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**New Theories / Re: Are all photons mediated in the same way through the quantum vacuum**

« **on:**09/09/2019 18:12:34 »

Catching up after being away, so short reply:

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.

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 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.

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.

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)

"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 universityThis 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)

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