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Elephant posted:Lasers carrying momentum/energy (and how much they carry) is a direct result of the theory of relativity. You need relativity to describe how a laser can have momentum, and how much energy it carries. No, you really don't need relativity to describe a laser. You need a quantum mechanical representation of electrons and light matter interactions but none of the systems need the relativistic Schrodinger equation to be represented. You can derive the phase matching geometry, the population inversion and stimulated emission with non-relativeistic theory.
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Jan 31, 2016 08:30
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Portable access to a decent, up-to-date encyclopedia and general knowledge such as first aid, maps, etc, on demand is pretty amazing. Not quite the same as "the sum of human knowledge," but not bad for something that I couldn't even afford to access before I was 16.
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Jan 31, 2016 08:37
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The whole instant access to the sum of human knowledge thing is also significantly affecting the day-to-day of medicine. You're on rounds, and a particular question comes up for a patient. Pull out your phone, and you have all your guidelines to inform your clinical decision making. 20-30 years ago, that wouldn't have worked. Guidelines can be rapidly updated, rapidly implemented, and far more detailed than before now that we aren't relying just on human memory. I don't need to remember an entire complex dosing regimen or decision flowchart for a condition--just that it exists and where to look it up. It allows me to be more efficient.
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Jan 31, 2016 09:00
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WhiskeyJuvenile posted:Because it's qualitatively different than "we used to have to burn whale oil and now we have electricity" or "we used to die and now we have vaccines" Have you tried an oil lamp? It puts out a white light that makes things visible and casts a shadow and such, just like the light from a light bulb. Light bulbs put out that same light without taking 10-20 seconds to light, which I mean, is better I guess, but it's not really different.
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Jan 31, 2016 09:09
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silence_kit posted:It's like telling a structural engineer that he really needs to know quantum mechanics to be able to do his job well. Quantum mechanics doesn't inform him on how to design a bridge. If QM had never existed, it wouldn't have changed how the structural engineer designs bridges. Or for a more extreme example, it's like telling biologists that all of their work hinges on the existence of the Higgs Boson or some other fundamental particle that physicists spend their entire careers trying to find. But that's totally absurd. If no one had ever worried about the Higgs Boson, our understanding of biology would not have been any different. This is a bit disingenuous - of course a structural engineer doesn't need to know about quantum mechanics. He or she is working with macro-scale objects that are described perfectly well by Newtonian physics because the wrinkles that QM adds to those equations are effectively nil at those scales. If, however, our prospective structural engineer decided one day to design incredibly small objects using Newtonian physics, then all of a sudden, QM would be incredibly relevant to his or her job. Same would hold true if her or she decided to start looking into using lasers for most practical applications - you need to understand how materials absorb laser light before you can understand which laser to use. Granted, you could simply purchase a wide spectrum of lasers and see which one is preferentially absorbed, but that's prohibitively expensive and it's a lot more effective to look at the material's absorption spectrum and choose a laser based on that. But yeah, long story short is that absorption/emission of photons is entirely described by quantum mechanics and is required for effective design and usage of a laser. It does you no good whatsoever to try to use a powerful laser to cut something if the material you're trying to cut reflects the wavelength of laser you're using. It can also be incredibly dangerous if you're trying to design a laser for, say, laser eye surgery, and you screw up and choose a laser that targets the cones in the eye instead of the cornea you actually want to reshape.
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Jan 31, 2016 09:12
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Dirk the Average posted:But yeah, long story short is that absorption/emission of photons is entirely described by quantum mechanics and is required for effective design and usage of a laser. It does you no good whatsoever to try to use a powerful laser to cut something if the material you're trying to cut reflects the wavelength of laser you're using. It can also be incredibly dangerous if you're trying to design a laser for, say, laser eye surgery, and you screw up and choose a laser that targets the cones in the eye instead of the cornea you actually want to reshape. Most laser cutters just use a big fuckoff CO2 laser and will cut anything regardless of the extinction.
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Jan 31, 2016 09:16
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Bip Roberts posted:Most laser cutters just use a big fuckoff CO2 laser and will cut anything regardless of the extinction. Fair enough, I was thinking more along the lines of surgeries where your choice of laser is actually important (too much excess heat/heat in the wrong place does very bad things to the body). It's also important for imaging applications.
