Making hydrogen results in a significant net loss of energy. After you've made it, transporting it is a huge problem because hydrogen likes to leak right through most "solid" materials. It has a very low energy density at one aatmosphere, so it has to be compressed to insane degrees to get any decent portability out of it. Both in tankers and/or pipelines and in the target vehicle. That also means fueling presents some serious issues.
Making hydrogen at STP is about 60% efficient. I've heard 80% claimed for dedicated plants. By comparison, an internal combustion engine is about 30% efficient. I remind you that supercapacitors and batteries aren't lossless either; internal resistance bites you hard at high currents, and equivalent series resistance of supercapacitors, especially, is quite high.
Hydrogen transport does have leakage, but leakage is only a serious problem if you're storing hydrogen for weeks before using it. Especially as you still wouldn't be able to store the equivalent of a full tank of gas with a hydrogen hybrid, you'll lose negligible amounts of hydrogen to diffusion.
Hydrogen does indeed have a storage density problem (it has to be stored as a compressed gas, which means a heavy cylinder for a relatively small amount of hydrogen). Still much better energy density than batteries or capacitors. My money's still on methane or methanol.
Ethanol has already caused corn prices to tweak all kinds of ways; not a good thing. At least at this point, that's a really bad side effect. Corn is a mega-important food crop. Ethanol is like gasoline, in that it must be delivered via tanker, at a hidden energy and pollution cost. It is carbon neutral, in that the carbon in the plant came from the atmosphere, and goes back to the atmosphere as exhaust.
I'm talking about methanol, not ethanol. If methane or methanol are adopted as fuels, they'll be strictly used as energy storage media, formed by burning waste hydrocarbons (chaff and other inedible plant parts) in a hydrogen atmosphere. Closed-loop systems could be built, too, but they tend to be too heavy and bulky to be worth putting into a car (CO2 is scrubbed and bound as a carbonate, then released by heating and reacted with hydrogen during recharge).
This means taking an efficiency hit vs. using hydrogen, but in return you get fuels that are much easier to handle and that can use existing infrastructure (natural gas pipelines for methane, liquid fuel transport network for methanol). You're still way, way ahead of batteries (the reaction that produces methane is quite efficient, and methanol only slightly trickier).
However, electrical vehicles can be 100% carbon negative, as a hydro plant, nuke plant, wind plant, tidal plant, geothermal plant, solar plant... none of them produce carbon at all.
This is still carbon-neutral, as no carbon goes into or out of any part of your system. With ethanol production or synthesized methane or methanol, you grow extra plants that would otherwise not be grown.
The last thing - but not the least - is that to get the most power to the ground, at the least cost, electric wins hands down. Electric motors today are easily manufactured to be lighter and provide better torque and power curves than any internal combustion engine ever made in even a slightly comparable size class.
Fuel cells use the same motors that a battery-powered car uses. The only difference is the delivery system. You could even use a gas turbine instead of a fuel cell, and still come out ahead (this is done for locomotives and ships all the time). In both cases, you don't have to worry about battery lifetime and disposal issues (the catalysts in fuel cells are much less nasty than the materials in most batteries).
It's the assumption of a "reasonable dielectric" that knocked you off your horse. That's where ultracaps have left the building. They're using altogether unreasonable dielectrics, and there is stuff on lab benches that is approaching battery levels right now.
Batteries have energy storage on the order of 1 MJ/kg. The numbers I quoted for the theoretical limits for capacitors are on the order of 1 MJ/kg. You aren't doing a very good job of disproving my point with your examples.
I assumed you had a magical dielectric with a dielectric constant of 1000 capable of supporting electric fields of 10 MV/m (capacitors are typically rated to half the breakdown voltage, so this means 20 MV/m). The best reported dielectrics I've heard of have constants of around 6000, but no breakdown information was provided (10+ MV/m is very hard to get).
Supercapacitors and ultracapacitors get their performance by using nanoporus materials to vastly improve surface area. Electric double-layer capacitors get their performance by using clever techniques to get a very uniform dielectric layer, which lets them work closer to maximum tolerances. No magic in either of these.
If you're claiming much more than 1 MJ/kg, provide citations, or it's vapour.
This is wrong. Sort of. Lithium-ion batteries can power a car for 200 to 250 miles, but they're expensive.
They do that by cheating. The Tesla, for example, carries half a tonne of batteries, and the car itself is built to be as light as possible (the batteries probably outweigh everything else put together, without passengers in it). Lithium batteries also tend to have lifetime issues; numbers I've heard quoted off-the-cuff for lithium batteries are losing 50% of their capacity within a year or two, and only being good for 100ish charge cycles, though this will vary with the specific battery model. This is tolerable for a cell phone or notebook, as you tend to upgrade these frequently and new batteries cost much less than a new unit, but a car will have serious problems under these conditions.
For a battery-powered car to be really competitive, we'd need a battery technology with at least 5 times the storage density per unit mass, that was good for a decade of daily use before needing replacement. This may or may not be possible; time will tell (unless the engineering difficulties with fuel cells are solved first). On one hand, we aren't anywhere near the theoretical limits to the energy density of batteries, but on the other hand, people have been working on the problem for centuries.
