Can somebody answer this : physics.stackexchange.com/q/514603/238497

Hello people, i have a soft question about studying physics. So next year I'll be starting uni as a physics major, and i want to get to the level of someone who coulddo reasonably well on a physics olympiad. My prep-plan is the following:

Do you all think this is a reasonable plan? Cheers

also im going through Mathematical Methods for physics and engineering

@PM2Ring hi, sir.,

If you are free I have a question.

@yuvrajsingh Ok.

Is it true that law are not symmetric with time. @PM2Ring

@yuvrajsingh That is sort of true. I'll try to explain, but I'm not an expert on this topic, so I might not do a good job. :) But if I make a mistake, hopefully ACM or someone will correct me.

Yes.

As far as we know, all the laws & all the forces are symmetric with CPT, that is, the combination of charge, parity, and time. However, the weak nuclear force is not symmetric with parity, so to conserve CPT, something has to give with either charge or time. But (as far as I know) it doesn't really matter which one you choose.

OK.

@PM2Ring Hello! How are you?

This is a similar situation to how it's sometimes said that a positron is like an electron going backwards in time. If you could wave a magic wand and send an electron backwards in time, and reverse its charge, it would be identical to a positron.

@user8718165 Hi. I'm ok, but I have a bit of a headache. So I may not be thinking clearly right now. ;)

Is it depend on what kind of system I choose.

@PM2Ring

@yuvrajsingh Yes. That problem only arises in interactions involving the weak force. In all other interactions, time symmetry is perfect. Here's a relevant Wikipedia link: en.wikipedia.org/wiki/CP_violation

Also see en.m.wikipedia.org/wiki/Parity_(physics)#Parity_violation and the Wu experiment.

The weak interaction arises in beta decay. It changes the flavor of quarks & leptons. Eg, in beta minus decay, a down quark inside a neutron is transformed into an up quark, which turns the neutron into a proton. An electron is emitted, which conserves charge, and an electron antineutrino is emitted which conserves lepton number.

Here's a Feynman diagram, from Wikipedia:

As you can see, the reaction actually releases a W- boson, which is one of the carriers of the weak force. That boson quickly decays into the electron & antineutrino.

A closely related reaction is when a neutron absorbs a neutrino. This reaction makes the flavor-swapping more obvious. down-quark + neutrino -> up-quark + electron. It's basically the same Feynman diagram.

@PM2Ring no worries...BTW I bet you'll get well soon. Well...its been a long time since I talked with you last :)

I think the example clear everything, one doubt can you prove it for Newtonian gravitation @PM2Ring

@JohnyO42 Looks good but Feynman is a waste of time

@yuvrajsingh Newtonian gravity is certainly symmetrical in time. If you make a movie of some bodies in orbit, then if you play the movie backwards the orbital motions in the reversed movie will still follow Newton's laws perfectly.

Here's another way to say the same thing. Say you have a program to simulate the orbital motions of some bodies. If you pause the simulation at any point, and reverse all the velocity vectors of all the bodies, then un-pause the simulation, all the bodies will reverse their motions perfectly.

Yes, let me research about it more.

Thank you.

Do you like cricket. @PM2Ring

@yuvrajsingh I've been thinking about your Astronomy question astronomy.stackexchange.com/q/34040/16685 As others have said, you should really only ask one question per question. The stuff in the edit is interesting, but even by itself (without the stuff about why stars & planets are round) it's a bit too broad, and it's probably a better fit for Physics.

But you will need to clean it up a bit first. Maybe some of the other h bar regulars can help you to turn it into a focused question that won't get downvotes & close votes. ;)

@yuvrajsingh My pleasure. Sorry, no I don't like cricket. I had to play it at school, and I found it boring, and a bit scary. Due to astigmatism, I'm not good at judging the distance of a ball that's coming towards me at certain angles.

There's one thing I do like about cricket: most Americans find it totally baffling. :D

So @PM2Ring should I ask it on physics site edit part.

@yuvrajsingh I think so, but you need to write it in a way that's more clear, and more narrow.

Can you out it as a question, I agree with it.

@PM2Ring

Are you OK with it.

