10ebbor10
DON'T PANIC
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Reading comprehension.
I bolded the relevant part.
The energy doesn't come from humans, but from cheating gravity.
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Last edited:
Reading comprehension.
I bolded the relevant part.
The energy doesn't come from humans, but from cheating gravity.
.
- Location
- At your local SPCA
Except for baseball, where every hit that isn't a groundball literally becomes a moonshot
Um, to get out of the tight corner that simply lowering the gravity field would cause (Earth expands and destroys the crust, atmosphere pressure instantly falls to 1/6 and we all suffocate, etc) and the biosphere crash that poor dumb animals would suffer from bouncing into the air if it were restricted to animals only, the OP made it so any object a human moves enjoys a temporary respite from 5/6 of the gravity field.Ignore this section, I thought he was responding to the original prompt
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Well. There's a lot to unpack here.
First off, why is the first thing your mind goes to having a human turn the crank? We're literally centuries past that, you could use a horse, or coal, or oil, or a power orb...
Secondly, that's not how energy works. You get less than the amount of energy you put in back out because nothing is perfectly efficient. That's why we use highly energy dense fuel that has already formed.
It's easier to lift a 50 ton weight in moon gravity (but by no means practical, 50 tons here is roughly equivalent to 5 tons on the moon), but a 50 ton weight also nets you less energy as it falls down because gravity is weaker. It's exactly the same as doing that process on Earth, and that's not a good way to get energy on Earth. You are losing energy, because in order to have a net 0 energy you'd need a perfectly motor, no air resistance, etc.
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The energy a human an put in isn't very much relative to the inefficiency, and anyway you may as well just have them turn a crank, it would be more efficient. A single liter of gasoline contains as much useable energy as days of human labor, there's a reason our civilization is almost literally built on it. The "infinite energy" you described is worse that our current system!
This is like invisible angels are following around every human and read our minds to discern when we wish to move an object of any kind; then they rush in to lift 5/6 its weight as long as we are thinking of lifting it or holding it up, or shoving across the ground or sea. So if some people get into a rowboat, and idly rest their hands on the oars, nothing happens, but since attempting to row the boat means we are trying to move the boat and everything in it, the angels must come in to lift 5/6 that weight, and so the boat bobs up until only 1/6 the volume it occupied before is displaced. If the rowers stop rowing it plops back down. Note that the people themselves always weigh 1/6 their proper Earth weight.
What this modification means in terms of the thought of experiment of a person lifting a sack of flour up and setting it down on some kind of power generating vertical treadmill is that the angels do 5/6 the work needed to lift the sack up to whatever height, whereas the sack, weighing whatever it does weigh and unassisted by any angels on the way down, can provide the full potential energy added to it by combined human-angel effort. The post is a bit clever too in pointing out that the human does not have to do all the work left undone by angels lifting it--as long as a human is doing some token share of the total work, the angels must take up the whole slack of 5/6 the weight. Since angels are not provided for in normal physics, we would see this as free energy coming from nowhere, added to Earth.
Indeed it should be possible to hire some people to turn little cranks that provide a small fraction of the power needed to lift up weights and then the power harvested by capturing their potential energy on the way down would be free energy, for the most part. It is magic; people have to be involved but I have no idea at what lower limit of fractional power input from humans the angels or still less some mindless made up ASB field would throw up its hands and slack off!
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Another comment mentioned the atmosphere raining out all the moisture (back when it was assumed the lower field applied uniformly to all objects alike including air molecules). No, that is the opposite of what happens I think. Note the pressure will take some time to die--one way of looking at the pressure on Earth's surface is that it is the weight of all the air above. Another way of looking at it is that it is the product of molar density times the average speed of the air molecules squared (squared because each molecule impact provides a certain impulse that depends on the speed times the fixed molecule mass, and because the frequency of such impacts at a given density also rises with the speed linearly). The latter does not change--immediately! For the pressure to drop, the air must expand. Now with a sudden reduction of it weight, it can expand; the air loses density and pressure approximately exponentially with altitude, but the characteristic scale height of that reduction depends among other things on the gravity field, inversely. Lower the gravity and the air, with the same average energy per a given mass fraction, will climb 6 times higher. Which is to say, the density falls at 1/6 the rate it used to, but the baseline density at sea level must be reduced in proportion.
