More quantum and relativity stuff.

[mistermack]

Thought I'd start a thread, instead of posting a derail all the time.

I have come across a bit more about entangled pairs, and the consensus in the physics world seems to be that actual information, in the true sense of the word, does appear instantly in both entangled particles, but that it's information that can never tell you anything.
The only thing that it can affect, is the pair particle. No observer can learn anything new from it.

That's the consensus, as far as I can tell. It may well be right. But there are plenty of top physicists prepared to investigate the possibility that it might be wrong.

One lot was trying to prove an apparent result, that information was arriving back where it was sent, two nano-seconds BEFORE it was sent. I'm not kidding.

I think, even if things like sending information via entangled pairs, or time travel, never happen, they figure that they are learning something while they attempt to prove or disprove it.

As far as entangled particles go, I'm tending to think that, even if it was possible to communicate using them, it's not faster than light communication, in the complete sense.
To communicate with point A, a million light years away, you would first have to send your paired particles across a million light years, at less than the speed of light. So the actual communication would take longer than a million years, not an instant.
How that affects the theoretical time travel consequences of faster-than-light communication, I don't know, as I've never seen it clearly explained.

[mistermack]

Bell's theorem is one of the foundation stones of the modern view that the principle of locality of classical physics doesn't match the facts.
There were known loopholes in the argument, and a lot of work has been done, to close two of the loopholes, but it's agreed that at least one still remains.

This is a nice article that explains all of that pretty well, and describes a proposed experiment that might close the main remaining loophole in Bell's Theorem.

And This is about the possibility of teleporting energy over long distances using entanglement. If it could be done, it could provide limitless clean energy from solar cells in space, teleported down to Earth, or to Mars, or wherever you needed it.

[macdoc]

Maybe he should start with mastering the optical properties of C02 before tackling something complex

[mistermack]

I downloaded this, but then lost the link.
Edit : just found the page again. It's a private blog, but it's often referred to on the web as a good summary of the entanglement question, without being an official work done for peer review.
http://ngxinzhaomonk.blogspot.co.uk/200 ... chive.html

Superluminal (faster than light) travelling is important to the colonisation of space in the future. The theory of relativity seems to forbid that as it means travelling back in time too. However, quantum nonlocality of nature is experimentally demonstrated with the violation of Bell’s inequality, thus raising the question: Does quantum nonlocality allows superluminal communication ?

*Superluminal Travelling, Communication and Time Travel will be regarded as the same and of equal footing here as they can be made to be the same. Superluminal Communication=Backward Time Travel +Forward Time travel +Displacement.*

Before going further, here’s a brief background in the world of physics. The field of theoretical physics is regarded highly as it is the foundation of all electrical, nuclear and nano technology. Most of these technologies highly make use of just one theory: quantum physics.

Ironically, the famous Albert Einstein who provided the first physical insight into quantum physics also highly dislikes the theory. He tried to show that quantum physics, with its inherent stochastic (probabilistic) mechanism, is not the most fundamental theory of the Universe. His final attack against quantum physics is known as the Einstein-Podolsky-Rosen (EPR) paradox. It shows that either quantum physics is incomplete or there has to be superluminal information transfer , which seems to be against the theory of relativity (A. Einstein May 15 1935). There has to be a local hidden variable theory then to replace quantum physics that requires this superluminal information transfer. The question of what is the true underlying mechanism of nature remained unsolved for almost 30 years, until Bell’s inequality came into the picture in 1964. Bell’s inequality enables physicists to verify, through experiment, how nature works in the fundamental level.

