Then reveal to us the correct answer, oh wise one.
If he did that, he'd get -5 redundant. Try reading outside of just 1 post.
All I see are multiple posts arguing over high-school text descriptions of refraction ("It says right here that light slows down!").
Pick up a university-level book on EM and materials science, and read it. Or go to any of the various physics tutorial sites online, if you want the "for non-physics-students" version.
Then why is the speed of light different when being measured in the atmosphere than it is when measured in a vacuum?
Because you are measuring the phase velocity, not the velocity of the photons themslves. Phase velocity can be anything you want it to be, depending on the materials tricks you play. Photon velocity, and the speed of propagation of electromagnetic effects, is always C.
What is the difference between the rate of travel (distance / time) in a medium and the time it takes to pass through a medium (distance / time)? It seems that the two are the same.
I drive between intersections at 50 km/hr. I stop at red lights, so my time to get from point A to point B indicates my average speed is, say, 30 km/hr. This does not change the fact that my car was travelling at 50 km/hr.
How does the light being "re-emitted in a fairly random direction" give us refraction, which is a predictable phenomenon that is analagous to the effect observed when a round projectile travels through mediums of differing density (such as carefully prepared gelatin layers, or from the atmosphere into water)?
These are wave effects based on the aggregate behavior of photons. For most everyday applications, the fact that wave energy propagates as discrete photons isn't relevant. Thus, the velocity of the photons doesn't usually matter, just the phase velocity of the wave.
Statistical effects and interference effects cause the photons to stay organized in waves. Detailed discussion of this is beyond the scope of this reply.
Nope. Think about it for a second. If this were the case how many colors would you see in light passing through a window? one? two? ten? certainly you would never see white sunlight.. and well if it were absorbed and reabsorbed a great deal and re-emitted in a _random_direction_ would you ever see _through_ a window?
The net effect turns out to be that the photons are emitted in the same direction (or that the wavefront continues propagating in the same direction). My understanding was that the photons actually _were_ emitted in the direction the absorbed photons were travelling, but I would have to doublecheck this with a greater physics geek to be sure.
but the speed of light can indeed be controlled experiementally in a laboratory setting. That's how lasers (Lightspeed Amplification by Stimulated Emission of Radiation) work.
Um, no, lasers work by stimulated emission: the fact that a photon emitted from the decay of one excited atom can trigger another excited atom to decay, releasing another photon in phase with the first.
Nothing about changing the speed of light or even using materials with different refractive indices in there.
Sorry dude. Yes the IOR is important; however the refractive index has nothing to do with the flexibility.
It directly determines the critical angle for total internal reflection, which affects the ratio of bending radius to fiber diameter that you can support without unacceptable light loss.
It also has everything to do with the materials you make the fiber with. A minimum required refractive index limits materials choices, which limits mechanical properties. A carefully-doped glass fiber will have a higher refractive index than a carefully doped plastic one.
The paper in Nature about on this research says the sponge fibers are more fracture resistant than commercial fibers because of a layer of organic ligands at the fiber's exterior. Now if we can just genetically engineer them to grow a few hundered miles in length...
Or look into better plastic coatings on fibers manufactured the boring way.
The ocean is far huger than you give credit. The effects we have on the ocean are incredibly small compared to the effects of volcanoes, earthquakes, and the sun.
Then why have cod stocks crashed? We don't have to fish throughout the entire ocean. We wait at locations where fish tend to gather.
The same applies to pollution. The volume of the ocean is huge. The surface area of the ocean is less huge. Mixing between upper and lower layers is actually quite small (among other things this is why people have been proposing that CO2 be sequestered down there; whether or not this is practical is left as an exercise to the reader). More importantly, regions of the ocean that have a linchpin effect on its biology can be very small indeed compared to the whole (fishing areas off the grand banks are a great example).
They are proving that no matter what we dump into the atmosphere, it has little to no effect.
You apparently live close enough to the equator that you haven't noticed the need for extra sunscreen vs. when you were a kid.
The solar flares we are experiencing are tiny, even during the so-called solar peaks. A larger than normal solar flare would literally burn our atmosphere off. The atmosphere is such a small, delicate part of our earth that many people are wondering why we still have one.
Earth holds an atmosphere because the mean velocity of molecules within it is much lower than escape velocity. The real question is why we don't have a much _thicker_ one (and that's explained by the oceans assisting in converting much of it to minerals). In order for the atmosphere to be boiled off in less than geologic time, temperature would need to increase several-fold, requiring solar light flux to increase by an order of magnitude or two (as a physicist, you are aware of the laws governing radiative heat loss). This is more along the lines of "going nova" than "having a flare".
