always saying on this podcast in other places
that we have so much to learn about the universe
that we've learned approximately zero percent of the physics of
the universe. And that might give you hope. It might
give you the idea that, well, there could be a
crack in that armor, or maybe later we'll learn that
that was wrong. And you know, there's always a possibility,
(11:51):
there's always a chance that future physics will discover that
that was not correct. But I'd be very surprised if
that were true. This is the kind of thing that
we have tested extensive We've come up with all sorts
of scenarios to try this. We've tested it out the wazoo,
We've even tested it into the wazoo, And it's the
cornerstone of modern quantum field theory. The special relativity and
(12:12):
the Lorenz groups that we used to build quantum field
theory would be totally broken if special relativity was wrong.
And this is the basic assumption of special relativity. So
it's one of the most well tested axioms in all
of modern physics that nothing can travel faster than the
speed of light. So I'd be really shocked if that
(12:32):
was cracked. If we found a way to move through
space faster than the speed of light. Now, I can't
rule it out definitively, because who knows what amazing things
the future physics will discover. Maybe we all live in
a simulation and there's a way to rewrite the program
so that things change, or who knows what. I can't
rule it out forever. But I don't think that that's
a fruitful path to developing a warp drive. And even
(12:54):
if you were to find a crack in that armor,
you'd still have all sorts of practical problems, like accelerating
to really high speeds. So you want to go a
million light years somewhere, traveling through space at those high
speeds is difficult because you have to accelerate to those
high speeds, which you can take a long long time
and a huge amount of energy. So theoretically I think
(13:14):
it's very unlikely, and practically I don't think it's a
good approach. But I think the lesson to learn from
that thought experiment is that we should look for loopholes.
After all, what is our goal is our goal to
travel faster than light. I don't have an inherent desire
to move through space faster than the speed of light.
What I want to do is I want to get
to some distant star faster than the lightwood get there.
(13:38):
I want to get to have Proximus Centauri, for example,
in less than four years. I'd love to do it
in an afternoon. So my goal is not actually to
travel through space faster than the speed of light. What
I want to do is to get there faster than
lightwood get there. And that sounds like it's basically saying
the same thing, but there's an important difference because the
(13:59):
rule the actual limitation according to special relativity, it's not
about arriving somewhere faster than the speed of light would
move through that space. It's about moving through space faster
than the speed of light. There's an opportunity there. Instead
of just moving through space and accepting that the space
between here and Proximus Centauri is four million light years,
(14:19):
what if we could somehow manipulate that space. What if
we could squeeze that space, or twist it or bend it,
or do something to it so that we didn't have
to move through as much space, so we could keep
under that speed limit but still get there in a
shorter amount of time. That's the key, and I think
there's there's some credit we owe here to science fiction
(14:40):
authors because a lot of these ideas, the possibility of
getting somewhere faster than life could get there, come originally
from science fiction. Those people are thinking about the impact
of new technologies and what the future might look like,
and so their job is to think most creatively, to
think how could we change human society or how human
(15:01):
society changed if we had this new technology. So they're
unbound by the rules of physics and certainly by the
practicalities of the engineering, free to think inventively about how
to change our lives and explore the universe. So kudos
to them for coming up with the whole concept of
a warp drive, and of course I love it in
all of those movies. But the next step, once the
(15:22):
science fiction authors have come up with the idea is
for physicists to figure out how to make it possible
to take an idea from woe that would be super awesome.
I wish we could do that too, you know, there
might be a way that we could do it. And
then figuring out how to sort of avoid the physics
blockades to work away around the rules of the universe
(15:43):
that seemed to be preventing that from being possible, and
once the physicists have figured out how to make it
sort of theoretically possible, then to hand it off to
the next people in the chain, which are of course
the engineers, because they have to actually build it, you know,
design it and build it and make it practical, build
something which less than ten quadrillion dollars or let use,
less than the mass of the universe. So that's the
(16:05):
sort of progression of how you go from I really
want this thing to you know, boarding the next flight
to Alpha Centauri at four o'clock. Start with the science fiction,
move through the physicists, and get to the engineers. So
where are we on that step of the process. Clearly
science fiction authors have thought of the idea of warp drive,
and now we're in this step where physicists are thinking
(16:25):
what could we do, what loopholes could we exploit? And so,
as I mentioned a few moments ago, the idea here
is not to move through space faster than light can
move through space, because that's just forbidden, but instead to
try to manipulate space. And if manipulate space sounds weird
to you, then get ready for some weirdness, because we're
gonna do a lot of this on the podcast, where
(16:47):
we use normal sounding words together in a way that
might make no sense initially, And that's because we're pushing
the boundaries of what we can do and what we
can understand, and doing that requires challenging our assumption. And
so what does it mean to manipulate space? Well, first
you have to let go of maybe your initial concept
of space, space being emptiness, space being nothing. If you
(17:11):
if I say the words space and you close your eyes,
do you imagine twinkling stars out there? Sure? But what's
between us and those stars? Maybe you imagine some sort
of wire frame grid of emptiness, right, just like the rulers,
just like the notches on a ruler between here and there.
And you might think, well, that's just sort of human interpretation,
is just an overlay we put onto the nothingness that's
(17:34):
between here and space. But space is not nothingness. And
I'm not talking about the quantum fields that are inside it,
or the particles that are zooming around, or the little
bits of radiation. I'm not making an argument that space
is never actually empty. I'm saying that space is more
than just the backdrop. It's not just the stage on
which the universe plays out. Space itself is dynamical. It
(17:57):
can do things that nothingness can't, like what well space
can bend. We've talked on this podcast about what gravity is.
Newton thought about gravity as a force between two objects,
pulling them together, but Einstein showed us that it's actually
more natural to talk about gravity as the bending of
(18:17):
space when the presence of mass and energy. So, for example,
you can imagine the Earth moving around the Sun, not
as the Sun pulling on the Earth using some force,
but the Sun distorting space so that it's most natural
for the Earth to move in this orbit, to blend
its velocity with the bending of space to come up
with a stable motion. So it's actually quite an old
(18:39):
idea that you could manipulate space. That space is not nothing,
that it can bend. This is an idea from Einstein's
theory of relativity that space can bend. So already that
breaks the idea that space is nothing, and it opens
the door to space doing other things right. Space can bend.
