I see your point. There are two reasons for going to the moon though:
1. The materials problems with the SE might just turn out to be much harder than we think, or some other problem might arise. If it's 50 yars off it's a different story.
2. For this moon programme they are developing a 125 ton to LEO launcher -- just what we need to launch a big heavy spool of ribbon. They are also developing a CEV that could be used to send people up to GEO if they are needed to deploy the ribbon. So by coincidence or otherwise, it could help a SE programme.
And it's getting them. Growing bigger better SWNT would pay off hugely for anyone who figures out how to do it, even without the elevator project. Strong light materials have any number of uses. All the world's chemicals and polymer companies know this and I'm sure they're spending whatever they think might help. It's not obvious that spending more money will help here.
Once you think 100 GPa ribbon is only a decade or so off, then there is a case for doing what some of the elevator companies are doing, and making sure that the climber and similar technologies are ready in time, to save a 5-10 year delay once the ribbon exists, but there is no point in throwing space money at the basic ribbon problem. If it can be solved in 10 years, it will be, by materials companies.
I think this really isn't true. They have occasional, rare, micron-long needles at the very bottom edge of the strength range needed. So, at a minimum, they need to
1) find even stronger individual needles -- this may not even be possible, if the theoretical strength calculations are wrong 2) grow them thousands or millions of times longer than seen so far 3) grow them in bulk quantities and reasonable yields 4) form them, with a small amount of binder into fibres and thus into ribbons without significant reduction in the strength
None of these is easy, any of them might turn out impossible
I don't think the tidal forces are that bad. Let's consider a 2million kilometer diameter star 0.1 light years from a 2.2 million solar mass black hole.
distance from centre of black holes (I know...) to inner edge of star: 0.999 * 10^15 meters, to outer 1.001*10^15 meters.
Acceleration due to black hole gravity at inner edge: 0.000292570237 ms^-2 Accleration due to black hole gravity at outer edge: 0.000291402294 ms^-2
for a difference of 0.0000012 ms^-2, or about 0.12 millions of a G, easily overcome by the stars gravity.
Indeed, I saw a detailed plan for a man-capable orbital electric launcher once. About 250km long, drawing 15GW of power for about a minute, with a 1 ton payload to (very) low Earth orbit. It looked like a fun project, but there were some significant issues, among them noise and vulnerability to terrorism. Suitable sites are also a bit limited, you need 250km of mostly level ground, close to the equator, with a mountain at the East end and access to 15GW of power.
A railgun, per se, by the way, won't work. Maintaining a sliding contact with the rails at orbital velocity is a bit too hard. The plan I saw was a coilgun, with a superconducting coil on the payload carrier and conventional ones around the vacuum tube. Launch was 15G (in various directions) for a minute, which is probably OK for a fit astronaut who doesn't need to do anything.
Current elevator designs get away with a very low anchor mass by putting it a long way out.
This calculation has been worked out. One very detailed study needed about three shuttle-loads of stuff shipped up to start the bootstrap. This unrolls to a ribbon about an inch wide, very thin, and 100 000 km long. Now you start sending climbers up it, towing more cable which they bond to the side of the ribbon as they go. The climbers stop at the end and add to the counterweight. After a few months, the ribbon is a foot or so wide and you can start moving cargo up it in modest amounts. Your first loads of cargo, are, of course, more ribbon for more elevators.
There are many engineering problems here, most pressingly, how to make a bulk material with the strength/mass ratio so far only observed in microscopic samples.
A fuel capable of launching payload in rockets as cheaply as an elevator could launch it is almost inconceivable in the next 50 years. There are simple physics arguments that rule out any chemical propellant, there just aren't chemicals with that much energy per kilogram locked up in them. Even nuclear-thermal rockets that use any kind of material nozzle or containment system for the nuclear reaction simply can't be efficient enough -- the maximum temperature of the exhaust (limited by the nozzle) will only force hydrogen out so fast. A magnetically confined nuclear rocket could work, but the closest thing we have to a magnetically confined nuclear reactor (JET) weighs hundreds of tons (at least) and still produced less power than it takes to run the magnets.
