- #1
- 15,168
- 3,374
This thread continues the discussion at https://www.physicsforums.com/showthread.php?t=767018
microsansfil said:Perhaps when you read this kind of articule "There are no particles, there are only fields" on arxiv. Calculate the position is not it already an interpretation ?
This is how I understand the sentence : "But some ph.d. in physics told me that no, that's wrong and when I use the word particle I'm already using an interpretation of QM".
However, I may be wrong.
Patrick
atyy said:The article is wrong.
bhobba said:I had a quick look - it looked fine to me.
What was your issue.
Thanks
Bill
atyy said:In non-relativistic quantum mechanics, there are certainly systems with a fixed number of particles. These are not classical particles. They are quantum particles, which do not simultaneously have definite position and momentum. Thus they do not have classical trajectories.
The matter of interpretation is whether they have non-classical trajectories. In Bohmian Mechanics, they do.
In exact relativistic quantum field theory, it can be argued that fields are more fundamental. Here the quantum particle is an excitation of the field. However, no one can guarantee that relativity is exact, so even to explain relativistic phenomena, quantum mechanics with a fixed number of entities is viable, as in lattice gauge theory.
atyy said:The abstract claims "As this paper shows, experiment and theory imply unbounded fields, not bounded particles, are fundamental." That is wrong. Experiment only goes up to a certain energy, and has a certain precision. Claiming to know the final theory is as much pseudoscience as all the things he criticizes.
For example, can he distinguish exact relativistic theories defined in infinite volume from a lattice gauge theory with fine but finite lattice spacing in large but finite volume? The Hilbert space of the latter is finite dimensional, and so more like quantum mechanics than quantum field theory.
bhobba said:Yea - fair point.
But I am sure the author would agree and point out you are reading more into it than intended.
QFT is a deeper more exact theory than standard QM - that's all that's meant - not that its the final theory.
Thanks
Bill
atyy said:If he is talking about QFT, then it is roughly a theory with an infinite number of particles, or at least a theory in which particles can be created and destroyed. So it is a theory with more than one particle. But he writes "Thus the Schroedinger field is a space-filling physical field whose value at any spatial point is the probability amplitude for an interaction to occur at that point." and "It follows that the Schroedinger matter field, the analogue of the classical EM field, is a physical, space-filling field." That is of course fine for one non-relativistic particle, and a very useful mental image. But given his concern about quantum field theory, this picture of the single particle wave function is one that does not generalize to more than one particle. The wave function of two particles is not in general "space filling" in the sense that he means.
bhobba said:Indeed, as the Fock space formalism shows. And even deeper, when deriving QFT, one often uses a model of a large number of interacting particles that you take the limit in the continuum.
That does not contradict the infinite particle picture.
A quantum field can be viewed as a field of operators. The space it operates on is spanned by the creation and annihilation operators. Its two sides of exactly the same coin.
I don't think its fine for a single particle. A matter field, just like any quantum field, is a field of quantum operators acting on the creation and annihilation operators. You can't speak of single particles in that formalism.
The paper is not meant to be a rigorous development of QFT. It is meant to be a review article of the idea that quantum fields are a deeper theory than normal QM, and as such explains many of the issues people get worried about with QM.
He freely admits it doesn't solve the measurement problem, but many things like the double slit experiment become clearer.
Also it soon will be published, if it already hasn't been, in the AJP. Articles with glaringly obvious issues are normally not published there, they are vetted thoroughly to ensure that doesn't happen. Of course no process is perfect and some incorrect things can creep through - but I don't think that's what's going on here. Since its explaining highly complex ideas that should really be expressed mathematically in English subtleties are bound to arise. IMHO that all that's going on - overall it is correct.
It's at a bit more advanced level to its beginner companion book - Fields Of Color:
https://www.amazon.com/dp/0473179768/?tag=pfamazon01-20
But if you want a more advanced look again check out:
https://www.amazon.com/dp/9812381767/?tag=pfamazon01-20
The author may have a copy on his site as well - but don't hold me to it.
That QFT explains many of the issues (not all - but many) with standard QM is for me not controversial at all.
Thanks
Bill
Last edited by a moderator: