## Wednesday, January 25, 2017

### gravity and retardation

the field equation of general relativity is invariant under time-reversal (and parity inversion). in what way is retardation of the gravitational field generated by a matter distribution is preferred over advanced potentials?

## Saturday, January 21, 2017

### forces in relativity

relativistic forces are always velocity dependent but velocity dependent forces are not necessarily relativistic... is that true?

this post is in celebration of $10^5$ views!

## Wednesday, January 18, 2017

### very heavy and very light

can you explain why the ratio between the Hubble mass (i.e. the mass inside the Hubble volume today for a critical universe) and the Planck mass is about $10^{60}$? why are stars roughly in the middle (on a logarithmic scale)? or even more puzzling: why's the ratio between Hubble and Planck-mass about equal to the ratio between stellar masses and the masses of nucleons?

## Wednesday, January 11, 2017

### forces on dust particles

can you compute the ratio between radiation pressure and gravity acting on a dust particle in the solar system? could one relate the two forces to the mass of the Sun and establish a minimal mass from which on there would be no dust and hence no planetary system?

we wish all CQW-readers a successful year 2017 full of cosmological discoveries.

## Wednesday, January 4, 2017

### funny way of writing Maxwell's equations

can you reformulate the Maxwell-equations in terms of the complex-valued field $\vec{X} = \vec{E}+\mathrm{i}\vec{B}$? would there be potentials $\Phi$ and $\vec{A}$ for $\vec{X}$, and can one even find a covariant formulation?