AOL and Gateway tried this but as far as I know it never went anywhere thanks to lousy marketing. Of course, the since-denied rumors that AOL/TW wants to buy RHAT might be an indication that they are still considering an AOL-on-linux play. I bet everyone's favorite media behemoth could wring some fancy concessions out of/.'s pet monopolist by threatening to mail out 10M CDs with linux as the foundation of a dedicated internet-appliance OS.
And yeah, I hate to keep that damn useless partition around, but it's a royal PITA to repartition a laptop harddrive, and it is handy to have a native win32 installation so I can run Mathematica under Wine on the rare occasion I need it. Someday I may spring for a UNIX version, but that costs money.
Democracy is mob rule, more or less. Of course, we don't live in a democracy, we live in a state that was originally conceived of as a constitutional representative republic, which has devolved into a mildly representative economically selecting oligarchy. Even so, getting a lot of people to do something would still be a good first step in making it right, legally. Ideally followed by petitions, public debate, elections, and eventually legislation. Then again, a few million dollars in campain contributions is generally easier.
If you meant morally right, on the other hand, I wouldn't bother having the argument -- you won't change any minds in this crowd.
Not to contribute to the me-too-ism on this thread, but I haven't felt the need to boot into the windows partition on my computer in a couple of years. Admittedly, I'm mostly using tools that have never been the traditional domain of MS -- data analysis, math stuff, writing papers in LaTeX. I've never had to embed a spreadsheet in a slideshow presentation in a word-processor document, and can't imagine why I would.
That said, I've built a few web/email/writing letters to grannie machines for various people, and not only was the result pretty much indistinguishable from what said people were expecting (NOT exactly like Win, mind you -- far more usable; have someone who's used to using Macs show you how to configure the Gnome UI sometime), but the whole experience was less of a headache for me than MS would have been. 15 minutes to install a base system, pop in a CD and let apt figure out how to install the 10 or so packages the user will really need, get a sandwhich and spend another 10 minutes tweaking configs and its done.
I'm not convinced that you're right about the impact of cheap online movies on ticket sales. For the forseeable future, the best quality movie that can be reasonably distributed electronically is going to be highly compressed, e.g. MPEG-4 or similar, video streams. While this format looks okay on a computer monitor, slap it up on your home entertainment system with 60-inch TV and 18 speakers, and the result will look and sound like absolute crap. That is why people are going to keep going to movie theaters -- to see a movie with very high fidelity on audiovisual equipment that they could never afford. If anything, look for ticket prices to keep going up as this will become the major draw of movie theaters.
Where this sort of streaming will have a big impact is in the video sale/rental market, which depending on the movie accounts for anywhere from 20-80% of total revenue. After all, an online stream or download is likely available before the video is released, is cheaper by far than buying the DVD, and likely looks better than the thouroughly beaten up VHS tapes at your local rental store. If anything, look for audiovisual effects to be regarded as a defense against online availability of movies in the future. Then people might actually go out and see the movie in a theater after downloading it, just to see/hear what they were missing.
On the other hand, $100M is an awful lot of money to spend making *anything*, and is certainly out of line with what is spent on most works of art. The protesters dancing outside the WEF in New York right now might have some ideas about how that money could have been more productively used. If summer action blockbusters go the way of pyrimid building as an art form, many would argue that cinematic art would be better off.
Nah, this won't work, because the string and axle will expand too - you just get the same stationary system, but a bit bigger.
Warning: really long ramble coming up. It's late, and I'm putting off more important stuff that I don't feel like doing.:-)
The string and axle can't expand, because they are made of matter, which is bound at small scales by (electromagnetic) forces that are far stronger than the repulsive force of de Sitter expansion. The string, as it happens, starts out minutely longer than it would be in a non-expanding universe since the molecular binding forces are at equilibrium with the small expansion force acting between adjacent molecules. For this kind of thing, think of matter as a bunch of masses connected by springs with some non-zero equilibrium length. Cosmic expansion acts to very gently push the two ends of the spring apart, but the spring doesn't expand forever -- only until the restoring force balances the expansion force.