It's very easy to calculate the fundamental limits for any capacitor-based technology (assume a maximum reasonable dielectric constant and breakdown field), and this ends up being vastly lower than chemical energy (about 0.1-1 MJ/tonne, vs. about 4 GJ/tonne for TNT and more for air-breathing engines). We're approaching the limits now. The energy storage medium of the future will be fuel cells (either hydrogen-based with relatively low capacity, or reforming cells and fuel synthesizers that use methane or methanol as a storage medium for much greater storage density at the cost of added complexity).
A "big rip" scenario only occurs with a fairly unrealistic choice for the value of the cosmological constant. The usual assumption at present is that the expansion will accelerate, but won't have the asymptotically-infinite behavior of a Big Rip.
Regarding femtotechnology, I find OA's assumptions about it to be unrealistic (though it makes for good stories). You're also assuming gravity manipulation, which is even more problematic (gravity's behavior is only expected to change from our current model at unification energies, which are utterly impractical to reach). So, I'd look for more boring, lower-tech approaches to waiting out the end of the universe.
Typical "surface" (upper atmosphere) temperatures of brown dwarf after the first billion years are quite cold (as with gas giants), and their luminosity decreases as they age.
We had enough mass to get several gas giants and ice giants out of our disc. As long as it was a Population I star with moderate to high metallicity, there will be more than enough rock available (and more than enough uranium and thorium to drive geothermal processes). Planets the size of Neptune have been found in orbit around them, as have brown dwarfs (though this is arguably closer to a failed binary star companion than a planetary companion).
Temperature-wise, there's a big difference between a red dwarf and a brown dwarf. Typical "surface" (upper atmosphere) temperatures of red dwarf after the first billion years are quite cold (as with gas giants), and their luminosity decreases as they age. A red dwarf has a minimum surface temperature of around 2500 K, and its luminosity never drops below about 1% that of the sun. This gives a strongest-emission wavelength of about 1.1-1.2 microns - near-IR, but still high enough to drive photochemical processes, unlike older brown dwarfs.
As a gravitationally bound system, the galaxy's size won't change. Long story short, you end up with orbital velocities being slightly different, but orbits remaining stable, even in an expanding universe that's driven by a cosmological constant. This applies to both the stars in the galaxy, and the vast clouds of hydrogen and helium that still make up a good fraction of its mass.
There are far, far more low-mass stars than there are high-mass stars. This means we have no shortage of red dwarf stars in the galaxy. Planets in the habitable zone tend to be tidally locked, and red dwarf stars tend to put out quite a bit of ionizing radiation from solar flares, but a thick atmosphere solves both problems (winds driven by the heat differential spread heat around at the surface, and the thick atmosphere blocks ionizing radiation). The surface ecosystem would have less light to drive it, but you'd still have geothermal sources, you might have an airborne microbial ecosystem higher up to produce energy (much as plankton do for the ocean), and you'd certainly have no lack of mechanical energy from the winds. So, I can definitely believe life could arise on its own in red dwarf systems.
In practice, I'd expect civilizations from the era of larger stars to colonize red dwarf systems and either build constellations of habitats, or move/tailor a planet to suit their long-term needs. None of this requires magic; just time, and good automation.
Actually, red dwarf stars last far longer than our sun. On the lower end of the mass scale, they end up having a convective zone deep enough to cycle all of their hydrogen into the core (unlike the sun, which will only ever use about 10% of its hydrogen). As they have a much lower rate of fusion to begin with, this results in lifetimes of trillions of years.
Red dwarf stars are also a lot more _common_ than our sun (there's a power-law distribution for number of stars vs. mass of stars).
So, no lack of energy for quite a while, even if you assume star formation stops.
As for the argument about whether or not evidence would be seen for the Big Bang, it'd be there, but a lot harder to observe. Distant quasars/AGNs would be much harder to see (though not impossible), and there would still be enough primordial hydrogen, deuterium, and helium around for its presence to be a mystery that SS wouldn't be able to explain. Proposals that the galaxy had existed for an _infinite_ length of time would have problems with the fact that hydrogen does get burned and stars do have finite lifetimes, even if the galaxy's active lifetime is much longer than the trillion-year lifetime of a dim red dwarf.
What I'd expect them to conclude is that they were in a universe that looks like anti-deSitter spacetime, containing an isolated galaxy or galaxy cluster inside their observation horizon, and that had existed in the same state for an extremely long but finite time. What's outside the horizon would be unknown. Where the galaxy and primordial elements came from would be unknown until they did a lot of very careful observation and analysis.
No, it's not. The tensile strength determines how often the width must double before reaching GEO - it's an exponential scaling.
While it's an exponential scaling, 60 GPa is enough to do it. The characteristic length for a material needed for a non-tapered space elevator is 4000-and-change km. The density of nanotubes is 2-and-change. For a length of 5000 km and a density of 3, you have a tension of 150 GPa. This is 2.5 times the tensile strength measured. The tapering factor is e^2.5, or a factor of about 12. Not a problem.
