I How Do Oscillations and Interference Define Particles in Quantum Field Theory?

[FilipLand]

I will soon start with the course introduction to QFT and are hence an amateur on the subject.

However I could not help but wonder,

If particles are describes by oschlliations in a field, how can a "bigger body" be made up of several such oscillation? (A bigger particle is made out of several smaller particles).

Imagine we have many particles (oscillations) which make up a bigger body, then the interference must be such that the "net-oscillation" is zero, hence no body (since it's as much constructive as amplifying interference over time).

The only case where the net-oscillation is not zero would be where the phase among all oschlliations is perfect and stationary.
- Which means that bodies is not an interference of oscillation fields, but an arrangemang of oscillating fields, which in turn raise a number of problems.

Any input on this thought-experiment?

(Thanks in advance for not just commenting something like "thats wrong"!)

 

[Orodruin]

If particles are describes by oschlliations in a field

This is very popularised. I suggest that you start your course and study hard using whatever actual textbook is suggested by the lecturer to learn what QFT actually states. You may think this is along the lines "that's wrong", which would not bee too far off. The reason is that the entire premise you have for asking your question is built on a vague understanding of the statements in QFT.

 

[FilipLand]

This is very popularised. I suggest that you start your course and study hard using whatever actual textbook is suggested by the lecturer to learn what QFT actually states. You may think this is along the lines "that's wrong", which would not bee too far off. The reason is that the entire premise you have for asking your question is built on a vague understanding of the statements in QFT.

Then how do one interpret bodies? If not something that is made of small particles characterized by a fields?

 

[Orodruin]

If not something that is made of small particles characterized by a fields?

This again sounds very popularised and you simply cannot understand or extrapolate understanding from popularised texts. Your best bet is to first learn actual QFT and what the statements made in QFT imply and how they relate to observations. In order to do this, taking an introductory QFT course is a good start. Just do not try extrapolate to the final conclusions without taking the intermediate steps.

 

[FilipLand]

This again sounds very popularised and you simply cannot understand or extrapolate understanding from popularised texts. Your best bet is to first learn actual QFT and what the statements made in QFT imply and how they relate to observations. In order to do this, taking an introductory QFT course is a good start. Just do not try extrapolate to the final conclusions without taking the intermediate steps.

Of course I know that I need to take a course to understand it better..

If it is that big of a miss conception, it should be very easy to point out what’s obviously wrong to someone familiar with the subject :)

 

[Vanadium 50]

If it is that big of a miss conception, it should be very easy to point out what’s obviously wrong to someone familiar with the subject :)

Aristotle was not Belgian.
The central tenet of Buddhism is not "every man for himself"
The London Underground is not a political movement.

Some things are just not so.

 

[PeroK]

Any input on this thought-experiment?

You are indulging in some very misplaced logic. You make sweeping statements about things without checking whether your sweeping generalisations are at all valid. For example:

Imagine we have many particles (oscillations) which make up a bigger body, then the interference must be such that the "net-oscillation" is zero

Counterexample: 100 musical instruments all playing different tunes will not result in zero sound.

The only case where the net-oscillation is not zero would be where the phase among all oschlliations is perfect and stationary.

Can you prove this? Can you even give one example in support of your hypothesis? 100 light bulbs in one room produce no light?

To me the statements you appear to accept as some sort of physical fact are groundless.

 

[Spinnor]

Imagine we have many particles (oscillations) which make up a bigger body, then the interference must be such that the "net-oscillation" is zero, hence no body (since it's as much constructive as amplifying interference over time).

So if you could do an interference experiment with both single atoms of type A and a diatomic molecule of two such atoms both with the same velocity the diatomic atom will have a de Broglie wavelength one half that of the single atom with the same velocity.

Why, please tell me when you know, I have wondered about that fact for a while. Words of warning from Feynman,

"I am going to tell you what nature behaves like. If you will simply admit that maybe she does behave like this, you will find her a delightful, entrancing thing. Do not keep saying to yourself, if you can possibly avoid it, ‘but how can it be like that?’ because you will get ‘down the drain,’ into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that.

Richard Feynman - The Character of Physical Law (Lecture 6)"

Maybe I will see you if you join me down the drain

 

[Stephen Tashi]

I will soon start with the course introduction to QFT

What physics courses have you already taken?

 

[FilipLand]

What physics courses have you already taken?

Besides the very basics I have taking Atomphysics (semi-advanced QM), light-matter interaction, a bunch statistical mechanics and Lagrangian mechanics.

 

[Demystifier]

The only case where the net-oscillation is not zero would be where the phase among all oschlliations is perfect and stationary.
- Which means that bodies is not an interference of oscillation fields, but an arrangemang of oscillating fields, which in turn raise a number of problems.

What problems?

Take an analogy with sound. A complex sound is a coherent superposition ("arrangement" in your language) of elementary sounds. Yet, in nature we often hear complex sounds. It's not that we only hear an incoherent noise.

 

[Stephen Tashi]

If particles are describes by oschlliations in a field

Take an analogy with sound.

Do we take it for granted that a particle is identified with an oscillation (a "place where the field goes up and down") or is it better to say that a particle is spot of high intensity in the field ( a "bump"), which need not oscillate?

 

[Demystifier]

Do we take it for granted that a particle is identified with an oscillation (a "place where the field goes up and down") or is it better to say that a particle is spot of high intensity in the field ( a "bump"), which need not oscillate?

The former. Particle has energy $E=\hbar\omega$, where $\omega$ is the frequency of oscillation. The energy of a non-oscillating bump contributes to the cosmological constant, that is energy of the vacuum.