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 Listen to 'Strange Days... Indeed' - The PodCast At: http://www.virtuallystrange.net/ufo/sdi/program/ These contents above are copyright of the author and UFO UpDates - Toronto. They may not be reproduced without the express permission of both parties and are intended for educational use only.
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