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back to article Spooky action at a distance is faster than light

As Einstein put it, it's impossible for anything – even information – to move faster than the speed of light. Yet the lower bound of that impossibility, the minimum speed at which entanglement can't possibly be transmitting information between two particles, appears to be around four orders of magnitude higher than c, the speed …

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seriously good research

I vaguely remember a report two years ago indicating about 8 times c for entanglement. This is orders of magnitude more. Decent interesting times for once. Facinating work. Well done and keep those cards and letters coming. Offtopic: Does this indicate Heim theory might not be crackpot ?

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Anonymous Coward

Re: seriously good research

"Does this indicate Heim theory might not be crackpot ?"

Since the only person who understands Heim theory - Heim himself - is dead, the answer is "No one knows."

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FAIL

Re: seriously good research

My experience with research in China is that there is so much data fakery going on, that anything spectacular is suspect. I'll wait until the experiment is repeated someplace reputable.

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@The Man Who Fell To Earth

"My experience with research in China is that there is so much data fakery going on, that anything spectacular is suspect. I'll wait until the experiment is repeated someplace reputable."

My reaction was sorta kinda similar: although I did not think "fakery" I did think "measurement error". It will be interesting to see if the results can be replicated.

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Re: seriously good research

One ponders tunneling and its apparent superluminal tunneling.

Now, this.

Why can't information travel at FTL velocity? It isn't matter nor energy, only quantum state.

An examination of this, should it be verified, could yield interesting information about the very nature of space, for there are models that showed superluminal expansion of the universe itself after the big bang.

Well, we'll see. It'll all come out in the wash, as others attempt to replicate this experiment.

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Holmes

Well done ... again.

Still measuring how quickly a statement about a system propagates?

This is basically a null experiment.

- You have a blue and a red car

- One car is a million miles away

- One of the cars is hidden behind a curtain

- When you peek behind the curtain and find out that the there car is blue...

...how fast does the other car become red?

Seriously fast!!

(Ok, so i QM the colors are not set at the start because the mathematics are an extension of classical probability calculus from R to C, but that's basically it)

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Headmaster

Re: Well done ... again.

AFAIK it's not "hidden" variables behind a curtain. It would appear the measuring device can effect the particle.

So those measuring at different settings get different results. But Alice and Bob still agree they say the same pairs of particles (even though this time Alice changed here measuring device). Check the Born probabilities page on wikipedia, the maths is over my head, but looks like they covered it all.

It could be the Monty Hall problem in disguise, but I don't think all of physics would fall for that one... would they?

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Facepalm

Re: Well done ... again.

Beat me to it.

Until such time as one can actually direct the collapsed quantum state of one of the entangled pair then presenting the process as 'communication' is a fallacy.

Anyway, weren't we told just last year how 'quantum information' in entagled pairs can travel back in time? Reg, please stop re-reporting the pig-ignorant press spin on this sort of stuff over and over and over again.

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Joke

Re: Well done ... again.

Oh no! That means Schrodinger's cat is...

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Re: Well done ... again.

Actually, it means Schrodinger's cat isn't ....

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Re: Well done ... again.

Yeah, but do you know _where_ it isn't?

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Re: Well done ... again.

Statistically speaking, I probably do know where it isn't but I'm uncertain of the magnitude of the error in that estimation since the measurement would be rather uncomfortable.

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Happy

Re: Well done ... again.

Yes, but only if we don't know how fast it isn't going ...

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Headmaster

Re: Speed of light fallacy

The actrociously named "quantum tunnelling" (there is no tunnel in sight anywhere) has nothing to do with signals moving at the speed of light or less (or more) nor the even more atrociously named "spooky action".

> I only read one sentence of this article, and decided to stop reading there and then, hehehe

Yeah, you should go on reading, Eadon. It is often helpful.

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Re: Speed of light fallacy

Since our event horizon is limited by expansion at the speed of light in all directions objects thereon that are diametrically opposite are departing from each other at twice the speed of light.