In summary, the points you make that I'm in a position to speak about are questionable. This raises concern about the other points you have made, which I'm sure others more knowledgeable than I will comment on.
I'd love to know where you heard 30 years. That would be a dream come true. Too bad it's not likely...
Why is this not likely? What makes you say this? I will turn 37 years old in just a couple months. In my first six years I was privileged to see humankind's first tentative steps into space. The advancement that has been made in technology since I turned 7 years old has been mind boggling to say the least.
By playing the odds. Practical fusion power has been 20 years away for the past 50 years. Don't hold your breath about it showing up within the next 20-30. Things look promising now. They've looked promising in the past, too. We won't know until the first commercial fusion plant comes online how long it'll really take to solve all of the problems with fusion.
My own guess is that it'll be possible to build a commercial fusion power reactor within 50 years, but that it won't be done, as it will be more expensive than other forms of power (the fusion schemes that have come close to working aren't cheap), and will still produce radioactive waste (all practical forms of fusion produce neutrons in copious quantity, and that makes your reactor housing radioactive).
However, my timeline guess isn't any more valid than the "20-30 years" one. Much like the end of the Wheel of Time series or the next Linux kernel, it'll get here when it's good and ready.
One local gamma-ray burst, and all life in the entire solar system is wiped out. On Earth, under the sea, on Mars on Europa, wherever. Sorry, start over.
You may wish to re-read my post, as you seem to have completely missed half of it and overlooked the point of the half that you did catch.
The fact that a local supernova, gamma ray burst, or other celestial disaster could sterilize the solar system doesn't change the fact that colonizing multiple planets reduces _other_ risks, which are arguably more likely (deliberately induced calamities being the most obvious, but not the only, example).
Interstellar colonization is most definitely possible, and even with a slow propagation time is likely to ensure that at least some of humanity is out of range of anything short of a galaxy-sterilizing catastrophe.
Before you start painting galaxy-sterilizing catastrophe scenarios, be advised that there are no young, active galactic nuclei in our vicinity, and that it will be an extremely long time before our galaxy passes close enough to another to interact significantly.
In summary, my points hold, and your points were already addressed in my original post.
So all we need is a movie review site that takes into account your tastes for calibrations. So you get a fuzzy-something like: "Critics who like the movies you like, rated this movie 7/10". I'm sure someone's doing this already.
IMDB does this. It just takes a while for a movie to get enough feedback/rating votes for this to be useful, so it isn't helpful for opening week.
So, text-messaging allows people to spread the word about a bad movie too fast?
As opposed to, oh, checking the Tomatometer at or before the day of release? Or reading reviews you trust? Or just making a _phone call_ to your friends instead of texting them?
Text messaging is an incremental improvement in our communications ability, not a revolution.
Sure, we could go to Mars. But what will it get you? Mars is a dead planet. There may be enough resources to run a colony. Fine, you have a million or so people living in a dome, breathing recycled air, drinking recycled water, and eating hydroponically grown soyburgers. That's just a drop in the population bucket. And if that's the way you're going to live, why go all the way to Mars to do it? Why not just build your dome here on Earth?
Colonies on multiple worlds is insurance against world-destroying events. A very large asteroid impact could disrupt the crust or kick up enough dust to freeze the oceans over, killing most non-bacterial life on the planet. On the more mundane front, toss a few cobalt bombs around and you can gamma-sterilize all landmasses. It is extremely unlikely for a natural cataclysm to take out multiple colonized worlds at once. It is far more difficult for an artificial cataclysm to be propagated between worlds than to have it occur on one world. This makes colonizing (and ideally terraforming) multiple worlds desirable for the long-term survival of our species.
This doesn't mean we have to devote all possible resources to it; just that it's a good thing to do at some point, and a nice long-term goal to shoot for.
Face it, we are trapped in our own solar system. Pioneer 10 has been travelling for thirty years, and is less than 0.03% of the way to the closest star. It should arrive in a little over 9000 years from now. The only two technologies that can get us away, are hibernation, and multi-generation craft. Are we going to put a couple of hundred people onto one of these spaceships and wait around for 9-10 thousand years to see if they find a habitable planet? No, we're stuck here.
First of all, we'd have picked out destination worlds and verified their ability to support life long before sending colonization craft. The cost of building a big enough telescope is far lower than the cost of building an interstellar colony ship.
Secondly, several approaches to building interstellar craft that don't carry their own power sources with them have been proposed. These would allow interstellar craft to reach their destinations within a human lifetime, if we're in that much of a hurry.
Heck, you can in principle do it with a big enough and efficient enough fusion craft (smallest mass ratio you can do it in is about 100:1, but even 1000:1 could be built, albeit expensively).
