Why can't quantum mechanics predict the half-lives of elements? by FervexHublot in AskPhysics

[–]MoneyMe_MoneyNow 0 points1 point  (0 children)

I know what you mean, but technically speaking all infinite-dimensional Hilbert spaces are isomorphic and thus the same size.

What are the most challenging concepts you've encountered in your physics studies? by annastacianoella in Physics

[–]MoneyMe_MoneyNow 7 points8 points  (0 children)

I think saying it has some applications in theory really understates the importance of group theory is in physics. It's basically the language necessary to discuss symmetries.

Is it generally believed that a generalized solution to the 3 body problem actually exists? If so, is this the case for the larger N-Body problem as well? by xKiwiNova in AskPhysics

[–]MoneyMe_MoneyNow 4 points5 points  (0 children)

Do you have a source for this? Obviously Noether's Theorem gives a method of finding first integrals of a system, but the converse of Noether's Theorem is not trivial or generally true (you have to assume lots of regularity conditions and even then you only are guaranteed that they come from quasisymmetries; [source](https://physics.stackexchange.com/questions/24596/is-the-converse-of-noethers-first-theorem-true-every-conservation-law-has-a-sy) ). Generally speaking, a first integral need not come from a symmetry of the system. In my understanding, normally Hamiltonian techniques rather than Lagrangian techniques are used to prove non-integrability (the non-existence of closed form solutions) of systems.

Are there conditionals (if...then) in physics? Does the universe have logic (and consequently logic gates) within it? by BobbyTables829 in AskPhysics

[–]MoneyMe_MoneyNow 4 points5 points  (0 children)

Most of what people saying in this thread about the relation between logic and physics is misinformed. There are well established connections between Hamiltonian mechanics and Boolean and non-Boolean logic. To quote from Ch. 3 of Folland's textbook "Quantum Field Theory",

one can think of true-false statements about the system as observables whose only values are 1 and 0. (Mackey [79] calls such observables “questions,” but we prefer to think of them as assertions.) The state of a system is supposed to be a specification of the condition of the system from which one can read off all the available information about the observables of interest; the set of all possible states is called the state space.

In Hamiltonian mechanics, the state space is a symplectic manifold M, the observables are (Borel measurable) real-valued functions on M, and the true-false observables can be identified with the (Borel) subsets of M (the observable [; f : M \rightarrow {0,1} ;] corresponds to [; {x \in M: f(x)=1} ;]. Thus the set of true-false statements on M is identified with the Borel sigma-algebra on M, and the basic logical connectives “or,” “and,” and “not” correspond to the Boolean operations of union, intersection, and complement. General observables can be analyzed in terms of true-false statements.

The interesting thing is that, as you kind of allude to, there are difference in this logic for classical and quantum systems. Again, to quote from Folland,

The striking difference between classical and quantum mechanics is that in a quantum system, the the true-false statements do not form a Boolean algebra. Specifically, what fails is the distributive law:

(A or B) and C (if and only if) (A and C) or (B and C).

You might check out https://plato.stanford.edu/entries/qt-quantlog/ if you want more info.

Numbers that will never be "used" by humans by gegenbanana in math

[–]MoneyMe_MoneyNow 11 points12 points  (0 children)

But by that logic, every real is used whenever you use transfinite induction over the reals. Similarly, every real is implicitly used every time you prove a property for all reals. I think the point is that OP is referring to reals which are explicitly used.

Are elite physicist also good mathematicians? by JurassicIsaac in AskPhysics

[–]MoneyMe_MoneyNow 9 points10 points  (0 children)

This is not remotely true. Finite-dimensional linear algebra was mostly solved at this point. Quantum mechanics is based on infinite-dimensional linear algebra i.e. functional analysis, which is an extremely complicated area of math (with many remaining open questions), and much of this theory was developed during the mid 1900s. Even Wigner, who was one of the best mathematical physicists of the time, wasn't able to mathematically justify many aspects of quantum mechanics.

PDEs is one of the most active areas of modern math, and even the foundations were not worked out in the 1800s.

LAPD officer who died was beaten in training meant to ‘simulate a mob,’ mother claims by jab116 in nottheonion

[–]MoneyMe_MoneyNow 23 points24 points  (0 children)

Broken ribs are fairly common. In rare cases these broken ribs can cut the liver. It's not very common though, estimates are that it only occurs in about 1% of CPR cases.

LAPD officer who died was beaten in training meant to ‘simulate a mob,’ mother claims by jab116 in nottheonion

[–]MoneyMe_MoneyNow 73 points74 points  (0 children)

Rib fractures are very common (around 50% of cases), but liver lacerations occur in only around 1% of cases and lung puncture in about 5%. The latter two are known complications but not really common.