It can also ripple. We've seen gravitational waves when huge
(19:00):
objects like binary black holes accelerate around each other and
collapse into a single black hole. Then you get ripples
in space. What does that mean. It doesn't mean anything
if space is emptiness. But it means something if space
is a thing, if it has properties, if it can
do stuff, if it can be distorted and twisted. So
we're familiar with space bending due to gravity, were recently
(19:24):
aware the space can do things like ripple, and space
can also expand we know from the Big Bang, we
know from dark energy that space is expanding. Right now.
Sixty of all the energy in the universe is devoted
to something we call dark energy, which we don't understand.
But whatever it is is expanding space all the time.
(19:45):
It's creating new space between us and other galaxies. Right now,
it's doing it. It's making a new space between you
and the person sitting next to you. It's everywhere. So
space can do all of these things, and the amazing
thing is that they're no limit to it. As far
as we know, there's no speed limit to how fast
you can shrink or expand space. Take for example, the
(20:08):
Big Bang. What happened in the very first moments of
the universe. The universe expanded very, very rapidly, much faster
than the speed of light, much faster than light could
have moved through that space. That's why, for example, the
universe now is larger than the speed of light times
the age in the universe. How is that possible? If
(20:29):
nothing can travel faster than the speed of light, how
could stuff get further away from each other than light
could have traveled through that space. The answer, of course,
is space expanded. Inflation in the Big Bang is more
than just stuff moving through space. It's space itself expanding.
So this is an idea we're familiar with that space
can expand you might almost say the universe warped. You
(20:52):
might even think of the Big Bang is a huge
warping of space, and dark energy now is the continued
warping of space, all right, So that gives us an opportunity.
We're talking about how to get somewhere faster than light
would get us there. And the idea we're working towards
is not to try to move through space using some
specially fast Zippi engine, but to change the nature of
(21:14):
the problem by shrinking the space. And that's the idea
for a warp drive. That's how we might actually make
it work. The idea is like this, you want to
get from here to Alpha Centauri. How do you do
it well, you don't just move through that space. You
somehow shrink the space between you and that star. You
squeeze it, just the way the Sun changes the shape
(21:37):
the whole nature of space in the Solar System. Use
some mass and energy, and in a moment we'll talk
about the details of what we know about how engineers
might actually make that happen. Use mass and energy in
some way to squeeze the space so that instead of
having four point two light years between you and the star,
you have four point two meters. And similarly, you turn
(21:57):
around behind you, and instead of having four point two
meters between you and and where you've left, you can
expand the space behind you. So the idea for a
warp drive is something which shrinks the space in front
of you and expands the space behind you. In that way,
you're sort of inside a little bubble, and inside that
bubble you don't even need to move with respect to space.
(22:21):
It's sort of like instead of running through the airport,
you stand on a moving walkway and the walkway moves
for you. That's not perfect analogy, because in that analogy
the walkway is still moving. And I'll be talking about
like pulling the terminal closer to you instead of running
there and stretching the distance behind you. But that's the idea.
(22:42):
So you'd build the sort of warp drive that shrinks
the space in front of you, expands the space behind you,
and then you're in this sort of warp bubble, and
then you pop out of the bubble right and then
you're there. And because there's no limit on how fast
you can expand space or how much con shrink space,
in theory, there's no limit to how far a warp
(23:04):
drive could take you, as long as you have the
ability to do this and the energy budget to get
it done. So let's talk about how you might actually
build a warp drive and how much progress science and
engineers and science fiction authors have made towards making it
a reality. But first let's take another break. All right,
(23:35):
So we're talking about warping through the universe, and the
basic idea is to avoid the limit of the speed
of light by saying we're not going to move through
space faster than the speed of light. Instead, we're gonna
somehow change the shape of space. We're gonna build an engine,
a warp engine, which changes the nature of the problem
it doesn't solve the problem directly, it changes it to
(23:56):
another problem. And you know that's a standard and very
classic approach, Like it's basically what mathematics is. Somebody asks
a mathematician, can you solve this problem? They go, no,
that seems hard, But I can solve this other problem,
and I can prove that the answer is the same.
So instead of solving a hard problem, transform it to
an easy problem and then solve that. So in this case,
(24:18):
we're taking an impossible problem travel through space faster than
the speed of light, and transforming it to an easier problem.
Still really hard, maybe not feasible, but not theoretically impossible
to get there faster than light would have moved through
unaltered space. There, the idea again is to change the space,
(24:39):
is to squeeze the space in front of you and
expand the space behind you. That's the basic operating principle
of a warp drive. So let's talk about how that happens, because,
like I said earlier, squeezing space. Those are two words
you understand, squeezing and space. But what does it mean
to squeeze space? How could you possibly do that? What
(24:59):
kind of thing we you building? Your lab? To make
that happen. What would a warp drive actually look like? Alright,
so there's two components there, right, there's squeezing the space
in front of you and expanding the space behind you.
Let's do the easy one first. That's squeezing the space
in front of you. How can you squeeze space? How
can you make it to the shape of space as
(25:19):
smaller there's sort of constrained and shrunk a little bit. Well,
it turns out that's actually not that hard. You're doing
it right now. Everything with mass is changing the shape
of space in exactly that way. It's squeezing it, it's constricting,
it's constraining it. I don't want to get into the
mathematical details of the metric solutions to Einstein's equations, but
(25:39):
that's the basic idea. In order to shrink space, all
you need is a huge amount of mass or energy density,
because space bends in that exact way that you need
in the presence of mass and energy. So it basically
just becomes an engineering problem. You have positive mass and energy,
you can shrink space. How how much mass and energy
(26:01):
do you need to shrink space enough to get somewhere
interesting in the universe. Well, now it's a problem for
the engineers, and a bunch of folks have thought about this,
and I've even heard there are people in NASA working
on it, and they've done some calculations. And as usual,
when you first start out, you make basic assumptions. You
try the simplest idea first, and it seems impossible. So
(26:22):
the first calculation anybody ever did of how much energy
you would take, how much mass it would take in
order to bend space to get somewhere, like Proximus Centauri,
took more mass than all the stuff available in the
observable universe. That's a hundred billion solar systems for galaxy
and two trillion galaxies. That's an enormous amount of mass.