In this case, the elevator seems like the right solution. All forms of rocket suffer from having to accelerate the engine (and some of the fuel) to orbital velocities. In an elevator setup the engine is a power station (or grid connection) on the ground and never goes anywhere.
Panspermia would require life to have arrived in a rather narrow window of time, between the last time at which the Earth's oceans were boiled by an impact, and the earliest time at which life was known to have existed. The simulation suggests that this would not have been a time at which many comets were hitting Earth, which, while not conclusive, is not supporting.
Well then... explain to me why calculating Newton's own law of gravitational force gives you mathmatical evidence that there is a strong gravitational pull toward the sun and his law of centripetal force would indicate that this gravitational pull exceeds what is neccessary to maintain an orbit around the sun.
Numbers? In pure Newtonian two-body physics, all closed orbits are stable, essentially because angular momentum is conserved.
In GR all such orbits lose energy and angular momentum by radiating gravity waves. This, however is extremely slow, and would have no measurable effect on the Earth-Sun system for many billions of years.
Perturbations from the other planets (mostly Jupiter) have an effect, which cannot, in general, by exactly described or predicted, however numerical calculations suggest that, while the eccentricity and incilinarion of Earth's orbit, and things like the orientation of the long axis of the ellipse, change roughly cyclically over long periods of time, I have never heard of a suggestion that the Earth is systematically moving closer to the Sun due to these effects.
why would man and animals need eyes if they couldn't see before, sight is a very high-level ability, a creature without sight doesn't realise he needs it? Also in 'natural selection' humans would have been eaten by everything without sight no matter how developed the brain was.
Darwin himself deals with this in "The Origin of Species". There are many steps from the basic light/dark sensing that some bacteria have to the fully developed vertebrate eye. Every step gives an evolutionary advantage in some circumstances. Interestingly, it seems that these steps have been followed twice independently, once leading to the vertebrate eye, and once, independently to the eyes of the squid, which are almost identical, but actually a bit better. It seems that our version of the path ended up more or less by accident with the nerve connection on the front of the retina, blocking some light and needing hole (the blind spot) to get the nerves back to the brain. The squids got this one right and have the nerve connection at the back.
If we came from the ocean then why can't we breath underwater and if we are the most 'evolved' of creatures then why are the birds flying around the earth like it's going out of fashion? We're wingless, can't go underwater without breathing equipment, the ascent of man? Yeah right.
We are not "more evolved" than any other contemporary species. All of us are the products of about 4 billion years of evolution from some little understood primordial cell. At a number of points along the way, splits have occurred. Those individuals in a species that happened to be best adapted for the purpose took to pursuing one ecological "niche", others took another "niche". Perhaps they were separated by an ocean or a desert. Pressures of one niche drove gradual evolution in a direction incompatible with the other niche until you had two different species. For instance, early proto-amphibians specializing in spending time on land and eating insects or land plants had evolutionary pressure towards smaller gills, which used less energy to grow and lost less moisture to the air. End result, theit surviving descendants couldn't breathe underwater. Meanwhile their cousins who had stayed in the water were becoming better and better fish, with more and more sophisticated gills.
How come nobody talks about entropy no more?
Sorry? Any statistical physics textbook talks about entropy, which is where it belongs. The entropy of the Universe as a whole is increasing, because all the high grade energy locked up in unfused hydrogen in stars is slowly turning into low-grade heat energy. Temporary local increases in apparent complexity (like life, humanity, culture, etc.) are just tiny "curlicues" on this big picture from a statistical physics point of view.
Oh if wewe're the offspring of monkeys then why arn't monkeys turning into humans?
