I'm trying to understand general relativity. Where in the field equations is it enforced that the metric will take on the (+---) form in some basis at each point? Some thoughts I've had: It's baked into the Ricci tensor. This doesn't make sense to me because you can define the Riemann curvature ...

For example let's take a simple example of velocity that is the object displaced per unit time or rate of change of position. It has some meaningful units i.e $m/s$, which means that the position is changed by $1$ meter per unit second. But there are some units which puts many of the novices like...

From the book where I am studying motion, It says Motion is a combined property of the object under study and the observer.There is no meaning of rest or motion without the viewer. I know that, for an object, it can be said that 'it is moving' in one frame of reference, and it can be said that ...

In page-385 of Roger Penrose's Road to Reality, the following is written: In our Aristotelian scheme, it is appropriate to think of spacetime as simply the product: $$ \mathbb{A}= \mathbb{E}^1 \times \mathbb{E}^3$$ and, in page-387, Galilean spacetime $G$ is not a product space $\mathbb{E}^1 ...

We know that the lagrangian can be written using constraints. Suppose I have constraint functions $$f_1=\cos(x) - (x+t)/R=0,\qquad f_2=\sin(x)-y/R=0 .$$ But I know that $1=\cos^2+\sin^2$, so do we use the the $f_1$ and $f_2$ constraints with this one, or only $1=\cos^2+\sin^2$? In other words, ca...

DISCLAIMER: I have not yet fully entered into the vast field of quantum mechanics and and was reading about the photoelectric effect as a part of chemistry, however I feel, the topic of structure of atom formally comes under physics so I will put forward my question over here. Please answer the q...