When we say that the universe is flat, this means that the sum of angles of any triangle will always be 180°. I believe that "flat" refers to the bending of spacetime in a 5-dimensional space (or a forth space dimension). This would however contradict the fact of the su of angles, as for warped s...

In the figure given below is block placed on an incline $\theta$. Now the lift is accelerating upwards with an acceleration $a_0$. Now if we make our measurements from the lift frame we will have to apply a pseudo force $-ma_0$. Which will have two components one in the direction of $Mg\cos\theta...

I'm struggling to see how $\langle x|\Psi\rangle =\Psi(x)$. I have read a few previous bra ket questions in here but still not clear. Any good book for understand the bra-ket notation in more rigorous way.