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I always enjoy a discussion about semantics, but only when both parties are very clear about the fact that it's semantics they're talking about, and not fundame
by kmm 10y ago
I always enjoy a discussion about semantics, but only when both parties are very clear about the fact that it's semantics they're talking about, and not fundamental nature of existence. I'm very wary of people trying to use physics to further an ontology, as physics almost by definition allows for multiple, completely equivalent descriptions of reality. That's not to say I think physics teaches us nothing about how the universe really works, but I don't think you can conclude from his interpretation of the mathematics of QFT that particles (whatever they are) don't exist, just as much as the Fermat principle[0] doesn't imply that light has a sentient mind which seeks out the shortest path. There exists a consistent, fully equivalent interpretation of (non-relativistic or relativistic) quantum mechanics that includes particles at the core of its ontology, Bohmian mechanics[1]. I'm personally not an adherent of it, but it shows that by nature, it's very hard to use physics to show what something fundamentally is.
Besides, the article doesn't define clearly what it means by particle, which is a priori just an English word, nor does it justify it well. I don't share the authors' problem with the excitations of a field being spread out all over the universe (by virtue of them being momentum-eigenstates). It's discrete, has a mass, has a momentum, and energy and interacts as a whole. The article calls these properties necessary but not sufficient, but doesn't explain why this doesn't suffice.
Particles are at least a useful abstraction. They emerge naturally at the classical level, interactions between fields are even at extremely high energy levels still very localised, electrons "scatter" a lot like they're bouncing off other particles, they leave neat tracks in bubble chambers, excitations of fields are discrete even at the lowest level, ... Feynman diagrams[2] are extremely handy, even if they don't "actually" happen, but are just a term in the series expansion of an interaction Hamiltonian between two fields.
What's the use of contorting oneself to the limit to fit every observation in a single mold, a field. Sure, classical particles are nothing like what we see at the quantum level, but classical fields are absolutely nothing like the fields in quantum field theory either. Why pick one term over the other?
0: https://en.wikipedia.org/wiki/Fermat%27s_principle https://en.wikipedia.org/wiki/Fermat%27s_principle
1: https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory
2: https://upload.wikimedia.org/wikipedia/en/f/fb/Feynman-diagram-ee-scattering.png https://upload.wikimedia.org/wikipedia/en/f/fb/Feynman-diagr...
- TheOtherHobbes 10y agoI think it's been proven fairly comprehensively that particles don't really exist in QFT in any useful sense. See e.g. http://arxiv.org/pdf/1304.7469.pdf http://arxiv.org/pdf/1304.7469.pdf http://www.sciencemag.org/news/2016/07/massive-neutrino-experiment-undermines-our-sense-reality http://www.sciencemag.org/news/2016/07/massive-neutrino-expe... Particles may be a useful abstraction, but they're also a very misleading one. It looks a lot as if what really happens is best described by a Two State Vector/Transactional interpretation. Which is very weird, because those are both time symmetric. And that's not a feature you'll find in any particle-oriented theory.
- tachyonbeam 10y agoNewbie question: if there are no particles, then why are there quantized packets of energy such as photons?
- slacka 10y agoI'm am not a physicist, but interested in QM. Photons behavior cannot be completely explained by treating them solely as particles. The simples counter example (one you can perform yourself with a laser pointer), is the double-slit experiment. If photons behaved classically (like billiard balls) they'd never interfere with themselves. If you'd like a good intro to QM, youtube is full of great material. Here are some of my favorites: NOVA - The Fabric of the Cosmos: https://www.youtube.com/watch?v=NbIcg0XsbFQ https://www.youtube.com/watch?v=NbIcg0XsbFQ The Secrets of Quantum Physics: https://www.youtube.com/watch?v=VgDlzGZAPcY https://www.youtube.com/watch?v=VgDlzGZAPcY Particle Fever: https://vimeo.com/125987472 https://vimeo.com/125987472
- tachyonbeam 10y agoYes, I'm aware of that, but how are fields quantized (divided into fixed-size packets of energy)?
- jostylr 10y agoParticles can interfere with themselves in the double-slit experiment if they are being guided by a wave. This explains wave behavior and particulate events as in Bohm's theory. Sadly, there are issues with photons as particles as their wave equations do not seem to allow for an easy particle interpretation unlike, say, electrons. Of course, the flexibility of QM allows for electrons to have a particle existence and photons to not: http://arxiv.org/abs/quant-ph/0404134 http://arxiv.org/abs/quant-ph/0404134 (I am a coauthor of that paper) And some videos to answer questions about BM: http://www.bohmian-mechanics.net/videos_faq.html http://www.bohmian-mechanics.net/videos_faq.html