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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."
Does this mean that once the effect shows up in the one light beam, before he does it in the other light beam, he is somehow locked in to his future actions? If not, what happens if he just turns off the device?
Also see the Renninger negative-result experiment, in which it was postulated and proven that a particle need not be detected in order for a measurement to have occured.
This solves about every communication problem that man has ever come up. Long-distance space communication not only becomes trivial.. our future explorers will be playing WOW all the way to Alpha Centauri.
Suppose an astronaut travels away from the earth at 99.9% of the speed of light. According to relativity, if he ever returns then everyone on earth will have aged considerably more than he has. But he has to turn around at some point in order for this to happen, hence he has to accelerate. And it doesn't take any reference points to judge that acceleration, so you can in effect say that he has travelled into (Earth's) future, and that the entire Earth has not travelled into the past.
There is a whole school of thought that "time" is just our perception, much like we perceive motion by flipping a flip-book of images. The images are already there and we see the progression. (Similarly, humans perceive temperature differences, pressure differences, etc, and not the temperature or pressure itself?) It is a kind of scary concept in that it seems to mean that free will is an illusion. There was a great article on different proposals on the nature of time in Scientific American about 5 years back.
The images are already there and we see the progression. It is a kind of scary concept in that it seems to mean that free will is an illusion.
Only if you assume that their is only one set of ordered images. If every possible image is in the 'book' and every page is 'adjacently linked' to every other page that differed 'only a little', then free will may determine which adjacent page you (individually or perhaps your entire universes shared consciousness) go to at each step.
When sending any signal, they need to consider that the signal grows weaker the further it travels. This is obvious with 3-dimensional travel but when adding that 4th dimension, it degragates exponentially. They also need to consider the displacement that occurs as well. Obviously, the Earth is not in the same exact place a few seconds ago as it is now. As such, they would need to conpensate for that as well. They should also consider that there is bound to be interference by all of the signals bouncing around these days and should use an untouched frequency. And finally, they should have the reciever up and running way BEFORE they ever attempt to send that signal.
As for avoiding paradoxes, I would suggest creating the message/recording/whatever and sending it to a point before it was sent but AFTER it was created. Also, they would need to have the device set up to send the signal no matter what, where transmission cannot be interupted after reception. Otherwise, the paradox will stop the reception from ever happening. I like to think of paradoxes as time's way of fixing itself by fizzling out/destroying such events from ever occuring. I would best describe one as a trick knot in a string (time) where each time the loop reoccurs (from happening to not happening to happening, etc) the string tightens and the loop shrinks until it 'pops' out of existance and the experiment fails. If scientists can avoid causing a paradox, their experiment will be a success otherwise time itself will adjust to keep it from happening at all.
DEAD DEAD DEAD DELETE ME
I apologize for the colorful title, but I can not describe my feelings towards the so called theorem of 'no communication faster than light' in any other way. There are no time paradoxes if FTL communication exists, for the simple reason that when an event happens, it happens for all the universe. The fact that photons would not have arrived to the FTL communication target when the FTL signal reaches that target is totally irrelevant. And there is no way to perceive an event before it happens and change the outcome, for the single reason that effect always follows cause. So even if FTL communication is real, there would not be possible to avoid doing events that already have happened, for the simple reason that the events have already happened.
Thanks for the link. I'm currently reading Beyond the Quantum which claims the Aspect Experiment shows that there is a reality currently beyond our senses (that's an extreme oversimplification).
It will be interesting to read the counter-argument.
Personally, I still believe that the outcomes of all the dice throws are predetermined. We just don't know how.
Also, for the record, while Einstein used the expression "spooky action at a distance", he did not "postulate faster than light" action. In fact, Einstein was intent on disproving the validity of quantum mechanics and dismissed many theories associated with QM, thus the use of the 'scientific' term 'spooky'.
Why would FTL have implications for conservation of energy?
As a serious question, I still don't understand why light speed is the limit - my understanding of relativity goes that it starts with the assumption that light is the fastest thing and then moves from there. This is them backed up by all the observations we have, so it is so far an excellent theory.