We're not their offspring, we're their cousins. Some of our common ancestors found themselves in a situation where hairlessness, swimming, two-legged running and living in larger groups favoured survival. We are the descendants of that group. Others found themselves in an environment where moving around in trees, living in smaller groups and so on was best. Their descendants are chimps, gorillas and so on,
The Earth orbits the Sun. Ironically enough it was Newton who worked out how this all happens. The Earth constantly accelerates towards the Sun, but since it's moving rather quickly "sideways" around the Sun, the effect of the accelaration is to curve it's path just enough that, one year later it is back exactly where it started, having gone all the way round the Sun.
I have a University degree including some mathematical physics (from Newton's alma mater, as it happens. his college rooms where about 50 yards (and 300+ years) from mine). I did pay attention and I did learn some stuff.
The Earth is not, on average getting closer to the Sun. The mean distance from Earth to the Sun has been essentially unchanged for 4 billion years or more. The sun is, on a timescale of BILLIONS of years, getting hotter, but we are dealing with much faster changes.
Melting of floating icecaps does, indeed, not raise sea level (although it may have other troubling consequences). Melting of the Greenland and Antarctic icecaps, on the other hand does raise sea level.
Finally, we could be talking about sea level rises of quite a few feet this century. Servers do not run well underwater.
Of course in this dense early universe, some other kind of signal may have travelled faster than light (although not faster than c) and would enable us to see a little further. Neutrino's maybe, or the hypothetical "axions" that might make up some of the dark matter in the universe or....
You can see supernovae if they are close enough. There are two notions of brightness: how much light (or other energy) we get from a thing, and how much it actually emits. The relationship between these is controlled by distance.
In the first sense, the brightest object is the sun unless you happen to be standing very very close to a search light or magnesium flare.
In the second sense, a galaxy is typically brighter than a supernova, but if it's close then it's diffuse, so it doesn't look so bright. Actually if you include its neutrino output, a supernova is, for a few seconds very much brighter indeed than it is for the next year or so, or indeed than pretty much anything we know. A quasar is brighter than a typical galaxy, but there are no nearby ones. A GRB might be (briefly) even brighter than that, or it might not be so bright, but beam it's output (in which case there are more of them than we see).
A GRB doesn't just emit gamma rays. It emits a short brief flash of gamma rays, followed by an "afterglow" of X-rays, UV, ordinary light and probably other things over an extended period. Alpha and beta are probably emitted too, but will be diverted by magnetic fields and slowed down and absorbed by the intergalactic medium.
The same computer that had the line printer (an ICL 1902T, for those who care), also had a loudspeaker wired into a couple of bus lines in the CPU. This was actually incredibly useful. After a while you got used to the sounds of different phases of the OS boot, the compilers and so on. If something got stuck, which it did quote often, you pretty much knew where it had got to by the last familiar noise it had made. Of course people wrote programmes to play tunes.
There are other dangers. The additional box that paginates the printout is (or at least was once) known as the Integral Burster Trimmer Stacker (IBTS). When correctly adjusted it was a wonderful thing: cutting the continuous paper into sheets, removing the perforations, stacking the pages the same way up, separating distinct print jobs, etc. When NOT correctly aligned, it earned it's other name: the Integral Burster Trimmer Shredder. It is quite amazing how fast one of these could fill your machine room with shredded paper!
I suspect you're describing a standard line printer. We had one of these at my secondary school. It's not quite as you put it. There is a solid drum, with 132 copies of every character. On the other side of the paper is an array of 132 flat hammers. Somewhere there is a ribbon as wide as the paper with ink on it. Now to print an A in column 5 you wait until the A's (132 of them) are next to the paper and the fire the hammer in column five (and any other column that needs an A). A moment later you fire all the hammers for Bs and so on. Once every drum rotation you move the paper on. It was very noisy and also very prone to catch fire.
Surprisingly, I think there is quite a lot. Most of the minerals that make up Earth's crust contain water, and water, under pressure is drawn down into the crust at spreading faults. Also the carbonate minerals would not exist without long-lasting oceans where CO2 and silicate rocks can slowly combine. These hydrated and carbonate minerals act, I think as a lubricant to plate movements. I am not a geologist, but I'm sure I read this somewhere once. I can't quickly find confirmation.
