I imagine it would be traumatic to think (even for a moment) that you were truly going to die or had just died. However, it is a very strange myth (sci-fi like the matrix) that a person would die just because they (or their brain) thought they were dead. If oxygenated blood is still flowing into your brain, then you're not going to suddenly drop dead.
As I said, however, the bigger concern would be the psychological effect of dealing with realistic death, or conversely experiencing simulated death so much that you were no longer afraid of death in real life (and thereby started acting dangerously).
Maybe I'm stating the obvious here, but this is a perfect example of why the current patent system needs to be reworked, or tightened up at the very least. If SONY's patent on this technology is actually upheld and valid, then this absolutely discourages innovation.
Why should some engineer or company try to actually make the proposed design work? As soon as they do, they lose the invention to SONY, who didn't do anything. By owning a patent on something that doesn't yet exist, they make it unlikely that the thing will ever be invented. Only SONY would have any incentive to develop this technology.
The only possible upshot is that if silly companies patent far-fetched ideas too early, then the patent might be running out exactly at the time when it is becoming technically feasible to build the damn thing. Then again, this would probably prompt court fights for extension of the patent (but your honour, we are only now starting to be able to make money off of the mistake we made years ago...).
Re:live performances vs. commercial product
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EZTree Shuts Down
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Even if the artist owns copyright on the performance, the people in the audience did pay for access to that performance (as another poster points out). Thus, they may be within their rights to make a recording of the performance. However, it would be a violation for them to *distribute* the recording. Keeping a recording for personal use would possibly be "fair use"? Of course its a grey area... Movie theatres ban bringing in video cameras, but it's distribution of copyrighted content that is illegal, not making a copy per se (at least where I come from).
IANAL and anyone who knows more about these issues please correct me if I'm wrong.
I really dislike live music, I prefer studio stuff. But it appears that alot of people really like live music. They are even interested in listening to multiple versions of the same artists doing the same song at different concerts. There is huge potential here that the industry is ignoring.
It is doubtful that many people would buy dozens of different CDs of the same music performed at different live concerts. However, these same people might very well download lots of different versions, just to see the difference, or maybe everytime they wanted to listen to a given song they would listen to a different live version of it. The music industry has all these millions of versions of songs that they are not even recording and distributing (even though people want to listen to it) because their distribution model is so archaic.
So what do I propose? I think the music industry could make tons of money by switching from music being a *product* to music being a *service*. You pay 5$/month to have unlimited downloads to a complete archive of everything the industry can pull together. With so much data, the risk of the users downloading and freely distributing it all doesn't really exist. Users will pay the 5$/month to have easy access to all the brand new music and all the archived music. The ease of use would make this very profitable.
This isn't my idea. It is well described and documented in a PDF from MIT. They strongly believe that a download-service business model would work. I tend to agree.
Re:and thus, R.Stallman was right after all
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RMS was not necessarily right. In TFA Linus is quoted as saying "three years of using BitKeeper has made some profound improvements to the workflow"
So linus apparently thinks that the increased productivity over the three years is enough to offset the pain that he must now endure to switch to a new system. (We'll have to ask Linus again after he actually endures the switch!) So from the pragmatic point of view, there is still a valid argument for using a superior product, even if support may discontinue at any time. It is a calculated risk that may be more efficient in the long run.
That having been said, I strongly support OSS and free software on ideological grounds, but Linus' argument has always been one of productivity, not ethics.
You are correct, but your figures were assuming that the family only takes one out-of-country trip every 5 years. The real tourist money probably comes from people that travel more often. Those people (families) will have up-to-date passports anyway (even for the kids), and it won't be a matter of getting a new passport, but just bringing your current passport. Most people I know have a valid passport at all times anyway, for one reason or another.
As you say, this will decrease the number of "impulse tourists" who don't otherwise travel abroad, but I doubt this will put a serious dent in the US tourism budget. Those people will probably just deal with the longer line at the border to get the proper tourist card or whatever.
AFAIK, this has only been proposed in places where no company is offering a viable wireless solution.
And it would appear that the public voted on the issue and approved the concept. Thus, their tax dollars are being spent on what they want. The local government is spending public money on the public. I think that's one of the basic tenants of democracy.
I might be cause for worry if the government were massively deploying ISPs, thereby shutting down legitimate companies, but so far that doesn't look like it's going to happen. The government doesn't really want to get involved, and people who live in places with good and affordable commercial ISPs won't vote for gov-supported ISPs. Besides, as many posters have mentioned, the internet has become a public commodity/infrastructure, like electricity or roads, and could be partially implemented by public funds.
Excellent point. I think you are right: it is easier to describe (i.e.: program) something that you had to laboriously understand yourself, rather than something that is second-nature and easy.