There is no frame to the universe so all speeds are relative to the observer.

Now consider objects departing from us at 0.6 c in opposite directions. They are separating from each other at above c but we could relay information between them.

.

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Happy

Re: Speed of light fallacy

To me its one of the enduring mysteries, why is it that "information" has physical properties?

In this case the signals will travel faster than light, as the remote particle "uncloaks" in order to complement the near one. BUT, no information is transmitted, you just get complementary truly random streams of bits.

~What is the difference therefore between an information-carrying signal and a signal?

The only two other peeks we get into this world are Boltzmann and Shannon, particularly Shannon who combines information-carrying capacity and signal power -well signal-to-noise actually, but it does invoke real physical quantities and line them up against dimensionless quantities.

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Re: Speed of light fallacy

Re: tunnelling

I think I prefer QM burrowing, or maybe for lower energy regimes, QM foraging.

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Boffin

Re: Speed of light fallacy

Now consider objects departing from us at 0.6 c in opposite directions. They are separating from each other at above c but we could relay information between them.

Special relativity states that the relative velocity between two objects is not the sum of their individual velocities (although it tends towards this at low velocities). The actual relative velocity is given by:

w = (u + v) / (1 + (uv/c^2))

where u and v are the two velocities, and w is the resultant relative velocity.

In your example, both u and v are 0.6c, so this works out as about 0.88c.

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Re: Speed of light fallacy

I am grateful to Eadon. I think I should have written that our event horizon is limited to expansion at the speed of light.

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Anonymous Coward

Yummie crypto

If this can be brought into commercial use you could have an interesting way to communicate, and one that isn't subject to intercept for quite a few years.

I wonder what the range of this is - if we could box one half up and send it along with a Mars mission you'd have something to drive your average physicist up the wall if it kept working because it would demand new theories on assumed maximum speeds (assuming this is possible - I'm no physicist so I may have this totally wrong).

Spooky indeed.

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Headmaster

Re: Yummie crypto

Its not possible. That's what this is about.

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Re: Yummie crypto

I doubt that is true. Regardless of the speed at which a signal may propagate, there are encoding schemes that self synchronize, like B8ZS. Each transceiver has no idea when the code is clocked into the circuit, but they sync up anyway.

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Holmes

IMHO

I've never had a problem with this...

you can't go faster than c...fact

you can entangle 2 "particles" and if you change the state of one "particle" you change the state of the other, no matter (no pun) how far they are apart (OK 14km at the moment or so)....fact

Therefore we see 2 "particles" but the entangled "particle" only knows about itself, so you have to look at what's happening from the "particle's" reference point not from ours.

From a computing viewpoint, there are 2 threads which both are using the same object. A public property called X in the object sets and gets a value. X is currently 0. Thread 1 sets X with a value of 5, so the internal value of the object is now 5. Thread 2 gets X and strangely thread 2 finds X is suddenly 5 whereas thread 2 thought X was 0. Thread 2 is left scratching its head as it thought the 2 threads were separate but didn't realise that they were using the same object.

This issue is that we understand about threads (spacetime), the object doesn't so what's the problem?

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Headmaster

Re: IMHO

> if you change the state of one "particle" you change the state of the other

That's not how it works. You can decide to extract information about the entangled system at once particle, which gives you a classical value - and fixes the classical value at the other end. This does not imply that you "change" anything here or that you "change" anything there.

> Therefore we see 2 "particles" but the entangled "particle" only knows about itself, so you have to look at what's happening from the "particle's" reference point not from ours.

It's two particles though they have correlated state.

The entangled particles "knows" nothing. And you can easily select relatively moving frames in which Alice measures before Bob, and others in which Bob measures before Alice. They will still find the same classical values, surprise! Actually not a surprise if you just drop the idea that states are described by classical vectors or hidden variables. Of course, one can posit magically invisible metaphysical mechanisms to keep this all in the classical space of ideas .. looking at you, Bohmians.