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Jan 31, 2016 09:28
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silence_kit posted:Does this level of description actually benefit you when trying to describe how a laser works? This is what I'm asking. What feature of lasers requires relativity to exist? Of course, I'm sure that there are things in solid state physics that require relativity to be explained. Are lasers one of them? It's not important for a layman's understanding of how a laser works, if that's what you're asking. But special relativity is fundamental to condensed matter physics, which allowed us to actually build the semiconductor lasers that you brought up. quote:It's like telling a structural engineer that he really needs to know quantum mechanics to be able to do his job well. It's not like that at all. I even explicitly said that you don't really need to invoke special relativity for industrial laser research, and that it's more of a cornerstone rather than something that you have to sit there thinking about. It's more like telling a car mechanic about the importance of thermodynamics in the development of automobiles. Better yet, it's more like telling a computer scientist that modern computers wouldn't exist without quantum mechanics. This person doesn't need to understand quantum mechanics, and you don't need quantum mechanics to build a basic "computer", but it's still really important to this field that quantum mechanics exists. quote:Quantum mechanics doesn't inform him on how to design a bridge. If QM had never existed, it wouldn't have changed how the structural engineer designs bridges. Or for a more extreme example, it's like telling biologists that all of their work hinges on the existence of the Higgs Boson or some other fundamental particle that physicists spend their entire careers trying to find. But that's totally absurd. If no one had ever worried about the Higgs Boson, our understanding of biology would not have been any different. More realistically, a lot of the tools that the structural engineer uses (like his loving computer) wouldn't exist without quantum mechanics. So if QM had never existed, then yes, his job would actually be quite different, although not for direct reasons. We're extremely off-topic at this point.
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Jan 31, 2016 09:52
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Phyzzle posted:Have you tried an oil lamp? It puts out a white light that makes things visible and casts a shadow and such, just like the light from a light bulb. Light bulbs put out that same light without taking 10-20 seconds to light, which I mean, is better I guess, but it's not really different. Anyway the Industrial Revolution also impoverished and immiserated huge numbers of people so we may just be in a transitional phase, though it sure does kind of suck for a lot of folks.
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Jan 31, 2016 09:59
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QuarkJets posted:Since you're a bit slow, let me make what I'm doing more clear. I personally agree that washing machines provide economic value to the people that use them. I'm pointing out that Pedro has made some false assertions and that he has now accidentally contradicted himself: There is no contradiction. I just should have explained myself more. The difference between the example of the washing machine and the example of Youtube is that the washing machine is creating free time. Youtube isn't. It is merely occupying the free time you already have. As I said earlier, since life is largely organized around labor of one kind of another, anything that changes that distribution of labor and the work you need to do has a much higher chance of having a substantial, noticeable effect in your life than something which doesn't. I guess you think the contradiction is saying "change isn't how you spend the time you have ..", but the point is that some technology changes the time you have. A Wizard of Goatse posted:I work every day with guys from California from my office, a bar in Virginia (or possibly bed if I don't feel like getting up and putting pants on yet) and spend the spare minutes between tasks where I'm not actually busy speccing out parts for machines you'd have needed a multimillion-dollar factory to produce 20 years ago but I do in my basement for fun. My boss is actually only about 40 miles away but we've met in person like twice because why bother. But yeah nothing big's changed about the way we do work since my dad was my age and people still couldn't figure out how to synchronize two clocks if one was moving, where's my flying car dammit The vast majority of people in the first world don't telecommute. They go to their work, and they know their boss. And it's not simply cultural. It's because technology hasn't actually made it possible that most jobs don't require a person to do physical tasks of some sort. I don't know if your comment about the multi-million dollar factory is referring to 3d printers, but that is a good example of technology affecting modern life or not. When people talk about 'the 3d printing revolution', they're talking about the idea that the traditional industrial process of producing, transporting, and obtaining factory-made products will be completely upended and that now people will simply 3d-print what they want at home. They're not really thinking 'cool, I can make stuff in my basement for fun'. Beowulfs_Ghost posted:It is weird how some of the technology of the past couple decades is clearly and measurably improved, but we can also be so unimpressed by it. And measurably unimpressed. Like the earlier example of having the power of a Cray Supercomputer in our hands. Hell, given to children as Christmas presents. We use to use that sort of computer power to solve serious problems, and now we use it to play Candy Crush on the toilet. The impressive thing about computers isn't just that they exist, is what we do with them. If you are thinking about their abiliy to be used for playing games or watching movies, then of course it's not going to seem very impressive. Pedro De Heredia fucked around with this message at 10:27 on Jan 31, 2016 |
