[pensador (OP)]

The most important line is "as if they had never been there."

It is so easy to overlook the subtleties.

Virtual particle pairs appear out of the quantum vacuum of space momentarily, and because they only exist for a very short duration, it is not a violation of the laws of thermodynamics, is this correct?

Is it correct to think that the Casimir effect is evidence for virtual particles? or are Van der Walls forces a more likely cause of the Casimir effect.

Zero Point energy is also evidence of virtual particles, this prevents absolute zero being obtainable?.

Virtual Particles(a form of temporary energy/wave/etc) momentarily appearing from or travelling through the quantum vacuum disturb very cold particles and raise their temperature from the ground state. Do you view the zero point energy to be in the form of waves or particles or mixture of both, waves interacting to produce peaks which appear as momentary particles.

[pensador (OP)]

An electromagnetic field is transmitted via polarizing space the quantum vacuum, around an antennae, not unlike written in my QFT book. A photon is a real packet of energy with no polarity.

Polarized radio waves are not made up of real photons. They are transmitted by polarized virtual particles waves which are sometimes viewed as virtual photons? Is this correct??

[jeffreyH]

An electromagnetic field is transmitted via polarizing space the quantum vacuum, around an antennae, not unlike written in my QFT book. A photon is a real packet of energy with no polarity.

Polarized radio waves are not made up of real photons. They are transmitted by polarized virtual particles waves which are sometimes viewed as virtual photons? Is this correct??

No. They are real photons.

[pensador (OP)]

No. They are real photons.

This statement disagrees with my text book, section on QED. I will re read the section very slowly, I do not think I have misunderstood what I read.

Are you possibly redefining what a photon is, and giving it EM characteristics?

[Colin2B]

I sorry, but we don’t have the time to run a detailed course on QED/QFT but I’ll try to answer as much as time allows and then suggest that you spend time trying to understand the theory via a course in Quantum Systems.

Feynmans virtual photons are just mathematical simplifications of field interactions, for peasants, which I think I realized already.

you obviously have a very poor opinion of students of quantum theory 
Feynman originally developed the diagrams as a calculation aid for students on his course on quantum theory. Just as Einstein had a ‘thing’ about quantum theory, Feynman had a ‘thing’ about field theory and wanted to express the interactions as particles - there are indications that he later regretted this terminology. The virtual particles are internal processes and are only metaphors for multivariate integrals. The term is often used between researchers as jargon/shorthand rather than meaning particles as we think of them eg electron. The real problem is that in physics a lot of prior understanding is taken for granted, so a QED/QFT text book doesn’t expect you to leap in without studying a few years of physics and quantum theory and so doesn’t bother to explain the background.

I am correct in concluding that Feynmans virtual particles do not exist in reality,

Correct.
The virtual particles are metaphors for multivariate integrals, there are no 'time processes of virtual particles. Nobody ever has written down an equation for the time evolution of virtual particles. While a case can be made that virtual particles exist at least as lines on paper, no such case can be made for their time evolution.

and are not the same virtual particles as those predicted to exist in space by Casimir via calculations based on the uncertainty principle, supported experimentally. Giving rise to various quantum foam/gravity theories.

They are the very same, but their ‘existence’ is not predicted or supported experimentally. Experiments can confirm that results of the calculations represented by the shorthand/diagrams are correct (real).

Further more virtual particle pairs borrowing there energy from the quantum vacuum of space momentarily, are nothing to do with QFT, other than they both use the term virtual particles.

They are the same.

You keep mentioning space when referring to vacuum.
3D space (which can have a vacuum) is not the same as quantum vacuum. A quantum vacuum is the lowest energy state of a quantum system, any quantum system eg molecular bonds, it is not the same as spacial vacuum. If we take a simple Newtonian system eg a weight hanging from a string it has zero energy as it hangs there (disregarding the energy in the mass of the weight and the potential energy which would be released if you cut the string); if you set this system oscillating it will have its maximum ke at the bottom and its minimum at the top of the arc - where it spends most of its time.
The quantum version of this oscillator has its minimum energy at the bottom - where it spends most of its time - but this energy is not zero. This none zero minimum energy is a feature of all quantum systems and is due to the fact that there is uncertainty in the position and momentum of the particles. It’s not that they are flitting about, it’s a way of handling the uncertainty of a probabilistic system.
You don’t really borrow energy from the quantum vacuum, the correct way to look at this is with time/energy uncertainty ie Δt ≥ h/2ΔE . What this is telling you is that if you want to detect the presence or absence of a particle whose rest mass energy (E = mc²) is equal to ΔE, you need to look for at least a time Δt. You can look for longer if you like, but this is the minimum observation time needed to ensure that the uncertainty in your measurement is less than the energy of the particle. If you look for less time, your energy uncertainty will be bigger than the mass energy, and you can't be sure whether the particle was really there or not and in QM the probability is nonzero, but if you look for a longer time they aren’t there - you didn’t see them. Again this is a way of handling uncertainty in the equations.