The real problem is that 1) we haven't yet been able to make pure enough single-walled carbon nanotubes to get close to the 110 GPa figure (60 GPa is the most I've heard of measured), and it'll be very hard to do so on a mass-manufacture scale, and 2) composites will have lower tensile strength than the fibers they're made of (though it may be close enough).
If a tapering factor of 100 is acceptable, the minimum tensile strength of the elevator material is about 33 GPa (150 GPa / ln(100)).
Your "proof that gasoline fumes ignite" test is slated for this month, BTW.
It's not a very hard problem. Driving on controlled-access roads with good paint is actually pretty easy.
Meanwhile, in the real world, you're driving on poorly-maintained roads with bad signage, sub-optimal weather conditions, and lots and lots of other drivers doing unpredictable and quite often illegal things.
Driving on a well-marked road under good conditions is a toy problem by comparison. IAACompEng, and a regular driver.
What I didn't put in the project web pages before it got/.'d: I'm making a case with integrated battery that mounts on the back of my R1150GS motorcycle. If I get the size trimmed a bit it should fit without taking up any of the bike's luggage space. Now to figure out how to make a lean-angle sensor to record that along with the speed/position data...:)
You could use the dual-axis accelerometer I used for the robot project to sense tilt changes. Have it integrate changes to guess at current tilt, and recalibrate itself by assuming that anything maintained for 30 seconds or more is a tilt of zero. You could combine it with one of the pseudo-gyro sensors made by the same company (Analog Devices), but be warned that they're ball-grid array packages (and it's probably overkill for your purposes).
If you want to be able to 'integrate per-vehicle information' and 'get realtime data on the best route to work', you're going to have to be able to track me.
And that's just not happening.
If one car in a hundred had a transponder, you'd get a good idea of how traffic was flowing on the major routes in and around a city. One in a thousand might even be enough for this.
You might actually be able to do this just by looking for cell phone emissions from tracking towers. I'm sure at least that many people use their cell phones while commuting. This gives you better coverage than traffic cameras/helicopters.
Why is it... That we have invented a million different ways to distract ourselves while blasting down the highway, without developing self-driving cars?
Building self-driving cars is a Very Hard Problem. It's being worked on, and great progress has been made, but it's not going to be ready for prime time yet.
The problem is that it has to work safely even under strange or pathological circumstances. Guaranteeing this is much, much harder than getting a car to drive on an empty road and stop at well-marked intersections.
On the plus side, as soon as a car autopilot drives better than the average driver, the insurance rate perk for getting one will make the switchover very rapid.
As for distraction, you'll note from the article that the access point was never used by the person driving the vehicle (and that it's in fact illegal to do so in California). It's a passenger perk (and great for when you get _out_ of the car, with the range it has).
Get the cost down, and this would be an interesting way to integrate per-vehicle information (speed and congestion [via vehicle proximities/GPS]) with map information to get realtime data on the best route to work.
I'm not sure how he'd get the cost down much further than it is already. He's using off the shelf parts at commodity prices. Building in quantity-100 might shave off 30% or so, but even fabbing your own integrated board with all widgets on it in quantity-1000 would only get to about half the current price.
Custom IC would get it down further, but that would take quantity-silly:).
Can we expect that fast neutron burner reactors can be produced using a smaller amount of area and for a cheaper cost than photovoltaics? You're darned right we can.
I respectfully disagree with the "cheaper cost" part. Here in Ontario, we generate a lot of our power using nuclear plants, and while they're cleaner than coal, they're expensive to build and a maintenance nightmare. They're a reasonably mature technology, so I don't expect the cost to change any time soon. Thin-film cell technology is still very immature, so I can definitely believe it will drop in price.
That said, I think you need to stop drinking the Kool-Aid. Sure it's less land than what is used for farming. Guess what? Farming produces food. If some of those cell farms reduces the area available for farming, we produce less food.
*Sigh*.
a) The land you'd use for solar power generation isn't farmland - it's roof area in industrial parks and urban sprawl areas that's currently going to waste, and any of the large amount of area that's _not_ used for farming. Farming requires arable land. Solar panels don't.
b) The amount of land required is far _less_ than that required for farmland. That is the point of the comparison. You keep pulling out your "thousands of square miles" figure - you do realize that about 1.8 _million_ square miles of land is allocated to farming in the contiental US, right?
As spelled out very clearly in my original post - the amount of land area needed for solar power is comparable to that used for habitation, and very small compared to the land area devoted to other purposes.
But I digress, go back to my previous post and find the math error. If my numbers are 10x what others have found, then my error should be easy to find.
Your error was saying, "Oh my goodness, the cost multiplied by 300+ million people is huge!", without realizing that _any_ cost multiplied by that many people is huge. You do the same thing with land area. You just don't seem to handle "per capita" or "fraction of total money/area used" concepts very well.