(26:43):
And there's no way you could ever gather that much
energy and use it for a warp drive. And anyway,
if you did, you would have already destroyed the universe
just trying to get somewhere. So it's a bit of
a chicken and egg problem. But this is the progression
of engineering, right. First you start out with a simple
solution that seems impossible and practical, and then somebody figures
out a way to do it with one percent of
(27:03):
the energy or costing a hundred times less money. That's
the way engineering works, and so people have already figured out,
oh wait, if you do do it this way and
that way, and you focus that this other direction, then
you can build a warp drive to get you to
the next star using only the amount of mass in
the planet Jupiter. Now, whether that seems like a big
(27:23):
number to you or not depends on your reference frame
if you start out comparing it to all the stars
and Solar system and stuff in the observable universe. Yeah,
it's a tiny amount of that, but compared to the
energy that any humans ever harnessed for any purpose, it's huge.
Remember we're talking about the energy stored in some object
(27:43):
that has mass. We're talking about releasing all of its energy.
And there's an enormous amount of energy stored in every
object that has mass because of E equals mc squared.
And the reason there's a huge amount of energy and
every piece of mass is because of the C squared bit,
see being the speed of light. Speed of light is
a really big number, and see squared is a really
(28:06):
big number squared. So you take a small amount of
mass like a raisin, which weighs maybe one gram. It
has an incredible amount of energy in it. It has
as much energy as a nuclear explosion. For example, you
wanted to build an antimatter weapon, if you had a
raisin and an anti raisin, that's all you would need
to have a device with as much explosive power as
(28:28):
the bombs that were dropped on Hiroshima. So now imagine Jupiter.
Jupiter is a lot of raisins, there's a huge amount
of energy, is an incredible amount of energy and jubiter.
So if somebody tells you I need I have a
warp drive, but we gotta refuel, and we gotta stop
by Jupiter and suck it all up, has to transform
all of Jupiter into energy to build my warp drive,
(28:49):
you'd probably say, we don't have the budget for that.
It's a huge reduction. But even requiring all the mass
of Jupiter to fuel your warp drive is not good enough.
All right, But recently I read an article that somebody
came up with a clever reduction in the amount of
energy required, so that you'd only need something like the
energy stored in a school bus or a large car.
(29:10):
And again that's another big step down. From all the
stuff in the universe down to Jupiter down to the
stuff in a car. Requires some real cleverness to focus
that energy in a way that's going to squeeze space
using only you know, hundreds and hundreds of kilograms of stuff.
Remember that's still a huge amount of energy compared to
the explosions of nuclear weapons. It's an enormous budget, but
(29:33):
it's not totally infeasible. So the engineers have already come
up with some sort of calculations to make this possible. No,
nobody's actually built a prototype. This is still just in
the planning stages that could this ever work stages, But
you know, the physicists have shown that to get there
you need to squeeze space, and they've pointed to the
engineers what we know about squeezing space, which is using
(29:54):
mass and energy to do things like gravity does. And
the engineers are working on it, they're chugging through it,
and there's all the reasons to believe that in a
few years, five years, ten years, fifty years, somebody might
be able to build something which begins this process. But
but to actually have warp drive, you need both sides.
You need the thing in front of you that squeezes space,
(30:16):
you also need the thing behind you that expands space. Right,
you can't have a moving walkway, and the whole walkway
isn't moving, So let's talk about that. How do you
expand the space behind you? Well, this is much harder.
You are not expanding space, right, You have positive mass,
and so you are shrinking space. You're doing that thing
that's the space that gravity does. But if shrinking space
(30:40):
requires having positive mass, you might be tempted to suggest,
sort of the first dumb idea for how to expand space,
that maybe you could expand space with negative mass. The
argument is not very sophisticated. It's really just that it says,
we don't know how to expand space, but we know
how to sort of shrink it using positive mass. What
(31:01):
if we use negative mass to expand it. It's not
a terrible argument. The problem is, of course, what does
negative mass mean. It's another of these examples. You take
two words that makes sense, negative and mass, and you
put them together and you go, huh, what is that?
Everything you've ever experienced has positive mass. I have positive
(31:21):
mass more than i'd like. Raisins of positive mass, hamsters, bananas, everything,
has positive mass. We've never seen anything with negative mass.
We talked about on this podcast for wormholes. You might
need negative mass exotic matter particles to stabilize wormholes, but
that doesn't mean that they exist. It just means that
if you write down the equations, that's the kind of
(31:43):
thing which could accomplish it. The things that are in
equations aren't necessarily also part of the universe. So we've
never seen negative mass, and we don't know how to
make negative mass. And also, even if you could make
negative mass, could you make a school bus size of
it a Jupiter, the planet Jupiter size negative mass? That
seems pretty difficult. It might even be a problem engineers
(32:06):
couldn't solve. But there is hope. Right, we know that
this thing can happen. We know that space can expand.
Decades ago, we might have imagined differently. We might have argued, Look,
gravity is just an attractive force. All it can do
is attract stuff. There's no repulsive side of gravity. Gravity
never pushes things apart the way magnetism can, or the
(32:26):
strong force can, or even the weak force. All of
these things can attract and repel because all those things
have both positive and negative charges. For their force. Gravity
has only positive charges. This is only positive mass, so
we can only attract That's what we think. However, we
also know that we don't really understand gravity, and we
(32:47):
do know that expansion of space does happen. We don't
know how to create negative mass. We don't know if
negative mass is the way to expand space, but we
do know that space can be expanded because we have
seen it happen. We believe that the Big Bang is
a huge expansion of space, though we don't know what
caused it. We know that dark energy is expanding space,
(33:08):
but we don't understand the mechanism. So we know it's possible,
but we don't know how to make it happen. We're
very far from being able to control it, and we're
super far from being able to put it in a
warp drive and take you to Alpha Centauri while you
stuff your face with junk food. So let's recap. It's
impossible to travel to Proximus Centauri or Alpha Centauri or
(33:30):
any of the Centauris by moving through space faster than
light could do it. You can't build a warp drive
that just moves through space. I think the kind of
warp drive to have. For example, in star Trek, does
that they traveled some factor of the speed of light
and they can get there more rapidly than light would
get there. That I'm gonna say it's flat out impossible.
It is always a possibility that sometimes the future physicists
(33:52):
will reveal that it wasn't actually impossible all along in
the some condition we assumed dot dot dot. I think
that's very unlikely. The more promising way to build a
warp drive is to change the problem from I'm gonna
move through space faster than the speed of light too,
I'm gonna try to squeeze the space. I'm gonna build
an engine which changes the nature of the problem. It
squeezes the space in front of me and expands the
(34:14):
space behind me. Space is not just to ruler you're
flying by. It's something we're in. It's like we're fish
and we're swimming in water, and to get to the
other side of the pond, you want to shrink the
amount of water that's between you and the other side
of the pond. So theoretically we think that could work.