Assuming less design optimization or smaller craft gives a longer travel time, but I don't see why this is intrinsically unacceptable. Fully colonizing a world will take a comparable amount of time (generations). Terraforming a world (as is desirable if the world is to support human life indefinitely) will take at least that long.
Interstellar colonization is desirable from a species point of view for two reasons. Firstly, there are some classes of catastrophe that can sterilize entire star systems (nearby supernovae are the most popular so far). Spreading between stars, even slowly, would put colonies out of range of such catastrophes in a time much shorter than their expected interval of occurrence, and so is a suitable long-term safeguard. More importantly, launching an interstellar war is possible, and arguably reasonably practical. Launching a slower-than-light interstellar war without some magical new physics making things a lot cheaper is far less practical. Interstellar colonization would give us very good protection against most conceivable species-destroying catastrophes, either natural or artificial.
Thus, as a long-term goal, I believe colonization both in-system and out-of-system is desirable.
Maybe i'm missing something here, but this nuclear station will "only" need six engineers to run it, and is proposed for use by other cosmonauts in future mars expeditions.
So it needs people on Mars to run it, and people on Mars to take advantage of it. Do they actually have any firm plans for getting people to Mars?
In practice, they don't have to. All that has to happen is for _anyone_ to have manned missions to Mars 30 years from now.
When the US, or Europe, or Japan, or China starts thinking seriously about a Mars base, they can step up with a power solution already in-hand. The design studies for a space project take at least as long as the project itself, so this is of considerable worth.
It's moot point, though, as this sounds more like a feasibility study done by a research institution than anything that they actually plan to build. Much like the current crop of space elevator proposals, or the large space station proposals of a few decades ago.
The "we're planning to do this" line is almost certainly spin from the reporting agency or someone higher up the political food chain.
I'm not certain how much safer they are in the case of a coolant loss (core exposure,) but the pile itself is more resistant to melting into a mass; if anything, individual pellets would melt through their containment and thus reduce the reaction. But still, those pellets are not light, and the accompanying machinery and generators will be very, very heavy. I think RTG's would be a better short-term solution...of course at the expense of irradiating their surroundings.
Actually, part of the point of a pebble-bed reactor is that it can't run away. Pellets expand as temperature increases, moving them outside of the envelope for criticality. The result is a core that automatically balances itself right at the critical threshold, resisting changes in either direction. The number of fuel spheres present (and the shape of the collection) determines the temperature at which the whole thing stabilizes (more material, and it needs to be farther apart - and so hotter - to stabilize). When designed with safety in mind (e.g. with the best possible core arrangement and little enough fuel to stay below problematic temperatures) there's no way for it to have a runaway reaction.
Tapping heat off drops the temperature, cooling the pile, and increasing the reaction rate until temperature stabilizes. Losing coolant causes it to heat and expand, dropping the reaction rate, and letting it stabilize. The only way you'd get an accident happening is by adding more fuel, or breaking up the fuel pebbles and carefully arranging fuel and graphite moderator for a higher reaction rate. Not going to happen by accident.
Re. RTGs, a radiothermal source generally doesn't cause activation of its surroundings. It's neutron radiation that does that; RTGs generally just emit alpha or beta radiation (depending on material used, of course). They're easy to shield, too (against primary radiation; you'll still get gama shining through, and x-rays as secondary radiation produced in the shielding).
A fission reactor, by contrast, produces neutron radiation and makes everything near the unshielded core radioactive.
But the corona and bulk resistance losses scale with the voltage, so you end up losing more power this way.
Modification: Resistive losses go down as voltage goes up, for fixed power, because current is lower, resulting in a lower voltage drop for a fixed bulk resistance. But this holds for both DC and AC, so the net effect is nil.
Before anyone mentions skin effect for AC changing the effective resistance (making AC worse), at frequencies this low it's negligeable.
True, the anti-nuclear crowd are a bit dogmatic, you forget the real issue with nuclear power. Where do you plan to put the waste, huh? Yucca Mountain? You mean the storage facility on the quake fault line? Nice.:)
Anywhere in the continental shield would work, as long as you seal your bore-holes up with clay to prevent seepage. The shield has been stable for about 3 billion years.
Unfortunately DC power distribution is highly inefficient. When transmitting power down a long lenght of wire DC creates a much higher voltage drop (power loss) across the line than AC.
I don't see how this is the case. For both DC and AC signals, you have to worry about the bulk resistance of the cable, which dissipates roughly the same amount of energy in each case (off by a factor of sqrt(2) or so, but not by a vast amount).
For DC and AC, you lose due to corona discharge through the atmosphere, but the majority of your losses should be elsewhere.
For DC, that's it.