OK: first there's spin-off from the design, building and operating of the probe itself -- materials, sensors, communication technology, robotics, etc. Missions like these present the designers and builders with difficult problems, and relatively much time and money to solve them. Some of the solutions turn out to have other uses.
Next, there are quite a lot of comets in the Solar system. From time to time they come close to Earth, or even hit it. They have hit other bodies, like the moon and Mars and Mercury, and may have had a lasting influence (for instance leaving ice in dark crater bottoms). Finally, they might be source of raw materials for future expansion into the solar system. Knowing more about comets helps us understand what we might be able to do if one were going to hit us; what we might expect to find on the Moon, Mars and Mercury, and what, if anything we might be able to use comets for in the future.
Next, comets seem to be mostly made of common elements: carbon, oxygen, hydrogen, nitrogen. Under the unique conditions applying on comets, they may have formed interesting new compounds with interesting, or useful, new properties. If so, we can, perhaps sythesise those compounds on Earth from air, water, coal and so on (basically cheap ingredients) for whatever purposes.
Finally, we just want to know. Long ago, we think much of the solar system, including you, me and this planet, was basically in the form of a bunch of comet-like bodies, which then collided, stuck together and grew into planets etc. Understanding comets gives us some clues as to how that may have happened.
So string theory suggests 11 dimensions 7 of which are really tiny. Think of a hosepipe: seen from a distance it looks 1-dimensional, and if you imagine creatures living in the rubber of the hose which were (say) a mile long and wrapped all around the pipe for that mile, they would see their world as 1-dimensional. If they somehow managed to examine themsselves in microscopic detail, though, they would find this second dimension just an inch or so around, which was vital to the way their internal organs worked. The suggestion is that the universe is like this. We see 4 dimensions, but if we want to understand really small things, we have to look at the other 7 dimensions as well. Many different kinds of particle are really the same kind of string, wrapped around the "small" dimensions in different ways, or vibrating in different ways.
So, now, more recently, people have proposed that the vast difference in strengths between electroweak forces and gravity can be explained by some of these small dimensions being rather less small that we thought. How small depends on how many of them there are. If it was one or two, they would have to be millimetres in size and we would have detected them by now. If it was three, they would be about a nanometer and we wouldn't have. Experimentalists are working on this.
Meanwhile, astronomers have noticed some anomalies between the prevailing theories of galaxy formation, and the observations. These theories say, very roughly that galaxies form as clumps of dark matter which gravitationally attract and hold normal matter, which may then condense to form stars and such. Different assumptions about the properties of the dark matter lead to different distributions of stars, which can be observed. When they are observed, it seems that the dark matter in small galaxies behaves a bit differently from that in large ones. This would be explained if there was a weak short-range force (in addition to the ones we know about) between the dark matter particles. People have theorised about such a force.
Which, finally brings us to the subject of today's article. The authors point our that if, the "large" dimensions theory is right, with three large dimensions, then gravity would feel stronger at distances of less than a nanometer or so. This could provide exactly the weak short-range force needed to get the dark matter to behave right. If this is true, it will have consequences that might be measures quite soon.
The only fusion reactor design that has really reached that level of engineering detail is the tokamak. That burns Deuterium and Tritium, producing helium and neutrons. The reactor wall is cooled, and the neutrons absorbed by a circulating liquid lithium behind it. This does two jobs: it carries the heat away, presumably to boil water, or otherwise drive a turbine; and it produces more tritium.
People have considered trying to get the charged particle energy out by some kind of MHD scheme that would generate electricity directly. This is especially nice if you are burning one of the fuel combinations that does not produce neutrons, like deuterium & helium 3, hydrogen and boron or pure deuterium (if you use the right tricks). As far as I know, no one has seriously worked out the engineering of this. All of these fuel combinations are harder to "ignite" that D+T and that's hard enough.
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I see your point. There are two reasons for going to the moon though:
1. The materials problems with the SE might just turn out to be much harder than we think, or some other problem might arise. If it's 50 yars off it's a different story.
