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That tends to be the case, it is a kinda vague term outside of specific context Isaac Send a noteboard - 24/08/2011 09:12:19 AM
Gonna kinda jump ahead here, you raise valids points on a lot of these but keep in mind I originally said we should expect aliens to have used coal and oil if they had them, I am merely establishing things can be done without them, so your objections kinda reinforce my original point, still your objections hit mostly out how impractical compared to what we have some of these things are, not impossible or even implausible.

I also had a mid-message power outage so I'm kinda repeating some points in haste I already typed, so excuse me if I get a bit hasty or jumpy in the new version. I am, from my POV, kinda repeating myself.

I should've been a bit less vague and a bit more specific since I know you know the technical distinction: I said, "energy" but when I was talking about high yield compact energy I meant "power". Yeah, burning hydrogen delivers more than burning octane, but you don't have to do electrolysis to get octane by the barrel. You're the scientist, so you tell me: If you burn 20 pounds of wood (the equivalent of a gallon of octane under ideal conditions) in half an hour (the rate at which a car getting 30 mpg at 60 mph would use it) will more of the energy go to your wheels, or your radiator?


Engines rarely run anywhere near 50% efficiency, so the answer for both is 'radiator', also keep in mind you don't have to throws logs on or something, you'd use compressed woodchips and such if you were actually building an infrastructure around this.

Geothermal seems a lot more plausible than nuclear to me, but you can't take it with you (that's always the rub with geothermal).

You can always 'take it with you' if you have to, you spin the energy into fly wheels or charge batteries with it.

And fight the Second Law every step of the way. I remember having this discussion years ago when my uncle was the first person to sing the praises of hydrogen fuel cells soon to hit the market and wondering how in the hell running cars with electrolysis could possibly be efficent, before finally deciding it MIGHT work if you could use some form of solar or an equivalent that could be exploited NO other way so that you weren't wasting energy to get your hydrogen. Near as I can tell that's basically what they are doing, but ultimately you have the same problem electric cars have always had: It may be cleaner if you're getting the juice from clean energy, but generating electricity at the local hydroplant and storing it in a battery for a car is automatically less efficient than simply hooking the car up to the power plant; it just has the advantage of actually being possible. Again, we BOTH know the reason geothermal hasn't caught on as a main stream power source is because it quickly becomes impractical the farther you get from a fault line.


Superconducting materials let you bypass distance and those materials aren't related to coal or oil, more Yttrium and nitrogen really than hydrogen or carbon, albeit the nitrgoen is for cooling them. And we've known how to build flywheels as power storage for a long time, they predate batteries by and large, we've only recently started screwing around with levitating flywheels in a vacuum over superconductors, that's also not coal/oil related. No particular reason they would not be pursued, the big boost of an oil economy might make us do stuff way faster but we've really only been at this for a century out of thousands of years of effort, some civ taking a millenia or two to go from ox-pulled plows to superconducting magnets instead of a century or two in't all that big a deal in the grand scheme of things.

All the issues about compact high yield energy sources increase significantly when we start talking about space travel;

Yes, so significantly that travel between even close stars in under a century is only possible if you either have and absurdly high energy to mass fuel (fusion or antimatter) or you don't carry fuel (laser sails), it doesn't matter if you're using coal, ethanol, or firewood to drive your economy they are all orders of magnitude to small to do the job.

No argument, but it seems slightly implausible to expect a civilization to jump straight from firewood to antimatter without any stops along the way at coal, petroleum or fission. If they lack any or all of those options that's still the only way it can happen, but I can't help thinking that will reduce the chance of it happening to a vanishingly small probability (although the expected value in a large unbounded universe of unknown extent is debatable). My point is simply that if they have little to no experience with seeking and finding compact high yield energy sources they'll be hard pressed to build a wood burning star destroyer.

first you have to get out of the planetary gravity well, and for interstellar travel you then have to get out of the stellar gravity well.

A minor issue, as fast as the escape velocity of a star tends to be, it's a pitifully tiny amount compared to the speeds necessary to carry out space travel on anything not resembling a geological timescale.

Minor by comparison only; it's an issue we've only recently licked ourselves and nothing like a large scale. People (often including, I admit, me :P) tend to think that once you get out of Earth orbit you can just keep going forever unless you get sucked in by some other massive objects gravity, but that just isn't so, it it? Unless you're move VERY fast initially you better have a remaining power source or the suns constant pull will slowly but inexorably slow you down until it pulls you back again, and the suns gravity technically has no more limit than that of any piece of matter. That's a pretty big hurdle to overcome, though it's nothing to the energy necessary to quickly traverse interstellar distances, and the same old issue of generating a LOT of energy in a VERY short time rears its head again. A species addressing that problem for the first time would likely envy our familiarity with it. Again, if they address it through some compact high yield energy source other than fossil fuels, no problem, but it's hard to imagine how they'd develop safe efficient nuclear or antimatter energy sources with nothing more than wood, water wheels and mirrors combined with lenses. Maybe if they've got an Olmpus Mons or two lying around, but frankly it's hard to think of many options, even if that's only because I'm an Earthling.


