Having read a number of books on cosmology and particle physics, I found my-self raking through 5 or 6 books or looking on the web as I tried to remember some tangible fact that had interested me. In the end, I decided to gather this info and post it under various headings as blogs on MySpace. With the introduction of LaTeX at Physics Forums, I decided to move a couple of them over here. Some are a year old, some are more recent. MySpace blogs
Uncategorized Entries with no category

## GPS and Relativity

Posted Aug26-11 at 03:42 AM by stevebd1

Time dilation due to gravity (GR)-

$$d\tau=dt\sqrt{1-\frac{2M}{r}}$$

where $M=Gm/c^2$

Time dilation due to velocity (SR)-

$$d\tau=dt\sqrt{1-\frac{v^2}{c^2}}$$

Quantities-

Earth's mass- 5.9736e+24 kg

Satellite's altitude- 2e+7 m

Satellite's velocity- 3.889e+3 m/s
...
Posted in Uncategorized

## Friedmann Acceleration Equation

Posted Jul4-11 at 05:52 AM by stevebd1
Updated Jul7-11 at 02:47 AM by stevebd1

Continued from Critical Density

Equations that demonstrate a flat and accelerating universe-

Friedmann equation-

$$H^2=\left(\frac{\dot{a}}{a}\right)^2=\frac{8\pi G}{3}\rho-\frac{kc^2}{a^2}+\frac{\Lambda c^2}{3}$$

Friedmann acceleration equation-

$$\dot{H}+H^2=\frac{\ddot{a}}{a}=-\frac{4\pi G}{3}\left(\rho+\frac{3P}{c^2}\right)+\frac{ \Lambda c^2}{3}$$

where $P$ is pressure and the...
Posted in Uncategorized

## Critical density

Posted Jan26-11 at 05:57 AM by stevebd1

Einstein field equations (EFE)-

$$G_{\mu\nu}+g_{\mu\nu}\Lambda=\frac{8\pi G}{c^4} T_{\mu\nu}$$

Gμν is the Einstein tensor of curvature (spacetime), gμν is the metric tensor, Λ is the cosmological constant, $8\pi$ is the concentration factor and Tμν is the energy tensor of matter (matter energy)

c and G are introduced to convert the quantity (which is expressed in physical units) to geometric units (G/c4 is used to convert units of...
Posted in Uncategorized

## Orbits in Kerr metric

Posted Dec11-10 at 08:35 AM by stevebd1
Updated Dec19-10 at 04:30 AM by stevebd1

Note: The following only applies at the equatorial plane.

local gravitational acceleration for an object in orbit at the equatorial plane-

[tex]
\begin{flalign}
&a(U)=-\gamma^2[g-2v\theta_{\hat{\phi}}-v^2k_{(\text{lie})}]\\[6mm]

&\vec{g}=-\vec{a}(n)\\[6mm]

&a(n)_{\hat{r}}=\frac{M\left[(r^2+a^2)^2-4a^2Mr\right]}{\sqrt{\Delta}\,r^2(r^3+a^2r+2Ma^2)}\\[6mm]

&\theta_{\hat{\phi}\,\hat{r}}=\frac{Ma(3r^2+a^2)}{r...
Posted in Uncategorized