Is it Possible to Travel Faster Than Light?

[MattRob]

First, let me be perfectly clear that I'm not implying Einstein was wrong. The lorentz equation clearly states that reaching the speed of light from a stationary perspective relative to the immediate gravitational potential is impossible ("relative to the immediate gravitational potential" i.e. the other end of the universe is expanding away from us at FTL, but that's okay because it's not local.). FTL is being used to mean at point A, then at point B sooner that it would take a beam of light to travel from A to B through undistorted space.

I also want to be perfectly clear I'm not postulating any new theories, or doing anything outside mainstream science. I'm honestly asking; is there any way it could be reasonably possible with our current understanding of the universe.

They key word being "reasonably". Maybe an alcubierre drive would be possible, but it would require exotic materials, and to top it off, huge, huge, huge amounts of exotic and regular materials to make it practical.
A wormhole would probably be more practical, and that would require energy on astronomical scales.

The question is, quiet simply; given current mainstream science, will it be possible with anything probable in the next few hundred years to be at point A, then be at point B faster than a beam of light would through undistorted space?

As a distinctly separate question, What are the chances that Heim theory, or even just the part about rotating to higher dimensions using magnetic fields but not the rest of it, being correct? Is it even considered mainstream?

 

[Drakkith]

I would say no to both your questions.

 

[DaveC426913]

The more accurate answer is:

Your guess is as good as anyone's.

You've mentioned two ideas that have been postulated - Alcubierre drive and worm holes. They don't violate known laws explicitly, so ... who knows? No one can know. No one can even guess.

 

[K^2]

As far as I know, both traversable wormholes and Alcubierre drive require negative energy densities in all known configurations. These do not violate any laws, but also have not been observed directly or indirectly, so it might be a violation of some sort. It is possible that a yet unknown configuration would allow for these effects under positive energy densities or that some way of producing negative energies is discovered. But at the moment, there is no reason to believe they can work.

With wormholes, there is an additional problem. GR does not suggest a method for altering topology of space-time, which you'd have to do to create a wormhole of any kind. So while finding ways to make existing traversable is a possibility, we have absolutely no indication that creating wormholes is at all a possibility.

 

[bcrowell]

FAQ: Why can't anything go faster than the speed of light?

In flat spacetime, velocities greater than c lead to violations of causality: observer 1 says that event A caused event B, but observer 2, in a different state of motion, says that B caused A. Since violation of causality can produce paradoxes, we suspect that cause and effect can't be propagated at velocities greater than c in flat spacetime. Special relativity is one of the most precisely and extensively verified theories in physics, and in particular no violation of this speed limit for cause and effect has ever been detected -- not by radiation, material particles, or any other method of transmitting information, such as quantum entanglement. Particle accelerators routinely accelerate protons to energies of 1 TeV, where their velocity is 0.9999996c, and the results are exactly as predicted by general relativity: as the velocity approaches c, a given force produces less and less acceleration, so that the protons never exceed c.

The corresponding speed limit in curved spacetime is far from being established. The argument from causality is not watertight. General relativity has spacetimes, such as the Godel solution, that are valid solutions of the field equations, and that violate causality. Hawking's chronology protection conjecture says that this kind of causality violation can't arise from realistic conditions in our universe -- but that's all it is, a conjecture. Nobody has proved it. In fact, there is a major current research program that consists of nothing more than trying to *define* rigorously what the chronology protection conjecture means.

There are certain things we *can* say about faster-than-light (FTL) motion, based on the fundamental structure of general relativity. It would definitely be equivalent to time travel, so any science fiction that has routine FTL without routine time travel is just plain wrong. It would probably require the existence of exotic matter, which probably doesn't exist. If it were possible to produce FTL artificially, it would certainly require the manipulation of godlike amounts of matter and energy -- so great that it is unlikely that beings able to carry it out would have anything like ordinary human concerns.

There are many ways that velocities greater than c can appear in relativity without violating any of the above considerations. For example, one can point a laser at the moon and sweep it across, so that the spot moves at a speed greater than c, but that doesn't mean that cause and effect are being propagated at greater than c. Other examples of this kind include a pair of cosmic-sized scissors cutting through a gigantic piece of paper at greater than c; phase velocities greater than c; and distant, observable galaxies receding from us at greater than c, which can be interpreted as an effect in which space itself is expanding in the space in between.

 

[K^2]

There are certain things we *can* say about faster-than-light (FTL) motion, based on the fundamental structure of general relativity. It would definitely be equivalent to time travel, so any science fiction that has routine FTL without routine time travel is just plain wrong.

No, there is nothing in the structure of general relativity to suggest that.

 

[arkajad]

What are the chances that Heim theory, or even just the part about rotating to higher dimensions using magnetic fields but not the rest of it, being correct? Is it even considered mainstream?

Which part exactly of Heim's theory you are talking about? Which particular equation?

 

[DaveC426913]

No, there is nothing in the structure of general relativity to suggest that.

Not GR, no. But SR allows it.

SR does not specifically forbid massive objects faster than the speed of light; it merely forbids the transition from STL to FTL. Hypothetical objects faster than light are collectively called tachyons. Tachyons, mirror-wise to their STL cousins, can never slow down to the speed of light, let alone cross the barrier to STL. Funny thing about tachyons is that they will be experienced to us as going backwards in time.

The upshot is that, if you could magically convert your spaceship into tachyons so that you are moving FTL, you would also be traveling backwards in time.

Note again that tachyons are entirely hypothetical - there is no evidence that they exist, nor even to suppose that they might. It is simply that SR does not forbid them.