272 reputation
18
bio website wildcatsformma.wordpress.com
location Somewhere over the rainbow
age
visits member for 3 years, 1 month
seen Nov 22 at 6:42

My scientific interests:

  • Mathematics: Category Theory, Algebra, Logic (Model-Theory, ATP), Control Systems
  • Physics: General Relativity, QFT
  • Amateur Astronomer and Astrophotographer
  • Mathematica programming

My Website:WildCats
Premiere Mathematica package for category theory

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My non-scientific interests:

  • Skiing, Sailing, Windsurfing
  • Argentine Tango dancer

More or less fluent in (random order):

Italian, English, German, French, Spanish, Dutch and struggling with Russian


Sep
24
awarded  Autobiographer
Jul
28
comment On the coordinate independence of general relativity
@BenCrowell Really??? That's curious because I am restating and expanding on the hole argument (a terminology not found in the standard textbooks mentioned in my answer) mentioned by benrg in his accepted answer and that the OP declared to be very happy with. It seems you either did not understand the question or benrg.s answer or mine or...neither of them. Indeed your own answer is merely a restatement of the second part of my answer.
Jul
28
answered On the coordinate independence of general relativity
Jun
23
awarded  Revival
Jun
23
revised Thermal equilibrium in general relativity
edited small typos
Jun
19
answered Thermal equilibrium in general relativity
May
18
awarded  Yearling
May
18
answered What was the Law of Gravity better explained by?
May
17
awarded  Critic
May
16
comment What was the Law of Gravity better explained by?
This means that you can measure curvature by measuring energy density and vice versa. There are many kinds of energy, one of them is ordinary matter (protons, electrons). But also a pure electromagnetic field (eg. light) has energy density, so it causes a (very small) curvature of space-time. Your example of a curved surface is pointless. A curved surface is NOT curved spacetime.
May
16
comment What was the Law of Gravity better explained by?
Curvature is the sole cause of natural non-inertial motion (that is orbits or accelerated linear motion without engines, ect). Curvature is caused by energy (energy density to be precise). Whenever you have energy, you have curvature. In GR, curvature is measured by the Einstein tensor (a descendent of the Riemann curvature tensor) and energy density is measured by the Stress-Energy tensor. In GR, they are equal!!!
May
16
comment What was the Law of Gravity better explained by?
Your sentence: "Because curvature of space(time) itself simply cannot make an apple move (toward another body or just toward a point). If curvature produces movement, it is only because there is gravitation underneath it. That's why an apple put on the ground rolls down the slope. It takes curvature (of the ground) and also it takes gravitation under (the ground) to do that. If you remove the force and leave only the curvature ... nothing happens to the apple; it will stay right where it was until it experiences real force." is simply wrong.
Apr
29
revised Covariant derivative of connection coefficients
edited small typos
Apr
29
comment Covariant derivative of connection coefficients
No, it would not involve the covariant derivative of the connection coefficient if you know what you are doing with the notation. I suggest you ask a new question along these lines: in a double covariant differentiation, do we have terms involving the covariant derivative of the $\Gamma$? and I will answer it properly.
Apr
29
answered Do Gravitational Waves Actually Repel Spacetime?
Apr
29
answered Covariant derivative of connection coefficients
Apr
17
comment Is there a way for an astronaut to rotate?
@LorenPechtel which spacecrafts actually use flywheels? For example the Apollo service module had lateral thrusters instead and I assumed this was always the case.
Apr
17
comment The Spin Connection
@Prahar what is a d.o.f. ?
Apr
17
comment Cosmological constant doubts
+1 The OP is not a physicist (see profile) and he mentions a non technical book (Universe in a nutshell). So this is by far the clearest and probably most satisfying answer to his question.
Mar
1
revised Is the curvature of spacetime invariant? Could it be characterized as the ether?
Edited some small typos