What do they mean by force particles exactly?

[Nano-Passion]

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?

 

[mathman]

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]

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)

So why do they keep calling it a particle so much if its not a particle?

 

[ZapperZ]

So why do they keep calling it a particle so much if its not a particle?

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]

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?

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.

 

[Nano-Passion]

First, I apology for my over-excitement haha, this is only just striking me to be interesting. However, don't mistaken that with a popular science fan-boy; its the math I'm really interested in.

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.

Actually at first I was uninterested in the standard model and particle physics because they kept conjuring everything up as particles. When I think of particles I usually envision the old view of matter. And I don't know why but I find particle physics much more exciting when I think of it from the point of view of quantum mechanics; including the wave-particle duality interpretation.

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.

This stuff sounds very interesting actually. I've always liked quantum field theory, quantum mechanics, etc. and general relativity but had a distaste for particle physics out of ignorance. Now I'm seeing the grander picture of physics and its beautiful!

I find it very interesting that there all these different "particles" going on. Please clarify this for me...

All these "particles" are different manifestations of wave functions(for lack of better words, I don't think that is the correct terminology). Different wave functions are classified and given names such as the pion, muon, etc. Force carriers such as w and z bosons are some type of ... okay I'm completely lost on what makes them different from other particles and what makes them force carriers.

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)

Gluons are very intriguing.. As I was researching on Brookhaven National Laboratory for an internship I stumbled upon a short video. It stated that the "gluon" force, for lack of better words, is the only known force that actually increases with distance!

Oh boy, I really can't dive into the mathematics of this now. Before quantum mechanics was interesting to me but now I see a whole different beast.

 

[juanrga]

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?

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).

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]

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).

Okay, interesting.

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.

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?

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.

 

[juanrga]

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.

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.

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?

I do not know how what I have said relates to what you say.

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.

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]

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).

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.

 

[cbetanco]

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.

I think you get confused about what is a particle, and what is a wave function. A wave function tells you the probability of finding the particle in a particular location, but the particle is not the wave function! The wave function is just describing the state of the particle in position space.

Also, the word oscillation in the context of neutrino oscillations has nothing to do with the wave particle duality in QM. The term oscillation comes from the fact that different flavors of neutrinos seem to change into each other (i.e. they oscillate between the different flavors, or types, of neutrinos). So don't confuse the term oscillation in this context with a wave oscillating, its a completely different concept. I would actually prefer the term neutrino mixing, as opposed to oscillation, but I didn't invent the term so I just go with it.

 

[juanrga]

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.

I have not said that you say. Of course, quantum mechanics continues being correct and working. Neutrino oscillations have nothing to see with waves, the neutrino is always a particle, the oscillation refers to flavor.

 

[Nano-Passion]

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]

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?

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).

 

[Nano-Passion]

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).

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.

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).

&

All particles are particles. They are not waves.

So then which is it??

 

[cbetanco]

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]

...And if you hypothetically shoot Neutrinos to a double slit it won't have interference patterns?

Yes - but you'd find it pretty hard to build a double-slit experiment for neutrinos!

 

[deccard]

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.

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]

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.

But you just told me that it has wave & particle like properties? So therefore wouldn't it be both a wave and a particle?

Yes - but you'd find it pretty hard to build a double-slit experiment for neutrinos!

Haha, which is why I added "hypothetical." =D

 

[juanrga]

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.

Effectively you misunderstood what I have said, but others already corrected you.

 

[juanrga]

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.

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 m_e mass and half spin, a photon has zero mass and spin 1, etc.

 

[PatrickPowers]

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?

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.

 

[Nano-Passion]

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.

Thank you! . I was going insane with members going back and forth of the particle and wave dilemma. You also had some big-picture insights in this, which helped.

 

[juanrga]

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.

Already Weinberg in his textbook in QFT warns to his readers that fields are not more fundamental than particles. In fact, in rigor a field is an unobservable entity. What we detect in experiments are particles as Weinberg notes correctly.

Moreover, there are formulations, as the action-at-a-distance QED, where fields are not used and, therefore, particles are not field excitations.

Physicists never used the word «particle» as synonym of «billiard balls».

It is confusing to say that a «big molecule like a buckyball has a wavelength» and wrong to say that everything has.

First a big molecule is not a quantum particle (a buckyball is not and nuclei structure is well-defined, otherwise it is not a buckyball).

The term wavelength is a property of a position representation of an one-body quantum state (incorrectly named one-body wavefunction in older and imprecise literature and giving many confusions as observed in this thread).

Precisely quantum field theory does not work in position representation but in the momentum representation and thus wavelengths are not even mentioned in scattering experiments.

 

[deccard]

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 m_e mass and half spin, a photon has zero mass and spin 1, etc.

Yes, that is true. But is there something in the SM or some other model that justifies the use of word "point"?

 

[juanrga]

Yes, that is true. But is there something in the SM or some other model that justifies the use of word "point"?

I am not sure, because in the SM, position x is not even an observable! Therefore, in rigor, you cannot say if a particle is spatially extended over a region of finite volume x³ or if it is point-like. These kind of questions are beyond the scope of the SM.

However, the particles in the SM are elementary, i.e. are not composite. And it is difficult to imagine (at least for me) a non-composite particle that was extended over a region of finite volume.

 

[QGP]

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?

 

[atyy]

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?

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.

 

[juanrga]

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?

Explained in the first paragraph of #24.

 

[QGP]

Explained in the first paragraph of #24.

What can't QED be explained using fields?

 

[Nano-Passion]

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.

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.

 

[cbetanco]

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.

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.

 

[belliott4488]

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.

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.

 

[Nano-Passion]

I'm starting to understand the gist of it a bit more. Thanks to everyone in this thread.

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.

Hm, thanks.

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.

Thank you.