You were also quoting current thick-cell prices for solar cells, as opposed to calculating what the cost crossover point is (i.e., the price that would be _needed_ for solar to be economical).
I actually believe that my numbers were too small since I didn't factor in the cost of batteries
At 10 kWh/day, a week's worth of power storage requires 35 off-the-shelf deep-cycle lead-acid batteries. Let's amortize over a 5-year lifetime, instead of a 10-year, to reflect shorter life cycle. That means 7 batteries replaced per year, or about $1400, for a household's power. This is manageable, though more expensive than buying power off the grid.
If solar power becomes more widespread, or even if fuel cells for things like cell phones and laptops continue to push the relevant technologies, expect fuel cell systems to drop this cost quite a bit (batteries are horrible for storage of large amounts of power).
Oh yeah! And how about reducing our dependence on foreign oil?
You can do that right now by building more nuclear plants. We're doing that up here. The US doesn't seem to like that solution, though.
Solar is an attractive long-term solution because the technologies are intrinsically simple and cheap, have a very high energy density per unit area used, and lend themselves to scalable implementations, unlike most other forms of power generation.
The biodiesel you mention is just recycled solar with a far, far worse system efficiency. Ditto wind power, with a better efficiency but lower power density per unit area. Using solar direcltly, either through photovoltaics or heat plants, is more efficient and probably cheaper.
You cannot base an energy policy like the US's on solar power. It doesn't add up. Do the math.
I've done it. Repeatedly. I've shown you how to walk through the steps, and where your mistakes are. If you continue to rant that "it doesn't add up", that's your privilege, but the numbers disagree with you.
On a side note, those consumption numbers are not projected. Those are Department of Energy figures from 2003. And yes, they include industry. I certainly hope you aren't pushing for a national energy policy that doesn't include at least gas stations.
Let me spell out what I've already spelled out in another reply:
Cost per unit power means that the breakeven cost for solar power is the same - $40 per square metre for 10% efficient cells with a 10% duty cycle.
Homeowners only pay for what homeowners use. Industry pays for what industry uses.
As for gasoline, at 100% efficiency (which cars don't get, but batteries and fuel cells won't either), 1L of gasoline is equivalent to about 14 kWh, or about $0.70 of electricity. This is about the cost of gasoline (actually $0.80/L right now), so the breakeven point for cars is the same as that for houses.
[Your power consumption numbers are about 10x higher than the figures I've heard quoted. This likely includes industrial power use and equivalent figures for things like vehicles. That pushes the price per unit area for breakeven to $4 per square metre,]..On second thought, it's still $40/m^2, because if you're using 10 times as much power, you're paying 10 times as much to the electric company, resulting in the same breakeven point.
If this sounds reasonable to you, I think you have a problem with your brain not being screwed on tight.
Do this per household. You will be enlightened.
The numbers I hear are along the lines of 10 kWh/day per household. Solar panels have about a 10% duty cycle, due to sunlight and weather. Let's take 10% as a ballpark efficiency value (by the time it became economical to roll this out, the technology would have improved, but this is a reasonable minimum). That means you need 10kWh / (0.01 * 24h * about 1 kW/m^2) = about 40 square metres of solar cells, per household.
Around here, in a medium-sized city, a typical lot that's not downtown is 20 m^2. This makes the panel area most definitely comparable to the area being lived on. Multiply this by 400M people, and sure, you'll get a scarily-large number, but remember - you're already building over a comparable area for roads, sidewalks, houses, and so forth, so the scariness is a red herring.
Let's give it an amortized lifetime of 10 years (some of it lasts longer, but it needs to be replaced, time value of money, and so on). You need to pay for 4 square metres per year. An equivalent power bill for that time period is $180 (at 5 cents per kWh; quite cheap, but we get that up here). That means you have about $40/m^2 for your panel costs for it to be _better_ to put in panels than to pay for power off the grid.
Can we expect thin-film cells that are 10% efficient be produced for $40 per square metre within the next couple of decades? You're darned right we can.
In summary, the numbers work out just fine. Re-check them yourself if you like.
[Your power consumption numbers are about 10x higher than the figures I've heard quoted. This likely includes industrial power use and equivalent figures for things like vehicles. That pushes the price per unit area for breakeven to $4 per square metre, though your longer maintenance interval pushes it back to $12 per square metre - assuming that home-owners are the ones footing the bill for industry, which is questionable. Main impact of accepting the higher power fictures is space, which is still far smaller than the farmland already allocated to human use, and can furthermore be in areas we don't currently care about, as opposed to nice, arable land.]
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Making hydrogen results in a significant net loss of energy. After you've made it, transporting it is a huge problem because hydrogen likes to leak right through most "solid" materials. It has a very low energy density at one aatmosphere, so it has to be compressed to insane degrees to get any decent portability out of it. Both in tankers and/or pipelines and in the target vehicle. That also means fueling presents some serious issues.
Making hydrogen at STP is about 60% efficient. I've heard 80% claimed for dedicated plants. By comparison, an internal combustion engine is about 30% efficient. I remind you that supercapacitors and batteries aren't lossless either; internal resistance bites you hard at high currents, and equivalent series resistance of supercapacitors, especially, is quite high.