So the thought experiment I like is, suppose there was an intelligent fish that was blind and used sound to communicate. This fish was intelligent enough to develop a theory of relativity based upon sound. All the experiments and observations he could perform would support his assumption that sound was the fastest thing possible.
So why would the fish discovering electricity violate the conservation of energy?
Why cannot there be signals in nature that do travel faster than light, they just don't occur in any phenomenon that we currently observe.
Now if we can't observe them or any repercussion of them then that's as good as not existing (for the moment). My understanding goes that if entanglement shows some FTL behaviour then that doesn't invalidate relativity, it just shows that relativity isn't a complete description of the entire universe. But we knew that already.
"The weirdest thing about a mind, is that every answer that you find, is the basis of a brand new cliche" -
'God does not play dice'
But we all know that since Einstein believed in God he must be a narrow-minded, naive, simpleton. Someone like that couldn't possibly have validity in modern science so these people are wasting their time trying to confirm Einstein's theories.
[/sarcasm]
It is interesting how most people get flamed for their religious beliefs on Slashdot, but nobody is flaming Einstein here.
Faith is a willingness to accept something w/o complete proof and to act on it. Reason allows you to correct that faith.
I've been reading up on and following this experiment for a while now. Personally, I don't think it will "work" in the sense that back-time signaling will be demonstrated. However, the experiment is still well worth doing, because we learn as much from how it "fails" as from success. Plus, it's just so interesting.
The proposed experiment is based on another experiment by B. Dopfer that has already been done and the results published. The original experiment shone a UV laser into a special crystal that split each incoming photon into two entangled photon going in different directions (you need a laser to get the right frequency of light into the crystal.) One photon (B) went through a double-slit and then to a, well, camera. You expect to see one of two patterns on the detector: if the photon is acting like a particle, then there's a 'hump'. If it's acting like a wave, there will be a diffraction pattern.
Now the other photon (A), goes through a lens and onto another detector. With the lens in the right position, you can observe A and tell which slit photon B went through. Move the lens and you can't tell anymore. What's interesting is that the pattern detected for B depends on where the lens is at detector A. This is exactly the 'spooky action at a distance' that Einstein pointed out.
Now, the original experiment filtered out all the noise by using a 'coincidence detector'. This also, in effect, re-synchronized the two signals via classical communications, eliminating any exciting possibilities like FTL communication. Unfortunately, the Dopfer paper doesn't say what happens without the coincidence detector.
Cramer is proposing two modifications to the Dopfer experiment.
First is to remove the coincidence detector. This will degrade the pattern that shows up at detector B, but (according to the QM math), not enough to make it go away. That means that a change in the setup at detector A will 'instantly' effect the pattern seen at detector B. Simply by looking at what pattern is seen at B, you can tell what the physical setup is at A.
Even if this is as far as the experiment goes, it will be extraordinary. Theoretically (yes, I know) A and B can be as far apart as you want, far enough to demonstrate that FTL communication is taking place.
The second modification that Cramer is proposing is even more radical. If you look closely at the original experiment, you can see something really unusual: the distance that photon B travels to it's detector is SHORTER than the distance photon A travels to it's detector. So what? So it looks like a change in how A is measured effects the measurement of B, even if B is measured before changing A. This is quite a bit like the 'delayed choice' experiment, except with much more measurable results.
Now the difference in path lengths between A and B in the original Dopfer experiment was on the order of centimeters, too short to measure directly. Cramer wants to route the A photons through a fiber optic cable, introducing enough delay between the A and B detectors that it can be measured. This is where the 'retrocausality' (I hate that term) comes in.
I doubt (and I'm pretty sure Cramer is skeptical too) that back-time signaling can be demonstrated. But you can work the experiment just via the math, using standard QM equations, to see what the predicted outcome is. And there's nothing in the math (so far) that prevents the experiment from working. QM predicts that it will work. If the experiment doesn't work, then we learn more about Quantum Mechanics. If it only partially works, then we get FTL communication. If it goes all the way, we've invented time travel (for information, anyway).
THAT'S why the experiment is so fascinating.