Does time exist at Quantum level?

[bhobba]

but they have been observed in nature (as I understand it) and bear explaining don't they?

Yes - and QM explains it.

Here is the explanation. Consider two systems that can only exist in state |a> and |b>. If system 1 is in state |a> and system 2 in state |b> that is written as |a>|b>. Similarly if system 1 is in state |b> and system 2 in state |a> that is written as state |b>|a>. From the principle of superposition you can have a superposition of the two states such as 1/√2|a>|b> + 1/2|b>|a> and is the state I will illustrate what's going on with. Such a state is called entangled - neither system is in state |a> or |b> - in fact it turns out they are now in mixed states - but I won't go into that here. Now let's observe system 1. Because it only has two states you must get |a> or |b>. If you get |a> then system 2 must be in state |b>, and similarly if you get |b> system 2 is in state |a>. Entanglement is broken and you can see the results are correlated by the way they are entangled. There is nothing mysterious going on - its fully explained by the principles of QM.

The issue is if you have an EPR type set-up where you observe each system at any distance apart. So that means if you observe system 1 you immediately know the state of system 2 that can, theoretically, be on the other side of the universe. That's all there is to it. It's not mysterious. Its simply an application of the principles of QM.

Thanks
Bill

 

[Jimster41]

Lucid, as always, Bill. I do appreciate it. Since I find even Susskin hard going. The sentence that seems undersold is "can only be in state A or B".

Until the measurement, potentially taking place at space-like separation, it is in neither and both as you say. At the moment of measurement, what space-like process reminds it of that "can only be in..." rule?

 

[bhobba]

Until the measurement, potentially taking place at space-like separation, it is in neither and both as you say. At the moment of measurement, what space-like process reminds it of that "can only be in..." rule?

Remember I said it can only be in state |a> or |b> - that means when you observe it for |a> or |b> you must get |a> or |b>. Although I didn't mention it because its rather obvious, they are orthogonal.

Thanks
Bill

 

[Jimster41]

Remember I said it can only be in state |a> or |b> - that means when you observe it for |a> or |b> you must get |a> or |b>.

Thanks
Bill

It's one thing for you to state that rule as an axiom in some formal logic. It seems another for nature herself to state it at space like separation for real observations.

 

[bhobba]

It's one thing for you to state that rule as an axiom in some formal logic. It seems another for nature herself to state it at space like separation for real observations.

Now that's the issue isn't it. It seems strange so you try to read more into it. That's the rock bottom issue here. As I have said time and time again QM is easy if you accept it without doing that. That's what I mean by - let go. Once you do that progress is swift in understanding.

Thanks
Bill

 

[yoron]

Time is no different in QM - its something we parameterise our theories with and it's measured the same way.

What you are talking about is the entanglement thing.
http://www.johnboccio.com/research/quantum/notes/paper.pdf

As you can see if it is instantaneous is open to question.

Suppose I put a red slip of paper in an envelope and a green slip in another then mix them up, keep one, and send another to the other side of the universe. I open the envelope and see green. Immediately I know the other is red. No communication took place - we simply have a correlation. Entanglement may simply be like that, its a bit different as the above on Bells Theorem shows, in that its not the same as classical correlations, but it's still a correlation.

In fact in what's called Quantum Field Theory (QFT) we have something called the cluster decomposition property which basically says for uncorrelated systems sufficiently separated regions behave independently. This is the notion locality in QFT. Note the key word - uncorrelated. Entangled systems are correlated. This leaves up in the air if locality is even applicable for entangled systems. Personally I don't think it is, but mine is very much a minority view.

Thanks
Bill

It's a really interesting thought. or thoughts. Assuming that 'time' exist everywhere locally tested and defined, a 'correlated system' then, in some way, should need to 'interact' some other way to be seen as 'instantaneous'. We have four dimensions normally, three of them belonging together creating a 'three dimensional space', the fourth being a local arrow defining its temporal direction. So, if the arrow becomes eliminated, where does that leave us?

 

[bhobba]

So, if the arrow becomes eliminated, where does that leave us?

It would seem rather difficult to eliminate because of this thin called entropy which is really what gives time its direction:
https://en.wikipedia.org/wiki/Entropy_(arrow_of_time)

Thanks
Bill

 

[akka69]

I wonder how time works for photons:
According to raltivity, since they travel at exactly the speed of light, there should be an infinite time difference between their "inner time" and the rest of the Universe time.

Then how can they interact with any thing (matter, other photons, electrons...) if they can't be at the same place at the same time?

 

[Nugatory]

I wonder how time works for photons:
According to raltivity, since they travel at exactly the speed of light, there should be an infinite time difference between their "inner time" and the rest of the Universe time.

That's a very common misconception, so common in fact that we have a FAQ for it: https://www.physicsforums.com/threads/rest-frame-of-a-photon.511170/

The last few issues raised in this thread have been far enough off-topic that they'd be better off in their own threads, so I'm closing this one.