Adding further to my confusion I googled for a link on evidence for the Casimir effect experiment which I know exists, and stumbled across this link https://www.scientificamerican.com/article/are-virtual-particles-rea/ Which leads me to think perhaps the terminology used by different Quantum theories leads to further confusion

.
He was criticised by a number of physicists for this article as being misleading. Remember also the difference between physics and the maths we use to describe it - "existence" for physics means "measurable", for mathematics "possible to be included in a self consistent theory”, quite often there is confusion in the use of these terms.
I’ve already given you links on the problems of virtual particles being considered real (in the physics sense) and the problem of considering them as cause of Hawking radiation, but here is another link explaining, try to read and understand beyond where it says “this visualization is not for real particles, but virtual ones. They are calculational tools only, not physically observable entities”. https://medium.com/starts-with-a-bang/ask-ethan-how-do-hawking-radiation-and-relativistic-jets-escape-from-a-black-hole-b7a4ef7d9bdf

Just to recap on virtual particles and vacuum fluctuation, important to read and understand before diving into your QED book:
https://www.physicsforums.com/insights/misconceptions-virtual-particles/
https://www.physicsforums.com/insights/physics-virtual-particles/
https://www.physicsforums.com/insights/vacuum-fluctuation-myth/
Also some comments by Prof Baez http://physicsfaq.co.uk/Relativity/BlackHoles/hawking.html

No. They are real photons.

This statement disagrees with my text book, section on QED. I will re read the section very slowly, I do not think I have misunderstood what I read.

Are you possibly redefining what a photon is, and giving it EM characteristics?

I think you must be misreading, it would be unusual for a book on QED to mention antenna and radio waves specifically, all em fields are treated in the same way no matter what their energy. Are you sure your not looking at the evanescent field close to the antenna?
A photon does not need to be redefined to have em characteristics, they are embedded in its Maxwell equation source where a photon is just a quantisation of the em gauge field (in other words it is the field measured with a value of one quanta when detected). See first few paragraphs of: https://www.imperial.ac.uk/media/imperial-college/research-centres-and-groups/theoretical-physics/msc/current/qed/Photons.pdf

[pensador (OP)]

Seems a very complicated way of moving compared with either a particle-projectile or an electromagnetic wave model, and not entirely compatible with observation.

And you thought that was complicated 

[pensador (OP)]

I sorry, but we don’t have the time to run a detailed course on QED/QFT but I’ll try to answer as much as time allows and then suggest that you spend time trying to understand the theory via a course in Quantum Systems.

Thanks for the long reply, it will take me some time to absorb. Once absorbed, I'll be back.

[Colin2B]

I sorry, but we don’t have the time to run a detailed course on QED/QFT but I’ll try to answer as much as time allows and then suggest that you spend time trying to understand the theory via a course in Quantum Systems.

Thanks for the long reply, it will take me some time to absorb. Once absorbed, I'll be back.

No probs. Can’t promise to reply quickly as busy on project at moment and we seem to be having a lot of attempting spammers.

Where did you get this from?

In QFT, a photon is transmitted through the vacuum by ripping electron positron pairs from the vacuum. This is not the same as the method of propagation of virtual photons which polarize space around them ? Virtual photons and real photons appear to propagate differently albeit at c.

As Alan points out it really is not observed and I’ve never come across it in QFT. QFT treats the photon as a quantisation of the em field, and virtual particles are Feynman diagram calculations.

[pensador (OP)]

Where did you get this from?
Quote from: flummoxed on 18/07/2019 10:28:00
In QFT, a photon is transmitted through the vacuum by ripping electron positron pairs from the vacuum. This is not the same as the method of propagation of virtual photons which polarize space around them ? Virtual photons and real photons appear to propagate differently albeit at c.
As Alan points out it really is not observed and I’ve never come across it in QFT. QFT treats the photon as a quantisation of the em field, and virtual particles are Feynman diagram calculations.

