mathman said:Quantum mechanics applies. There are four fundamental forces, each of which has a force particle.
electromagnetism - photon
strong nuclear - gluon
weak nuclear - W and Z
gravity - graviton (hypothetical - it has not been discovered)
antonmek said:So why do they keep calling it a particle so much if its not a particle?
Nano-Passion said:Can someone shed light on this. I'm VERY interested in high-energy/particle physics and I would love to have a little insight on this till I can study this stuff mathematically.
Are they really particles? Or waves? Or both? Doesn't quantum mechanics apply?
ZapperZ said:Let's not get hung up on semantics, here. Physicists often give labels to things without having to think what it would sound like to the rest of the population. What is more important is understanding what the physics mean, rather than visualizing what the name conjures up.
Zz.
ZapperZ said:This is not just a "high energy/particle physics" issue. It is a more general formalism of quantum field theory. QFT is applicable in a huge variety of field, including condensed matter physics that is the domain of the stuff you use everyday in your electronics. Phonons, spinons, magnons, polarons, etc. are equivalent "force particles" that transfer interactions.
Zz.
mathman said:Quantum mechanics applies. There are four fundamental forces, each of which has a force particle.
electromagnetism - photon
strong nuclear - gluon
weak nuclear - W and Z
gravity - graviton (hypothetical - it has not been discovered)
Nano-Passion said:Can someone shed light on this. I'm VERY interested in high-energy/particle physics and I would love to have a little insight on this till I can study this stuff mathematically.
Are they really particles? Or waves? Or both? Doesn't quantum mechanics apply?
Okay, interesting.juanrga said:There are not particle forces: the correct term is interaction, not force.
Second, interactions in the Standard Model of particle physics are modeled using a kind special of particles that transmit the interaction (as a kind of messengers).
That's messy. I don't see things that small as particles, there is so much complexity that labeling it as a particle seems unattractive to me. The word particle to me comes off as the classical picture of neutrons and protons.. but now we know they are much more complex than that. Zapperz mentioned that its just semantics, that it doesn't mean that its a particle from what I picture? I'm confused now.Yes those particles are particles (all particles are particles, they are not waves).
The Standard Model is based in QFT, which is a quantum theory, but it is not equivalent to quantum mechanics.
Nano-Passion said:juanrga said:Yes those particles are particles (all particles are particles, they are not waves).
That's messy. I don't see things that small as particles, there is so much complexity that labeling it as a particle seems unattractive to me. The word particle to me comes off as the classical picture of neutrons and protons.. but now we know they are much more complex than that. Zapperz mentioned that its just semantics, that it doesn't mean that its a particle from what I picture? I'm confused now.
Nano-Passion said:juanrga said:The Standard Model is based in QFT, which is a quantum theory, but it is not equivalent to quantum mechanics.
That strikes me as rather counter-intuitive, in the sense that QFT is based from quantum mechanics and you state that standard model doesn't hold true to the wave-particle duality interpretation?
Nano-Passion said:EDIT: So you also consider something as the neutrino which has been very elusive and thought to have 0 mass, simply a particle?
To make sure we are not playing with semantics; I'm defining a particle as "a small localized object to which can be ascribed several physical properties such as volume or mass."
Doesn't the particle-wave duality hold? It wouldn't make sense otherwise, at least to me.
Can anyone confirm this?juanrga said:I do not know what do you mean by «the classical picture of neutrons and protons», but in the standard model of particle physics the concept of particle is well defined.
I do not know how what I have said relates to what you say.
The neutrino is one of the particles considered in the standard model.
In the Standard Model (SM), particles are not defined as you define them. In fact, I think that I have never found a definition as yours in any field of physics.
The «particle-wave duality» is a misname that has a historical basis, but that would be best abandoned from the language of modern physics. A particle (as defined in the SM) is always a particle and is always detected as a particle in experiments (e.g., at CERN).
Nano-Passion said:Can anyone confirm this?
