New Warp Drive Possibilities…Maybe!

Since Einstein blessed us with his general relativity theory, we started to have a glimmer

of hope.

He opened a new frontier in astrophysics, and in science in general.

Perhaps, Einstein’s most famous rule is “nothing can travel faster than light”.

And it seems to ensure that exploration of even the local part of our galaxy would be

implausible.

But he also showed us that space and time can be curved, that space and time can be

warped.

That’s how some physics fans and sci-fi writers started to think about travelling in space

at superluminal (that means, faster than light) velocities.

That’s how the warp drive idea was born.

Scientists are always been fascinated by this topic, and that’s how we soon had some math

to describe a hypothetical warp drive.

It went pretty much like this.

They asked themselves “if we want to travel faster than light, what do we need?”

And they started collecting solutions from Einstein’s field equations, in order to solve

for superluminal speeds.

One of the most famous solutions was Alcubierre’s warp drive solution, and it made us dream

of faster than light travel all over the years.

Just recently, a paper came out that discussed some solutions to Alcubierre’s warp drive.

Follow me in this video to get to know more about warp drive, how it works and about new

frontiers of space travelling!

In 1915, Albert’ Einstein’s general theory of relativity revealed that the fabric of

space and time is mutable and dynamic.

It can, in fact, be warped.

Let’s be clear: one can’t travel faster than the speed of light, but there is no speed

limit for the fabric of space itself!

What does this mean?

It means that one could possibly seat in a comfortable sort of bubble, drinking his tea,

perfectly still, and let the space-time move faster than light.

You got it right!

The bubble would be perfectly still.

The spacetime would do all the work!

In certain circumstances, in fact, we can think of space itself as moving – and there

is no limit to the relative motion of two patches of space – and so objects in those

patches could have superluminal speeds relative to each other.

Do you want one example of this?

Black holes.

Inside black holes, we can think of space as flowing downwards faster than light.

The warp drive takes advantages of this, by accelerating a patch of space relative to

its surroundings.

Objects in that warp bubble move with that patch without themselves ever feeling any

acceleration.

This is what the Alcubierre drive is supposed to do.

The idea is a lot simple: one should quickly expand the space behind the spaceship and

at the same time should contact the space ahead of it.

In other words, the spaceship stops in a bubble of space, but this bubble moves quickly in

the universe, due to contraction and the expansion of the surrounding space.

It is pretty much the same thing that happens when a surfer rides a wave: the board does

not move relative to the water, but the wave pushes the board forward.

In short, the space-ship is not moving faster than the speed of light in its local reference

frame.

But, since the space around the bubble is distorted, it would come to its destination

sooner than light would take travelling in normal conditions.

Alcubierre, inspired by Star Trek published an article in which he describes the way which

– hypothetically – it could be obtained such a thing, starting from Einsteins’ equations.

The article became very popular (especially among fans of science fiction).

In fact, nowadays we talk about the “Alcubierre warp drive”.

However, Alcubierre didn’t really invent a new engine.

He just proved that the relativity equations allow (in theory) to describe a geometry of

spacetime that can allow us to travel faster than light.

But what kind of physical conditions should be fulfilled in order to shift from mathematics

to physical reality?

Since the curvature of space is caused by matter distribution, we must ask ourselves

what kind of matter we would need to run such a warp drive.

The answer is: we need a kind of matter with negative mass!

General relativity works by solving einstein’s field equations.

Here they are:

Einstein’s equations then tell you that the distribution of different types of energy

determines the curvature, and the curvature in return determines how the distribution

of the stress-energy changes.

The way you normally solve these equations is to use a distribution of energies and masses

at some initial time.

Then you can calculate what the curvature is at an initial time and you can calculate

how the energies and masses will move around, and how the curvature changes with that.

So this is what physicists usually mean by a solution of general relativity.

It is a solution for the distribution of mass and energy, but you can instead just take

any space-time, put it into the left side of einstein’s equations, and then the equations

will tell you what the distribution of mass and energy would have to be to create.

This space-time on a purely technical level will then indeed be solutions to the equations,

for whatever is the stress-energy tensor you get.

The problem is that, in this case, the energy distribution which is required to get a particular

space-time is in general, entirely unphysical and that’s the problem with the Alcubierre

drive.

It is a solution to general relativity, but in and by itself this is a completely meaningless

statement.

Any space-time will solve the equations of general relativity, provided you assume that

you have a suitable distribution of masses and energies to create it.

The real question is therefore not whether space-time solves einstein’s equations,

but whether the distribution of mass and energy required to make the solution to the equations

is physically reasonable and for there could be a drive.