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Jan 31, 2016 10:24
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Pedro De Heredia posted:There is no contradiction. I just should have explained myself more. The mechanization of labor in the early 20th century had obvious measurable effects. The dissemination of information in the late 20th century had more abstract effects. Electrical stoves are clearly more convenient than wood burning stoves. I can measure how long it takes to split the wood, carry it to the stove etc. The whole process can be reduced to a flow chart. Conversely having a huge amount of information instantaneously available is more convenient than relying on the books I can afford or is available in the local library. It does not primarily afford you more time but rather greater opportunity. Prices can be compared and products reviewed allowing you to make informed choices. You can develop and maintain valuable networks on the fly and strike deals quickly. You can get a basic grasp of any subject from canoe construction to stock investment while sitting on the bus. Every job ad and company profile is available when you want it. You can solve problems with people from across the globe without ever meeting them. The effects are different and comparing them is not necessarily useful. If the measure of technological advancement is the amount of work saved then there's only marginal advances left until there is none at all. It is not, I think, fair to set it up in that way. I don't know how to compare it and I don't know that we can but the proliferation of the internet and personal computers have absolutely made life easier in a number of ways.
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Jan 31, 2016 11:40
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I don't disagree with a lot of what you just said, but the effects you are talking about don't sound all that abstract and we should be able to measure them directly or indirectly.
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Jan 31, 2016 11:51
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You can calculate ballistic trajectories without calculus but you can't go to the moon with that math.
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Jan 31, 2016 14:44
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Technological decline? how can you look at this and tell me the future isn't bright?
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Jan 31, 2016 14:55
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Ra Ra Rasputin posted:Technological decline? how can you look at this and tell me the future isn't bright? 
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Jan 31, 2016 15:35
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Ra Ra Rasputin posted:Technological decline? how can you look at this and tell me the future isn't bright? We need to do something about all the people too lazy/stupid to develop economically useful STEM skills. This seems like a humane form of population control to prevent stagnation/decline.
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Jan 31, 2016 15:42
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I think people are still missing the original point and arguing only one leg of support that the original author presented, basically a retrospective of technology. Giving one or two specific examples doesn't really show that economic growth will continue as it has been. I really hate these cherry picked futurology graphs. - It seems more of a function of size of the object than decade of invention. Radio has a similar slope to more 'late-model' inventions. - The slopes of techs that take a long time to adopt don't suddenly accelerate in later decades (or even just push as a linear trend), continue to follow the slow down at the asymptote - 2005 is picked where it looks like computer has a downturn, and lol VCRs (though I dunno when this was made) - No large-form techs are selected for the recent inventions, like home PV or EV charging stations. People really champion that information can be found anytime now with smartphones, but Home PV means you can turn your private home into an electricity producer, which is also bad rear end yet I doubt the adoption slope is very steep. Another tech I'd like to see is home sumps. - Another cause of the uptick of slopes in the later half of the graph may be due to the overall increase of the US economy after WWII relative the world. If you had the worldwide adoption of these things, it would be seriously different. Clothes dryers are still really rare in many developed countries.
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Jan 31, 2016 16:54
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Uncle Jam posted:I think people are still missing the original point and arguing only one leg of support that the original author presented, basically a retrospective of technology. Giving one or two specific examples doesn't really show that economic growth will continue as it has been. Nothing will show that, and it's boring to try to discuss that.