*In the context of this text, information transfer is not the same as communication. Information transfer is just the correlation between entangled pairs, and it does not necessary allows communication through them as will be seen. Instantaneous information transfer between the two entangled pairs is the nonlocality in quantum physics.*

Bell’s inequality is based on quantum entanglement which is explained below. In quantum theory, when two (or more) quantum objects interact with each other, they are in an entangled state. This means that the two objects lose their individual states and only the pair, considered together can have well defined states. Quantum physics is a stochastic theory because it does not give a well defined property of an object. Only when a measurement is made, will the property be fixed, based on a certain probability determined by its state. If a measurement of say, momentum is done on one particle, it will randomly choose a value of momentum, and the other entangled particle will have a well defined momentum (because of momentum conservation) instantaneously. If the pair does not interact with external objects, thus still remains entangled, no matter how far they are in space, once a measurement of a property is done on one particle, the other particle will instantaneously gain the information of what has been done on the first particle to fix its property!

Bell’s inequality is formulated in such a way that if the particle pair transmitted information faster than the speed of light as required by quantum entanglement, then the equality is violated. And current experiments verified that the inequality is violated, nature is nonlocal (instantaneous information transfer).
Thus it becomes interesting to know does quantum nonlocality allows superluminal communication?

The question is important as superluminal travelling and communication is essential for the colonisation space in a short time. Currently the Earth is undertaking a large toll of greenhouse gases and global warming is slowly but surely spelling massive damage to human civilisation in this century and the next. Environmental efforts maybe one of the solution to this problem but it is a dim hope as the call for it has been around for decades and comparatively little effort has been done in that direction. Moving to a new planet on the other hand, is an attractive alternative. However with the current state of space travel technology, it will be generations before any humans can make it safely to even the nearest star.

If we are able to master the technology of superluminal travelling, the whole galaxy, the whole universe is opened up to us. Space colonisation will be as easy as building a new city on Earth. Looking at the limited amount of time left before global warming takes its toll on research grants, it is imperative that the technology of superluminal travelling be developed as soon as possible. However, before going into the technology, it must be known whether superluminal travelling is theoretically allowed or not. Hence the question of interest.


Returning to physics, quantum entanglement seems to be superluminal communication itself. Many experiments (including Delayed “Choice” Quantum Eraser (Yoon-Ho Kim 3 January 2000), Bell’s inequality and even Quantum Teleportation (Zeilinger 1999)) have been designed to make use of entanglement and all of them failed to enable superluminal communication (to be fair, almost none of them were designed in mind to enable superluminal communication). These lead to a theorem called the no communication theorem.

To illustrate this further, some definitions are long overdue. Let’s call the two observers at two sides of a quantum entangled pair Alice and Bob respectively. Alice and Bob are also sharing a continuous beam of entangled pairs from a source. The only input is from the choice of which property of the quantum object to measure. The only output is from the values of the measured property. For Bob to communicate with Alice using the quantum entangled pair, Alice must be able to differentiate from her output (for some input she put in) what input Bob put into his entangled pair and vice-versa.




Even through Bob is free to choose his input; his output is governed by probability and beyond the control of anyone. The output of Alice is coupled to Bob’s output by quantum entanglement, thus it reflects the probability of Bob’s output. Since the output of Alice is random and beyond Bob’s control whatever his input is, Alice can never gain any useful information about Bob by just looking at her output. Hence the no communication theorem holds.


The technical details are more subtle than the argument above; however, the general idea remains the same: Nature seems to conspire to cover up any possibility of superluminal communication. Below shows a preview of some technical details of quantum eraser that will automatically “cover up” its trail so that superluminal communication or information travelling back in time is prevented.


“That tricky detail that we omitted earlier is what saves the day: to see the interference of the particles after applying the quantum eraser, we first have to divide them into two groups and observe the groups separately. One group will display the original pattern of fringes; the other will display the inverse of that pattern, with particles landing on what were originally the dark bands and avoiding the places where the bright fringes were. The two groups combined fill in all the gaps, hiding the interference.

The paradox is avoided because we need data from the photon measurement to know which group each particle belongs to. Thus, we cannot observe the fringes until after we have done the photon measurements (thus requiring results from both detectors), because only then do we know how to split the particles into groups.” (Kwiat 2007)


In other words, the stochastic nature of quantum physics prevents superluminal communication. Or it seems to as John Cramer sees it.


