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Tends to moot that part of the debate though. Joel Send a noteboard - 26/08/2011 12:31:21 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.

Fair enough, on both counts; naturally any species with fossil fuels is likely to industrialize through them rather than poorer energy options, and likewise any species without them will perforce industrialize through those inferior fuels or not at all. The argument for "not at all" looks pretty strong though; the bad thing (or one of them... ) about fossil fuels is that we have no way to replace them once they're gone, but the good thing is that we don't have to confront that issue as quickly as we would if we switched to, say, ethanol.

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.

Which apparently contain not quite 16% more energy than hardwood logs; that ain't gonna do it.

And yes, I realize the issue with low efficiency (that's why radiators exist, after all) but strongly suspect a car burning wood instead of gasoline will need a MUCH thicker firewall.

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.

Yes and no; there's real reason to believe the Holocene Era is more like the "Holocene Error", an aberrant period in the Earths history that just happened to be ideal for the birth of human civilization. More generally, anything that significantly slows technical advancement greatly increases the chance an extinction level event will wipe out a species before it spreads beyond its native planet. As for superconductors letting you bypass distance, that's certainly true as far as it goes, but you need a way to cool (not to mention create) your superconductors. We keep coming back to the same Catch 22 very familiar in alternative energy discussions: Every energy souce we can think of with fossil fuels utility and capacity requires trans-fossil fuel industrialization.

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

) 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,

Right, I'M discounting it because stable reproduction (and thus native species) seems unlikely anywhere fission would be a viable Industrial Revolution energy.

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.

) where he recounted the story of a woman viewing Faradays first demonstration of electromagnetism and remarking, "Very impressive, but of what use is it?" to which the scientist replied, "Madam, can you tell me the use of a newborn child?" It's a valid comparison; both have nearly unlimited POTENTIAL use, but no IMMEDIATE use. Though on that note, IIRC scientists (and SF writers) in Newtons day assumed we'd use blackpowder to get to space rather than rail guns, for obvious reasons.

Meanwhile, efficient energy sources have always been in great demand; the Second Law of Thermodynamics makes that somewhat inevitable because we need energy to do pretty much anything and it's always in short supply. The Industrial Revolution simply raised the stakes and drove the point home a bit more, which is why your earlier response got me thinking we might have been darned lucky (or blessed) that we just happened to have the compressed biomass of hundreds of millions of years lying around waiting for us to find a use for it. The Romans knew coal burned; they just didn't need it because they had slaves and didn't have railroads.

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.

OK then, though it does seem like using interstellar molecules for braking would be counterproductive. Racing to some significant fraction of c to quickly cross interstellar distances then using stray atoms struck along the way to slow while still traversing those distances is just throwing away energy no one has to spare (particularly if interstellar drag is so great it could significantly slow your craft; until you get where you're headed it's just one more thing to overcome).

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.

For us I'm still betting on vacuum cooled fusion as the long term answer; the big issue with fusion has always been getting a reaction big enough to be useful but small enough to control, and both the ease of the latter and the risk of failing seem much more favorable in high orbit. We might even be able to make batteries or hydrogen cells and drop them back down the well to Earth. But OK, if fusion makes gravity wells a negligible obstacle scooping hydrogen out of the nearest gas giant becomes viable; now all you have to do is develop an industrial capacity for controlled commercial fusion without fossil fuels. It's another case where that would be more plausible if we hadn't spent half a century (so far... ) trying and failing to do that even WITH fossil fuels. That's not to say it's impossible, I just still don't think it very plausible.

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.

Probably; I'm reminded of James Burke again: Gears are a much bigger deal for industrialization (and printing presses) than fossil fuels, and predate widespread use of the latter. "Widespread use" is a key concept here, and why I keep fudging the distinction between "ability" and "mass production; " if you can't do it on a large scale, and repeatedly, it's just an impractical one hit wonder. I'm sure every ancient Egyptian would've been buried in a shiny giant limestone pyramid if he'd had the means, but half the reason pharoahs did it was because they wanted a monument to the fact THEY had the means practically no one else did. To take a more pertinent example, the same applies to Apollo 11; it's very impressive and hard to equal, but it wasn't the dawn of extraterrestrial man many hoped to see because by then it had long been well known that we simply had no means to travel to another star within a human life time, and the only extraterrestrial place we MIGHT be able to create a permanent residence in the Solar system is a heavily modified and/or encapsulated Mars. Of course, the flip side of Earthcentrism is that all of that could radically change for a species that just happens to inhabit a system where MULTIPLE planets can support them (though that might be unlikely unless they're either EXTREMELY adaptable, evolved in VERY common planetary conditions, or both).