This sentence "In QFT, a photon is transmitted through the vacuum by ripping electron positron pairs from the vacuum." came from memory of what I had read from my text book. It should have read "the bare photon propagates while tearing electron positron pairs from the vacuum" . As discussed with Alan the words electron and positron might not be exactly correct, perhaps virtual particle pairs or electron hole pairs would have been a better analogy.

It was an illustration offered by the authors to illustrate how a photon is propagated in QED via a creator and annihilator virtual particle pair. One of the authors is from Durham university and the other from Oxford university

Vacuum polarization via virtual particles is confirmed via the Lamb shift measured in Hydrogen atoms. Vacuum polarisation looks like a radio wave to me, but I might be wrong.

[alancalverd]

how a photon is propagated in QED

There's the rub. It is analagous to how a mouse runs in a cartoon - not how a mouse runs in real life. QED, like all physics, is an attempt to create a mathematical model of what actually happens.

[yor_on]

Beautifully described Collin

[yor_on]

Sometimes you guys live up to what I expect. The ability to explain the thought processes defining how we think it works. That's a clarity of mind.

[pensador (OP)]

You keep mentioning space when referring to vacuum. 3D space (which can have a vacuum) is not the same as quantum vacuum. A quantum vacuum is the lowest energy state of a quantum system, any quantum system eg molecular bonds, it is not the same as spacial vacuum. If we take a simple Newtonian system eg a weight hanging from a string it has zero energy as it hangs there (disregarding the energy in the mass of the weight and the potential energy which would be released if you cut the string); if you set this system oscillating it will have its maximum ke at the bottom and its minimum at the top of the arc - where it spends most of its time

My understanding is that space is not an empty vacuum it is full of quantum fluctuations. Also my QFT book used the term in the intro quantum vacuum of space. https://en.wikipedia.org/wiki/Vacuum_state . My terminology might be incorrect, but if Im right the quantum vacuum does exist in all of space, and between particles.



 

how a photon is propagated in QED

There's the rub. It is analagous to how a mouse runs in a cartoon - not how a mouse runs in real life. QED, like all physics, is an attempt to create a mathematical model of what actually happens.

The photon mouse/s trajectory between particle A and B would be affected by all the absorptions and emissions via ghost particles that dont exist in life, and if it was modelled by a mathematician, trying to maintain symetry via eigen vectors it would have to be a siamese mouse that could annihilate itself, and be absorbed by a cat representing particle B.

[Colin2B]

Catching up after being away, so short reply:

"In QFT, a photon is transmitted through the vacuum by ripping electron positron pairs from the vacuum." came from memory ....should have read "the bare photon propagates while tearing electron positron pairs from the vacuum" .

I think you’ll agree that these 2 sentences convey very different meanings so it’s important not to misquote. Mention of bare photon sounds as though you are going through renormalisation at this stage. I also assume you understand bare particles, if not it’s important to go through the derivation because it gives some insights into the models being used and why adjustments are necessary.

It was an illustration offered by the authors to illustrate how a photon is propagated in QED via a creator and annihilator virtual particle pair. One of the authors is from Durham university and the other from Oxford university

This sounds like Stephen Blundell’s book. Because this is aimed at the amateur they quite rightly stick to the formal (shorthand) Feynman descriptions of the calculations, but it does a good job of showing the calculations that lie behind the jargon. Feynman used a very restricted pallet of operations and creation and annihilation are at some of the vertices of the diagrams. The photon is not propagated in QED by creation annihilation operators, they only describe its creation at point eg at A(x,t) and annihilation at say B(x,t) - unlike QM, in QFT/QED the probability of finding an electron or a photon integrated over space does not have to be one, it can change with time. Remember, QED (charged particle interactions) is a simplified subset of QFT - in QFT the photon propagation is described by quantisation of the em field as per Maxwell’s equations.

Why do we, and the science advisors on main Physics fora, plus  top physicists like John Baez, Matt Strassler, etc, say that virtual particles are shorthand for the calculations rather than objects - the legendary Sidney Coleman described them as fairy tales. Well for one it’s what Freeman Dyson said and he was the person who developed Feynman diagrams into the form we see today. When we were undergraduates Feynman’s papers were required reading and in there Feynman says that the particles, eg electrons, interact directly via their fields (no virtual mediation). So what we are looking at are the complex and dynamic interactions of those fields as described by the Feynman diagrams and the underlying calculations. Also, as you will also know from your book, an internal line doesn’t represent a single interaction or even a specific time ordering, unlike the external lines. Interpretation of the internal lines is a temptation but fraught with pitfalls, this is why Feynman said “shut up and calculate. Quite rightly the book you have is teaching you what every student of QED needs to know; how to calculate.