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Jan 31, 2016 17:44
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Bip Roberts posted:No, you really don't need relativity to describe a laser. You need a quantum mechanical representation of electrons and light matter interactions but none of the systems need the relativistic Schrodinger equation to be represented. You can derive the phase matching geometry, the population inversion and stimulated emission with non-relativeistic theory. Yeah, what I'm asking QuarkJets is whether there are some features of lasers which require relativity to be explained. He is just obfuscating things by bringing up extra formalisms which are required in modern solid state physics to explain more unusual things. He has not answered my pretty direct question after many posts in this exchange. Dirk the Average posted:This is a bit disingenuous - of course a structural engineer doesn't need to know about quantum mechanics. He or she is working with macro-scale objects that are described perfectly well by Newtonian physics because the wrinkles that QM adds to those equations are effectively nil at those scales. Look, I'm not accepting this kind of reasoning. Structural engineers do not design bridges for Rick Moranis in Honey I shrunk the Kids. The fact that QM is a generalization isn't interesting to the structural engineer because it doesn't really inform him on how to design bridges. Before you bring it up, I am not questioning whether the theory of quantum mechanics has borne technological fruit. What I am asking is whether relativistic physics is essential to certain technologies. Relativity providing a one part in a million or whatever correction to GPS calculations is not very impressive, sorry. That's kind of embarrassing if that is the killer app of the theory of relativity. QuarkJets posted:It's not important for a layman's understanding of how a laser works, if that's what you're asking. But special relativity is fundamental to condensed matter physics, which allowed us to actually build the semiconductor lasers that you brought up. How? What about semiconductor lasers could not have been done without special relativity? Edit: I found this quote from Sheldon Glashow: ”Modern elementary–particle physics is founded upon the two pillars of quantum mechanics and relativity. I have made little mention of relativity so far because, while the atom is very much a quantum system, it is not very relativistic at all. Relativity becomes important only when velocities become comparable to the speed of light. Electrons in atoms move rather slowly, at a mere of one percent of light speed. Thus it is that a satisfactory description of the atom can be obtained without Einstein’s revolutionary theory.” Basically, what I am asking here is why is he wrong here in the case of lasers? silence_kit fucked around with this message at 20:08 on Jan 31, 2016 |
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Jan 31, 2016 19:39
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silence_kit posted:Look, I'm not accepting this kind of reasoning. Structural engineers do not design bridges for Rick Moranis in Honey I shrunk the Kids. The fact that QM is a generalization isn't interesting to the structural engineer because it doesn't really inform him on how to design bridges. We're more or less in agreement on that - QM has very little impact on structural engineering. It is, however, about as relevant as stating that evolution has no impact on structural engineering though. There are quite a few engineering disciplines that do use QM (or technology/principles derived from QM) on a regular basis though. Ask an electrical, chemical, or biomedical engineer how relevant QM is to their job and you're likely to get a far different answer.
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Jan 31, 2016 19:55
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Dirk the Average posted:We're more or less in agreement on that - QM has very little impact on structural engineering. It is, however, about as relevant as stating that evolution has no impact on structural engineering though. Oh, I put in an edit: silence_kit posted:Before you bring it up, I am not questioning whether the theory of quantum mechanics has borne technological fruit. What I am asking is whether relativistic physics is essential to certain technologies. Relativity providing a one part in a million or whatever correction to GPS calculations is not very impressive, sorry. That's kind of embarrassing if that is the killer app of the theory of relativity.
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Jan 31, 2016 20:13
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silence_kit posted:Oh, I put in an edit: Are you Andy Schlafly?
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Jan 31, 2016 20:16
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McDowell posted:Are you Andy Schlafly? You know, saying that a relativistic correction to the physics at room temperature, low velocity (which is where our current microelectronic devices operate) is exceedingly small is not the same as denying the existence of relativity.
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Jan 31, 2016 20:21
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In response to OP: No, we have just hit a wall with certain technology until we can exploit more extreme laws of physics to get around those limits. The latter may or may not be possible but there are signs it is (quantum computing etc). Quantum computing alone will open up solutions to problems that classical computers are incapable of solving in a reasonable time frame, just as a single example. We live in an unparalleled age of technological progress for all societies, if you don't think this you are looking in the wrong places.
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Jan 31, 2016 20:27
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silence_kit posted:Oh, I put in an edit: The "killer app" of relativity is literally the most killer app we've ever discovered: E=mc^2.