@yuvrajsingh As Mazura said, on the very large scale, the universe is homogeneous and isotropic. But obviously on the small scale, that's not true. So you're asking if the local irregularity is ultimately due to quantum randomness, or if there are other causes.

Please sir. Because already I receive so many comment to edit the question, can you put this question on physics main site.. @PM2Ring

@JMac I already await the random emails from nutcases who will claim to have discovered this even before 2014.

@yuvrajsingh Don't bother editing that Astronomy question now. You should've done that earlier, before Mazura answered the edit part. If you remove the edit part now, it will invalidate Mazura's answer.

OK.

@yuvrajsingh If you ask the edit part on Physics, I'll look at it and edit it if it has English grammar problems.

Actually problem, is system suspended me to ask the question, for 6 months. So I can, t ask the question @PM2Ring

@yuvrajsingh Oh, I see. So you want me to ask the question. I'll think about it. Maybe it'd be better to just discuss it in here. It's usually quiet in chat on the weekends, but we can discuss it some more in a few days when more people are around.

Yes. That, s OK, but please ping me whenever you discuss it, one thing more, that is other user on h bar I think are not interested to chat with me. Will they be ready to include me. @PM2Ring

You are the only one in the room other than Indian student and John rennie.

@yuvrajsingh One reason you tend to get downvotes and closevotes on your questions is that because people think they are not clear. I think you need to do more work to improve your English grammar. We aren't so strict about grammar in chat, unless messages are so bad that we can't figure out what the person is saying.

But on the main site, the quality standards are higher. Stack Exchange questions & answers should use proper English, like you'd expect to see in Wikipedia articles (although some of those have grammar problems...).

@yuvrajsingh John & I have a lot of experience dealing with Indian people, so we are used to Indian English. Other chat members may not be so patient if they have trouble fully understanding your posts. And sometimes even I can be unsure of what you're trying to say. ;)

I think you are right that can be a reason, we'll I will try my best to improve my grammar, so the my comment and answer will be more understandable and clear to the reader. @PM2Ring

@yuvrajsingh I'm sure it will make a difference. And improving your English will also be good for your school and university work.

Everyone makes mistakes, even native speakers. As long as the mistakes are rare, it's not a big deal. Eg, I made an editing mistake earlier: "One reason you tend to get downvotes and closevotes on your questions is that because people think they are not clear." I should have used either "that" or "because" not both words together. :)

Is it ok to answer physics.stackexchange.com/q/515688/123208 or is it too homework-like?

@JohnyO42 As @bolbteppa pointed Feynman is childish and useless. I'd prefer Irodov (beginners), SS Krotov, or norman for Olympiads

@AbhasKumarSinha really? I liked feynman when i read it a couple months ago, atleast Vol.1. I suppose it would be for insight not serious pedagogical reasons

@PM2Ring problem is that there is very, thin difference between asking answer of the question, and student who is seeking for the concept error, some one who know the concept, but he is making error. But no system, even the users and moderators too. See the question like that straight away closed it. Without thinking it carefully, but as user of this site, I think it is better to keep mum shut in this, because no thing can happen, so i am saying it totally depend upon you. @PM2Ring

You are older user than me, so you know what exactly is right.

And thanks, I genuinely I improve my English, as well as knowledge, so some day I might in your chair answering the question.

@JohnyO42 if you like it and you think that it's helping you, then you can use it. Personally, I don't like it. I'm like rigorous, theoritical books... Feynman's all 3 volumes are mostly like lengthy story book (lengthy) that's the part I don't like

The Feynman lectures do have problem sets to go with them, but they are so old and outdated that they won't be much help on Olympiad questions.

Sorta like nobody really studies directly from Euclid's Elements anymore...

...or even Einstein's original work.

maybe try my hand at Griffiths Quantum

Zemansky and Dittman is good for thermo.

@JohnyO42 I've heard meh things about Griffiths Quantum

What do you recommend then

considering it would be more about curiosity than the necessity since Olympiad problems hardly require any QM

@JohnyO42 mine was Townsend but it it was very bad in the intuition aspect

a better one for intuition, if you're just looking for an introduction, would be this

amazon.com/Nonclassical-Physics-Beyond-Newtons-View/dp/…

Can I add an entropy axis?

For anybody that feels like looking at a few lines of work

can anybody see where I’ve messed up?