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A 9-line summary of textbook physics

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Re: A 9-line summary of textbook physics

#101

Post by B1FF_PSUVM »

gus_massa wrote: post #71
323 wrote: post #41

I've read a few times that you can derive the Maxwell equations from knowing that U(1) exists, as this article implies, that every point in space has (among other things) the symmetry of a circle. But I've never seen this derivation. I assume it's either trivial or too complicated. Anyone has a link or thoughts on this?

I wrote an ELI25 explanation in a comment a few months ago, and I'll copy it here: In quantum mechanics the wave function Ψ is has complex values. If you multiply everything in the universe by -1, nothing changes because all the physical results use ΨΨ* (where * is the complex conjugation). You can also multiply everything by i or -i. Moreover by any other complex number of modulo 1 because ΨΨ* does not change. (The…

> studding Physics

Typo or rhetoric?

A collectible, either way ;-)

Re: A 9-line summary of textbook physics

#102

Post by gus_massa »

whimsicalism wrote: post #91
gus_massa wrote: post #71

Earlier quoted context omitted.

I wrote an ELI25 explanation in a comment a few months ago, and I'll copy it here: In quantum mechanics the wave function Ψ is has complex values. If you multiply everything in the universe by -1, nothing changes because all the physical results use ΨΨ* (where * is the complex conjugation). You can also multiply everything by i or -i. Moreover by any other complex number of modulo 1 because ΨΨ* does not change. (The…

What does it mean to "add a new field A"? Add to what? The wave function?

Look at the first formula in https://en.wikipedia.org/wiki/Quantum_electrodynamics#Mathem...

If A and B are zero then F is zero and you can forget the second part of the right hand part of the equation. Also, you must replace D with ∂.

Now you have equation of electrons and positrons that move in a universe that has no electromagnetism. The important part is that in that equation, the only variable is ψ(t,x,y,z) that appears twice, the rest of the things written there are just derivatives, constants or indices.

Now you can turn on B(t,x,y,z) that represents the external field, so the electrons and positions move in a more interesting patterns, but they don't "see" each other. Again, the only variable is ψ(t,x,y,z).

Now you do the trick with a local U(1) symmetry, and the only way to do the trick is to add a new variable A(t,x,y,z). But you must use the complete equation because as explained in Wikipedia F(t,x,y,z) is calculated using the derivatives of A(t,x,y,z). So now you have two variables ψ(t,x,y,z) and A(t,x,y,z).

So you "add a new field A" to the list of variables that appear in the right hand of the equation, or to be more precise, you get a new equation that has one additional variable A.

Re: A 9-line summary of textbook physics

#103

Post by podiki »

whimsicalism wrote: post #91
gus_massa wrote: post #71

Earlier quoted context omitted.

I wrote an ELI25 explanation in a comment a few months ago, and I'll copy it here: In quantum mechanics the wave function Ψ is has complex values. If you multiply everything in the universe by -1, nothing changes because all the physical results use ΨΨ* (where * is the complex conjugation). You can also multiply everything by i or -i. Moreover by any other complex number of modulo 1 because ΨΨ* does not change. (The…

What does it mean to "add a new field A"? Add to what? The wave function?

Add to your theory/model. In order to make the symmetry work, you need something to "fix" the discrepancy you would otherwise have in the equations. So you add this field (variable) to make the whole thing consistent. In the end, you see you needed this "gauge field" (for historical reasons these are called "gauge symmetries") which is electromagnetism.

Re: A 9-line summary of textbook physics

#104

Post by PrettyPebble »

_Nat_ wrote: post #95
PrettyPebble wrote: post #86

Earlier quoted context omitted.

No, it is fun! The scientists who are looking for exceptions to the standard model and to general relativity since 50 years are having a crisis at present, as often told. The 9 lines imply all equations of physics. Every Lagrangian of physics is included. The lines are also coherent: none contradicts another. They are complementary: the cover all observations and all fields of physics. No field of physics is left out…

Those 9-lines don't imply all of physics. They don't even mention most of physics. A lesser problem is that they're not correct, either. For example, Line-5 suggests that entropy is never below the Boltzmann-constant. Which simply isn't true; there're notions of zero-entropy, where zero is less than the Boltzmann-constant. For another example, Line-2 suggests that nature itself is local; this would contradict non-loc…

Of course the 9 lines imply all of physics. Just mention a part of physics that is missing, and I'll buy you a beer.

"Zero entropy" is indeed against the laws of physics - in this universe. It may be different in other universes.

Line 2 does not speak about locality, but about the speed of light. Entanglement does not violate the speed of light - in this universe. It may be different in other universes.

If you know what a Lagrangian is - in quantum theory, in quantum field theory, in the standard model and in general relativity - you also know that there is no random interpretation in the 9 lines.

