From: Michael Tarbell <mtarbell.nul>
Date: Sun, 16 Dec 2012 12:14:19 -0700
Archived: Mon, 17 Dec 2012 05:59:12 -0500
Subject: Re: Update To Our View Of The Drake Equation


>From: David Rudiak<drudiak.nul>
>To: post.nul
>Date: Sat, 15 Dec 2012 11:59:07 -0800
>Subject: Re: Update To Our View Of The Drake Equation

>>From: Michael Tarbell<mtarbell.nul>
>>To: post.nul
>>Date: Fri, 14 Dec 2012 15:36:08 -0700
>>Subject: Re: Update To Our View Of The Drake Equation

>>>From: Edward Gehrman<egehrman.nul>
>>>To:<post.nul
>>>Date: Fri, 14 Dec 2012 08:08:53 -0800
>>>Subject: Re: Update To Our View Of The Drake Equation

>>>If Einstein is correct, then travel by even a grain of sand,
>>>using external energy (so fuel wouldn't have to be carried), at
>>>the speed of light would require all the energy in the universe.
>>>So if we travel at 10% of the speed of light, does that require
>>>10% of the energy in the universe? And that's just to power a
>>>grain of sand.

>>>Under these circumstances, I don't think star travel is probable
>>>or will ever be possible. Yes we have visitors, but a more
>>>mundane explanation is possible: we share our planet with an
>>>ancient civilization.

>>At 0.1c, the relativistic change in mass is ~0.5%, which I think
>>may be reasonably neglected. The energy required to bring a
>>typical (0.01 gm) grain of sand to 0.1c is thus on the order of
>>(0.5)x(.01gm)x(3x10^9cm/sec)^2, or ~4.5 gigajoules. This is
>>equivalent to the detonation of ~1 ton of TNT, not a trivial
>>amount, but substantially less than 10% of the energy in the universe.

>>If this has been the basis of your pessimism about interstellar
>>travel, you may want to reconsider. Although, if interstellar
>>travel is occurring routinely, I must say I'd be surprised if
>>the brute-force acceleration of mass were the predominant
>>technique.

<snip>

>Taking the grain of sand example, 4.5 gigajoules is roughly the
>chemical energy in 30 gallons of gasoline. Kicking that grain of
>sand up to half light speed would take less than a thousand
>gallons, not much different than the American family uses in
>their gas-guzzling SUV every year.

Hi David,

Your gasoline equivalent brings the point home better than my TNT
equivalent. It's really a fairly modest amount of energy.

<snip>

>These "back of a napkin" type schemes are massive and expensive
>engineering projects, but not that far beyond present
>technology, something we could probably pull off in a hundred
>years. The basic point is we humans in a relatively early stage
>of technological development can conceive of reasonably
>plausible schemes of how interstellar travel might be possible.
>Some much older and technologically sophisticated civilization
>can probably come up with something much more elegant. That is
>why I say ruling out interstellar travel and migration in the
>Drake equation is not a scientific assumption but one of dogma
>or lack of imagination. With migration, the number of ET
>civilizations could be many orders of magnitude greater than the
>non-migratory calculations come up with, so ET's could be very
>close and concerned about what we aggressive apes with H-bombs
>are up to.


There's no question we're close to being able (in principle) to
initiate some kind of crude migratory process, perhaps even an
autonomous one (e.g., self-replicating factories, etc).

I'm not so sure we would pursue it in practice, even if our
civilization held together long enough to try it. Indeed, one
might speculate that projects of such magnitude that yield no
'payoff' to the creators themselves, perhaps that don't even
yield feedback for dozens of generations (if ever), are probably
not widely pursued even among civilizations that have such
capability.

But given a sample space of (quite plausibly) hundreds of
thousands of civilizations, it's hard to imagine that none of
them launched such an expansion. And it would only take a few
such, along with some millions of years, to clutter things up
pretty thoroughly. Which, of course, is what makes the Fermi
paradox so palpable, even if some UFOs _are_ ET.

Apparently no roving colonies of self-replicating automata have
had any substantive impact in our vicinity, unless perhaps some
even more advanced visitors have taken it upon themselves to
clean up after these crude early efforts, concealing (for
whatever reason) both themselves and any other overt evidence of
ETs. I'm about as comfortable with that as I am with, say,
crypto-terrestrials tracking down and destroying any fossil
evidence of their developmental history. Bit of a stretch,
either way.

Hence the nagging possibility that, in fact, there is some
reason in principle that such brute force, virus-like expansions
are uniformly extinguished. As we've both pointed out, it's
certainly not the energetic constraints, nor the time
constraints (for a sufficiently motivated civilization). Perhaps
some unknown hazard in the interstellar environment?

Anyway, enjoyed your informative post.


Mike



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