# Thread: Is faster-than-light travel or communication possible?

1. ## Is faster-than-light travel or communication possible?

John Baez says that faster-than-light travel in the forms seen in Star Trek will perhaps never be possible to achieve. But he says that it cannot be completely ruled out though:

http://math.ucr.edu/home/baez/physic...Light/FTL.html

2. Star Trek types maybe not, but hopefully wormholes pan out.

3. Originally Posted by pluto2
John Baez says that faster-than-light travel in the forms seen in Star Trek will perhaps never be possible to achieve. But he says that it cannot be completely ruled out though:

http://math.ucr.edu/home/baez/physic...Light/FTL.html
Are you sure he wasn't just considering the possibility of yet another Star Trek movie?

4. Originally Posted by Believe
Star Trek types maybe not, but hopefully wormholes pan out.
I feel I should point out this isn't technically faster than light travel. FTL is when you travel the same path as light but quicker. A wormhole is opening a new path which is shorter. If someone traverses a wormhole they are going to be slower than the light which moves through the wormhole, so they don't violate causality or relativistic constraints.

Communication or travel which doesn't open shorter routes is proper 'faster than light', which at the moment doesn't have any basis in any part of physics.

5. But wormholes are simply impossible according to current physics. I'm pretty sure that current thought is that the possibility of wormholes has been debunked by many experts.

Black holes and wormholes are completely different phenomena, and black holes are the only ones with observational evidence. If wormholes exist, they would tend to only be quantum-scale phenomena. Having one big enough for even a bacteria to move through would require an outrageous amount of energy and that is not possible to achieve.

6. Wormholes are not necessarily completely absent from general relativity when considering realistic space-times. For example, there's a region of space-time for the Schwarzchild metric, which describes the simplest type of black hole, which has the same structure as a worm hole (for those which understand what I'm about to say, it's the region in the middle of the Penrose diagram with $\textrm{d}s^{2} = \textrm{d}\rho^{2} + 4M^{2}\cosh^{2}\chi \textrm{d}\phi^{2}$), in that space-time looks cylindrical and the region joins two otherwise separate spaces.

7. Originally Posted by pluto2
But wormholes are simply impossible according to current physics. I'm pretty sure that current thought is that the possibility of wormholes has been debunked by many experts.

Black holes and wormholes are completely different phenomena, and black holes are the only ones with observational evidence. If wormholes exist, they would tend to only be quantum-scale phenomena. Having one big enough for even a bacteria to move through would require an outrageous amount of energy and that is not possible to achieve.
It would likely work out to be easier to make the universe a simulation and mess with it's internal parameters than build a wormhole as standard. You've still got the potential concerns of energy in both instances, just one is of greater control universally than the other.

As to FTL communication, we'll it's something that has been debated over, especially in light (no pun intended) of Günter Nimtz work.

8. Physicists are living in a fantasy world because humans will never have to technology or the resources to change the universe on a large scale.

We can hardly get to Mars or even to the Moon so changing the universe is a little bit far-fetched I think.

What you see on Star Trek and on popular utopian post-scarcity novels like the Culture by Lain Banks is just not possible to achieve in the world.

https://en.wikipedia.org/wiki/The_Culture

We cannot change the universe but what we can do is inhale its lessons and accept them. We must enjoy the times when we walk in the light and endure the times when we are in the dark, content with the knowledge that it will change again.

As Albert Einstein said: “Maybe we cannot change the Universe but by raising our voices we could help goodwill causes among people and peace on Earth"

9. Originally Posted by AlphaNumeric
I feel I should point out this isn't technically faster than light travel. FTL is when you travel the same path as light but quicker. A wormhole is opening a new path which is shorter. If someone traverses a wormhole they are going to be slower than the light which moves through the wormhole, so they don't violate causality or relativistic constraints.

Communication or travel which doesn't open shorter routes is proper 'faster than light', which at the moment doesn't have any basis in any part of physics.
Whoa I'm having a hard time processing this. What's the difference between "opening shorter routes" and, say, using a standard Star Trek transporter? It seems to me that from particular frames causality between event A and event B could appear to be violated if there was a worm-hole connecting the two.