As discussed with Alan the words electron and positron might not be exactly correct, perhaps virtual particle pairs or electron hole pairs would have been a better analogy.

There are a lot of models used in physics and some historical ones are still used in teaching because they can help understanding (eg Bohr atom, although no one now thinks of atoms as small solar systems).
Dirac’s model which used electron holes underwent a number of changes, but never really hit the mark. It was left to Feynman who, under John Wheeler, began to look at the electron under time symmetry (as you know, many models in physics are time symmetric). He found that if you modelled an electron going backwards in time you end up with a positron going forward in time - this is why you will note in the diagrams an antiparticle goes in the opposite direction to its particle, moving backwards against the time axis.

Vacuum polarization via virtual particles is confirmed via the Lamb shift measured in Hydrogen atoms.

Yes, you can model the Lamb Shift  via the Feynman diagrams (http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/lamb.html) and it does confirm the accuracy of those calculations using QED, but does not confirm the existence of virtual particles.
Vacuum polarization describes changes in the distribution of charges and currents of an em field by those generating the original electromagnetic field, it is also sometimes referred to as the self-energy. Again you can model this shielding using the Feynman diagrams and virtual particles, but the Lamb shift only confirms the accuracy of the calculations not the existence of virtual particles as objects.
Again it’s worth understanding the bare electron and why we have to postulate shielding  and renormalisation in the models to reduce the infinities of mass and charge.
Remember, the Shrodinger/Dirac model did not predict Lamb shift, it predicted that the energy levels were only determined by the primary quantum number. This is a problem with the model which considered the electron to be a free electron with point charge, when this is used to model interactions between fields, eg between electron and proton, you end up with infinities for charge and mass. The big contribution of Lamb and particularly Hans Bethe was being able to derive the Lamb shift using the idea of renormalization, which allowed him to calculate the observed energy shift as the difference between the shift of a bound electron and the shift of a free electron. If you look at the 2S & 2P orbitals you can see a difference of how closely the electron approaches the proton and hence the difference in the field interaction/modification.

Vacuum polarisation looks like a radio wave to me, but I might be wrong.

Very wrong. Radio waves are em radiation same as IR, visible light, UV, x rays and gamma rays.
I know you have a personal theory that radio waves are not part of the em spectrum and cannot be described by a photon model, but this goes against all of current QFT. In fact the Lamb Shift experiment is a good example of the existence of radio frequency photons.

My understanding is that space is not an empty vacuum it is full of quantum fluctuations. Also my QFT book used the term in the intro quantum vacuum of space. https://en.wikipedia.org/wiki/Vacuum_state . My terminology might be incorrect, but I think ive got the right end of the stick.

I’m not saying you’ve got totally the wrong end of the stick, although it’s worth noting what the science advisors on one physicsforum say about the Wiki quantum vacuum articles  “written by someone who has only read popsci articles and doesn’t understand real physics”.
What I am saying is the the quantum vacuum is not the energy of space, but of a quantum vacuum in space eg for QED this is the lowest state of the quantised electromagnetic field. It may seem a subtle difference, but it is similar to saying “the stage speaks the authors words” when in fact the stage (space) is where the actors (fields, vacuums, particles, etc) exist. It is also important to recognise that quantum vacuums can exist for any quantum system so it’s important to be specific, see:
https://en.wikipedia.org/wiki/Quantum_vacuum_(disambiguation)

[pensador (OP)]

Thanks for the lengthy reply.

My memory is sometimes flawed, I am crap at remembering names, but almost photographic with faces, pictures, circuit diagrams etc. I normally remember the key points reasonably well, but if they are wrapped in word salad, they can lose their meaning.

Yes Lancaster and Blundell are the authors of my book. and I do recognize math is just a tool to predict an outcome from known inputs, and it does not necessarily represent the actual process in between. 

There are a lot of models used in physics and some historical ones are still used in teaching because they can help understanding (eg Bohr atom, although no one now thinks of atoms as small solar systems).

Speaking of which do you have an opinion on SED, stochaistic electrodynamics the physics behind quantum mechanics. ? being developed by a number of theoretical physicists for the last 30 years I understand, but might be older.

