Recent content by ShayanJ

A while back I was watching an interview with Sean Carroll and for some reason his explanation of the Everett's interpretation at that particular interview clicked for me and I became a proponent of it. But I always thought it made more sense to look at it at as the universe being a giant...

Well, black holes were never like the stars they were created from, even before this. When you're talking about a star, you can always separate the matter from the spacetime. But when a blackhole is formed, there is no matter anymore, you just have a little region in spacetime that is behaving...

This is very interesting, but unfortunately I'm a bit rusty on the subject so... Is this after inflation or the same as inflation? Sorry if my question doesn't make sense, but it seems like that, if this is true, we can establish this timeline: Big Bang => Inflation => temperature goes down as...

I didn't spend that much time on your code, but the one obvious problem I can see is that the if(L==R) block is unreachable because the while loop is over when that happens!

As you can see, Landau and Lifshitz explain that there are 2s-1 constants of motion and then goes on to say that the first one is energy. And there is motion in r direction because r is not constant, it's just a function of z. And when you want all the constants of motion, you will get the...

It seems correct. Now you can see that this is independent of r, ## \phi ## and t. So the corresponding momenta(including energy), are the constants of motion.

Yes, that's corerct. Just remember the ## \dot z^2 ##. Now you can substitute ## r = a + b \cos (\frac z c )##. Remember you need to use the chain rule again to calculate ##\dot r##.

Maybe I misunderstood what you were doing because this actually produces a very simple equation. You just have to simplify it using the fact that after the substitution you will get similar terms with opposite signs and also using ## \sin^2 \vartheta+\cos^2 \vartheta = 1 ##. You don't need to...

Noether's theorem just establishes the connection between symmetries and conservation laws. But just finding the conserved quantities is not that hard. You just need to write down the Lagrangian in the appropriate coordinates. Let me give an example of how to use the chain rule here: ## x=r \cos...

Remember ## x=r \cos \phi, y=r\sin \phi, z=z ## and also the chain rule. Well, write it down and find out!

It's not a good idea to actually use Cartesian coordinates to solve the problem. Of course things are going to be complicated when you ignore the symmetry of the problem which is a cylindrical symmetry. It's better to write e.g. ## T=\frac 1 2 m(\dot x ^2 +\dot y ^2 + \dot z ^2) ## and then...

To make it easier, first write the Lagrangian in Cartesian coordinates and then transform to cylindrical coordinates. But remember you also have the constraint r - a + b cos(z/c) = 0. So you should make take that into account when writing the Lagrangian too.

Sorry, I just thought that reply wasn't helpful and deleted it, but you saw it. Doesn't matter. Anyway, forget about this problem for a moment. Do you know how to write the Lagrangian of a system and then use it to write the Lagrange equations?

Summary:: Curious whether this story about this kid could be real, and if yes, is there any explanations? I just came across this reddit thread. I know, it could be fake. But I've seen a similar story before about a little girl who openly talked about wanting to kill her adoptive parents and...

I agree. Bell's work is one of the monumental milestones in the history of quantum mechanics. EPR just proved that there are still unanswered questions about quantum mechanics. But it was Bell who showed that those questions are actually not just philosophical, but deeply physical. But I should...