Practically there's some big issues. Shrinking space in front of
you is very difficult. Maybe impractical, though theoretically we know,
(34:38):
we think we know what's going on, but expanding the
space behind you that's much harder. We have no idea
how to accomplish the expanding of space, but we think
it's probably possible because we see it happening in the universe.
We just have no handle on what's doing it or
how to make it happen in a controlled way where
you'd want to invite your grandmother on a trip to
(34:58):
the neighboring star. All right, So that's the explanation of
where we stand in terms of building warp drives. There's
lots of other really fascinating issues connected to space propulsion,
and people have written and asking us to talk about
e M drives and all sorts of other stuff. We'll
get to that, but until then, thanks very much for
all the folks who requested this topic, and thank you
in advance to anybody who sends in a request for
(35:21):
a future episode. We love hearing what you'd like to
hear about. So until Jorge gets back, this is Daniel
signing off for Daniel and Jorge explain the universe. Thanks
for tuning in. If you still have a question after
(35:41):
listening to all these explanations. Please drop us a line.
We'd love to hear from you. You can find us
at Facebook, Twitter, and Instagram at Daniel and Jorge That's
one Word, or email us at Feedback at Daniel and
Jorge dot com. Thanks for listening, and remember that Daniel
and Jorge Explain the Universe is a production of I
Heart Radio. For more podcasts for my heart Radio, visit
(36:03):
the i Heart Radio, a Apple Podcasts, or wherever you
listen to your favorite shows. H
Traveling to the stars always seems so exciting in the movies.
At least it involves lots of dramatic wooshing noises. There's
some strengths of light, exotic planets to visit, probably dramatic
meetings with aliens. You also noticed in those movies everybody
is always well rested. They walk everywhere with a purpose,
and they're wearing a well fitting uniform, and everybody seems
(00:31):
to be in great shape. I don't know about you,
but that's not like any travel experience that I've ever had. Realistically,
a trip to the stars is more likely to involve
tired people eating junk food and shopping at duty free stores.
It probably resembles the experience of a cruise ship more
than a trip on the Star Trek Enterprise. So load
(00:51):
up on the buffet because we're going to Alpha Centauri. Hi.
I'm Daniel. I'm a particle physicist, and you're listening to
(01:15):
the podcast Daniel and Jorge Explain the Universe, brought to
you by My Heart Radio. Jorge is still away. He's
my friend and collaborator and usual co host of this podcast,
in which we zoom all around the universe and try
to find interesting, amazing facts and talk to you about
them and explain them to you so that you really
understand them, so they're not just words that you hear
(01:37):
coming out of your mouth to try to impress your friends,
but actual concepts in your mind you can manipulate and
talk about with intelligence. And today we're gonna do more
than just zoom around the universe. We're going to talk
about how we're going to zoom around the universe. And
if you're like me, you like looking up at the
stars and imagining what it's like to be over there.
What would it be like to orbit that other star?
(01:59):
Are there planning it over there? Could you put your
foot on them? And I think there's a natural human
desire to explore, to see other parts of the world
and other parts of the universe. Well, the problem is
that the universe is big, frustratingly big, stubbornly huge. Like
the nearest star, the closest one to our sun, is
(02:20):
four point two light years away. It's called Proximus Centauri.
That's a huge distance by any measure. If you use kilometers,
which is sort of absurd, you've got a number like
forty trillion kilometers. It's sort of like we're on a
little island in the middle of nowhere. If anybody out
there has been to like Tahiti or a tiny little
dot in the Pacific Ocean, you know, the feeling of
(02:42):
standing on an island and being surrounded by water and
feeling like maybe there's nothing else out there. That's sort
of the way I feel standing on Earth, where in
an ocean of space, and everything else out there is
super duper far away. These distances, they're sort of hard
to grasp. You know. Let's talk about how long would
it take to get there. Well, if you travel on
(03:03):
speeds that are familiar here on Earth, like if you
traveled at the speed of a car, then going forty
trillion kilometers would take you about forty five million years.
Even if you travel at the speed of an airplane,
it would take you five million years. Now, nobody's actually
gonna drive to Alpha Centauri or even fly an airplane.
You can imagine some technology that might take you there
(03:25):
in a spaceship at a respectable fraction in the speed
of light, maybe five percent or ten percent. Even those
kind of ships would take hundreds of years to get
to Alpha Centauri. And who wants to board a ship
knowing that they're going to die on it, And who
wants to have kids on a ship knowing that those
kids will probably never set foot on land, any land,
(03:45):
on any planet. This kind of structure, of course, is
called a colony ship, where you have generations upon generations
of humanity living on board, and then eventually one day
some some group of people generations down the road, get
to actually land on that planet. That would work. That's
one way to explore the universe. But I want more.
I'm greedy, and I want to walk on those other
(04:06):
planets myself. But even if you traveled like at the
speed of light, it would still take you four years
to get to proximates centauri. That's a long time to
spend eating junk food and shopping duty free, And so
it makes you wonder is there any way to get
there faster? So today on the podcast, we're asking the
question can we build a warp drive to travel the universe?
(04:35):
I want to take a step back and talk about
how we travel the universe and sort of the size
of our horizons. You know, a hundred years ago or
five hundred years ago, things on the other side of
the Earth seemed unreachable. To travel to China, for example,
would take months or years. It's not the kind of
thing you could do in an afternoon or even a week. Now,
of course, because we have better technology for transportation, it's
(04:59):
not a big deal to go to the other side
of the planet. You can go there, you can come
back a couple of days later. So the scope about
the universe that we can explore has expanded and has
expanded because our technology has improved. And so the thing
to understand is that it's not actually distances that are important.
The number, the actual number of kilometers between you and
(05:20):
and another location, isn't the thing that determines whether or
not it's in sort of your sphere of explorability. What
determines that is the maximum speed you can travel. Back
when the fastest thing you can do is ride a horse,
then going across country was a huge endeavor, not something
you can do in days of weeks. Going to the
(05:40):
other side of the planet in less than months or
years was impossible. Now, of course, the top speed we
can travel is much much higher. We have airplanes who
can go hundreds of kilometers per hour, and so our
sphere of explorability now encompasses essentially the entire Earth, And
if you talk to old people who remember the day
when when those kind of technologies weren't wide the available
(06:00):
to them, the world seems to have suddenly gotten smaller.