But this is why I think more communication between people doing research in neuroscience/cognitive science/evolutionary psychology and people doing AI programming is critical. There are some very interesting psych experiments that attempt to reverse engineer how the brain works. For instance, determining what algorithm is used in the human brain to differentiate surfaces in a scene, or predict the path of a thrown object, and so forth. The algorithms used in our brains are the ones that evolution "decided" were optimal for solving real-world problems with limited ressources. Thus, it is likely that they will be optimal for our AI coding purposes.
Neural nets are interesting and have had some successes, but they drastically ignore the layers of organization (and genetically hard-wired algorithms) that our brains have.
As someone who posts using links to wikipedia occasionally, I must say that I object. When I'm looking for a source to explain what I'm talking about, I simply reference the best URL I can find. Very often, that is wikipedia. It doesn't really matter who hosts the data if I know it to be valid.
As someone who has done some research on surface plasmons, I find the wikipedia article on Plasmon to be accurate and useful, so I think it is a good reference. Not all wikipedia articles are so good, but then again I don't reference the bad ones.
On the other hand, you are pointing out that we shouldn't accept wikipedia articles just because wikipedia is cool and lots of people edited the article so it must be right. Yes, that's valid. However, as with *all* sources of information, whether it is a wiki or slashdot or an encyclopedia or the local news, the end-consumer MUST use his judgement to decide if the information is valid or BS. It is an illusion to think that traditional sources of information are error free. In all cases, the reader must simply use judgement and double-check if things seem wrong.
In addition to what other posters have mentioned (there being X-ray and other energetic indicators of black holes), it's worth noting that using adaptive optic telescopes, astronomers have measured the orbital acceleration of stars near the center of the Milky Way. These stars are orbiting around an area that appears black and empty. The only explanation is some massive dark source at that location. This observation of stars orbiting is fairly direct. Of course, it doesn't rule out other dense and dark matter sources.
For the original article in Nature, you will need a subscription of some sort. Here's the reference for anyone interested: Nature 407, 349 - 351 (21 September 2000); doi:10.1038/35030032
Not quite. Dark matter is material that does not emit light. This matter obviously has an energy content.
Dark Energy is not merely energy that doesn't emit light. It is a hypotehtical form of energy that exerts a *negative* pressure on space-time. It is a uniquely relativistic prediction. The evidence for dark energy is that (based on the most recent observations of distant supernova) the expansion rate of the universe is actually *increasing* instead of decreasing. So the universe is not only expanding, but it's expansion is accelerating. The only way this could be (based on relativity that is) is for there to be an extra form of energy that operates in a direction "opposite" to conventional gravity: instead of causing matter to attract together, it causes spacetime to push itself apart, with the force *increasing* as the universe gets bigger and less dense. This counter-intuitive prediction/measurement is of course the subject of much investigation.
I wasn't arguing for "absolute truth", only for logical consistency
Sorry, my mistake. I'm glad we agree on this point.
Intuition is not a method of science. Logic is the method of science
Again, I agree, and from that perspective I will say that QM has no mathematical or logical inconsistency. The only inconsistency is with intuition, common sense, and our subjective perception of reality. The math is rigorous and the theory is predictive. It is only at the level of *interpretation* that problems arise. Now, you argue that relativity and thermodynamics provide us with "explanations" whereas QM does not. I disagree. Every theory can have explanation ascribed to it by humans, but ultimately we assume that there is a link between the theory and the physical world. You accept this think for relativity but do not accept it for QM. I accept it in both cases.
You seem, however, to be bothered by what I will call (for lack of an official term) "the old interpretation." That is, the genius founders of QM described what they derived in terms of probability and uncertainty. However, this is not the only interpretation, and I would go so far as to say it is no longer the interpretation used by QM theorists today. The unfortunate part is that it *is* still the interpretation being taught at schools. In the "more modern" interpretation, a particle is inherently delocalized (not in a probabilistic sense), and the HUP describes the coupling between delocalization in different dimensions (position, momentum, etc.).
Thus, I think we are arguying from different assumptions about the interpretation of QM. I do not like the old interpretation either... but that is because the old interpretation is based on an *assumption* that the universe is classical. In such a paradigm, then yes, by *definition* QM is wrong, but only because one of the axioms was "the universe is actually classical." If this (unnecessary) axiom is not present, then QM is consistent, and a new interpretation becomes apparent: that the universe is, fundamentally, based on delocalized wave packets interacting as described by the Schrodinger equation.
I have more that I could say, but I think our discussion has spread way beyond what is of interest to the Slashdot community! If you're keen on continuing this discussion, you can contact me at my Google-mail account: my username is kebes.hunter
Otherwise, thanks for an interesting discussion!
Well, we will just have to agree to disagree on this one. We have entered the "philosophy of QM" debate, which I have read up on and written on extensively (as it appears you have). Indeed we cannot verify QM to be "true" anymore than we can verify any other theory to be "true." One metric that many scientists accept is that "if it predicts correctly, and every element in the theory maps to an element in the universe, then we assume the theory has physical meaning." It is, at the end of the day, just an assumption, with an acknowledgment that it may be wrong.
