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Concept of a particle?

by Farsight
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Farsight
#1
May26-06, 07:42 PM
P: 447
Marlon: I'm having a bit of a crisis about particles. Can you tell me, what is your concept of a particle?
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marlon
#2
May27-06, 02:16 AM
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Quote Quote by Farsight
Marlon: I'm having a bit of a crisis about particles. Can you tell me, what is your concept of a particle?
Hi Farsight,

Please, to post your questions, don't use this thread. Just create a new thread in the nuclei and particles subforum. As for your question, what do you mean by "concept of a particle" ?


regards
marlon
Nuclear on the Rocks
#3
May27-06, 05:23 AM
P: 11
a particle is evidently a distortion in space-time which basically implies that it may or may not have mass.however it must "exist" classically by affecting its field co ordinates.also it must in itself not exceed an atomic radius.conceptually even a beta particle is a partical whereas classically it is an electron.eventually the matter(as in discussed subject) justifies self answering.

Reshma
#4
May27-06, 09:32 AM
P: 777
Concept of a particle?

Quote Quote by Farsight
Marlon: I'm having a bit of a crisis about particles. Can you tell me, what is your concept of a particle?
A particle is a body having finite mass and internal structure but negligible dimensions.
neutrino
#5
May27-06, 09:49 AM
P: 2,046
Quote Quote by Reshma
A particle is a body having finite mass and internal structure but negligible dimensions.
As of today, that definition rules out the leptons and quarks (and Force-carrying bosons?) from being particles.
marlon
#6
May27-06, 09:52 AM
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Quote Quote by Reshma
A particle is a body having finite mass and internal structure but negligible dimensions.
That's a bit of a strange definition, no ? I mean i don't get the "internal structure" part. Does an electron have an internal structure ? If so, then what are elementary particles ?

I my opinion not particles but quantumfields are the most basic constituent of matter. Particles arise when such fields start to fluctuate. It is the energydifference dE associated with the transition from one field configuration to another that mimics a physical enetity with mass m and momentum p. This entity is what we call a particle. Keep in mind that both mass and momentum are concepts that come from classical physics. We just use them to describe the quantummechanical fenomena as well because such concepts are easy to grasp. For the same reason, the particle/wave duality does not imply that there are TWO ways in which nature can behave. This duality arises because we like to look at QM with "classical eyes"...




marlon
Reshma
#7
May27-06, 10:07 AM
P: 777
Quote Quote by marlon
That's a bit of a strange definition, no ? I mean i don't get the "internal structure" part. Does an electron have an internal structure ? If so, then what are elementary particles ?

I my opinion not particles but quantumfields are the most basic constituent of matter. Particles arise when such fields start to fluctuate. It is the energydifference dE associated with the transition from one field configuration to another that mimics a physical enetity with mass m and momentum p. This entity is what we call a particle. Keep in mind that both mass and momentum are concepts that come from classical physics. We just use them to describe the quantummechanical fenomena as well because such concepts are easy to grasp. For the same reason, the particle/wave duality does not imply that there are TWO ways in which nature can behave. This duality arises because we like to look at QM with "classical eyes"...




marlon
Sorry, I was just going by the definition of a "particle" and missed the keyword "elementary" . An elementary particle or fundamental particle would be a particle not known to have substructure.

Anyways, your quantum mechanical explanation takes care of any defintion of a particle. Since, we generally associate particles with matter, QM also takes in account of photons as particles.
marlon
#8
May27-06, 10:10 AM
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Quote Quote by Reshma
Sorry, I was just going by the definition of a "particle" and missed the keyword "elementary" . An elementary particle or fundamental particle would be a particle not known to have substructure.
But than the proton was not a particle prior to the detection of quarks (well partons to be exact but you get the point, right :)).

For this reason, I would not use the internal structure as a criterium.
Anyways, your quantum mechanical explanation takes care of any defintion of a particle. Since, we generally associate paticles with matter, QM also takes in account of photons as particles.
Well, the explanation i gave is not just the QM version, it's the quantum field's version (QFT).

Also, when talking about particles we refer to both matter and force carriers. Some force carriers do have mass (eg :W boson)

marlon
Rade
#9
May27-06, 04:57 PM
P: n/a
According to text by D. Bohm, 1951, Quantum Theory, page 24--a particle = an object that can always be localized within a certain minimum region, which we call its size.
marlon
#10
May27-06, 06:34 PM
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Quote Quote by Rade
According to text by D. Bohm, 1951, Quantum Theory, page 24--a particle = an object that can always be localized within a certain minimum region, which we call its size.
Ok, this is a definition that contains a lot of truth. But, don't you think we should be defining this "minimum region" ? I mean, let's take the photon as an example. A photon is not defined as a particle with finite spatial boundaries. The finite boundaries are defined in energy space. Photons are just chuncks of energy. What do you think ?

Regards

marlon
Rade
#11
May29-06, 08:54 PM
P: n/a
Quote Quote by marlon
Ok, this is a definition that contains a lot of truth. But, don't you think we should be defining this "minimum region" ? I mean, let's take the photon as an example. A photon is not defined as a particle with finite spatial boundaries. The finite boundaries are defined in energy space. Photons are just chuncks of energy. What do you think ?
Again, I refer to D. Bohm, p. 31, where he refers to photons as "equivalent particles" having energy = hv. I would think the issue of finite spatial boundary of a photon (or electron) results from the limitation on localizability that is inherent in the wave-particle nature of matter, but I may be incorrect.
Farsight
#12
Jun19-06, 08:07 PM
P: 447
Sorry, I didn't see this thread.

"In my opinion not particles but quantumfields are the most basic constituent of matter. Particles arise when such fields start to fluctuate. It is the energydifference dE associated with the transition from one field configuration to another that mimics a physical entity..."

Thanks for that Marlon. Sounds good to me. I presume the "chunks of energy" is just loose talk, a figure of speech?

Hey Rade, I wonder what D. Bohm would have thought of a photon that was a mile long?

http://www.lwca.org/


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