2. For this moon programme they are developing a 125 ton to LEO launcher -- just what we need to launch a big heavy spool of ribbon. They are also developing a CEV that could be used to send people up to GEO if they are needed to deploy the ribbon. So by coincidence or otherwise, it could help a SE programme.
And it's getting them. Growing bigger better SWNT would pay off hugely for anyone who figures out how to do it, even without the elevator project. Strong light materials have any number of uses. All the world's chemicals and polymer companies know this and I'm sure they're spending whatever they think might help. It's not obvious that spending more money will help here.
Once you think 100 GPa ribbon is only a decade or so off, then there is a case for doing what some of the elevator companies are doing, and making sure that the climber and similar technologies are ready in time, to save a 5-10 year delay once the ribbon exists, but there is no point in throwing space money at the basic ribbon problem. If it can be solved in 10 years, it will be, by materials companies.
Why do you think Cyg X1 isn't rotating?
I think this really isn't true. They have occasional, rare, micron-long needles at the very bottom edge of the strength range needed.
So, at a minimum, they need to
1) find even stronger individual needles -- this may not even be possible, if the theoretical strength calculations are wrong
2) grow them thousands or millions of times longer than seen so far
3) grow them in bulk quantities and reasonable yields
4) form them, with a small amount of binder into fibres and thus into ribbons without significant reduction in the strength
None of these is easy, any of them might turn out impossible
Oops wrong black hole. So multiply by 70. 8+ microgravities is still not going to pull a star apart.
I don't think the tidal forces are that bad. Let's consider a 2million kilometer diameter star 0.1 light years from a 2.2 million solar mass black hole.
distance from centre of black holes (I know...) to inner edge of star: 0.999 * 10^15 meters, to outer 1.001*10^15 meters.
Acceleration due to black hole gravity at inner edge: 0.000292570237 ms^-2
Accleration due to black hole gravity at outer edge: 0.000291402294 ms^-2
for a difference of 0.0000012 ms^-2, or about 0.12 millions of a G, easily overcome by the stars gravity.
Indeed, I saw a detailed plan for a man-capable orbital electric launcher once. About 250km long, drawing 15GW of power for about a minute, with a 1 ton payload to (very) low Earth orbit. It looked like a fun project, but there were some significant issues, among them noise and vulnerability to terrorism. Suitable sites are also a bit limited, you need 250km of mostly level ground, close to the equator, with a mountain at the East end and access to 15GW of power.
A railgun, per se, by the way, won't work. Maintaining a sliding contact with the rails at orbital velocity is a bit too hard. The plan I saw was a coilgun, with a superconducting coil on the payload carrier and conventional ones around the vacuum tube. Launch was 15G (in various directions) for a minute, which is probably OK for a fit astronaut who doesn't need to do anything.
Current elevator designs get away with a very low anchor mass by putting it a long way out.
This calculation has been worked out. One very detailed study needed about three shuttle-loads of stuff shipped up to start the bootstrap. This unrolls to a ribbon about an inch wide, very thin, and 100 000 km long. Now you start sending climbers up it, towing more cable which they bond to the side of the ribbon as they go. The climbers stop at the end and add to the counterweight. After a few months, the ribbon is a foot or so wide and you can start moving cargo up it in modest amounts. Your first loads of cargo, are, of course, more ribbon for more elevators.
There are many engineering problems here, most pressingly, how to make a bulk material with the strength/mass ratio so far only observed in microscopic samples.
A fuel capable of launching payload in rockets as cheaply as an elevator could launch it is almost inconceivable in the next 50 years. There are simple physics arguments that rule out any chemical propellant, there just aren't chemicals with that much energy per kilogram locked up in them. Even nuclear-thermal rockets that use any kind of material nozzle or containment system for the nuclear reaction simply can't be efficient enough -- the maximum temperature of the exhaust (limited by the nozzle) will only force hydrogen out so fast. A magnetically confined nuclear rocket could work, but the closest thing we have to a magnetically confined nuclear reactor (JET) weighs hundreds of tons (at least) and still produced less power than it takes to run the magnets.