For AC, you get extra power loss from the fact that your power lines are emitting extremely low frequency (60 Hz) radio (they're antenae). The effect of this is fairly small, especially since you have multiple cables at different phases near each other (end up just storing power inductively between wires instead of radiating most of it).
For AC, you also have cable impedence due to the inductance of the cables. While this doesn't _waste_ power - just stores it on part of the cycle and returns it on another - it means that you need a higher voltage to drive a given amount of current across the wire (impedence of the cables goes up). But the corona and bulk resistance losses scale with the voltage, so you end up losing more power this way.
In summary, if anything, DC looks like it should lose _less_ power. I'm probably missing something, though, so if a power geek can elighten me, it would be appreciated.
My understanding was that DC had problems with local ground drifting relative to source ground.
That's one way. I remember when superconduction came on the scene. One of the ideas was an underground superconduction coil. Basically an induction coil, on a much bigger scale.
Energy density that can be stored in an inductor is much lower than the energy density of chemical fuels. This is especially true given that high-temperature superconductors break down at on the order of a 1 T magnetic field, but even without a superconducting breakdown field limit, tensile stress goes up enough to produce a limit that falls far short of chemical energy densities.
That's why fuel cells are so nice, even with something as annoying to store in bulk as hydrogen.
If hydrogen storage became a serious problem they could use methane as a fuel (with reforming cells), and burn the high-carbon reform byproducts with the hydrogen produced from electrolysis to get methane again, but that would arguably be more annoying than just storing the hydrogen.
This interesting technology could potentially lead to some better new-age energy sources. I'm not sure why we always focus on warfare, when there are other ways to use the explosive power of new military technology.
A gamma pulse is very useful as a weapon, but very hard to draw power from unless you put the gamma source inside a building-sized tank of water and run a steam turbine. This makes metastable isomers useless for compact power storage (the energy storage medium is compact, but you can't tap it with compact equipment).
As others have pointed out, this is not an energy _source_.
My basic question concerning this is two-fold, is this realy needed, and if it is created will we be able to control the techology. With world events the way they are now it seems like one of the last things that we end is a small high yeild weapon that can fall into the worng hands. At least with nuclear weapons there are some means of detecting their presence, but it seems that these weapons will not have the same signature.
The metastable isomers used for this type of weapon decay naturally - the new discovery is just a way to accelerate this decay so that it happens all at once. You can still detect the source material from its gamma ray glow (in much the same manner as you'd detect fissile material).
and if it is created will we be able to control the techology
Now that it's know to be feasible, whether the US develops it or not is irrelevant. Joe Random Terrorist State could look up the papers published on use of the effect for a power source tomorrow, and start their own bomb program.
Control, if required, is accomplished by making sure the states your concerned about don't build the equipment needed to produce the weapons (large and expensive equipment for all methods of producing the explosives, including charging by gamma excitation).
I hope the authours of this project do their homework. My impression is that most of the good search and indexing schemes have already been patented, which will make it difficult to release such a project without stepping on someone's toes.
Taking advantage of the fact that light emitted from a laptop display is naturally polarized to begin with, a 3D stereoscopic effect can be achieved by covering half the screen with a cellophane sheet in order to construct orthogonally polarized left and right scenes while the viewer wears eyeglasses holding two polarizers oriented 90 degrees apart...
You appear to have missed the parent poster's point.
If the images for each eye are on different halves of the screen, then polarizing is pointless. It removes phantom images, but the phantoms are far away from the real image, so there's no advantage to doing so.
Polarizing filters, as the parent poster pointed out, are useful when you have both images in the same place on the screen (overlapping). As overlapping images can't be distinguished by position, some other method is needed (polarization, colour, light direction, etc). When the images don't overlap, they can be distinguished without aids (just cross your eyes).
For years, we've heard about semiconductors the size of human hairs and how it would revolutionize the computing world.
I still see an AMD chip in my computer, and nice, large visible chips in the stores.
The same technology that allows you to produce an 8086 smaller than a grain of sand is what lets you run that AMD chip with its 38 million transistors. You _are_ using and reaping the benefits of this technology.
Pervasive, miniaturized electronics are showing up. Mainly the miniaturizationn is manifested in price (we can do today in a cheap 1-2mm^2 chip what would have taken a larger and much more expensive chip 5-10 years ago). However, the RFID tags that you have been hearing so much about require microprocessors to handle communication. "Pervasive" will certainly be the word to describe it in a few years.
So now it's diamonds? I'm not trying to troll, but when will mainstream applications (see: desktop computers, or at least universities) come around?
Universities have been studying diamond semiconductors for years. Where do you think all of the papers on them come from? Do you think papers are all based on theoretical models? Someone had to build doped diamond films before the electrical properties of them could be measured.
