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?