In this case, the elevator seems like the right solution. All forms of rocket suffer from having to accelerate the engine (and some of the fuel) to orbital velocities. In an elevator setup the engine is a power station (or grid connection) on the ground and never goes anywhere.
1G is 9.8 meters/second/second, NOT 9.8 miles/second/second. This makes rather a big difference
Panspermia would require life to have arrived in a rather narrow window of time, between the last time at which the Earth's oceans were boiled by an impact, and the earliest time at which life was known to have existed. The simulation suggests that this would not have been a time at which many comets were hitting Earth, which, while not conclusive, is not supporting.
Well then... explain to me why calculating Newton's own law of gravitational force gives you mathmatical evidence that there is a strong gravitational pull toward the sun and his law of centripetal force would indicate that this gravitational pull exceeds what is neccessary to maintain an orbit around the sun.
Numbers? In pure Newtonian two-body physics, all closed orbits are stable, essentially because angular momentum is conserved.
In GR all such orbits lose energy and angular momentum by radiating gravity waves. This, however is extremely slow, and would have no measurable effect on the Earth-Sun system for many billions of years.
Perturbations from the other planets (mostly Jupiter) have an effect, which cannot, in general, by exactly described or predicted, however numerical calculations suggest that, while the eccentricity and incilinarion of Earth's orbit, and things like the orientation of the long axis of the ellipse, change roughly cyclically over long periods of time, I have never heard of a suggestion that the Earth is systematically moving closer to the Sun due to these effects.
why would man and animals need eyes if they couldn't see before, sight is a very high-level ability, a creature without sight doesn't realise he needs it? Also in 'natural selection' humans would have been eaten by everything without sight no matter how developed the brain was.
Darwin himself deals with this in "The Origin of Species". There are many steps from the basic light/dark sensing that some bacteria have to the fully developed vertebrate eye. Every step gives an evolutionary advantage in some circumstances. Interestingly, it seems that these steps have been followed twice independently, once leading to the vertebrate eye, and once, independently to the eyes of the squid, which are almost identical, but actually a bit better. It seems that our version of the path ended up more or less by accident with the nerve connection on the front of the retina, blocking some light and needing hole (the blind spot) to get the nerves back to the brain. The squids got this one right and have the nerve connection at the back.
If we came from the ocean then why can't we breath underwater and if we are the most 'evolved' of creatures then why are the birds flying around the earth like it's going out of fashion? We're wingless, can't go underwater without breathing equipment, the ascent of man? Yeah right.
We are not "more evolved" than any other contemporary species. All of us are the products of about 4 billion years of evolution from some little understood primordial cell. At a number of points along the way, splits have occurred. Those individuals in a species that happened to be best adapted for the purpose took to pursuing one ecological "niche", others took another "niche". Perhaps they were separated by an ocean or a desert. Pressures of one niche drove gradual evolution in a direction incompatible with the other niche until you had two different species. For instance, early proto-amphibians specializing in spending time on land and eating insects or land plants had evolutionary pressure towards smaller gills, which used less energy to grow and lost less moisture to the air. End result, theit surviving descendants couldn't breathe underwater. Meanwhile their cousins who had stayed in the water were becoming better and better fish, with more and more sophisticated gills.
How come nobody talks about entropy no more?
Sorry? Any statistical physics textbook talks about entropy, which is where it belongs. The entropy of the Universe as a whole is increasing, because all the high grade energy locked up in unfused hydrogen in stars is slowly turning into low-grade heat energy. Temporary local increases in apparent complexity (like life, humanity, culture, etc.) are just tiny "curlicues" on this big picture from a statistical physics point of view.
Oh if wewe're the offspring of monkeys then why arn't monkeys turning into humans?