Of course, the effect actually at work is changing the metric, which doesn't actually "push" on anything. Instead, it is changing how distance is measured, making the distance between two unrelated points scale up with time. This effect doesn't care about masses small enough to be gravitationally uninteresting, so we see distant galaxies zooming away from us -- they are too far away to gravitationally couple to us.
Similarly, the two masses in my "free energy" machine must be small enough not to gravitationally couple, but they must have inertia for us to work against. Placed far apart, in a given unit of time the distance between the masses will get some small fraction larger, which in the reference frame of an observer in the middle (or of one of the masses, for that matter) looks like each one has acquired a kinetic energy. We can use a string or something similar -- anything that doesn't expand -- to reduce the apparent kinetic energy, which we then get to use if we do it right, just like lowering a weight into an infinitely deep well and driving something off of the resulting torque.
Cool related fact: gravitationally bound systems don't expand either. Hence galaxies and solar systems don't eventually disperse due to the cosmic expansion. In fact, in a de Sitter space (most usually, empty space with a central point mass) space contracts, even if space outside is expanding. Look at the solar system: two unrelated points get closer together with time, and eventually end up in the center, i.e. fall into the sun. Give a mass some angular momentum, though, at it eventually stops falling inward, since we're keeping rotational symmetry. Exercise: what kind of momenta would you need to give my masses so that they forever stop moving apart?
I hate to break it to you, but our universe isn't even symmetric under time translation, much less time reversal. It is expanding after all, and this means that you can tell how much time has passed since the big bang by measuring the ambient photon temperature (the CMB), and can tell what direction you are moving in by noting whether the universe is expanding or contracting.
In fact, if the cosmological constant is real (probably) and is due to a non-zero vacuum energy (quite possibly), then energy is not conserved globally. But even if this isn't the case, you can get "free energy" out of an expanding universe with relative ease: just tie a string to two masses and wind it around an axle, place the masses many megaparsecs apart, and let the expansion of the universe pull them apart and consequentially spin the axle. Just make sure you can keep extending the string for all eternity, and you're set until the mass of the length of string becomes comparable to that of your masses on the ends.:-)
Really, though -- our universe is symmetric under time translation to very high accuracy for the distances and timescales that engineers are interested in, so in that regime yes, energy is conserved.
According to the article (in gr-qc/0109035, not the horrible thing linked from the/. article above), we essentially have a phase transition that results in an inflationary subspace inside this thin shell! I grant that, for some odd assumptions, this might be a stable solution, but I kind of doubt it. It has been proposed before that the collapse to a singularity triggers internal inflation, which is plausible but still gives a black hole, not a "gravstar".
Anyway, and I quote from their own article, "Here we forgo any discussion of the details of the quantum phase transition and present only the solution of Einstein's eqs." Mazur and Mottola have no clue how to make such a beast, either. If nothing else, the energy density wouldn't approach that needed for a phase transition until long after the entire assemblage was well within its own event horizon, again giving -- you guessed it! -- a Schwartzchild black hole. Recall, when a solid mass reaches the density required to fall within its own event horizon, the total density isn't much above nuclear densitites. During big bang baryosynthesis, densities are easily this large and inflation obviously didn't occur then (or else we'd have no protons in the universe).
>Secondly, black hole theory is a mess and only looks acceptable to modern eyes due to familiarity. The singularity in the system is a BIG clue that it's wrong.
Actually, all the singularity tells us is that we don't know shit about quantum gravity. Which, well, we already knew.
Well, then pay attention in QFT next semester, and don't try what you just described on the final exam. While you can kind of treat radiative corrections as a "math trick", they aren't precisely equivalent to zero-point fluctuation. You actually need this vacuum behavior to make boson force transmission work properly, not to mention keeping the electron mass finite.