You won't see them on the desktop first. You'll see them in industry. There are many places where having a miniaturized control computer in an extreme environment would be quite useful (the oil industry was the example I'd heard about; with diamond semiconductors it's easier to monitor conditions in situ as you drill).
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Then reveal to us the correct answer, oh wise one.
If he did that, he'd get -5 redundant. Try reading outside of just 1 post.
All I see are multiple posts arguing over high-school text descriptions of refraction ("It says right here that light slows down!").
Pick up a university-level book on EM and materials science, and read it. Or go to any of the various physics tutorial sites online, if you want the "for non-physics-students" version.
Wrong!
Then reveal to us the correct answer, oh wise one.
Insightful my ass, flat out wrong.
Then enlighten us on the correct answer, oh wise one.
Then why is the speed of light different when being measured in the atmosphere than it is when measured in a vacuum?
Because you are measuring the phase velocity, not the velocity of the photons themslves. Phase velocity can be anything you want it to be, depending on the materials tricks you play. Photon velocity, and the speed of propagation of electromagnetic effects, is always C.
What is the difference between the rate of travel (distance / time) in a medium and the time it takes to pass through a medium (distance / time)? It seems that the two are the same.
I drive between intersections at 50 km/hr. I stop at red lights, so my time to get from point A to point B indicates my average speed is, say, 30 km/hr. This does not change the fact that my car was travelling at 50 km/hr.
How does the light being "re-emitted in a fairly random direction" give us refraction, which is a predictable phenomenon that is analagous to the effect observed when a round projectile travels through mediums of differing density (such as carefully prepared gelatin layers, or from the atmosphere into water)?
These are wave effects based on the aggregate behavior of photons. For most everyday applications, the fact that wave energy propagates as discrete photons isn't relevant. Thus, the velocity of the photons doesn't usually matter, just the phase velocity of the wave.
Statistical effects and interference effects cause the photons to stay organized in waves. Detailed discussion of this is beyond the scope of this reply.
Nope. Think about it for a second. If this were the case how many colors would you see in light passing through a window? one? two? ten? certainly you would never see white sunlight.. and well if it were absorbed and reabsorbed a great deal and re-emitted in a _random_direction_ would you ever see _through_ a window?
The net effect turns out to be that the photons are emitted in the same direction (or that the wavefront continues propagating in the same direction). My understanding was that the photons actually _were_ emitted in the direction the absorbed photons were travelling, but I would have to doublecheck this with a greater physics geek to be sure.
but the speed of light can indeed be controlled experiementally in a laboratory setting. That's how lasers (Lightspeed Amplification by Stimulated Emission of Radiation) work.
Um, no, lasers work by stimulated emission: the fact that a photon emitted from the decay of one excited atom can trigger another excited atom to decay, releasing another photon in phase with the first.
Nothing about changing the speed of light or even using materials with different refractive indices in there.
Sorry dude. Yes the IOR is important; however the refractive index has nothing to do with the flexibility.
It directly determines the critical angle for total internal reflection, which affects the ratio of bending radius to fiber diameter that you can support without unacceptable light loss.
It also has everything to do with the materials you make the fiber with. A minimum required refractive index limits materials choices, which limits mechanical properties. A carefully-doped glass fiber will have a higher refractive index than a carefully doped plastic one.
The paper in Nature about on this research says the sponge fibers are more fracture resistant than commercial fibers because of a layer of organic ligands at the fiber's exterior. Now if we can just genetically engineer them to grow a few hundered miles in length...
Or look into better plastic coatings on fibers manufactured the boring way.
The ocean is far huger than you give credit. The effects we have on the ocean are incredibly small compared to the effects of volcanoes, earthquakes, and the sun.
Then why have cod stocks crashed?
We don't have to fish throughout the entire ocean. We wait at locations where fish tend to gather.
The same applies to pollution. The volume of the ocean is huge. The surface area of the ocean is less huge. Mixing between upper and lower layers is actually quite small (among other things this is why people have been proposing that CO2 be sequestered down there; whether or not this is practical is left as an exercise to the reader). More importantly, regions of the ocean that have a linchpin effect on its biology can be very small indeed compared to the whole (fishing areas off the grand banks are a great example).
They are proving that no matter what we dump into the atmosphere, it has little to no effect.
You apparently live close enough to the equator that you haven't noticed the need for extra sunscreen vs. when you were a kid.
The solar flares we are experiencing are tiny, even during the so-called solar peaks. A larger than normal solar flare would literally burn our atmosphere off. The atmosphere is such a small, delicate part of our earth that many people are wondering why we still have one.
