Warp schrieb:
>   Matter-based complex life in general. Complex life requires complex
> molecules, and you can't have complex molecules made purely from the first
> few elements a star produces, ie. hydrogen and helium.

You're forgetting lithium, which - along with hydrogen and helium 
(though at a different isotope relation) - is primordial.


> 
>   Coincidentally, the next chemical element a star produces is, surprise
> surprise, carbon.

Strictly speaking, beryllium is produced first; but only few of it ends 
up outside the star, as it will readily be processed further into carbon 
even while it is being "bred".

As another "surprise, surprise", part of the carbon is also processed 
further already, into - guess what - oxygen!


 > After that it only gets more complicated. Carbon is a
> rather versatile molecule, besides being abundant in more developed star
> systems, which is probably the reason why we are based on it.
> 
>   (The elements in-between those are not formed in the core of the star at
> all, but in supernova explosions, which means that any of the more complex
> chemical elements must come from remnants of old supernovas (which might in
> turn have been formed from remnants of even older supernovas, and so on).
> AFAIK these stars don't tend to form at the edges of galaxies.)

Not precisely: The breeding of some elements as heavy as iron happens 
earlier already.


>   I'd say that if you want complex life which is not carbon-based, the
> conditions must be even more ideal than for us, so it's not like it makes
> things simpler, but on the contrary, it probably makes life even less
> likely.

While there's some reasonable point to that, the argumentation is 
flawed, missing out the fact that during the formation of planets (and 
even stellar systems as a whole) the relation of elements is subject to 
additional pyhsical influences, resulting in much different relations 
between elements in regions accessible to life. For instance, carbon 
makes up for only 0.03% of the mass in earth's crust and atmosphere, 
while silicon accounts for some whopping 25% - only surpassed by oxygen 
(about 50%).

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Warp wrote:
>   It's hard to imagine any kind of life (much less intelligent life) forming
> on or in a neutron star. 

Robert Forward wrote some SF novels about that, starting with Dragon's Egg. 
He's actually a cutting edge physicist as well, which is pretty cool, so 
when he tells you how to put a space ship in orbit around a neutron star 
such that you don't wind up being eaten by tidal forces, chances are he 
actually did the math. :-)

-- 
   Darren New, San Diego CA, USA (PST)
   I ordered stamps from Zazzle that read "Place Stamp Here".

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Darren New <dne### [at] sanrrcom> wrote:
> Warp wrote:
> >   It's hard to imagine any kind of life (much less intelligent life) forming
> > on or in a neutron star. 

> Robert Forward wrote some SF novels about that, starting with Dragon's Egg. 
> He's actually a cutting edge physicist as well, which is pretty cool, so 
> when he tells you how to put a space ship in orbit around a neutron star 
> such that you don't wind up being eaten by tidal forces, chances are he 
> actually did the math. :-)

  Maybe, but let's not forget what the F in SF stands for.

-- 
                                                          - Warp

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Warp wrote:
> Darren New <dne### [at] sanrrcom> wrote:
>> Warp wrote:
>>>   It's hard to imagine any kind of life (much less intelligent life) forming
>>> on or in a neutron star. 
> 
>> Robert Forward wrote some SF novels about that, starting with Dragon's Egg. 
>> He's actually a cutting edge physicist as well, which is pretty cool, so 
>> when he tells you how to put a space ship in orbit around a neutron star 
>> such that you don't wind up being eaten by tidal forces, chances are he 
>> actually did the math. :-)
> 
>   Maybe, but let's not forget what the F in SF stands for.

Of course. You said "it's hard to *imagine* any kind of life." ;-) I was 
simply  pointing you at a fun, interesting book set imaginatively in that 
kind of setting. I like sharing book recommendations, since so much out 
there is dross it's hard to find good stuff.

-- 
   Darren New, San Diego CA, USA (PST)
   I ordered stamps from Zazzle that read "Place Stamp Here".

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clipka wrote:
> Reactor schrieb:
>> (c) Lucky coincidence, since it did not and will not always appear to 
>> be the
>> same size of the sun.
> 
> Quite mind-bogglingly unlike for intelligent life to "wake up" just at 
> such a time when it does.
> 
> (BTW, are you sure it will not? After all, not only does the lunar orbit 
> around earth change, but also earth's orbit around the sun. Maybe the 
> two effects will happen to cancel out?)

so many unlikely random factors leading to us... ;)

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Warp wrote:
>   The video posits that life in other planets is likely due to the humongous
> amounts of stars and planets out there. On the other hand, the opposite
> hypothesis is scientifically sound as well:
> 
> http://en.wikipedia.org/wiki/Rare_Earth_hypothesis
> 
>   In short, the hypothesis states that life requires such ideal conditions
> that most planets, and even most galaxies simply don't provide them.

Wow! I never considered that entire galaxies could be ruled out at 
roughly a single glance. That surely reduces the number of possible 
Earth-like planets by a large amount.

-Mike

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clipka wrote:
> Quite mind-bogglingly unlike for intelligent life to "wake up" just at 
> such a time when it does.
> 
> (BTW, are you sure it will not? After all, not only does the lunar orbit 
> around earth change, but also earth's orbit around the sun. Maybe the 
> two effects will happen to cancel out?)

I think the eccentricity of the Earth's orbit changes over time, not 
it's distance. I.e. the Earth's orbit continually oscillates over time 
between a more circular and highly elliptical shape. At those times 
where the Earth's orbit is highly elliptical, the sun's apparent 
diameter might vary noticeably *within a single year* as the seasons change.

-Mike

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SharkD wrote:
> I think the eccentricity of the Earth's orbit changes over time,

The moon is also receeding from the earth due to tidal forces.

-- 
   Darren New, San Diego CA, USA (PST)
   I ordered stamps from Zazzle that read "Place Stamp Here".

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On 09/19/09 13:49, Warp wrote:
>    Maybe, but let's not forget what the F in SF stands for.

	That F may encompass the whole concept of alien life, if you want to be 
picky...

-- 
No, Taco Bell is NOT the Mexican Phone Company!

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Darren New <dne### [at] sanrrcom> wrote:
> The moon is also receeding from the earth due to tidal forces.

  But isn't this recession decelerating? It will stop when the Earth is
tidally locked with the Moon. Thus the Moon is not going to get very much
farther than it already is.

-- 
                                                          - Warp

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