You can engage in copyright infringement as an act of civil disobedience because you disagree with the specifics of copyright law while still believing copyright infringement is wrong.
Rights and privileges are pretty much the same thing. If you try to interfere with my government-backed *privilege* to live, I expect the government to do something to stop you.
Yes, there will. The GPL requires things that would not be required if there were no copyright. For example, if I distribute binaries that were generated from modified GPLed code, I need to make the code available too. If there is no copyright, I don't need to do that, and there's nothing you can do about it.
No, the GPL takes rights away from everyone, just like copyright does, because GPL IS copyright. It's not a legal hack.
Not copyrighted is public domain. No license. Free to do whatever you want with it. You have all the rights, the creator has none. The GPL restricts those rights. Yes, it restricts particular rights that RMS disagrees are a good thing, but it restricts them nevertheless.
I've been to Nevada. As I recall it's somewhat less than 1600 km across.
You could bury the magnets, but you probably wouldn't want to walk, and especially not drive or fly anywhere near them.
You could theoretically build the launcher track across the US starting around New York and ending in New Mexico, with the elevated part in the foothills of the mountains. Only the elevated part would be really dangerous. But you'd have to buy a lot of decently expensive real estate. On the other hand, you could build it through the Sahara on land that some of the countries care so little about they don't even bother defining accurate borders. You'd also have a nice source of power there. As for locals... there aren't any.
We build things all the time in unstable parts of the world. It might even be easier in less developed countries - just grease a few palms and no civil liberties or freedom of movement to worry about. Someone you don't like gets too close to your expensive space launcher and you just disappear them.
In an emergency, yes, you could quench the superconductors and lower the track. You'd want to build somewhere where weather isn't much of a problem though (another vote for the desert). There's no such thing as a conductor carrying current sans magnet. It is a magnet.
I'm not sure if you think I'm wrong or you think I'm right but misunderstood what I said. I do not think it's possible, at this time, to directly (i.e. without causing two signals to interfere with each other) measure the phase of high frequency waves, EM or electron. IIRC people are starting to talk about doing direct phase measurement (sort of) with infrared. If you do think it's possible, and know of an example, I would be very interested to read about it.
The Sheffield people aren't measuring the phase of the electron wave directly (as you said). They're measuring relative phase using interference by arranging for multiple images from the scattering to interfere with each other, a la classic interferometric imaging. That's why their raw image is a Fourier spectrum.
I don't know the details of what they're doing, it's definitely not my specialty, but they are definitely not doing an EM version of optical phase contrast imaging as described by Zernike.
"Whilst the method and technology of acquisition is responsible for some of this I suspect a lot of it is researchers simply not knowing what is going on in other fields."
Yes... but adding to that, I think a lot of researchers are so tied up in their own terminology (like phase encoding spatial information) that they have trouble recognizing the same or similar processes described in other fields. I had never thought of MRI as interferometry until I had to look into it. Now when I teach it to graduate students I throw up a picture of the VLA and take five minutes to talk about the similarities.
We've all seen the pictures of interference patterns from a double slit experiment. But did you ever wonder what exactly that pattern is? Optical interference is a Fourier transform, so that pattern is the Fourier spectrum of the image of the light source, convolved with the spectrum of the slits! (or something like that - it's been a long day)
The only place where 4 tons is mentioned is in "a levitating force of about 4 tons per meter of cable length".
So the total force the cables need to support is less than this.
Have you never seen the equation F=MA.
I do have a certain familiarity with it, yes. Try as I might, I can't find a v in it anywhere. And you did specifically refer to speed in your post. You'll note that my post specifically said that the system needed to be designed for a sufficient acceleration.
Now that you mention it though, you also said there was a problem with sparks welding the shuttle to the rails. You know maglev trains don't use rails right? And sparks from superconducting coils? Maybe you've got some kind of link to back up that claim?
I'm getting the impression you're really not that solid on some of the basic ideas here. Certainly it would seem advisable to take a less smug know-it-all tone. Just on the off chance you might be wrong....
Nope, it shouldn't matter, although for putting things in orbit it's better to have it nearer the equator. The Sahara desert would be a good place.