This is a pretty much common obstacle in physics problem solving, or the development of a theory:

mathematics tells you which solution is acceptable in the realm of math, but a physician can

accept only solutions that fit in the real world.

So, is there a physically reasonable distribution of mass and energy in order to create a warp

drive?

The answer is probably no.

First, as we already said, it requires negative energy.

Second, it requires a huge amount of that.

Third, the energy is not conserved.

We can summarize this by saying that it requires a negative energy density, which should be

impossible except perhaps on the tiniest, quantum scales.

Sometimes people talk about the drive requiring negative mass – also called exotic matter

– and yeah, that would do the trick too – and is also probably impossible.

So that sounds like a dealbreaker.

The other minor hiccup is that Alcubierre’s original field required more energy than is

contained in all the matter in the visible universe to move a moderate-sized starship.

Subsequent studies improved on Alcubierre’s warp design and brought down the energy requirement

to less insane levels – although they typically remained somewhat insane.

But the requirement of exotic matter didn’t go away, and in fact, subsequent studies demonstrated

that any superluminal warp drive MUST use negative energy densities.

Before we dive into the new-published paper, and if you like this video, we strongly recommend

you to watch our previous video about Warp Speed: (https://www.youtube.com/watch?v=phz3y5mKkA4&ab_channel=InsaneCuriosity)

So we said there is a new paper treating the warp drive subject.

This paper is titled: “introducing physical warp drives” and it was written by Alexey

Bobrick and Gianni Martire.

In this paper, Bobrick and Martire describe the geometry of a general warp drive space-time.

As we said earlier, the warp drive geometry is basically a bubble.

(I think it would be very fun to move across the universe in a bubble…)

The bubble has an inside region, which the authors call “ the passenger area”.

In the passenger area, Space-Time is flat, so there are no gravitational forces.

Then the warp drive has a wall of some sort of material that surrounds the passenger area,

as well as an outside region.

This outside region is the key to warped spacetime.

It has the gravitational field of the warp drive itself, but the gravitational field

falls off and in the far distance one has normal flat spacetime.

What makes this fairly general construction a warp drive is that the passage of time inside

of the passenger area can be different from that outside.

This is what we exactly need in order to follow Einstein’s rule “nothing moves faster than

light”.

I mean, we are seating in our bubble and then the space-time is curved and it, and not us,

moves faster than light.

So you keep moving normally in the bubble, but then you move the bubble itself superluminally

as explained earlier.

The real question here is; what does the wall of the passenger area have to be made of?

In fact, we have to ask ourselves is this a physically possible distribution of mass

and energy, i.e. a physically possible solution.

Bobrick and Martire explain that if you want superluminal motion, you need negative energy

densities.

If you want acceleration, you need to feed energy and momentum into the system.

This is something impossible to achieve at the moment.

We simply don’t know how to do that, and also we can say it is probably impossible!

This paper is a very important one because it really demystifies warp drives.

Of course, now it might seem that we are less excited than before because really it says

that we still don’t know how to accelerate to superluminal speeds.

But if you think more about it, you will notice that, as it closes some doors, it opens up

a lot more possibilities.

In fact, we now have a much better mathematical basis to study warp drives.

For example, studying math, Bobrick and Martire showed that for the Alcubierre drive you can

decrease the amount of energy by seating passengers next to each other, instead of behind each

other because the amount of energy required depends on the shape of the bubble.

In particular, the flatter it is in the direction of travel, the less energy you need for other

warp drives.

And maybe there are a lot of other geometries that may work better.

This is the kind of question you can really only address if you have the mathematics in

place.

Another exciting thing is that, while it may look now like you can’t do superluminal

warp drives, this is only correct if general relativity is correct, and maybe it is not!

We know that general relativity is the ACTUAL best theory we have to describe the universe

and how it works.

But we have a lot of problems and questions to answer.

Astrophysicists have introduced dark matter and dark energy to explain what they observe,

but it is also possible that general relativity is ultimately not the correct theory for space-time.

Could this mean something for warp drives?

Could it have implications for them?

We really don’t know, but now we have the mathematics to study this question.

As you can see it turns out that, as Sabine Hossenfelder said:

“scientific research is a double-edged sword.

Sometimes, if you look closely at a really exciting idea, it turns out to be not so exciting

and maybe you’d rather not have known, but I think the only way to make progress is to

not be afraid of learning more.”

“This video ends here!

Thanks for watching everyone!

Did you find this content interesting?

? Do you think it will be possible to build and use a warp drive?

Do you have any question for us?

Let us know in the comment below!

See you next time on the channel!

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