Can a Single Particle Move in an Empty Universe?

[CaptDude]

Question: If there were only a single elementary particle in the entire universe - could it move, and if so, how would its movement be measured?

 

[Garth]

Question: If there were only a single elementary particle in the entire universe - could it move, and if so, how would its movement be measured?

The only reference frame to measure any movement would be its own, in which by definition it cannot move.

Garth

 

[Chalnoth]

Question: If there were only a single elementary particle in the entire universe - could it move, and if so, how would its movement be measured?

Well, any constant motion would be undetectable. But if it were possible for the particle to accelerate, that could (probably) be detected, because if this particle had electric charge, acceleration would cause it to radiate. A change in the acceleration would cause it to emit gravitational waves.

That said, if there wasn't some other particle around, there'd be nothing to cause it to accelerate (or change its acceleration), so it'd just have constant motion which is undetectable and indistinguishable from being stationary.

 

[PeterDonis]

If there were only a single elementary particle in the entire universe - could it move, and if so, how would its movement be measured?

If there is only a single elementary particle in the universe, what measuring device would be used to measure its movement?

 

[nitsuj]

lol it takes physics to do physics!

 

[CaptDude]

If there is only a single elementary particle in the universe, what measuring device would be used to measure its movement?

New
Well, since my post says it is a "thought experiment" I'm sure you could think of something....

 

[PeterDonis]

since my post says it is a "thought experiment" I'm sure you could think of something

No, I can't. That's why I asked the question. It's your thought experiment. If you can't think of something either, what does that tell you?

 

[DaveC426913]

If there is only a single elementary particle in the universe, what measuring device would be used to measure its movement?

New
Well, since my post says it is a "thought experiment" I'm sure you could think of something....

While thought experiments do allow for highly impractical parameters ("...imagine I flew my starship to the centre of the sun"), those parameters have to be ones that aren't directly relevant to the thought experiment.

In your scenario, the concept of measuring movement is directly relevant: movement is not an absolute - it must be relative to something (Einstein taught us that) - requiring at least two particles.

So, I guess you have answered your own question.

 

[CaptDude]

While thought experiments do allow for highly impractical parameters ("...imagine I flew my starship to the centre of the sun"), those parameters have to be ones that aren't directly relevant to the thought experiment.

In your scenario, the concept of measuring movement is directly relevant: movement is not an absolute - it must be relative to something (Einstein taught us that) - requiring at least two particles.

So, I guess you have answered your own question.

Thank you for your CONSTRUCTIVE comment. I see your point and thank you for taking the time to write something that is informative.