Can a Single Particle Move in an Empty Universe?

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Discussion Overview

The discussion revolves around the hypothetical scenario of a single elementary particle existing in an empty universe, focusing on whether such a particle could move and how its movement could be measured. The scope includes conceptual reasoning and thought experiments related to motion and reference frames in physics.

Discussion Character

  • Exploratory, Conceptual clarification, Debate/contested, Meta-discussion

Main Points Raised

  • Some participants propose that if only one particle exists, it cannot move relative to anything else, as it lacks a reference frame.
  • Others argue that while constant motion would be undetectable, acceleration could potentially be measured if the particle had charge, as it would radiate energy.
  • A participant questions the feasibility of measuring movement in such a scenario, emphasizing that movement is relative and requires at least two particles.
  • Some participants engage in a meta-discussion about the nature of thought experiments and the relevance of parameters used in them.
  • There is a challenge regarding the ability to conceptualize a measuring device for movement in the absence of other particles.

Areas of Agreement / Disagreement

Participants generally agree that measuring movement requires a reference point, leading to a consensus that a single particle cannot be measured in isolation. However, there are competing views on the implications of acceleration and the nature of thought experiments.

Contextual Notes

Limitations include the assumption that movement is only meaningful relative to other particles, and the discussion does not resolve the practicalities of measuring movement in such a hypothetical scenario.

CaptDude
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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?
 
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CaptDude said:
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
 
CaptDude said:
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.
 
CaptDude said:
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?
 
lol it takes physics to do physics!
 
PeterDonis said:
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....
 
CaptDude said:
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?
 
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PeterDonis said:
If there is only a single elementary particle in the universe, what measuring device would be used to measure its movement?

CaptDude said:
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.
 
DaveC426913 said:
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.
 
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