So you might wonder, like, can science just continue? Can
science deliver and engine that brings the stars into our
sphere of explorability so that you'll be talking one day
to your great great grandkids about how amazing it is
that you can go to Alpha Centauri and and come
(06:21):
back in the same afternoon. That's the question we're focusing
on today. Is it possible for science to bring those
stars into our grasp. So before we dig into the question,
I of course walked around campus that you see Irvine,
and I asked people if they thought that a warp
drive is possible. How much faith did they have in
science or do they think that we have them already.
(06:42):
Before you hear these answers, think to yourself, do you
believe a warp drive is possible now or in the future.
Here's what people that you see Irhune had to say,
I honestly don't know enough about that to even answer it.
I don't know what a warp drive is yes, you
think like possible in the few you're possible today, uh future,
(07:02):
you know, I think so. I remember seeing a guide
that proved that it was possible, but you would have
to use a lot of energy, and it was changing
to spacetime ahead and afterwards maybe like today or in
the future or in the future today. Probably not at
(07:25):
the most point, I think it can well certainly not now.
So if all the questions I've ever asked people on
the street, this is the one that maybe got the
broadest set of responses. You have people saying I don't
know what a warp drive is. You have people saying
very confidently, yeah, I'm pretty sure we'll figure it out,
to people saying I think people could build them today.
It's crazy. And let me clarify again what I mean
(07:48):
by a warp drive. I mean an engine that could
take a spaceship from here to somewhere else faster than
light could get there. That's the goal. We don't want
to travel just close to the speed of light, because
even that would take us years and years to get anywhere.
The nearest stars for light years away, but other stars,
many more stars that we would love to visit in
our galaxy are hundreds or thousands of light years away.
(08:11):
Remember that our galaxy is a hundred thousand light years
across and the next galaxy is millions of light years away.
So if we want to explore the universe, if we
want to find alien life, if we want to see
crazy things that would never happen in our neighborhood of
the universe, after all, that's what's so amazing about traveling,
then we need to develop some sort of technology that
(08:33):
lets us get to places faster than lightwood get there.
And that's the question we're going to dig into today.
But first, let's take a quick break. We're back and
(08:54):
we're talking about whether we can build an engine we
could put in a starship that would take us somewhere
faster than light would get there. So the naturally, the
first question you might ask is can we travel faster
than light? And here physics is pretty specific. Physics says no,
nothing can move through space faster than light moves through space.
(09:15):
And there's already a little clue there, there's a little wrinkle,
a little loophole you might want to try to take
advantage of. Nothing moves through space faster than light moves
through that space those of you either who know something
about physics and particle physics might have heard of Churenkoff light.
For example, when a muan moves really fast through ice,
(09:35):
it can emit this special kind of radiation of blue
glow called turank Off light, and it does that because
it's moving faster than the light moves through the ice. Right,
So muans can go through ice faster than light goes
through ice, and they produced this turank Off radiation sort
of for the same reason that a plane produces a
sonic boom. The muans are traveling faster than the light
(09:58):
they make, and so the light they catch up to
the light they make and they're adding to it creates
this wake, right, So it's sort of like alluminal bloom,
not a sonic boom. But that doesn't mean that you
could travel through space faster than light can travel through space.
It just means that in some materials, some particles can
travel through that material faster than light travels through that material.
(10:21):
But the speed of light in a vacuum is still
the absolute top speed anything can move through space. It
just so happens that ice slows light down more than
it slows down muance. For example, so you get this
special little loophole. But loopholes are a key. We want
to pay very careful attention to exactly what the laws
of physics say so we can try to exploit them later.
(10:45):
But back to traveling faster than the speed of light.
You've probably heard me say it and learned it in
lots of other places. Is impossible to travel faster than
the speed of light, and not just because it would
require you to have infinite mass or anything else, but
just because the universe does not out according to special relativity.
There is no way to get faster than the speed
of light. In fact, you can't even travel at the
(11:07):
speed of light if you have any mass at all.
Only massless things like photons and gravitons can travel at
the speed of light. So unless you have a way
to transform your spaceship into light and beam it over there,
you can't even travel at the speed of light. And
you might ask, okay, but that's the way we think today,
that's today's physics idea of the way the universe works.
(11:29):
Isn't it possible that we're wrong? And that's a good point,
And I'm always saying on this podcast in other places
that we have so much to learn about the universe
that we've learned approximately zero percent of the physics of
the universe. And that might give you hope. It might
give you the idea that, well, there could be a
crack in that armor, or maybe later we'll learn that
that was wrong. And you know, there's always a possibility,
(11:51):
there's always a chance that future physics will discover that
that was not correct. But I'd be very surprised if
that were true. This is the kind of thing that
we have tested extensive We've come up with all sorts
of scenarios to try this. We've tested it out the wazoo,
We've even tested it into the wazoo, And it's the
cornerstone of modern quantum field theory. The special relativity and
(12:12):
the Lorenz groups that we used to build quantum field
theory would be totally broken if special relativity was wrong.
And this is the basic assumption of special relativity. So
it's one of the most well tested axioms in all
of modern physics that nothing can travel faster than the
speed of light. So I'd be really shocked if that
(12:32):
was cracked. If we found a way to move through
space faster than the speed of light. Now, I can't
rule it out definitively, because who knows what amazing things
the future physics will discover. Maybe we all live in
a simulation and there's a way to rewrite the program
so that things change, or who knows what. I can't
rule it out forever. But I don't think that that's
a fruitful path to developing a warp drive. And even
(12:54):
if you were to find a crack in that armor,
you'd still have all sorts of practical problems, like accelerating
to really high speeds. So you want to go a
million light years somewhere, traveling through space at those high
speeds is difficult because you have to accelerate to those
high speeds, which you can take a long long time
and a huge amount of energy. So theoretically I think
(13:14):
it's very unlikely, and practically I don't think it's a
good approach. But I think the lesson to learn from
that thought experiment is that we should look for loopholes.
After all, what is our goal is our goal to
travel faster than light. I don't have an inherent desire
to move through space faster than the speed of light.