In the end I have to agree that it may only seem fossil fuels are necessary due to biological bias; a microscopic species with brains based on quantum computing rather than electrochemical reactions might be able to do things with a single planets resources that would require a galaxy for us, and their centuries of fossil fuels might be no more than an Earthman who crashed and was crushed ages ago. Part of what makes things so dicey for us now is that we have ability to alter our ecosystem on a planetary level, so if we screw things up too badly we can't just pick up and move somewhere else.

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If ever there was a reason to cut greenhouse gas emissions Camilla - 19/08/2011 10:14:00 AM 865 Views

I've seen Start Trek, I know the real threat is you killing whales. snoopcester - 19/08/2011 10:34:08 AM 526 Views

I know

Camilla - 19/08/2011 10:36:22 AM 473 Views

You make a fair point snoopcester - 19/08/2011 11:22:53 AM 448 Views

Re: You make a fair point Camilla - 19/08/2011 02:06:05 PM 424 Views

Re: You make a fair point snoopcester - 19/08/2011 02:10:43 PM 422 Views

It's the other other white meat.

Joel - 19/08/2011 07:13:19 PM 476 Views

There's so much wrong with that Isaac - 19/08/2011 01:08:57 PM 504 Views

"They don't recycle; kill them all. "

Joel - 19/08/2011 07:11:15 PM 498 Views

Very Space Hippy

Isaac - 19/08/2011 10:39:10 PM 516 Views

It's still debatable whether we've abandoned the evolutionary ladder. Joel - 19/08/2011 11:16:58 PM 596 Views

You'll welcome to debate that with a biologist, it's not my specialty or interest Isaac - 20/08/2011 04:46:43 AM 551 Views

I've seen a lot of mainstream biologists suggest human evolution may be mostly mental now. Joel - 21/08/2011 11:32:48 AM 569 Views

Neither of us are biologists though and it's not really relveant anyway Isaac - 21/08/2011 01:21:06 PM 516 Views

I'm not ignoring it, just wondering why over half the planet ignores it and lives in misery. Joel - 21/08/2011 01:55:53 PM 525 Views

If you have occassion to spend time in those places you'll know why Isaac - 21/08/2011 02:38:44 PM 456 Views

How does literal mud huts as the norm respresent living standards rising "a lot". Joel - 22/08/2011 12:29:35 AM 575 Views

You seem to have cherry-picked what you wanted to hear out of my comments Isaac - 22/08/2011 01:07:10 AM 347 Views

"It's a stability thing, not a Western greed thing" seemed to encapsulate your comments. Joel - 22/08/2011 03:10:17 PM 484 Views

Only if you really cherry pick them Isaac - 23/08/2011 02:48:08 AM 497 Views

This seems to have descended into an insoluble partisan debate. Joel - 23/08/2011 07:43:07 PM 559 Views

You're the one who dragged it to that Isaac - 23/08/2011 08:10:03 PM 473 Views

Did I? Joel - 25/08/2011 10:18:29 PM 464 Views

*rudely butts in* Vodalus - 23/08/2011 04:38:33 AM 540 Views

American companies don't go to China SOLELY to screw the working class, no;that's largely incidental Joel - 25/08/2011 08:03:05 PM 585 Views

we should abdon the myth of the evolutionary ladder random thoughts - 20/08/2011 11:49:35 PM 390 Views

Probably; as discussed in Brams thread it should never be seen as predictive, let alone prophetic. Joel - 21/08/2011 11:55:09 AM 498 Views

Well, for this context I think the use is okay Isaac - 21/08/2011 11:59:19 AM 467 Views

That's an interesting point about the NEED for fossil fuels as a stepping stone to advanced culture. Joel - 21/08/2011 12:33:59 PM 567 Views

Not a need, just an edge Isaac - 21/08/2011 02:06:23 PM 384 Views

There's industrialization and then there's industrialization. Joel - 22/08/2011 12:53:35 AM 745 Views

If you were more familiar with engineering you'd not say something like that Isaac - 22/08/2011 01:53:33 AM 741 Views