Hydrogen transport does have leakage, but leakage is only a serious problem if you're storing hydrogen for weeks before using it. Especially as you still wouldn't be able to store the equivalent of a full tank of gas with a hydrogen hybrid, you'll lose negligible amounts of hydrogen to diffusion.
Hydrogen does indeed have a storage density problem (it has to be stored as a compressed gas, which means a heavy cylinder for a relatively small amount of hydrogen). Still much better energy density than batteries or capacitors. My money's still on methane or methanol.
Ethanol has already caused corn prices to tweak all kinds of ways; not a good thing. At least at this point, that's a really bad side effect. Corn is a mega-important food crop. Ethanol is like gasoline, in that it must be delivered via tanker, at a hidden energy and pollution cost. It is carbon neutral, in that the carbon in the plant came from the atmosphere, and goes back to the atmosphere as exhaust.
I'm talking about methanol, not ethanol. If methane or methanol are adopted as fuels, they'll be strictly used as energy storage media, formed by burning waste hydrocarbons (chaff and other inedible plant parts) in a hydrogen atmosphere. Closed-loop systems could be built, too, but they tend to be too heavy and bulky to be worth putting into a car (CO2 is scrubbed and bound as a carbonate, then released by heating and reacted with hydrogen during recharge).
This means taking an efficiency hit vs. using hydrogen, but in return you get fuels that are much easier to handle and that can use existing infrastructure (natural gas pipelines for methane, liquid fuel transport network for methanol). You're still way, way ahead of batteries (the reaction that produces methane is quite efficient, and methanol only slightly trickier).
However, electrical vehicles can be 100% carbon negative, as a hydro plant, nuke plant, wind plant, tidal plant, geothermal plant, solar plant... none of them produce carbon at all.
This is still carbon-neutral, as no carbon goes into or out of any part of your system. With ethanol production or synthesized methane or methanol, you grow extra plants that would otherwise not be grown.
The last thing - but not the least - is that to get the most power to the ground, at the least cost, electric wins hands down. Electric motors today are easily manufactured to be lighter and provide better torque and power curves than any internal combustion engine ever made in even a slightly comparable size class.
Fuel cells use the same motors that a battery-powered car uses. The only difference is the delivery system. You could even use a gas turbine instead of a fuel cell, and still come out ahead (this is done for locomotives and ships all the time). In both cases, you don't have to worry about battery lifetime and disposal issues (the catalysts in fuel cells are much less nasty than the materials in most batteries).
It's the assumption of a "reasonable dielectric" that knocked you off your horse. That's where ultracaps have left the building. They're using altogether unreasonable dielectrics, and there is stuff on lab benches that is approaching battery levels right now.
Batteries have energy storage on the order of 1 MJ/kg. The numbers I quoted for the theoretical limits for capacitors are on the order of 1 MJ/kg. You aren't doing a very good job of disproving my point with your examples.
I assumed you had a magical dielectric with a dielectric constant of 1000 capable of supporting electric fields of 10 MV/m (capacitors are typically rated to half the breakdown voltage, so this means 20 MV/m). The best reported dielectrics I've heard of have constants of around 6000, but no breakdown information was provided (10+ MV/m is very hard to get).
Supercapacitors and ultracapacitors get their performance by using nanoporus materials to vastly improve surface area. Electric double-layer capacitors get their performance by using clever techniques to get a very uniform dielectric layer, which lets them work closer to maximum tolerances. No magic in either of these.
If you're claiming much more than 1 MJ/kg, provide citations, or it's vapour.
This is wrong. Sort of. Lithium-ion batteries can power a car for 200 to 250 miles, but they're expensive.
They do that by cheating. The Tesla, for example, carries half a tonne of batteries, and the car itself is built to be as light as possible (the batteries probably outweigh everything else put together, without passengers in it). Lithium batteries also tend to have lifetime issues; numbers I've heard quoted off-the-cuff for lithium batteries are losing 50% of their capacity within a year or two, and only being good for 100ish charge cycles, though this will vary with the specific battery model. This is tolerable for a cell phone or notebook, as you tend to upgrade these frequently and new batteries cost much less than a new unit, but a car will have serious problems under these conditions.
For a battery-powered car to be really competitive, we'd need a battery technology with at least 5 times the storage density per unit mass, that was good for a decade of daily use before needing replacement. This may or may not be possible; time will tell (unless the engineering difficulties with fuel cells are solved first). On one hand, we aren't anywhere near the theoretical limits to the energy density of batteries, but on the other hand, people have been working on the problem for centuries.
It's very easy to calculate the fundamental limits for any capacitor-based technology (assume a maximum reasonable dielectric constant and breakdown field), and this ends up being vastly lower than chemical energy (about 0.1-1 MJ/tonne, vs. about 4 GJ/tonne for TNT and more for air-breathing engines). We're approaching the limits now. The energy storage medium of the future will be fuel cells (either hydrogen-based with relatively low capacity, or reforming cells and fuel synthesizers that use methane or methanol as a storage medium for much greater storage density at the cost of added complexity).