What I want to do is I want to get
to some distant star faster than the lightwood get there.
(13:38):
I want to get to have Proximus Centauri, for example,
in less than four years. I'd love to do it
in an afternoon. So my goal is not actually to
travel through space faster than the speed of light. What
I want to do is to get there faster than
lightwood get there. And that sounds like it's basically saying
the same thing, but there's an important difference because the
(13:59):
rule the actual limitation according to special relativity, it's not
about arriving somewhere faster than the speed of light would
move through that space. It's about moving through space faster
than the speed of light. There's an opportunity there. Instead
of just moving through space and accepting that the space
between here and Proximus Centauri is four million light years,
(14:19):
what if we could somehow manipulate that space. What if
we could squeeze that space, or twist it or bend it,
or do something to it so that we didn't have
to move through as much space, so we could keep
under that speed limit but still get there in a
shorter amount of time. That's the key, and I think
there's there's some credit we owe here to science fiction
(14:40):
authors because a lot of these ideas, the possibility of
getting somewhere faster than life could get there, come originally
from science fiction. Those people are thinking about the impact
of new technologies and what the future might look like,
and so their job is to think most creatively, to
think how could we change human society or how human
(15:01):
society changed if we had this new technology. So they're
unbound by the rules of physics and certainly by the
practicalities of the engineering, free to think inventively about how
to change our lives and explore the universe. So kudos
to them for coming up with the whole concept of
a warp drive, and of course I love it in
all of those movies. But the next step, once the
(15:22):
science fiction authors have come up with the idea is
for physicists to figure out how to make it possible
to take an idea from woe that would be super awesome.
I wish we could do that too, you know, there
might be a way that we could do it. And
then figuring out how to sort of avoid the physics
blockades to work away around the rules of the universe
(15:43):
that seemed to be preventing that from being possible, and
once the physicists have figured out how to make it
sort of theoretically possible, then to hand it off to
the next people in the chain, which are of course
the engineers, because they have to actually build it, you know,
design it and build it and make it practical, build
something which less than ten quadrillion dollars or let use,
less than the mass of the universe. So that's the
(16:05):
sort of progression of how you go from I really
want this thing to you know, boarding the next flight
to Alpha Centauri at four o'clock. Start with the science fiction,
move through the physicists, and get to the engineers. So
where are we on that step of the process. Clearly
science fiction authors have thought of the idea of warp drive,
and now we're in this step where physicists are thinking
(16:25):
what could we do, what loopholes could we exploit? And so,
as I mentioned a few moments ago, the idea here
is not to move through space faster than light can
move through space, because that's just forbidden, but instead to
try to manipulate space. And if manipulate space sounds weird
to you, then get ready for some weirdness, because we're
gonna do a lot of this on the podcast, where
(16:47):
we use normal sounding words together in a way that
might make no sense initially, And that's because we're pushing
the boundaries of what we can do and what we
can understand, and doing that requires challenging our assumption. And
so what does it mean to manipulate space? Well, first
you have to let go of maybe your initial concept
of space, space being emptiness, space being nothing. If you
(17:11):
if I say the words space and you close your eyes,
do you imagine twinkling stars out there? Sure? But what's
between us and those stars? Maybe you imagine some sort
of wire frame grid of emptiness, right, just like the rulers,
just like the notches on a ruler between here and there.
And you might think, well, that's just sort of human interpretation,
is just an overlay we put onto the nothingness that's
(17:34):
between here and space. But space is not nothingness. And
I'm not talking about the quantum fields that are inside it,
or the particles that are zooming around, or the little
bits of radiation. I'm not making an argument that space
is never actually empty. I'm saying that space is more
than just the backdrop. It's not just the stage on
which the universe plays out. Space itself is dynamical. It
(17:57):
can do things that nothingness can't, like what well space
can bend. We've talked on this podcast about what gravity is.
Newton thought about gravity as a force between two objects,
pulling them together, but Einstein showed us that it's actually
more natural to talk about gravity as the bending of
(18:17):
space when the presence of mass and energy. So, for example,
you can imagine the Earth moving around the Sun, not
as the Sun pulling on the Earth using some force,
but the Sun distorting space so that it's most natural
for the Earth to move in this orbit, to blend
its velocity with the bending of space to come up
with a stable motion. So it's actually quite an old
(18:39):
idea that you could manipulate space. That space is not nothing,
that it can bend. This is an idea from Einstein's
theory of relativity that space can bend. So already that
breaks the idea that space is nothing, and it opens
the door to space doing other things right. Space can bend.
It can also ripple. We've seen gravitational waves when huge
(19:00):
objects like binary black holes accelerate around each other and
collapse into a single black hole. Then you get ripples
in space. What does that mean. It doesn't mean anything
if space is emptiness. But it means something if space
is a thing, if it has properties, if it can
do stuff, if it can be distorted and twisted. So
we're familiar with space bending due to gravity, were recently
(19:24):
aware the space can do things like ripple, and space
can also expand we know from the Big Bang, we
know from dark energy that space is expanding. Right now.
Sixty of all the energy in the universe is devoted
to something we call dark energy, which we don't understand.
But whatever it is is expanding space all the time.
(19:45):
It's creating new space between us and other galaxies. Right now,
it's doing it. It's making a new space between you
and the person sitting next to you. It's everywhere. So
space can do all of these things, and the amazing
thing is that they're no limit to it. As far
as we know, there's no speed limit to how fast
you can shrink or expand space. Take for example, the
(20:08):
Big Bang. What happened in the very first moments of
the universe. The universe expanded very, very rapidly, much faster
than the speed of light, much faster than light could
have moved through that space. That's why, for example, the
universe now is larger than the speed of light times
the age in the universe. How is that possible? If
(20:29):
nothing can travel faster than the speed of light, how
could stuff get further away from each other than light
could have traveled through that space. The answer, of course,
is space expanded. Inflation in the Big Bang is more
than just stuff moving through space. It's space itself expanding.
So this is an idea we're familiar with that space
can expand you might almost say the universe warped. You
(20:52):
might even think of the Big Bang is a huge
warping of space, and dark energy now is the continued
warping of space, all right, So that gives us an opportunity.