What KjetilK is saying is that you won't learn anything about cosmology by reading their paper, because if you aren't already educated in the field it won't make a lick of sense to you.
That said, I have read this paper, and I think it would probably be comprehensible to anyone who has made it through Kolb & Turner or equivalent, and good undergraduate GR and QM textbooks. Alternately, you could read something like Shapiro & Teukolsky on black holes, but I wouldn't recommend buying it out of curiosity because it's $130 for a not-very-large paperback.
If you really want to read the stuff in the preprint archive, feel free by all means. Just wait until its not getting lots of hits from a story on the front page of/., and if you're out to learn generally about the field search for survey type articles.
This is a good point that really doesn't get made often enough -- namely, that every time a proprietary software company takes action to combat illegal sharing, they open the door a little wider to Free software. Usually this argument shows up when antipiracy measures are adopted to increase the cost of copyright infringement. One hopes that some of those who can no longer afford (or, as in this case, will no longer be able) to illegally acquire a given piece of proprietary software will turn to Free alternatives.
Mind now, I don't fundamentally care how many users gFoo has. Userbase is important to Free software in a couple of indirect ways: some of those users will submit bug reports or patches, or help in other ways with development; also, many users of Free software make it difficult for proprietary vendors to lock users into their products through closed formats, much less force new users to their product by making such formats into de facto standards.
Should Adobe go through with this withdrawal, I forsee (or at least hope for) benefits to Free software in that some former unlicensed users will go on to help make real Free substitutes for Adobe products -- e.g. Gimp has potential, but it ain't Photoshop yet -- or help i18nize various packages to their native locale.
This is beyond "trying to have a baby in one month". This is more like putting 5900 women in a room and trying to get a baby in one hour.
And as everyone knows, if you put 5900 randomly chosen (American, normally distributed) women in a room, you have to wait roughly 18 days for one of them to have a kid. You actually need 2.5 million to get a kid in an hour, and not even MS employs that many programmers. Though to hear some tell, the Open Source Movement might. Of course, they're predominantly male geeks, so you'd probably have to wait several years before 5900 open source programmers produced offspring, and even then it might just be a replicant.
"That basic fact immediately discounts and proves impossible any compressibility of random data, absolutely and non-refutably."
Well, that's a little harsh for talking about a statistical phenomenon. Since random numbers are randomly distributed in state space as well as numerically, it is true that roughly 50% of N-bit numbers will contain N bits of entropy; the other 50% will contain less. 25% will contain N-2 bits of entropy, and so on. In fact, one randomly chosen number in every 2^(N-1) will contain only one bit of entropy (you have to pick all 1's sooner or later)!
Specifically, the immutable sections are intended to be a place to put stuff
that deals exclusively with the relationship of the publishers or authors of the Document to the Document's overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (For example, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.)
Because the invariant sections (which are specially designated Secondary Sections) cannot contain information that the work is primarily about, it shouldn't go out of date in any way that is meaningful to the work in question. And anyway, if the author really screwed up and put something totally wrong in such a section, you can feel free to add your own errata.
At least in the sense you are talking about, the fate of the universe is already sealed. The result of interest was discovered about four years ago now, but I'm too lazy to look up the exact reference.
It turns out that you can calculate the absolute brightness of a type Ia supernova from its light curve (how quickly it fades away). By measuring the apparent brightness of a bunch of these events at large distances, we can find their physical distance. By measuring the redshift of the light arriving here, we can find out how long the light has been traveling (sorta; general relativity makes it slightly more complicated to explain what I'm talking about here. Look up "comoving distances" for yourself.).
The thing is, up until then everyone assumed that the universe is expanding but slowing down. Not so! Turns out, it is accelerating. We know from GR that only a vacuum energy density could produce this effect, and that is a constant per *physical* volume, while everything else in the universe spreads out with the increasing size of the comoving volume. As a result, the amount of vacuum energy can only increase, barring some kind of phase transition. Therefore, the acceleration can only increase with time.