A "big rip" scenario only occurs with a fairly unrealistic choice for the value of the cosmological constant. The usual assumption at present is that the expansion will accelerate, but won't have the asymptotically-infinite behavior of a Big Rip.
Regarding femtotechnology, I find OA's assumptions about it to be unrealistic (though it makes for good stories). You're also assuming gravity manipulation, which is even more problematic (gravity's behavior is only expected to change from our current model at unification energies, which are utterly impractical to reach). So, I'd look for more boring, lower-tech approaches to waiting out the end of the universe.
ObTypoFix:
Typical "surface" (upper atmosphere) temperatures of brown dwarf after the first billion years are quite cold (as with gas giants), and their luminosity decreases as they age.
We had enough mass to get several gas giants and ice giants out of our disc. As long as it was a Population I star with moderate to high metallicity, there will be more than enough rock available (and more than enough uranium and thorium to drive geothermal processes). Planets the size of Neptune have been found in orbit around them, as have brown dwarfs (though this is arguably closer to a failed binary star companion than a planetary companion).
Temperature-wise, there's a big difference between a red dwarf and a brown dwarf. Typical "surface" (upper atmosphere) temperatures of red dwarf after the first billion years are quite cold (as with gas giants), and their luminosity decreases as they age. A red dwarf has a minimum surface temperature of around 2500 K, and its luminosity never drops below about 1% that of the sun. This gives a strongest-emission wavelength of about 1.1-1.2 microns - near-IR, but still high enough to drive photochemical processes, unlike older brown dwarfs.
In short, no show-stopping problems.
As a gravitationally bound system, the galaxy's size won't change. Long story short, you end up with orbital velocities being slightly different, but orbits remaining stable, even in an expanding universe that's driven by a cosmological constant. This applies to both the stars in the galaxy, and the vast clouds of hydrogen and helium that still make up a good fraction of its mass.
There are far, far more low-mass stars than there are high-mass stars. This means we have no shortage of red dwarf stars in the galaxy. Planets in the habitable zone tend to be tidally locked, and red dwarf stars tend to put out quite a bit of ionizing radiation from solar flares, but a thick atmosphere solves both problems (winds driven by the heat differential spread heat around at the surface, and the thick atmosphere blocks ionizing radiation). The surface ecosystem would have less light to drive it, but you'd still have geothermal sources, you might have an airborne microbial ecosystem higher up to produce energy (much as plankton do for the ocean), and you'd certainly have no lack of mechanical energy from the winds. So, I can definitely believe life could arise on its own in red dwarf systems.
In practice, I'd expect civilizations from the era of larger stars to colonize red dwarf systems and either build constellations of habitats, or move/tailor a planet to suit their long-term needs. None of this requires magic; just time, and good automation.
Actually, red dwarf stars last far longer than our sun. On the lower end of the mass scale, they end up having a convective zone deep enough to cycle all of their hydrogen into the core (unlike the sun, which will only ever use about 10% of its hydrogen). As they have a much lower rate of fusion to begin with, this results in lifetimes of trillions of years.
Red dwarf stars are also a lot more _common_ than our sun (there's a power-law distribution for number of stars vs. mass of stars).
So, no lack of energy for quite a while, even if you assume star formation stops.
As for the argument about whether or not evidence would be seen for the Big Bang, it'd be there, but a lot harder to observe. Distant quasars/AGNs would be much harder to see (though not impossible), and there would still be enough primordial hydrogen, deuterium, and helium around for its presence to be a mystery that SS wouldn't be able to explain. Proposals that the galaxy had existed for an _infinite_ length of time would have problems with the fact that hydrogen does get burned and stars do have finite lifetimes, even if the galaxy's active lifetime is much longer than the trillion-year lifetime of a dim red dwarf.
What I'd expect them to conclude is that they were in a universe that looks like anti-deSitter spacetime, containing an isolated galaxy or galaxy cluster inside their observation horizon, and that had existed in the same state for an extremely long but finite time. What's outside the horizon would be unknown. Where the galaxy and primordial elements came from would be unknown until they did a lot of very careful observation and analysis.
No, it's not. The tensile strength determines how often the width must double before reaching GEO - it's an exponential scaling.
While it's an exponential scaling, 60 GPa is enough to do it. The characteristic length for a material needed for a non-tapered space elevator is 4000-and-change km. The density of nanotubes is 2-and-change. For a length of 5000 km and a density of 3, you have a tension of 150 GPa. This is 2.5 times the tensile strength measured. The tapering factor is e^2.5, or a factor of about 12. Not a problem.
The real problem is that 1) we haven't yet been able to make pure enough single-walled carbon nanotubes to get close to the 110 GPa figure (60 GPa is the most I've heard of measured), and it'll be very hard to do so on a mass-manufacture scale, and 2) composites will have lower tensile strength than the fibers they're made of (though it may be close enough).
