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."

Been there, Done that

[sconeu]

Didn't the Aspect Experiment [roxanne.org] back in the '80s demonstrate this effect?

Re:Been there, Done that

[target562]

Quantum teleportation and entanglement have been proven bunches of times. It's the basis for quantum computing, too -- I doubt folks would be wasting their time on THAT if it wasn't valid.

Re:Isn't all time travel impossible?

[OptimusPaul]

Don't be ridiculous! We are all practicing time travel into the future right now... it's just taking longer than anticipated, at any moment I will be in the future, reading this post.

Re:Causality

[fractoid]

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 [wikipedia.org]. by I.A. et al.

Re:Isn't all time travel impossible?

[Nyeerrmm]

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.

What happens when....

[ChronoFish]

"...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

recursion

[Mr EdgEy]

so, let's say Beam A and B are split from one beam.. you change beam A, B changes before you changed A so then B's change should change A before you changed it and it would recur ... so how would you be able to measure a change that would effectively be happening in an infinitely small amount of time?

Re:Causality

[G-funk]

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?

Re:future doesn't exist?

[SavvyPlayer]

If time travel were possible and we manage to survive long enough to discover it, today's world would be full of future gamblers. entrepreneurs, megalomaniacs & soldiers of fortune. Technology changes -- human nature doesn't.

Problems with classical intuitions.

[chub_mackerel]

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?

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.

Eternalism and Reverse Causality

[Pfhorrest]

Relativistic physics imply a sort of eternalism, whereby nothing is really "moving" through time at all - spacetime is a four-dimensional construct which is itself timeless, inasmuch as the four-dimensional spacetime does not change across some fifth "hypertime" dimension, so nothing in 4D spacetime really "moves"; there are just changes across the time dimension of spacetime (as a cone "narrows" in the vertical dimension even when it's not "changing" when considered as a 3D object in time, things "change" across the time dimension of spacetime even though spacetime itself never change when considered as a 4D object). So in a sense, yes, if the relativistic model is completely correct, we cannot travel to the past OR to the future, because nothing's really moving at all, four-dimensionally. Things are just different in the four-dimensional construct of spacetime at different points in time.

So when you talk about backward time travel, really all you're talking about is backward causation: can I, now, make it the case that something happened in the past, the way I seem to make it the case that things will happen in the future? This, interestingly enough, happens all the time, for antimatter is nothing but time-reversed matter. An electron and a positron being created and then annihilating with each other looks, in the four-dimensional model of spacetime, as a causal loop; the electron moves forward in time, then releases a ton of energy and turns around to go back in time - or, when you play things the other direction, a ton of energy converges on the electron to make it turn around. this electron (now with various properties reversed when viewed "forward", appearing to us as a positron) then travels back in time until it turns around, releasing a ton of energy - or, viewed the other way around in "forward" time, when a ton of energy converges upon it, turning it around. Of course, as this particle doesn't exist in times before or after its turn-around points, it doesn't look to us like we shoved a bunch of energy in with a positron and turned it into an electron; it looks to us like we shoved a bunch of energy together and a positron and an electron were created.

So, if you were to successfully travel back in time, there would have to be a backward-moving anti-you around somewhere, with whom you would have to annihilate, perfectly; from your perspective the world would then seem as antimatter, moving backward in time, and you'd somehow have to avoid annihilating yourself by touching anything, get back to the past that you want to go to, and then find another perfect anti-you to annihilate with to turn around. In forward time, this would mean that somehow, a copy of you with your future memories, and his antimatter clone, would have to be created somehow in the past; the antimatter clone would then have to be slowly changed and preserved in a precise way such that its evolution is the reverse of the normal processes that a person witnessing an antimatter universe moving backward around him would undergo, until it reaches such a state that it is a precise antimatter clone of future-you at the moment that future-you collides with it. Of course, since experiencing the trip backwards in time really isn't all that important, then the people in the past could just create a bunch of matter and antimatter, arrange the matter into a perfect clone of what you'll be like in the future when you decide to travel back in time, and then just leave the vat of antimatter in containment until that time comes that you want to travel back in time, whereupon you jump into the vat of antimatter and are annihilated... ...and your particles then reverse their temporal direction, travel haphazardly back in time, safely within the backward-moving containment field, until such a point as they collide with an identical bunch of antiparticles (or, viewed in forward time, regular matter), annihilating with them, or as viewed in 4D time, turning around and becoming them, and then being reassembled by some helpful scienti

Re:Causality

[MellowTigger]

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.

This does NOT break causality as we know it

[zevans]

Beam A does some stuff. Beam B does some corresponding stuff. Sounds like cause and effect to me.

Now either we can throw Copenhagen away, and state that B must have anticipated what A was going to do, and change B's own state 'in advance,' which appears to be what all the hullabaloo is about here... ...or equally, we can say that invisibly small pixies used time machines to do all this tweaking of beams...

But to some dude tweaking A and watching AND IN ALL CIRCUMSTANCES -WAITING- to see what happens to B... it doesn't matter what the mechanism is. Decoherence, Bell, pixies, or whatever, there is no way to surface the mechanism and use it to influence the chain of events, with time's arrow or against it.