In his passion for daring research into this field, he and his team worked on the problem of setting up an experiment to show that superluminal communication is possible with quantum entanglement. This is done in the climate of most other physicist taking for granted that the no communication theorem will rule out any superluminal communication and save relativity and causality from facing the effects of time travel. According to Cramer:

“Recently it has been pointed out, however, that at least some of these proofs (of no communication theorem) are tautological, with their seemingly reasonable assumptions subtly building in the conclusion, and that key assumptions are inconsistent with some aspects of standard quantum mechanics.” (J. G. Cramer n.d.)


Thus he said that there is still a glimmer of hope for superluminal communication. Inspired by the PhD thesis of Birgit Dopfer in 1998, Cramer modified her EPR experiment to create a final experimental setup as shown.


The basic idea of the experimental setup is based on the splitting of a single photon (laser light) into two entangled beams which enters two similar detectors that are capable of distinguishing whether the photon acts like a wave or a particle. On the sending end of the detector, a controllable variable will decide to measure the photon as a wave or as a particle. Then the corresponding entangled photon pair at the receiving end will automatically correlate with the sending end, thus enabling the receiver to see what was varied in the sending end of the arm.


Note that the special feature in the experiment is that the sending arm lags the receiving arm by 50 microseconds. That is the message is received 50 microseconds before it is sent!
(Cramer 2009)



After years of research on this topic, he recently announced his positive results during the John Cramer Symposium on the occasion of his 75th birthday. However, there’s a noticeable lack of paper on this discovery in the physics journals and the electronic preprint website, ArXiv. Therefore one possible way to conduct a research is to recreate Cramer’s experimental setup and see if his results can be independently verified.


Most of the apparatus used is able to be found in a quantum optics laboratory and National University of Singapore have the very facility in Center for Quantum Technology. The main research cost should be the cost of the long optical fibre. The experimental skills are easily available and the learning opportunities from the existing researchers are immense. The procedure of the research is then to setup the experiment as shown above, then to modify the measurements in the sender leg and observe if there is any corresponding signal in the receiver’s leg. The time difference can also be carried out using an atomic clock and thus demonstrating the weird effects from quantum entanglement.

If Cramer’s experiment can be verified, information at least can travel back in time and this opens up many new applications. Solutions from the future can be downloaded into the present thus solving most of the problem faced by society today. The laws of time travel can be brought into experiment instead of remaining in theoretical/philosophical grounds. The world will never be the same again.


However, if there is any loophole or error in Cramer’s theory of backward time travel, and the no communication theorem still holds, then it will be a sober wake up call to humanity as the only way to survive is to care about the Earth.



In conclusion, the question: “Does quantum nonlocality allows superluminal communication?” is one of the most important and urgent question to be answered as it plays a great role in determining the fate of humanity.


Works Cited
A. Einstein, B. Podolsky, N. Rosen. "Can Quantum Mechanical Description of Reality Be Considered Complete?" Physical Review vol. 47, May 15 1935: 777.

Cramer, John G. The Alternate View. http://www.analogsf.com/0612/altview.shtml (accessed November 20, 2009).

Cramer, John. The John Cramer Symposium. September 10-11, 2009. http://www.physics.ohio-state.edu/~lisa ... Symposium/ (accessed November 20, 2009).

Kwiat, Rachel Hillmer and Paul. "A Do-It-Yourself Quantum Eraser." Scientific American. May 2007. http://www.scientificamerican.com/artic ... ser&page=3 (accessed November 20, 2009).

Yoon-Ho Kim, Rong Yu, Sergei P. Kulik, Yanhua Shih, Marlan O. Scully. "Delayed "Choice" Quantum Eraser." Physical Review Letters Vol. 84 No. 1, 3 January 2000: 1-5.

Zeilinger, Anton. "Experiments and Foundations of Quantum Physics." Reviews of Modern Physics Vol 71 No. 2 Centenary , 1999: S288-S297.



P.S. My quantum physics prof had told me straight that quantum physics maybe non-local but it never allows superluminal signalling. That fact is known. So you can regard this post as a pretty fantasy.

