690 reputation
616
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location United Kingdom
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visits member for 3 years, 1 month
seen 14 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.


Nov
12
comment Inertial frames of reference
sb1 - if the only definition of an inertial frame is that Newton's laws of motion are valid, why isn't my ice sheet an inertial frame in GTR. For both GTR and STR doesn't there also need to be a notion that the frame is "full" of synchronized clocks, which isn't possible in a gravitational field? Thank you.
Nov
12
comment Inertial frames of reference
Ben Crowell - Does your final paragraph mean that you are saying my two examples (train and ice sheet) are (1) not good approximations in GR, and (2) SR cannot discuss trains and ice sheets because of the presence of a gravitational field? Thank you.
Nov
12
asked Inertial frames of reference
Oct
24
accepted Defining a Riemannian manifold - made easy?
Oct
23
comment Defining a Riemannian manifold - made easy?
Thanks all. I seem to have opened some sort of multidimensional (Riemannian? Hausdroffian?) Pandora's Box. I wish I could speak fluent maths - learning GTR would be so much easier. Trouble is, there's such a steep learning curve and to the uninitiated a page of symbols is incomprehensible and scary. I like a nice real-world mental picture myself - a sheet of paper resting on a ball for a tangent space, that kind of thing. Probably my ideal textbook would contain rigorous maths and pretty cartoons!
Oct
21
comment Defining a Riemannian manifold - made easy?
Thanks, but that's (a) a counsel of perfection and (b) pitched way over my head ("second countable Hausdroff topological space M equipped with a maximal atlas"!). I was hoping for more of a dumbed down answer to my dumbed down, "naive" question, which actually (he say's plaintively) took me ages to formulate. I'm not a physics or mathematics graduate. I'm a manual worker trying, for the fun of it, to learn the basics of GTR. Schutz ("A first course in general relativity") defines a manifold as "essentially a continuous space which looks locally like a Euclidean space". That's about my level!
Oct
21
asked Defining a Riemannian manifold - made easy?
Sep
30
comment Schwarzschild metric
@ Ron Maimon. Thanks, but what's the difference between a weak field and a self-sourcing field. It just seems odd that you can describe a weak field using two methods that are based on opposite assumptions. Please don't worry about making your explanation too simple.
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)