I What Came First the Magnet or the Field?

[Dadface]

Below I paraphrase David Tong from:

David Tong -- What is Quantum Field Theory? You can find this by googling.

1. "According to our best laws of physics the fundamental building blocks of nature are fields."

2." Every particle in the universe ... is a tiny ripple of the underlying field"

According to basic school physics if we move the magnet we move the field. But it seems that according to QFT it's sort of the other way round and to move the magnet we must move the field. The only way I can think of moving the field is by moving something else, for example moving a second magnet. It's a bit chicken and egg.

So is the field more fundamental than the particles of the magnet? Or, perhaps, should particles and fields share equal dominance as being considered as fundamental?

 

[Vanadium 50]

. But it seems that according to QFT it's sort of the other way round and to move the magnet we must move the field.

How on Earth did you get that?

 

[Dadface]

How on Earth did you get that?

I got it from the article I referred to where it was stated that fields (not particles) are the "fundamental building blocks of nature".. One way I see of interpreting that is to assume that to make changes to the particles you need to make changes to the fields. But traditionally it's the other way round which is to make changes to the fields you need to make changes to the particles eg move the magnet. I imagine particles and fields as being interlinked as a particle/field construct and I can't see why one aspect of that construct, namely the field aspect should be considered as being more fundamental than the other aspect.

Sorry I tried to include a link but it didn't work.

 

[atyy]

In QFT, the magnet is also made from fields.

 

[Dadface]

In QFT, the magnet is also made from fields.

And particles.

 

[atyy]

And particles.

Particles are excitations of fields.

 

[Ben Wilson]

And particles.

the 'magnet' and the 'magnetic field' are different things, so they are described with different fields.

 

[Dadface]

Particles are excitations of fields.

Changes in fields can cause changes in particles.
Changes in particles can cause changes in fields.
What came first?

 

[Dadface]

the 'magnet' and the 'magnetic field' are different things, so they are described with different fields.

Not sure about the point being made. What of the two different fields describes the magnetic field?

 

[Ben Wilson]

Not sure about the point being made. What of the two different fields describes the magnetic field?

two fields do not describe the magnetic field. the magnetic field is ONE field, the magnetic field. however, with your taking about a magnet and a magnetic field: particles are electron* and photon, fields are electron and electromagnetic respectively.

*for example

 

[Ben Wilson]

Changes in fields can cause changes in particles.
Changes in particles can cause changes in fields.
What came first?

no that's a sloppy description of what's going on, particles are excitations of a quantum field.

 

[Dadface]

the 'magnet' and the 'magnetic field' are different things, so they are described with different fields.

two fields do not describe the magnetic field. the magnetic field is ONE field, the magnetic field. however, with your taking about a magnet and a magnetic field: particles are electron* and photon, fields are electron and electromagnetic respectively.

*for example

It was you who suggested that the magnetic field is described by a field (post 7). That was unclear but now you've cleared it up. But I still don't see the relevance of your comments.

 

[Ben Wilson]

It was you who suggested that the magnetic field is described by a field (post 7). That was unclear but now you've cleared it up. But I still don't see the relevance of your comments.

when you move the magnet what particles are you moving?

 

[Dadface]

no that's a sloppy description of what's going on, particles are excitations of a quantum field.

I'm not disagreeing that particles can be described as excitations of the field. I quoted David Tongs description of a particle in post one and I did not dispute atyy's definition, which is worded in the same way as yours in post six. So to make it clear I am not disputing anything about QFT. In fact I don't know enough about it yet to be able to do that.
What I am questioning is the assumption that fields are more fundamental than particles. And I am doing that by reference to changes. So why is my reference to changes in post 8 an example of sloppy thinking? Please take another look at post one.

 

[Ben Wilson]

I'm not disagreeing that particles can be described as excitations of the field. I quoted David Tongs description of a particle in post one and I did not dispute atyy's definition, which is worded in the same way as yours in post six. So to make it clear I am not disputing anything about QFT. In fact I don't know enough about it yet to be able to do that.
What I am questioning is the assumption that fields are more fundamental than particles. And I am doing that by reference to changes. So why is my reference to changes in post 8 an example of sloppy thinking? Please take another look at post one.

I do not mean sloppy thinking, just a sloppy description in an academic sense, i.e. not very pedantic or precise. I'm saying that when these things are more clear and defined, the chicken and egg problem goes away in my view.

 

[Dadface]

when you move the magnet what particles are you moving?

To a large extent that depends on the system within which the magnet is moved.