Yes, the falloff from a long thing conductor is roughly linear. Making it wider probably wouldn't be as practical as adding more wires alongside the existing one to add more force.
Yes, you could theoretically land the track, but it would cost you a lot in electricity. Since it's a superconductor, once you get the thing up there, it only costs you energy to keep the wire cool. If you want to land the track you have to pull the power out of the superconducting wire, and then charge it up when you next want to fly. Unless you're going to be idle for a long time, it would probably be cheaper just to leave it charged. If it really can launch things to orbit for $100/kg or less, I think we'd quickly find it utilized to 100%.
I wasn't aware they did interferometric CT at synchrotrons. Cool.
Phase encoding spatial information, interferometry, different words, but they mean the same thing. You are literally measuring interference, thus interfer-ometry. The only distinction is that in MR you get to manipulate the source, which is a little harder in astronomy.
About ten years ago there were some quite enthusiastic researchers who were trying to do super-resolution MRI. Some thought it was the best thing since phase encoding, others thought it was all bunk. They were both kind of right. I knew a grad student who was about to get an srMRI project dumped on her and she was a little unsure about it, so we looked into it carefully. It turns out that most of the srMRI experiments were just doing sync interpolation in a very convoluted (he he, literally) way.
In optical super resolution microscopy you acquire data in the image domain and to do super resolution you shift in space by half a pixel and then, from the two images, can reconstruct a higher resolution image. So the srMRI people were acquiring their data then shifting the object in space... which doesn't give you anything. srMRI DOES work, but since you're acquiring in the Fourier domain you need to shift in the same domain - i.e. apply a phase ramp in the image domain. And what you end up with is higher resolution in the Fourier domain - greater field of view in the image domain. We couldn't think of a use for a synthetically enhanced field of view and the noise characteristics weren't particularly good so we didn't pursue it.
The connection with interferometry comes because one of the srMRI researchers tried to coin the term synthetic aperture MRI. Synthetic aperture radar is (more or less) a kind of interferometry where instead of two receivers you have one, moving receiver. Of course, since MRI is already interferometry, if you were to actually do synthetic aperture MR (or two-receiver interferometry MR) you'd end up imaging in the image domain.
Thanks. I'm in academia and, unlike some (definitely not all) of my colleagues I get a lot of satisfaction from sharing all the bits of esoteric knowledge I've gathered over the years. Seriously, the idea of measuring the light intensity at different distances from an all-white LCD occurred to me while I was replying to you. If you try it, let me know what result you get.
So what they refer to in the article is basically a long, thin superconducting wire 1600 km long, which is quite possible. There's one under New York right now. IIRC it's only about 7 miles long, but there really is no reason it shouldn't scale up. I think if they used a long line of individual coils the effect would be the same. Of course, in either case, the Earth is curved and the track isn't actually infinite (especially the part that needs the higher field to levitate the track) so your actual falloff will be worse than linear, but probably significantly better than inverse squared. If you did build a plane (which would be impractical) there would be no falloff (until you got high enough that the finite size of your plane came into play).
I'm sure this particular part got a lot of attention from the team at Sandia Labs who studied the proposal, and they must have checked the numbers pretty thoroughly. The article does give the proposed current through the wire though, so using that, some guesses about the mass of the track, and the height, you could make a rough estimate of what kind of falloff they're expecting.
I should have been more clear. There are several different types of interferometry. The one you're referring to measures the relative phase between a reference beam and a beam that's had something done to it (passing through a substance or travelling a different distance). Michelson and Morley, as you point out, is probably the most famous example. They were measuring (or trying to measure) very small differences in the time it took two light beams to travel the same distance, in different directions.
A different type of interferometry measures the size (or can be used to form an image) of objects. It's what the various forms of radio interferometers do. The oldest example I know of is, interestingly, attributed to the same Michelson: http://en.wikipedia.org/wiki/Michelson_stellar_interferometer. Note that the distinction here is that you make measurements at two (or more) different locations, combine the signals, and measure the interference pattern. You're not measuring what happened (or didn't happen) to the beam as it travelled, you're measuring things relating to the source of the signal. If you sample all the directions you end up with a Fourier spectrum that you can transform into an image.