Which brings up another question...a worm-hole doesn't simply connect two points in space; it must connect two points in spacetime. How is that relationship determined, exactly? Because it seems to me that this is the deciding factor as to any potential causality issues.

10. Originally Posted by RJBeery
Whoa I'm having a hard time processing this. What's the difference between "opening shorter routes" and, say, using a standard Star Trek transporter? It seems to me that from particular frames causality between event A and event B could appear to be violated if there was a worm-hole connecting the two.

Which brings up another question...a worm-hole doesn't simply connect two points in space; it must connect two points in spacetime. How is that relationship determined, exactly? Because it seems to me that this is the deciding factor as to any potential causality issues.
Since we can't make one yet I'm guessing he can't answer your question.

11. It is only within the last ten years that it has been discovered that the universe is expanding at an increasing rate.

http://news.nationalgeographic.com/n...nergy-science/

I don't know how they figured that out or how much credence to put into it. But the point is that there is still unknown physics to be discovered and figured out. On the FTL business our current understanding indicates not. But that is "current understanding".

A lot of people think science is what we have already figured out. But science is really the process of figuring out new things. The stuff we have figured out already is just the excreta of science.

But who needs FTL. If we can get up to 20% of light speed and extend our life spans to 300 years and create some kind of hibernation technique slowing bodies down at a 5 to 1 ratio we could still send interstellar ships out after von Neumann probes have found interesting stuff.

But we do have too much sci-fi with FTL travel and people expect too much.

It undoubtedly makes for better stories.

psik

12. Originally Posted by pluto2
Physicists are living in a fantasy world because humans will never have to technology or the resources to change the universe on a large scale.
How does this mean the physicists are living in a fantasy world? Physicists don't go around canvassing for money to build starships.

When asked if wormholes are possible, the physicists are the first ones to say sure but it'll likely never be practical.

13. The need for speed--to increase the efficiencies of travel times and product/passenger delivery times between the asteroid regions and Earth--will continue to test the engineering envelope, and refine the knowledge with observations of the higher-speed environment(s).

14. Originally Posted by pluto2
Physicists are living in a fantasy world because humans will never have to technology or the resources to change the universe on a large scale.
It doesn't involve changing the universe on a large scale. Black holes aren't necessarily vast cosmic galaxy eaters.

Originally Posted by RJBeery
Whoa I'm having a hard time processing this. What's the difference between "opening shorter routes" and, say, using a standard Star Trek transporter? It seems to me that from particular frames causality between event A and event B could appear to be violated if there was a worm-hole connecting the two.
A transporter in Star Trek works by disassembling something on a quantum level, tending the matter's energy to the other location and then converting back. Obviously it doesn't have a sound scientific basis but it doesn't have anything to do with causality because it's just moving things about in normal space. A wormhole is about 'cutting corners', it's something to do with the structure of space-time.

Originally Posted by RJBeery
Which brings up another question...a worm-hole doesn't simply connect two points in space; it must connect two points in spacetime. How is that relationship determined, exactly? Because it seems to me that this is the deciding factor as to any potential causality issues.
Different points in space are different points in space-time but yes, a wormhole can provide paths to different times, not just different spaces. A wormhole to different spatial locations isn't too abhorrent a concept but to different times brings into focus the whole horrible mind buggery that is closed time-like curves.

15. Originally Posted by AlphaNumeric
A wormhole is about 'cutting corners', it's something to do with the structure of space-time.
But space-time is an hypothetical object. We don't know whether such an hypothetical object really exists in nature or not and as far as we know general relativity may even turn out to be false.

16. Originally Posted by pluto2
But space-time is an hypothetical object. We don't know whether such an hypothetical object really exists in nature or not
Spacetime is a model of how our universe works. And so far, it is passing with flying colours. If you have a smartphone (and billions of people do), every moment it is on, it is validating GR, which is based on spacetime.

Originally Posted by pluto2
and as far as we know general relativity may even turn out to be false.
Regardless of what evidence comes along that causes us to refine GR, it is working now.

17. Originally Posted by pluto2
But space-time is an hypothetical object. We don't know whether such an hypothetical object really exists in nature or not and as far as we know general relativity may even turn out to be false.
The same can be said for anything which we don't directly observe. Hell, if you want to bore yourself to death going into a philosophy department and proclaiming "The world we experience is real!" will promptly be met by dozens of arguments why even observable reality isn't real.

