What does it mean that photons are force carriers for electromagnetism? Updated 2025-01-10 +Created 1970-01-01
TODO find/create decent answer.
I think the best answer is something along:
- local symmetries of the Lagrangian imply conserved currents. gives conserved charges.
- OK now. We want a local symmetry. And we also want:Given all of that, the most obvious and direct thing we reach a guess at the quantum electrodynamics Lagrangian is Video "Deriving the qED Lagrangian by Dietterich Labs (2018)"
- Dirac equation: quantum relativistic Newton's laws that specify what forces do to the fields
- electromagnetism: specifies what causes forces based on currents. But not what it does to masses.
A basic non-precise intuition is that a good model of reality is that electrons do not "interact with one another directly via the electromagnetic field".
A better model happens to be the quantum field theory view that the electromagnetic field interacts with the photon field but not directly with itself, and then the photon field interacts with parts of the electromagnetic field further away.
The more precise statement is that the photon field is a gauge field of the electromagnetic force under local U(1) symmetry, which is described by a Lie group. TODO understand.
This idea was first applied in general relativity, where Einstein understood that the "force of gravity" can be understood just in terms of symmetry and curvature of space. This was later applied o quantum electrodynamics and the entire Standard Model.
From Video "Lorenzo Sadun on the "Yang-Mills and Mass Gap" Millennium problem":
- www.youtube.com/watch?v=pCQ9GIqpGBI&t=1663s mentions this idea first came about from Hermann Weyl.
- youtu.be/pCQ9GIqpGBI?t=2827 mentions that in that case the curvature is given by the electromagnetic tensor.
Bibliography:
- www.youtube.com/watch?v=qtf6U3FfDNQ Symmetry and Quantum Electrodynamics (The Standard Model Part 1) by ZAP Physics (2021)
- www.youtube.com/watch?v=OQF7kkWjVWM The Symmetry and Simplicity of the Laws of Nature and the Higgs Boson by Juan Maldacena (2012). Meh, also too basic.
His website is down as of 2020, shame: wiki.dandascalescu.com/essays/english-universal-language
This dude is interesting. Quite crazy type. It is hard to differentiate genius from mad.
Ciro Santilli bumps on his Stack Overflow from time to time: stackoverflow.com/users/1269037/dan-dascalescu.
Uses photons!
The key experiment/phenomena that sets the basis for photonic quantum computing is the two photon interference experiment.
The physical representation of the information encoding is very easy to understand:
- input: we choose to put or not photons into certain wires or no
- interaction: two wires pass very nearby at some point, and photons travelling on either of them can jump to the other one and interact with the other photons
- output: the probabilities that photos photons will go out through one wire or another
Jeremy O'Brien: "Quantum Technologies" by GoogleTechTalks (2014)
Source. This is a good introduction to a photonic quantum computer. Highly recommended.- youtube.com/watch?v=7wCBkAQYBZA&t=1285 shows an experimental curve for a two photon interference experiment by Hong, Ou, Mandel (1987)
- youtube.com/watch?v=7wCBkAQYBZA&t=1440 shows a KLM CNOT gate
- youtube.com/watch?v=7wCBkAQYBZA&t=2831 discusses the quantum error correction scheme for photonic QC based on the idea of the "Raussendorf unit cell"
The step busy beaver is a variant of the busy beaver game counts the number of steps before halt, instead of the number of 1's written to the tape.
As of 2023, it appears that BB(5) the same machine, , will win both for 5 states. But this is not always necessarily the case.
I think they are a tool to calculate the probability of different types of particle decays and particle collision outcomes. TODO Minimal example of that.
And they can be derived from a more complete quantum electrodynamics formulation via perturbation theory.
At Richard Feynman Quantum Electrodynamics Lecture at University of Auckland (1979), an intuitive explanation of them in termes of sum of products of propagators is given.
- www.youtube.com/watch?v=fG52mXN-uWI The Secrets of Feynman Diagrams | Space Time by PBS Space Time (2017)
fafnir.phyast.pitt.edu/py3765/ Phys3765 Advanced Quantum Mechanics -- QFT-I Fall 2012 by E.S. Swanson mentions several milestone texts including:
- twitter.com/saylor 2.6 M followers as of 2022. Because of Bitcoin? Or was he famous before that?
- www.michael.com/ yes, he is Michael.com lol. When did he get the domain, and at what price? He's mildlly obsessed with domain names it seems: www.domainsherpa.com/saylor/. He also bought
frank.com,mike.com.emma.com. This was between 1994 and 2000. He mentions that his email issaylor@strategy.com.strategy.comredirects tomicrostrategy.comas of 2022, so seems still valid.We actually got a backlink from tvt.phishlabs.com to this page in August 2022, a phising security provider, presumably for showing his email here. This reminds Ciro of the All GitHub Commit Emails event!A quick google for that address also leads to www.washingtonpost.com/wp-srv/liveonline/00/business/saylor0621.htm, a year 2000 profile page by the Washington Post, followed by a Q&A. In the Q&A, Michael himself gives his email in relation to Saylor Academy:so it was already beyond leaked. Ciro did hit that email address seeking funding for OurBigBook.com, but no reply unfortunately. Maybe you gotta be part of the Rockefeller family to get a reply from these people? Well, at least this led to Ciro learning about the Rockefeller Foundation.Kensington, Maryland: What has happened to your vision of an internet university? I believe it is an important initiative and it doesn't require $100 million to get started. We at the Rockefeller Foundation would like to become involved. How can we do this?Michael Saylor: The internet university is alive and well. My goal is to initially roll out a cyber-libary of digital video that can be used by any for-profit or non-profit organization in order to accelerate the free education initiative. Eventually, people may just go direct to the web site.I think the entire thing will unfold over about 10 years.Send me an email if you would like to get involved. (saylor@strategy.com)
A suggested at Physics from Symmetry by Jakob Schwichtenberg (2015) chapter 3.9 "Elementary particles", it appears that in the Standard Model, the behaviour of each particle can be uniquely defined by the following five numbers:
E.g. for the electron we have:
- mass:
- spin: 1/2
- electric charge:
- weak charge: -1/2
- color charge: 0
Once you specify these properties, you could in theory just pluck them into the Standard Model Lagrangian and you could simulate what happens.
Setting new random values for those properties would also allow us to create new particles. It appears unknown why we only see the particles that we do, and why they have the values of properties they have.
- web.archive.org/web/20150623011722/http://users.physik.fu-berlin.de/~kleinert/b6/psfiles/qft.pdf by Hagen Kleinert (2015). 1500 pages!
- The Quantum Theory of Fields by Steven Weinberg (2013) www.cambridge.org/core/books/quantum-theory-of-fields/22986119910BF6A2EFE42684801A3BDF
- Quantum Field Theory by Lewis H. Ryder 2nd edition (1996) www.amazon.co.uk/Quantum-Field-Theory-Lewis-Ryder/dp/0521478146
- Lectures of Quantum Field Theory by Ashok Das (2018) www.amazon.co.uk/Lectures-Quantum-Field-Theory-Ashok-ebook/dp/B07CL8Y3KY
- A Modern Introduction to Quantum Field Theory by Michele Maggiore (2005) www.amazon.co.uk/Modern-Introduction-Quantum-Theory-Physics/dp/0198520743
There are unlisted articles, also show them or only show them.