This is not especially different from any other theory, such as relativity, thermodynamics, Newtonian gravity, and so on. They all contain things that seem counter-intuitive, yet are fully predictive and "get the right answer" (whereas our common sense fails in many instances). All physical theories were, at first, seen to be incompatible with "common sense" views of reality. So whether or not you accept them as being "real" or merely "predictive" is just a matter of personal taste.
My view is that it would be arrogant of humans to presuppose what form a fundamental theory would take, to assume that it must necessarily meet our preconceptions about reality and "explanation." I could argue that your acceptance of subjective human reality as being the "true" reality is an article of faith. When you say that "probability clouds have no place in reality" you are just making an unverifiable assumption about reality, no different than when I say "predictive theories correspond to reality."
In any case, that's why I enjoy learning about all the recent advances in these theories: because they push up against the boundaries of fundamental knowledge, and challenge our very perception of reality.
Well if you don't want to adopt the naming conventions of mainstream physics, then that's fair enough. The way you look at it works well, and when the dust settles (after a calculation), we'll all agree on the right answer.
However, I wouldn't say that gauge theories are untested hypotheses. Quantum Electrodynamics (QED) has been tested extensively. If the correct predictions for high-energy (particle accelerator) reactions don't convince you (which can only be predicted with proper use of QED, QCD, and the Standard Model in general), then what about the fact that these theories correctly merge field theories with quantum mechanics. Without them, there is no consistent explanation for everyday electromagnetism (that doesn't come into conflict with quantum mechanics). Similarly, explanations of antiparticles and consistency with relativity are all deeply integrated into these theories.
There's much work left to be done on these theories, but the Standard Model *has* been rigorously tested experimentally.
Yes, a manned mission might be able to squeeze a few more years out of Hubble. However, let us keep in mind that Hubble has lasted much longer than it was originally intended. There will reach a point of diminishing returns, where repairs don't extend the lifetime very much at all.
Keep in mind that each manned mission is very expensive, and that this money might be put to a better use by (partially) funding the next orbital telescope.
My point is that there reaches a point where it really is smarter to put efforts into alternate projects. NASA has deliberated extensively, and they think we have reached that point.
Blowing up old satellites is a very bad idea. Orbital debris is already dangerous for rockets and (especially) manned missions into space. Collision with a piece of debris in orbit is usually a very high-speed impact and can severely damage or even destroy a launch vehicle. For the future safety of space exploration, it really is safest to send satellites into the atmosphere to burn up cleanly.
Shooting a derelict satellite into deep space is much more costly (in terms of fuel) and is not as easy as it sounds. If it isn't done right, it might end up in an eccentric orbit around the Earth (or moon) and cause problems much later on.
According to the accepted formulation of relativity, photons do indeed have relativistic momentum.
A photon is not 'merely' an electromagnetic radiation packet. It is the force-carrying particle (gauge boson) of the quantized EM-field. It *is* a fundamental subatomic particle, and it *is* valid to say that it has a zero rest mass.
Without mass a photon exerts no gravitational force on other particles, but it is indeed deflected by a gravitation field (distortion in space-time, if you like).
This is not an april fool's prank. It is real. The joke is the "infinity + 1" storage that appears on the gmail main page. But if you follow the link they have, which reads:
"Gmail turns 1 today. And we've always loved a good joke. We know we won't reach infinity, but check out what we will do..."
You will see that they are very serious about increasing to 2 GB of storage. The counter on the Gmail page seems to be increasing from 1000 Mb to 2000 Mb at a rate that will reach the goal by the time the day is over.
NASA rightly plans missions well ahead of time. They need to plan years into the future in order to work out all the kinks, find the right launch window, and so forth. Yet this article seems to be rather naive in assuming that this current concept will be carried to completion 30 years from now. Alot can happen in 30 years. Alot. Investigating this concept is certainly worthwhile, but in all likelihood a new technology that none of us can specifically predict will emerge that will make this concept silly and obsolete. So while I applaud NASA for investigating this cool concept, I think it is silly to expect this particular project to actually be implemented one day. (For the record, the vast majority of NASA projects and proposals never see the light of day, and most are not nearly so strange and ambitious as this one!)
We the users are willing to put up with ads to a certain extent, but beyond that, we will use whatever technology it takes to remove them because they are too annoying.
Advertisers simply have to learn to place ads below this annoyance threshold, and they will reap the rewards. One example of a company that 'gets it': Google. Their ads are sufficiently innocuous that it's not worth the trouble to block them or get rid of them. The result? They make lots of money off of ads.
The big networks should realize this. They want to keep their current paradigm, where a person watches 15 minutes of commercials for every hour of TV. That won't work in the future, since the users will use something like TiVo or a download that has no ads in order to get around the annoyance. If, on the other hand, the network offered us a free download of our favourite show, and during each ad segment, there was a single 10-second ad (and it was relatively funny or cool), then we wouldn't skip past it, and they would make lots of ad money.
