6 ms·

I feel like a lot of people here misunderstand the speed of light as a cosmic speed limit. The speed of light as a speed limit is a local constraint. On a large

by stryker 14y ago

I feel like a lot of people here misunderstand the speed of light as a cosmic speed limit. The speed of light as a speed limit is a local constraint. On a larger scale there is no such speed limit. Just because you travel faster than light on a non-local scale does not mean you break causality. For example, light "travels" more slowly through water than vacuum. Well, actually, photons travel at c always -- it's just that light gets bounced around by water molecules, getting absorbed and reabsorbed many many times before arriving at the destination. It's like driving to a destination as opposed to running to it. If the roads are curvy enough, the runner will win because he is not constrained by roads. Could it be that the Alcubierre drive gets past the roads of empty space in a way light cannot? For a better example, consider the expansion of the universe. Link: http://curious.astro.cornell.edu/question.php?number=575 http://curious.astro.cornell.edu/question.php?number=575. I quote: The fact that galaxies we see now are moving away from us faster than the speed of light has some bleak consequences, however. Astronomers now have strong evidence that we live in an "accelerating universe," which means that the speed of each individual galaxy with respect to us will increase as time goes on. If we assume that this acceleration continues indefinitely, then galaxies which are currently moving away from us faster than the speed of light will always be moving away from us faster than the speed of light and will eventually reach a point where the space between us and them is stretching so rapidly that any light they emit after that point will never be able to reach us. In other words, vacuum fills in between us and far away galaxies faster than light can traverse it. Again, locally, the derivative of position with respect to time is c, but the universe is able to "cheat" by messing around with the definition of position. If the Alcubierre drive messes with the fabric of the universe in a similar way, I don't see any reason why it cannot succeed. Here's a related link: http://curious.astro.cornell.edu/question.php?number=56 http://curious.astro.cornell.edu/question.php?number=56. I quote: Technically speaking, the speed of light limit only applies when you are in an "inertial frame" -- that is, sitting where you are, without any forces acting on you, and measuring the speed of an object that moves past a ruler and clock that you are holding in your hand. Across the large distances in the universe, however, we have a very different set of circumstances. No one is in an inertial frame, because everyone is being accelerated with respect to everyone else, due to the universe's gravitational field and the fact that the universe is expanding. In effect, the universe's expansion isn't really due to galaxies moving "through space" away from each other, but rather due to the stretching of space itself, which isn't governed by the same limits that we are. I'm not sure whether the Alcubierre drive contradicts causality, but if it does, I highly doubt that it is because of the arguments presented on this forum.

nessus42 14y ago
I'm not sure whether the Alcubierre drive contradicts causality, but if it does, I highly doubt that it is because of the arguments presented on this forum. The Alcubierre drive most certainly does violate causality, and this follows from just the most basic amount of Special Relativity that you might learn if only you'd spend your time learning real things, rather than spreading disinformation.
- stryker 14y ago
  I'm going to ignore your condescension. I'm also going to assume you didn't read the rest of my post, because you presented no arguments to counter my points. I'd like to point out that the wikipedia article on the Alcubierre drive writes at length to show how this warping process does not violate causality: http://en.wikipedia.org/wiki/Alcubierre_drive http://en.wikipedia.org/wiki/Alcubierre_drive. I know you feel strongly about people not understanding special relativity and I actually agree with you on that point, but you're not addressing any of the valid counterpoints that people are making. You're simply closing your ears and exclaiming "special relativity" which only applies locally (if you want an appeal to authority, I talked about this with a former physicist who worked with Stephen Hawking). 1) The universe is expanding faster than the speed of light. In other words, galaxies are moving away from us faster than c (evidenced by the growing redshift of light emitted by galaxies when they were NOT traveling away from us faster than c). That does not violate causality (as I mentioned in my post) because the topology of space itself is changing. Locally, everything still obeys special relativity. 2) Virtual particles, EPR Paradox (I know it's not actually a paradox). (http://math.ucr.edu/home/baez/physics/Quantum/virtual_particles.html http://math.ucr.edu/home/baez/physics/Quantum/virtual_partic...) My point with these phenomena is that locality and the speed of light are not very intuitive concepts. You can still have "spooky action at a distance" without violating causality.
  - nessus42 14y ago
    You're simply closing your ears and exclaiming "special relativity" which only applies locally (if you want an appeal to authority, I talked about this with a former physicist who worked with Stephen Hawking). If you come up with a mathematical "proof" and I can use its conclusion to prove that 1 + 1 = 3, then I have shown your proof to be incorrect via contradiction, no matter how hard you continue to argue for it. Special Relativity does not only apply locally. It applies to any system where information can be transmitted between two points that are in inertial frames. The universe expanding at faster than the speed of light is neither here nor there, since you cannot use the expanding universe to transmit information between two points in at FTL speeds. On the other hand, you CAN use an FTL drive to transmit information between two points in inertial frames at FTL speeds. QM spooky action at a distance does not let you transmit information between two points at FTL speeds. This is all you need to do to show that any FTL scheme violates Special Relativity: Information transmitted between two points in inertial frames at FTL speeds. If you can do that, you've either disproven causality, or you've disproven Special Relativity.

