Bazza Posted September 5, 2012 Report Share Posted September 5, 2012 Re: Longest Running Thread EVER Accordig to modern cosmology' date=' if the expansion of the universe continues to accelerate, there won't be any motion at all -- or any kind of energy. So, no perpetual motion.[/quote'] ahem... What are you talking about? Perpetual motion exists. It is a law of science the Law of Conservation of Energy. Quote Link to comment Share on other sites More sharing options...
L. Marcus Posted September 5, 2012 Report Share Posted September 5, 2012 Re: Longest Running Thread EVER A finite amount of energy in a -- for all purposes -- infinite universe, makes the energy per cube meter basically nil. Quote Link to comment Share on other sites More sharing options...
Cancer Posted September 5, 2012 Report Share Posted September 5, 2012 Re: Longest Running Thread EVER Well, my mind inserted "machine" into Bazza's post. Remember Newton's 1st Law ... "If an object experiences no net force, then its velocity is constant; the object is either at rest (if its velocity is zero), or it moves in a straight line with constant speed (if its velocity is nonzero)." Quote Link to comment Share on other sites More sharing options...
Bazza Posted September 5, 2012 Report Share Posted September 5, 2012 Re: Longest Running Thread EVER my thinking is that with the Law of Conservation of Energy that no energy can be created, it can only go from one form to another. Thus it seems logical to conclude that there is motion (is anything truly at rest?) and thus there is constant motion of this energy one way or the other. In other words "perpetual motion". I said nothing about a machine, but Cancer wisely picked up the general drift of my cleverly disguised intention. Quote Link to comment Share on other sites More sharing options...
Cancer Posted September 6, 2012 Report Share Posted September 6, 2012 Re: Longest Running Thread EVER Just remember the concept of the zero point for energy: for any energy scale there is an arbitrary choice of reference point against which one measures energy content. The choice is free to make, but you MUST be careful to maintain consistency with that choice. Lots of mistakes, conceptual errors, confusions, result from a failure to maintain consistency with an initial choice of energy zero point. Quote Link to comment Share on other sites More sharing options...
L. Marcus Posted September 6, 2012 Report Share Posted September 6, 2012 Re: Longest Running Thread EVER I have zero energy. Quote Link to comment Share on other sites More sharing options...
Bazza Posted September 9, 2012 Report Share Posted September 9, 2012 Re: Longest Running Thread EVER anyone know the mean radius for Earth in metres? I want to confirm some information in a book. Quote Link to comment Share on other sites More sharing options...
RPMiller Posted September 9, 2012 Report Share Posted September 9, 2012 Re: Longest Running Thread EVER 6371 kilometers Quote Link to comment Share on other sites More sharing options...
Cancer Posted September 10, 2012 Report Share Posted September 10, 2012 Re: Longest Running Thread EVER Note that the original intent of the designers of the metric system was to have the circumference of Earth (measured on the meridian that runs through the poles and through Paris) be exactly 4,000,000 meters. They were off a little, but only a little. Quote Link to comment Share on other sites More sharing options...
RPMiller Posted September 10, 2012 Report Share Posted September 10, 2012 Re: Longest Running Thread EVER That must have been one heck of a tape measure... Quote Link to comment Share on other sites More sharing options...
RPMiller Posted September 10, 2012 Report Share Posted September 10, 2012 Re: Longest Running Thread EVER Hey Cancer. Crazy thought exercise for today. I was thinking about Mars and how we could heat it up and make an atmosphere using today's technology. I started thinking about it when I was thinking about the Curiosity and its onboard computers, and the realization that computers need to stay cool and considering Mars' temps that isn't a problem. However, that heat, as minuscule as it is, is leaching into the atmosphere of Mars, and escaping into space. But that got me thinking about the aforementioned heating/terraforming. Do we have any methods currently that could be used to at least start the process on Mars? Even something crazy like a giant orbiting space magnifier that aimed the Sun's rays at the poles and melted them. I'm thinking from the perspective of cost wasn't an issue nor were things like nuclear energy, etc. Could we do it with today's technology? Quote Link to comment Share on other sites More sharing options...
Cancer Posted September 10, 2012 Report Share Posted September 10, 2012 Re: Longest Running Thread EVER Behold the power of trigonometry. Quote Link to comment Share on other sites More sharing options...
Cancer Posted September 10, 2012 Report Share Posted September 10, 2012 Re: Longest Running Thread EVER Re: Terraforming Mars The root problem isn't heat; it's that Mars doesn't have the gravity needed to retain what we would call an adequate atmosphere over geologic time. And that's a hard thing to deal with under any tech. You would sort of need to double the mass of the planet, I think. I think you could build a steady-state CO2 atmosphere, but that's not liveable: it is impressive how intolerant macroscopic animal life is of atmospheric CO2. I think at the distance of Mars (with the current Sun) you need a two-pronged greenhouse (both CO2 and water vapor) to warm the planet up to what we'd call comfortable, but that's a big problem because Mars can't retain water vapor. We don't really understand why Mars's atmosphere is as scrawny as it is; where did all the N2 go? It's hard to get across just how odd Earth's atmosphere is, with its "cold trap" at the bottom of the stratosphere that is under the ozone layer of the upper-mid stratosphere. That arrangement is crucial for retaining water. If the UV (which the ozone blocks) ever reaches the water vapor below, then the water gets photodissociated into H and O, and the hydrogen escapes very quickly, leading to the loss of all the water. As near as we can tell, Earth started with water and CO2 and N2 and a little methane -- how much isn't clear, but current feeling is that it wasn't much -- and over about 2.2 billion years plate tectonics and the geochemical carbon cycle got most of the CO2 sequestered via the ocean into carbonates, while photosynthetic life built up enough oxygen to change the fundamental chemical state from reducing to oxidizing. Then it took another 1.5 billion years after that to make multicellular life. Quote Link to comment Share on other sites More sharing options...