If a tapering factor of 100 is acceptable, the minimum tensile strength of the elevator material is about 33 GPa (150 GPa / ln(100)).
Your "proof that gasoline fumes ignite" test is slated for this month, BTW.
Not that it invalidates your point Rei, but wouldn't that be more of a geometric, rather than exponetial, rate of change?
ObPedantry: these are the same (the difference is that one is discrete, the other is continuous).
It's not a very hard problem. Driving on controlled-access roads with good paint is actually pretty easy.
Meanwhile, in the real world, you're driving on poorly-maintained roads with bad signage, sub-optimal weather conditions, and lots and lots of other drivers doing unpredictable and quite often illegal things.
Driving on a well-marked road under good conditions is a toy problem by comparison. IAACompEng, and a regular driver.
I prefer the 14-SOIC version of the accelerometer, but it doesn't seem to be in stock at the moment. Have fun :).
What I didn't put in the project web pages before it got /.'d: I'm making a case with integrated battery that mounts on the back of my R1150GS motorcycle. If I get the size trimmed a bit it should fit without taking up any of the bike's luggage space. Now to figure out how to make a lean-angle sensor to record that along with the speed/position data... :)
You could use the dual-axis accelerometer I used for the robot project to sense tilt changes. Have it integrate changes to guess at current tilt, and recalibrate itself by assuming that anything maintained for 30 seconds or more is a tilt of zero. You could combine it with one of the pseudo-gyro sensors made by the same company (Analog Devices), but be warned that they're ball-grid array packages (and it's probably overkill for your purposes).
If you want to be able to 'integrate per-vehicle information' and 'get realtime data on the best route to work', you're going to have to be able to track me.
And that's just not happening.
If one car in a hundred had a transponder, you'd get a good idea of how traffic was flowing on the major routes in and around a city. One in a thousand might even be enough for this.
You might actually be able to do this just by looking for cell phone emissions from tracking towers. I'm sure at least that many people use their cell phones while commuting. This gives you better coverage than traffic cameras/helicopters.
Why is it... That we have invented a million different ways to distract ourselves while blasting down the highway, without developing self-driving cars?
Building self-driving cars is a Very Hard Problem. It's being worked on, and great progress has been made, but it's not going to be ready for prime time yet.
The problem is that it has to work safely even under strange or pathological circumstances. Guaranteeing this is much, much harder than getting a car to drive on an empty road and stop at well-marked intersections.
On the plus side, as soon as a car autopilot drives better than the average driver, the insurance rate perk for getting one will make the switchover very rapid.
As for distraction, you'll note from the article that the access point was never used by the person driving the vehicle (and that it's in fact illegal to do so in California). It's a passenger perk (and great for when you get _out_ of the car, with the range it has).
According to the article, the embedded platform used was actually a Soekris net4521. There's no such board as the net2421.
Given that the person who wrote the submission is the person who wrote the project page, I think we can file this in the "accidental typo" category".
Get the cost down, and this would be an interesting way to integrate per-vehicle information (speed and congestion [via vehicle proximities/GPS]) with map information to get realtime data on the best route to work.
:).
I'm not sure how he'd get the cost down much further than it is already. He's using off the shelf parts at commodity prices. Building in quantity-100 might shave off 30% or so, but even fabbing your own integrated board with all widgets on it in quantity-1000 would only get to about half the current price.
Custom IC would get it down further, but that would take quantity-silly
Can we expect that fast neutron burner reactors can be produced using a smaller amount of area and for a cheaper cost than photovoltaics? You're darned right we can.
I respectfully disagree with the "cheaper cost" part. Here in Ontario, we generate a lot of our power using nuclear plants, and while they're cleaner than coal, they're expensive to build and a maintenance nightmare. They're a reasonably mature technology, so I don't expect the cost to change any time soon. Thin-film cell technology is still very immature, so I can definitely believe it will drop in price.
That said, I think you need to stop drinking the Kool-Aid. Sure it's less land than what is used for farming. Guess what? Farming produces food. If some of those cell farms reduces the area available for farming, we produce less food.
*Sigh*.
a) The land you'd use for solar power generation isn't farmland - it's roof area in industrial parks and urban sprawl areas that's currently going to waste, and any of the large amount of area that's _not_ used for farming. Farming requires arable land. Solar panels don't.
b) The amount of land required is far _less_ than that required for farmland. That is the point of the comparison. You keep pulling out your "thousands of square miles" figure - you do realize that about 1.8 _million_ square miles of land is allocated to farming in the contiental US, right?
As spelled out very clearly in my original post - the amount of land area needed for solar power is comparable to that used for habitation, and very small compared to the land area devoted to other purposes.
But I digress, go back to my previous post and find the math error. If my numbers are 10x what others have found, then my error should be easy to find.
Your error was saying, "Oh my goodness, the cost multiplied by 300+ million people is huge!", without realizing that _any_ cost multiplied by that many people is huge. You do the same thing with land area. You just don't seem to handle "per capita" or "fraction of total money/area used" concepts very well.
