Relativity fails with quantum particles?

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Discussion Overview

The discussion revolves around the implications of special relativity when applied to quantum particles, specifically muons, and the apparent contradictions arising from different reference frames. Participants explore the concepts of time dilation and length contraction in relation to the behavior of muons in various scenarios.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions the validity of special relativity by presenting a scenario involving a muon and a spaceship, suggesting that the outcomes differ based on the reference frame, which seems contradictory.
  • Another participant points out that the original poster has overlooked the concept of length contraction, emphasizing that all aspects of relativity must be considered together.
  • A third participant identifies the scenario as a variation of the "barn and pole paradox," which is typically resolved through the relativity of simultaneity.
  • Further clarification is provided that from the spaceship's perspective, the muon does not decay due to time dilation, while from the muon's perspective, it experiences a length-contracted spaceship, resulting in a brief interaction time.

    • Areas of Agreement / Disagreement

    Participants express differing views on the implications of special relativity, with some agreeing on the necessity of considering multiple aspects of the theory, while the original question remains unresolved.

    Contextual Notes

    The discussion highlights the complexity of applying special relativity to scenarios involving quantum particles and the potential for misunderstandings when not all principles are applied simultaneously.

PeterNoodles
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It seems to me there is a problem with special relativity - at least involving a particle which is commonly used as evidence to support it! Am I missing something?

Here it is:
A spaceship is stationary in space next to the moon. An interstellar muon traveling near the speed of light passes through the front of the ship, and - even though it's half life is much shorter than the time it should take to travel through to the back of the ship - it still survives to make it through the back end. This has been used to prove that time slows down as per SR when things travel fast.

Now, if instead, the muon is stationary, and the spaceship is traveling near the speed of light (the same as the muon was but in the opposite direction), the muon will be inside the spaceship for the same amount of time, but in this case it will decay before leaving the ship because it's time is not slowed.

So for the passengers of the ship, in one case the muon will decay, in the other, the muon will not decay. Where is the relativity?
 
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Hi PeterNoodles, welcome to PF

You remembered time dilation but forgot length contraction. You can't use one aspect of the theory in isolation, you need to use all three aspects together (time dilation, length contraction, relativity of simultaneity).
 
This looks like a variation on the classic "barn and pole paradox" which is resolved using relativity of simultaneity.
 
jtbell said:
This looks like a variation on the classic "barn and pole paradox" which is resolved using relativity of simultaneity.

I think Dale's description is all you need.

From the spaceship's point of view, you see a fast muon which doesn't decay because it's time dilated.

From the muon's point of view, you see a length contracted spaceship, so you spend very little time inside.
 
Very cool. So simple. Thanks!
 

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