 

[Ben Wilson]

To a lsrge extent that depends on the system within which the magnet is moved.

I'm asking you what particles the 'magnet', e.g. an iron bar magnet, is made of? its electrons, which are not excitations of the magnetic field, but they do 'cause' the magnetic field in some physical sense.

 

[Dadface]

I'm asking you what partices the 'magnet', e.g. a simple bar magnet, is made of.

I think we both know the answer to that but what's the point of the question?

 

[Dadface]

Will be back here later on.

 

[tech99]

Below I paraphrase David Tong from:

David Tong -- What is Quantum Field Theory? You can find this by googling.

1. "According to our best laws of physics the fundamental building blocks of nature are fields."

2." Every particle in the universe ... is a tiny ripple of the underlying field"

According to basic school physics if we move the magnet we move the field. But it seems that according to QFT it's sort of the other way round and to move the magnet we must move the field. The only way I can think of moving the field is by moving something else, for example moving a second magnet. It's a bit chicken and egg.

So is the field more fundamental than the particles of the magnet? Or, perhaps, should particles and fields share equal dominance as being considered as fundamental?

You can move the magnet by means other than the magnetic field maybe? A magnet contains charges, which although in motion, might perhaps be moved by an electric field?

 

[Dadface]

You can move the magnet by means other than the magnetic field maybe? A magnet contains charges, which although in motion, might perhaps be moved by an electric field?

Yes there are different ways of moving the magnet.

 

[Ben Wilson]

Yes there are different ways of moving the magnet.

what particles are your magnets made of? If you pick somethin then i can explain the qft behind it and answer your question

 

[Dadface]

what particles are your magnets made of? If you pick somethin then i can explain the qft behind it and answer your question

Lets go with up and down quarks and electrons.

 

[Ben Wilson]

Lets go with up and down quarks and electrons.

Just focusing on the one important particle for magnetic fields out of those, electrons are excitations of an electric field. Interacting electrons exchange photons between each other and even themselves because the dynamics of the electron field is coupled with the electromagnetic field in a QED. Photons are excitations of the electromagnetic field. If you move the 'magnet', you will move the electrons. The electrons will interact through the electromagnetic interaction in the new place, giving excitations of the em field.

magnets rarely use nuclei as their magnetic moment is thousands of times smaller than electrons, however MRI scanners utilize the magnetic properties of nuclei.

 

[Ben Wilson]

According to basic school physics if we move the magnet we move the field. But it seems that according to QFT it's sort of the other way round and to move the magnet we must move the field. The only way I can think of moving the field is by moving something else, for example moving a second magnet. It's a bit chicken and egg.

you say to move the magnet we must move the field. Now you have to distinguish between em(magnetic) field or electron field.

 

[PeterDonis]

According to basic school physics if we move the magnet we move the field. But it seems that according to QFT it's sort of the other way round and to move the magnet we must move the field.

No, according to QFT moving the magnet is moving the field. Everything is fields--you are fields, so when you move the magnet it is fields moving fields.

You need to stop and seriously think about what "fields are the fundamental building blocks of everything" actually means.

 

[Demystifier]

Lets go with up and down quarks and electrons.

What you fail to understand is that electric and magnetic field are not the only fields out there. There is also quark field, electron field, etc. The world is not made of particles and fields. Instead, according to QFT, the world is made of fields. It doesn't mean that particles do not exist. They do, but they are made of fields too.

 

[Dadface]

Thank you everyone who commented but before I reply to specific comments may I please ask you to look again at my original post..

 

[weirdoguy]

may I please ask you to look again at my original post..

I think that you should look at it again. It seems that you completely don't uderstand what "particles are excitations of fileds" imply.

 

[Dadface]

What you fail to understand is that electric and magnetic field are not the only fields out there. There is also quark field, electron field, etc. The world is not made of particles and fields. Instead, according to QFT, the world is made of fields. It doesn't mean that particles do not exist. They do, but they are made of fields too.

I know from my comments it may seem that I don't know about other fields but I do. At odd times during the last few weeks I've been reading up on the subject. In the article I referred to David Tong stated:

"The most familiar example of fields are the electric and magnetic field."

I used the example of a magnet because it's familiar.

 

[Dadface]

No, according to QFT moving the magnet is moving the field. Everything is fields--you are fields, so when you move the magnet it is fields moving fields.

That's fine. I'm not disagreeing with the theory at all. Moving the magnet moves the field. but that can also be described as moving the magnet moves the particles. And fields moving fields can be described as particles moving particles.You need to stop and seriously think about what "fields are the fundamental building blocks of everything" actually means.