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xyz

Re: IMHO

OK...I apologise for my use of words. All I'm saying is that the particle "preceives" itself as a single thing whereas we perceive it as 2 things. The universe probably "perceives" it/them as the outliers of a line of probability which >>IMHO<<< has the properties of something moving very, very fast but because they/it are/is not, then the c rule doesn't get invoked.

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Pint

Thank God...

"...The system only breaks down into two particles once entanglement is disrupted by the environment (an "observation")..."

Thank God it only occurs at a Quantum scale; - just imagine if seeing Harman, Miliband or Balls meant there were two of 'em..

come to think of it, with the Millipedes....

Scary thought

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xyz

Re: IMHO

Thanks Eadon...I'm still working on it! Thing that still bugs the bejesus out of me is that if I'm in an expanding universe by travelling through time (standing stillish in space) and I then travel to a planet say 5 light years away (and therefore resisting expansion whilst doing so (time slowing down), have I actually travelled through space (i.e. a vector towards the planet at 90 degrees to expansion, if time was the y axis with x being space) or have I merely increase the length of my probability being someplace and that I haven't really moved along the x axis. This is what keeps me up!

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Holmes

Fallacy?

The 'speed of light' is a distraction. Light is instant (in the frame of reference of the photon doing it). Anyone else watching has to consider a universal constant called 'c'. You can't do without 'c' for spacetime, just as you can't do without 'pi' for circles. If you think something has travelled 'faster than light' you have simply misunderstood the problem. Go square a circle.

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Headmaster

Re: Fallacy?

There is no "frame of reference of the photon". That's what light speed is.

You can do without "c" for spacetime very well indeed. Just stay Galilean.

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Re: Spooky Action

It has nothing to do with free will over measurements does it? A "thermometer" has no free will. The LHC has no free will. The detection of particles is thus not applicable to such comments, is it? A thermometer in a different place gets a different measurement, is that free will?

We can have free will, but I don't see how such particle physics applies to it. Other than an observation that some systems are not deterministic (which allows some space for a theory on free will).

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Some context ...

You can interpret QM predictions of separated measurements on entangle systems like this in two ways:

(a) You insist that any quantum uncertainty might be a result of ``hidden variables'', and so follow the rules of classical (ordinary) probability. This requires the two parts of the experiment to be able to signal to each other instantaneously: i.e. the so-called ``spooky action at a distance''

(b) You prefer to retain the speed-of-light speed limit for cause and effect, but at the cost of disallowing hidden variable (standard probabilistic) models, and thus need to describe things using complex probability amplitudes - i.e. quantum probability.

Most physicists prefer to choose (b), because they prefer to retain causality over a model respecting classical probability theory.

Nevertheless, it is valuable to test both ideas. As I understand it, here the authors' have said: if we choose a hidden variable interpretation (choice (a)), what is the experimental bound on the speed of information transfer?

This doesn't mean that the interpretation (a) is the ``true'' interpretation. It doesn't even mean that the authors necessarily prefer (a) over (b). But it does tell us something about how things (might) work /if/ (a) were the best interpretation.

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Re: You cannot make the test you mention

I didn't mention any specific test, therefore there is no way you can claim it cannot be made :-)

But to help clarify, by "test", I meant examine the experimental consequences of both interpretations; and which the authors (claim to) have done for this one setup.

Just because the predictions of HV (of interpretations (a)) produce the same results as those of (b) is beside the point here - they have different consequences for how we think and motivate or justify results. Results of the type in this reported experiment have serious consequences for those who prefer HV whilst sidelining the issue of speed-of-light causality.

Neither (a) nor (b) allows a traditional physical intuition relying on both standard probability /and/ speed-of-light causality to survive. I think (b) proponents have come to terms with the weird nature of quantum probability. This experiment forces the (a) proponents to do the same regarding causality.