Earth holds an atmosphere because the mean velocity of molecules within it is much lower than escape velocity. The real question is why we don't have a much _thicker_ one (and that's explained by the oceans assisting in converting much of it to minerals). In order for the atmosphere to be boiled off in less than geologic time, temperature would need to increase several-fold, requiring solar light flux to increase by an order of magnitude or two (as a physicist, you are aware of the laws governing radiative heat loss). This is more along the lines of "going nova" than "having a flare".
In summary, the points you make that I'm in a position to speak about are questionable. This raises concern about the other points you have made, which I'm sure others more knowledgeable than I will comment on.
I'd love to know where you heard 30 years. That would be a dream come true. Too bad it's not likely...
Why is this not likely? What makes you say this? I will turn 37 years old in just a couple months. In my first six years I was privileged to see humankind's first tentative steps into space. The advancement that has been made in technology since I turned 7 years old has been mind boggling to say the least.
By playing the odds. Practical fusion power has been 20 years away for the past 50 years. Don't hold your breath about it showing up within the next 20-30. Things look promising now. They've looked promising in the past, too. We won't know until the first commercial fusion plant comes online how long it'll really take to solve all of the problems with fusion.
My own guess is that it'll be possible to build a commercial fusion power reactor within 50 years, but that it won't be done, as it will be more expensive than other forms of power (the fusion schemes that have come close to working aren't cheap), and will still produce radioactive waste (all practical forms of fusion produce neutrons in copious quantity, and that makes your reactor housing radioactive).
However, my timeline guess isn't any more valid than the "20-30 years" one. Much like the end of the Wheel of Time series or the next Linux kernel, it'll get here when it's good and ready.
You may wish to re-read my post, as you seem to have completely missed half of it and overlooked the point of the half that you did catch.
Before you start painting galaxy-sterilizing catastrophe scenarios, be advised that there are no young, active galactic nuclei in our vicinity, and that it will be an extremely long time before our galaxy passes close enough to another to interact significantly.
In summary, my points hold, and your points were already addressed in my original post.
So all we need is a movie review site that takes into account your tastes for calibrations. So you get a fuzzy-something like: "Critics who like the movies you like, rated this movie 7/10". I'm sure someone's doing this already.
IMDB does this. It just takes a while for a movie to get enough feedback/rating votes for this to be useful, so it isn't helpful for opening week.
So, text-messaging allows people to spread the word about a bad movie too fast?
As opposed to, oh, checking the Tomatometer at or before the day of release? Or reading reviews you trust? Or just making a _phone call_ to your friends instead of texting them?
Text messaging is an incremental improvement in our communications ability, not a revolution.
Sure, we could go to Mars. But what will it get you? Mars is a dead planet. There may be enough resources to run a colony. Fine, you have a million or so people living in a dome, breathing recycled air, drinking recycled water, and eating hydroponically grown soyburgers. That's just a drop in the population bucket. And if that's the way you're going to live, why go all the way to Mars to do it? Why not just build your dome here on Earth?
Colonies on multiple worlds is insurance against world-destroying events. A very large asteroid impact could disrupt the crust or kick up enough dust to freeze the oceans over, killing most non-bacterial life on the planet. On the more mundane front, toss a few cobalt bombs around and you can gamma-sterilize all landmasses. It is extremely unlikely for a natural cataclysm to take out multiple colonized worlds at once. It is far more difficult for an artificial cataclysm to be propagated between worlds than to have it occur on one world. This makes colonizing (and ideally terraforming) multiple worlds desirable for the long-term survival of our species.
This doesn't mean we have to devote all possible resources to it; just that it's a good thing to do at some point, and a nice long-term goal to shoot for.
Face it, we are trapped in our own solar system. Pioneer 10 has been travelling for thirty years, and is less than 0.03% of the way to the closest star. It should arrive in a little over 9000 years from now. The only two technologies that can get us away, are hibernation, and multi-generation craft. Are we going to put a couple of hundred people onto one of these spaceships and wait around for 9-10 thousand years to see if they find a habitable planet? No, we're stuck here.
First of all, we'd have picked out destination worlds and verified their ability to support life long before sending colonization craft. The cost of building a big enough telescope is far lower than the cost of building an interstellar colony ship.
Secondly, several approaches to building interstellar craft that don't carry their own power sources with them have been proposed. These would allow interstellar craft to reach their destinations within a human lifetime, if we're in that much of a hurry.
Heck, you can in principle do it with a big enough and efficient enough fusion craft (smallest mass ratio you can do it in is about 100:1, but even 1000:1 could be built, albeit expensively).
Assuming less design optimization or smaller craft gives a longer travel time, but I don't see why this is intrinsically unacceptable. Fully colonizing a world will take a comparable amount of time (generations). Terraforming a world (as is desirable if the world is to support human life indefinitely) will take at least that long.