The moment the gravity changes then, Earth's air is not in equilibrium, any more than the water in a cup you suddenly turn upside down at a height can be expected to stay there. The result will be a surge of air upward, and I think it would bounce too--momentum will take the surge past the new equilibrium point and cause even lower pressure on Earth's surface, then fall down again and surge up above the average and oscillate around like that for a while.
Now I think the suggestion water would rain out is half right--the suddenly expanding, climbing air column would be doing work--in a reduced gravity field, yes, but still the center of mass is climbing upward in 1/6 G. The energy for this must come from somewhere, and the air will supply it by cooling, just as it always does when expanding against a force. This cooling will lower the temperature and thus lower the vapor pressure of any water in the air, and probably I suppose some of it will thus precipitate out since vapor pressure falls very fast with modest changes in temperature.
But on the other hand--I objected and said it was the opposite because with the reduction in density by a factor of 6, the absolute vapor pressure of all water vapor at a fixed temperature will also be reduced by 6! The chilling of the atmosphere we would expect from the sudden lowering of gravity is temporary too. Eventually the surface will come back to thermal equilibrium, and if we guess that is the same temperature as before, then the water vapor pressure on open water surfaces is the same, whereas if the absolute pressure of all species of gas are all reduced to 1/6, any gases in equilibrium with condensed sources on the surface, mainly water, must evaporate until the absolute vapor pressure matches--this really means that water molecules are escaping liquid water masses all the time, but when the pressures match, other water molecules are colliding with the open water and being absorbed into it at the same rate, so the net mass of water does not change. In this situation, temporarily, the water surfaces will be giving up water at the same rate, but only getting back 1/6 as many initially, so the ratio of water molecules to air in the lower atmosphere must rise by a factor of 6. Then that layer will lose water to the upper layers, for the water molecule is light versus the typical nitrogen air molecule, and has a higher scale height. Actually in dense gases the molecules stay mixed pretty well and the fractioning of higher ratios of light ones is something that happens on scales larger than air scale height, and the absolute density is going to be low. So only a fraction of Earth's surface water will be absorbed into the air, assuming overall equilibrium when it all settles down again is at similar temperatures for a given fraction of scale height.
Now the stretched atmosphere might react with various factors governing Earth's surface heat to change that temperature perhaps. The major factor that would be most significantly different would be the sextupled absolute water mass. But wait...if the water is relatively six times the concentration and the absolute density of the baseline dry air is 1/6, that means the mass of water suspended in the air is in fact equal to the original mass! Basically the water that was in the air before stays there, and then an equivalent mass above that is added, so the total amount of water merely doubles. But that could have major effects on surface temperature because water is a powerful greenhouse gas!
So--in the short run, we have two waves of cooling, first as the air rapidly expands to climb toward 6 times its original scale height. If the Earth were dry, it would then settle toward equilibrium at the old temperature, so the air will gradually reach that sextupled height.
Then as the surface pressure rapidly drops initially, another cause of cooling is the evaporation of water which will absorb a lot of heat. But if the Earth cools for these temporary reasons, it will radiate less heat into space, whereas in the short run I think all the clouds will evaporate or sublimate. Whether there is any precipitation initially is a boat race between the falling temperature lowering the vapor pressure, and the falling absolute pressure--if the latter stays below the former, the clouds vanish and we have a temporary arid period. Eventually a new equilibrium is approached as temperatures rise back toward normal at a given index of scale height--and possibly, due to the water molecules near sea level being restored to their old absolute levels, while those formerly in the air remain somewhere in it, higher up, we have doubled greenhouse retention of heat and thus higher surface temperature than before. This in turn must raise the vapor density further near the surface!
I don't know if this means runaway greenhouse or if it stabilizes at some moderate temperature or what. Anyway I think we are very safe from snowball Earth!
But we are all dead of asphixiation of course, and as mentioned the Earth will shake and the surface expand, cracking it open.
