Particle Stability: Wave Packets & Target Interactions

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    Particle Stability
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Discussion Overview

The discussion revolves around the stability of particles conceptualized as wave packets, particularly in the context of their interactions with targets. Participants explore the implications of diffraction of different frequencies within wave packets and how this affects the integrity of particles during measurements and observations.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question how particles, viewed as wave packets with a range of frequencies, maintain stability after interacting with a target, suggesting that diffraction could disrupt this stability.
  • One participant proposes that the wave packet represents the quantum state rather than the particle itself, indicating that while the quantum state may spread out, it does not imply that the particle is physically splattered across space.
  • Another participant emphasizes that static observables like mass and charge remain constant despite the dynamic nature of wave functions, which apply to observables like position and momentum.
  • There is a discussion about the collapse of the wave function upon observation, with some participants agreeing that this is a standard interpretation, while others express differing views on the nature of this collapse.
  • One participant raises a conceptual issue regarding the term "particle," suggesting that it may mislead understanding, as particles like photons do not conform to traditional notions of solidity or boundaries.
  • There is a challenge regarding the reconciliation of observed momentum and mass at different locations, with participants debating the implications of having multiple wave functions for different properties of a particle.

Areas of Agreement / Disagreement

Participants express a range of views on the nature of particles and wave functions, with no clear consensus reached on the implications of wave packet behavior or the interpretation of quantum states. The discussion remains unresolved on several key points, particularly regarding the nature of particle identity and measurement outcomes.

Contextual Notes

Participants highlight limitations in the language used to describe particles, suggesting that terms like "particle" may not accurately convey the underlying physics. There is also an acknowledgment of the complexities involved in reconciling different aspects of particle behavior, such as momentum and mass, which may depend on the definitions and interpretations employed.

Who May Find This Useful

Readers interested in quantum mechanics, the nature of particles, and the philosophical implications of wave-particle duality may find this discussion relevant.

sphay
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If particles consist of wave packets, and thus a range of frequencies, how does the partciel stay intact after interacting with a target?

Wouldn't the different frequencies diffract at different angles thereby destroying the stability of the particle? Whilst I realize this problem was recognised a long time ago, I am finding it hard to recognise a coherent answer to this problem in the literature. Any views, pointers or clarification appreciated.
 
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sphay said:
Wouldn't the different frequencies diffract at different angles thereby destroying the stability of the particle? Whilst I realize this problem was recognised a long time ago, I am finding it hard to recognise a coherent answer to this problem in the literature. Any views, pointers or clarification appreciated.

Well, the answer is that the "wave packet" is not the particle itself, but its quantum state. And indeed, its quantum state will diffract all over the place. In quantum mechanics, this then means simply that the particle can now be found in different places, and that the amplitude of this quantum state, squared (in the position basis) will give you the probability of finding it in different places, and not that you will find "fractions" of the particle splattered all over the place.
 
If particles consist of wave packets, and thus a range of frequencies, how does the partciel stay intact after interacting with a target?

The wave description applies for dynamic observables, i.e. position, momentum, energy, direction of spin. Mass, charge, magnitude of spin and other static observables remain constant.
 
vanesch said:
And indeed, its quantum state will diffract all over the place. In quantum mechanics, this then means simply that the particle can now be found in different places
OK, then if I make an observation at B, the wave function collpases at that position, right?

Ratzinger said:
The wave description applies for dynamic observables, i.e. position, momentum, energy, direction of spin. Mass, charge, magnitude of spin and other static observables remain constant.
OK, so mass diffracts to one position at say A, (is not "splattered"), and A in general will be at a different location to B.

So how do we then reconcile an observed momentum at B, with the mass at A?
 
sphay said:
OK, then if I make an observation at B, the wave function collpases at that position, right?

That's a way to look upon it. It is not my way, but it is the "standard" way for sure. Especially for starters, it is the best way to see it.

OK, so mass diffracts to one position at say A, (is not "splattered"), and A in general will be at a different location to B.

So how do we then reconcile an observed momentum at B, with the mass at A?

Eh, you do not have different wavefunctions for different "aspects" of the particle. You will not have "momentum" in A, "mass" in B or something of the kind if that's what you want to suggest.

I think that the main confusion comes about by thinking that somehow the particle IS the quantum state. No, the quantum state is the DYNAMICAL DESCRIPTION of the particle. In the same way as "position and momentum" are the dynamical description of a particle in classical mechanics, but is not the particle itself, which is a postulated entity, in both theories. As such, it will keep all its "particle properties" *by postulate*. The wavefunction is just a means to find out where you'll find it after a measurement, or how fast you will find it moving, or so (in the same way as in the case of a classical dynamical state, except that there's now a random aspect to it).
 
If particles consist of wave packets, and thus a range of frequencies, how does the particle stay intact after interacting with a target?

Are some of these conceptual problems to do with words like "particle"? It suggests tiny billiard balls, and it just can't be like that. A photon is a propagating electromagnetic variation. It doesn't have a surface, or an edge. You can't pin it down. It isn't something intact in the first place.

Can anybody advise me on what a "particle" is?
 
OK, then if I make an observation at B, the wave function collpases at that position, right?

vanesch said:
That's a way to look upon it. It is not my way, but it is the "standard" way for sure.
I am curious then how you look upon it?
 

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