"...bootstrappers find that many different spin-0 particles are possible." Is that a typo, or is it really possible to have spin -0?
Maybe for small values of 0?
;)
Simple Rules ‘Bootstrap’ the Laws of Physics
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Re: Simple Rules ‘Bootstrap’ the Laws of Physics
#32> When bootstrapping, physicists determine how elementary particles with different amounts of “spin,” or intrinsic angular momentum, can consistently behave. In doing this, they rediscover the four fundamental forces that shape the universe. They have derived gravity through quantum mechanics? What rock have I been living under?
There is a nice derivation of Newton’s law from quantum field theory in Zee‘s book „Quantum Field theory in a nutshell“. You can also arrive at Einstein’s field equations by deriving the beta function of bosonic string theory and (2-2 scattering to be precise) and requiring that it is constant.
Interesting, is there any reading material on the second point?
Re: Simple Rules ‘Bootstrap’ the Laws of Physics
#33Wondering if anyone could recommend a layman's introduction to "spin". I've read the Wikipedia article, I broadly understand it, but just curious as to how it was discovered, why it is considered an "intrinsic" form of angular momentum, and why it is so fundamental a concept in our universe.
I recommend reading about the Stern Gerlach experiment. I think that nails down what makes spin counterintuitive, and is a really clear example of how the predictions of quantum mechanics can't come from classical mechanics. The fundamental nature of it and the units can be reasoned out by looking at conservation of angular momentum.
Re: Simple Rules ‘Bootstrap’ the Laws of Physics
#34"...bootstrappers find that many different spin-0 particles are possible." Is that a typo, or is it really possible to have spin -0?
An example is a helium nucleus in the ground state
Re: Simple Rules ‘Bootstrap’ the Laws of Physics
#35"As the Nobel Prize winner Steven Weinberg showed in 1964, the existence of a spin-2 particle leads inevitably to general relativity"
Huh?!?
spin-2 particle leading to GR was the prime essence of Feynman lectures on Gravitation, 1962
Re: Simple Rules ‘Bootstrap’ the Laws of Physics
#36> When bootstrapping, physicists determine how elementary particles with different amounts of “spin,” or intrinsic angular momentum, can consistently behave. In doing this, they rediscover the four fundamental forces that shape the universe. They have derived gravity through quantum mechanics? What rock have I been living under?
Feynman lectures on Gravitation, 1962
Re: Simple Rules ‘Bootstrap’ the Laws of Physics
#37The content of the article is very interesting and worth reading, but the framing feels circular. Some laws of nature are fundamental and other laws are inevitable consequences of those laws. If the inevitable laws were not inevitable, then they would be fundamental. As our knowledge and explanatory power grows, some laws that first appeared fundamental have been explained in terms of deeper laws, but we must still a…
I agree with this. I've always found theories of everything to be unsatisfying in this way, because they never explain how the laws of physics got the way they are. Assuming the existence of some abstraction called spin to derive the fundamental forces is a great exercise in internal consistency, but hardly meets any definition of "bootstrapping" as I understand the term. The only theory I've ever encountered that pa…
As to how the laws got where they are Lee Smolin and Roberto Ungar say that it's possible they were not always the way they are and that they evolved spontaneously over time. And that the spontaneity just is the way things are i.e. there's no explanation for it. At least that's my recollection from reading their book.
https://en.m.wikipedia.org/wiki/The_Singular_Universe_and_th...
The other explanation seems to be the multiverse. i.e. we just got a random set of self consistent laws. Again there seems to be no explanation as to why or how the multiverse came to be, is there?
Re: Simple Rules ‘Bootstrap’ the Laws of Physics
#38"As the Nobel Prize winner Steven Weinberg showed in 1964, the existence of a spin-2 particle leads inevitably to general relativity" Huh?!? spin-2 particle leading to GR was the prime essence of Feynman lectures on Gravitation, 1962
There is a link pointing to https://journals.aps.org/pr/abstract/10.1103/PhysRev.135.B10.... Some quick Googling shows quantum gravity being referred to as Feynman-Weinberg gravity, so both must have contributed parts of the theory.
Re: Simple Rules ‘Bootstrap’ the Laws of Physics
#39The content of the article is very interesting and worth reading, but the framing feels circular. Some laws of nature are fundamental and other laws are inevitable consequences of those laws. If the inevitable laws were not inevitable, then they would be fundamental. As our knowledge and explanatory power grows, some laws that first appeared fundamental have been explained in terms of deeper laws, but we must still a…
I agree with this. I've always found theories of everything to be unsatisfying in this way, because they never explain how the laws of physics got the way they are. Assuming the existence of some abstraction called spin to derive the fundamental forces is a great exercise in internal consistency, but hardly meets any definition of "bootstrapping" as I understand the term. The only theory I've ever encountered that pa…
I was expecting Noether’s theorem to make an appearance in this article, because it is utterly fundamental to this kind of work. Her insight was that mathematical symmetries (like the spin symmetries that the article discusses) lead to laws of conservation, and vice versa. So laws like conservation of momentum correspond to translation symmetry, i.e. the assumption that the laws of the universe apply everywhere equally.
https://www.discovermagazine.com/the-sciences/how-mathematic...
Re: Simple Rules ‘Bootstrap’ the Laws of Physics
#40The content of the article is very interesting and worth reading, but the framing feels circular. Some laws of nature are fundamental and other laws are inevitable consequences of those laws. If the inevitable laws were not inevitable, then they would be fundamental. As our knowledge and explanatory power grows, some laws that first appeared fundamental have been explained in terms of deeper laws, but we must still a…
> ... but we must still ask why the deeper laws exist.
Don't things have to stop somewhere, otherwise there's an infinite regress ("turtles all the way down")?