I think these companies need to wake up to what consumers are really willing to put up with. We are willing to watch ads and buy products we like, but we are not willing to have our time wasted.
Well I'm a chemist by training, not a physicist, so hopefully I'm getting all of this right... but here's my take on it.
With reference to thermodynamics: yes the solar sail gets hotter and hotter, and eventually will radiate infra-red photons (say) in order to come into equilibrium with the rest of the universe. But thermal radiating, by its nature, is random and isotropic, so the sail will radiate as many photons from its front side as its back side, hence these don't cause any net propulsion, which is why I'm considering it a 'loss' from the POV of propulsion.
With regard to the photon momentum, we have to remember that momentum is a vector, not a scalar, and that momentum must be conserved (and energy must also be conserved, of course). Let's deal with momentum conservation. In an elastic collision (even one involving a photon), the net momentum is conserved. The photon bounces off the sail, and reverses direction, so it's momentum change is twice its initial homentum. The ship is pushed in the +x direction (say), but the photon bounces back in the -x direction, so momentum is conserved. And when you have two solar sails bouncing a photon back and forth forever, one ship moves in one direction, but the other ship moves in the opposite direction, so net momentum is being conserved.
What's less obvious is how energy would be conserved in a case like this. As you say, it seems like the kinetic energy of both spacecraft is increasing, without any loss of energy in the photon they are exchanging. Upon thinking about it further, I agree with you. The photons are red-shifted, but this red-shift is a Doppler shift (not a change in frequency upon reflection, which is what bothered me before). This relativistic effect is very small, of course, but then again the force of a single photon is also very small. So from the POV of the two solar sails, the single (hard-working) photon becomes more and more red-shifted, as it essentially transfers energy into the spacecraft.
You are correct that solar wind is a negligible contribution (I was hasty in my original post).
The poor efficiency of solar sails is partially due to reflection losses (which helps the solar sail!), but quite a lot would also be lost in absorption events that don't lead to current... i.e. we have the inescapable thermodynamic effects where the solar sails will heat up rather than convert energy with 100% efficiency. This energy that is converted into heat doesn't get us electricity, and doesn't help the solar sail, either.
My figure of 2 in the momentum calculation assumes that the photons hit at a 90 degree angle, which is of course not always going to be true. There will be inefficiencies associated with that, of course. But assuming 90 degrees, then the figure of 2 is in fact *due* to conservation of energy. This assumes the photon is reflected elastically, and does not change frequency. AFAIK, photons do not change frequency (red-shift) during reflections, except to a very small extent (refer to
Raman scattering).
Your scenario of two ships using a single photon to accelerate indefinitely ignores things like the blackbody spectrum of the universe, quantum mechanics, Casimir forces, etc. If we ignore those for a moment, then yes the two ships would accelerate for forever, but as they approach the speed of light (which would take a *very* long time), the apparent wavelength of the photon in question would appear to be longer and longer (due to relativistic distortions), and thus the momentum boost they would get on each reflection would get smaller and smaller. I'm not going to attempt the integral right now, but I suspect the situation is not a runaway to infinite speed. In any case, as I said, this ignores many other effects that would dominate.
For the record, my comment was mostly pointing out the hyperbole of the article. It was the article that was incorrectly implying that the technology was mature, not the company showing off its prototype, and I was taking issue with their analysis.
Furthermore, not all features are created equal. Some are so new and innovative that consumers are worth sacrificing something (like paying money, spending time, carrying something heavey, etc.). Other features are not worth much, and are only accepted once they are so innocuous that they don't get in the way of other features. Cell phones were sufficiently revolutionary that they were worth the cost and bulk. That hardly proves that every new feature is worth bulk and cost.
It is my opinion that this feature is insufficiently useful to be worth any added bulk. Of course, I may be wrong and I'm certainly willing to be convinced otherwise if someone has persuasive arguments (or perhaps I'll use one and fall in love with it). Saying that my concerns are groundless is, itself, groundless.
Food for thought: if your solar sail is using photon pressure, then by coating it in a photoelectric, you're halving its efficiency as a solar sail. Why? Well if your solar sail is a perfect reflector, then the photons bounce off and reverse direction, so the momentum change is twice the initial photon momentum (yes photons are massless but they do have momentum). If the sail is absorbing the photons for electricity, then they are not reflecting, so you merely absorb their momentum, making your forward impulse half what it would otherwise have been.
But, as we all know, solar sails work both by exploiting photon pressure, and solar wind (particles emitted by the sun), so the situation is maybe not that bad.
Slashdot Mirror
I imagine it would be traumatic to think (even for a moment) that you were truly going to die or had just died. However, it is a very strange myth (sci-fi like the matrix) that a person would die just because they (or their brain) thought they were dead. If oxygenated blood is still flowing into your brain, then you're not going to suddenly drop dead.
