Open or closed Casimir system?

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Discussion Overview

The discussion revolves around whether a system exhibiting the Casimir effect, specifically two plates attracting each other in a vacuum, should be classified as an open or closed system. Participants explore definitions and implications of these terms in the context of classical and quantum physics.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants question the definitions of open and closed systems, particularly in relation to the Casimir effect.
  • One participant suggests that a closed system is defined as one where no energy or matter enters or leaves, while an open system allows for such exchanges.
  • Another participant proposes that in the case of two plates in a vacuum, there is no energy or matter entering or leaving the system.
  • Some participants introduce the concept of virtual photons, debating whether they should be considered as part of the system or as entering/leaving it.
  • One participant argues that the presence of the plates alters the vacuum state, leading to the force that attracts the plates, implying that nothing is entering or leaving the system.
  • There is a discussion on the relationship between conservative forces and system classification, with a participant noting that conservative forces are not necessarily limited to closed systems.

Areas of Agreement / Disagreement

Participants express differing views on the definitions of open and closed systems, particularly in the context of the Casimir effect. There is no consensus on how to classify the system, and the discussion remains unresolved.

Contextual Notes

Participants acknowledge that the definitions of open and closed systems may vary depending on classical versus quantum interpretations, and there are unresolved questions regarding the role of virtual photons in this classification.

gildomar
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If you had the Casimir effect pushing two plates together, would that be an open or closed system? And why? I haven't been able to find a satisfying answer/explanation to that.
 
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gildomar said:
would that be an open or closed system?

What is your definition of these terms?
 
That's the thing: I'm not sure how they'd be defined here. It's obviously easy if you have a classical system, but things get fuzzy when you have virtual energy.
 
gildomar said:
It's obviously easy if you have a classical system, but things get fuzzy when you have virtual energy.

I'm not sure why you would think so. But let's start with the classical definition: what do you think that is?
 
Isn't it closed if no energy/matter is entering or leaving the system, and open otherwise?
 
gildomar said:
Isn't it closed if no energy/matter is entering or leaving the system, and open otherwise?

That'll work. Now, if we have two plates sitting in vacuum, nothing else present, what energy or matter could be entering or leaving the system?
 
Possibly the virtual photons. But due to their nature, I'm not sure if that would constitute entering/leaving the system, or if they would be considered to be already part of the system. Hence my confusion.
 
gildomar said:
Possibly the virtual photons.

The virtual photons are part of the system. They aren't coming in from outside.

More precisely, "virtual photons" is only a heuristic way of describing what is causing the Casimir Effect. A better way is to say that the presence of the plates changes the vacuum state between the plates, in such a way as to create a force that attracts the plates to each other.

But no matter how you describe it, it should be evident that there is nothing entering or leaving the system as a whole; you could draw a boundary around the whole apparatus and measure energy flow across the boundary and find that it is zero. That's part of the specification of the scenario.
 
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Fair enough. Would that also be related to it apparently being a conservative force?
 
  • #10
gildomar said:
Would that also be related to it apparently being a conservative force?

Not really; conservative forces are not limited to closed systems, unless you want to consider the entire universe as part of the "system".
 
  • #11
Fair point. :P
 

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