Yes, the notion of space-time is a model but this far viewing whatever reality is in terms of a space-time has worked extremely well in describing gravity. Yes, you could say "But it might not be so!" about any prediction made by any model, be it wormholes in GR, the Higgs in QFT or magnetic monopoles in electromagnetism. Hence why physicists are always coming up with experiments to test such predictions as best as technology (and bloody funding councils) will allow.

The Schwarzchild metric is the one with a wormhole somewhere in the space-time, specifically on the event horizon for particular geodesics. The same metric is used to model the gravitational field around the Sun or Earth, it's used to make GPS networks work! This is because while the Earth isn't a black hole to an object orbiting it it has the same gravitational effect as a black hole. The joys of Gauss's theorem!

My point was that wormholes arise in gravitational models not just via some wacky negative pressure exotic matter moving through the central ring of a Kerr-Newman black hole (there be horrific algebra dragons!) but in more mundane set ups (yes, the Schwarzchild black hole is mundane). How much GR accurately describes such phenomena is a matter of constant research.

/edit

Oh and it isn't a matter of GR perhaps being false, it IS false. False in the sense of not being universally valid in all gravitational phenomena. We know it falls apart for quantum scales but it's still an extremely good effective model for physics above the quantum gravity scale, as motivated by all the experiments we keep doing to test it.

18. Originally Posted by AlphaNumeric
Communication or travel which doesn't open shorter routes is proper 'faster than light', which at the moment doesn't have any basis in any part of physics.
I disagree. From what I've seen, if its possible it would be done using quntum mechanics.

Faster than Light?, Raymond Y. Chiao, Paul G. Kwiat and Aephraim M. Steinberg, Scientific American, August 1993. The abstract reads
Experiments in quantum optics show that two distant events can influence each other faster than any signal could have traveled between them.
Faster-than-light speeds, tachyons, and the possibility of tachyonic neutrinos, Robert Ehrlich, Am. J. Phys. 71(11), November 2003. The abstract reads
Faster-than-light speeds and hypothetical FTL particles known as tachyons are exciting subjects for students, given their speculative and controversial nature. This article presents an overview of these subjects and their role in special relativity and examines the possibility that one or more of the three neutrinos is a tachyon. The paper also describes several low tech demonstrations useful for teaching about faster-than-light speeds and tachyons in intermediate and advanced introductory college-level physics courses.
Can EPR-correlations be used for the transmission of superluminal signals? P. Mittelstaedt, Ann. Phys (Leipzig) 7 (1998), 7-8, 710-715. The abstract reads
In a compound quantum system with EPR-like correlations a measurement of one subsystem induces instantaneously changes of the subsystem, irrespective of the relative distance of the two subsystems. We consider several arguments which were put forward in recent years in order to show that these nonlocal effects cannot be used for superluminal communication. It turns out that arguments mentioned above are merely plausible but not really stringent and convincing. This means that the question in the title of this paper is still open.
Superluminal signal velocity, G. Nimtz, Ann. Phys (Leipzig) 7 (1988), 7-8, 618-624. The abstract reads
It recently has been demonstrated that signals conveyed by evanescent modes can travel faster than light. In this report some special features of signals are frequency band limited. Evanescent modes are characterized by extraordinary properties: Their energy is negative, they are not directly measurable, and he evanescent region is not causal since the modes traverse this region instantaneously. The study demonstrates the necessity of quantum mechanics in order to understand the superluminal velocity of classical evanescent modes.

19. Originally Posted by pmb
I disagree. From what I've seen, if its possible it would be done using quntum mechanics.
No FTL signaling has ever been found to be possible using quantum effects.

20. Originally Posted by Syne
No FTL signaling has ever been found to be possible using quantum effects.
I don't follow. Please clarify what the purpose of this statement is. Nobody here claimed beyond all doubt that its already been observed. In fact I stated quite clearly "if its possible". There was no need to claim that it hasn't been observed since nobody claimed otherwise.

I merely suggested that if it observed in the future it will probably be in a QM experiment.

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