I Does QM allow for a photon to travel at 800,000 km/s?

[gamow99]

I realize this type of question has been asked elsewhere on competitor websites but I want to make it more precise. Usually, the person asks if anything in QM is possible to which the answer is no, for example, a photon cannot have spin 0, hence some things in QM are impossible. But what about a photon existing at point A at second 1 and then at point B which is 800,000 km distant at second 2? Is there a non-zero probability of that happening?
Or let's even make the question more broad: for any distance is there a non-zero probability of a photon being at that distance one second from now?

 

[Paul Colby]

So, given any two points and any two times, how does one tell they are the same photon? Last I checked these things aren't labeled.

 

[gamow99]

Of course, it is the case that this is not experimentally verifiable, but is there anything in the equations of QM that prohibit this?

 

[Vanadium 50]

I realize this type of question has been asked elsewhere on competitor websites but I want to make it more precise.

Then do so. Are you talking about relativistic QM, non-relativistic QM, or QFT?

 

[Boing3000]

But what about a photon existing at point A at second 1 and then at point B which is 800,000 km distant at second 2? Is there a non-zero probability of that happening?

It is not clear what you are asking. If you are talking about fluctuation in the photon field ? Maybe this will help you.

 

[vanhees71]

You cannot talk about photons in non-relativistic QM. I'm not aware of a working interpretation of relativistic QM. Thus I'd rather stick to relativistic QFT. The very successful Standard Model of elementary-particle physics is based on local, microcausal relativistic QFT, and within such a theory by construction nothing causal can travel with faster than the speed of light. Formally that's worked into the theory by demanding that local observables commute at space-like separated arguments.

 

[Paul Colby]

Of course, it is the case that this is not experimentally verifiable, but is there anything in the equations of QM that prohibit this?

I find such statements mystifying. The are many things unmeasurable for practical reasons but observable in principle about which question may be asked. Your question strikes me as possibly being unobservable in principle. If this were the case, isn't it then a meaningless question?

 

[gamow99]

Actually, I did not realize that the speed of light is a constant. So let me rephrase the question. Is there a probability of every atom in my body suddenly traveling at 99% the speed of light in a straight line for, say, a minute?As for:

Your question strikes me as possibly being unobservable in principle. If this were the case, isn't it then a meaningless question?

This is a question for philosophy, in particular, conceptual analysis. In order to come up with a plausible answer to this solution we have to have some sort of calculus which can reliably calculate the truth-value of sentences which contain very hard to understand words such as 'observable', and 'meaningless'. We do not have that calculus now so we won't argue about it. I want to encourage you as a scientist to ask yourself how do you determine the truth-value of that sentence since it is not the sort of thing that can be measured, observed or calculated? I think you'll find that at present there are no available methods. It is here that we need to turn to philosophy for at least a grip on the question since it is philosophers who have done the most work on them.

 

[Nugatory]

And on that note...
This thread is closed.