Re: A 9-line summary of textbook physics

#106

Post by Maursault »

WalterGR wrote: post #77
7373737373 wrote: post #68

Earlier quoted context omitted.

https://math.ucr.edu/home/baez/constants.html the mass of the up quark the mass of the down quark the mass of the charmed quark the mass of the strange quark the mass of the top quark the mass of the bottom quark 4 numbers for the Kobayashi-Maskawa matrix the mass of the electron the mass of the electron neutrino the mass of the muon the mass of the mu neutrino the mass of the tau the mass of the tau neutrino 4 numbe…

^—— “How Many Fundamental Constants Are There?” by John Baez

Good to know the speed of light in a vacuum is not a fundamental constant.

Re: A 9-line summary of textbook physics

#107

Post by KineticLensman »

graderjs wrote: post #49

s/nature/the simulation/g 1. Total compute capacity is limited and redistributes toward areas of high activity. 2. Processor speed is limited. 3. Mutations are sensibly constrained to prevent overflow. 4. Smallest addressable memory space. 5. No process is ever fully idle. 6. IPC is done using circles. 7. The kernel however operates at the level of spheres, and pointers to pointers to pointers to spheres. 8. There's…

Religion: "God did it"

Simulation hypothesis: "God did it, with a computer"

Re: A 9-line summary of textbook physics

#108

Post by _Nat_ »

PrettyPebble wrote: post #104
_Nat_ wrote: post #95

Earlier quoted context omitted.

Those 9-lines don't imply all of physics. They don't even mention most of physics. A lesser problem is that they're not correct, either. For example, Line-5 suggests that entropy is never below the Boltzmann-constant. Which simply isn't true; there're notions of zero-entropy, where zero is less than the Boltzmann-constant. For another example, Line-2 suggests that nature itself is local; this would contradict non-loc…

Of course the 9 lines imply all of physics. Just mention a part of physics that is missing, and I'll buy you a beer. "Zero entropy" is indeed against the laws of physics - in this universe. It may be different in other universes. Line 2 does not speak about locality, but about the speed of light. Entanglement does not violate the speed of light - in this universe. It may be different in other universes. If you know w…

There's no Lagrangian in those 9-lines. Nor is there Quantum-Theory, nor the Standard-Model, nor General-Relativity. Nor is science there, really.

Which is kinda my point -- those 9-lines aren't all of science.. unless, I guess, if you assume that all of science is a given. But then, why even have 9-lines when 0-lines could do?

Then it's hard to avoid critiques because there're obvious flaws. For example, yes, there're totally productive notions of zero-entropy -- even if not in the models you're used to. For another example, macroscale-constants haven't been demonstrated to emerge from the Standard-Model -- for example, it hasn't been demonstrated that astronomical-scale measurements aren't influenced by unknown factors, such as many-body forces, which might cause results that'd differ from those predicted by the Standard-Model. And since we can measure some of those things not known to emerge from the Standard-Model, the idea that the Standard-Model captures everything -- including those things not known to emerge from it -- doesn't follow.

But then that seems to be getting off-topic, because while there'd seem to be many things off about this, the one I'd really stress is that those 9-lines don't contain what they claim to.

Re: A 9-line summary of textbook physics

#109

Post by analog31 »

Maursault wrote: post #106
WalterGR wrote: post #77

Earlier quoted context omitted.

^—— “How Many Fundamental Constants Are There?” by John Baez

Good to know the speed of light in a vacuum is not a fundamental constant.

Apparently, even vacuum is not a fundamental constant.

Re: A 9-line summary of textbook physics

#110

Post by didericis »

gus_massa wrote: post #55

> Lines 1, 2 and 3, together, uniquely determine special and general relativity, cosmology, the Hilbert Lagrangian and Einstein's field equations, as told here. This is a huge exaggeration. For example 1 says "W=∫L" but L is never defined. The definition of L hides a lot of details, in particular that each point of the universe is equivalent, so there is translation invariance that using the Noether's theorem implies…

These kinds of comments block me from doing a physics dive; I don’t know where to start/am worried about starting from a bad point. I don’t know whether to follow some of the trails the linked author has laid out if I want to learn more, whether you’re nitpicking, or whether you’re advocating for a much better approach that starts with the details you say this obfuscates. When I was younger and had more time I’d be willing to eat the inefficiency, and the bigger reason for not doing a deep dive is the difficulty, my own laziness, and lack of practical need, so take what I’m saying with a grain of salt, but the time needed to parse criticism like this to see whats legitimate and whats not drives me a bit nuts.

I’ve done enough self learning to know that there is no perfect starting point/backtracking is inevitable, but something about the modern intellectual landscape feels very noisy/jargony and particularly prone to inefficient learning.

When you say “there is translation invariance that using the Noether's theorem implies the conservation of momentum”, I have no idea what that means. It sounds like a description of a turbo encabulator. I’m sure its not, and that your description is much more efficient than spelling it out from the ground level, but it annoys me how difficult it is to distinguish between a legitimate domain expert jargon meant to condense complexity and unnecessarily obfuscatory jargon that works more like a status/club membership symbol.

Maybe its always been like this somewhat and that problem is inevitable, idk.

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