In special relativity, one typically works in the spacetime manifold with the Minkowski metric:$$ds^2=-c^2dt^2+d\vec x^2.$$However, I find it intuitive that in the nonrelativistic limit, if one also ...

The Wikipedia pages for the Particle horizon of the universe has the following statement:"Due to the expansion of the universe, it is not simply the age of the universe times the speed of light ...

I am trying to understand triangulation, especially I am focused on the triangulation Méchain and Delambre achieved in the end of the 18th century, in order to measure the distance between Dunkirk and ...

I'm reading the book Gravitation and Cosmology by Weinberg. I've a question regarding the derivation of tha parallax distance.On page 420 Weinberg derives the parallax distance:$$d_P= a(t_0) \frac{...

I’m confused about what a specific observer, comoving with the Hubble flow, would measure as the distance to another comoving observer (galaxy) “far away”. I would’ve thought that this should be the “...

How would a moving observer, travelling at a “relativistic” velocity, determine the distance to a star towards which they were moving, while they were in motion? (“Relativistic” meaning a large ...

At the present time, we - as observers comoving with the Hubble flow - measure the value for the Hubble constant to about 70 km/s/Mpc and the distance to the our particle horizon as 46,5 Gly. Now ...

Suppose there is a stationary mass located at some point in space, and the coordinate system $(t, x, y, z)$ of an observer at infinity. Consider two spatial points, (A) and (B), located along the (x)-...

The relation between the chordal distance, $u$ and the geodesic distance $d$ is given in D'Hoker and Freedman at the bottom of page 53. They say,The chordal distance, is given by $u=\zeta^{-1}-1$. ...

By "trajectory", I mean a time-like worldline, or maybe even a null worldline or even one that can be time-like and null in different parts. By "distance" between trajectories and, ...

Consider any non-conservative force, say friction, since the force is path dependent will the work done formula be altered accordingly. The formula for work done is $$W=\vec{F} \cdot \vec{s}\tag{1}$$...

We often read in scientific publications about the diameter of massive objects like black holes. These objects are known to distort space and time, in a way that I believe we're not quite certain to ...

I'm aware that the Big Crunch is practically ruled out, but I need it to ask my question. Imagine, that we live at the cosmic time of the reversal of the expansion, precisely when it stops. At the ...

Comoving and proper distances on wiki.What value of the scale factor $a(t)$ for the present time $t$ should we put into the equation of the relation between the proper distance $d(t)$ and the ...

Suppose, there is a fluid inside a container and the container itself is moving with a constant velocity'v'. Since, the velocity of each and every particle of the liquid will be same, their relative ...