I have thought seriously about it and I am still doing so. Consider the following part statement from David Tong:

"Every particle is a ripple of the underlying field."

From this, in my imagination and depending what the field is, I see ripples as particles. For example for one type of field I can see electrons. And I see that the electrons have certain properties which can be measured. And I see that the electrons can be moved and that there are various ways of doing this. I could go on but in summary I am fairly confident in saying that we can make observations on those areas of the underlying field where there are ripples in other words observations on particles. And we can make most (if not all) of these observations without any knowledge of the non ripply parts of the field, or indeed any knowledge of QFT.

But my imagination spreads to other areas of the underlying field where there are no ripples. And here I get stuck. If the non ripply parts have properties how do we make observations on those properties without making reference to, or observations about, the ripply parts? It can seem that the observations we can make on the ripply parts, the particles, can be made without recourse to observations on the non ripply parts. But it doesn't work the other way round.

Now if we go right back to basics we should remember that all theories are based on observations and if a theory is any good it should conform to observations. Observations are the starting point of every theory and as far as QFT is concerned observations are made on the particles, the ripply parts, not on the non ripply parts. So I would suggest that from a point of view of what it is possible to observe, particle properties are fundamental .We can observe particle properties without recourse to QFT.

 

[Dadface]

I think that you should look at it again. It seems that you completely don't uderstand what "particles are excitations of fileds" imply.

What gave you that impression?

 

[Ben Wilson]

From this, in my imagination and depending what the field is, I see ripples as particles. For example for one type of field I can see electrons. And I see that the electrons have certain properties which can be measured. And I see that the electrons can be moved and that there are various ways of doing this. I could go on but in summary I am fairly confident in saying that we can make observations on those areas of the underlying field where there are ripples in other words observations on particles. And we can make most (if not all) of these observations without any knowledge of the non ripply parts of the field, or indeed any knowledge of QFT.

This part is incorrect, which is why you get stuck at the next part.

 

[Dadface]

I have thought seriously about it and I am still doing so. Consider the following part statement from David Tong:

"Every particle is a ripple of the underlying field."

From this, in my imagination and depending what the field is, I see ripples as particles. For example for one type of field I can see electrons. And I see that the electrons have certain properties which can be measured. And I see that the electrons can be moved and that there are various ways of doing this. I could go on but in summary I am fairly confident in saying that we can make observations on those areas of the underlying field where there are ripples in other words observations on particles. And we can make most (if not all) of these observations without any knowledge of the non ripply parts of the field, or indeed any knowledge of QFT.

But my imagination spreads to other areas of the underlying field where there are no ripples. And here I get stuck. If the non ripply parts have properties how do we make observations on those properties without making reference to, or observations about, the ripply parts? It can seem that the observations we can make on the ripply parts, the particles, can be made without recourse to observations on the non ripply parts. But it doesn't work the other way round.

Now if we go right back to basics we should remember that all theories are based on observations and if a theory is any good it should conform to observations. Observations are the starting point of every theory and as far as QFT is concerned observations are made on the particles, the ripply parts, not on the non ripply parts. So I would suggest that from a point of view of what it is possible to observe, particle properties are fundamental .We can observe particle properties without recourse to QFT.

This part is incorrect, which is why you get stuck at the next part.

I know you're trying to be helpful and I'm grateful for that but I can't see what you think is wrong with the first paragraph of the post. Let me summarise and break the paragraph down:

1. Ripples in the field are particles
2. In one type of field electrons are the particles.
3. Electrons have properties that can be measured
4. Electrons can be moved.
5. We are able to make observations on electrons without any knowledge of QFT

What's wrong with it?
Thank you

 

[Ben Wilson]

I know you're trying to be helpful and I'm grateful for that but I can't see what you think is wrong with the first paragraph of the post. Let me summarise and break the paragraph down:

1. Ripples in the field are particles
2. In one type of field electrons are the particles.
3. Electrons have properties that can be measured
4. Electrons can be moved.
5. We are able to make observations on electrons without any knowledge of QFT

What's wrong with it?
Thank you

1. Particles are excitations of a field.
2. Electrons are excitations of the electron field.
3. These Excitations display themselves as physical phenomena that we can observe.
4. How can you move a single electron?
5. What observations do you mean?

Also QFT is deeply layered, and doesn't translate well into analogies like ripples in sheets.

