General purpose thread where Kitty advises posters on whatever they ask

[chequita guevara]

What is dark matter?

[KrazyHorse]

What is dark matter?

It is very probably some sort of heavy particle which has only very very low interactions with regular matter. I would place the probability of that being true as >80%. By introducing a single new particle you can explain dark matter to as many decimal places as we have available to us.

Now, there is a very interesting result (believe it's called the weak scale miracle) . It goes as follows: in order to describe the hypothetical dark matter candidate you need two things:

1) Its annihilation cross-section; the more it annihilates the less of what was produced would still be around

2) Its mass; the heavier it is the less number of particles you need (sort of)

(Please note that I am greatly oversimplifying this). 1 and 2 are therefore complementary if we want the dark matter candidate to explain the quantity of dark matter around us today. The higher the mass, the higher an annihilation cross-section you're allowed and vice versa.

The weak-scale miracle is that a particle with interactions of the strength of the weak force and a mass near that of electroweak symmetry breaking (100 GeV to 1 TeV) fits the data just fine (to within an order of magnitude). That doesn't sound that exciting except that most other things you would try are many many orders of magnitude off.

So this is reason to believe that something funny is happening at the weak scale (which we already knew!). Call it 40% that dark matter lives near here. Furthermore, the class of theories which have weak-scale supersymmetry breaking would predict this type of particle (the dark-matter candidate being the lightest SUSY particle). Call it 20% that weak-scale SUSY breaking leads to dark matter.

[chequita guevara]

Is it necessary that dark matter be a particle? Would "ripples" in space-time cause the same effects?

[KrazyHorse]

1) Some sort of primordial gravitational wave would disappear quickly as the universe expanded (its density goes down, like other forms of radiation, with the fourth power of the scale factor of the universe, whereas cold matter's density goes down as the third power)

2) "ripples in space-time" sounds suspiciously to my ear like "gravitons". And insofar as we understand gravity at all, no.

[KrazyHorse]

Che, you should note that all elementary field excitations like the one you seem to be describing are presumed to be quantized in modern physics. The quantum of excitation IS a "particle".

[chequita guevara]

[Krill]

Is that stuff actually interesting to you? Or do you view it as a job that you have to do to get your Ph.D and earn megabucks afterwards?

[KrazyHorse]

It's somewhat interesting, but not as much as it used to be. Basically, I think I would be just as happy thinking about something else, and would be happier because of pay and getting to be smarter than most/all of the people around me again

[KrazyHorse]

At this point I'm just closing out. I don't really feel like I have a horse in this race so I now try to avoid learning anything I don't have to.

[Naked Gents Rut]

What's a good book on solar physics? I've gotten pretty interested in the subject due to the delayed ramp-up of Solar Cycle 24 and would like to expand my knowledge. This book seems to be the best introductory text available on Amazon, but I was wondering if you knew of another book that was a) cheaper or b) more informative.

[KrazyHorse]

Absolutely no idea. I know no solar physics. I will, however, inquire around tomorrow.

[TCO]

Despite your not being willing to take Lubos Motl in a math fight (although I would back you), what do you think of his pro stringer behavior?

[TCO]

Do you think current men's elite gymnasts use roids?

[Guynemer]

I'm sitting at a $1-$3 NL Hold 'Em table, second to act, the guy under the gun folds. I look down and see A-8 suited. Assuming I have a stack of about $300, roughly average for the table of ten players, and I've already gone once around and have tossed absolute rags so far, what should be my play?

[KrazyHorse]

Despite your not being willing to take Lubos Motl in a math fight (although I would back you), what do you think of his pro stringer behavior?

****. Strings suck. The only people who like them are those who do them. They don't tell anybody else anything remotely testable. **** 'em.