So the answer is -- no, the universe will never collapse back on itself, but will expand forever at an ever increasing rate. The only thing that could change this would be a vacuum decay event, which would unfortunately probably destroy all matter in the universe.
Re:Um, if it's a star it can't be dark matter....
on
"Dark Matter" Observed
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· Score: 3, Informative
The term "dark matter" has wound up being overloaded in astrophysical discussions, because it has been used to name the solution to a number of different problems.
First, people noticed that we cannot observe enough luminous matter to either produce a flat universe, or account for the dymanical behavior of large-scale systems. This was long assumed to consist of halos of cold gas, dust, brown dwarfs, etc.
However, cosmological considerations (especially primordial nucleosynthesis) rules out this scenerio, because we can use the deuterium mass fraction to calculate the ratio of photons to baryons in the early universe. We know how many photons there are (per comoving volume, as usual), and it turns out that there are only enough baryons to account for about 4% of the density needed to produce a flat universe. Since the universe is not noticably non-flat, we can assume there is "a lot" of non-baryonic matter out there, in axions, massive neutrinos, or something more exotic. This stuff is called non-baryonic dark matter, unsurprisingly, and often gets confused with the other kind.
Finally, in the last five years or so we have received a couple of cool new data points: the angular size of the first harmonic mode of perturbations in the cosmic microwave background, and the distance scale to various redshifts, as seen using type Ia supernovae. The CMB data tells us that the universe really is flat, to high accuracy; otherwise, the perturbations -- we know how big they should be after all -- would be "lensed" by the curvature of spacetime. The supernovae data tells us that -- BIG surprise! -- the universe's expansion is accelerating, not slowing down at all. This implies that there is actually more vacuum energy than matter and energy combined. Best guess, the universe is roughly 70% vacuum energy, 30% matter. For some bizarre reason, people have been calling this the "dark energy" lately. Thus, even more confusion about what you mean when you say "dark matter".
If you feel that strongly that the world needs anonymous, untraceable email, stop whining and do somthing about it. Set up a server, host it somewhere, and let people know where it is and how to use it.
The world has already got anonymous, untraceable email in the cypherpunk and mixmaster remailer networks. If you really want to help out, set up one of these servers and announce yourself on alt.privacy.anon-server. If you want to know more about these systems, the best web page these days is probably here.
Of course, you should be aware that doing so will get you a lot of flames, a lot of network abuse, and such. Why? Because a lot of people don't know how to deal with real, hardcore anonymity. The people who run the remailers are dedicated privacy advocates who believe in the right to speak without fear, even if that enables some evils (spam, harassment, etc) and even if they have no control whatsoever over the data flowing through their servers.
Think about that: would you be comfortable providing an encrypted, anonymous service so powerful that neither you nor the FBI/NSA/etc would ever know about the kiddie porn and terrorist plots that could be flowing through your computer if, in return, you helped dissidents and human rights workers communicate without fear of reprisals from hostile governments and corporations? It's a tough call, but I'm certainly glad that at least a few people have the guts to publicly answer that one in the affirmative.
The debate here is between the idea there is and that there is not a net benefit in having an open society, where individuals by virtue of citizenship have access to whatever information they want so long as it doesn't post an immediate and vital security threat. Once you start censoring papers and publications because they can fathomably be used to hurt the government, you limit the public's ability of oversight in public health, security, and spending.
Indeed. As far as I can tell, nearly everyone here missed this juicy little tidbit from the article:
Indeed, chemical and water industry groups are lobbying the Bush administration to curtail regulations providing public access to the operations of public facilities, data that environmentalists say are critical to ensuring safety.
Hmm... now why on Earth would they do that? Everyone knows that the chemical industry has always had the best interests of the citizenry and the environment at heart. Obviously, if this operational data is removed from public view, these industries will just work that much harder to police themselves with respect to public health and the like.
Next information-restriction order that comes down, ask yourself: who could possibly have lobbied for that?