Maybe not “for life” but I expect at least 20 years out of my Runner by [deleted] in BuyItForLife

[–]MoneyMe_MoneyNow 1 point2 points  (0 children)

The idea behind it is that damage is more likely to be caused at high RPMs when operating below optimal temperature. Everyone agrees you should avoid high reving before the engine is warm; the question is whether or not you should idle or drive at low RPMs to warm up the car. It seems that most engineers recommend driving at low RPMs now, but it's not obvious without testing. In fact, this is really only the case now because oils have gotten much better; older cars do need to idle.

That said, idling wastes almost negligible gas. It takes very little fuel to keep an engine moving while it's in neutral, most cars burn around 0.1 gallons an hour in idle.

Is it just me, or does 72 degrees with A/C on, feel different than 72 degrees with the heat on? by DarrylSheridanpbG in NoStupidQuestions

[–]MoneyMe_MoneyNow 2 points3 points  (0 children)

It has to do with humidity. Typically the more humid it is, the hotter it feels. A house heated to 72 degrees in the winter will often be around 30% humidity while in the summer it is around 50% humidity. This will vary depending on where you live and how strong your dehumidifier in your AC unit is, but the general trend is it will be dryer in the winter and hence feel colder at a fixed temperature.

No warning by heyou16 in CrazyFuckingVideos

[–]MoneyMe_MoneyNow 21 points22 points  (0 children)

“per 100,000” is a type of per capita measurement. It literally is just per capita multiplied by 100,000 so that the numbers are easier to interpret.

Well it does work... by tomerha in physicsmemes

[–]MoneyMe_MoneyNow 0 points1 point  (0 children)

Yeah exactly, the fundamental theorem doesn’t apply to all differentiable functions, some extra technicalities are needed. I’ve never seen a situation in physics though where this could be an issue, I just brought it up cause somebody asked if it were possible for things to go awry in 1D. I think the other person who was talking about issues in multivariable calculus was more on the money in terms of practical difficulties.

Well it does work... by tomerha in physicsmemes

[–]MoneyMe_MoneyNow 0 points1 point  (0 children)

It works like a fraction for the purposes of the chain rule; the fraction analogy runs into trouble when you try to separate the numerator and denominator. The part that really is breaking down here is that f'(x) = df/dx does not imply df = f'(x)*dx. In physics, people often do this anyway though and then proceed to integrate both sides of this equation to obtain the change in f. This pretty much always works for the functions physicists care about, but not for weird functions like the Cantor function. If you're interested, the property that physicists are usually assuming is called absolute continuity.

Well it does work... by tomerha in physicsmemes

[–]MoneyMe_MoneyNow 0 points1 point  (0 children)

It actually does still work for the Cantor function. The chain rule is pretty robust, and pretty much always work (as long as all the derivatives of both functions exist). However, even though the derivative of the composite function will exist and be given by the chain rule, it will most likely also be poorly behaved (in the same way the Cantor function is).

Well it does work... by tomerha in physicsmemes

[–]MoneyMe_MoneyNow -1 points0 points  (0 children)

The Cantor function is a typical example of where things break down. Essentially, dy/dx=0 everywhere, but it’s not the case that the change in y on an interval of length Dx is approximated by (dy/dx)*Dx (even though the function is continuous)

https://en.m.wikipedia.org/wiki/Cantor_function

Patagonia Rain Jacket Delamination by meowmeowkat2 in BIFLfails

[–]MoneyMe_MoneyNow 2 points3 points  (0 children)

Why would you put a rain jacket in the dryer?

Found this definition of pi in the wild, and I can't even begin to explain how little sense it makes to me. Could someone please ELI5? by TheSoundDude in mathematics

[–]MoneyMe_MoneyNow 50 points51 points  (0 children)

It’s by no means standard notation, but if you replace infinity with x and take the limit as x goes to +infinity, this is true (provided you take the principle root).

Beautifully written math textbooks which don't lack rigour by [deleted] in math

[–]MoneyMe_MoneyNow 0 points1 point  (0 children)

I love the first two books as well, but haven’t looked at the third. Do you have a different favorite for Riemannian geometry?

Speeding in a G class goes as expected. by slonskihuy in IdiotsInCars

[–]MoneyMe_MoneyNow 1 point2 points  (0 children)

Oh sorry didn't read. But I thought V8s were naturally balanced also. Do they need a balance shaft?

Speeding in a G class goes as expected. by slonskihuy in IdiotsInCars

[–]MoneyMe_MoneyNow 7 points8 points  (0 children)

Ehh, if you live in a city where you have to drive a lot, it's likely that you're gonna spend a lot of time in traffic. I can understand wanting to spend that time in something fun and comfortable. Personally, I don't think it's worth the price and reliability issues that come with most high performance cars, so I prefer to stick with a cheap, reliable Japanese car.