167 reputation
5
bio website wildcatsformma.wordpress.com
location Somewhere over the rainbow
age
visits member for 2 years, 5 months
seen 3 hours ago

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


1d
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.
1d
comment The Spin Connection
@Prahar what is a d.o.f. ?
1d
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
Mar
1
suggested suggested edit on Is the curvature of spacetime invariant? Could it be characterized as the ether?
Nov
26
revised An electron falling into a black hole
Edited some small typos
Nov
26
answered An electron falling into a black hole
Nov
15
awarded  Commentator
Nov
15
comment Where did Karl Schwarzschild derived his solution?
Never mind...it's still wrong :-)
Nov
15
comment Where did Karl Schwarzschild derived his solution?
Your last sentence "which didn't matter in vacuum" is completely wrong. $G_{μν}=−κT_{μν}$ ARE the FULL and COMPLETE Einstein field equations .They are a system of 2nd order non linear PDEs $T_{μν}$ is the stress energy tensor which describes matter and energy (movements/fluxes) and $G_{μν}$ is the Einstein tensor (a measure of curvature).If you are in vacuum, $T_{μν}$ is simply 0 and the equations reduce to: $G_{μν} =0$. Schwarzschild used a spherical coord. system for space coord. and used static symmetries to reduce $G_{μν} =0$ to simple ODEs This is the standard procedure used since then.
Nov
14
comment Where did Karl Schwarzschild derived his solution?
Schwarzschild could not have found an exact solution to the field equations if he had not known the final (Dec 2 1915) form of the equations. He knew them and he used spherical coordinates to obtain a form closely related to the standard one (en.wikipedia.org/wiki/Karl_Schwarzschild#Relativity ). Lemaitre in 1933 already realized that the Schwarzschild radius is not a phisical singularity (MTW pag 822)
Nov
14
comment Where did Karl Schwarzschild derived his solution?
Nice story! How did he arrive at his solution? Same way we do it now (as described in many GR books) ?
Oct
6
comment What is the physical size of a black hole?
this answer might be a bit misleading. Incoming matter may appear to be frozen at the Schwarzschild radius, never seen crossing it, but in reality incoming matter does cross the Schwarzschild radius and keeps on going into the singularity at r=0. Only the outgoing light rays are frozen. So the real size of any black hole is 0, as stated in the first answer. Of course this does not take into account any quantum effect at Planck length.
Jul
23
comment Can general relativity be completely described as a field in a flat space?
Congratulations for the very detailed and long answer! +1 from me. By the way, welcome to Physics.SE.
Jul
19
comment Are “typical” black holes rotating, or stationary?
When you say that there are 4 solutions, are you referring to charged/non-charged, rotating/non-rotating holes?
Apr
21
awarded  Revival
Mar
14
answered Tension on a cable in a gravitational field
Jan
27
answered What does it mean for objects to follow the curvature of space?
Jan
24
comment How long would it take to travel through a wormhole?
@RonMaimon Absolutely, that's why I quoted the exotic matter paragraph. CTC (closed timelike curves) are another problem. But the OP was asking a very specific fact, assuming that wormholes exist. So the question appears to me more mathematical than physical
Jan
24
answered How long would it take to travel through a wormhole?