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Re: Some context ...

Physicists choose (b) because there's no experimental evidence for (a), and plenty of reason (e.g. Bell's inequality) for believing that hidden variable theories don't make sense. (The Bohm-ists have never been able to produce a complete theory that can be tested.)

In (b), there are no 'particles' in any classical sense - there are only probability distributions. Ultimately QM isn't about little bits slapping into other bits, it's about event probabilities.

In fact I suspect there's nothing but probability going on, and reality is just a fog of probability densities which look as solid as clouds do when you fly over them, but have no more substance.

If stop expecting QM to talk about physical things and start thinking about event possibilities, it stops being quite so weird.

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Headmaster

Re: At the moment what I can see from the comments...

It's not impossible in the case of "impossible to fly to the moon" it's impossible in the case of "impossible to make the moon the sun".

It's not a system described as sending information. It's like a shadow that is 1000km long. You can make two hand shadows of thumbs up between the two points 1000km apart, but the people watching your shadow puppetry cannot use those shadows to send a signal. If they send their own shadows, they take the normal time (lightspeed). But observed from your point, they both get your shadows at the same time ("instant").

So it's "impossibly impossible", not "practically (limited by our resources and time) impossible". One can be overcome, the other not.

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Re: It's impossible to send data this way ...

Its impossible to send information FASTER THAN LIGHT, because in order to know whether your measurement ("here") is an encoded 1 or 0, you need to compare it against the other distant measurement ("there"). E.g. if they both are the same, it's "1", if they differ, its "0". So to understand your result, you have to wait for the results from over there to be sent to you here, and that waiting time depends on the speed of light.

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Holmes

Re: It's impossible to send data this way ...

Why couldn't you just record a minutes worth of "information" being transmitted, then compare the timestamps after the fact? What you said is like saying a telephone can't work because by the time you run over to the other end the sound is already gone.

Anyway, if data is being transmitted 6 times faster than the speed of light or more, maybe the problem is that the information they are trying to measure at the distant end is coming from only one possible future, and by stopping the experiment "before" that future event has caught up with current events, therefore screwing up the results. I guess what I'm asking is has anyone working with entangled quantum particles ever encoded something like PI in the spin of of one of their entangled particles and "kept" encoding it for an extended period of time, while measuring the spin of the opposite end to see if that same data ever starts coming in. I know they say that viewing the spin of the opposite end changes the result, but what if that is only for tests shorter than the event lag?

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Anonymous Coward

I find this stuff fascinating but I'm a total idiot who knows absolutely nothing...

Could someone break down what this actually means in lay-mans terms for Dummies...?

#1. For instance does it mean two entangled particles can communicate faster than light....?

#2. Or does it mean that two entangled particles separated by a vast distance can fold space or something similar, so distance becomes meaningless?

#3. After that please explain if entangled particles translate to the macro world on any level...?

#4. Lastly, discuss Einstein's protege David Bohm and his Holographic Universe theory where he argued mediums or physics might be actually be able to gain insights, but not from anything metaphysical, but rather that thought is distributed and non-localised...

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Re: I find this stuff fascinating but I'm a total idiot who knows absolutely nothing...

#1 no, the have entangled properties, but the properties are created in the entangled common source. There is no communication ('information transfer') between the particles.

#2 no, think about the two particles as a single two-particle state of matter. The matter wave is as large as the distance of the two particles -- and once you measure a property of the wave at one point, you also know about some properties of the wave at another point.

#3 yes, the world is composed of entangle particles. But for an object of macroscopic size , the complex entangled (quantum mechanical) properties average out to classical properties, hence we cannot predict them. So even though the answer is a yes, you might pretend that the answer is no and you wont miss anything.

#4 this point is related to #3: we cannot predict observations on the level of the universe, so you can hypothesize all you want about local or non-local properties and nobody can prove you wrong.

Hope this helps.

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