Interstellar colonization is desirable from a species point of view for two reasons. Firstly, there are some classes of catastrophe that can sterilize entire star systems (nearby supernovae are the most popular so far). Spreading between stars, even slowly, would put colonies out of range of such catastrophes in a time much shorter than their expected interval of occurrence, and so is a suitable long-term safeguard. More importantly, launching an interstellar war is possible, and arguably reasonably practical. Launching a slower-than-light interstellar war without some magical new physics making things a lot cheaper is far less practical. Interstellar colonization would give us very good protection against most conceivable species-destroying catastrophes, either natural or artificial.
Thus, as a long-term goal, I believe colonization both in-system and out-of-system is desirable.
Maybe i'm missing something here, but this nuclear station will "only" need six engineers to run it, and is proposed for use by other cosmonauts in future mars expeditions.
So it needs people on Mars to run it, and people on Mars to take advantage of it. Do they actually have any firm plans for getting people to Mars?
In practice, they don't have to. All that has to happen is for _anyone_ to have manned missions to Mars 30 years from now.
When the US, or Europe, or Japan, or China starts thinking seriously about a Mars base, they can step up with a power solution already in-hand. The design studies for a space project take at least as long as the project itself, so this is of considerable worth.
It's moot point, though, as this sounds more like a feasibility study done by a research institution than anything that they actually plan to build. Much like the current crop of space elevator proposals, or the large space station proposals of a few decades ago.
The "we're planning to do this" line is almost certainly spin from the reporting agency or someone higher up the political food chain.
Still makes for interesting reading.
I'm not certain how much safer they are in the case of a coolant loss (core exposure,) but the pile itself is more resistant to melting into a mass; if anything, individual pellets would melt through their containment and thus reduce the reaction. But still, those pellets are not light, and the accompanying machinery and generators will be very, very heavy. I think RTG's would be a better short-term solution...of course at the expense of irradiating their surroundings.
Actually, part of the point of a pebble-bed reactor is that it can't run away. Pellets expand as temperature increases, moving them outside of the envelope for criticality. The result is a core that automatically balances itself right at the critical threshold, resisting changes in either direction. The number of fuel spheres present (and the shape of the collection) determines the temperature at which the whole thing stabilizes (more material, and it needs to be farther apart - and so hotter - to stabilize). When designed with safety in mind (e.g. with the best possible core arrangement and little enough fuel to stay below problematic temperatures) there's no way for it to have a runaway reaction.
Tapping heat off drops the temperature, cooling the pile, and increasing the reaction rate until temperature stabilizes. Losing coolant causes it to heat and expand, dropping the reaction rate, and letting it stabilize. The only way you'd get an accident happening is by adding more fuel, or breaking up the fuel pebbles and carefully arranging fuel and graphite moderator for a higher reaction rate. Not going to happen by accident.
Re. RTGs, a radiothermal source generally doesn't cause activation of its surroundings. It's neutron radiation that does that; RTGs generally just emit alpha or beta radiation (depending on material used, of course). They're easy to shield, too (against primary radiation; you'll still get gama shining through, and x-rays as secondary radiation produced in the shielding).
A fission reactor, by contrast, produces neutron radiation and makes everything near the unshielded core radioactive.
But the corona and bulk resistance losses scale with the voltage, so you end up losing more power this way.
Modification: Resistive losses go down as voltage goes up, for fixed power, because current is lower, resulting in a lower voltage drop for a fixed bulk resistance. But this holds for both DC and AC, so the net effect is nil.
Before anyone mentions skin effect for AC changing the effective resistance (making AC worse), at frequencies this low it's negligeable.
True, the anti-nuclear crowd are a bit dogmatic, you forget the real issue with nuclear power. Where do you plan to put the waste, huh? Yucca Mountain? You mean the storage facility on the quake fault line? Nice. :)
Anywhere in the continental shield would work, as long as you seal your bore-holes up with clay to prevent seepage. The shield has been stable for about 3 billion years.
Unfortunately DC power distribution is highly inefficient. When transmitting power down a long lenght of wire DC creates a much higher voltage drop (power loss) across the line than AC.
I don't see how this is the case. For both DC and AC signals, you have to worry about the bulk resistance of the cable, which dissipates roughly the same amount of energy in each case (off by a factor of sqrt(2) or so, but not by a vast amount).
For DC and AC, you lose due to corona discharge through the atmosphere, but the majority of your losses should be elsewhere.
For DC, that's it.
For AC, you get extra power loss from the fact that your power lines are emitting extremely low frequency (60 Hz) radio (they're antenae). The effect of this is fairly small, especially since you have multiple cables at different phases near each other (end up just storing power inductively between wires instead of radiating most of it).