 

[bhobba]

Also QFT is deeply layered, and doesn't translate well into analogies like ripples in sheets.

And that is the real answer.

Its fields of quantum operators. Mathematical abstractions used to describe reality, whatever that is. Only by studying QFT can you appreciate it.

The book to delve into it is the following
https://www.amazon.com/dp/3319367560/?tag=pfamazon01-20

But it is just the start.

The real question is why are symmetries so important in physics. We simply do not know but it is without doubt the deepest discovery mankind has ever made, yet outside of physics hardly ever talked about.

Thanks
Bill

 

[Dadface]

I know you're trying to be helpful and I'm grateful for that but I can't see what you think is wrong with the first paragraph of the post. Let me summarise and break the paragraph down:

1. Ripples in the field are particles
2. In one type of field electrons are the particles.
3. Electrons have properties that can be measured
4. Electrons can be moved.
5. We are able to make observations on electrons without any knowledge of QFT

What's wrong with it?
Thank you

1. Particles are excitations of a field.
2. Electrons are excitations of the electron field.
3. These Excitations display themselves as physical phenomena that we can observe.
4. How can you move a single electron?
5. What observations do you mean?

Also QFT is deeply layered, and doesn't translate well into analogies like ripples in sheets.

Your summary points 1,2 and 3 are paraphrases of my summary points.
4 You know as well as I do some methods by which an electron can be moved. I'll just mention a couple of key words: ionisation,collision.
5 Observations include measurements eg of bare charge and mass. Some, of the methods used eg the use of mass spectrometry can be explained in terms of classical physics.
I think the analogies are used for the sake of brevity. You used an analogy in post 24.

 

[Ben Wilson]

Your summary points 1,2 and 3 are paraphrases of my summary points.
4 You know as well as I do some methods by which an electron can be moved. I'll just mention a couple of key words: ionisation,collision.
5 Observations include measurements eg of bare charge and mass. Some, of the methods used eg the use of mass spectrometry can be explained in terms of classical physics.
I think the analogies are used for the sake of brevity. You used an analogy in post 24.

Where is there an analogy in post 24?
Honestly, these questions aren't just to annoy. I have a problem with the wording you have used from a technical standpoint and i need to clarify what you mean with the terms that you are using. As others have said, the fields in qft are not a mental picture of what's going on at the particle scale, they are rigorously defined mathematical concepts that allow calculations to be made about observable phenomena; we as humans can then infer ripples in sheets as particles but this is not qft.
1.2.3. not paraphrased but made more precise, particles are not 'ripples' unless you had a precise mathematical description of what you mean by a ripple. When i say excitation, I know what i mean on a technical level, as I understand the concept of excitation from ordinary quantum mechanics.

4. I do not know as well as you do. I personally do not know how to move a single electron, QFT makes it possible (as far as my understanding goes) for there to be only one electron in the entire universe. How can i move this one electron by means of collision with another electron, when i only have one electron for instance. the point is that the particle picture is insufficient to describe 'moving an electron' if you intend to view the world through qft.

5. mass and charge are properties of quantum fields.

there's a subtle difference between brevity and poetry, brevity can still be technical but electrons are ripples is an analogy which is removed from the mathematical truth. you are trying to understand a quantum field in terms of other things. see http://www.damtp.cam.ac.uk/user/tong/qft/qft.pdf , if you don't understand this course then learn the prerequisites or accept that all analogies of an electron or a magnet or any quantum phenomena will be incomplete and insufficient. This is the nature of quantum mechanics.

 

[SEG]

@Dadface, it's a nice question about the foundations of physics. However, quantum fields are no building blocks, the combined fields are the structure of the universe. And phenomena like particles are no ripples but concentrations of quanta that emerge from the "primary" quantum fields (existend everywhere in the universe). That's why the electromagnetic field of an electron is a local quantum field. Without the electron, there is no electromagnetic electron field although the electron and the electromagnetic electron field emerge from the "underlying" primary quantum fields (vector field and scalar field).
Unfortunately, the biggest problem in theoretical physics is the existence of so many different concepts (hypotheses) and the lack of consensus. You easily can spoil your live by publishing a new concept. All the supporters of the other concepts will tell you you are wrong. ;-))

 

[Dadface]

Your summary points 1,2 and 3 are paraphrases of my summary points.
4 You know as well as I do some methods by which an electron can be moved. I'll just mention a couple of key words: ionisation,collision.
5 Observations include measurements eg of bare charge and mass. Some, of the methods used eg the use of mass spectrometry can be explained in terms of classical physics.
I think the analogies are used for the sake of brevity. You used an analogy in post 24.

