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Apr
5
comment Dark energy and conservation of energy
@JohnRennie: you can read more of Philip and Luboš in the comments of Philip's blog posts on energy conservation in GR ( blog.vixra.org/2010/08/06/energy-is-conserved blog.vixra.org/2010/08/08/energy-is-conserved-the-maths blog.vixra.org/2010/08/17/energy-is-conserved-in-cosmology )
Apr
5
comment Dark energy and conservation of energy
@JohnRennie: I disagree with energy not being conserved in FLRW cosmology; the relevant papers are linked from this comment
Apr
5
comment Dark energy and conservation of energy
Friedmann-type universes have zero total energy - the positive contributions by matter and dark energy are cancelled by the negative contribution due to gravitational energy
Apr
4
awarded  Nice Answer
Apr
4
comment How can water evaporate at room temperature?
@JohnRennie: I expanded the answer and made it community wiki - feel free to improve upon it as yous ee fit...
Apr
4
revised How can water evaporate at room temperature?
expanded answer, made community wiki
Apr
4
answered How can water evaporate at room temperature?
Apr
4
revised Why is superdeterminism generally regarded as a joke?
typos
Apr
4
answered Why is superdeterminism generally regarded as a joke?
Apr
2
comment Is the universe flat?
@user12262: see en.wikipedia.org/wiki/Torus#Flat_torus
Apr
2
answered Is the universe flat?
Mar
30
answered Is it foolish to distinguish between covariant and contravariant vectors?
Mar
24
comment What is the intepretation of the electromagnetic tensor?
geometrically, it's a Lie-algebra valued 2-form representing the curvature of a principal connection and thus describes the obstruction to integrability of the horizontal subbundle; depending on your mathematical background, I suspect this comment is rather unhelpful...
Mar
24
revised Many times speed of light
typos
Mar
24
comment Many times speed of light
@AlanSE: no, I do mean that they had recession velocities $> c$ at time of emission; basically, the Hubble sphere is arbitrary - as long as we don't move beyond the event horizon, we're good to go
Mar
24
answered Many times speed of light
Mar
15
answered Why can we assume torsion is zero in GR?
Feb
27
awarded  Nice Question
Feb
24
comment How far could the LHC “fire” a particle
@Zephyr: the value I was getting at was at solar system galactic radius; you're right that the relevant quantity is actually the root of the sum of the appropriate escape velocities (earth from surface, sun from earth orbit, milky way from solar system) squared, but the first two are negligible
Feb
24
comment How far could the LHC “fire” a particle
LHC protons are ultrarelativistic and should basically be able to escape anything that's not a black hole; as to the escape velocity of the Milky Way, according to Wikipedia it's less than that of the sun and thus well below the speed of light (though I cannot confirm right now as it's nightime where I'm sitting ;)).