I was looking at how beats work. You use a amplitude wave $A = \cos\left(2\pi f_1x\right) + \cos\left(2\pi f_2x\right) = 2\cos\left(\frac{2\pi x\left(f_1-f_2\right)}{2}\right)\cos\left(\frac{2\pi x\left(f_1+f_2\right)}{2}\right)$ (frequencies $f_1$ and $f_2$). According to Wikipedia, "Because t...

I understand that an observer outside the event horizon (EH) of a black hole (BH) will not see anything disappearing from outside the EH - only the effects of the time dilution near the EH. Assume that a large number of objects are on its way towards the EH and the last objects can observe all ...