Where is there an analogy in post 24?
Honestly, these questions aren't just to annoy. I have a problem with the wording you have used from a technical standpoint and i need to clarify what you mean with the terms that you are using. As others have said, the fields in qft are not a mental picture of what's going on at the particle scale, they are rigorously defined mathematical concepts that allow calculations to be made about observable phenomena; we as humans can then infer ripples in sheets as particles but this is not qft.
1.2.3. not paraphrased but made more precise, particles are not 'ripples' unless you had a precise mathematical description of what you mean by a ripple. When i say excitation, I know what i mean on a technical level, as I understand the concept of excitation from ordinary quantum mechanics.

4. I do not know as well as you do. I personally do not know how to move a single electron, QFT makes it possible (as far as my understanding goes) for there to be only one electron in the entire universe. How can i move this one electron by means of collision with another electron, when i only have one electron for instance. the point is that the particle picture is insufficient to describe 'moving an electron' if you intend to view the world through qft.

5. mass and charge are properties of quantum fields.

there's a subtle difference between brevity and poetry, brevity can still be technical but electrons are ripples is an analogy which is removed from the mathematical truth. you are trying to understand a quantum field in terms of other things. see http://www.damtp.cam.ac.uk/user/tong/qft/qft.pdf , if you don't understand this course then learn the prerequisites or accept that all analogies of an electron or a magnet or any quantum phenomena will be incomplete and insufficient. This is the nature of quantum mechanics.

Firstly let me reply to your comments up to and including points one two and three and beyond that to your closing paragraph. I think this discussion has deviated somewhat into semantics for example in post 24 and other places reference has been made to the word "excitation" whereas I referred to the word "ripples"... ripples is the word used by David Tong in the paper I referred to in the opening post.
David Tong has quite an impressive background in the world of theoretical physics. Amongst other places he has had a research career at TIFR Mumbai, Stamford, MIT and Cambridge. He has a bunch of prizes, fellowships and awards and at present is a professor at university of Cambridge and a fellow of Trinity College. He works on QFT and he described particles in terms of ripples. Because of his experience in the subject I consider it reasonable for me to adopt his terminology. But you prefer to describe particles in terms of excitation's That's fair It's a word I can use .In fact I probably will use it.

4. I think you've pointed out another example of so called quantum weirdness. If QFT really makes it possible for there to be only one electron in the whole universe then I think that's a failing of QFT. I base that on a mega powerful theory, the theory of general knowledge and common sense. How can the electrons involved in the biochemical process of digesting my fish and chips and the electrons smashing into the targets of X ray tubes and so on and so on all be a single electron? By the way I don't want to discuss that here.

5. I agree with point 5 but to clarify your statement and be more precise I would add that mass and charge are properties of excitations of fields in other words properties of particles. And that's one of the points i was trying to make.

I think we've gone about as far as we can go with this discussion and I thank you very much for all your input. It has made made me think more deeply about the matter and as a result my understanding has improved.

 

[weirdoguy]

David Tong has quite an impressive background in the world of theoretical physics.

Oh please. Still pop-science is pop-science no matter who is doing it.

 

[Ben Wilson]

Oh please. Still pop-science is pop-science no matter who is doing it.

think this discussion has deviated somewhat into semantics for example in post 24 and other places reference has been made to the word "excitation" whereas I referred to the word "ripples"... ripples is the word used by David Tong in the paper I referred to in the opening post.

i linked you to david tongs qft course, he says ripple for a quick mental picture for the reader in the intro, this is an analogy. In the course he says excitation, because there's a consensus amongst physicists about what this means in a mathematical sense (see p 29). It doesn't matter what word you use, you are allowed to say ripple, provided the word ripple carries a precise physical meaning e.g. a creation operator applied to a Fock space. For the final time, it has nothing to do with semantics or picking on words you are using.

 

[Dadface]

Oh please. Still pop-science is pop-science no matter who is doing it.

I would appreciate it if you don't comment on small sections of posts out of context but try to look at the whole thing. Is your comment relevant when you look at post fourteen? is your comment constructive in any way?

 

[PeterDonis]

try to look at the whole thing

We already have, and the correct response has been given to you repeatedly: if we are talking about quantum field theory, then everything is made of quantum fields. "Particles" are made of quantum fields. "Electric and magnetic fields" are made of quantum fields. You and I are made of quantum fields. That's all there is to it.

This thread has already beaten the above point to death. Thread closed.