As I said, however, the bigger concern would be the psychological effect of dealing with realistic death, or conversely experiencing simulated death so much that you were no longer afraid of death in real life (and thereby started acting dangerously).
Maybe I'm stating the obvious here, but this is a perfect example of why the current patent system needs to be reworked, or tightened up at the very least. If SONY's patent on this technology is actually upheld and valid, then this absolutely discourages innovation.
Why should some engineer or company try to actually make the proposed design work? As soon as they do, they lose the invention to SONY, who didn't do anything. By owning a patent on something that doesn't yet exist, they make it unlikely that the thing will ever be invented. Only SONY would have any incentive to develop this technology.
The only possible upshot is that if silly companies patent far-fetched ideas too early, then the patent might be running out exactly at the time when it is becoming technically feasible to build the damn thing. Then again, this would probably prompt court fights for extension of the patent (but your honour, we are only now starting to be able to make money off of the mistake we made years ago...).
Even if the artist owns copyright on the performance, the people in the audience did pay for access to that performance (as another poster points out). Thus, they may be within their rights to make a recording of the performance. However, it would be a violation for them to *distribute* the recording. Keeping a recording for personal use would possibly be "fair use"? Of course its a grey area... Movie theatres ban bringing in video cameras, but it's distribution of copyrighted content that is illegal, not making a copy per se (at least where I come from).
IANAL and anyone who knows more about these issues please correct me if I'm wrong.
I really dislike live music, I prefer studio stuff. But it appears that alot of people really like live music. They are even interested in listening to multiple versions of the same artists doing the same song at different concerts. There is huge potential here that the industry is ignoring. It is doubtful that many people would buy dozens of different CDs of the same music performed at different live concerts. However, these same people might very well download lots of different versions, just to see the difference, or maybe everytime they wanted to listen to a given song they would listen to a different live version of it. The music industry has all these millions of versions of songs that they are not even recording and distributing (even though people want to listen to it) because their distribution model is so archaic.
So what do I propose? I think the music industry could make tons of money by switching from music being a *product* to music being a *service*. You pay 5$/month to have unlimited downloads to a complete archive of everything the industry can pull together. With so much data, the risk of the users downloading and freely distributing it all doesn't really exist. Users will pay the 5$/month to have easy access to all the brand new music and all the archived music. The ease of use would make this very profitable.
This isn't my idea. It is well described and documented in a PDF from MIT. They strongly believe that a download-service business model would work. I tend to agree.
RMS was not necessarily right. In TFA Linus is quoted as saying "three years of using BitKeeper has made some profound improvements to the workflow"
So linus apparently thinks that the increased productivity over the three years is enough to offset the pain that he must now endure to switch to a new system. (We'll have to ask Linus again after he actually endures the switch!) So from the pragmatic point of view, there is still a valid argument for using a superior product, even if support may discontinue at any time. It is a calculated risk that may be more efficient in the long run.
That having been said, I strongly support OSS and free software on ideological grounds, but Linus' argument has always been one of productivity, not ethics.
You are correct, but your figures were assuming that the family only takes one out-of-country trip every 5 years. The real tourist money probably comes from people that travel more often. Those people (families) will have up-to-date passports anyway (even for the kids), and it won't be a matter of getting a new passport, but just bringing your current passport. Most people I know have a valid passport at all times anyway, for one reason or another.
As you say, this will decrease the number of "impulse tourists" who don't otherwise travel abroad, but I doubt this will put a serious dent in the US tourism budget. Those people will probably just deal with the longer line at the border to get the proper tourist card or whatever.
AFAIK, this has only been proposed in places where no company is offering a viable wireless solution.
And it would appear that the public voted on the issue and approved the concept. Thus, their tax dollars are being spent on what they want. The local government is spending public money on the public. I think that's one of the basic tenants of democracy.
I might be cause for worry if the government were massively deploying ISPs, thereby shutting down legitimate companies, but so far that doesn't look like it's going to happen. The government doesn't really want to get involved, and people who live in places with good and affordable commercial ISPs won't vote for gov-supported ISPs. Besides, as many posters have mentioned, the internet has become a public commodity/infrastructure, like electricity or roads, and could be partially implemented by public funds.
Excellent point. I think you are right: it is easier to describe (i.e.: program) something that you had to laboriously understand yourself, rather than something that is second-nature and easy.
But this is why I think more communication between people doing research in neuroscience/cognitive science/evolutionary psychology and people doing AI programming is critical. There are some very interesting psych experiments that attempt to reverse engineer how the brain works. For instance, determining what algorithm is used in the human brain to differentiate surfaces in a scene, or predict the path of a thrown object, and so forth. The algorithms used in our brains are the ones that evolution "decided" were optimal for solving real-world problems with limited ressources. Thus, it is likely that they will be optimal for our AI coding purposes.