Very wrong. Radio waves are em radiation same as IR, visible light, UV, x rays and gamma rays.
I know you have a personal theory that radio waves are not part of the em spectrum and cannot be described by a photon model, but this goes against all of current QFT. In fact the Lamb Shift experiment is a good example of the existence of radio frequency photons.

My Hang up here is a single photon or a laser beam can not be deflected in any way by an electric or magnetic field, it has momentum and spin, it therefore can not have a electric or magnetic field. A magnetic field line is clearly curved so how can a magnetic field be transmitted by photons unless there is more than one type of photon, or perhaps when a photon is dressed it can have more properties, than the photons that meet the eye I am still mulling this one over ? I think it might be down to wordology, bare dressed and quasi 

What I am saying is the the quantum vacuum is not the energy of space, but of a quantum vacuum in space eg for QED this is the lowest state of the quantised electromagnetic field. It may seem a subtle difference, but it is similar to saying “the stage speaks the authors words” when in fact the stage (space) is where the actors (fields, vacuums, particles, etc) exist. It is also important to recognise that quantum vacuums can exist for any quantum system so it’s important to be specific, see:
https://en.wikipedia.org/wiki/Quantum_vacuum_(disambiguation)

Is the zero point energy of the vacuum the same as Quantum vacuum energy, an underlying background energy that exists in space throughout the entire Universe ?

[alancalverd]

How about getting rid of unnecessary salad dressing? The question is how does elecrtromagnetic radiation propagate?

The answer lies in Maxwell's equations and has nothing to do with quantisation, mediation, or virtual anything.

We know from experiment that a moving charge creates a magnetic field, and a changing magnetic field induces a charge. https://integratedscienceathome.blogspot.com/2011/02/maxwells-equations-for-dummies.html  puts it very nicely (and also reproduces the equations for those of a mathematical persuasion)

We now know that radio waves, for example, can be generated by switching an electric current on and off at high speed. The electrons in the wires wiggle back and forth, creating wiggling electric fields, which create magnetic fields, and so on - the overall effect being radio waves. 

which is all there is to it.

Where the initial wiggle is quantised, say an electron changing state in an atom, the electromagnetic energy is clearly emitted in a single lump with a fixed frequency. You may need to invoke unseen virtual particles to explain quantised nuclear gamma radiation, but the selfpropagation of EM waves has nothing to do with their source.

[pensador (OP)]

How about getting rid of unnecessary salad dressing? The question is how does elecrtromagnetic radiation propagate?

The answer lies in Maxwell's equations and has nothing to do with quantisation, mediation, or virtual anything.

What part of your ramblings answer any of the questions in my previous post ref bare dressed and quasi particles. Dont even bother answering. This just another attempt at a high jack with a subject unrelated to the questions. I can see there is no point discussing anything with you after reading your ramblings on Brexit.

[alancalverd]

When we study science we are generally taught to look for a complete and simple explanation of a phenomenon. Those who prefer unending and unanswerable questions are advised to study philosophy.

[pensador (OP)]

When we study science we are generally taught to look for a complete and simple explanation of a phenomenon. Those who prefer unending and unanswerable questions are advised to study philosophy.

I think you have lost the plot, I took the trouble to view some of your historical posts from years ago, they were reasonable, albeit in some instances wrong, your posts recently have been putting it mildly pointless, why do you even bother posting responses when you have no interest in answering or addressing the questions asked.
 
When people study religion they are taught to believe God created everything, this is a very simple but incorrect statement, as are most of your boris johnson style answers of late.

One of my questions in response to Colins answer was reference dressed and bare photons. After a bit of reading I now realize that was a misdirect. A photon can not be dressed as it is a particle in its own right, it has no electromagnetic properties unlike an electron for example which can be dressed in QFT

As for your obsession with Maxwells equations they describe a wave not a particle as you have been told time and time again. They do not describe a photon, and are not helpful in answering the point of this thread.

[pensador (OP)]

A lot of the misunderstandings on this thread are to do with what a photon is.

Einsteins photon is a particle in its own right, and is not the same as the photon defined in QED. The photon in QED can have lots more properties than Einsteins photon.  https://www.researchgate.net/post/Is...the_QED_photon

Should the term virtual photon be used in QED instead of photon? Here they use the term virtual photon as transmitting the electro magnetic forces https://www.researchgate.net/post/Ho...irtual_photon2