October 11, 2011 2 Comments
Faster than light (FTL) travel.
Most physicists says that you can only hope for at most two of these three concepts to hold.
Special Relativity has the advantage of 100 years of supporting experimental evidence.
Causality has the advantage of 1000s of years of philosophic thought, and daily experience (at least until very recently – see Rewriting the Past)
Which seems to be bad news for faster than light travel. But we all so much want FTL travel to be true. How else are we supposed to communicate with ET?
Well, Special Relativity may have received its first chink in the armor. Particle physicists at CERN recently released a report on the experimental evidence of FTL neutrinos. The 6-sigma quality factor reported implies that the margin of error for this experiment is insignificant, meaning that these results may need to be taken seriously.
So, which concept falls by the wayside: Special Relativity (sorry, Albert)? Or Causality (sorry, Aristotle)? Alternatively, maybe the “2 outta 3” rule needs revision.
As usual, I have an opinion.
And it is…
1. Special Relativity holds for the moment. But we need to stop using circular logic for relativistic effects. We need to stop drawing FTL paths on Minkowski diagrams that are based on the assumption that FTL is impossible. And, finally, we have to come to terms with the fact that Special Relativity has to do with subluminal speeds and is UNDEFINED at FTL.
2. Causality holds for the moment. At least in the context of our conventional space-time. Throw in inter-Hilbert Space travel or Programmed Reality and all bets are off for Causality. (again see Rewriting the Past for more on the latter)
3. Given the caveats in #1, maybe we can get 3 outta 3.
Here’s just one example where it seems to fit:
Imagine a supersonic jet travelling at twice the speed of sound (2S meters/second) in the land of the blind. A blind observer stands at 10*S meters from the jet at t=0. At t=0, an audible event (call it Event A, the cause) occurs on the jet, such as an explosion on board the plane. The sound waves from Event A reach the observer in 10 seconds. At t=1 second, the entire jet explodes as the gas tanks catch fire (Event B, the effect). At t=1, the jet is 8*S meters from the observer since it is traveling at 2S, so the observer hears Event B eight seconds later. In other words, the observer hears event B at t=9 and event A at t=10. Therefore the observer observes the effect before the cause.
But that doesn’t mean that the effect happened before the cause. It only appeared to happen that way in the observer’s reference frame. Similarly, anyone on the jet (who could actually hear things happening outside) would observe a full sequence of events happening backwards in time. Is this time travel? No. No one is going back in time. They are just experiencing a sequence of events in reverse chronological order happening in someone else’s reference frame. Is there any reason to assume that the same arguments would not also hold in the domain of light?
In fact, the same thing might happen if you hopped aboard the tachyonic neutrino express. First of all, I should note that there is some debate about this whole idea of time unfolding in reverse at superluminal speeds. Much of it stems from the nature of the Lorentz factor:
This is the factor that gets applied to time and distance to calculate time dilation and Lorentz contraction effects at relativistic speeds. It is also the factor applied to mass in general relativity. It can easily be seen that as the velocity approaches c (the speed of light), the factor under the square root sign approaches zero, causing the Lorentz factor to approach infinity. For this reason, time stands still, mass goes to infinity, and the apparent size of the rest of the universe shrinks to zero at the speed of light. Or, more accurately, “apparent size” as you would SEE it. But, what happens if you go past the speed of light? In that case, the factor under the square root sign is negative. For mathematics, this is not allowed for real numbers. However, trigonometry has a trick, which is to define an entity i that, by definition, is the square root of -1. Numbers containing i are considered “imaginary” or complex numbers. In the real world, these numbers actually have a great deal of use in fields like electrical engineering, where they are used to determine the phase between periodic signals, or in physics, where they are used to determine the relative angle between field vectors. But what they might mean to relativity is really anybody’s guess. But it is for this reason that many physicists claim that you can’t accelerate past light speed; that is, that it would necessitate mass exceeding infinity or becoming “imaginary”. Thus, the entire idea of traveling back in time is just one interpretation of what happens when the Lorentz factor goes imaginary.
So, let’s go with that idea on our tachyonic neutrino express, for the moment. If you had hurtled through space superluminally in 1804 toward Aaron Burr and Alexander Hamilton, you would watch Hamilton “fall up” into a standing position, the bullet flying out of his stomach and back into Aaron Burr’s gun. The assassination would still have taken place in their reference frame. Once you arrived in Weehawkin, NJ and got off the transport, your reference frame would have shifted back to theirs.
One might wonder what happens when you land. Does the sequence of events go forward again, in which case you could predict the future? No, that would truly violate causality. What happens is that you have to decelerate to stop, and as you approach light speed, the backwards time effect slows down. When you cross over into subluminal, it reverses and the events start forward again from whatever point in the “past” was hit at light speed. Then, you get to watch the events unfold again in the normal temporal direction. By the time you decelerate and land, you are at the same point in time as Burr’s reference frame, well ahead of the event that you just witnessed. Hamilton would be dead, of course. No time travel, no ability to interact with the past. No grandfather paradox to solve. All relativity equations still make sense, from the standpoint of the observations that we can make via known observational methods. We would still experience time dilation and Lorentz contraction up until we hit light speed. After that, what happens is anybody’s guess. But I have a theory.
It’s just going to have to wait until Part 2.