Semi-OT: A General Tech Question Thread for me :)

[dogscoff]

Hunpecked said:
According to the article below the first stars in our galaxy formed about 13.6 billion years ago. That makes our sun, at 5 billion years, a relative youngster.

http://www.space.com/scienceastronom...ge_040817.html

But according to that same article, our galaxy is almost as old as the universe. When the universe was born, it was all hydrogen- there were no heavy elements. It is the ongoing process of star-burning that turns dull old hydrogen into stuff like carbon and oxygen that we need for life. The older the universe gets, the more hydrogen is turned into heavy elements. Therefore, looking at it the other way, as you look back in time towards the Big Bang the amount of heavy elements in the universe dwindles down to nothing.
Since these heavy elements are needed for life, shouldn't the probablilty of life dwindle away with it?

Or, to put it another way, we may be among the first life to emerge, because it's not the amount of stars that have existed over the last 13.whatever billion years that matters, it's the availability of heavy elements- and they've never been more available than right now. Give it another 10 billion years and there could be life springing up all over the place, because the universe will be a much heavier place than it is now. It may even get *too* heavy for life at some point, which would mean the Drake equation would have to factor in some sort of bell curve with "suitability for life of heavy element/ hydrogen ratio" on one axis and "time since big bang" on the other.

[Hunpecked]

Dogscoff writes: "...as you look back in time towards the Big Bang the amount of heavy elements in the universe dwindles down to nothing. Since these heavy elements are needed for life, shouldn't the probablilty of life dwindle away with it?"

Absolutely. Note, however, that we're dealing with averages and probabilities here. In regions of unusually rapid star formation (galactic cores, globular clusters) the interstellar medium could be sufficiently enriched with "metals" (atomic number 3 and above) in a billion years (the most massive stars are thought to go supernova in under a hundred million years). Such regions are also pretty hostile to life (black holes, sterilizing radiation), but given the vast number of galaxies in the universe, it seems likely that suitable combinations of conditions would exist in many of them. If so, even after 4-5 billion years of evolution, life forms in these regions would have a 7 billion year head start on us.

While researching this post I came across an interesting article from 1996:

http://hubblesite.org/newscenter/new...eases/1996/37/

Judging from Hubble images of distant galaxies, it appears that the rate of star formation in the universe peaked about 3 billion years after the Big Bang (BB), at about 10-15 times the current rate. By the time our sun was formed, some 8-9 billion years post-BB, most of the stars the universe will ever have had already been born. That means we've also already had most of our supernovas, so Dogscoff's curve (lovely diagram, BTW) should probably be skewed to the left.

[Renegade 13]

dogscoff said:
When the universe was born, it was all hydrogen- there were no heavy elements.

As far as I know, when the universe was born, it was essentially an electrically charged soup of particles. Free atomic nuclei and free electrons were everywhere, since the temperature for a few hundred million years was far too hot to allow electrons to 'permanently' bond with the free atomic nuclei. So for quite a while in there it was an electromagnetically opaque universe, until things cooled off enough to allow the first elements to form.

[narf poit chez BOOM]

...Why would all of those elements be hydrogen?

[Wolfman77]

Protons atract electrons. 1 proton + one electron = hydrogen. Protons, having the same electric charge, need to be forced together to form larger atoms. Which happened only after stars formed.

[narf poit chez BOOM]

That makes sense.

But...Wouldn't 1 proton + 1 electron = neutron?

[Wolfman77]

Sort of, if you force them together, they could create a neutron and some energy, I think. There is something that keeps them from doing that on their own, can't remember what it is off the top of my head, and need to go do some work for a half hour or so, I'll look it up when I get back here. Or you can try wikipedia if you want.

[Suicide Junkie]

Wolfman77 said:
Sort of, if you force them together, they could create a neutron and some energy, I think. There is something that keeps them from doing that on their own, can't remember what it is off the top of my head, and need to go do some work for a half hour or so, I'll look it up when I get back here. Or you can try wikipedia if you want.

You don't get energy out. You have to put energy in.

Free neutrons have a half-life of 11 minutes, and decay back to a Proton and Electron.

Neutrinos get thrown around too, but I don't think you care.

[Hunpecked]

According a Wikipedia article, right after the Big Bang there was about 74% hydrogen-1, 1% hydrogen-2, 25% helium-4, and trace amounts of lithium and beryllium. Nucleosynthesis stopped there because there are no stable 8-nucleon elements (2 x helium-4) and there was insufficient time for many triple-alpha collisions (3 x helium-4).

http://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis