Does quantum field theory supersede quantum mechanics?

[arupel]

In discussing the wave/particle duality, a friend stated basically that the discussion in quantum mechanics is not relevant because quantum mechanics is superseded by quantum field theory.

1. I do not know if this statement is relevant with respect to the wave/particle duality.

2. I am not that familiar with quantum field theory, but if it is, how is the wave/particle duality looked at in quantum field theory?

Thanks

 

[e.bar.goum]

QFT is indeed more general than quantum mechanics (QFT is fully relativistic, treats space the same as time, allows particles to be created and annihilated, gets rid to negative energy problems, and describes atom-light interactions more naturally), so it's fair to say it supersedes it. Quantum mechanics is rather a lot easier than QFT, so where quantum mechanics is useful, it tends to be used.

In quantum field theory, rather than describing particles with a wave-function, which is a function of time, you replace it with a field, which is a function of space and time. Then, particles become excitations of the underlying quantum field.

It's worth noting, however, that you don't need to invoke QFT to deal with wave-particle duality. In plain old QM, particles are described by wave-functions, which are neither waves, nor particles - it's a quantum mechanical object.

The "issue" of wave-particle duality is an interesting one, because it's one that physicists haven't really been worried about for about 100 years, but it still persists in lay discussions of physics.

 

[arupel]

Thanks,
Arthur Rupel

 

[bhobba]

E.Bar is correct.

Interestingly some authors believe at the beginning level its better to start with QFT:
https://www.amazon.com/dp/0473179768/?tag=pfamazon01-20

Personally I am inclined to agree.

Thanks
Bill

 

[e.bar.goum]

I think it's a good idea to make sure students are aware that QFT exists as they're learning QM, but I'm not sure about starting with it, the formalism is really not that easy!

Whether you derive it using second quantization, or through many paths, it is still helpful to at least have a passing acquaintance with them.

I get the sentiment, but I feel it's a little like teaching GR before Newtonian gravity.

 

[bhobba]

Its at the beginner level before the formalism is developed. Things like the wave particle duality are a doodle because you see its neither - its a quantum field.

Here is a video that explains the idea:


That is not a 100% endorsement of all his views - he slightly misconstrues Feynmans position for example, but for someone starting out its way better than the usual populist junk.

Added Later:
Of course it goes without saying you would not teach the formalism of QFT first (that said I have recently found a book - QFT For The Gifted Amateur where you don't need advanced QM - an intermediate book like Griffiths is perfectly fine) but by starting out conceptually viewing it that way and understanding QM is simply a limiting case less confusion arises IMHO.

Thanks
Bill