[ExI] Drake Equation Musings

BillK pharos at gmail.com
Mon May 16 11:51:22 UTC 2016

On 16 May 2016 at 03:16, Rafal Smigrodzki  wrote:
> ### I find it fascinating that looking at the universe means an analysis
> stretched in time. Anything outside of our galaxy supercluster is already
> hundreds of millions of years back in time. If there is a time-dependent
> process that has to finish before technogenesis, then looking outside
> Laniakea might mean observing galaxies at the time when were still too young
> to have star extinction bubbles, even if in fact all the stars there were
> already eaten by aliens.
> The only part of the universe which we see in close to real time is our
> direct neighborhood, so we only need to explain absence of civs here, not in
> the whole universe (of which we do not have current images). Our
> supercluster has only 10e15 solar masses, which is 10e-7th part of the
> visible universe (if the Wikipedia article is correct). So if the likelihood
> of technogenesis at this time since the big bang is on the order of 10e-15
> per solar mass, then observing just one civ would not be surprising.
> Is the technogenesis likelihood of 10e-15 per solar mass a reasonable
> estimate?

Looking at the galaxies in the Hubble Deep Field is indeed seeing
those galaxies as they were 13 billion years ago, as young galaxies,
so signs of technology would not be expected.

But our Milky Way galaxy is also about 13 billion years old and it
hasn't been colonised by an expanding civilisation.
The Milky Way is only about 150,000 light years across and contains
about 400 billion stars (though that may be up to 1000 billion stars).
Life on earth started very soon after the formation of the Earth,
around 4 billion years ago.

Our Laniakea Supercluster has about 100,000 galaxies stretching over
only 520 million light-years.
So there are plenty of galaxies within a few million light years,
(millions - not billions) with no signs of technical civilisation


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