A third type is synthetic aperture radar where you have one receiver but it's moving relative to the source. A fourth type is MRI, where you manipulate the phase of the source and measure... etc.
In your OP you asserted that what the researchers in the article are doing is the equivalent of phase contrast microscopy. It's not. Phase contrast microscopy, as you point out, is the first type of interferometry - measuring what happened to the beam as it travelled. What they're doing in the article appears to be (roughly) the second type - imaging the source of the signal via interferometry. A tipoff is that in phase contrast microscopy your signal is formed in the image domain - you can look into the microscope and see the image. In a radio or optical interferometer, or in this application, the signal is in the Fourier domain - you have to transform to get an image.
When I said that we can only recently directly measure (sort of) the phase of light, and only for low enough frequencies, I meant just that. All the types of interferometry we've both mentioned normally work using interference. In the first case you combine two beams of light and they interfere, giving you a measure of the relative phase. In the second, you combine signals from two spatially separated receivers and they interfere, giving you a Fourier spectrum (and thus a more complicated measure of relative phase). Recently, as in, not in Michelson's time, if the signal is low enough frequency you can use electronics to measure the phase directly - a 60 Hz household electrical supply, for example. You don't need to cause two signals to interfere, you just measure the phase directly. Even more recently, radio astronomers who wanted to put their telescopes so far apart it was impractical to run a cable between them have figured out how to directly (sort of) measure the phase of higher frequency signals, allowing very long baseline interferometry (VLBI): http://en.wikipedia.org/wiki/Very_Long_Baseline_Interferometry.
So basically, when you said "it's not a type of interferometry as they don't measure phase-shifts directly" I didn't realize that you weren't familiar with the second type of interferometry and assumed you meant it wasn't interferometry because they didn't directly measure the phase, but instead used interference to indirectly measure it.
"Both black, flat, rounded-rectangles with a touchscreen that covers substantially the whole front of the device."
What does his UI look like? Apple is suing Samsung based on the look and feel of their device being too close to the iPad. They're NOT suing lots of other tablet manufacturers who make tablets that look very similar because they either a) aren't quite the same in hardware design or b) aren't quite the same in UI.
There was a good article illustrating, using tablets from makers that are not being sued by Apple, what Samsung would have had to have done. The conclusion was it would have taken a mediocre designer about ten minutes to come up with something sufficiently different from the iPad yet still perfectly functional.
The tablet in the video, for example, looks more like any number of other tablets that are not the subject of lawsuits than it looks like an iPad. Resistive stylus, different size bezel, bezel not at the same level as the screen, uneven bezel, no silver trim around the edges, different corner radius, completely different UI.
"Apple is suing Samsung to set a precedent where if they win, it gives the ability to go after other manufacturers who have similar designs and demand licensing fees with a threat of a lawsuit if those companies don't pay for the licensing fee."
That's the argument the OP made up, yes. There's nothing to support it. In fact, since Apple isn't suing Samsung for ALL their designs that look similar to iPads and iPhones, just the ones most similar, it seems unlikely.
Most (all?) interpreted languages let you do this. I remember a WWDC demo from almost a decade ago where they demonstrated changing running Objective-C code and seeing the result live. I'm sure there are older examples.
I think I pay something like $20 a month for a bunch of extras that I never use, but it's the only way I can get the texting plan, which is something like 1000 texts. That's two cents a text. A text message is 160 characters, which, as far as the end user is concerned, is 160 bytes, so that's $131 / MB. Kind of expensive, even on the plan, hey? Now, I only notice a difference in price if I can cancel the texting plan. It's getting very close.
I sure as hell notice the difference when I travel outside the country though. Instead of paying $0.50 - $1.00 per text it's about a hundredth of a cent per text, even with the extortionate data roaming fees, or free if I'm using wifi.