People, this is about not being quite so liberal with the plans for our US infrastructure. Note the article says that the information was "yanked", and not destroyed.
Erm... nope. Sez the article:
But then came last month's federal directive to U.S. libraries: "Destroy the report."
So a Syracuse University library clerk broke the disc into pieces, saving a single shard to prove that the deed was done.
...
Because the water survey was published and owned by the U.S. Geological Survey, the libraries that participate in the depository program said they had little choice but to comply. Some librarians asked if they could simply pull the CD from shelves and put it in a secure place, but federal officials told them it had to be destroyed.
So if by "yanked" you mean that a copy may still exist somewhere in the massive archives of the Government Printing Office, then I can't really argue. But from a public perspective, the disks have been smashed with no particular reason to believe that they will be made available again.
On the other hand, I'd be curious to know how many of those librarians quietly burned copies of those disks first, for safe keeping. Don't underestimate librarians: they are some of the most tenaciously pro-first amendment types you'll ever meet, and they are surprisingly technically sophisticated to boot. Corporate publishers have hated them for years; I guess now its the government's turn.
If you could get an patent on a method for doing something by using LEGO bricks, you could likewise get a patent on a method for doing the same thing using software.
What's the big deal?
This is more or less how software patents are supposed to work over here in the U.S., too. However, because the PTO has pathetically little software expertise, the result is that you can patent pretty much any stupid idea that is obvious to everyone else if your patent description ends with "...on a computer!"
The other big problem with this is that the patent system is explicitly not supposed to cover algorithms or mathematical formulae, because these are deemed fundamental properties of nature. However, patenting software is a surprisingly easy backdoor to patenting algorithms. E.g. RSA Data Security and the RSA patent which held back public key cryptography by a decade or more, and would have been worse if RSA had succeeded in convincing the PTO that their patent actually covers all forms of PK crypto.
Strictly speaking, there's always the revised steady-state model people -- many of whom are accomplished scientists who are IMHO mostly just being tenured and perverse.
I believe that their current model states that we live in an infinitely expanding universe filled with a false vacuum, out of which condenses a slow, steady stream of new matter at a just sufficient rate to keep the universe looking forever as it does now. Since this relies on some very poorly understood physics, they can just barely get away with this on a purely intellectual level, although nobody really takes them seriously.
I do occasionally find it kind of creepy that there isn't much (any?) solid evidence that PROVES them wrong, except for the bit that their version of the universe it totally constructed and assumes some pretty big coincidences. On the other hand, they're dead on in pointing out that in an expanding universe, time-translation symmetry is broken and thus conservation of mass-energy is no longer required.
Relativity imposes no limit on how fast space can expand. During the inflationary era, the Universe expanded faster than the speed of light.
So to speak. How would you measure the velocity of the expansion of space, anyway? You can't measure the velocity of objects that aren't at your exact location (cosmically speaking) in GR. You could take the mean velocity (distance they end up away from you divided by the time elapsed on your watch) but that is a function of how far away they started. The best units for this sort of thing are those of the Hubble constant, which is something like 68 (km/s)/Mpc (megaparsec). But this sort of unit isn't really amenable to saying "And now, space is expanding faster than light!" And anyway, this value has some serious fudge factors included that hinge on our assumptions about the geometry and evolution of the universe.
One thing you can say is that, in some regions, space is contracting faster than the speed of light -- it's called a black hole. Of course, objects (falling) inside a black hole can't tell that this is the case, although they can infer that this is the case based on the distribution of photons arriving from outside (being able to see the back of your head, etc).
It's sort of a similar statement to say that, in the absense of photons arriving from elsewhere in the universe (for elsewhere defined to be cosmically large), we could not tell that the universe is expanding. Of course, during the period of rapid inflation, the horizon would have been on the order of femptometers or less, meaning that unles you were significantly smaller than an atomic nucleus, you would definitely notice the expansion, as neighboring atoms went flying off at nearly the speed of light and dissapearing from your observable universe!