If you are watching B there is no way to confirm B's behaviour relates to A, unless you also know what A did and you sit down and correlate it. In other words you cannot infer anything from B until you have looked at what A was doing anyhow...

Everyone is very free with the word 'before' in this discussion... before with regard to whom, what cones, and what worldlines?

Re:Paradoxes my a$$

[Aris Katsaris]

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 problem with that is the theory of relativity states that there's no universal simultaneity. The value of "When an event happens" is meaningless when you encompass the whole of the universe. Given some coordinate system you'll inevitably have placed the effect before the cause, if you allow FTL.

Re:Things they need to consider....

[Control Group]

Strictly speaking, he could have been referring to the Earth's rotation. Since you can always detect if you're in a rotational frame, that's motion that's real in a more absolute sense than linear motion.

Of course, an interesting thought experiment is to consider a universe consisting of exactly one particle...and then ask if that particle is spinning.

He's a quack selling snake oil

[gr8_phk]

He is talking about an issue I've raised before - there is no way to tell the difference between a particle whose entangled twin has been "measured" and one that has not. If you can tell the difference, this would allow faster than light communication. I contend there is no difference - physics has a lot to explain here. But he claims to have an experiment to confirm it - great. However:

Where do you get a laser that produces entangled pairs with the ability to separate the pairs into 2 coherent beams?

Then from TFA we have this:

Now brace yourself for the backward-causality part: Because Signal B followed a shorter route to its detector, the fiddling in Signal A could theoretically show up in Signal B before Cramer actually fiddles with Signal A. It would be as if Cramer's actions had an effect that worked backward in time.

This guy doesn't think that the detector for B will "fiddle" with the photons at A before they reach their fiddler?

He also seems to be getting money from people who believe his BS. Not to mention publicity.

If someone honestly believed they could send information back in time, the logical thing to do is fund the experiment any way you can while keeping it secret. You recover the funds by playing the stock market using future data (minutes to hours is the required time frame here). You keep it secret so "they" don't come after you - for whatever "they" you may be concerned about.

Re:Been there, Done that

[egyptiankarim]

brilliant physicist, but a C student in math.

See, I never got statements and claims like this one. Physics (even the highly theoretical kind) is just a practical application of math. How can someone like Einstein not be a brilliant mathematician? I think I read somewhere once that maybe he did poorly in grade school math, but I can see that being more out of boredom with the drudge of arithmatic than failure to comprehend. You need a solid foundation in calculus before you can even begin to truly understand the most basic physics, so I'm sure Einstein had his math skills up to par to be doing the type of stuff he was doing.

"Faulty math" here has more to do with the inconsistency in theoretical models that deal with things at the quantum level as compared to everything else we currently "understand." It's not like Einstein factored a polynomial wrong, or dropped a remainder, or forgot to carry or something :)

Re:Causality

[loqi]

It seems that, if you subscribe to something like quantum immortality [wikipedia.org] and further assume that a violation of causality results in uniform annihilation, things would appear to an internal observer exactly as if the universe did protect causality.

That's sci-fi, don't confuse with science

[DMiax]

The wrong points are so many, I will name just a few.

The idea that photons (and electrons) are both waves and particles have nothing to do with quantum entanglement.

The "being a particle or a wave" property is not a physically observable one. It's not like spin, position or momentum.

All photons are waves. period. They can be counted due to indetermination principle, which provides that the electromagnetic field moves around orbits in the configuration space that are quantized. This has nothing to do with slits.

Moreover every "particle" is just a field which evolves like a wave. The particle-like behaviour comes in some particular conditions, under which the field has a compact spike in one position and is quite absent in any other position. This provides that it can be seen as a single point moving.

Still its equations are those of a wave.

Saying "a superposition of it being a particle or a wave" is just like saying that we can choose whether it will follow Galilei's or Einstein's relativity. It will follow Einstein's. In some cases it will seem it is following Galilei's, it is still following Einstein's.

This is nothing but a sign of how badly the experiment is explained. Yet it gives some suspects.

To confirm that this is not science I could point out that even if he will use spin (a much simpler and precise measure, and it is even a proper observable) he will demonstrate nothing [slashdot.org].

Or that no energy transport will happen, so it's not really violation of causality.

Or that the two photons start together so that they interacted while causality violation require they did not.

Or that he will not be able to choose which result to get from signal A after signal B will be measured, so no paradox is involved (RTFA for definitions).

Or that he failed to provide calculations of how this thing works. Physics is not done with buzzwords. That's interpretation. You can't do physics by reading divulgative works nor understand how it really works. A good divulgative work explains nothing but the thing it speaks of and cannot be used as a source for experiments. Nothing can be logically deduced from buzzwords. E.g. the "ball over cloth" explaination of general relativity does not suggest that you can "cut the cloth". This guy is doing this kind of things.

Instead I will just point out one of the first lines in the article: "thanks in part to tens of thousands of dollars in contributions sent in by his fans".

People, please...