7,962 reputation
22563
bio website astro.uvic.ca/~koman
location Canada
age 26
visits member for 2 years, 10 months
seen 19 mins ago

I am an astrophysics graduate student.


May
20
reviewed Close Does the Holographic Principle explain Dark Energy?
May
20
reviewed Close Changing variables in a Lagrangian to obtain mass terms of gauge fields
May
20
reviewed Reopen Drift of Earth's orbit?
May
20
reviewed Reviewed what size puddle does a gallon of water produce?
May
20
reviewed Approve Electric field of two infinitely long and thin, straight wires
May
20
reviewed Approve Speed to power conversion
May
20
reviewed Leave Open Is MOND dead or still being actively researched?
May
20
reviewed Leave Open Is the time “direction” in General Relativity equivalent to a spatial volume
May
20
reviewed Leave Open Matrix elements of four-quark operators
May
20
reviewed Leave Open Can one detect cosmic ray muons with a DSLR camera?
May
20
reviewed Close Significance of $U(1)$ extensions of SM
May
20
reviewed Close $AdS_2$ Black Hole
May
20
reviewed Close Centrifugal And Centripetal Forces
May
18
comment How can dark matter collapse without collisions or radiation?
@Hypnosifl Yeah, at least that's my understanding.
May
15
comment How does dark matter collapse?: Entropy considerations
I think I see your point of confusion: virialized and "obeys the virial theorem" are distinct. The virial theorem (the one I'm talking about in my other answer) is $\frac{1}{2}\frac{d^2I}{dt^2}=2K+W+\Sigma$. The statement "$2\langle K\rangle=-\langle W\rangle$" is sometimes also called the virial theorem, but this is in fact a special case of the theorem, when (quasi-)equilibrium is reached. Note that on Baez's page, he assumed virialization throughout (which may be fine for a collisional gas cloud, but is not for collisionless DM). He says he'll check his assumption later, but never does...
May
15
revised How can dark matter collapse without collisions or radiation?
edited body
May
15
comment How can dark matter collapse without collisions or radiation?
Note I had my factor of 2 in the wrong place - have corrected this!
May
15
comment How can dark matter collapse without collisions or radiation?
@Hypnosifl I'm not sure what you're asking... I'm arguing that when $K<-2W$ the system obeys both the Jeans equations and the virial theorem, and indeed it is by the virial theorem that we can most easily see that the DM must collapse. I would agree that "virialization occurs" when $K=-2W$, but this is distinct from obeying the virial theorem, which is obeyed also when $K\neq -2W$, and drives the evolution of $I$ until virialization occurs.
May
14
comment How do eagles fly slowly for a long time?
This doesn't answer the question, and indeed doesn't seem to contain any physics.
May
3
reviewed Close “Hollow Earth” like Theories for pedagogical porpuses