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Location: UFOUpDatesList.Com > 2012 > Dec > Dec 16

Re: Update To Our View Of The Drake Equation

From: David Rudiak <drudiak.nul>
Date: Sat, 15 Dec 2012 11:59:07 -0800
Archived: Sun, 16 Dec 2012 07:04:44 -0500
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

>>>From: David Rudiak<drudiak.nul>
>>>To: post.nul
>>>Date: Thu, 13 Dec 2012 10:22:33 -0800

>>>Subject: Re: Update To Our View Of The Drake Equation

>>>Quite! There is the hidden assumption in these calculations that

>>>interstellar migration is impossible. This is not a scientific
>>>assumption but dogma. There are many conceivable ways that such
>>>migrations could take place without resorting to assumptions of
>>>Star Trekian warp drives, but at sub-light speeds.

>>>E.g., assume machine intelligence and length of travel doesn't

>>>really matter. Time to nearest star at a very modest 1% light
>>>speed is then less than 500 years. NASA propulsion experts for
>>>years have been thinking in terms of 10% light speed for a
>>>probe.

>>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.

Michael,

I was about to respond similarly. Bad understanding of physics
makes for bad arguments.

Newtonian kinetic energy for mass m and velocity v (or energy to
accelerate a mass that velocity) is 1/2mv^2. The relativistic
formula is mc^2(sqrt(1-v^2/c^2) -1), which reduces to the
Newtonian formula for velocities substantially less than the
speed of light (c). Even at 30% light speed, the difference is
only about 2.5%. At .5c, only about 7.5%.

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.

Now yes, if you get very, very near light speed, then the energy
begins to skyrocket. For v=c, the energy becomes infinite
because that square root term goes to zero and dividing by zero
gives you infinity. But .99c is still pretty darn good. That
would take about 700 times more energy than .10c, or roughly the
energy of a passenger jet's worth of fuel.

Of course, we're talking about something substantially larger
than a grain of sand for interstellar migration. About 15 years
ago, NASA was toying with the idea of accelerating an
interstellar probe to 0.1c. The key contender was a probe
propelled by high-power lasers with a large sail capturing the
laser light. (Light has momentum, and thus imparts thrust on the
sail.) All propulsion energy is provided externally, which gets
around the limitations of typical highly inefficient rocket
propulsion where you need to carry huge amounts of propellant on
board to kick out the back to provide the thrust.

If you assume 10 metric tons (10,000 kg) for a small probe and
sail, this a billion times the mass of the grain of sand, so a
billion times more energy is needed. This works out to be
~5*10^18 joules for 10% light speed. World civilization consumes
about 10^20 joules per year, so roughly 3 weeks of world energy
use. That's a lot of energy and very expensive, but still a far
cry from 10% of the energy of the universe.

About 30 years ago, NASA also put together a think tank on how
to make space exploration economical. Assuming continued rapid
development in cybernetics, they projected that in the future it
should be possible to create a robotic factory on the moon that
manufactured solar cells and solar energy farms for beaming
energy back to Earth with microwave antennas. Furthermore, such
factories would be self-reproducing, making copies of
themselves, transporting them to other sites to make more solar
cells, etc., etc., so like a virus of solar energy producers
spreading across the moon's surface.

The first such factory would be very expensive to develop and
establish on the moon, but after that you have a virtual free
lunch and more energy than you know what to do with. E.g.,
Earth's surface gets about 2*10^17 joules/sec of solar energy,
the moon about 10% of that. Assume the self-replicating
factories blanket 10% of the moon's surface facing the sun at
any one time and with various inefficiencies, conversion to
electricity and transmission has an overall efficiency of only
5%. That would be 10^14 joules/sec, about the energy of an A-
bomb per second and about 30 times earth's present power
consumption. Not only would there be plenty of energy to power
everybody's air conditioner and iPhone on Earth, but plenty of
energy left over for other things, like accelerating
interstellar probes. The energy to accelerate that 10 ton probe
to 10% light speed would be the equivalent of less than one
day's operation of such a system.

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.


David Rudiak



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