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Classical and quantum fields 
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#1
May1414, 05:36 PM

P: 86

In QFT, all particles can be interpreted as excitations of some fundamental quantum fields in the vacuum. This is the quantum picture. But in classical world, only photons and gravitons have classical counterparts. How to explain this? The common feature of these two is that they are intermediate particles of longrange interactions. But This is far from satisfactory to me. So I was wondering whether there is a deeper and better explanation of this problem.



#2
May1414, 05:59 PM

P: 865

Roughly speaking, quantum fields look like classical waves when there are many particles in the same state. So classical electromagnetic waves are states of many photons and classical gravitational waves are states of many gravitons.
Fermion fields don't have any states that look classical, because you cannot put more than one fermion in the same state. So there is no classical analog of the electron field. The W, Z, and Higgs fields are bosonic but they never look classical because these bosons all decay long before you could hope to construct a state containing lots of them. (This is pretty much the same thing as saying that they don't mediate longrange interactions.) The gluon field undergoes confinement and so there aren't actually any states that look like gluons, let alone states with many coherent gluons. There are only hadrons and glueballs. 


#3
May1414, 09:16 PM

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#4
May1514, 02:38 AM

P: 86

Classical and quantum fields



#5
May1514, 03:03 AM

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#6
May1514, 10:42 PM

P: 86

If there is no test particle, where do the scalar and longitudinal modes end? 


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