Thread: I have a Cosmology question

Originally Posted by wopmanfixit

I’ve heard this (I'm paraphrasing)- “expansion of the universe is accelerating, scientists don’t know why.”

It really depends on when in the universe's history you are talking about. IIRC, and I could be wrong here as this was explained to me some years ago, is that the expansion of the universe works in an unintuitive way. It was space that was expanding, and all space was expanding. That's probably not very clear.

Consider the time shortly after the Big Bang (if it did indeed happen), and imagine that you are at the outer limit of the universe. Since it is all of space that is expanding, as opposed to you moving away from the center at a constant velocity, your velocity will increase as you move farther away, because as you move farther away there is more space between you and the center and that space is expanding.

Or maybe think of 10 people in a line, each one foot apart. So the two people on the end will be... 9 feet apart. But if space doubles, there will be two feet between each person and the ends are 18 feet apart. Double again, and there will be 4 feet between each person and the ends are 36 feet apart. The gain is exponential instead of linear.

...Sorry for not multiquoting

I can't remember clearly, but isn't there some kind of xray activity associated with blackholes? Or does that go along with their formation?

Originally Posted by crazycliff200843

I can't remember clearly, but isn't there some kind of xray activity associated with blackholes? Or does that go along with their formation?

I'm really not 100% sure on that one. One more time with feeling, it's been a while...


Anyway, since black holes have such incredible gravity that photons can't escape them, it follows naturally that other forms of radiation like xrays can't either.

As for their formation, that's certainly possible. Lot's of really crazy stuff happens when normal matter collapses into a black hole, and a I can imagine that a wide variety of radiation is emitted in the early stages of it's formation.

Hawking did show that black holes can "evaporate" as the shed particles out the pole, like a quasar. At least on paper, right. This is all on paper.

X

Originally Posted by crazycliff200843

I can't remember clearly, but isn't there some kind of xray activity associated with blackholes? Or does that go along with their formation?

There is X-Ray radiation associated with black holes. As matter falls in, it typically orbits the hole as well. The acceleration from falling and the acceleration from the orbit causes the emission of high energy electromagnetic radiation, such as x-rays

Originally Posted by xman

Hawking did show that black holes can "evaporate" as the shed particles out the pole, like a quasar. At least on paper, right. This is all on paper.

X

Black holes do indeed evaporate; I don't remember the equation, but their lifetime is a function of their mass (which can also be represented as a function of their size). The smaller they are, the shorter their lifetime is. This is why black holes formed in our atmosphere and particle accelerators pose no threat to us; their lifetimes are fractions of a second (and small fractions at that).

Originally Posted by holli4pirating

Black holes do indeed evaporate; I don't remember the equation, but their lifetime is a function of their mass (which can also be represented as a function of their size). The smaller they are, the shorter their lifetime is. This is why black holes formed in our atmosphere and particle accelerators pose no threat to us; their lifetimes are fractions of a second (and small fractions at that).

You mean the LHC isn't going to cause the end of the earth?