Particles VS Quanta

[Eldad Eshel]

Carriers of forces are generally called virtual particles, a very confusing term. I think this term should
be abandoned, in favor of the term "carriers of the force" or .. something better. These are not particles at all, but are quanta of the force in question. Basically forces break up into quanta, just like electromagnetic energy, they are also a type of energy. The term "virtual photons" is even more confusing, leading you to think these are some kind of photon, when it isn't. It should be clear that not everything is a particle, and so also their names should be in accordance. Even the photon isn't a particle, but a quanta of electromagnetic energy. Maybe a new term is needed here too. Well the term quanta seems best.

[John Cuthber]

OK, you don't understand it so we should rewrite all the text books.
well, it's a point of view...

 

Incidentally re "Even the photon isn't a particle"; well it sure acts like one.

[Phi for All]

In much the same way, the term "nose" is very confusing, since it sounds like it's a plural word, like "eyes", but you only have one of them. And "nose" sounds like it's intelligent, but it's not. It runs but has no legs, and it constantly smells.

 

Therefore, we need to start using the term "Donald" instead of "nose", because I said so.

[ajb]

Virtual has a specific meaning in quantum field theory, maybe it is not the best term one could think of, but it is now the standard one.

 

To understand any of this you need some basic knowedge of perturbation theory in quantum field theory. Thankfully, you only need to recognise Feynman diagrams. A virtual particle is the particle (i.e., the quanta) associated with an internal line of a Feynman diagram. And as such they are not constrained to obey the classical equations of motion.

 

So-called 'physical particles' are then the external lines. However, this is not quite right as these external legs of a Feynman diagram correspond to asymptotically free particles. All particles that we can measure, we measure via their interactions and so everything we detect is 'off mass-shell' (does not obey the classical equations of motion), it is just that they are only off mass-shell by a tiny amount and so we do think of free particles.

Edited May 16, 2016 by ajb

[Strange]

Carriers of forces are generally called virtual particles, a very confusing term.

 

 

 

This is one of the best non-technical explanations of this I have seen: https://profmattstrassler.com/articles-and-posts/particle-physics-basics/virtual-particles-what-are-they/

 

"The best way to approach this concept, I believe, is to forget you ever saw the word “particle” in the term. A virtual particle is not a particle at all."

 

[elfmotat]

OK, you don't understand it so we should rewrite all the text books.

well, it's a point of view...

 

Incidentally re "Even the photon isn't a particle"; well it sure acts like one.

 

In much the same way, the term "nose" is very confusing, since it sounds like it's a plural word, like "eyes", but you only have one of them. And "nose" sounds like it's intelligent, but it's not. It runs but has no legs, and it constantly smells.

 

Therefore, we need to start using the term "Donald" instead of "nose", because I said so.

 

I don't think you guys are being very fair. While I agree 'virtual particles' are well-defined (namely, internal lines in Feynman diagrams), and that it would be hard/impossible to change the term, I also think the term is confusing. See e.g. the link Strange provided.

 

Perhaps the biggest thing to note about virtual particles is that they only make sense in perturbative QFT. They are mathematical objects (propagators) that arise from a Taylor series approximation of the full theory. People (i.e. popsci documentaries) attribute much more meaning to them than they should really have.

Edited May 16, 2016 by elfmotat

[John Cuthber]

What happens when one of a pair of virtual particles falls into a black hole?

[elfmotat]

What happens when one of a pair of virtual particles falls into a black hole?

 

I understand the point you're making (that this results in Hawking radiation), but really you're oversimplifying things a lot. It's not nearly so simple as "virtual particles are created, one falls in and the other is ejected." That's a nice picture that humans have an easy time visualizing, but again, speaking in terms of virtual particles only makes sense in perturbation theory. The full, non-perturbative model of interacting quantum fields on a Schwarzschild background would describe what's going on better, and with no such reference to internal lines on Feynman graphs.

