Don't stop me now! Superluminal travel in Einstein's universe

November 27, 2015 by Geraint Lewis, The Conversation
Hyperspace may one day be a reality. Credit: Shutterstock

The story of the drawn-out development of Albert Einstein's revolutionary rewrite of the laws of gravity has been told many times, but over the past 100 years it has given us extreme stars and black holes, expanding universes and gravitational mirages. Einstein also ensured you will never get lost, enabling the technology that helps your phone find your location with pinpoint accuracy!

Despite this scientific bounty, relativity appears to place strict limits on our exploration of Einstein's universe, with any rocketship limited to travelling no faster than the of light. With the distance between stars measured in light years, and the distance across galaxies being hundreds of thousands of light years, not to mention the complexities of time dilation, establishing and running a galactic empire is going to be a drawn out and messy affair.

Bending time, bending space

I've already written that all is not lost, as in 1994 physicist Miguel Alcubierre discovered something wonderful: that by bending space and time just the right way will allow you to travel at any speed you want! While there are some downsides, with such a warp drive, the speed of light can be broken.

However, a couple of questions spring to mind, not least how can this superluminal bubble of a warp drive be consistent with the rules of relativity. And if it is, why did it take until the 1990s for someone to notice this was the case.

After E = mc², the fact that nothing can move faster than light is probably the most common fact known about Einstein's special theory of relativity. So just what can actual mean?

Let's begin with what Einstein was actually saying about racing a light beam. To Einstein, the race takes place "locally", such as in a laboratory, where you start a particle with mass and a light beam off at the same time. In this case, the light beam always gets ahead.

But in his special theory, the details of space and time are the same everywhere. More technically, the union of the two – known as spacetime – is flat, and we can compare the speed of a particle in the laboratory to a light ray somewhere off in the universe.

Things get messier in the general theory, as the presence of gravity ensures that the curvature of spacetime here is different to spacetime over there, and it is not possible to uniquely compare the speed of the particle in your laboratory to a light ray off in the distant universe. The only sensible comparison you can make is in your laboratory, and here the light ray still always wins.

The same is true in the curved spacetime of the warp drive. If your traveller in the warp bubble tries to race a particle and a light beam together, the light beam will always win.

An observer watching the bubble go by would calculate the to be travelling faster than any light ray they create in their own laboratory. But this is not a problem, as it really makes no sense to compare velocities "there" with velocities "here".

It is precisely this reason that cosmologists are happy to talk about galaxies receding from us faster than the speed of light due to the expansion of the universe.

Metric mechanics

Relativity had been around for almost 80 years before Alcubierre uncovered his solution. Why hadn't people realised superluiminal travel was part of the theory?

The problem, of course, is the mathematically fiendish nature of Einstein's equations. It is extremely difficult to calculate the curvature of spacetime and resultant action of gravity from any old distribution of mass and energy.

It can be mathematically simpler to define the properties of spacetime and then calculate the required distribution of mass and energy. And Alcubierre's great insight was to realise a bubble could move at any speed as a rolling wave in spacetime.

However, such "metric mechanics" come with a downside: we may be able to find spacetimes that allow superluminal motion, but the required distribution of mass and energy may not be physically possible.

Those familiar with classical mechanics may remember that it is easier define a gravitational potential to determine forces, but these might require negative matter to physically exist.

The same is true for the warp drive solution, requiring material with a negative energy density to bend and shape space-time appropriately. And while we have hints that such properties exist in the universe, we have no idea if we will be able to mine and forge it to fashion our spaceships. So we may never be able to build an Alcubierre .

But we should not allow this to demoralise us! Alcubierre's insights should inspire us to continue to bend and stretch , to tease out the possibles still hidden within the mathematics. Most may be physically impossible to ever realise, but with sufficient imagination, and a stroke of luck, we may stumble across our pathway to the stars.

Explore further: Will we have to rewrite Einstein's theory of general relativity?

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antialias_physorg
4.7 / 5 (12) Nov 27, 2015
you to travel at any speed you want! While there are some downsides, with such a warp drive, the speed of light can be broken.

I think this part is misleading (although it is later mentioned that the speed of light is still the supreme speed locally - even with such a drive)
The Alubierre drive doesn't travel at any speed at all. The object inside the bubble is locally stationary. The notion of speed is very misleading in this context. It's like galaxies being pushed away due to intervening space expanding. They are not moving at any speed WRT local space.

Speed of light limit only applies to (massive) particles. But in the idea of the drive is that spacetime is moving (being contracted at the front end and expanded at the rear end). spacetime is not a particle and hence it has no (or possibly just a very much higher) 'speed' limit.
Benni
1.8 / 5 (10) Nov 27, 2015
Speed of light limit only applies to (massive) particles.
.......No, again you are clueless as to what you are talking about, "speed of light" only applies to electro-magnetism. Actually study Special Relativity, then come back. I'm surprised your Stumpo mentor has missed this (or, maybe I shouldn't be surprised).
Torbjorn_Larsson_OM
4.6 / 5 (10) Nov 27, 2015
Also, while the Alcubierre 'drive' transport a spacetime volume faster than the universal speed limit within spacetime, it can't magically populate it with matter that moves FTUSL. So it won't make any practical difference regarding matter transportation.

