Reputation
18,157
Top tag
Next privilege 20,000 Rep.
Access 'trusted user' tools
Badges
6 53 90
Newest
 Good Answer
Impact
~485k people reached

Nov
4
revised How does rogue planet PSO J318.5-22 stay 800ºC?
added 657 characters in body
Nov
4
comment How does rogue planet PSO J318.5-22 stay 800ºC?
@HDE226868 the greenhouse effect works by trapping heat from the Sun. In principle, a planet with a thick hydrogen atmosphere could have a much stronger greenhouse effect than Earth, and thus be warm while being much further from its star; but without any incoming radiation at all the greenhouse effect cannot occur.
Nov
4
answered How does rogue planet PSO J318.5-22 stay 800ºC?
Nov
1
comment Is there a Lagrangian formulation of statistical mechanics?
Ah - now I get it. What you've written down is not $S[p_i]$ but $\partial S/\partial p_i$ with Lagrange multipliers. This is the MaxEnt approach to stat mech. Indeed I already know it, and the question is about its extension to systems in which there is time.
Nov
1
comment Is there a Lagrangian formulation of statistical mechanics?
Can you explain what the terms in this equation mean, and/or give some kind of reference for further reading? It looks rather odd at a first glance - is $p(x)$ the same as $p_i$? (In which case $\sum_i(p(x)-1)$ is zero.) Is $\langle E \rangle$ defined differently from $\sum_i p_i E_i$? (If not, why do both appear in the equation?)
Oct
30
awarded  Nice Answer
Oct
27
comment Black hole no-hair theorems vs. entropy and surface area
@Robotbugs fixed. (I'm not sure what happened there.)
Oct
27
revised Black hole no-hair theorems vs. entropy and surface area
added 14 characters in body
Oct
27
awarded  Nice Answer
Oct
26
comment Is there $\frac{1}{f^{0.5}}$ noise?
Not in the sense I intended. A 6 dB/Octave filter ($1/f^2$), for example, can be implemented exactly using a simple IIR method.
Oct
26
comment Is there $\frac{1}{f^{0.5}}$ noise?
Actually, creating a digital filter with a given response is a major challenge, and it's not always possible to do it exactly. In particular, I think a $1/f$ (aka "3 dB/octave") filter is not possible. Of course you can approximate it with an FFT or by a clever combination of other filters, but there will always be deviations from the ideal response.
Oct
25
comment Can matter have 100% reflection?
See en.wikipedia.org/wiki/Total_internal_reflection . While storing light indefinitely isn't possible, because there are always losses, I believe it's possible to have light bouncing around inside an optic fibre for a measurable fraction of a second. (This happens whenever signals are sent over under-sea fiber-optic cables.)
Oct
24
revised Why are exploding HHO bubbles louder then pure HHO?
edited tags
Oct
17
comment Angular momentum transfer in a bottle vortex
I've done the experiment with flowing water in at the top now, and found that it kills the vortex pretty quickly - which would suggest that there is no influx of angular momentum and the extra water just dilutes the angular momentum that's there initially. Still it would be nice to get a better handle on the dynamics.
Oct
17
comment If the expansion of the Universe accelerates, why its horizon does not shrink?
@Anixx some people think that the area of the cosmic horizon puts a bound on the total entropy of the universe (though people argue about that point), but the actual entropy of the universe is much lower than that bound.
Oct
17
comment Why collide a moving particle with a particle at rest, rather than two moving particles?
@kasperd to be precise: $(u+v)/(1+uv) = 1/(1+\frac{1}{4}) = 0.8$.
Oct
16
asked Angular momentum transfer in a bottle vortex
Oct
13
comment What is the significance of the imaginary unit in Deutsch gate?
While it could be improved with more context, I don't think someone with the knowledge required to answer the question will need it. (The question is quite clear to me. I don't know the answer.)
Oct
8
awarded  Popular Question
Oct
6
comment Does the poisson bracket $\{f,g\}$ have any meaning if neither of $f$ or $g$ is the system's Hamiltonian?
But the question is about Poisson brackets in classical mechanics, not commutators in quantum mechanics...