12:32 AM
1

Assuming the two lasers have identical characteristics and power output except their wavelength, which one would be more successful and easy in cutting clear glass? In case there is doubt that you can even cut clear glass with a laser, see here these two video demonstrations: Visible spectrum blu...

3 hours later…
3:53 AM
1

The old Usenet Physics FAQ, is a page originally by Matt Austern, says that all protons have identical rest masses, and so do all electrons, and so do all neutrons; these masses can be looked up in a table. As the particle is accelerated to ever higher speeds, its relativistic mass increases w...

1 hour later…
5:09 AM
1

From here I learn that, if Pauli vector is defined as $\boldsymbol\sigma=\sigma_\alpha\hat x_\alpha$, and $\boldsymbol a$ denotes a vector, whose components are all numbers, not matrices, then $$\det(\boldsymbol{a}\cdot\boldsymbol{\sigma})=-\boldsymbol a\cdot\boldsymbol a$$ That website proves ...

5 hours later…
10:34 AM
4

Sigh. Approaching retirement age and still deeply confused about something I first encountered in highschool 40 years ago. Consider the usual double slit experiment. Make the light source be a laser with a beam 1 mm wide. And put it 5 meters away from the slits. On the other side of the slits the...

10 hours later…
8:35 PM
1

As shown in the diagram, a long rod has ends A and B, a spaceship is at A. A, B and the spaceship all have clocks attached to them. The clocks are then synchronized to time $t_0$, and immediately The spaceship flies with velocity $u$ relative to the rod from A to B. Suppose relative to the rod, ...