RPMiller Posted September 10, 2012 Report Share Posted September 10, 2012 Re: Longest Running Thread EVER I see. So it is all about gravity and chance. So, what if Mars was bombarded by thousands of asteroids from the asteroid belt? Would that possibly increase its mass enough, or would the bombardment simply displace a like amount of mass? Quote Link to comment Share on other sites More sharing options...
Cancer Posted September 10, 2012 Report Share Posted September 10, 2012 Re: Longest Running Thread EVER Depends sort of on how you did the bombardment, but now there is not enough mass in the asteroid belt to matter. There's substantially more mass in Earth's Moon than in the whole belt. Quote Link to comment Share on other sites More sharing options...
RPMiller Posted September 10, 2012 Report Share Posted September 10, 2012 Re: Longest Running Thread EVER Interesting factoid. Mars is smaller than our moon, correct? Quote Link to comment Share on other sites More sharing options...
Cancer Posted September 10, 2012 Report Share Posted September 10, 2012 Re: Longest Running Thread EVER No; in terms of mass, Moon ~ 1/80 Earth, Mars ~ 1/10 Earth. Total asteroid mass ~ 1/20 Moon. Quote Link to comment Share on other sites More sharing options...
RPMiller Posted September 10, 2012 Report Share Posted September 10, 2012 Re: Longest Running Thread EVER Ah, Mars is ~half the size of the Earth and the Moon is ~half the size of Mars (mass not withstanding)? I always seem to switch the last two for some reason. That's actually kind of surprising regarding the asteroid belt. So, how are we going to increase the mass of Mars to get its gravity where it needs to be to hold on to its atmosphere? Quote Link to comment Share on other sites More sharing options...
Cancer Posted September 10, 2012 Report Share Posted September 10, 2012 Re: Longest Running Thread EVER The densities of Mars and Moon aren't too different; Earth is rather denser than either. Mass, of course, goes as the third power of radius, so small differences in radius turn into rather bigger differences in size. At this point in the Solar System's history, I don't think you can rustle up enough matter to make Mars substantially more massive. The populations of the small bodies have been drastically reduced over the 4.5 Gyr evolution of the Solar System; they have all been accreted already or ejected from the system. If you combined all the Main Belt asteroids, plus the planet Mercury, plus Earth's Moon, plus Jupiter's moon Io, that's not enough mass to double the mass of Mars, and it's pretty much a complete inventory of the available rocky-metallic bodies remaining. (The other moons and the Kuiper Belt are largely icy bodies; you'll need some of those to add the water and volatiles to the resulting post assembly Mars, but they won't supply much in the way of mass.) Quote Link to comment Share on other sites More sharing options...
RPMiller Posted September 10, 2012 Report Share Posted September 10, 2012 Re: Longest Running Thread EVER So by all counts, it sounds like the only way to colonize Mars would be with self-contained buildings/ecologies that wouldn't rely on Mars' atmosphere? Quote Link to comment Share on other sites More sharing options...
Cancer Posted September 10, 2012 Report Share Posted September 10, 2012 Re: Longest Running Thread EVER Well, I think the idea of getting Mars to have a global Earthlike atmosphere where a human being could walk around in the open in shirtsleeves (or even a parka) just can't happen. Under sealed domes, though, it's possible. Quote Link to comment Share on other sites More sharing options...
RPMiller Posted September 10, 2012 Report Share Posted September 10, 2012 Re: Longest Running Thread EVER Which brings me back to the original question. Does current technology have the ability to make that a possibility, or do we still need to perfect a few things before we do that? Quote Link to comment Share on other sites More sharing options...
Cancer Posted September 10, 2012 Report Share Posted September 10, 2012 Re: Longest Running Thread EVER I don't think we have successfully built a completely closed long-term environment that operated with humans in it for an extended period of time yet. That sort of needs to be done here on Earth so we can work the bugs out. Previous attempts have failed for various reasons, and until all those are worked out here I would hesitate to say we can operate one on a large scale on a different planet. Quote Link to comment Share on other sites More sharing options...
RPMiller Posted September 10, 2012 Report Share Posted September 10, 2012 Re: Longest Running Thread EVER So, it is a definite "no, we don't currently have the technology/ability to colonize Mars." Quote Link to comment Share on other sites More sharing options...
Cancer Posted September 10, 2012 Report Share Posted September 10, 2012 Re: Longest Running Thread EVER Well, you need that long-term sealed environment capacity both on the planet as well as getting there. So ... yeah. My understanding is that an ion engine could be made that could get a human-occupied package from Earth to Mars (and back) with the nominal not-quite-a-year one-way flight time. To my mind, that's not the issue. It's the long-duration closed ecosystem, and the questions about radiation shielding which, again, I haven't seen addressed adequately (though I haven't gone looking). Quote Link to comment Share on other sites More sharing options...
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