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A few sci-fish queries

  1. Mar 8, 2005 #1

    I don't know anything about astronomy so bear with me. How old is the solar system, and how old is that relative to the rest of the star systems in the galaxy? That is, is the solar system a young star system or an old one what?

    Is this just a function of the solar system's location in the Milky Way (i.e., older star systems toward the perimeter, younger towards the center, or vice-versa)?

    If it matters, I'm entertaining thoughts on ETs and I'm wondering a bit about likelihoods. I'm just going to post a few rambling thoughts here:

    1) I take transhumanism as a given, and that it will make humans a potentially very dangerous species in this century (if you don't buy transhumanism that's okay, but let's not make this a TH thread); rapidly expansionist and extraordinarily dangerous to enemies.

    2) I take it as a given that a logical, advanced, spacefaring race would give very serious thought to exterminating a species that showed strong signs of achieving direction 1) above. In fact, I think any biosphere could be argued to show that kind of potential and is a candidate for extermination.

    3) Modern humans have been around for c. 100k years, and it wouldn't take a galactic genius to figure out their potential for 1).

    4) The Milky Way is roughly 100k light years across (correct me if I'm wrong there, as I know nothing of astronomy) and the speed of light represents an absolute bounds on the speed of travel as far as we know (practical limits are likely to be significantly lower).

    Obviously I'm going somewhere with this (it isn't "there is no intelligent spacefaring species in the Milky Way" so don't worry), but I'd like to hear some thoughts since I don't know exactly where I'm going with this. :D

    Any SETI nerds here who want to help me throw this around?

    I just found that and I haven't read through it, but this speculation is very interesting and germane.
    Last edited: Mar 8, 2005
  2. jcsd
  3. Mar 10, 2005 #2


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    The sun is about 5000 million years old. Of course it is not the youngest star, but it can be considered to be young. Stars are classified according to their composition on elements heavier than hydrogen (metalicity). Younger stars are called population I stars. They formed from the debris of the supernovae from the previous generation; the population II stars, which produced heavier elements in their cores by nuclear fussion. Most of the population II stars are currently red giants. This will be probably the fate of our sun in another 5 billion years. Also, most of the population II stars are located in the bulge of the galaxy. The population II stars in turn formed from population III stars, a postulated class of primordial stars composed only of primordial hydrogen and helium, which remains currently unobserved.

    Actually, the metalicity is a essential factor for the existence of life. It is postulated that it exists a Galactic Habitable Zone (GHZ) at a distance of 20 to 30 kLy from the galactic center (in analogy to the Circumstellar Habitable Zone CHZ around a star, where the temperature and other conditions could make life possible).

    You may find these papers interesting:
    The Galactic Habitable Zone I. Galactic Chemical Evolution: http://arxiv.org/abs/astro-ph/0103165
    The Galactic Habitable Zone and the Age Distribution of Complex Life in the Milky Way: http://arxiv.org/abs/astro-ph/0401024
  4. Mar 10, 2005 #3
    Thanks hellfire, that's good stuff.
  5. Mar 11, 2005 #4
    I think u should remember that ETs are unlikely to exist , or at least exist anywhere near us. Intelligent life is an unlikely occurence.
  6. Mar 11, 2005 #5
    and you have a sample size of precisely one to base those stats on!
  7. Mar 11, 2005 #6


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    Last time I checked, a sample size of 1 was not statistically significant. But, I'm an engineer by trade.
  8. Mar 11, 2005 #7
    hehehe. exactly, so how can it be said that "intelligent life is an unlikely occurence"????
  9. Mar 11, 2005 #8
    First of all, when we say "intelligent life" in this context, generally people mean "tool-using/making, communicating" life. In other words, species that might establish contact with us.

    Second, there isn't a sample size of 1, there's a sample size of 9. Actually, it's much bigger than that since we've been waiting for radio signals for x years and heard nothing, since when we're wondering about "species that might establish contact with us" what we're really wondering about is "species that might compete with us"... then again there's no guarantee that an intelligent species would want to broadcast radio signals throughout the universe as we stupidly do...

    Third, statistics aren't everything. The educated guess is that intelligent life is a relatively rare occurrence.
  10. Mar 11, 2005 #9


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    The lack of any ET radio signals does indicate critters with the same level of technology as ourselves are not common in this galaxy at any given time in galactic history. But, if the pace of technological advance accelerates the way it has in human history, the window of opportunity to detect EM based communication is extremely narrow - only a couple centuries. So all we can deduce from this is intelligent civilizations in this galaxy do not pass through this technological phase more than once every couple hundred years or so. It is impossible to rule out the possibility a large number of societies currently exist outside this window. A few centuries is no time at all on geological time scales. Your chances of hitting the lottery might not look all that bad compared to the odds of us detecting a signal of the type sought given the time we've spent looking.
  11. Mar 12, 2005 #10
  12. Mar 13, 2005 #11


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    Agreed matt. But we could receive signals originating from anywhere in the galaxy - assuming they are strong enough. You are correct in noting that our signals have traveled less than a mere century. And the last of our routinely detectable EM signals will probably end before the end of this century. That's where the 200 year window fits in. It takes billions of years for intelligent life to evolve, yet you only have about a 200 year window to detect them using our technology. 200 chances out of 4.5 billion is very low odds. There could be thousands, even millions of other civilizations out there that have not yet reached, or already zipped past the 200 year window.
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