Well--the magma below the crust, and the core materials, are indeed compressed, but they are in a condensed state. Liquids and solids do compress under pressure, but only a small fraction of reduced volume corresponds to a huge surge in pressure. Therefore if the pressure is reduced to a sixth, it will indeed expand, but only by a small fraction before the reduced intermolecular pressure falls to 1/6. To be sure a small volume change in percentage is huge in absolute volume, and corresponds to a substantial addition to Earth's surface area and the average distance between objects on the surface. I don't think opening of huge fissures exposing raw magma will be all that common! But the Earth will shake, massively, expansion will happen fast, and major geological shakeups will happen. Volcanoes will blow, all the fault lines let loose at once, mountains will tend to crumple down--though in the long run, once the Earth's upper crust reaches normal equilibrium again, over millions of years ongoing tectonic forces will be working against much lowered weight, and the outcome will be that mountains and plateaus and so forth will be more compressed and rise to greater heights, while the angle of repose of slopes of hills, mountain faces, sand dunes etc will be much steeper. But that will manifest only over millions of years, at least the part about mountains and so forth. Sand dunes will start to become gradually steeper immediately; normally they are kept at a certain average angle of repose by the probability of sand avalanches matching the rate of pile up, but the former will be much reduced and so for a long time dunes will not have avalanches at the same rate, they will become rare and minor for a time until the new angle of repose is approached. Of course with the air at 1/6 density, the rate of deposit might drop.
The same thermal energy goes into driving the same masses of air, albeit sprawled out over 6 times the volume, so I expect wind speeds to settle at the same level, assuming a similar thermal profile for Earth anyway. But the force of the winds on objects on the surface will be 1/6 as great.
Airplanes and helicopters can fly at the same speeds, assuming they have a power source! We'd need just 1/6 the power. But piston engines are going to have problems. At best they can put out just 1/6 the power. I think turbine engines will be somewhat less disadvantaged. But all will have reduced power and require the fuel input to be reined back to 1/6 their old maximum flow rates.
With zero warning, all humans die, or all but a handful perhaps, who probably have no opportunity to engineer solutions to enable long term survival. Examples of people who might survive would include the crews of nuclear powered submarines, which can be sealed against the pressure drop. It is hard to think of many other categories of human beings who can hope to be near or already in some pressurized vessel, and with equipment enabling people to go outside and mess around with the hardware to extend these habitations, get power for their compressors and so forth.
The ASBs might be gentler. They could give us a warning, or perhaps better yet, ramp down the gravity gradually. Of course we still have the earthquake issue to contend with. Perhaps the reduced gravity only begins a few dozen meters below the surface and most of the mass of Earth's condensed material remains in normal gravity?
Given a long period to prepare, I suspect a large fraction of humanity can be kept alive with improvised pressure chambers and some sort of pressure suit enabling work crews to operate outside.
The ecosystems perish completely of course. I expect if humanity got caught off guard or all the survivors were killed by a plague or some such, over tens or hundreds of millions of years, various surviving organisms would adapt and recolonize and recreate complex ecologies again. Life living in thermal vents for instance might be OK; it depends on how many gases they have in their bodies that might bubble out with a sudden pressure drop. If the pressure drop is drawn out over a year or even a month, I suppose excess gas just slowly seeps out and most of them survive. Some microbes can probably survive with the air pressure down to 1/6. These will find all the niches wide open, as will any complex multicellular forms from deep in the sea or otherwise able to survive the pressure drop. Eventually the land will teem with plants that soar up high without needing wood to bear their weight, and animals that hop great distances easily--flight will be somewhat challenging. Less so than OTL, because the power demands are 1/6 as great, but the ratios of wing area to body mass will be comparable.
If humans can survive in sealed quarters, growing crops in greenhouses, and solve the problems of maintaining and starting turbine engines in low pressure, not to mention the issues high outside temperatures might pose, our aircraft are adaptable to function; power needs for road vehicles would be dramatically less, and space travel would be much easier. Orbital speed would be 40 percent what it is now, about 3000 meters per second, bearing in mind the lowest orbits must be much higher. Note that all the satellites in orbit around Earth including the Moon would be well above escape velocity and so would have drifted off into solar orbit, unless the ASB kindly slows them down for us. Periods at a given distance would be about 2 and a half times as long, so the Lunar month would become some 70-80 days if the ASB keeps the Moon in its orbit for us. Geosynchronous orbit on the other hand would be much lower.