I only removed fission as a route for a hypothetical where life took a long time to evolve around a slightly dimmer star, and there's really no difference between coal or wood when we start talking about fusion or antimatter. For that matter a big old rail gun could fire a slug with a tether up into space sans coal/oil/rocket fuel and leave you with a space elevator and prototypes could give you the sattelites we have... that is actually how we always we assumed we'd do it. Newton and the lot knew perfectly well how to get a satellite up there just had no damn reason to do it, what with no radio or computers or micro-stuff. Very little of our tech is even vaguely related to fossil fuels, they just provide the cheap power that let's us devote a lot of people to research, hell a culture with better memories or longer lives or a mild obsession with math - say a religious devotion to numbers - might be able to devote an effectively equal amount of resources to research, physical scientists and engineers make up way less than 1% of the pop, a feudal culture where the noble ladies pursued the 'feminine art' of math or chemistry instead of embroidery might end up with semiconductors while everyone was still drag plows behind oxen, don't make the mistake of assuming science is some ladder you climb in one specific route. If I knew latin I could teach an old roman aquaduct engineer how build and power telegraph system in a few days, he might come up with it on his own if he was dwelling on how to send messages fast after seeing a bolt of lightning hit a metal rod. They could easily end up with TVs and a 200 cable channels while still trying to figure out how the hell to make a useful steam engine. The processes are not linear.

Unless you plan on using a gravity whip at the end,

Decelerating isn't a big issue, the matter around an alien star all moves fairly close to it's own speed, if you've got a big sail of dumb cheap material you just spread it and allow micro collisions with all the local gas to slow you, that's how theoretical light sail ships work, you shove them with lasers until you get the right speed, they retract their sails, then reopen them near their destination to brake. Seeing as most of the local material will tend to already be doing a nice orbit around the star, you can still use gravitational assist or slingshot pretty effectively too. The sail would also get significant braking force from the solar illumination coming from the approaching star. Even a more conventional 'fueled' ship would probably use this.

That makes sense; I certainly see how it would help, but are you saying a ship moving at the rate necessary for interstellar travel at any decent speed would be able to dissipate all that energy just by bouncing rarefied random gas molecules off its sails? Seems like they'd have to start doing it as soon as they hit the edge of a system and hope they were going all the way down the well anyway.


There's maybe a 1000 atoms per cubic meter in the space between local stars, the 'local bubble' isn't very dense as these things go, so serious vacuum there, but a ship trucking along a decent fraction of light speed with be hitting about a trillion atoms a second per square meter of cross-section. That gas is moving at speed pretty much dead-stop relative to local stars meaning at 1/3 light speed each little bit of hydrogen you smack is going to give you a braking energy of ~ 10^-11 Joules, pretty tiny but every square meter is hitting 10^11 of those things a second at .33c, or basically 1 joule per square meter [yes I cherry picked that speed for the example]. That's not a lot of drag, some 1 ton spaceship with a meter of cross-section at that speed would decelerate under that braking force over many trillions of year, more since as it slowed the braking energy would decrease with the cube of velocity. Cube because you're breaking comes from how many atoms you hit... which is linear to your speed, and their kinetic energy, square of relative velocity, so cube total... works great at very close to light speed to slow but not well at lower speeds... but close to stars density rises and more importantly you start getting light pushing on you too, here near earth that's around 1000 watts per square meter. If you're using something like Graphene, which a 1 ton sheet literally cover a few billions square meters, a cargo bay full of sail is giving you something the size of Texas to slow down with. Realistically it's the sort of thing you'd want to combine with other propulsion to basically save fuel and thus get a higher top speed, but yeah it can play a role.

you'll probably want to keep enough fuel to brake with when you get wherever you're going (though several forms of propulsion do offer the option of letting you use scoops on the nearest gas giant, but then you need a way to carry those scoops out of the well along with your crew, life support and engine).

If you're using fusion, as fueling off gas giants implies, the energy needed to remove hydrogen from the gravity well is pretty tiny compared to what it will produce and is expended during topping off your tanks so you'll already have paid your energy bill. If you're running of methane and straight chemical burn of it, you'd probably want to go for a very high orbit, using a hollow tether to pump fuel up, with your height limited by the tensile strength of the cord, same as a space elevator.

I'm thinking more in terms of the bigger you make the scoops to get more fuel, the more fuel you need to move that mass out of the planetary and stellar wells, then through the cosmos. We needed a whole Saturn V just to put an RV on the Moon and drop a subcompact back on Earth; once again, stellar gravity is much stronger and farther reaching than the Earth or Moons, so tacking on matter retreival devices big enough to do any good and still being able to haul them out of a gas giants gravity PLUS exit a star system means they better be grabbing a LOT of fresh fuel. Of course, the more they snag, the bigger they have to be; I'm not saying a decent engineer couldn't find the optimal size and shape, but the power needed just to get it off its home planet would necessarily shoot well above even what it took to launch a crew, ship and engine.


