# General Relativity, Quantum Mechanics, Motion and Virtual Particles Oh my!

JDude13
Okay...
In the quantum world, is all motion absolute? As in, can you pinpoint whether or not a particle is actually moving using space as a reference point? Or is it like in general relativity where the only motion that matters is motion relative to other particles?

If it is like the model of motion in general relativity, then what direction are virtual particles moving relative to other particles?

As I understand it, when a virtual particle is created, so is its virtual anti-particle moving in opposite directions. Is this motion unique to each observer? or does their wave-function mean they move in every direction to each observer?

Or am I being naive, mentioning observers because virtual particles cannot be observed because, if they are, the consequences of their existence is prolonged to such a degree that the cannot be virtual?

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Okay...
In the quantum world, is all motion absolute? As in, can you pinpoint whether or not a particle is actually moving using space as a reference point? Or is it like in general relativity where the only motion that matters is motion relative to other particles?

The latter.

Or am I being naive, mentioning observers because virtual particles cannot be observed

Yes. Look at Chapter A7: ''Virtual particles and vacuum fluctuations'' of my theoretical physics FAQ at http://www.mat.univie.ac.at/~neum/physfaq/physics-faq.html#A7

asimov42
The latter.

Yes. Look at Chapter A7: ''Virtual particles and vacuum fluctuations'' of my theoretical physics FAQ at http://www.mat.univie.ac.at/~neum/physfaq/physics-faq.html#A7

I just read the (very helpful) FAQ. So, if I understand correctly, only relative motion matters (as per general relativity) because virtual particles are 'exchanged', but do not have a definite direction of motion, speed, etc.?

J.

I just read the (very helpful) FAQ. So, if I understand correctly, only relative motion matters (as per general relativity) because virtual particles are 'exchanged', but do not have a definite direction of motion, speed, etc.?

Your statement about virtual particles is a correct inference from my FAQ.

But the question of relativity is unrelated to virtual particles.

The laws of mechanics are relative, whether in Newtonian mechanics, classical relativity,
quantum mechanics, or relativistic quantum field theory. In each case you need to define a frame of reference before you can talk about position.

asimov42
The latter.

Yes. Look at Chapter A7: ''Virtual particles and vacuum fluctuations'' of my theoretical physics FAQ at http://www.mat.univie.ac.at/~neum/physfaq/physics-faq.html#A7

Your statement about virtual particles is a correct inference from my FAQ.

But the question of relativity is unrelated to virtual particles.

The laws of mechanics are relative, whether in Newtonian mechanics, classical relativity,
quantum mechanics, or relativistic quantum field theory. In each case you need to define a frame of reference before you can talk about position.

Ah, right. I guess my question is more about the interpretation of 'virtual particles'.

Virtual particles are often presented as 'popping in and out of existence' in the vacuum. But this would imply, as mentioned in JDude13's original post, that the background of 'space' can be used as a reference. Or, e.g., the way in which a real particle is moving would determine how many 'virtual particles' it runs into etc. But if all motion is relative, then this can't be the case.

As a layman, I think my confusion comes from reading too much into the popular (intuitive) descriptions of virtual particles.

Ah, right. I guess my question is more about the interpretation of 'virtual particles'.

Virtual particles are often presented as 'popping in and out of existence' in the vacuum. But this would imply, as mentioned in JDude13's original post, that the background of 'space' can be used as a reference. Or, e.g., the way in which a real particle is moving would determine how many 'virtual particles' it runs into etc. But if all motion is relative, then this can't be the case.

As a layman, I think my confusion comes from reading too much into the popular (intuitive) descriptions of virtual particles.

The virtual particle imagery stems from the 1940s and 1950s when people tried to understand how quantum electrodynamics and its generalizations can make sense. For the experts of today, the term is fully exchangable with ''internal lines in a Feynman diagram'', without any intended meaning beyond that.

Popularizations take the imagery for real since it seems far more understandable that the formal stuff, but these popularization pay for it by having to ascribe to the virtual particles very strange properties far from both ordinary experience and measurable facts.

But quantum mechanics is much more rational and intelligible if one avoids such spurious imagery. So it is best to unlearn it as soon as possible.