Neural nets are interesting and have had some successes, but they drastically ignore the layers of organization (and genetically hard-wired algorithms) that our brains have.
As someone who posts using links to wikipedia occasionally, I must say that I object. When I'm looking for a source to explain what I'm talking about, I simply reference the best URL I can find. Very often, that is wikipedia. It doesn't really matter who hosts the data if I know it to be valid.
As someone who has done some research on surface plasmons, I find the wikipedia article on Plasmon to be accurate and useful, so I think it is a good reference. Not all wikipedia articles are so good, but then again I don't reference the bad ones.
On the other hand, you are pointing out that we shouldn't accept wikipedia articles just because wikipedia is cool and lots of people edited the article so it must be right. Yes, that's valid. However, as with *all* sources of information, whether it is a wiki or slashdot or an encyclopedia or the local news, the end-consumer MUST use his judgement to decide if the information is valid or BS. It is an illusion to think that traditional sources of information are error free. In all cases, the reader must simply use judgement and double-check if things seem wrong.
In addition to what other posters have mentioned (there being X-ray and other energetic indicators of black holes), it's worth noting that using adaptive optic telescopes, astronomers have measured the orbital acceleration of stars near the center of the Milky Way. These stars are orbiting around an area that appears black and empty. The only explanation is some massive dark source at that location. This observation of stars orbiting is fairly direct. Of course, it doesn't rule out other dense and dark matter sources.
For the original article in Nature, you will need a subscription of some sort. Here's the reference for anyone interested:
Nature 407, 349 - 351 (21 September 2000); doi:10.1038/35030032
Not quite. Dark matter is material that does not emit light. This matter obviously has an energy content.
Dark Energy is not merely energy that doesn't emit light. It is a hypotehtical form of energy that exerts a *negative* pressure on space-time. It is a uniquely relativistic prediction. The evidence for dark energy is that (based on the most recent observations of distant supernova) the expansion rate of the universe is actually *increasing* instead of decreasing. So the universe is not only expanding, but it's expansion is accelerating. The only way this could be (based on relativity that is) is for there to be an extra form of energy that operates in a direction "opposite" to conventional gravity: instead of causing matter to attract together, it causes spacetime to push itself apart, with the force *increasing* as the universe gets bigger and less dense. This counter-intuitive prediction/measurement is of course the subject of much investigation.
I wasn't arguing for "absolute truth", only for logical consistency
Sorry, my mistake. I'm glad we agree on this point.
Intuition is not a method of science. Logic is the method of science
Again, I agree, and from that perspective I will say that QM has no mathematical or logical inconsistency. The only inconsistency is with intuition, common sense, and our subjective perception of reality. The math is rigorous and the theory is predictive. It is only at the level of *interpretation* that problems arise. Now, you argue that relativity and thermodynamics provide us with "explanations" whereas QM does not. I disagree. Every theory can have explanation ascribed to it by humans, but ultimately we assume that there is a link between the theory and the physical world. You accept this think for relativity but do not accept it for QM. I accept it in both cases.
You seem, however, to be bothered by what I will call (for lack of an official term) "the old interpretation." That is, the genius founders of QM described what they derived in terms of probability and uncertainty. However, this is not the only interpretation, and I would go so far as to say it is no longer the interpretation used by QM theorists today. The unfortunate part is that it *is* still the interpretation being taught at schools. In the "more modern" interpretation, a particle is inherently delocalized (not in a probabilistic sense), and the HUP describes the coupling between delocalization in different dimensions (position, momentum, etc.).
Thus, I think we are arguying from different assumptions about the interpretation of QM. I do not like the old interpretation either... but that is because the old interpretation is based on an *assumption* that the universe is classical. In such a paradigm, then yes, by *definition* QM is wrong, but only because one of the axioms was "the universe is actually classical." If this (unnecessary) axiom is not present, then QM is consistent, and a new interpretation becomes apparent: that the universe is, fundamentally, based on delocalized wave packets interacting as described by the Schrodinger equation.
I have more that I could say, but I think our discussion has spread way beyond what is of interest to the Slashdot community! If you're keen on continuing this discussion, you can contact me at my Google-mail account: my username is kebes.hunter
Otherwise, thanks for an interesting discussion!
Well, we will just have to agree to disagree on this one. We have entered the "philosophy of QM" debate, which I have read up on and written on extensively (as it appears you have). Indeed we cannot verify QM to be "true" anymore than we can verify any other theory to be "true." One metric that many scientists accept is that "if it predicts correctly, and every element in the theory maps to an element in the universe, then we assume the theory has physical meaning." It is, at the end of the day, just an assumption, with an acknowledgment that it may be wrong.
This is not especially different from any other theory, such as relativity, thermodynamics, Newtonian gravity, and so on. They all contain things that seem counter-intuitive, yet are fully predictive and "get the right answer" (whereas our common sense fails in many instances). All physical theories were, at first, seen to be incompatible with "common sense" views of reality. So whether or not you accept them as being "real" or merely "predictive" is just a matter of personal taste.