That's part of it. Virtualization and remote desktop servers also help. When I first started my PhD we used Macs because they could run all the unixy software we needed and still had Office so we could share documents. There was some software that was Windows only though, and it was a huge pain. About halfway through we bought a server to run Windows and used remote desktops whenever we needed to run something on Windows. Now you'd just make virtual machines on the server, or on your local machine, as needed.
Electric fields and EM waves do the same thing, except it's a little harder to make an electric field that shape.
The size of the light source does matter. If you're very close to the sun the falloff in intensity is NOT inverse squared. Think about it. As you get further away, the falloff of light from the points directly beneath you is inverse squared. But as you move higher, your horizon expands, so you're illuminated by more of the sun's surface. Technically the falloff isn't inverse squared even at Earth because the sun still shows a disk, but it's close enough not to matter. If you've got an omnidirectional light meter and you're careful, you can probably demonstrate it with a big computer monitor or TV.
There is no decrease in intensity from an infinite plane by the way. Demonstrating that (and the infinite line case) are usually problems in first or second year calculus and/or electromagnetics.
"I think getting your friends to buy an iDevice is a *tad* more burdensome than getting them to use their free gmail acount...."
No, you've missed the point. If the person you're texting has an idevice, your message will be sent through iMessage. If he doesn't, it will be sent via conventional SMS. Completely transparently. You don't have to get your friends to buy idevices. The only reason people use SMS is that everyone has it. iMessage capitalizes on that by using SMS as a transparent failover while all the other text/IM programs try to replace it. It's also always on, just like SMS, and unlike IM programs.
I have What's App, Skype, GTalk, MSN, Yahoo, generic Jabber, and a few other accounts (only a couple people I know have AIM accounts). I even have an app that ties most of them together. Those are great for longer, arranged conversations, usually typing on the computer, but almost never get used for the same things as SMS.
Slashdot Mirror
You can engage in copyright infringement as an act of civil disobedience because you disagree with the specifics of copyright law while still believing copyright infringement is wrong.
Rights and privileges are pretty much the same thing. If you try to interfere with my government-backed *privilege* to live, I expect the government to do something to stop you.
Yes, there will. The GPL requires things that would not be required if there were no copyright. For example, if I distribute binaries that were generated from modified GPLed code, I need to make the code available too. If there is no copyright, I don't need to do that, and there's nothing you can do about it.
No, the GPL takes rights away from everyone, just like copyright does, because GPL IS copyright. It's not a legal hack.
Not copyrighted is public domain. No license. Free to do whatever you want with it. You have all the rights, the creator has none. The GPL restricts those rights. Yes, it restricts particular rights that RMS disagrees are a good thing, but it restricts them nevertheless.
I've been to Nevada. As I recall it's somewhat less than 1600 km across.
You could bury the magnets, but you probably wouldn't want to walk, and especially not drive or fly anywhere near them.
You could theoretically build the launcher track across the US starting around New York and ending in New Mexico, with the elevated part in the foothills of the mountains. Only the elevated part would be really dangerous. But you'd have to buy a lot of decently expensive real estate. On the other hand, you could build it through the Sahara on land that some of the countries care so little about they don't even bother defining accurate borders. You'd also have a nice source of power there. As for locals... there aren't any.
The Kessel run was 16 parsecs through real space, was it? Uh huh.
We build things all the time in unstable parts of the world. It might even be easier in less developed countries - just grease a few palms and no civil liberties or freedom of movement to worry about. Someone you don't like gets too close to your expensive space launcher and you just disappear them.
No, the magnetic field from a long conductor falls of linearly. If you don't believe me, do the math, do the experiment or here's a web page that gives the formula (note, no exponents): http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/wirfor.html. The magnetic force from a plane does not decrease with distance: http://en.wikipedia.org/wiki/Current_sheet#Magnetic_field_of_an_infinite_current_sheet
In an emergency, yes, you could quench the superconductors and lower the track. You'd want to build somewhere where weather isn't much of a problem though (another vote for the desert). There's no such thing as a conductor carrying current sans magnet. It is a magnet.
