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I read Ryder's book on QFT but I couldn't understand what in facts are localized particles which are really observed and do they have any place at all in QFT. So I watched a Zee lecture in YT https://www.youtube.com/watch?v=jT1pM0aQ4AY at 12.42 he talks about localized wave packes of the normal modes on the matress of pointmasses with harmonic springs which he sets moving as particles. In my opinion such packets can exist for a very short time and disipate without reaching any macroscopic distance to be regarded as real particles. Zee also adds that the springs must be in fact unharmonic so the packets can interract with each other. Then the packets will disipate much sooner IMO. So what is in fact the current status of packets representing particles in QFT? Is Zee right and is there any scientific paper or better a book where the question of particles made of packets is made clear as much as possible?

Mercury
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  • There are literally dozens on this site on your nexus of questions, and a single answer cannot possibly cover them adequately. Sections you *must* have read and understood are this and this. – Cosmas Zachos Aug 08 '22 at 12:45
  • Phonons are not localizable. They extend the whole grid. In Wiki section about Wave packets there are the Gaussian wavepacket which spreads when moving and the Airy wavepacket which does not spread but accelarates in force free medium. Which of these looks like a localizable particle? – Mercury Aug 08 '22 at 15:37
  • Schroedinger wavepackets are localizable. QFTs are repackaged harmonic oscillators. Due diligence. – Cosmas Zachos Aug 08 '22 at 15:44
  • @CosmasZachos Thank you for your kind attention. You surely refer to the coherent state but it must have also many other properties to be regarded as particle. In QFT the Fock states are called 1 particle states and corent states are superpositions of infinite number of Fock's. And Fock states are wider then Universe. I dont understand why this subject is so neglected. IMO it must be the foremost in QFT. Is it too obvious or too inpenetrable? I can not see. – Mercury Aug 09 '22 at 11:52
  • Fock states are the building blocks/states-of-the-Hilbert-space of the theory (QFT), of which particles are made in ways not always easy to visualize... Most QFT texts don't dwell on such issues, as they are "soft" and counterproductive, and distract attention from the actual quantities computed precisely and effectively. – Cosmas Zachos Aug 09 '22 at 12:54
  • In many (not all) experiments the particles are very visualizable though. But I see your idea that QFT is meant to calculate different quantities abandoning the particles idea -even more there are investigations on non locality of of single photons. I am not in string theory - do you know if it is more near to vizualization than QFT or is there any other theory more visual and say half as succesful than QFT in calculations? – Mercury Aug 09 '22 at 13:15
  • The last link is very useful. – Mercury Aug 09 '22 at 13:18
  • Sorry, I'm not familiar with that cottage industry... I think there are several questions on this site on the localization of photons... – Cosmas Zachos Aug 09 '22 at 13:52
  • It seems that Zee is not right to talk about packets representing particles in QFT. He was just attracting audience. – Mercury Aug 09 '22 at 19:18

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