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Landau & Lifshitz introduce what are known as Lemaître coordinates (the coordinates and associated Schwarzschild metric were first used by G. Lemaître in 1932-1935). The figure (Figure 20) on p. 310 is a magnificent illustration of why all timelike and null paths within the black hole region... Read more

This problem has been addressed before under https://www.physicsforums.com/threads/trouble-understanding-coordinates-for-the-lagrangian.1006528/ I also copied the following problem statement with Landau's very sketchy solution from this old post, because I don't have the English edition of... Read more

As was repeatedly shown by Anders Persson, https://rmets.onlinelibrary.wiley.com/doi/10.1002/qj.2477 http://rus.ums.rshu.ru/file1654 the "carousel experiment" is a poor case to show the Coriolis force despite claims it show the "Coriolis effect". Indeed, the Coriolis force, if it... Read more

A video of the Aurora Australis (Southern Lights) was captured from the SpaceX capsule Dragon.

A simple linear problem goes min c'x such that f_i(x)<= 0 and Ax=b x Suppose we make all constraints affine. Then Dx-e<=0 and Ax-b =0 We get the Langrangian function as c'x + λ'(Dx-e) +ν'(Ax-b) and since Ax-b is 0, we reduce L to c'x + λ'(Dx-e) The dual function g is inf L(x,λ) x Then I... Read more

Hello all, I indulged myself a curiosity today on the question of how much the sea levels would rise if we covered them with tennis balls. (Don't ask why, because I don't know!) Here's the rough breakdown of my calculations and assumptions: 1: Tennis balls are, on average, 6.7cm (0.067m) in... Read more

In 1959, rotating systems were still studied through "elastoid-inertial" oscillations. https://journals.ametsoc.org/view/journals/atsc/16/2/1520-0469_1959_016_0199_anooat_2_0_co_2.pdf This expression was clever and profoundly meaningful because it exactly describes what physics lies... Read more

If your Lowe's survey code doesn't work, first check that you entered the code exactly as printed on your receipt. Ensure the receipt is still within the valid survey period, as expired codes may no longer be accepted. Try using a different browser, clearing your cache, or accessing the survey... Read more

I came across this YouTube Short from The Action Lab. I thought it was pretty cool that he searched Reddit and PhysicsForums when researching a reason for the effect.

This piece was published in 1921, so five years after Einstein wrote "Relativity: The Special and the General Theory" for a general audience... Read more

timeisfundamental - 0 - 0 - How did you find PF? do we really have individual nows or its just a prespective issue There is not one universal "now" if that is what you mean. People on the earth all have a "now" give or take, but things start get more complicated where velocities and large distances are involved. As interested as I am …

I'm not sure how wrong this guy Monroe Pattillo is, or if he is just a bad explainer: .

Hello everyone, Maintaining a proper diet is widely recognized as the foundation of a healthy pregnancy and successful IVF journey. I wanted to share a structured breakdown of essential nutritional categories, recommended food sources, and their specific health benefits based on insights shared... Read more

I would like to explain to someone about why the Sun's gravity does not pull the Earth into the Sun. I know that the reason that the Sun's gravity does not pull the Earth into the Sun is that the momentum of the Earth orbiting the Sun is in equilibrium with the Sun's gravity. What I need to... Read more

I tried to simulate a circuit from MIT Power Electronics Lecture 2, and this is the simulation when it has reached periodic steady state. I added ground, original circuit didn't have one. Yellow line - v(vy, vz) - should be voltage across inductor L2. I know that the negative... Read more

I would like to explain to someone about why the Sun's gravity does not pull the Earth into the Sun. I know that the reason that the Sun's gravity does not pull the Earth into the Sun is that the momentum of the Earth orbiting the Sun is in equilibrium with the Sun's gravity. What I need to... Read more

I took 1 semester course sequences and did independent research. I still get research ideas but I am not as sharp as I used to be.

TL;DR: This thread is a review of the book Our Mathematical Universe. This thread is a review of Max Tegmark's book Our Mathematical Universe. The thesis of Our Mathematical Universe is that not only does mathematics perfectly describe the universe, the universe is mathematics.. In... Read more

Been working through some advanced calc problems and the definition of continuity keeps feeling kinda weird. The epsilon-delta thing doesn't quite click intuitively for all cases, especially with those piecewise functions. Seems like there's a persistent disconnect between the formal proof and... Read more

Hello everyone, As a freshman Physics student, I plan to learn MCNP and improve my skills in this field over the summer break. This might not be the ideal place to ask, but I am currently looking for a laptop that can smoothly run MCNP for this purpose. My main question is regarding the... Read more