I'm not sure if you think I'm wrong or you think I'm right but misunderstood what I said. I do not think it's possible, at this time, to directly (i.e. without causing two signals to interfere with each other) measure the phase of high frequency waves, EM or electron. IIRC people are starting to talk about doing direct phase measurement (sort of) with infrared. If you do think it's possible, and know of an example, I would be very interested to read about it.
The Sheffield people aren't measuring the phase of the electron wave directly (as you said). They're measuring relative phase using interference by arranging for multiple images from the scattering to interfere with each other, a la classic interferometric imaging. That's why their raw image is a Fourier spectrum.
I don't know the details of what they're doing, it's definitely not my specialty, but they are definitely not doing an EM version of optical phase contrast imaging as described by Zernike.
"Whilst the method and technology of acquisition is responsible for some of this I suspect a lot of it is researchers simply not knowing what is going on in other fields."
Yes... but adding to that, I think a lot of researchers are so tied up in their own terminology (like phase encoding spatial information) that they have trouble recognizing the same or similar processes described in other fields. I had never thought of MRI as interferometry until I had to look into it. Now when I teach it to graduate students I throw up a picture of the VLA and take five minutes to talk about the similarities.
We've all seen the pictures of interference patterns from a double slit experiment. But did you ever wonder what exactly that pattern is? Optical interference is a Fourier transform, so that pattern is the Fourier spectrum of the image of the light source, convolved with the spectrum of the slits! (or something like that - it's been a long day)
So the total force the cables need to support is less than this.
I do have a certain familiarity with it, yes. Try as I might, I can't find a v in it anywhere. And you did specifically refer to speed in your post. You'll note that my post specifically said that the system needed to be designed for a sufficient acceleration.
Now that you mention it though, you also said there was a problem with sparks welding the shuttle to the rails. You know maglev trains don't use rails right? And sparks from superconducting coils? Maybe you've got some kind of link to back up that claim?
I'm getting the impression you're really not that solid on some of the basic ideas here. Certainly it would seem advisable to take a less smug know-it-all tone. Just on the off chance you might be wrong....
Capitalism seems to have produced that effect.
Nope, it shouldn't matter, although for putting things in orbit it's better to have it nearer the equator. The Sahara desert would be a good place.
Yes, the falloff from a long thing conductor is roughly linear. Making it wider probably wouldn't be as practical as adding more wires alongside the existing one to add more force.
Yes, you could theoretically land the track, but it would cost you a lot in electricity. Since it's a superconductor, once you get the thing up there, it only costs you energy to keep the wire cool. If you want to land the track you have to pull the power out of the superconducting wire, and then charge it up when you next want to fly. Unless you're going to be idle for a long time, it would probably be cheaper just to leave it charged. If it really can launch things to orbit for $100/kg or less, I think we'd quickly find it utilized to 100%.
I wasn't aware they did interferometric CT at synchrotrons. Cool.
Phase encoding spatial information, interferometry, different words, but they mean the same thing. You are literally measuring interference, thus interfer-ometry. The only distinction is that in MR you get to manipulate the source, which is a little harder in astronomy.
About ten years ago there were some quite enthusiastic researchers who were trying to do super-resolution MRI. Some thought it was the best thing since phase encoding, others thought it was all bunk. They were both kind of right. I knew a grad student who was about to get an srMRI project dumped on her and she was a little unsure about it, so we looked into it carefully. It turns out that most of the srMRI experiments were just doing sync interpolation in a very convoluted (he he, literally) way.
In optical super resolution microscopy you acquire data in the image domain and to do super resolution you shift in space by half a pixel and then, from the two images, can reconstruct a higher resolution image. So the srMRI people were acquiring their data then shifting the object in space... which doesn't give you anything. srMRI DOES work, but since you're acquiring in the Fourier domain you need to shift in the same domain - i.e. apply a phase ramp in the image domain. And what you end up with is higher resolution in the Fourier domain - greater field of view in the image domain. We couldn't think of a use for a synthetically enhanced field of view and the noise characteristics weren't particularly good so we didn't pursue it.
The connection with interferometry comes because one of the srMRI researchers tried to coin the term synthetic aperture MRI. Synthetic aperture radar is (more or less) a kind of interferometry where instead of two receivers you have one, moving receiver. Of course, since MRI is already interferometry, if you were to actually do synthetic aperture MR (or two-receiver interferometry MR) you'd end up imaging in the image domain.