Hence in a strictly classical approximation, the two objects must be travelling apart at a relative velocity of 0.93c, in reality relativity and cosmology would probably tell you they don't have to moving apart nearly that fast, but the idea is there.
In reality, general relativity doesn't have a concept of relative velocity for objects that are separated by nonzero distance. In an expanding universe, it isn't the objects that are moving, for any sensible definition of motion. Instead, the space between them is getting bigger on its own. In the same sense, there isn't a well-defined concept of time across distances -- the elapsed time for a photon to traverse any path is identically zero. Thus, as far as GR is concerned, those stars are shining right now.
The best you can really do is measure the redshift, solve the Friedman equation, and say that our local chunk of space looked like that stuff over there about X years ago.
However, your classical approximation is correct for stuff that's merely moving, in the fictitious God's Eye View reference frame at least -- which is good enough for plenty of things.
IANAAstroPhysicist, so whether this explains the visibly red shift (since scientific spectrographs are much more sensitive than our eyes ), I cannot say.
Bingo! The article mentioned that this star cluster was found at a redshift of z=5.58 I believe. The formula of interest here is that
1+z=(Lamda_em - Lamda_ob)/Lamda_ob
This means that the light we observe from this star cluster is arriving at a bit less than a quarter of its original wavelength -- the red light seem in the picture was emitted as hard ultraviolet radiation from young massive stars! Yes, young stars are really hot.
If you think that's impressive, consider the quasars the Sloan Digital Sky Survey keeps finding out at z>6. We see them as faint red dots, but they are actually outshining entire galaxies, mostly in the form of hard X-rays. And then there's the cosmic microwave background, sitting out there at z~1300. That was once a sea of energetic photons, just slightly too cool to ionize all the hydrogen in the universe; now it is a 2.7 degree Kelvin hiss in your radio.
Executive summary: you'd better believe you can see cosmological redshifts.
Oh, and PS -- don't ever call it a "doppler shift", that really pisses off cosmologists (or at least the ones in my department). Doppler shifts are the result of objects moving toward/away from you emitting photons that are a different wavelength in your rest frame. In the case of cosmological redshifts, the objects in question are not only not moving away from us, but general relativity doesn't even have a concept of "relative velocities" on these scales. Instead, the photons are actually arriving with a different wavelength, because space expanded underneath them en route.
If you aren't sure there is a difference, try this thought experiment: an observer and an emitter are at relative rest in a static universe, when a photon is emitted. While the photon is in transit, the observer and emitter move farther apart, then come to rest again. The observer sees the photon at its original wavelength, since the motion occurred totally independantly of the photon. Now imagine that, while the photon was en route, the universe expands for a little while. The observer and emitter are in the same end state (i.e. farther apart and at relative rest), but the photon arrives with a reduced wavelength, because this time space expanded underneath the photon.
Lessee now... the article estimated the kinetic energy released at around 75 Ktons for 2 million kids. So bounce ~10^9 people with an average mass slighly greater than a British schoolkid and you should manage in the neighborhood of 50 Mtons or so. Of course, this would be dispersed over the whole of China (mostly the coastal regions, really).
On the other hand, if you could synchronize them, taking into account the propogation velocity of the leading compression wave, you might have a hope of delivering 1-10% of that energy to a target. So, they can deliver.5-5 Mtons of energy to the remoter parts of Mongolia or ships docked on their east coast. Not too shabby, actually.
Slashdot Mirror
AOL and Gateway tried this but as far as I know it never went anywhere thanks to lousy marketing. Of course, the since-denied rumors that AOL/TW wants to buy RHAT might be an indication that they are still considering an AOL-on-linux play. I bet everyone's favorite media behemoth could wring some fancy concessions out of /.'s pet monopolist by threatening to mail out 10M CDs with linux as the foundation of a dedicated internet-appliance OS.