I dispute that industrialization is primarily about non-agricultural production. Joel - 22/08/2011 03:10:19 PM 647 Views

Well you can argue that with a dictionary I suppose Isaac - 23/08/2011 03:50:52 AM 505 Views

I'm not above that, but the dictionary definitions I've found are disappointingly self-referential. Joel - 24/08/2011 02:25:21 AM 430 Views

That tends to be the case, it is a kinda vague term outside of specific context Isaac - 24/08/2011 09:12:19 AM 590 Views

Tends to moot that part of the debate though. Joel - 26/08/2011 12:31:21 AM 605 Views

Re: Tends to moot that part of the debate though. Isaac - 26/08/2011 05:52:59 PM 761 Views

Re: Tends to moot that part of the debate though. Joel - 28/08/2011 09:44:52 AM 546 Views

yes I was just jumping into the middle of the discussion. random thoughts - 22/08/2011 03:03:49 PM 427 Views

and we wonder why so many people ignore "scientist" random thoughts - 19/08/2011 01:17:38 PM 521 Views

Think it's better to ignore "reporters on a slow news day," to be honest *NM* beetnemesis - 19/08/2011 02:38:23 PM 192 Views

Or even acquire a sense of humour. *NM* Camilla - 19/08/2011 08:36:07 PM 215 Views

That was the City of Pearl series by Karen Traviss Aeryn - 19/08/2011 02:04:51 PM 490 Views

Re: That was the City of Pearl series by Karen Traviss Camilla - 19/08/2011 02:06:27 PM 447 Views

Hypothetical aliens are perfectly wise aerocontrols - 19/08/2011 06:24:13 PM 435 Views

You may be confusing aliens with God.

Joel - 19/08/2011 07:08:01 PM 463 Views

Not confused aerocontrols - 19/08/2011 11:41:56 PM 482 Views

It's a an amusing disconnect to watch. Joel - 20/08/2011 12:25:00 AM 477 Views

Naturally. Camilla - 19/08/2011 08:36:28 PM 565 Views

So, basically, we're the poor white trash of the universe. Joel - 19/08/2011 07:06:23 PM 523 Views

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<quote id="222850">
<quote id="222571">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.</quote>

Fair enough, on both counts; naturally any species with fossil fuels is likely to industrialize through them rather than poorer energy options, and likewise any species without them will perforce industrialize through those inferior fuels or not at all.  The argument for "not at all" looks pretty strong though; the bad thing (or one of them... ) about fossil fuels is that we have no way to replace them once they're gone, but the good thing is that we don't have to confront that issue as quickly as we would if we switched to, say, ethanol.

<quote id="222571"><quote id="222518">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?</quote>

Which apparently contain <a href="http://en.wikipedia.org/wiki/Wood_pellets#Energy_output_and_efficiency">not quite 16% more energy than hardwood logs</a>; that ain't gonna do it. ;) And yes, I realize the issue with low efficiency (that's why radiators exist, after all) but strongly suspect a car burning wood instead of gasoline will need a MUCH thicker firewall.

<quote id="222571"><quote id="222518"><quote id="222341"><quote id="222205">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). </quote>

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

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.</quote>

Yes and no; there's real reason to believe the Holocene Era is more like the "Holocene Error", an aberrant period in the Earths history that <a href="http://en.wikipedia.org/wiki/Holocene_climatic_optimum">just happened to be ideal for the birth of human civilization</a>.  More generally, anything that significantly slows technical advancement greatly increases the chance an extinction level event will wipe out a species before it spreads beyond its native planet.  As for superconductors letting you bypass distance, that's certainly true as far as it goes, but you need a way to cool (not to mention create) your superconductors.  We keep coming back to the same Catch 22 very familiar in alternative energy discussions:  Every energy souce we can think of with fossil fuels utility and capacity requires trans-fossil fuel industrialization.

<quote id="222571"><quote id="222518"><quote id="222341"><quote id="222205">All the issues about compact high yield energy sources increase significantly when we start talking about space travel;</quote>

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.

<quote id="222341"><quote id="222205">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. </quote>

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.</quote>

I only removed fission as a route for a hypothetical where life took a long time to evolve around a slightly dimmer star,</quote>

Right, I'M discounting it because stable reproduction (and thus native species) seems unlikely anywhere fission would be a viable Industrial Revolution energy.