Oh look, a clueless one calling a spot on comment 'clueless', and arguing about the wrong relativity theory for the article. (But SR US limit is a limit on local energy transport, using photons for ease, so it works too.) Incompetence syndrome in action, and damn hilarious! =D
SuperThunder
3.4 / 5 (5) Nov 27, 2015
As soon as a I get the Photon Purge Overdrive screwed down on my Negelectric Impeller, you can all eat my warp-space translated dust! Prepare to walk around my awesomeness in a mathematically straight line, slowpokes! Uh... anybody got one of those star-head screwdrivers... dang...

I don't remember who, and I am sincerely sorry for that, but The Evolution of Physics by Einstein and Infeld was recommended to me here, and I picked up a copy. Thank you to the one who suggested it!
Hyperfuzzy
1.7 / 5 (6) Nov 27, 2015
The speed of light is undefined. Only frequency times wavelength, obvious; wave-front, completely ignored. We are as idiotic as Einstein! If time dilation and length contraction were real, the wavelength of light would be zero. Mass is only an un-reconciled constant. Do the math. But since most believe by defining "all" possibilities, QM, at the same time actually is the reason why, while simultaneity does not exist according to Dr. E. Complete nonsense. Well, I for one prefer reality! Why should we wear these goggles to view anything? What exist has always existed, without this stupidity. All I see are two particles.
SuperThunder
3.9 / 5 (7) Nov 27, 2015
Well, I for one prefer reality!

Extraordinary claims require extraordinary evidence.
antigoracle
4 / 5 (4) Nov 27, 2015
As soon as a I get the Photon Purge Overdrive screwed down on my Negelectric Impeller, you can all eat my warp-space translated dust! Prepare to walk around my awesomeness in a mathematically straight line, slowpokes! Uh... anybody got one of those star-head screwdrivers... dang...

Hmm.... speaking of warp(ed)
Any who, superluminal travel is so last millennium, the real thing is time travel.
SuperThunder
3.7 / 5 (6) Nov 27, 2015
Any who, superluminal travel is so last millennium, the real thing is time travel.

Space travel is time travel. With my Super Thunder Drive(tm), I will be observed at the destination before I leave. If I observe myself blow up, I will simply go somewhere else, thus I will never observe myself blowing up in the future. It works!
Benni
2 / 5 (8) Nov 27, 2015
Oh look, a clueless one calling a spot on comment 'clueless', and arguing about the wrong relativity theory for the article. (But SR US limit is a limit on local energy transport, using photons for ease, so it works too.) Incompetence syndrome in action, and damn hilarious! =D
......one more clueless one spinning in out of control on the behalf of another who also gets SR mixed up with GR because he too is unable to distinguish between the Mass/Energy Equivalence Principle & Equivalence of Inertia & Gravitational Mass.
Captain Stumpy
4.3 / 5 (6) Nov 28, 2015
With my Super Thunder Drive(tm)
@Super
STD?
was that intentional?
ROTFLMFAO
Mimath224
5 / 5 (4) Nov 28, 2015
@antialias_physorg yes! I remember being reminded in another similar article that also SR & GR do not place restrictions on the rate at which Space can move (it might have been you that reminded me).
@Benni the speed of light does in fact mean 'the speed at which light travels' and makes no other assertion. For most of the posters here SR is but a stepping stone to the next level and Einstein was also aware of this. Sounds as though you are still there.
flag
5 / 5 (1) Nov 28, 2015
This paper explains the Special and General Relativity from the observed effects of the accelerating electrons, causing naturally the experienced changes of the electric field potential along the moving electric charges. The accelerating electrons explain not only the Maxwell Equations and the Special Relativity, but the Heisenberg Uncertainty Relation, the wave particle duality and the electron's spin also, building the bridge between the Classical and Relativistic Quantum Theories. The changing acceleration of the electrons explains the created negative electric field of the magnetic induction, the electromagnetic inertia, the changing relativistic mass and the Gravitational Force, giving a Unified Theory of the physical forces. Taking into account the Planck Distribution Law of the electromagnetic oscillators also, we can explain the electron/proton mass rate and the Weak and Strong Interactions.
https://www.acade...lativity
viko_mx
2.3 / 5 (6) Nov 28, 2015
GR bend the light, the 3D abstract geometric space without physical properties and limitations (not physical object or medium), the time and the truth at all.