Thanks. I'm in academia and, unlike some (definitely not all) of my colleagues I get a lot of satisfaction from sharing all the bits of esoteric knowledge I've gathered over the years. Seriously, the idea of measuring the light intensity at different distances from an all-white LCD occurred to me while I was replying to you. If you try it, let me know what result you get.
So what they refer to in the article is basically a long, thin superconducting wire 1600 km long, which is quite possible. There's one under New York right now. IIRC it's only about 7 miles long, but there really is no reason it shouldn't scale up. I think if they used a long line of individual coils the effect would be the same. Of course, in either case, the Earth is curved and the track isn't actually infinite (especially the part that needs the higher field to levitate the track) so your actual falloff will be worse than linear, but probably significantly better than inverse squared. If you did build a plane (which would be impractical) there would be no falloff (until you got high enough that the finite size of your plane came into play).
I'm sure this particular part got a lot of attention from the team at Sandia Labs who studied the proposal, and they must have checked the numbers pretty thoroughly. The article does give the proposed current through the wire though, so using that, some guesses about the mass of the track, and the height, you could make a rough estimate of what kind of falloff they're expecting.
I should have been more clear. There are several different types of interferometry. The one you're referring to measures the relative phase between a reference beam and a beam that's had something done to it (passing through a substance or travelling a different distance). Michelson and Morley, as you point out, is probably the most famous example. They were measuring (or trying to measure) very small differences in the time it took two light beams to travel the same distance, in different directions.
A different type of interferometry measures the size (or can be used to form an image) of objects. It's what the various forms of radio interferometers do. The oldest example I know of is, interestingly, attributed to the same Michelson: http://en.wikipedia.org/wiki/Michelson_stellar_interferometer. Note that the distinction here is that you make measurements at two (or more) different locations, combine the signals, and measure the interference pattern. You're not measuring what happened (or didn't happen) to the beam as it travelled, you're measuring things relating to the source of the signal. If you sample all the directions you end up with a Fourier spectrum that you can transform into an image.
A third type is synthetic aperture radar where you have one receiver but it's moving relative to the source. A fourth type is MRI, where you manipulate the phase of the source and measure... etc.
In your OP you asserted that what the researchers in the article are doing is the equivalent of phase contrast microscopy. It's not. Phase contrast microscopy, as you point out, is the first type of interferometry - measuring what happened to the beam as it travelled. What they're doing in the article appears to be (roughly) the second type - imaging the source of the signal via interferometry. A tipoff is that in phase contrast microscopy your signal is formed in the image domain - you can look into the microscope and see the image. In a radio or optical interferometer, or in this application, the signal is in the Fourier domain - you have to transform to get an image.
When I said that we can only recently directly measure (sort of) the phase of light, and only for low enough frequencies, I meant just that. All the types of interferometry we've both mentioned normally work using interference. In the first case you combine two beams of light and they interfere, giving you a measure of the relative phase. In the second, you combine signals from two spatially separated receivers and they interfere, giving you a Fourier spectrum (and thus a more complicated measure of relative phase). Recently, as in, not in Michelson's time, if the signal is low enough frequency you can use electronics to measure the phase directly - a 60 Hz household electrical supply, for example. You don't need to cause two signals to interfere, you just measure the phase directly. Even more recently, radio astronomers who wanted to put their telescopes so far apart it was impractical to run a cable between them have figured out how to directly (sort of) measure the phase of higher frequency signals, allowing very long baseline interferometry (VLBI): http://en.wikipedia.org/wiki/Very_Long_Baseline_Interferometry.
So basically, when you said "it's not a type of interferometry as they don't measure phase-shifts directly" I didn't realize that you weren't familiar with the second type of interferometry and assumed you meant it wasn't interferometry because they didn't directly measure the phase, but instead used interference to indirectly measure it.
"Both black, flat, rounded-rectangles with a touchscreen that covers substantially the whole front of the device."