[Strange]

What happens when one of a pair of virtual particles falls into a black hole?

 

 

That is also a rather poor analogy to what the maths says (even though both the maths and the analogy are due to Hawking).

 

I posted a couple of links about this before but didn't keep them....

Edited May 16, 2016 by Strange

[John Cuthber]

 

I understand the point you're making (that this results in Hawking radiation), but really you're oversimplifying things a lot. It's not nearly so simple as "virtual particles are created, one falls in and the other is ejected." That's a nice picture that humans have an easy time visualizing, but again, speaking in terms of virtual particles only makes sense in perturbation theory. The full, non-perturbative model of interacting quantum fields on a Schwarzschild background would describe what's going on better, and with no such reference to internal lines on Feynman graphs.

I'm allowed to oversimplify physics- I'm a chemist.

However, as you have pointed out, the "particles" are only a handy way to visualise what's happening without doing "jolly hard maths" (JHM).

I can't imagine Eldad doing the JHM so he's stuck with an imperfect model .

(Nothing to be ashamed of- the JHM is over my head too; I used to be able to do time dependent perturbation theory, but that was many years ago, and I wasn't good at it then).

Sometimes there just isn't an easy answer.

[Phi for All]

I don't think you guys are being very fair.

 

It's not the first time I've encountered this "I don't get it, so it should be changed" argument from Eldad. I've tried reason and I've tried encouragement. This time I tried to show the absurdity, but I guess I failed.

[elfmotat]

I'm allowed to oversimplify physics- I'm a chemist.

However, as you have pointed out, the "particles" are only a handy way to visualise what's happening without doing "jolly hard maths" (JHM).

I can't imagine Eldad doing the JHM so he's stuck with an imperfect model .

(Nothing to be ashamed of- the JHM is over my head too; I used to be able to do time dependent perturbation theory, but that was many years ago, and I wasn't good at it then).

Sometimes there just isn't an easy answer.

 

True. I think the key (for Eldad and others) is to recognize when things are being simplified to make them easier to explain and visualize without the JHM, but that at the end of the day the JHM is what defines the theory. Many tend to take analogies, mathematical objects with physical-sounding names, etc., too seriously and derive meaningless predictions by extrapolation.

 

 

It's not the first time I've encountered this "I don't get it, so it should be changed" argument from Eldad. I've tried reason and I've tried encouragement. This time I tried to show the absurdity, but I guess I failed.

 

Fair enough. I haven't been around for a while, so I'm unfortunately no longer "in the loop" in regard to many users' habits.

[Eldad Eshel]

A question that rises from modern physics is - Is our universe really that complicated ? I personally think that the answer is - no.

And that overall things needs to be simplified, mainly in theory. (Math is math.) Not because I don't understand it, but because the nature of the universe isn't really as complicated as modern physics make it look like. Such a basic force like electromagnetism should also be able to be described in a basic and simple way. And without such a confusing term as virtual particles.

Edited May 17, 2016 by Eldad Eshel

[ajb]

Perhaps the biggest thing to note about virtual particles is that they only make sense in perturbative QFT.

In the context of QFT, particles full stop only make sense in perturbation theory and in flat space-times (or similarly nice space-times).

 

 

A question that rises from modern physics is - Is our universe really that complicated ?

Well, quantum field theory has proved to be a good framework to discuss the fundamental interactions of nature, with the exception of gravity. In this sense, nature 'is' that complicated.

 

I personally think that the answer is - no.

Based on what?

 

You should not just make this statement without some reasoning. And the reason 'because I don't understand modern physics' is not enough.

 

And that overall things needs to be simplified, mainly in theory. (Math is math.) Not because I don't understand it, but because the nature of the universe isn't really as complicated as modern physics make it look like. Such a basic force like electromagnetism should also be able to be described in a basic and simple way. And without such a confusing term as virtual particles.