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Jan 31, 2016 20:28
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McDowell posted:Are you Andy Schlafly? I'm not questioning whether it is true. I am questioning whether it is as important to technology as Quarkjets claims. All I want is a non-inflated evaluation of the technological applications.
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Jan 31, 2016 20:31
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Also relativity affects GPS more than 1 in a million, you would be off by kilometers very quickly if we stopped accounting for it. - http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html
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Jan 31, 2016 21:00
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silence_kit posted:All I want is a non-inflated evaluation of the technological applications. And you got one. GPS literally does not work without relativity. EFB
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Jan 31, 2016 21:13
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silence_kit posted:How? What about semiconductor lasers could not have been done without special relativity? Thanks to SR, we know that a static electric field looks like an electric field plus a magnetic field when you're moving through it. Without SR, you wouldn't be able to accurately predict the behavior of electrons in a semiconductor. You also wouldn't have any of the important CM results that were derived from the Dirac Equation quote:Edit: I found this quote from Sheldon Glashow: He's not; you can satisfactorily describe a laser without relativity. This is something that I've said already. You don't need relativity to describe generally how lasers work, nor do you need relativity to describe satisfactorily how gravity works. But without a solid understanding of condensed matter physics, which includes a number of nods from special relativity, you won't ever reach the point where you can build a semiconductor laser.
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Jan 31, 2016 21:20
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silence_kit posted:He has not answered my pretty direct question after many posts in this exchange. I've answered your question many many times and in many many ways. Repeating the question doesn't mean that I haven't answered it.
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Jan 31, 2016 21:23
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Relativity is an example of a big change in the way stuff is understood. In a sense, it's like looking at a problem from a new perspective. The theory of general relativity is a big deal not because of the number of ways you can apply it practically, but in the way it changed the way we think of stuff. But really the place where it has influenced the most is in astrophysics. Aka poo poo that no one will care about for a million years. When you ask "is this theory essential to this technology" there's different ways of considering that. One is "do we need this knowledge to build and use this technology", which is no in a lot of cases. There were people making electrical circuits to do crap way before any modern understanding of electromagnetism. You can throw a lot of stuff into an "empirically determined coefficient" which is perfectly useful for just plain doing stuff. The other way is, well, the one that mentions the way each and every theory s involved with a process, which is... all of them. For everything. I mean like statistical thermodynamics, quantum mechanics, electrodynamics, relativity, etc. All these things interact with each other to do everything there is to do, because that's just what physics is; how does poo poo happen? Will I be able to predict the acceleration of a block when I push it by using general relativity? ... sure I guess but why the hell would you. But does that mean general relativity has no importance, because it has almost no impact on our day to day lives? Or in our lives in general? Idk maybe we'll use it to discover a nearby potential gamma ray burst-candidate and predict when it's gonna go and oh no it's gonna toast us. That's impossible given today's technology, but whatever. I was just having this kind of discussion about "what's the point of learning for its own sake?" I suppose it's a complicated question.
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Jan 31, 2016 21:45
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Would the invention and development of lasers have been seriously delayed by not having the theory of relativity? That's actually a difficult, technical question. But, I have a bit of evidence. I've had two textbooks on lasers and lasing, one from a physical point of view rather than engineering. Neither mentioned relativity at all. That suggests relativity had only a minor time-saving effect by predicting some empirical fudge factors like spin-orbit coupling. People could have done without.
