What contradictions remain between SR and QM?

[thenewmans]

In your view, what contradictions remain? My guess is some might say none since entanglement can’t be used for FTL communication. Still others might say something (wave collapse and such) goes nondeterministic (FTL or back in time) between entangled particles so there is still a conflict. I’m sure that’s not all there is to it. What are your views?

 

[tim_lou]

I don't think there is anything, as QFT entirely incorporates SR.

 

[Demystifier]

What are your views?

My view is this:
http://xxx.lanl.gov/abs/0811.1905 [accepted for publication in Int. J. Quantum Inf.]

 

[Demystifier]

I don't think there is anything, as QFT entirely incorporates SR.

But does QFT entirely incorporates QM? For example, what about the particle-position operator in QFT?
I think it can be incorporated too, provided that QM itself is somewhat reinterpreted as in the paper I mentioned above.

 

[tim_lou]

I've heard of the space-time operator formalism but am unaware of its detailed implementations. The website you gave seems to be an interesting read. For me, the standard field formalism is written entirely in a Lorentz invariant form, I don't see any obvious contradictions with it. When you say particle-position operator, do you mean ψ and ψ† ? These transform appropriately under Lorentz transformation and I don't see any problem with it.

 

[thenewmans]

Let me see if I can put it another way. So far, every legitimate QM interpretation I’ve tried to understand breaks locality in some way. (I need to learn more about QFT.) Some effect either propagates instantly between entangled particles or travels back in time to affect the source of the entangled particles. My understanding is that SR depends on locality and causality. So doesn’t QM contradict SR?

Demystifier, thanks. But I am not equipped to digest it. Thankfully it’s short and I am reading it all.

 

[Demystifier]

But I am not equipped to digest it.

Can you explain why?

 

[Demystifier]

My understanding is that SR depends on locality and causality. So doesn’t QM contradict SR?

I would not say that SR depends on locality and causality. I would say that SR depends on invariance with respect to Lorentz transformations. In this sense, nonlocality and violation of causality may still be compatible with SR. In particular, motion faster than light, by itself, is compatible with SR.

 

[Demystifier]

When you say particle-position operator, do you mean ψ and ψ† ?

No. I mean a relativistic generalization of the particle-position operator in nonrelativistic QM.

 

[thenewmans]

Can you explain why?

Demystifier, I'm not a QM guy. I'm not even a physics guy. I just like trying to understand this stuff. The math and Greek letters are beyond me. If I can't type it in Excel, I'm lost. ;) Maybe some day.

 

[Demystifier]

Demystifier, I'm not a QM guy. I'm not even a physics guy. I just like trying to understand this stuff. The math and Greek letters are beyond me. If I can't type it in Excel, I'm lost. ;) Maybe some day.

I see. In this case, you may visit my blog, in which some main ideas of quantum mechanics and its Bohmian interpretation are explained for non-physicists in terms of everyday analogies.

 

[thenewmans]

I see. In this case, you may visit my blog, in which some main ideas of quantum mechanics and its Bohmian interpretation are explained for non-physicists in terms of everyday analogies.

Actually I have and I love it! A very nice twist!

 

[QuantumDevil]

I would not say that SR depends on locality and causality. I would say that SR depends on invariance with respect to Lorentz transformations. In this sense, nonlocality and violation of causality may still be compatible with SR. In particular, motion faster than light, by itself, is compatible with SR.

How so? Can you explain it? I though that invariance with respect to Lorentz transformation imposed causality and locality

 

[Demystifier]

I though that invariance with respect to Lorentz transformation imposed causality and locality

Only if you make some additional assumptions. The assumption of the Lorentz invariance alone does not impose causality and locality. Show me any concrete derivation of causality and locality and I will tell you what are the underlying additional assumptions.

 

[QuantumDevil]

Only if you make some additional assumptions. .

Such as?

 

[Demystifier]

Such as?

As I already said, show me any concrete derivation and I will ...

But just to catch the flavor of required assumptions, one of the standard assumptions is that the square of the 4-momentum should be non-negative. Lorentz invariance alone allows also this to be negative, in which case we deal with tachions, i.e., particles that travel only faster than light. Someone might say "Yes, but tachions are inconsistent because ... bla bla bla", but my answer will be "Yes, but your argument also involves some additional assumptions beyond Lorentz invariance".

For a counter-example, see also my recent paper that I mentioned above, in which I explicitly formulate QM in a nonlocal but Lorentz-invariant manner.