We're talking about how to get somewhere faster than light
would get us there. And the idea we're working towards
is not to try to move through space using some
specially fast Zippi engine, but to change the nature of
(21:14):
the problem by shrinking the space. And that's the idea
for a warp drive. That's how we might actually make
it work. The idea is like this, you want to
get from here to Alpha Centauri. How do you do
it well, you don't just move through that space. You
somehow shrink the space between you and that star. You
squeeze it, just the way the Sun changes the shape
(21:37):
the whole nature of space in the Solar System. Use
some mass and energy, and in a moment we'll talk
about the details of what we know about how engineers
might actually make that happen. Use mass and energy in
some way to squeeze the space so that instead of
having four point two light years between you and the star,
you have four point two meters. And similarly, you turn
(21:57):
around behind you, and instead of having four point two
meters between you and and where you've left, you can
expand the space behind you. So the idea for a
warp drive is something which shrinks the space in front
of you and expands the space behind you. In that way,
you're sort of inside a little bubble, and inside that
bubble you don't even need to move with respect to space.
(22:21):
It's sort of like instead of running through the airport,
you stand on a moving walkway and the walkway moves
for you. That's not perfect analogy, because in that analogy
the walkway is still moving. And I'll be talking about
like pulling the terminal closer to you instead of running
there and stretching the distance behind you. But that's the idea.
(22:42):
So you'd build the sort of warp drive that shrinks
the space in front of you, expands the space behind you,
and then you're in this sort of warp bubble, and
then you pop out of the bubble right and then
you're there. And because there's no limit on how fast
you can expand space or how much con shrink space,
in theory, there's no limit to how far a warp
(23:04):
drive could take you, as long as you have the
ability to do this and the energy budget to get
it done. So let's talk about how you might actually
build a warp drive and how much progress science and
engineers and science fiction authors have made towards making it
a reality. But first let's take another break. All right,
(23:35):
So we're talking about warping through the universe, and the
basic idea is to avoid the limit of the speed
of light by saying we're not going to move through
space faster than the speed of light. Instead, we're gonna
somehow change the shape of space. We're gonna build an engine,
a warp engine, which changes the nature of the problem
it doesn't solve the problem directly, it changes it to
(23:56):
another problem. And you know that's a standard and very
classic approach, Like it's basically what mathematics is. Somebody asks
a mathematician, can you solve this problem? They go, no,
that seems hard, But I can solve this other problem,
and I can prove that the answer is the same.
So instead of solving a hard problem, transform it to
an easy problem and then solve that. So in this case,
(24:18):
we're taking an impossible problem travel through space faster than
the speed of light, and transforming it to an easier problem.
Still really hard, maybe not feasible, but not theoretically impossible
to get there faster than light would have moved through
unaltered space. There, the idea again is to change the space,
(24:39):
is to squeeze the space in front of you and
expand the space behind you. That's the basic operating principle
of a warp drive. So let's talk about how that happens, because,
like I said earlier, squeezing space. Those are two words
you understand, squeezing and space. But what does it mean
to squeeze space? How could you possibly do that? What
(24:59):
kind of thing we you building? Your lab? To make
that happen. What would a warp drive actually look like? Alright,
so there's two components there, right, there's squeezing the space
in front of you and expanding the space behind you.
Let's do the easy one first. That's squeezing the space
in front of you. How can you squeeze space? How
can you make it to the shape of space as
(25:19):
smaller there's sort of constrained and shrunk a little bit. Well,
it turns out that's actually not that hard. You're doing
it right now. Everything with mass is changing the shape
of space in exactly that way. It's squeezing it, it's constricting,
it's constraining it. I don't want to get into the
mathematical details of the metric solutions to Einstein's equations, but
(25:39):
that's the basic idea. In order to shrink space, all
you need is a huge amount of mass or energy density,
because space bends in that exact way that you need
in the presence of mass and energy. So it basically
just becomes an engineering problem. You have positive mass and energy,
you can shrink space. How how much mass and energy
(26:01):
do you need to shrink space enough to get somewhere
interesting in the universe. Well, now it's a problem for
the engineers, and a bunch of folks have thought about this,
and I've even heard there are people in NASA working
on it, and they've done some calculations. And as usual,
when you first start out, you make basic assumptions. You
try the simplest idea first, and it seems impossible. So
(26:22):
the first calculation anybody ever did of how much energy
you would take, how much mass it would take in
order to bend space to get somewhere, like Proximus Centauri,
took more mass than all the stuff available in the
observable universe. That's a hundred billion solar systems for galaxy
and two trillion galaxies. That's an enormous amount of mass.
(26:43):
And there's no way you could ever gather that much
energy and use it for a warp drive. And anyway,
if you did, you would have already destroyed the universe
just trying to get somewhere. So it's a bit of
a chicken and egg problem. But this is the progression
of engineering, right. First you start out with a simple
solution that seems impossible and practical, and then somebody figures
out a way to do it with one percent of
(27:03):
the energy or costing a hundred times less money. That's
the way engineering works, and so people have already figured out,
oh wait, if you do do it this way and
that way, and you focus that this other direction, then
you can build a warp drive to get you to
the next star using only the amount of mass in
the planet Jupiter. Now, whether that seems like a big
(27:23):
number to you or not depends on your reference frame
if you start out comparing it to all the stars
and Solar system and stuff in the observable universe. Yeah,
it's a tiny amount of that, but compared to the
energy that any humans ever harnessed for any purpose, it's huge.
Remember we're talking about the energy stored in some object
(27:43):
that has mass. We're talking about releasing all of its energy.
And there's an enormous amount of energy stored in every
object that has mass because of E equals mc squared.
And the reason there's a huge amount of energy and
every piece of mass is because of the C squared bit,
see being the speed of light. Speed of light is
a really big number, and see squared is a really
(28:06):
big number squared. So you take a small amount of
mass like a raisin, which weighs maybe one gram. It
has an incredible amount of energy in it. It has
as much energy as a nuclear explosion. For example, you
wanted to build an antimatter weapon, if you had a
raisin and an anti raisin, that's all you would need
to have a device with as much explosive power as
(28:28):
the bombs that were dropped on Hiroshima. So now imagine Jupiter.
Jupiter is a lot of raisins, there's a huge amount
of energy, is an incredible amount of energy and jubiter.
So if somebody tells you I need I have a
warp drive, but we gotta refuel, and we gotta stop
by Jupiter and suck it all up, has to transform
all of Jupiter into energy to build my warp drive,
(28:49):
you'd probably say, we don't have the budget for that.
