Thursday, 31 July 2025
Jose and Eugene Saletan, Classical Dynamics
I will say more about this later when I write about the Landau-Lifshitz pseudotensor and the Rosenfeld-Belifante pseudotensor
Landau and Lifshitz - Volume 1 Mechanics
V. I. Arnold has said that there are mistakes in Landau's mechanics. I am afraid I have to disagree. This is very difficult to understand. This book is far beyond perfect. It is the most immaculate conception.
A beautiful formula discovered by Feynman
Feynman discovered this formula using Hamiltonian mechanics
The wobbling rate of a top is twice the angular speed of rotation
$$ \dot{\phi} \simeq 2\omega $$
Wednesday, 30 July 2025
Tuesday, 29 July 2025
Solving simple problems 4
$u_n = \alpha + \beta - \frac{\alpha \beta}{u_{n - 1}}$
Show that
$u_n = \frac{\alpha^{n+ 1} - \beta^{n + 1}}{\alpha^n - \beta^n}$
$ = \alpha^n + \beta^n $
solution
$\alpha + \beta + \left( \alpha + \beta - \frac{\alpha \beta}{\alpha + \beta} \right) + \ ...$
Monday, 28 July 2025
prize for proof
$\int_M \ f^* \Omega = (deg f) \int_N \Omega$
acceptable solution -
Whitney number $W(\gamma )$ is equal to either deg f - 1 or deg f + 1
"I would like to continue. question : what is a Hopf fibration?"
fiber $S^3$ - Hopf fibration
fun -
what is a one sided surface?
Möbius strip in $\mathbb{R}^3$
New
M-theory and a couple of other mathematical physicists were standing on a hill in Edinburgh, talking about modular lie algebras. Some people who were around put a question to M-theory - What do you think about loop quantum gravity? He said "isn't that just lattice gauge theory?"
they say that the 'calculus and sheaf theory' comment was also made here, but no one remembers clearly.
Something so exciting
Abel wrote a monumental work on elliptic functions which, however, was not discovered until after his death. When asked how he developed his mathematical abilities so rapidly, he replied "by studying the masters, not their pupils."
On this note, I did tell the strange people from youth that 90% of the arxiv is nonsense. Let me clarify, I read all kinds of papers. If you want to remember the comment that I only check Bousso and Douglas Stanford and so on, remember Abel's remark.
When I was young, one of the principles close to my heart: everyone except Einstein is a moron. This is probably exactly how Einstein thinks of it, but he might have changed his mind when he found out about Feynman.
Sunday, 27 July 2025
Math Tripos
If x, y, z are unequal, and if
$2d - 3y = \frac{(z - x)^2}{y} $
solution
The answer follows because
$\left( \frac{z}{y} \right)^2 = 1 + \frac{1}{2} + \frac{3}{2} + 1 + \ ... $
$x + y + z = \alpha$
$x = \frac{\alpha}{3}$
$y = 3x$
$z = 3\alpha + 5 + 2$
Solving simple problems 3 - Dieudonne 'Infinitesimal Calculus'
This is not really a simple problem, but still fun.
In the neighborhood of $+\infty$, the function $\frac{\sin x}{\sqrt{x}} + \frac{\sin^2 x}{x}$ has for generalized principal part the function $\frac{\sin x}{\sqrt x}$; but the integral $\int^{+\infty}_1 \frac{\sin t}{\sqrt t} \ dt$ is convergent whereas the integral $\int_{1}^{+\infty} \left( \frac{\sin t}{\sqrt t} + \frac{\sin^2 t}{t} \right) \ dt$ is not convergent.
Solution
$\int_{1}^{+\infty} \left( \frac{\sin t}{\sqrt t} + \frac{\sin^2 t}{t} \right) \ dt < 0$
$\epsilon > \frac{1}{2} + 1$
$\delta = 1 + \frac{1}{2}$
$ \frac{\sin x}{\sqrt x} > \frac{1}{5} + \frac{1}{2} + 1$
Saturday, 26 July 2025
How does Niels Bohr view Galois theory?
the profundity cannot be explained
fundamental theorem of algebra
$ (z - a_1)(z - a_2) ... = 0$
root field
Friday, 25 July 2025
Thursday, 24 July 2025
Wednesday, 23 July 2025
Tuesday, 22 July 2025
Notes for 'Advanced General Relativity' (Warwick postgraduate course)
Pseudo-Riemannian space
It is not very difficult to understand the Einstein field equation, but writing them in a form in which they can be manipulated is very hard












