And yeah, I hate to keep that damn useless partition around, but it's a royal PITA to repartition a laptop harddrive, and it is handy to have a native win32 installation so I can run Mathematica under Wine on the rare occasion I need it. Someday I may spring for a UNIX version, but that costs money.
Democracy is mob rule, more or less. Of course, we don't live in a democracy, we live in a state that was originally conceived of as a constitutional representative republic, which has devolved into a mildly representative economically selecting oligarchy. Even so, getting a lot of people to do something would still be a good first step in making it right, legally. Ideally followed by petitions, public debate, elections, and eventually legislation. Then again, a few million dollars in campain contributions is generally easier.
If you meant morally right, on the other hand, I wouldn't bother having the argument -- you won't change any minds in this crowd.
Not to contribute to the me-too-ism on this thread, but I haven't felt the need to boot into the windows partition on my computer in a couple of years. Admittedly, I'm mostly using tools that have never been the traditional domain of MS -- data analysis, math stuff, writing papers in LaTeX. I've never had to embed a spreadsheet in a slideshow presentation in a word-processor document, and can't imagine why I would.
That said, I've built a few web/email/writing letters to grannie machines for various people, and not only was the result pretty much indistinguishable from what said people were expecting (NOT exactly like Win, mind you -- far more usable; have someone who's used to using Macs show you how to configure the Gnome UI sometime), but the whole experience was less of a headache for me than MS would have been. 15 minutes to install a base system, pop in a CD and let apt figure out how to install the 10 or so packages the user will really need, get a sandwhich and spend another 10 minutes tweaking configs and its done.
I'm not convinced that you're right about the impact of cheap online movies on ticket sales. For the forseeable future, the best quality movie that can be reasonably distributed electronically is going to be highly compressed, e.g. MPEG-4 or similar, video streams. While this format looks okay on a computer monitor, slap it up on your home entertainment system with 60-inch TV and 18 speakers, and the result will look and sound like absolute crap. That is why people are going to keep going to movie theaters -- to see a movie with very high fidelity on audiovisual equipment that they could never afford. If anything, look for ticket prices to keep going up as this will become the major draw of movie theaters.
Where this sort of streaming will have a big impact is in the video sale/rental market, which depending on the movie accounts for anywhere from 20-80% of total revenue. After all, an online stream or download is likely available before the video is released, is cheaper by far than buying the DVD, and likely looks better than the thouroughly beaten up VHS tapes at your local rental store. If anything, look for audiovisual effects to be regarded as a defense against online availability of movies in the future. Then people might actually go out and see the movie in a theater after downloading it, just to see/hear what they were missing.
On the other hand, $100M is an awful lot of money to spend making *anything*, and is certainly out of line with what is spent on most works of art. The protesters dancing outside the WEF in New York right now might have some ideas about how that money could have been more productively used. If summer action blockbusters go the way of pyrimid building as an art form, many would argue that cinematic art would be better off.
Nah, this won't work, because the string and axle will expand too - you just get the same stationary system, but a bit bigger.
Warning: really long ramble coming up. It's late, and I'm putting off more important stuff that I don't feel like doing. :-)
The string and axle can't expand, because they are made of matter, which is bound at small scales by (electromagnetic) forces that are far stronger than the repulsive force of de Sitter expansion. The string, as it happens, starts out minutely longer than it would be in a non-expanding universe since the molecular binding forces are at equilibrium with the small expansion force acting between adjacent molecules. For this kind of thing, think of matter as a bunch of masses connected by springs with some non-zero equilibrium length. Cosmic expansion acts to very gently push the two ends of the spring apart, but the spring doesn't expand forever -- only until the restoring force balances the expansion force.
Of course, the effect actually at work is changing the metric, which doesn't actually "push" on anything. Instead, it is changing how distance is measured, making the distance between two unrelated points scale up with time. This effect doesn't care about masses small enough to be gravitationally uninteresting, so we see distant galaxies zooming away from us -- they are too far away to gravitationally couple to us.