What does his UI look like? Apple is suing Samsung based on the look and feel of their device being too close to the iPad. They're NOT suing lots of other tablet manufacturers who make tablets that look very similar because they either a) aren't quite the same in hardware design or b) aren't quite the same in UI.
There was a good article illustrating, using tablets from makers that are not being sued by Apple, what Samsung would have had to have done. The conclusion was it would have taken a mediocre designer about ten minutes to come up with something sufficiently different from the iPad yet still perfectly functional.
The tablet in the video, for example, looks more like any number of other tablets that are not the subject of lawsuits than it looks like an iPad. Resistive stylus, different size bezel, bezel not at the same level as the screen, uneven bezel, no silver trim around the edges, different corner radius, completely different UI.
"Apple is suing Samsung to set a precedent where if they win, it gives the ability to go after other manufacturers who have similar designs and demand licensing fees with a threat of a lawsuit if those companies don't pay for the licensing fee."
That's the argument the OP made up, yes. There's nothing to support it. In fact, since Apple isn't suing Samsung for ALL their designs that look similar to iPads and iPhones, just the ones most similar, it seems unlikely.
Most (all?) interpreted languages let you do this. I remember a WWDC demo from almost a decade ago where they demonstrated changing running Objective-C code and seeing the result live. I'm sure there are older examples.
Not new.
I think I pay something like $20 a month for a bunch of extras that I never use, but it's the only way I can get the texting plan, which is something like 1000 texts. That's two cents a text. A text message is 160 characters, which, as far as the end user is concerned, is 160 bytes, so that's $131 / MB. Kind of expensive, even on the plan, hey? Now, I only notice a difference in price if I can cancel the texting plan. It's getting very close.
I sure as hell notice the difference when I travel outside the country though. Instead of paying $0.50 - $1.00 per text it's about a hundredth of a cent per text, even with the extortionate data roaming fees, or free if I'm using wifi.
And higher usage costs.
That's part of it. Virtualization and remote desktop servers also help. When I first started my PhD we used Macs because they could run all the unixy software we needed and still had Office so we could share documents. There was some software that was Windows only though, and it was a huge pain. About halfway through we bought a server to run Windows and used remote desktops whenever we needed to run something on Windows. Now you'd just make virtual machines on the server, or on your local machine, as needed.
Electric fields and EM waves do the same thing, except it's a little harder to make an electric field that shape.
The size of the light source does matter. If you're very close to the sun the falloff in intensity is NOT inverse squared. Think about it. As you get further away, the falloff of light from the points directly beneath you is inverse squared. But as you move higher, your horizon expands, so you're illuminated by more of the sun's surface. Technically the falloff isn't inverse squared even at Earth because the sun still shows a disk, but it's close enough not to matter. If you've got an omnidirectional light meter and you're careful, you can probably demonstrate it with a big computer monitor or TV.
There is no decrease in intensity from an infinite plane by the way. Demonstrating that (and the infinite line case) are usually problems in first or second year calculus and/or electromagnetics.
"Actually, Imessage will turn into a text message and charge the receiver(or take it off of their text package) if they are not using an iPhone."
Yes, that's what I said.
"But it still takes off of their data plan."
Which, even at the worst overage rates is essentially free.
"Apple TV does it wirelessly, though, which is far more convenient."
Thus, the equivalent of an adapter.
"I think getting your friends to buy an iDevice is a *tad* more burdensome than getting them to use their free gmail acount...."
No, you've missed the point. If the person you're texting has an idevice, your message will be sent through iMessage. If he doesn't, it will be sent via conventional SMS. Completely transparently. You don't have to get your friends to buy idevices. The only reason people use SMS is that everyone has it. iMessage capitalizes on that by using SMS as a transparent failover while all the other text/IM programs try to replace it. It's also always on, just like SMS, and unlike IM programs.
I have What's App, Skype, GTalk, MSN, Yahoo, generic Jabber, and a few other accounts (only a couple people I know have AIM accounts). I even have an app that ties most of them together. Those are great for longer, arranged conversations, usually typing on the computer, but almost never get used for the same things as SMS.