How does QFT explain the world around us?

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Discussion Overview

The discussion revolves around the application of Quantum Field Theory (QFT) to explain molecular interactions and the nature of momentum and position in quantum systems. Participants explore concepts related to the momentum basis, its selection in molecular systems, and the implications for energy and localization within the context of QFT.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the selection of the momentum basis in molecular systems and its effects on molecular energies, particularly in biological contexts.
  • Another participant argues that most interactions in cells are radial and suggest that the position basis is more relevant than the momentum basis.
  • Questions are raised about how to induce a molecular system to choose a momentum basis and the potential effects of such an induction.
  • Examples of measuring momentum in quantum systems are discussed, including the use of an electron beam in a magnetic field, but the relationship to position remains unclear.
  • There is a claim that momentum is not equivalent to energy, which is challenged by another participant who references classical physics.
  • Participants discuss the independence of operators and states from the basis used, noting that sometimes the momentum basis is more useful in QFT.
  • Concerns are expressed about the applicability of QFT to explain macroscopic objects like chairs and tables, questioning the absence of a position basis in QFT.

Areas of Agreement / Disagreement

Participants express differing views on the relevance and application of the momentum basis versus the position basis in quantum mechanics and QFT. There is no consensus on how these concepts apply to molecular systems or their implications for energy and localization.

Contextual Notes

Participants reference various assumptions about the nature of quantum measurements and the relationship between momentum and energy, but these assumptions remain unresolved. The discussion includes links to external resources that may provide additional context but do not settle the debate.

jlcd
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In molecules, the system (say dna or ribosomes) environment are the cells.. id like to know how much is the momentum basis selected and how this can affect the molecules energies and to what extend and actual examples of that in this internal human body decoherence scenerio. Thank you.
 
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jlcd said:
id like to know how much is the momentum basis selected

I would say not at all. Most interactions, and that certainly would be the interactions in a cell, are radial in nature (ie have rotational symmetry) and it is well known that singles out the position basis.

Singling out the momentum basis is pretty much a contrived thing - not occurring naturally.

Thanks
Bill
 
bhobba said:
I would say not at all. Most interactions, and that certainly would be the interactions in a cell, are radial in nature (ie have rotational symmetry) and it is well known that singles out the position basis.

Singling out the momentum basis is pretty much a contrived thing - not occurring naturally.

Thanks
Bill

Could you give an example of inducing a molecular system to choose momentum basis? What would be the effect of it? Can it make the molecular have more kinetic energy?
 
jlcd said:
Could you give an example of inducing a molecular system to choose momentum basis?

I have zero idea how to do that.

The only momentum outcomes I know of are contrived where you have a set-up designed to measure momentum.

Thanks
Bill
 
bhobba said:
I have zero idea how to do that.

The only momentum outcomes I know of are contrived where you have a set-up designed to measure momentum.

Thanks
Bill

Can you give example of a simple quantum system where the momentum is measured.. and does it mean the system has no position or localization? Or does momentum measurement also involve position?
 
jlcd said:
Can you give example of a simple quantum system where the momentum is measured.

Sure. Run an electron beam through a magnet an the circular path gives you the momentum. And no I can't really think of others - you will need to chat to an experimental type.

Thanks
Bill
 
bhobba said:
Sure. Run an electron beam through a magnet an the circular path gives you the momentum. And no I can't really think of others - you will need to chat to an experimental type.

Thanks
Bill

Does this this running electron beam through a magnet an the circular path giving the momentum also give the position? Or is there no localization?

For molecules. Giving it more kinetic energy or even causing electron transitions is still related to position basis or momentum?
 
added: but momentum is supposed to be the energy of the atom.. so I thought giving it more kinetic energy means it is momentum related...
 
jlcd said:
Does this this running electron beam through a magnet an the circular path giving the momentum also give the position?

Of course not - how does it tell the position of any electron in the beam.

Thanks
Bill
 
  • #10
jlcd said:
added: but momentum is supposed to be the energy of the atom..

It isn't. That's really basic classical physics.

Thanks
Bill
 
  • #11
bhobba said:
It isn't. That's really basic classical physics.

Thanks
Bill

http://chemwiki.ucdavis.edu/Physica...nics/10:_Multi-electron_Atoms/Quantum_Numbers

"The Orbital Angular Momentum Quantum Number (l'>l l )
The orbital angular momentum quantum number l determines the shape of an orbital, and therefore the angular distribution. The number of angular nodes is equal to the value of the angular momentum quantum number l'>l"

Mr. Hobba. The orbital angular momentum still use the position basis?? Then what is the momentum basis about?
 
  • #12
jlcd said:
Mr. Hobba. The orbital angular momentum still use the position basis?? Then what is the momentum basis about?

Operators are basis independent, as are states.

Sometimes the momentum basis is better for solving problems than the position basis - mostly the wave-function which is a state expanded in terms of the position basis is used, but sometimes its better to use the momentum basis - especially in Quantum Field Theory.

Thanks
Bill
 
  • #13
bhobba said:
Operators are basis independent, as are states.

Sometimes the momentum basis is better for solving problems than the position basis - mostly the wave-function which is a state expanded in terms of the position basis is used, but sometimes its better to use the momentum basis - especially in Quantum Field Theory.

Thanks
Bill

In QFT.. there is no position.. so no position basis is used.. but how come chairs and tables based on QFT (and momentum basis) has position and localizations?
 

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