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Oct
19
answered Why has the trace of the energy-momentum tensor to vanish for conserved scaling currents to exist?
Oct
17
awarded  Custodian
Oct
17
reviewed Approve Distribution of charge on a hollow metal sphere
Oct
17
comment Einstein tensor in Friedmann equations : where is the missing $c^2$?
Now, whether there are the right numbers of $c^2$ floating around is a different issue; I haven't checked the computations on Wiki myself so can't say anything. But because of the identification of space and time, one cannot use dimensional analysis to check whether the number of $c$s are correct, since $c$ is essentially dimension free.
Oct
17
answered Einstein tensor in Friedmann equations : where is the missing $c^2$?
Oct
16
answered What is the spatial derivative of strain tensor?
Oct
15
comment Killing vector fields
Consider the Lagrangian functional evaluated among the "functions" (in this case the spacetime metric and manifold) that admit a certain symmetry. Not all symmetries can be easily captured at the level of initial conditions (search arXiv for Killing initial data to see related current research).
Oct
15
comment Killing vector fields
@Prathyush: a priori, none are necessary. One can however postulate the existence of symmetries (time-translation, spherical, axial) and see what happens.
Oct
15
revised Schrödinger equation with complex potential
fixed spelling, replaced inline graphics with MathJax.
Oct
15
answered Killing vector fields
Sep
7
revised What does adding a scalar field component to the Einstein field equations mean for black holes and string theory?
included the relavent EOM
Sep
7
comment Why a black hole sucks nearly everything, but emits gravitons?
It may help to indicate where you came across that claim so we know better in what context to address your question.
Sep
6
comment Discarded by Relativity
"all are relative" is precisely the wrong way to think about relativity. One of the tenets of relativity theory is that "the laws of physics appear the same to all inertial observers"; one may argue from this that relativity postulates a more absolute law of physics compared to the Newtonian version.
Jul
13
comment Why is an Aircraft Runway NOT like a Teaspoon?
Not "vertical lift" (at least in the case of non "jump" jets); it should be "vertical momentum". In the PDF document @Martin linked to, on p.4: "When the Navy first considered using inclined ramps, the objective was to reduce or eliminate the aircraft sinking below the carrier flight deck ... The aircraft leaves the ramp with a vertical velocity ... The speed, however, is below the minimum level flight speed, so the aircraft is not able to maintain its upward velocity. The vertical velocity decreases as the aircraft accelerates and at some point the degradation is stopped."
Jul
12
answered Are there devices which convert thermal energy to electric energy?
Jul
12
answered Why is an Aircraft Runway NOT like a Teaspoon?
Jul
12
revised Why is an Aircraft Runway NOT like a Teaspoon?
spelling.
Jul
11
comment Why does water flow out of an upside-down bottle? (Rayleigh Taylor Instability)
@Alex thanks! I just kept timing out on UBC's server, but your link worked great. Those are some impressive photographs, considering it was done in the 70s and he was accelerating a bathtub downwards at 1.5g.
Jul
11
comment Why does water flow out of an upside-down bottle? (Rayleigh Taylor Instability)
The instability has apparently also been examined experimentally. I'm having some difficulty downloading the actual PDF file, but am looking forward to seeing the pictures.
Jul
11
answered Why does water flow out of an upside-down bottle? (Rayleigh Taylor Instability)