Your saying that wave-particle duality no longer holds true after quantum mechanics.. when quantum mechanics is the basis of much of our knowledge today? So then why are they studying Neutrino oscillations?
I'm no expert and I don't have the mathematics behind this, can anyone else come in and put perspective on this.
Nano-Passion said:Can anyone confirm this?
Your saying that wave-particle duality no longer holds true after quantum mechanics.. when quantum mechanics is the basis of much of our knowledge today? So then why are they studying Neutrino oscillations?
I'm no expert and I don't have the mathematics behind this, can anyone else come in and put perspective on this.
Nano-Passion said:This has been bothering me for a while. I've been increasingly perplexed on what constitutes a wave and what doesn't?
And if you hypothetically shoot Neutrinos to a double slit it won't have interference patterns?
cbetanco said:Neutrinos will have an interference pattern, then obey the same rules as the other particles. But when one says neutrino oscillation, it means something else. It means that they are oscillating between different flavors (different types). Neutrinos still have a wave function AND they can change type (oscillate between flavors).
juanrga said:The «particle-wave duality» is a misname that has a historical basis, but that would be best abandoned from the language of modern physics. A particle (as defined in the SM) is always a particle and is always detected as a particle in experiments (e.g., at CERN).
juanrga said:All particles are particles. They are not waves.
Yes - but you'd find it pretty hard to build a double-slit experiment for neutrinos!Nano-Passion said:...And if you hypothetically shoot Neutrinos to a double slit it won't have interference patterns?
cbetanco said:The wave function (in the position basis) gives you the probability of finding the particle at a particular location, but that does not mean the wave function is the particle. Particles are still represented as point like objects.
cbetanco said:juanrga is right, particles are particles. The wave function is NOT the particle, it describes the state of the particle in position space (or momentum space, whichever basis you are using). The wave function (in the position basis) gives you the probability of finding the particle at a particular location, but that does not mean the wave function is the particle. Particles are still represented as point like objects.
AdrianTheRock said:Yes - but you'd find it pretty hard to build a double-slit experiment for neutrinos!
Nano-Passion said:Well, juanrga was saying that they are strictly particles and don't have wave-like properties [unless I misunderstood]. Which was my question in the first place.
deccard said:But how does this pointness manifest itself?
I mean, I can understand that if, let's say an electron, hits a thin atom layer and makes a hole in it. The size of the hole can be smaller than the "size" of the wave function.
Does the pointness only mean that an elementary particle does not have any internal structure?
I have really hard time to picture how any particle could be represented as a point like objects in the sense that it would have zero volume.
Nano-Passion said:Can someone shed light on this. I'm VERY interested in high-energy/particle physics and I would love to have a little insight on this till I can study this stuff mathematically.
Are they really particles? Or waves? Or both? Doesn't quantum mechanics apply?
PatrickPowers said:Here's my view, for whatever it is worth.
In Quantum Field Theory(QFT), developed circa 1950 and increasingly polished ever since, all of these tiny things are "field excitations" and described by the same mathematical model. For better or worse this term never caught on and scientists just call them "particles" even though they do not behave like billiard balls. It is confusing, but now you know. Field excitations. Everything has a wavelength. A big molecule like a buckyball has a wavelength and has been demonstrated to interfere with itself.
I used to think that the concept of particles conveying forces was a convenient mathematical abstraction, but I was wrong. If the right amount of energy is concentrated in a small enough area then the predicted theoretical particle will materialize. Usually it explodes immediately: it is an unstable field excitation. Right now CERN is trying to materialize the Higgs boson.
The pre-QFT, pre-1950 theory is called quantum mechanics.
PatrickPowers said:Here's my view, for whatever it is worth.
In Quantum Field Theory(QFT), developed circa 1950 and increasingly polished ever since, all of these tiny things are "field excitations" and described by the same mathematical model. For better or worse this term never caught on and scientists just call them "particles" even though they do not behave like billiard balls. It is confusing, but now you know. Field excitations. Everything has a wavelength. A big molecule like a buckyball has a wavelength and has been demonstrated to interfere with itself.
