685 reputation
315
bio website
location United Kingdom
age
visits member for 2 years, 10 months
seen 11 hours ago

Manual worker. Live in England. Formal scientific education "peaked" many years ago when I failed maths and chemistry A-level and scraped a bare pass in physics. Still enjoy pottering about in maths and physics.


Sep
28
asked Schwarzschild metric
Sep
15
comment Trying to understand the weak gravitational field metric (3)
After thinking about this, can I try to answer my own question by saying that all I need to do is replace $dt$ with $d\left(ct\right)$ which becomes $cdt$. This will then eventually give the correct value of $h_{00}=\frac{-2\phi}{c^{2}}$ .
Sep
15
revised Trying to understand the weak gravitational field metric (1)
edited title
Sep
15
asked Trying to understand the weak gravitational field metric (3)
Sep
13
accepted What does scalar phi represent in spacetime?
Sep
13
accepted Trying to understand the weak gravitational field metric (2)
Sep
13
comment Trying to understand the weak gravitational field metric (2)
Q1 - Understood. I was confused at first by $\frac{\partial t}{\partial t'}$ but realised the prime was a comma! In other word because the particles are moving slowly the time-component (ie the 0th component of the particle's four-velocity) dominates the other (spatial) components. Q2 & 3 - Understood after a night's sleep. Thanks
Sep
13
revised Trying to understand the weak gravitational field metric (2)
added 3 characters in body
Sep
12
comment Trying to understand the weak gravitational field metric (2)
I've corrected my original mess up with various indexes. Thank you Nikolaj.
Sep
12
awarded  Editor
Sep
12
revised Trying to understand the weak gravitational field metric (2)
added 2 characters in body
Sep
12
asked Trying to understand the weak gravitational field metric (2)
Sep
11
comment Trying to understand the weak gravitational field metric (1)
Ron Maimon - Thank you. Does that mean when Carroll says $g^{\mu\nu}g_{\mu\sigma}$ equals some form of the kronecker delta ($\delta^\mu_\sigma $) he is also saying $g_{\mu\nu}g^{\mu\nu}$ equals the identity matrix? I didn't realize that.
Sep
11
accepted Trying to understand the weak gravitational field metric (1)
Sep
10
asked Trying to understand the weak gravitational field metric (1)
Aug
30
comment Two masses in deep space - collide or orbit?
Thanks. There's an orbital period calculator at the end of the Wikipedia article. When I inputted the figures for my example (two 1kg masses, 10m apart, assuming of course they are in orbit) it gave a period of 0.54 years! For some reason I thought they'd be buzzing round each other.
Aug
30
accepted Two masses in deep space - collide or orbit?
Aug
26
asked Two masses in deep space - collide or orbit?
Aug
14
accepted Einstein's “happiest thought”
Aug
14
comment Einstein's “happiest thought”
So, in my little box I drop 2 stones and they experience the same gravitational acceleration (to 1st order). To 2nd order, they drift ever so slightly together (tidal forces). My little box is shoved over a cliff. I then again drop' 2 stones. In my box's new coordinate system, to 1st order, they remain in the same position. To 2nd order (tidal forces) they move slightly together. Freefall therefore automatically/'magically' creates a new coordinate system which (to 1st order) is flat spacetime. The spacetime hasn't changed but the coordinates have. That's clearer. Thanks for persevering.