Science a GoGo's Home Page Forums General Discussion Physics Forum Does QM preclude CTCs?

If QM requires a constant universal time, does this rule out closed time-like curves?

There is no easy or agreed answer to that Bill S and it would depend upon which interpretation.

The answer is yes/no and maybe and since it's QM lets make it all at the same time :-)

There are some novel ideas probably start here if you wish to discuss specifics

http://en.wikipedia.org/wiki/Quantum_mechanics_of_time_travel

If you are feeling particually brave I can recommend Kip Thorne

http://www.its.caltech.edu/~kip/scripts/ClosedTimelikeCurves-II121.pdf

And if you are feeling crazy brave here are the five postulates of QM go to postulate 4 and try and sort of read around the mathematics you have enough understanding to do that I think.

http://arxiv.org/ftp/physics/papers/0602/0602145.pdf

What it covers for you is time evoltion and conservation of energy

-: The time evolution of a quantum state is governed by a unitary transformation.

-: Equation (102) is, also, the Schrödinger equation, but, this version of the equation is independent of time. In other words, it is the stationary Schrödinger equation. This equation (102) is the energy eigenvalue equation, which tells us that if the physical system has the energy E at the initial time, then at any subsequent time it will have the same energy.

Thanks, Orac. I started by reading David Deutsch’s explanation: trying to contain an octopus in a string bag comes to mind.

I shall read some more and do some thinking before trying to go any further.

Orac, I tried reading round the maths and my increasing feeling was "Run away!"

At http://arxiv.org/pdf/gr-qc/0407033v2.pdf I found:

"The various developments of quantum field theory in curved space-time have left the false impression that general relativity and quantum mechanics are compatible. Actually though certain predictions of classical general relativity such as close time-like curves and event horizons are in conflict with a quantum mechanical description of space-time itself. In particular, a quantum mechanical description of any system requires a universal time."

This seemed to address the original question, but with no more than a dogmatic statement.

The article continues:

"In practice, universal time is defined by means of synchronization of atomic clocks, but such synchronization is not possible in space-times with event horizons or closed time-like curves. It has been suggested that the way a global time is established in Nature is via the occurrence of off-diagonal long-range quantum coherence in the vacuum state."

By this time I was floundering because I had no idea what off-diagonal long-range quantum coherence might be.

Okay lets see if I can fill in some gaps




It's the first postulate under Quantum Mechanics you have to assume it for now (in the near future we may be able to prove it I will discuss a bit later) but for now it is the number one assumption and if it is wrong then the predictions of QM should be wrong.

You can try wading thru the first postulate in http://arxiv.org/ftp/physics/papers/0602/0602145.pdf but probably goto the time as an operator section in the wiki link
http://en.wikipedia.org/wiki/Mathematical_formulation_of_quantum_mechanics

The key point


So the entire framework of QM is built upon the premise that time is intrinsic and real. It has to be that under QM for you to be able to define a waveform for time evolution of a system.

Note that this QM time is also outside and seperated from time within space and thats what the following parts of the wiki entry deal with that QM also says time may become observable within space but it will be a function of the QM time.

So QM real time being outside space is a fundemental thing and one which Einstein and friends disagreed with because time in GR/SR is bound as a 4th dimension in spacetime.

This set the foundation for the famous EPR paradox (http://en.wikipedia.org/wiki/EPR_paradox) and Einstein, Podolsky and Rosen assertion that QM is incomplete and or inconsistant and there are hidden variables that are not accounted for in the framework.

Now if you go back to the framework almost all the classic quantities are there some are quantized but by and large they are the same the big difference is time which is the number one assumption of QM.

If time is not the same between QM and GR/SR then you will find a reality problem between QM and GR/SR.

In 1964 John bell released his paper "On the Einstein Podolsky Rosen paradox" in which he setout a simply analogy which showed mathematically and by using simple reasoning that EPR was incorrect and there is no local reality you can read up on it (http://en.wikipedia.org/wiki/Bell's_theorem).



By 1981 we had enough technical background in dealing with entangled particles to try the experiment which was done by Alain Aspect (http://en.wikipedia.org/wiki/Alain_Aspect).

The background to Bells Theorem is so simple it has now been converted to a simple computer code and Sascha has an online site for all crackpots who don't accept it to have an attempt to solve it (http://www.science20.com/alpha_meme/official_quantum_randi_challenge-80168)

Now we talk about "reality" and "observation" but if we cut to the bottom we saying is QM time differs from our local reality time. So while things seem wrong in terms of timing for us as observers if you look at it from QM time prespective it makes perfect sense.

So while QM time is not conclusively proved it is the only theory that currently exists that predicts such a weird outcome. There is no classic physics interpretation that allows such a strange result that local reality does not exist and makes predictable and testable experiments.

There are lots of more extensive probes on QM time being done but most involve complexity that will require some detailed discussion and I would like to see what you make of all that so far.

I will also pick up Coherence in another post once I am sure we have answered all your questions about what time is in QM.