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Jan
16
comment Group notation $\otimes$ and $\oplus$ used for representations of quarks and mesons
Something useful to keep in mind: when mathematicians say "introductory group theory" they are thinking of stuff like the Sylow theorems. When physicists say "group theory" they really mean representation theory or module theory or linear algebra -- basically most of introductory abstract algebra except group theory proper.
Jan
16
answered Is it in general true that $\nabla_\mu T^{\mu\nu}=0$ implies the matter equations of motion?
Jan
15
answered What besides the metric do you need to set up the EFEs and the geodesic equation?
Jan
15
reviewed No Action Needed Do particle decays happen instantly?
Jan
15
reviewed Looks OK The mass-energy equivalence for rest mass
Jan
15
comment The mass-energy equivalence for rest mass
Word of warning: never, never, never use the "relativistic mass" as a single symbol. Rest mass is $m$, "relativistic mass" is $\gamma m$. Hiding the $\gamma$ factor in with the $m$ is something physicists did about a century ago, before they knew any better, and it only leads to confusion.
Jan
15
reviewed Reopen Why will this plan for a perpetual motion device not work?
Jan
15
reviewed Leave Open Do quartz watches actually implement the SI definition of the second?
Jan
14
answered If two photons collide, does the resulting particle have zero velocity?
Jan
14
reviewed Close Is this xkcd comic feasible?
Jan
13
answered Curved paths through spacetime when standing still?
Jan
13
comment How to demonstrate frame dragging through the Kerr metric?
What form of the metric do you have then? And what have you tried? For instance, what do you take frame dragging to be mathematically? You should show what you've done so we know where to start with an answer.
Jan
13
reviewed Leave Open Uniqueness of the angular velocity
Jan
12
awarded  Enlightened
Jan
12
awarded  Nice Answer
Jan
12
comment How do we stabilise satellites so precisely?
If you're impressed with Hubble's pointing, you may be interested in Gaia.
Jan
11
comment Curvature of spacetime as a real thing?
@barongbaron While it is true (but highly nontrivial to prove!) that one can always embed spacetime in a higher-dimensional flat manifold, this is emphatically not how anyone thinks about or does general relativity. Curvature can be measured without venturing into other dimensions, just as you can empirically prove the Earth is round without ever leaving the surface.
Jan
7
awarded  Good Answer
Jan
7
awarded  Nice Answer
Jan
7
reviewed Leave Open Time coordinate inside black hole horizon