We're not their offspring, we're their cousins. Some of our common ancestors found themselves in a situation where hairlessness, swimming, two-legged running and living in larger groups favoured survival. We are the descendants of that group. Others found themselves in an environment where moving around in trees, living in smaller groups and so on was best. Their descendants are chimps, gorillas and so on,
The Earth orbits the Sun. Ironically enough it was Newton who worked out how this all happens. The Earth constantly accelerates towards the Sun, but since it's moving rather quickly "sideways" around the Sun, the effect of the accelaration is to curve it's path just enough that, one year later it is back exactly where it started, having gone all the way round the Sun.
I have a University degree including some mathematical physics (from Newton's alma mater, as it happens. his college rooms where about 50 yards (and 300+ years) from mine). I did pay attention and I did learn some stuff.
OK, let's take this a step at a time.
The Earth is not, on average getting closer to the Sun. The mean distance from Earth to the Sun has been essentially unchanged for 4 billion years or more. The sun is, on a timescale of BILLIONS of years, getting hotter, but we are dealing with much faster changes.
Melting of floating icecaps does, indeed, not raise sea level (although it may have other troubling consequences). Melting of the Greenland and Antarctic icecaps, on the other hand does raise sea level.
Finally, we could be talking about sea level rises of quite a few feet this century. Servers do not run well underwater.
Of course in this dense early universe, some other kind of signal may have travelled faster than light (although not faster than c) and would enable us to see a little further. Neutrino's maybe, or the hypothetical "axions" that might make up some of the dark matter in the universe or....
You can see supernovae if they are close enough. There are two notions of brightness: how much light (or other energy) we get from a thing, and how much it actually emits. The relationship between these is controlled by distance.
In the first sense, the brightest object is the sun unless you happen to be standing very very close to a search light or magnesium flare.
In the second sense, a galaxy is typically brighter than a supernova, but if it's close then it's diffuse, so it doesn't look so bright. Actually if you include its neutrino output, a supernova is, for a few seconds very much brighter indeed than it is for the next year or so, or indeed than pretty much anything we know. A quasar is brighter than a typical galaxy, but there are no nearby ones. A GRB might be (briefly) even brighter than that, or it might not be so bright, but beam it's output (in which case there are more of them than we see).
A GRB doesn't just emit gamma rays. It emits a short brief flash of gamma rays, followed by an "afterglow" of X-rays, UV, ordinary light and probably other things over an extended period. Alpha and beta are probably emitted too, but will be diverted by magnetic fields and slowed down and absorbed by the intergalactic medium.
The same computer that had the line printer (an ICL 1902T, for those who care), also had a loudspeaker wired into a couple of bus lines in the CPU. This was actually incredibly useful. After a while you got used to the sounds of different phases of the OS boot, the compilers and so on. If something got stuck, which it did quote often, you pretty much knew where it had got to by the last familiar noise it had made. Of course people wrote programmes to play tunes.
There are other dangers. The additional box that paginates the printout is (or at least was once) known as the Integral Burster Trimmer Stacker (IBTS). When correctly adjusted it was a wonderful thing: cutting the continuous paper into sheets, removing the perforations, stacking the pages the same way up, separating distinct print jobs, etc. When NOT correctly aligned, it earned it's other name: the Integral Burster Trimmer Shredder. It is quite amazing how fast one of these could fill your machine room with shredded paper!
I suspect you're describing a standard line printer. We had one of these at my secondary school. It's not quite as you put it. There is a solid drum, with 132 copies of every character. On the other side of the paper is an array of 132 flat hammers. Somewhere there is a ribbon as wide as the paper with ink on it. Now to print an A in column 5 you wait until the A's (132 of them) are next to the paper and the fire the hammer in column five (and any other column that needs an A). A moment later you fire all the hammers for Bs and so on. Once every drum rotation you move the paper on. It was very noisy and also very prone to catch fire.
Surprisingly, I think there is quite a lot. Most of the minerals that make up Earth's crust contain water, and water, under pressure is drawn down into the crust at spreading faults. Also the carbonate minerals would not exist without long-lasting oceans where CO2 and silicate rocks can slowly combine. These hydrated and carbonate minerals act, I think as a lubricant to plate movements. I am not a geologist, but I'm sure I read this somewhere once. I can't quickly find confirmation.