I used to think that the concept of particles conveying forces was a convenient mathematical abstraction, but I was wrong. If the right amount of energy is concentrated in a small enough area then the predicted theoretical particle will materialize. Usually it explodes immediately: it is an unstable field excitation. Right now CERN is trying to materialize the Higgs boson.
The pre-QFT, pre-1950 theory is called quantum mechanics.
juanrga said:Volume is not one of the properties that defines an elementary particle. An elementary particle in the SM is defined by properties as mass, spin...
An electron has me mass and half spin, a photon has zero mass and spin 1, etc.
deccard said:Yes, that is true. But is there something in the SM or some other model that justifies the use of word "point"?
QGP said:I have been looking for a thread like this for a long time. What I don't understand why particles are needed to explain force carriers rather than just using fields to explain forces. The idea seemed to be popularized by Feynman but I have failed to find why it is necessary. Anyone know?
QGP said:I have been looking for a thread like this for a long time. What I don't understand why particles are needed to explain force carriers rather than just using fields to explain forces. The idea seemed to be popularized by Feynman but I have failed to find why it is necessary. Anyone know?
What can't QED be explained using fields?juanrga said:Explained in the first paragraph of #24.
atyy said:Particle is just a bad, but standard name for a quantized excitation of a field. See ZapperZ's posts #4 & 5 for other "force carriers" in condensed matter physics.
Nano-Passion said:I would have rather heard the term "quantized excitation" than "particle" a loong time ago. Which is why I was frustrated with the thread earlier, there were too many inconsistencies with respect to terms and semantics.
You won't hear people use the expression "wave/particle duality" much in the context of modern quantum theory. It's more a term that was used in the early days (first half of the 20th century) when people were still struggling with the question of whether the fundamental constituents of nature were better described as particles or as waves.Nano-Passion said:I would have rather heard the term "quantized excitation" than "particle" a loong time ago. Which is why I was frustrated with the thread earlier, there were too many inconsistencies with respect to terms and semantics.
belliott4488 said:You won't hear people use the expression "wave/particle duality" much in the context of modern quantum theory. It's more a term that was used in the early days (first half of the 20th century) when people were still struggling with the question of whether the fundamental constituents of nature were better described as particles or as waves.
I prefer to say that both terms are classical in nature, and that neither one correctly (or completely) captures the behavior of quantum "entities". Rather, I like to think of everything as a quantum field. Such a thing can be observed, and in the process it will exhibit particle-like properties. To predict its behavior, however, you must propagate a field, which is where it exhibits wave-like behavior.
As for why the interactions are mediated by fields that can exhibit particle-like behavior - they just do. The oldest example is the photon, whose existence Einstein first postulated in 1905 in his photoelectric effect paper - the electromagnetic field was behaving like a particle. Nowadays W and Z particles leave traces in particle detectors, i.e. they behave like particles. But they also mediate the electroweak interaction - they just do.
I suppose you could say that these fields behave like particles when they are observed and like waves when they propagate ... but I'd rather just say that they behave like quantum fields and leave it at that.
cbetanco said:In post 24, juanrga already points out that fields are not more fundamental than particles. So while it is useful to think of particles as excitation of fields, and indeed the one particle states of a particle at a position x in QM can be written as |x>=\psi (x) |0>, where |0> is the vacuum state and \psi (x) is the field at point x. That is, when a field operates on the vacuum, it creates a particle at point x.
Perhaps your confusion is that you are thinking of a particle in the traditional sense, that is a infinitely small billard ball with a definite position. In field theory, particles are really irreducible representations of the Poincare group and some gauge groups (U(1), SU(2), etc.). I like to think of them as little chunks of the symmetry of our universe, but maybe this is not entirely correct. That is, to me the universe has some symmetry, and particles are the simplest form of how the symmetry manifests itself.