My view is that it would be arrogant of humans to presuppose what form a fundamental theory would take, to assume that it must necessarily meet our preconceptions about reality and "explanation." I could argue that your acceptance of subjective human reality as being the "true" reality is an article of faith. When you say that "probability clouds have no place in reality" you are just making an unverifiable assumption about reality, no different than when I say "predictive theories correspond to reality."
In any case, that's why I enjoy learning about all the recent advances in these theories: because they push up against the boundaries of fundamental knowledge, and challenge our very perception of reality.
Well if you don't want to adopt the naming conventions of mainstream physics, then that's fair enough. The way you look at it works well, and when the dust settles (after a calculation), we'll all agree on the right answer.
However, I wouldn't say that gauge theories are untested hypotheses. Quantum Electrodynamics (QED) has been tested extensively. If the correct predictions for high-energy (particle accelerator) reactions don't convince you (which can only be predicted with proper use of QED, QCD, and the Standard Model in general), then what about the fact that these theories correctly merge field theories with quantum mechanics. Without them, there is no consistent explanation for everyday electromagnetism (that doesn't come into conflict with quantum mechanics). Similarly, explanations of antiparticles and consistency with relativity are all deeply integrated into these theories.
There's much work left to be done on these theories, but the Standard Model *has* been rigorously tested experimentally.
Yes, a manned mission might be able to squeeze a few more years out of Hubble. However, let us keep in mind that Hubble has lasted much longer than it was originally intended. There will reach a point of diminishing returns, where repairs don't extend the lifetime very much at all.
Keep in mind that each manned mission is very expensive, and that this money might be put to a better use by (partially) funding the next orbital telescope.
My point is that there reaches a point where it really is smarter to put efforts into alternate projects. NASA has deliberated extensively, and they think we have reached that point.
Blowing up old satellites is a very bad idea. Orbital debris is already dangerous for rockets and (especially) manned missions into space. Collision with a piece of debris in orbit is usually a very high-speed impact and can severely damage or even destroy a launch vehicle. For the future safety of space exploration, it really is safest to send satellites into the atmosphere to burn up cleanly.
Shooting a derelict satellite into deep space is much more costly (in terms of fuel) and is not as easy as it sounds. If it isn't done right, it might end up in an eccentric orbit around the Earth (or moon) and cause problems much later on.
According to the accepted formulation of relativity, photons do indeed have relativistic momentum.
A photon is not 'merely' an electromagnetic radiation packet. It is the force-carrying particle (gauge boson) of the quantized EM-field. It *is* a fundamental subatomic particle, and it *is* valid to say that it has a zero rest mass.
Without mass a photon exerts no gravitational force on other particles, but it is indeed deflected by a gravitation field (distortion in space-time, if you like).
If you check the source code for gmail's login page, you'll see how they are calculating the "running tally" of your current storage limit:
var START = 1112331600000;
var END = 1112439600000;
function updateQuota() {
if (!quota) {
return;
}
var now = (new Date()).getTime();
if (now END) {
quota.innerHTML = 'Over 2000';
} else {
quota.innerHTML = format(((now - START)/(END - START)*1025) + 1025);
setTimeout(updateQuota, 50);
}
}
It looks like it's counting from 1000 to 2000 over the course of the day.
This is not an april fool's prank. It is real. The joke is the "infinity + 1" storage that appears on the gmail main page. But if you follow the link they have, which reads:
..."
"Gmail turns 1 today. And we've always loved a good joke. We know we won't reach infinity, but check out what we will do
You will see that they are very serious about increasing to 2 GB of storage. The counter on the Gmail page seems to be increasing from 1000 Mb to 2000 Mb at a rate that will reach the goal by the time the day is over.
NASA rightly plans missions well ahead of time. They need to plan years into the future in order to work out all the kinks, find the right launch window, and so forth. Yet this article seems to be rather naive in assuming that this current concept will be carried to completion 30 years from now. Alot can happen in 30 years. Alot. Investigating this concept is certainly worthwhile, but in all likelihood a new technology that none of us can specifically predict will emerge that will make this concept silly and obsolete. So while I applaud NASA for investigating this cool concept, I think it is silly to expect this particular project to actually be implemented one day. (For the record, the vast majority of NASA projects and proposals never see the light of day, and most are not nearly so strange and ambitious as this one!)
We the users are willing to put up with ads to a certain extent, but beyond that, we will use whatever technology it takes to remove them because they are too annoying.
Advertisers simply have to learn to place ads below this annoyance threshold, and they will reap the rewards. One example of a company that 'gets it': Google. Their ads are sufficiently innocuous that it's not worth the trouble to block them or get rid of them. The result? They make lots of money off of ads.
