Astronomy/cosmology questions...

[Buster's Uncle]

...He spent quite a few years as a professional sketch comedian first...

[Rusty Edge]

Well, is there something Lori should watch, or a drama  course he should audit or something?

[Buster's Uncle]

Time as an improv comedian wouldn't be the worse possible prep, actually.

[Spacy]

And, get on your local PBS / Talk Radio show as well, to get that "show biz" start and see how they really work (particularly behind the scenes).  I cannot imagine it would be super easy. 

[Rextraos]

This thread is pretty cool, right up my alley. However, don't you think it's kind of a dark matter to talk about? *snicker*

[Buster's Uncle]

Gamma-ray background yields no evidence of dark matter

[Lorizael]

So the thing about dark matter is... we don't really have a good handle on how to detect it by non-gravitational means. Astrophysicists are essentially hoping that dark matter is something like the rest of the particles known, which means they have to pop into existence due to fluctuations in some quantum field, and the leading candidate is that weak interactions are involved, because if it were anything else, we definitely would have seen dark matter by now. So the continuing failure of these searches means it's harder to get dark matter out of standard particle physics, but the failures don't in any way negate the evidence from gravity. (And as I've gone over before, much of the gravitational evidence cannot be accounted for by modifications to how gravity works.)

[E_T]

How does dark matter fit into the string theories?  I think is something fundamental that is under our noses...

[Rusty Edge]

Is The Universe is held together with string OR is The Universe held together by The Force? ( Yeah, I know that's not what ET said, I'm just going off on a tangent as per usual )

My usual reaction to a question like this is "Why does it have to be so binary?" Couldn't it be both? Sometimes people say one is lying and one is telling the truth. Not necessarily. Maybe they simply have different perspectives, like the blind men and the elephant parable. OR maybe they're both wrong, or both being deceptive, in whole or in part. 

Well, I guess I'm being more philosophical than scientific. Fortunately for us, our resident thread expert is knowledgeable of both disciplines.

[E_T]

String Cheese!!

[Buster's Uncle]

The Case Against Dark Matter

...I can't say I entirely understood this...

[Rusty Edge]

Suppose Dark Matter is simply the gravitational shadow of particles moving at the speed of light. You can't detect them by other means because they no longer exist in that time and place.

[Lorizael]

Sorry for not participating in this thread lately. Brain has been mush recently. But in terms of dark matter being speed of light particles, that's probably not the case. In general relativity, gravity comes not from mass but from the stress-energy tensor at every point in space. For situations we're familiar with, the main contribution to the stress-energy tensor is mass. But as the name suggests, energy plays into it as well. So photons and other massless, speed-of-light particles--which do possess energy--already contribute to gravity in a known, quantifiable way. And we know how many photons are out there in the universe (roughly) based on things like the temperature of the cosmic microwave background.

[Buster's Uncle]

We Still Don't Know How Fast The Universe Is Expanding

[Rusty Edge]

Suppose Dark Matter is simply the gravitational shadow of particles moving at the speed of light. You can't detect them by other means because they no longer exist in that time and place.

So much for that improvised theory. Lucky for us that the universe had a cosmic microwave to make the primordial soup.

I hope you get the rest or relaxation you need to get your brain back to normal, Lori. I enjoy and appreciate your explanations in this thread, and your general presence on this board. Thanks!