For AC, you also have cable impedence due to the inductance of the cables. While this doesn't _waste_ power - just stores it on part of the cycle and returns it on another - it means that you need a higher voltage to drive a given amount of current across the wire (impedence of the cables goes up). But the corona and bulk resistance losses scale with the voltage, so you end up losing more power this way.
In summary, if anything, DC looks like it should lose _less_ power. I'm probably missing something, though, so if a power geek can elighten me, it would be appreciated.
My understanding was that DC had problems with local ground drifting relative to source ground.
That's one way. I remember when superconduction came on the scene. One of the ideas was an underground superconduction coil. Basically an induction coil, on a much bigger scale.
Energy density that can be stored in an inductor is much lower than the energy density of chemical fuels. This is especially true given that high-temperature superconductors break down at on the order of a 1 T magnetic field, but even without a superconducting breakdown field limit, tensile stress goes up enough to produce a limit that falls far short of chemical energy densities.
That's why fuel cells are so nice, even with something as annoying to store in bulk as hydrogen.
If hydrogen storage became a serious problem they could use methane as a fuel (with reforming cells), and burn the high-carbon reform byproducts with the hydrogen produced from electrolysis to get methane again, but that would arguably be more annoying than just storing the hydrogen.
This interesting technology could potentially lead to some better new-age energy sources. I'm not sure why we always focus on warfare, when there are other ways to use the explosive power of new military technology.
A gamma pulse is very useful as a weapon, but very hard to draw power from unless you put the gamma source inside a building-sized tank of water and run a steam turbine. This makes metastable isomers useless for compact power storage (the energy storage medium is compact, but you can't tap it with compact equipment).
As others have pointed out, this is not an energy _source_.
My basic question concerning this is two-fold, is this realy needed, and if it is created will we be able to control the techology. With world events the way they are now it seems like one of the last things that we end is a small high yeild weapon that can fall into the worng hands. At least with nuclear weapons there are some means of detecting their presence, but it seems that these weapons will not have the same signature.
The metastable isomers used for this type of weapon decay naturally - the new discovery is just a way to accelerate this decay so that it happens all at once. You can still detect the source material from its gamma ray glow (in much the same manner as you'd detect fissile material).
and if it is created will we be able to control the techology
Now that it's know to be feasible, whether the US develops it or not is irrelevant. Joe Random Terrorist State could look up the papers published on use of the effect for a power source tomorrow, and start their own bomb program.
Control, if required, is accomplished by making sure the states your concerned about don't build the equipment needed to produce the weapons (large and expensive equipment for all methods of producing the explosives, including charging by gamma excitation).
I hope the authours of this project do their homework. My impression is that most of the good search and indexing schemes have already been patented, which will make it difficult to release such a project without stepping on someone's toes.
Taking advantage of the fact that light emitted from a laptop display is naturally polarized to begin with, a 3D stereoscopic effect can be achieved by covering half the screen with a cellophane sheet in order to construct orthogonally polarized left and right scenes while the viewer wears eyeglasses holding two polarizers oriented 90 degrees apart...
You appear to have missed the parent poster's point.
If the images for each eye are on different halves of the screen, then polarizing is pointless. It removes phantom images, but the phantoms are far away from the real image, so there's no advantage to doing so.
Polarizing filters, as the parent poster pointed out, are useful when you have both images in the same place on the screen (overlapping). As overlapping images can't be distinguished by position, some other method is needed (polarization, colour, light direction, etc). When the images don't overlap, they can be distinguished without aids (just cross your eyes).
For years, we've heard about semiconductors the size of human hairs and how it would revolutionize the computing world.
I still see an AMD chip in my computer, and nice, large visible chips in the stores.
The same technology that allows you to produce an 8086 smaller than a grain of sand is what lets you run that AMD chip with its 38 million transistors. You _are_ using and reaping the benefits of this technology.
Pervasive, miniaturized electronics are showing up. Mainly the miniaturizationn is manifested in price (we can do today in a cheap 1-2mm^2 chip what would have taken a larger and much more expensive chip 5-10 years ago). However, the RFID tags that you have been hearing so much about require microprocessors to handle communication. "Pervasive" will certainly be the word to describe it in a few years.
So now it's diamonds? I'm not trying to troll, but when will mainstream applications (see: desktop computers, or at least universities) come around?
Universities have been studying diamond semiconductors for years. Where do you think all of the papers on them come from? Do you think papers are all based on theoretical models? Someone had to build doped diamond films before the electrical properties of them could be measured.
You won't see them on the desktop first. You'll see them in industry. There are many places where having a miniaturized control computer in an extreme environment would be quite useful (the oil industry was the example I'd heard about; with diamond semiconductors it's easier to monitor conditions in situ as you drill).