<quote id="222571">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.</quote>

True up to a point, but there are many examples of pivotal scientific discoveries that languished until forgotten (most famously the steam engine and atomic theory) because no parallel technology existed that made it practical.  I recall an episode of Bill Nye (always the most reliable source for scientific history :P) where he recounted the story of a woman viewing Faradays first demonstration of electromagnetism and remarking, "Very impressive, but of what use is it?" to which the scientist replied, "Madam, can you tell me the use of a newborn child?"  It's a valid comparison; both have nearly unlimited POTENTIAL use, but no IMMEDIATE use.  Though on that note, IIRC scientists (and SF writers) in Newtons day assumed we'd use blackpowder to get to space rather than rail guns, for obvious reasons. ;)

Meanwhile, efficient energy sources have always been in great demand; the Second Law of Thermodynamics makes that somewhat inevitable because we need energy to do pretty much anything and it's always in short supply.  The Industrial Revolution simply raised the stakes and drove the point home a bit more, which is why your earlier response got me thinking we might have been darned lucky (or blessed) that we just happened to have the compressed biomass of hundreds of millions of years lying around waiting for us to find a use for it.  The Romans knew coal burned; they just didn't need it because they had slaves and didn't have railroads.

<quote id="222571"><quote id="222518"><quote id="222341"><quote id="222205">Unless you plan on using a gravity whip at the end,</quote>

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.</quote>

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.</quote>

OK then, though it does seem like using interstellar molecules for braking would be counterproductive.  Racing to some significant fraction of c to quickly cross interstellar distances then using stray atoms struck along the way to slow while still traversing those distances is just throwing away energy no one has to spare (particularly if interstellar drag is so great it could significantly slow your craft; until you get where you're headed it's just one more thing to overcome).

<quote id="222571"><quote id="222518"><quote id="222341"><quote id="222205">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).  </quote>

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.</quote>

For us I'm still betting on vacuum cooled fusion as the long term answer; the big issue with fusion has always been getting a reaction big enough to be useful but small enough to control, and both the ease of the latter and the risk of failing seem much more favorable in high orbit.  We might even be able to make batteries or hydrogen cells and drop them back down the well to Earth.  But OK, if fusion makes gravity wells a negligible obstacle scooping hydrogen out of the nearest gas giant becomes viable; now all you have to do is develop an industrial capacity for controlled commercial fusion without fossil fuels.  It's another case where that would be more plausible if we hadn't spent half a century (so far... ) trying and failing to do that even WITH fossil fuels.  That's not to say it's impossible, I just still don't think it very plausible.

<quote id="222571"><quote id="222518"><quote id="222341"><quote id="222205">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.</quote>

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.... ;))</quote>

Probably; I'm reminded of James Burke again:  Gears are a much bigger deal for industrialization (and printing presses) than fossil fuels, and predate widespread use of the latter.  "Widespread use" is a key concept here, and why I keep fudging the distinction between "ability" and "mass production; " if you can't do it on a large scale, and repeatedly, it's just an impractical one hit wonder.  I'm sure every ancient Egyptian would've been buried in a shiny giant limestone pyramid if he'd had the means, but half the reason pharoahs did it was because they wanted a monument to the fact THEY had the means practically no one else did.  To take a more pertinent example, the same applies to Apollo 11; it's very impressive and hard to equal, but it wasn't the dawn of extraterrestrial man many hoped to see because by then it had long been well known that we simply had no means to travel to another star within a human life time, and the only extraterrestrial place we MIGHT be able to create a permanent residence in the Solar system is a heavily modified and/or encapsulated Mars.  Of course, the flip side of Earthcentrism is that all of that could radically change for a species that just happens to inhabit a system where MULTIPLE planets can support them (though that might be unlikely unless they're either EXTREMELY adaptable, evolved in VERY common planetary conditions, or both).

In the end I have to agree that it may only seem fossil fuels are necessary due to biological bias; a microscopic species with brains based on quantum computing rather than electrochemical reactions might be able to do things with a single planets resources that would require a galaxy for us, and their centuries of fossil fuels might be no more than an Earthman who crashed and was crushed ages ago.  Part of what makes things so dicey for us now is that we have ability to alter our ecosystem on a planetary level, so if we screw things up too badly we can't just pick up and move somewhere else.
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