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14h
comment Why would a modern smartphone not work if the theory of general relativity hadn't been discoverd?
If GPS didn't work, you're right we would just develop something that did. But even without an understanding of GR, GPS would work just as well as it does today. See this answer for why the necessity of GR is a myth.
14h
comment How does the inclusion of vacuum energy modify Newtonian gravity equation of motion?
@Javier I've actually half written an answer to that effect. It's tricky, though, because in fact no experiment, neither local nor global, could locate $r = 0$, since with this particular potential the acceleration pushing any two points apart is exactly proportional to their separation. That is, Newton+metric expansion is self-consistent, it's just the more subtle issue of Newton+nonzero homogeneous gravity source that falls apart on consistency.
1d
comment Solving the Tolman–Oppenheimer–Volkoff (TOV) equation
@Elnur What you suggested isn't wrong, but it's actually equivalent to what is already there ;)
1d
comment How to draw a quantum circuit like this?
This seems to be about graphics rather than physics.
Apr
30
comment On the proof of the existence of geodesics coordinates
The author made a mistake -- switching $d$ and $b$ -- and in fact you made the same mistake in a different place. Every term in the first equation you want to derive should have an upper $a$ and a lower $d$ and nothing else other than possibly summed upper/lower pairs that are neither $a$ nor $d$.
Apr
29
comment Can the density of a black hole be altered (if at all) by absorption?
You should go back and reconsider the notion that black holes are necessarily dense. A billion solar mass black hole (as exists at the centers of some galaxies) has a density of about $20\ \mathrm{kg/m^3}$, $50$ times less dense than water.
Apr
27
comment Converting between matrix multiplication and tensor contraction
@Dargscisyhp The key is the word represent. There is a well-defined, right and proper representation of rank-2 tensors as matrices. The problem is matrices are insufficiently rich objects to represent rank-(1,1), rank-(0,2), and rank-(2,0) tensors simultaneously in any sort of consistent way. An analogy might be streamlines representing either electric or magnetic fields, but if you have both simultaneously your diagrams are quickly going to get messy, since streamlines don't capture the relationship between $E$ and $B$.
Apr
27
comment Ideal gas equation and atmosphere of Venus
I didn't mean to imply you were dishonest, certainly -- just that scientific culture could construe it that way were it to come from someone more familiar with the practices.
Apr
26
comment Ideal gas equation and atmosphere of Venus
@pr1268 That only makes Floris's comment all the more important to pay attention to. We do not know the pressure that precisely, so you cannot calculate density that precisely either. And the standard for scientific communication is that reporting so many significant figures implies that you in fact have calculated the result so precisely. That is, reporting so many significant figures is not just cumbersome, it is misleading and almost dishonest.
Apr
25
comment How do we know the Schwarzschild solution contains an object of mass $M$?
@knzhou Moreover, if you want to involve other branches of physics you're going to have to do more than just that. Any real matter will couple to itself, and so the sum of individual masses ("baryonic mass" to some) differs from the $M$ you want to recover ("gravitational mass") by the binding energy. This is a very measurable effect, being ${\sim}10\%$ or so in neutron stars.
Apr
24
comment Relative velocity of light beams
@MohamedOsama No, Einstein said the laws of physics hold in all reference frames. At the same time, relativity says that there is no valid reference frame moving at the speed of light relative to another. That is, physics doesn't even have the concept of how things might appear if moving at the speed of light.
Apr
23
comment Where can i get an online version of original works of Aristotlean physics (for free)?
Aristotle is more philosophy than physics, since his "physics" pretty blatantly disagrees with reality. Aside from that, we aren't really in the business of locating files upon request (that's for your friendly neighborhood librarian).
Apr
19
comment How would it be to look at the sky if the earth were near the edge of the universe?
Not only is there evidence (with a dash of Occam and Copernicus) that there is no inhomogeneity, there is simply no edge whatsoever in the model. Classical GR is formulated on boundaryless manifolds. If you want to talk about "edges" to the universe, you need to figure out what that means mathematically.
Apr
16
comment Failure of Superposition principle at high amplitudes
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Apr
16
comment Basic question about light
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Apr
16
comment A conceptual question about work
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Apr
16
comment Force, Mass, Motion? $E = mc^2$
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Apr
16
comment Confusion regarding gauss law
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Apr
16
comment ionizing radiation and energy
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Apr
16
comment Boson in Superstring
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