The big networks should realize this. They want to keep their current paradigm, where a person watches 15 minutes of commercials for every hour of TV. That won't work in the future, since the users will use something like TiVo or a download that has no ads in order to get around the annoyance. If, on the other hand, the network offered us a free download of our favourite show, and during each ad segment, there was a single 10-second ad (and it was relatively funny or cool), then we wouldn't skip past it, and they would make lots of ad money.
I think these companies need to wake up to what consumers are really willing to put up with. We are willing to watch ads and buy products we like, but we are not willing to have our time wasted.
Well I'm a chemist by training, not a physicist, so hopefully I'm getting all of this right... but here's my take on it.
With reference to thermodynamics: yes the solar sail gets hotter and hotter, and eventually will radiate infra-red photons (say) in order to come into equilibrium with the rest of the universe. But thermal radiating, by its nature, is random and isotropic, so the sail will radiate as many photons from its front side as its back side, hence these don't cause any net propulsion, which is why I'm considering it a 'loss' from the POV of propulsion.
With regard to the photon momentum, we have to remember that momentum is a vector, not a scalar, and that momentum must be conserved (and energy must also be conserved, of course). Let's deal with momentum conservation. In an elastic collision (even one involving a photon), the net momentum is conserved. The photon bounces off the sail, and reverses direction, so it's momentum change is twice its initial homentum. The ship is pushed in the +x direction (say), but the photon bounces back in the -x direction, so momentum is conserved. And when you have two solar sails bouncing a photon back and forth forever, one ship moves in one direction, but the other ship moves in the opposite direction, so net momentum is being conserved.
What's less obvious is how energy would be conserved in a case like this. As you say, it seems like the kinetic energy of both spacecraft is increasing, without any loss of energy in the photon they are exchanging. Upon thinking about it further, I agree with you. The photons are red-shifted, but this red-shift is a Doppler shift (not a change in frequency upon reflection, which is what bothered me before). This relativistic effect is very small, of course, but then again the force of a single photon is also very small. So from the POV of the two solar sails, the single (hard-working) photon becomes more and more red-shifted, as it essentially transfers energy into the spacecraft.
You are correct that solar wind is a negligible contribution (I was hasty in my original post).
The poor efficiency of solar sails is partially due to reflection losses (which helps the solar sail!), but quite a lot would also be lost in absorption events that don't lead to current... i.e. we have the inescapable thermodynamic effects where the solar sails will heat up rather than convert energy with 100% efficiency. This energy that is converted into heat doesn't get us electricity, and doesn't help the solar sail, either.
My figure of 2 in the momentum calculation assumes that the photons hit at a 90 degree angle, which is of course not always going to be true. There will be inefficiencies associated with that, of course. But assuming 90 degrees, then the figure of 2 is in fact *due* to conservation of energy. This assumes the photon is reflected elastically, and does not change frequency. AFAIK, photons do not change frequency (red-shift) during reflections, except to a very small extent (refer to Raman scattering).
Your scenario of two ships using a single photon to accelerate indefinitely ignores things like the blackbody spectrum of the universe, quantum mechanics, Casimir forces, etc. If we ignore those for a moment, then yes the two ships would accelerate for forever, but as they approach the speed of light (which would take a *very* long time), the apparent wavelength of the photon in question would appear to be longer and longer (due to relativistic distortions), and thus the momentum boost they would get on each reflection would get smaller and smaller. I'm not going to attempt the integral right now, but I suspect the situation is not a runaway to infinite speed. In any case, as I said, this ignores many other effects that would dominate.
For the record, my comment was mostly pointing out the hyperbole of the article. It was the article that was incorrectly implying that the technology was mature, not the company showing off its prototype, and I was taking issue with their analysis.
Furthermore, not all features are created equal. Some are so new and innovative that consumers are worth sacrificing something (like paying money, spending time, carrying something heavey, etc.). Other features are not worth much, and are only accepted once they are so innocuous that they don't get in the way of other features. Cell phones were sufficiently revolutionary that they were worth the cost and bulk. That hardly proves that every new feature is worth bulk and cost.
It is my opinion that this feature is insufficiently useful to be worth any added bulk. Of course, I may be wrong and I'm certainly willing to be convinced otherwise if someone has persuasive arguments (or perhaps I'll use one and fall in love with it). Saying that my concerns are groundless is, itself, groundless.
Food for thought: if your solar sail is using photon pressure, then by coating it in a photoelectric, you're halving its efficiency as a solar sail. Why? Well if your solar sail is a perfect reflector, then the photons bounce off and reverse direction, so the momentum change is twice the initial photon momentum (yes photons are massless but they do have momentum). If the sail is absorbing the photons for electricity, then they are not reflecting, so you merely absorb their momentum, making your forward impulse half what it would otherwise have been.
But, as we all know, solar sails work both by exploiting photon pressure, and solar wind (particles emitted by the sun), so the situation is maybe not that bad.