# What is Quanfum field theory: Definition and 19 Discussions

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1. ### Possible research directions for a beginner in TQFT

I am highly interested in Topological Quantum Field Theory (TQFT) and am currently planning on doing a project on this topic this year. Some of my relevant background: Algebra (Groups, Rings, Fields, basics of Categories and Modules), Topology (Munkres), Smooth Manifolds (John Lee's book, first...
2. ### I String theory vs Quantum field theory

So QFT treats particles as excitations of their underlying quantum field, meaning that fields are more fundamental than particles. Then String theory comes in and says that actually strings are the fundamental building block of the universe and that the different particles are vibrating strings...
3. ### I Is the Black Hole Information Paradox Truly Resolved?

from what I understand it is believed that information is preserved but we are still working out how exactly, is this the case?
4. ### I Compton scattering amplitude and propagator

Hi everyone How can i prove that the propagator is And then

11. ### B Missing mass in atomic systems

Hi! My name's Logan Knox and I'm aspiring to eventually understand the physics and nature of the quantum world in its totality, and I have a LONG way to go, but I have to get there by asking the right questions, and I think this is the first step to finding the right question to ask for this...
12. ### B Question about QM and Neuroscience

I have one request, I hope you could answer it…. I saw this article that makes heavy assumptions based on Quantum Electrodynamics, like something like formation of an energy domain or sorts, and it connects it with brain activity which is super weird, I did ask a neuroscientist and he said he...
13. ### A Two loop Feynman diagram with quartic vertex

I am trying to calculate the effective potential of two D0 branes scattering in Matrix theory and verify the coefficients in this paper: K. Becker and M. Becker, "A two-loop test of M(atrix) theory", Nucl. Phys. B 506 (1997) 48-60, arXiv:hep-th/9705091. The fields are expanded about a constant...
14. ### I Many-Worlds Theory: Simulation Program in C#

Here is the Code File in an txt. I can on request provied the whole Program, which includes the PSE, AtomFunctions and many useful but not all implemented Funtions to solve the Many Worlds Problem in C#. Please feel free to ask questions via here or email [e-mail address deleted by Mentors] I...
15. ### I Virtual particle content of the vacuum state....

Hi all, One more virtual particle question (sorry all!): for individuals who would take virtual particles as being 'real' (but unobservable), what is their understanding then of the content of the vacuum? For example, if I place a electron all by itself in the vacuum (thus making it no longer...
16. ### I De Broglie-Bohm theory and Bohm-like models - how is vacuum treated?

Hi all, I've been looking at de Broglie-Bohm theory and more recent attempts at Bohm-like models that are relativistic and attempt to reproduce QFT. What I'm not clear on (non-expert) is how the vacuum is modeled in these cases? If we have a set of infinite quantum harmonic oscillators...
17. ### I Back to Muller's 'Now and the Flow of Time'

Folks, I'm back to reading Muller's paper (https://arxiv.org/pdf/1606.07975.pdf) about the flow of time. He postulates that time is expanding similar the way space is expanding (ok... so if you can swallow that). He asks: "why are the new nows created at the end of time, rather than uniformly...
18. ### A Quantum fields and the harmonic oscillator

When defining quantum fields as a sum of creation and annihilation operators for each momenta, we do it in analogy with the simple example of the harmonic oscillator in quantum mechanics. But why do we assume that the coefficients in the expansion can be interpreted in the same way as in the...
19. ### A Polarization vector sums in QED

I'm working through Lahiri & Pal's book A First Book of Quantum Field Theory, Second Edition and I'm stuck on their explanation of the polarization vector in quantum electrodynamics in Chapters 8 and 9. In section 8.8, they derive a formula for the sum over the transverse polarization modes of...