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Testing Einstein's 'Spooky Action at a Distance'
smooth wombat writes "Travelling to a time in the past is, as far as we know, not possible. However, Einstein postulated a faster-than-light effect known as 'spooky action at a distance'. The problem is, how do you test for such an effect? That test may now be here. If all goes well, hopefully by September 15th, John Cramer will have experimented with a beam of laser light which has been split in two to test Einstein's idea. While he is only testing the quantum entanglement portion, changing one light beam and having the same change made in the other beam, his experiment might show that a change made in one beam shows up in the other beam before he actually makes the change."
Didn't the Aspect Experiment back in the '80s demonstrate this effect?
General Relativity: Space-time tells matter where to go; Matter tells space-time what shape to be.
Or, alternately, reality and causality conspire to ensure that event A does happen, irrespective of any efforts made to stop it. Refer to the experiments conducted on resublimated thiotimoline. by I.A. et al.
Rampant carbon sequestration destroyed the Dinosaurs' tropical paradise. I'm here to help repair the damage.
As others have pointed out, we are in fact time travelling all of the time. However, to time travel as I'm sure you mean, significantly faster than our surroundings, Einsteins time dilation does the trick nicely, its just a matter of propulsion technology.
Note that also, too, we can observe the past due to the finite speed of light. Thus, given our current knowledge it is always possible to travel to the future and observe the past, but never the other way around (except maybe at quantum scales as discussed in TFA).
This, according to my random ponderings makes me think that if its possible to travel to the past, it will also be possible to observe the future, and in fact in some respects, they could be two aspects of the same thing.
Just for the record, I'm not a physicist, so beyond the first couple of facts this is all random amateur speculation.
"...his experiment might show that a change made in one beam shows up in the other beam before he actually makes the change...."
What happens when he notices the change, before he makes the change, and changes his mind and doesn't make the change?
-CF
If you can't fake the universe, and you can really see results before the action is taken, what happens if you decide wether or not to hit the button based on the flip of a coin? Does that make the coin flip result predicted by whichever result you see?
Send lawyers, guns, and money!
I'd guess we could never create such a paradox even if the effect is real.
Classical relativity imposes one set of constraints, and quantum mechanics another. Einstein was bothered because it seemed like the classical limits (think "light cone") would be inapplicable here. Quantum physics requires us to consider the actual mechanisms by which we measure and communicate as PART of the experiment.
Even if it works out that information at point B shows up "before" (in the same reference frame) an action at point A causes that message to be sent... it's possible that there's no practical way to detect this fact and use it in any way that would make for a "paradox." It may be that the best we can do is *record* the fact that such a backward transmission happened.
Example: Your instrument records a signal at B "before" the timestamp of the interference of the beam at A. This shows that entanglement is real, and gets you out of the "light cone" limits of classical relativity, which is what bothered Einstein. But if you go further and try to create a logical paradox, by using this information at A to stop the sending of the signal, then you will likely run into other, quantum mechanical limits... E.g. the actual means by which you detect the signal at B and send that information back to A will likely overwhelm or destroy whatever time differences we're talking about, bringing them back within classical limits...
This would be similar to things like the particle/wave experiments, where the experimental apparatus itself affects the outcome of the experiment.
So while something like "instantaneous" or even slightly "backward in time" messages may seem spooky in some ways may be possible, I'd bet that the time differences we're talking about wouldn't be large enough to make for any of the paradoxes people imagine using sci-fi based "time travel" notions.
I think that causality will be preserved, even if the effect occurs prior to the cause.
Consider: Researcher prepares to activate device, but researcher views results first. He already plans to perform an action (activate or not activate) in a way designed to contradict the results. He views the results, then takes the appropriate contradictory action. He succeeds in contradicting the theory. What does he prove? Not much, I think. How do you prove that the experiment was successful in sending an appropriate signal rather than it showing some false signal based upon noise or some other failure? In other words, how do you backtrack (forward-track?) the results to determine that the point of failure was actually the researcher's decision rather than some other mechanical issue?
Far more interesting would be an experiment in which a random number generator is in control of the device activation. Perform a long series of tests. Review the results afterwards. Does the activation always match with the pre-recorded results? Now that would be interesting. It still seems impossible to "backtrack" and prove no mechanical errors, but it would be possible to compile statistically important results this way.