by stryker 14y ago

nessus42 14y ago

I'm not sure whether the Alcubierre drive contradicts causality, but if it does, I highly doubt that it is because of the arguments presented on this forum. The Alcubierre drive most certainly does violate causality, and this follows from just the most basic amount of Special Relativity that you might learn if only you'd spend your time learning real things, rather than spreading disinformation.

stryker 14y ago
I'm going to ignore your condescension. I'm also going to assume you didn't read the rest of my post, because you presented no arguments to counter my points. I'd like to point out that the wikipedia article on the Alcubierre drive writes at length to show how this warping process does not violate causality: http://en.wikipedia.org/wiki/Alcubierre_drive http://en.wikipedia.org/wiki/Alcubierre_drive. I know you feel strongly about people not understanding special relativity and I actually agree with you on that point, but you're not addressing any of the valid counterpoints that people are making. You're simply closing your ears and exclaiming "special relativity" which only applies locally (if you want an appeal to authority, I talked about this with a former physicist who worked with Stephen Hawking). 1) The universe is expanding faster than the speed of light. In other words, galaxies are moving away from us faster than c (evidenced by the growing redshift of light emitted by galaxies when they were NOT traveling away from us faster than c). That does not violate causality (as I mentioned in my post) because the topology of space itself is changing. Locally, everything still obeys special relativity. 2) Virtual particles, EPR Paradox (I know it's not actually a paradox). (http://math.ucr.edu/home/baez/physics/Quantum/virtual_particles.html http://math.ucr.edu/home/baez/physics/Quantum/virtual_partic...) My point with these phenomena is that locality and the speed of light are not very intuitive concepts. You can still have "spooky action at a distance" without violating causality.
- nessus42 14y ago
  You're simply closing your ears and exclaiming "special relativity" which only applies locally (if you want an appeal to authority, I talked about this with a former physicist who worked with Stephen Hawking). If you come up with a mathematical "proof" and I can use its conclusion to prove that 1 + 1 = 3, then I have shown your proof to be incorrect via contradiction, no matter how hard you continue to argue for it. Special Relativity does not only apply locally. It applies to any system where information can be transmitted between two points that are in inertial frames. The universe expanding at faster than the speed of light is neither here nor there, since you cannot use the expanding universe to transmit information between two points in at FTL speeds. On the other hand, you CAN use an FTL drive to transmit information between two points in inertial frames at FTL speeds. QM spooky action at a distance does not let you transmit information between two points at FTL speeds. This is all you need to do to show that any FTL scheme violates Special Relativity: Information transmitted between two points in inertial frames at FTL speeds. If you can do that, you've either disproven causality, or you've disproven Special Relativity.