then there is the Coma Cluster, that is larger in xrays than optical wavelengths, indicating a lot of mass in hot gas:
http://chandra.harvard.edu/photo/2002/0150/ http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/galaxydist.htm http://www.iop.org/EJ/abstract/0004-637X/696/2/1700 http://www.lsw.uni-heidelberg.de/users/mcamenzi/Coma_X.html http://astronomy.swin.edu.au/coma/project-overview-objective1.htm
by the way, re/ "spherical volume of matter much larger than the center must be taken into account":
according to Newtonian theory (which turns out to hold in Einstein's gravitational theory), only (spherically symmetric) halo matter interior to the visible stars plays any role in the rotation rate. the stuff outside the visible stars cannot influence their velocities UNLESS the spherical symmetry is broken.
> I got through lecture 4, which is pretty tough in some parts. But it had a lot of interesting stuff.
it's also where he is doing some fast footwork. sometimes i think he should have answered certain questions more honestly. the problem is that you do need some general relativity to keep the picture sane. maybe better to say "at the level we are talking about today, we should leave your question be".
OTOH, i think overall that the lectures are great. much better way to be introduced to a subject than stale static textbooks. i think this whole thing of universities posting lectures in video format is one of the greatest things the web has done for us to date.
> In particular the difficult part had to do with the work done by pressure in 3-d on some container, and how energy density changes with the size of the container, then deriving the vacuum energy. Susskin uses a box.
i actually hate the piston/cylinder version of this, for a couple reasons. the way to really think about it, IMHO, is to think about the ground state energies on a spherical surface who's scale factor is growing. but, yea, i GOT the piston/cylinder thing first...
also of interest: vacuum energy. there is a quiet but interesting debate going on in the physics community about the reality of vacuum energy (needed for that 3d container, amongst other things).
see Jaffe:
on the other hand, if you believe in vacuum energy and its contribution to the spacetime metric (errr, gravitation), how come the observed lambda is so small???
> I was familiar with most of this from using gas welding tanks. It is amazing how much physics and chemistry you absorb by learning to weld.
>
acetylene, or MIG / TIG?
you know, modern quantum mechanics can, in one sense, be traced back to the development of the Bunsen burner. it was developed specifically so that spectra of burning compounds would not be contaminated by the flame source. which led to focus on the weird discreteness of spectra, which led to ...
> Meanwhile astronomy, which Susskin calls gas-tronomy is getting closer and closer to the period of early post recombination, and finds fully grown galaxies with supernova in the early matter dominated universe,
> close to 350,000yrs.
>
speaking of youthful galaxy formation, this just came out:
http://www.physorg.com/news188379319.html
Les