It's a huge reduction. But even requiring all the mass
of Jupiter to fuel your warp drive is not good enough.
All right, But recently I read an article that somebody
came up with a clever reduction in the amount of
energy required, so that you'd only need something like the
energy stored in a school bus or a large car.
(29:10):
And again that's another big step down. From all the
stuff in the universe down to Jupiter down to the
stuff in a car. Requires some real cleverness to focus
that energy in a way that's going to squeeze space
using only you know, hundreds and hundreds of kilograms of stuff.
Remember that's still a huge amount of energy compared to
the explosions of nuclear weapons. It's an enormous budget, but
(29:33):
it's not totally infeasible. So the engineers have already come
up with some sort of calculations to make this possible. No,
nobody's actually built a prototype. This is still just in
the planning stages that could this ever work stages, But
you know, the physicists have shown that to get there
you need to squeeze space, and they've pointed to the
engineers what we know about squeezing space, which is using
(29:54):
mass and energy to do things like gravity does. And
the engineers are working on it, they're chugging through it,
and there's all the reasons to believe that in a
few years, five years, ten years, fifty years, somebody might
be able to build something which begins this process. But
but to actually have warp drive, you need both sides.
You need the thing in front of you that squeezes space,
(30:16):
you also need the thing behind you that expands space. Right,
you can't have a moving walkway, and the whole walkway
isn't moving, So let's talk about that. How do you
expand the space behind you? Well, this is much harder.
You are not expanding space, right, You have positive mass,
and so you are shrinking space. You're doing that thing
that's the space that gravity does. But if shrinking space
(30:40):
requires having positive mass, you might be tempted to suggest,
sort of the first dumb idea for how to expand space,
that maybe you could expand space with negative mass. The
argument is not very sophisticated. It's really just that it says,
we don't know how to expand space, but we know
how to sort of shrink it using positive mass. What
(31:01):
if we use negative mass to expand it. It's not
a terrible argument. The problem is, of course, what does
negative mass mean. It's another of these examples. You take
two words that makes sense, negative and mass, and you
put them together and you go, huh, what is that?
Everything you've ever experienced has positive mass. I have positive
(31:21):
mass more than i'd like. Raisins of positive mass, hamsters, bananas, everything,
has positive mass. We've never seen anything with negative mass.
We talked about on this podcast for wormholes. You might
need negative mass exotic matter particles to stabilize wormholes, but
that doesn't mean that they exist. It just means that
if you write down the equations, that's the kind of
(31:43):
thing which could accomplish it. The things that are in
equations aren't necessarily also part of the universe. So we've
never seen negative mass, and we don't know how to
make negative mass. And also, even if you could make
negative mass, could you make a school bus size of
it a Jupiter, the planet Jupiter size negative mass? That
seems pretty difficult. It might even be a problem engineers
(32:06):
couldn't solve. But there is hope. Right, we know that
this thing can happen. We know that space can expand.
Decades ago, we might have imagined differently. We might have argued, Look,
gravity is just an attractive force. All it can do
is attract stuff. There's no repulsive side of gravity. Gravity
never pushes things apart the way magnetism can, or the
(32:26):
strong force can, or even the weak force. All of
these things can attract and repel because all those things
have both positive and negative charges. For their force. Gravity
has only positive charges. This is only positive mass, so
we can only attract That's what we think. However, we
also know that we don't really understand gravity, and we
(32:47):
do know that expansion of space does happen. We don't
know how to create negative mass. We don't know if
negative mass is the way to expand space, but we
do know that space can be expanded because we have
seen it happen. We believe that the Big Bang is
a huge expansion of space, though we don't know what
caused it. We know that dark energy is expanding space,
(33:08):
but we don't understand the mechanism. So we know it's possible,
but we don't know how to make it happen. We're
very far from being able to control it, and we're
super far from being able to put it in a
warp drive and take you to Alpha Centauri while you
stuff your face with junk food. So let's recap. It's
impossible to travel to Proximus Centauri or Alpha Centauri or
(33:30):
any of the Centauris by moving through space faster than
light could do it. You can't build a warp drive
that just moves through space. I think the kind of
warp drive to have. For example, in star Trek, does
that they traveled some factor of the speed of light
and they can get there more rapidly than light would
get there. That I'm gonna say it's flat out impossible.
It is always a possibility that sometimes the future physicists
(33:52):
will reveal that it wasn't actually impossible all along in
the some condition we assumed dot dot dot. I think
that's very unlikely. The more promising way to build a
warp drive is to change the problem from I'm gonna
move through space faster than the speed of light too,
I'm gonna try to squeeze the space. I'm gonna build
an engine which changes the nature of the problem. It
squeezes the space in front of me and expands the
(34:14):
space behind me. Space is not just to ruler you're
flying by. It's something we're in. It's like we're fish
and we're swimming in water, and to get to the
other side of the pond, you want to shrink the
amount of water that's between you and the other side
of the pond. So theoretically we think that could work.
Practically there's some big issues. Shrinking space in front of
you is very difficult. Maybe impractical, though theoretically we know,
(34:38):
we think we know what's going on, but expanding the
space behind you that's much harder. We have no idea
how to accomplish the expanding of space, but we think
it's probably possible because we see it happening in the universe.
We just have no handle on what's doing it or
how to make it happen in a controlled way where
you'd want to invite your grandmother on a trip to
(34:58):
the neighboring star. All right, So that's the explanation of
where we stand in terms of building warp drives. There's
lots of other really fascinating issues connected to space propulsion,
and people have written and asking us to talk about
e M drives and all sorts of other stuff. We'll
get to that, but until then, thanks very much for
all the folks who requested this topic, and thank you
in advance to anybody who sends in a request for
(35:21):
a future episode. We love hearing what you'd like to
hear about. So until Jorge gets back, this is Daniel
signing off for Daniel and Jorge explain the universe. Thanks
for tuning in. If you still have a question after
(35:41):
listening to all these explanations. Please drop us a line.
We'd love to hear from you. You can find us
at Facebook, Twitter, and Instagram at Daniel and Jorge That's
one Word, or email us at Feedback at Daniel and
Jorge dot com. Thanks for listening, and remember that Daniel
and Jorge Explain the Universe is a production of I
Heart Radio. For more podcasts for my heart Radio, visit
(36:03):
the i Heart Radio, a Apple Podcasts, or wherever you
listen to your favorite shows. H
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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