Wednesday, February 3, 2016

correlation function

can you show that the integral $\int\mathrm{d}^nx\:C(r)$ of the correlation function $C(r)$ as a function of distance $r$, $r^2=\sum_{i=1}^n x_i^2$, of a random field in $n$ dimensions vanishes?

Wednesday, January 27, 2016

Lorentz boosted resistor

last post in the series "relativistically moving electric circuits": a resistor heats up due to an electric current moving through. but could you boost into a frame in which the electrons are at rest, in which case there would be no heat generation? how would you reconcile the two observations with Lorentz-transforms?

Wednesday, January 20, 2016

Lorentz boosted capactitor

imagine to observe a charged capacitor from a moving frame of reference. can you explain inituitively how the electric field is Lorentz-transformed?

Wednesday, January 13, 2016

Lorentz boosted coil

can you explain how the magnetic field of a moving coil would be transformed into an electric field if the coil is in motion relative to an observer?

Wednesday, January 6, 2016

redshift drift

welcome back to CQW in 2016 with a question about redshifting:

can you construct a cosmological model in which the redshift of distant objects stays constant? would that mean that the last-scattering surface of the CMB has a constant distance?

Wednesday, December 23, 2015


can you show that the density inside a sphere which contracts according to a Hubble-law $\upsilon(r)\propto -r$ remains homogeneous? what's the relation between density $\rho$ and time $t$?

we wish all our readers and followers merry x-mas and a happy and successful year 2016. we hope to see you again in january.

Wednesday, December 16, 2015

Schwarzschild radius of electrons

if electrons are truly pointlike particles, would it be a problem for the field lines emanating from the charge to cross the Schwarzschild radius?