You were also quoting current thick-cell prices for solar cells, as opposed to calculating what the cost crossover point is (i.e., the price that would be _needed_ for solar to be economical).
I actually believe that my numbers were too small since I didn't factor in the cost of batteries
At 10 kWh/day, a week's worth of power storage requires 35 off-the-shelf deep-cycle lead-acid batteries. Let's amortize over a 5-year lifetime, instead of a 10-year, to reflect shorter life cycle. That means 7 batteries replaced per year, or about $1400, for a household's power. This is manageable, though more expensive than buying power off the grid.
If solar power becomes more widespread, or even if fuel cells for things like cell phones and laptops continue to push the relevant technologies, expect fuel cell systems to drop this cost quite a bit (batteries are horrible for storage of large amounts of power).
Oh yeah! And how about reducing our dependence on foreign oil?
You can do that right now by building more nuclear plants. We're doing that up here. The US doesn't seem to like that solution, though.
Solar is an attractive long-term solution because the technologies are intrinsically simple and cheap, have a very high energy density per unit area used, and lend themselves to scalable implementations, unlike most other forms of power generation.
The biodiesel you mention is just recycled solar with a far, far worse system efficiency. Ditto wind power, with a better efficiency but lower power density per unit area. Using solar direcltly, either through photovoltaics or heat plants, is more efficient and probably cheaper.
You cannot base an energy policy like the US's on solar power. It doesn't add up. Do the math.
I've done it. Repeatedly. I've shown you how to walk through the steps, and where your mistakes are. If you continue to rant that "it doesn't add up", that's your privilege, but the numbers disagree with you.
Have a nice day.
On a side note, those consumption numbers are not projected. Those are Department of Energy figures from 2003. And yes, they include industry. I certainly hope you aren't pushing for a national energy policy that doesn't include at least gas stations.
Let me spell out what I've already spelled out in another reply:
Cost per unit power means that the breakeven cost for solar power is the same - $40 per square metre for 10% efficient cells with a 10% duty cycle.
Homeowners only pay for what homeowners use. Industry pays for what industry uses.
As for gasoline, at 100% efficiency (which cars don't get, but batteries and fuel cells won't either), 1L of gasoline is equivalent to about 14 kWh, or about $0.70 of electricity. This is about the cost of gasoline (actually $0.80/L right now), so the breakeven point for cars is the same as that for houses.
"Around here, in a medium-sized city, a typical lot that's not downtown is 20 m^2."
That's a square 15 feet per side, or a small living room. Methinks you don't know how to convert imperial to metric.
You realize this actually makes my case _better_, right?
I dropped a zero. The numbers I was trying to convert were 30'x60' (about 10mx20m).
Several thousand square miles of the stuff.
And hundreds of thousands of people per square mile of panels to pay for it.
You just don't get this "per capita" thing, do you?
[Your power consumption numbers are about 10x higher than the figures I've heard quoted. This likely includes industrial power use and equivalent figures for things like vehicles. That pushes the price per unit area for breakeven to $4 per square metre,] ..On second thought, it's still $40/m^2, because if you're using 10 times as much power, you're paying 10 times as much to the electric company, resulting in the same breakeven point.
If this sounds reasonable to you, I think you have a problem with your brain not being screwed on tight.
Do this per household. You will be enlightened.
The numbers I hear are along the lines of 10 kWh/day per household. Solar panels have about a 10% duty cycle, due to sunlight and weather. Let's take 10% as a ballpark efficiency value (by the time it became economical to roll this out, the technology would have improved, but this is a reasonable minimum). That means you need 10kWh / (0.01 * 24h * about 1 kW/m^2) = about 40 square metres of solar cells, per household.
Around here, in a medium-sized city, a typical lot that's not downtown is 20 m^2. This makes the panel area most definitely comparable to the area being lived on. Multiply this by 400M people, and sure, you'll get a scarily-large number, but remember - you're already building over a comparable area for roads, sidewalks, houses, and so forth, so the scariness is a red herring.
Let's give it an amortized lifetime of 10 years (some of it lasts longer, but it needs to be replaced, time value of money, and so on). You need to pay for 4 square metres per year. An equivalent power bill for that time period is $180 (at 5 cents per kWh; quite cheap, but we get that up here). That means you have about $40/m^2 for your panel costs for it to be _better_ to put in panels than to pay for power off the grid.
Can we expect thin-film cells that are 10% efficient be produced for $40 per square metre within the next couple of decades? You're darned right we can.
In summary, the numbers work out just fine. Re-check them yourself if you like.
[Your power consumption numbers are about 10x higher than the figures I've heard quoted. This likely includes industrial power use and equivalent figures for things like vehicles. That pushes the price per unit area for breakeven to $4 per square metre, though your longer maintenance interval pushes it back to $12 per square metre - assuming that home-owners are the ones footing the bill for industry, which is questionable. Main impact of accepting the higher power fictures is space, which is still far smaller than the farmland already allocated to human use, and can furthermore be in areas we don't currently care about, as opposed to nice, arable land.]