 

Well, people would like to build such models. But like I said, QFT seems to be a great framework for describing fundamental interactions. The standard model had been tested to some huge degree of accuracy. It is not at all clear what would replace QFT and the methods of perturbation theory. You can of course look at non-perturbative methods, generally these are either looking at 'special' solutions like instantons or using numerical methods (Lattice Field Theory). Either way, we still think that QFT is the best framework we have right now.

 

Maybe some better framework will appear, or better methods... who knows?

[Strange]

A question that rises from modern physics is - Is our universe really that complicated ? I personally think that the answer is - no.

And that overall things needs to be simplified, mainly in theory. (Math is math.) Not because I don't understand it, but because the nature of the universe isn't really as complicated as modern physics make it look like. Such a basic force like electromagnetism should also be able to be described in a basic and simple way. And without such a confusing term as virtual particles.

 

There are simpler explanations. However, they suffer from the, not insignificant, disadvantage of being wrong.

[swansont]

A question that rises from modern physics is - Is our universe really that complicated ? I personally think that the answer is - no.

And that overall things needs to be simplified, mainly in theory. (Math is math.) Not because I don't understand it, but because the nature of the universe isn't really as complicated as modern physics make it look like. Such a basic force like electromagnetism should also be able to be described in a basic and simple way. And without such a confusing term as virtual particles.

 

 

What justification do you have for this claim?

[Phi for All]

A question that rises from modern physics is - Is our universe really that complicated ? I personally think that the answer is - no.

And that overall things needs to be simplified, mainly in theory. (Math is math.) Not because I don't understand it, but because the nature of the universe isn't really as complicated as modern physics make it look like. Such a basic force like electromagnetism should also be able to be described in a basic and simple way. And without such a confusing term as virtual particles.

 

This is wishful, incredulous thinking, not science. It's very common for humans to desire simplicity in the face of sometimes overwhelming complexity. But that doesn't mean the universe has to comply with human wishes.

 

Science isn't about shortcuts and cutting corners. A theory can only be made so simple before becoming worthless as an explanation for a particular phenomenon.

[Eldad Eshel]

I can actually take QED and make it simpler. It is mainly in the terms used. What I do is I look at the electromagnetic forces as bssic forces in the universe, sort of like the electron is a basic particle with basic properties. The basic layout of our universe, made to work and create. Then I take the "virtual photons" (probably the most confusing term) and see them as quanta of the electric field. Particles also emit photons in their turn, but these two aren't necessarily related.

[ajb]

I can actually take QED and make it simpler.

So have developed some calculation methods for QED that are simpler to use than the standard ones?

 

If not then... well I am not sure what to say.

[Strange]

I can actually take QED and make it simpler. It is mainly in the terms used. What I do is I look at the electromagnetic forces as bssic forces in the universe, sort of like the electron is a basic particle with basic properties. The basic layout of our universe, made to work and create. Then I take the "virtual photons" (probably the most confusing term) and see them as quanta of the electric field. Particles also emit photons in their turn, but these two aren't necessarily related.

 

Can you show that the results calculated in this way match experiment to the same high accuracy as the standard method?

[Eldad Eshel]

The math I believe stays the same. But the theory is a bit different. Or am I missing something ?

[Strange]

The math I believe stays the same. But the theory is a bit different. Or am I missing something ?

 

The math is the theory. If the theory is different then how can the math be the same?

 

If you are not simplifying the math then you are not simplifying anything. (Except, perhaps, the story you tell yourself to pretend you understand.)

[ajb]

The math I believe stays the same. But the theory is a bit different. Or am I missing something ?

As above, the mathematics is the theory.

 

All you might have done is offer an interpretation. However, as I do not think you know the calculations well I doubt you really have a new or novel interpretation.

 

Just renaming some of the concepts is not really adding anything new. Moreover, one should try to avoid calling known concepts by new names. It just adds confusion. (It sometime happens in the literature that old concepts are rediscovered with new names )