OK: first there's spin-off from the design, building and operating of the probe itself -- materials, sensors, communication technology, robotics, etc. Missions like these present the designers and builders with difficult problems, and relatively much time and money to solve them. Some of the solutions turn out to have other uses.
Next, there are quite a lot of comets in the Solar system. From time to time they come close to Earth, or even hit it. They have hit other bodies, like the moon and Mars and Mercury, and may have had a lasting influence (for instance leaving ice in dark crater bottoms). Finally, they might be source of raw materials for future expansion into the solar system. Knowing more about comets helps us understand what we might be able to do if one were going to hit us; what we might expect to find on the Moon, Mars and Mercury, and what, if anything we might be able to use comets for in the future.
Next, comets seem to be mostly made of common elements: carbon, oxygen, hydrogen, nitrogen. Under the unique conditions applying on comets, they may have formed interesting new compounds with interesting, or useful, new properties. If so, we can, perhaps sythesise those compounds on Earth from air, water, coal and so on (basically cheap ingredients) for whatever purposes.
Finally, we just want to know. Long ago, we think much of the solar system, including you, me and this planet, was basically in the form of a bunch of comet-like bodies, which then collided, stuck together and grew into planets etc. Understanding comets gives us some clues as to how that may have happened.
So string theory suggests 11 dimensions 7 of which are really tiny. Think of a hosepipe: seen from a distance it looks 1-dimensional, and if you imagine creatures living in the rubber of the hose which were (say) a mile long and wrapped all around the pipe for that mile, they would see their world as 1-dimensional. If they somehow managed to examine themsselves in microscopic detail, though, they would find this second dimension just an inch or so around, which was vital to the way their internal organs worked. The suggestion is that the universe is like this. We see 4 dimensions, but if we want to understand really small things, we have to look at the other 7 dimensions as well. Many different kinds of particle are really the same kind of string, wrapped around the "small" dimensions in different ways, or vibrating in different ways.
So, now, more recently, people have proposed that the vast difference in strengths between electroweak forces and gravity can be explained by some of these small dimensions being rather less small that we thought. How small depends on how many of them there are. If it was one or two, they would have to be millimetres in size and we would have detected them by now. If it was three, they would be about a nanometer and we wouldn't have. Experimentalists are working on this.
Meanwhile, astronomers have noticed some anomalies between the prevailing theories of galaxy formation, and the observations. These theories say, very roughly that galaxies form as clumps of dark matter which gravitationally attract and hold normal matter, which may then condense to form stars and such. Different assumptions about the properties of the dark matter lead to different distributions of stars, which can be observed. When they are observed, it seems that the dark matter in small galaxies behaves a bit differently from that in large ones. This would be explained if there was a weak short-range force (in addition to the ones we know about) between the dark matter particles. People have theorised about such a force.
Which, finally brings us to the subject of today's article. The authors point our that if, the "large" dimensions theory is right, with three large dimensions, then gravity would feel stronger at distances of less than a nanometer or so. This could provide exactly the weak short-range force needed to get the dark matter to behave right. If this is true, it will have consequences that might be measures quite soon.
Yes it is.
The only fusion reactor design that has really reached that level of engineering detail is the tokamak. That burns Deuterium and Tritium, producing helium and neutrons. The reactor wall is cooled, and the neutrons absorbed by a circulating liquid lithium behind it. This does two jobs: it carries the heat away, presumably to boil water, or otherwise drive a turbine; and it produces more tritium.
People have considered trying to get the charged particle energy out by some kind of MHD scheme that would generate electricity directly. This is especially nice if you are burning one of the fuel combinations that does not produce neutrons, like deuterium & helium 3, hydrogen and boron or pure deuterium (if you use the right tricks). As far as I know, no one has seriously worked out the engineering of this. All of these fuel combinations are harder to "ignite" that D+T and that's hard enough.