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Jan 31, 2016 21:51
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QuarkJets posted:Thanks to SR, we know that a static electric field looks like an electric field plus a magnetic field when you're moving through it. Without SR, you wouldn't be able to accurately predict the behavior of electrons in a semiconductor. Even when they attempt to capture this effect they can't accurately predict the energy spectrum of electrons in a semiconductor. It's also a pretty weak effect in the semiconductors used in making lasers. Magnetism is weak in most materials. I think you are overstating the importance of this. I just learned a couple of days ago that tantalum nitride, a material sometimes used in integrated circuits to make resistors, has a negative temperature coefficient of resistivity. I thought hmmm, that's interesting, TaN must not be a metal and must be an unintentionally doped semi-conductor. I checked a paper where they did ab-initio calculations of the band structure, and they didn't really even know what the band gap was. Different techniques gave different results and both were 1 eV off from experiment. That's a huge error in the calculation of a pretty basic property of a material. They have bigger problems to worry about than to fiddle with small relativistic corrections. It doesn't really inform people very much. Now sometimes the relativistic physics leads to qualitatively new phenomena and I'm sure the solid state physicists are all over that. I'm not questioning that. Phyzzle posted:Would the invention and development of lasers have been seriously delayed by not having the theory of relativity? That's actually a difficult, technical question. Yeah, I totally agree and this is what I'm saying. It's totally misleading to call lasers a triumph of special relativity. If you are saying stuff like that then you may as well list every technology ever as being a triumph of theorizing/finding the Higgs Boson, which is ludicrous. silence_kit fucked around with this message at 22:41 on Jan 31, 2016 |
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Jan 31, 2016 22:31
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QuarkJets posted:But without a solid understanding of condensed matter physics, which includes a number of nods from special relativity, you won't ever reach the point where you can build a semiconductor laser. It would absolutely be possible to develop most of modern semiconductor physics without the input of special relativity.
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Jan 31, 2016 22:49
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computer parts posted:Nothing will show that, and it's boring to try to discuss that. It's more interesting than 'there's no progress!' 'No way, my phone screen is huge now!'
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Feb 1, 2016 00:53
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Bip Roberts posted:It would absolutely be possible to develop most of modern semiconductor physics without the input of special relativity. I disagree for the reasons that I've already laid out. Before silence_kit dragged us into the weeds with semiconductor lasers, the other concept that invoked his incredulity was the importance of special relativity to medical imaging. Would you disagree there, and if so, why?
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Feb 1, 2016 02:02
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Sylink posted:In response to OP: No, we have just hit a wall with certain technology until we can exploit more extreme laws of physics to get around those limits. The latter may or may not be possible but there are signs it is (quantum computing etc). I also want to add that this wall has only been of relevance in the past few years, and that we've made gigantic leaps in the decades before that. It has transformed our society, and while breakthrough technologies are being researched, keep in mind that stuff like power consumption and storage are only a few of the many other aspects of computers that are still evolving at breakneck speeds. It's just the boneheads in this thread that call the past 70 years a technological decline. I wish I'd be able to call them something else, but you basically must refute reality or live underneath a rock to claim a technological decline. I'll just imagine that these boneheads magically transmit up the words they type. To refute humanity's progress and accomplishments, like some in this thread do, is just disgusting. It's akin to claiming the pyramids are impossible and must be of alien origin. Batham fucked around with this message at 02:17 on Feb 1, 2016 |
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Feb 1, 2016 02:12
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QuarkJets posted:I disagree for the reasons that I've already laid out. While you have pointed out that sometimes in condensed matter physics people worry about relativity, you haven't closed the loop by pointing out where in laser science relativity actually matters. Your earlier claim that lasers are a technological fruit of the theory of relativity is very misleading. Edit: Not worth adding to a new post. QuarkJets posted:I've done this, you just keep handwaving away all of my posts and creating strawman arguments in their place. If you want to continue believing that special relativity is useless to the physics of lasers and MRI machines then I no longer feel compelled to stop you I'm ignoring a lot of the words of your posts because they aren't logical arguments and are mostly personal attacks on me in an attempt to discredit my opinion. Not really having a systematic understanding of how MRI works, I never claimed that relativity was irrelevant to MRI. I'd suggest you do the same when you are out of your element. That's why I asked you. You never actually concretely explained why special relativity is relevant to MRI. silence_kit fucked around with this message at 02:51 on Feb 1, 2016 |
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Feb 1, 2016 02:21
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silence_kit posted:You actually haven't reasoned at all about the subject. While you have pointed out that some people in condensed matter physics worry about relativity, you haven't closed the loop by pointing out where in laser science it actually matters. I've done this, you just keep handwaving away all of my posts and creating strawman arguments in their place. If you want to continue believing that special relativity is useless to the physics of lasers and MRI machines then I no longer feel compelled to stop you 
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Feb 1, 2016 02:37
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https://www.youtube.com/watch?v=ckNsMeWc_Cs The Human Adventure is Only Beginning This is the Star Trek 60th Anniversary Post
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Feb 1, 2016 02:38
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