Simple Rules ‘Bootstrap’ the Laws of Physics • Hacker News Board

Re: Simple Rules ‘Bootstrap’ the Laws of Physics

#81

Post by ISL » Tue, Dec 10, 2019, 4:57 AM UTC

chongli wrote: post #18

ISL wrote: post #11

Earlier quoted context omitted.

Objects with spin can be point-like but carry angular momentum. The electron is one such particle. It is "intrinsic" because it has no known moving parts. If it had moving parts, and that motion had net angular momentum, we would refer to it in many contexts as "orbital angular momentum". Spin should seem counterintuitive. There are no macroscopic objects that I am aware whose spin you can feel with your hands. Our r…

It's totally counterintuitive. Classical angular momentum requires a choice of origin. All angular momentum is then relative to that origin. Any point particle lying at the origin should not be able to have any angular momentum. Imagining the classic "figure skater experiment", the figure skater speeds up as she draws her arms inward, due to conservation of angular momentum. If she could shrink down to a point, her a…

You need not worry about infinity in the black-hole case. Known physics ends at the black hole's event horizon, for an external observer. Black holes of a given mass can only have so much angular momentum.

As a rule of thumb, that angular momentum corresponds to that at which the equator of the black hole is moving at the speed of light.

This has important consequences for the mergers of two high-spin black holes that have aligned spins. The merger is actually delayed for a little while, just before merger, as the binary dumps angular momentum through gravitational radiation.

Re: Simple Rules ‘Bootstrap’ the Laws of Physics

#82

Post by ISL » Tue, Dec 10, 2019, 4:59 AM UTC

criddell wrote: post #60

ISL wrote: post #11

Earlier quoted context omitted.

Objects with spin can be point-like but carry angular momentum. The electron is one such particle. It is "intrinsic" because it has no known moving parts. If it had moving parts, and that motion had net angular momentum, we would refer to it in many contexts as "orbital angular momentum". Spin should seem counterintuitive. There are no macroscopic objects that I am aware whose spin you can feel with your hands. Our r…

> Objects with spin can be point-like but carry angular momentum. This is where I get stuck. The particles are all excitations of a quantum field. So what does spin mean in that context?

It simply turns out that, in order to be a stable excitation of the vacuum, an electron must have all the properties of an electron.

I've not yet encountered an experimentally-testable explanation that goes deeper than that.

Re: Simple Rules ‘Bootstrap’ the Laws of Physics

#83

Post by Iv » Tue, Dec 10, 2019, 6:30 AM UTC

jetrink wrote: post #8

The 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 think the bigger mystery is why there are less fundamental laws than inevitable ones. That the universe principles arise from simple rules.

How comes there are not millions of different quark types? Why not 5180 fundamental forces? Going smaller nature becomes simpler.

It is hard to express but I have always felt this universe has a complexification ability, where at every level it seems possible for simple rules to lead to complex outcomes.

Re: Simple Rules ‘Bootstrap’ the Laws of Physics

#84

Post by int_19h » Tue, Dec 10, 2019, 6:39 AM UTC

jetrink wrote: post #8

The 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 think we still have too poor understanding of the what to be pondering the why. If past history is any guide, such attempts tend to mislead - e.g. Einstein's "God doesn't play dice".

Re: Simple Rules ‘Bootstrap’ the Laws of Physics

#85

Post by Geee » Tue, Dec 10, 2019, 7:52 AM UTC

jordanpg wrote: post #42

discreteevent wrote: post #37

Earlier quoted context omitted.

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 th…

> not always the way they are and that they evolved spontaneously over time But how did they get any way at all? How and why do they evolve? > multiverse. i.e. we just got a random set of self consistent laws. This raises even more questions. Why are there any multiverses with any laws at all? From where did the stuff in the multiverses come from? What initiated this chain of multiverse creation, or why is it inevita…

It's insanely difficult to understand why there is something.

Re: Simple Rules ‘Bootstrap’ the Laws of Physics

#86

Post by bsder » Tue, Dec 10, 2019, 8:10 AM UTC

saagarjha wrote: post #57

bsder wrote: post #55

Earlier quoted context omitted.

And yet, funnily enough, your phone needs a more thorough understanding of gravity than you do. The GPS system must correct for relativistic effects that cause the atomic clocks to shift relative to ground.

Isn’t this corrected by the satellites themselves?

Mostly, but there are still correlations between the satellites that are corrected by the receiver.

The Earth's gravity field is not deterministic.

Re: Simple Rules ‘Bootstrap’ the Laws of Physics

#87

Post by beaconstudios » Tue, Dec 10, 2019, 9:08 AM UTC

mannykannot wrote: post #75

beaconstudios wrote: post #66

Sounds to me like the higher order laws of physics are emergent properties of the lower level properties. Is this surprising? Every system in existence is the result of the emergent organisation of lower systems - why would the laws of physics be different?

It is one thing to say that something is plausible, and something quite a bit more to be able to show that not only is it plausible, but also that it is the way things actually are, and in a very specific way.

yes, but the reporting is as if the fact that emergence exists is itself surprising. I'm sure the actual science is a lot more sober and focused on the genuine revelations, around how such emergence plays out.

Re: Simple Rules ‘Bootstrap’ the Laws of Physics

#88

Post by robocat » Tue, Dec 10, 2019, 10:30 AM UTC

jordanpg wrote: post #29

jetrink wrote: post #8

The 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…

Mathematics is just a set of internally consistent rules.

There is no reason the universe needs to follow an internally consistent ruleset (although so far our measurements seem to find it to be, quite precisely).

Re: Simple Rules ‘Bootstrap’ the Laws of Physics

#89

Post by sunstone » Tue, Dec 10, 2019, 12:26 PM UTC

Geee wrote: post #85

jordanpg wrote: post #42

Earlier quoted context omitted.

> not always the way they are and that they evolved spontaneously over time But how did they get any way at all? How and why do they evolve? > multiverse. i.e. we just got a random set of self consistent laws. This raises even more questions. Why are there any multiverses with any laws at all? From where did the stuff in the multiverses come from? What initiated this chain of multiverse creation, or why is it inevita…

It's insanely difficult to understand why there is something.

Now there's an understatement for you.

Re: Simple Rules ‘Bootstrap’ the Laws of Physics

#90

Post by solarist » Tue, Dec 10, 2019, 2:26 PM UTC

hprotagonist wrote: post #23

maxnoe wrote: post #9

Earlier quoted context omitted.

Proven is the wrong word. You cannot prove a theory. Deriving a description of gravity from first principles would be more appropriate

*an empirical theory. I can certainly prove things about, say, addition.

if you mean you can prove 2+2==4, it's actually tautology: | | + | | == | | | |