The light is refracted at the boundary of two optical environments and to be bended it is not necessary to cross the curved space whatever that means, according vain philosophers that like to invent their own reality.
viko_mx
2.3 / 5 (6) Nov 28, 2015
In the living organisms there is structure and hierarchy. The family have structure and hierarchy. The same is with society and corporations. This hierarchy support order and proper functioning of these units.
The GR are denying the structures and their hierarchy. This mythological theory which denying the order in the systems is addressed to majority of people. The minority of people who have financial and political power and wants to control the majority of people, are needed of "scientific" explanation of double standards and moral relativism which GR must ensure, but in fact recognize the structure and obey the hierarchy in their environment.
earthling98765
3 / 5 (2) Nov 28, 2015
I like the comment of Antialias. There is a "sub-space" to spacetime through which gravity travels at a much faster speed than EM radiation (which given the dimensions of the universe is pathetically slow - much too slow to be the means of "data" transfer generally). An experiment done by the late author of metaresearch.com entitled "The Speed of Gravity" showed that the gravity from the Sun gets here much faster than the light. During a total eclipse the gravity is strongest when the Moon moves off the visible Sun and positions itself in alignment with the actual position of the Sun. The conclusion is that while light travels from the Sun to the Earth in a curved path, the gravity is virtually immediate. This is why LIGO and now LISA and LIGO II will not discover gravity waves...because they are looking in spacetime, and it is in some "sub-space" of spacetime. LOOK THERE!!
Whydening Gyre
5 / 5 (6) Nov 28, 2015
Oh look, a clueless one calling a spot on comment 'clueless', and arguing about the wrong relativity theory for the article. (But SR US limit is a limit on local energy transport, using photons for ease, so it works too.) Incompetence syndrome in action, and damn hilarious! =D
......one more clueless one spinning in out of control on the behalf of another who also gets SR mixed up with GR because he too is unable to distinguish between the Mass/Energy Equivalence Principle & Equivalence of Inertia & Gravitational Mass.

Benni@ How bout a DE or two to explain what you mean?
TimLong2001
3 / 5 (2) Nov 28, 2015
The velocity of light is just the characteristic velocity of E-M radiation, nothing more. When the giddyness of Einstein's centennial celebration has passed, maybe we can get back to the development of advances in our understanding of the universe. BTW, he was correct in stating that "God does not play dice with the universe." Non-linear (chaos) theory has demonstrated this. The mathematics of statistical methodology should not cloud our understanding of the deterministic dynamical laws underlying physical processes, originating in rotations induced by charge interactions at sub-quantum scales.
baudrunner
2.3 / 5 (3) Nov 28, 2015
If Einstein was correct in his "nothing can travel faster than light" declaration, then the difference in velocity between two objects, each traveling at light speed and moving in opposite directions, should be equal to the speed of light.

Well, I beg to differ, and I think that it is indeed possible to travel faster than light, it's just another speed barrier, like the sound barrier. I think that we should call it, the light barrier. After all, one traveling at the speed of light should not be judged by one who is static.
SuperThunder
3.4 / 5 (5) Nov 28, 2015
baudrunner, you seem to have no knowledge of Relativity and how it is observed in the actual universe.

@Super
STD?
was that intentional?
ROTFLMFAO

@Stumpy
My original comment talked of spreading Super Thunder Drive technology all over the universe, but I thought that was too obvious.
thaken
not rated yet Nov 28, 2015
If the outer shell of our foreseeable universe was once the center of the universe, there are probably only local galaxies to travel to and anything else would be ghost light waves / particles of past existence.
Mimath224
5 / 5 (5) Nov 28, 2015
@Whydening Gyre Oh please, don't start benni on DE's again...means I'll have quote another he can't solve, Ha!
baudrunner
not rated yet Dec 03, 2015
baudrunner, you seem to have no knowledge of Relativity and how it is observed in the actual universe.
That's the thing, you see. It is observed, from the point of view of an observer who exists within a static frame of reference. Then all those theoretical assumptions can be applied after doing the mathematics. The traveler at light speed does not observe what you observe, for he exists within his own static frame of reference. He breaks the light barrier and generates a massive shock wave, leaving photonic wave fronts behind him, the same applies to breaking Mach 1, only that is sound.

Faster than light motion does not remove relativity from the equation.
MaxwellsDemon
2.3 / 5 (3) Dec 04, 2015
There are at least three phenomena that suggest that negative mass may not be required to design a spacetime propulsion system:

1.) Cosmic inflation – spacetime expanded billions of times faster than the speed of light in the early universe. This phenomenon originally motivated Alcubierre's paper. We don't yet know how inflation works, but it certainly didn't require any negative mass.

2.) Dark energy – GR actually predicts an inverse gravitational effect if spacetime is imbued with some bizarre kind of massless energy field. It's possible that this effect could be synthesized and amplified once we understand it.

3.) The Casmir effect and squeezed light experiments – it appears that tiny regions of vacuum energy can be suppressed, creating an effective form of negative energy state.

So I don't think we should rule out spacetime propulsion just because negative-mass exotic matter isn't physical. Anything that simulates the effect of negative mass would suffice.
MaxwellsDemon
1 / 5 (2) Dec 04, 2015
@SuperThunder
With my Super Thunder Drive(tm), I will be observed at the destination before I leave.

Imagine that your Super Thunder Drive(tm) could get you to the nearest star system, roughly 4LYs distant, in a single millisecond. Your local time on board always remains the same as mine here on the Earth, where I'm observing your trip. You hit the button and leap to your destination. It will take roughly 4 years and one millisecond for me to see you arrive, because the light has to propagate across the intervening distance. So from my POR, you never quite reached the speed of light. Superluminal travel can't be witnessed as such. Alcubierre missed that in his original paper, and White missed it as well more recently.

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