[MiM]

As far as entangled particles go, I'm tending to think that, even if it was possible to communicate using them, it's not faster than light communication, in the complete sense.
To communicate with point A, a million light years away, you would first have to send your paired particles across a million light years, at less than the speed of light. So the actual communication would take longer than a million years, not an instant.

Without going further into the discussion at this point, I think you go wrong here. That's a bit like claiming it takes a month to send a telegram between two towns, because it takes a month to build the telegraph lines. Setting up the connection is one thing, sending the message another.

[mistermack]

As far as entangled particles go, I'm tending to think that, even if it was possible to communicate using them, it's not faster than light communication, in the complete sense.
To communicate with point A, a million light years away, you would first have to send your paired particles across a million light years, at less than the speed of light. So the actual communication would take longer than a million years, not an instant.

Without going further into the discussion at this point, I think you go wrong here. That's a bit like claiming it takes a month to send a telegram between two towns, because it takes a month to build the telegraph lines. Setting up the connection is one thing, sending the message another.

You might be right. Like I said, it's just speculation, and I have no idea how it would affect the time question.
The fact remains though, that it would be impossible to communicate at superluminal speeds, unless you have laid the foundations previously, as slower than light speeds.
So there is no chance whatsoever of us chatting to beings a million light years away, using paired particles. Unless someone set up the system, at least a million years ago.

If you have no telegraph lines, it WILL take at least the month, in your example. That's just a fact.

[pErvinalia]

What about the old wormhole time travel bizo but for information only? That is, could we create a stable wormhole that could allow info to travel through it and appear somewhere else before we sent it?

[mistermack]

I don't know much about wormholes, except that they are theoretical possibilities, through the mathematics of general relativity. Nobody has ever made one, or seen one, or seen the effects of what might be one, but that doesn't rule them out I guess.
I thought that they were something that might occur in the vicinity of black holes, which would rule out any useful application that we could make of them, I would think. But that could be bollocks.

But it's no comparison to entangled paired particles, which can be made fairly easily.

What interests me about the paired particles is the way that they impinge on relativity. It is a fundamental part of relativity, that the speed of light is the absolute ultimate, and nothing can happen faster. The apparent instantaneous transfer of information from one of the pair to the other seriously contradicts that.
Einstein thought that, and never liked quantum physics as a result, and did some serious work to prove that it didn't reflect reality, and that there must be something else at work.
The fact that we can't make use of the transferred information doesn't really affect the fact that it happens, when it shouldn't, according to relativity.
Relativity doesn't say that c is the limit for information that we can read. It says that c is the absolute limit, but it's clearly not.
It's no wonder that Einstein didn't like it.

Just to repeat a bit from what I quoted above on this page,

His final attack against quantum physics is known as the Einstein-Podolsky-Rosen (EPR) paradox. It shows that either quantum physics is incomplete or there has to be superluminal information transfer , which seems to be against the theory of relativity (A. Einstein May 15 1935).

[hackenslash]

A really interesting way to look at all of these things is through the lens of M-Theory, because it provides a ready explanation via the existence of compactified dimensions.

M-Theory has it that, in addition to the familiar 3 extended dimensions of space, there are an additional 6 or 7 (one of them may be a time-like dimension), some of which are compactified to Planck scale. The limitation of c applies to the extended dimensions, and indeed would apply to the other dimensions as well, except that if any of them are compactified to Planck scale, any point in space is a mere Planck length away. This nullifies the need for superluminal information transfer and gives a mechanism for wormholes at a stroke.

Worth reading The Elegant Universe by Brian Greene, which deals with all of this in more detail. His excellent Fabric of the Cosmos deals with non-locality, Bell's theorem, wormholes and quantum teleportation as well.

[mistermack]

It has to be something like that. Either extra dimensions, or contact through other universes.

Before reading this thread, I always found the speed of light to be mind-blowing. You get sort of used to it, when you've seen it repeated enough times, but when I actually picture 300,000 kilometers, traveled in one second, my sense of scale breaks down.