Like I said, if you've got fusion then stellar or planetary gravity wells are like mild uphill slopes to a formula 1 racecar. Lacking fusion or something better you might want to on-site construct say a bigger laser platform than ran by burning methane in orbit around the local Neptune or whatever to push you, or a bunch of locally fabricated mirrors, you work with what you got. We have the tech to do a lot of this stuff already it's just the difference between a little retaining wall in your terraced garden behind the house and the Great Wall of China, kinda sucks if you're halfway through with the wall and someone invents landmines to render big walls redundant.

If a civilization can reach that point without fossil fuels they can probably find a non-fossil fuel alternative (after all, we've never used fossil fuels for space travel, and the fuel we DO use isn't ultimately energy efficient, it's just that the energy cost of electrolysis in FL doesn't directly impact fuel consumption on the shuttle), but it's hard to imagine many scenarios where they COULD reach that point without fossil fuels. That may just be a limitation of my imagination, but either way it's started me thinking, belatedly or not.

Well, as I've said, I can't see a civilization choosing not to use fossils fuels if they had them available, they're handy in the same way a bunch of half rotted furniture inside a castle in the forest is handier as firewood than all those trees but not necessary. Theoretically a culture might develop that viewed black rock or fluid as 'evil', buried by the gods in Hades where it occasionally seeps up to ooze into men's hearts, in which case even when they know it's handy they might avoid using it for the same reason we get queasy about using insects or fecal matter as food sources or all the queasiness that used to be and to some degree still does surround organ transplants. Our first useful medical nanotech is likely to use viruses in some fashion, it will take some selling to get a lot of people comfortable with their docs come in and saying "I'm going to inject you with this big hypodermic full of viral material to cure you" if vaccines are any guide. One doesn't necessarily overcome such things, if the chemical model of a specific hydrocarbon happened to coincidentally look identical to their symbol for the Evil God of Fire and Greed, for instance, their own green zealots would probably have a pretty easily sale convincing people not to use it. Absent those factors, or maybe if the had good computers before a fossil fuel economy got going and had discovered AGW and it was, or they thought it was, just as bad as we tend to assume, I can't really see anyone bypassing a fossil fuel economy if they're available to be used.


The problem I keep having, and maybe it is just Earthcentrism, is that all our large scale alternative energy sources have been products of an industrial era that almost literally exploded through the use of fossil fuels. How do you get silicon solar cells or gas centrifuges to run your manufacturing if you need manufacturing to get them? You can do a lot of things with a Franklin stove, but I doubt those are among them. Geothermal, maybe, if you can harness a big enough source (I guess you don't HAVE to have carbon to coke steel, but you're going to need something a little more heat resistant than wood to build a geothermal generator, and if you're going to make a wood turbine you better lubricate it VERY well.... ;))


Your mistaking cheap mass production with ability, that's why I keep talking about $5 and $50 hammers. You don't need coal to make steel, charcoal works, so would dried out algae put through the same process if it comes to it. Ceramics and glass can do a lot stuff steel can, so could aluminum. Silicon, the main ingredient of glass really, does not turn into microchips through any petroleum based process I know off. Fundamentally it's important use is that it's cheap, it means we can devote large portions of our pop to doing other things, but I feel pretty confident that if we only had a few hundred scientists alive at once, which even a tiny agrarian society of a million could support without too high a burden, we'd get all those things just take longer and likely in different orders. When we're talking about alien physiology keep in mind some species of sapient whales with long lives and good memories might sit around for a billion years belching calculus back and forth to each other without having ever developed a tool culture or a race of smart raccoons whose love of grubs let's them mega-breed because insects get you very high calories per acre compared to cattle... on top of agriculture, they might only need 1/10th of their pop to produce food way back in their megalith days and jump from Stonehenge to Hubble in a century or two just because they're really curious and don't need coal or oil to let them have 10% of their pop doing research and engineering. Earthcentrism is fairly legit, if probably limiting, but species centrism is a bigger problem when thinking about this stuff. If you're curious tool users with language who can spare a decent percent of your pop for curiosity, you probably can and will develop advanced tech, coal and oil just were handy for us because they let us spare a lot of people from normal toil and incline to toward more development. In my opinion, moveable type printing presses and an obsession with teaching everyone to read so they could read the bible probably had a much huger effect in causing the industrial revolution than coal or oil did.
The intuitive mind is a sacred gift and the rational mind is a faithful servant. We have created a society that honors the servant and has forgotten the gift.
- Albert Einstein

King of Cairhien 20-7-2
Chancellor of the Landsraad, Archduke of Is'Mod
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That tends to be the case, it is a kinda vague term outside of specific context - 24/08/2011 09:12:19 AM 588 Views
Tends to moot that part of the debate though. - 26/08/2011 12:31:21 AM 600 Views
Re: Tends to moot that part of the debate though. - 26/08/2011 05:52:59 PM 759 Views
Re: Tends to moot that part of the debate though. - 28/08/2011 09:44:52 AM 543 Views
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and we wonder why so many people ignore "scientist" - 19/08/2011 01:17:38 PM 518 Views
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So, basically, we're the poor white trash of the universe. - 19/08/2011 07:06:23 PM 519 Views

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