But this paired particle business puts the speed of light into the rubbish bin. It's a breathtaking phenomenon, whether it could ever be used to communicate or not.

I'm still sceptical about the theoretical consequence of time travel being possible, if you could use it to communicate. I've got a feeling there's something wrong in the interpretation of that.

In relativity, time slows for an object, as it approaches the speed of light. If it were to go through c, and beyond, ( which is impossible ) time could become negative, I guess, in theory.
But this isn't something travelling faster than c, it's something that happens instantly, in zero time, or independent of the rules of space time. The rules of relativity don't apply to it.

[mistermack]

More about Prof. John G Cramer :

http://www.komonews.com/news/local/UW-p ... 91071.html

SEATTLE -- Physicists, mathematicians, philosophers and that guy talking to himself on a street corner all have opinions about validity of time travel.

So does Dr. John Cramer, professor Emeritus of Physics at the University of Washington. He wants to make it a reality.

But Cramer's form of time travel is not the teleportation characterized by Hollywood and science fiction. As time travel goes, Cramer thinks in baby steps. He's working on the possibility receiving a message milliseconds before it's sent.

"I have to admit, this is pushing the envelope and often the envelop pushes back," says Cramer, a nuclear physicist who has worked on projects involving the Large Hadron Collider in Switzerland.

In the basement of the campus physics building, Cramer is fiddling with laser beams to prove what Einstein called "spooky action at a distance". He's splitting photons through a series of synthetic crystals to demonstrate that quantum non-locality can be used to communicate.

For those of us who never took high school physics, this is what he's trying to do in layman's terms: If you took a pair of photons created at the same time and altered one of those photons, in theory the other photon would be altered instantly -- even if it was separated by an entire galaxy.

That would mean communication could travel faster than the speed of light over long distances. The ramifications of something Einstein didn't think was possible but theoretically could happen would be incredible. Physicists call it "nonlocal quantum communication."

"You could do real-time communication with objects on other plants," says Cramer. "You could put on a virtual reality helmet and be driving your remote dune buggy on Mars."

That means NASA could operate a rover on Mars in real time. Normally it takes 22 minutes for a signal traveling at the speed of light to reach Mars.

That's step one in a two-step process. Cramer admits it's big first step.

"I think it's a long shot but it's a long shot with such important implications, it's worth it," says Cramer.

But Cramer has been at step one for nearly a decade with no success. He's had funding issues and technical problems.

"You have to be able to efficiently detect the entangled photons before you can do any real measurements and we have not been able to do that yet," says Cramer.

If Cramer can prove step one, step two becomes even more fascinating.

"If you can communicate using non-locality then you can communicate faster than light and backwards in time," says Cramer. "I'm a little scared of what happens if it does happen because the implications are so bizarre."

And who could most likely profit immediately from such technology? Wall Street. Sixty-percent of the daily trade volume on the New York Stock Exchange involves high frequency trades made by computer programs. These trades happen in fractions of a second with traders earning or losing fractions of a penny at a time.

"Milliseconds is what it's all about now," says Tom Cock, Managing Director of Vestory, an investment advisory firm in Kirkland.

Speed and distance is now so important, large brokerage houses have their trading computers inches away from the main computers running the exchanges in order to cut down on lag time.

"So that when trades are made in the exchange, they can immediately see those trades and respond to them in an algorithmic way that allows them to have advantages over the everyman," says Cock.

If a trader's computer could see how the market responds to a trade milliseconds before it's actually made, the implications would be enormous.

"Then the field is not level at all," says Cock.

"I think 50 milliseconds might be interesting to Goldman Sachs," says Cramer sheepishly.

While some interpret Einstein’s theory of relatively to mean nothing can travel faster than the speed of light, Cramer says that doesn’t apply to his experiments.

"If there is something lurking in the woodwork which actually prevents you from doing this, I don't know what it is," says Cramer.

That's coming from a scientist who knows what he's talking about. Then again, maybe it's already happened.