Similarly, the two masses in my "free energy" machine must be small enough not to gravitationally couple, but they must have inertia for us to work against. Placed far apart, in a given unit of time the distance between the masses will get some small fraction larger, which in the reference frame of an observer in the middle (or of one of the masses, for that matter) looks like each one has acquired a kinetic energy. We can use a string or something similar -- anything that doesn't expand -- to reduce the apparent kinetic energy, which we then get to use if we do it right, just like lowering a weight into an infinitely deep well and driving something off of the resulting torque.
Cool related fact: gravitationally bound systems don't expand either. Hence galaxies and solar systems don't eventually disperse due to the cosmic expansion. In fact, in a de Sitter space (most usually, empty space with a central point mass) space contracts, even if space outside is expanding. Look at the solar system: two unrelated points get closer together with time, and eventually end up in the center, i.e. fall into the sun. Give a mass some angular momentum, though, at it eventually stops falling inward, since we're keeping rotational symmetry. Exercise: what kind of momenta would you need to give my masses so that they forever stop moving apart?
I hate to break it to you, but our universe isn't even symmetric under time translation, much less time reversal. It is expanding after all, and this means that you can tell how much time has passed since the big bang by measuring the ambient photon temperature (the CMB), and can tell what direction you are moving in by noting whether the universe is expanding or contracting.
:-)
In fact, if the cosmological constant is real (probably) and is due to a non-zero vacuum energy (quite possibly), then energy is not conserved globally. But even if this isn't the case, you can get "free energy" out of an expanding universe with relative ease: just tie a string to two masses and wind it around an axle, place the masses many megaparsecs apart, and let the expansion of the universe pull them apart and consequentially spin the axle. Just make sure you can keep extending the string for all eternity, and you're set until the mass of the length of string becomes comparable to that of your masses on the ends.
Really, though -- our universe is symmetric under time translation to very high accuracy for the distances and timescales that engineers are interested in, so in that regime yes, energy is conserved.
According to the article (in gr-qc/0109035, not the horrible thing linked from the /. article above), we essentially have a phase transition that results in an inflationary subspace inside this thin shell! I grant that, for some odd assumptions, this might be a stable solution, but I kind of doubt it. It has been proposed before that the collapse to a singularity triggers internal inflation, which is plausible but still gives a black hole, not a "gravstar".
Anyway, and I quote from their own article, "Here we forgo any discussion of the details of the quantum phase transition and present only the solution of Einstein's eqs." Mazur and Mottola have no clue how to make such a beast, either. If nothing else, the energy density wouldn't approach that needed for a phase transition until long after the entire assemblage was well within its own event horizon, again giving -- you guessed it! -- a Schwartzchild black hole. Recall, when a solid mass reaches the density required to fall within its own event horizon, the total density isn't much above nuclear densitites. During big bang baryosynthesis, densities are easily this large and inflation obviously didn't occur then (or else we'd have no protons in the universe).
>Secondly, black hole theory is a mess and only looks acceptable to modern eyes due to familiarity. The singularity in the system is a BIG clue that it's wrong.
Actually, all the singularity tells us is that we don't know shit about quantum gravity. Which, well, we already knew.
Well, then pay attention in QFT next semester, and don't try what you just described on the final exam. While you can kind of treat radiative corrections as a "math trick", they aren't precisely equivalent to zero-point fluctuation. You actually need this vacuum behavior to make boson force transmission work properly, not to mention keeping the electron mass finite.
What KjetilK is saying is that you won't learn anything about cosmology by reading their paper, because if you aren't already educated in the field it won't make a lick of sense to you.
/., and if you're out to learn generally about the field search for survey type articles.
That said, I have read this paper, and I think it would probably be comprehensible to anyone who has made it through Kolb & Turner or equivalent, and good undergraduate GR and QM textbooks. Alternately, you could read something like Shapiro & Teukolsky on black holes, but I wouldn't recommend buying it out of curiosity because it's $130 for a not-very-large paperback.
If you really want to read the stuff in the preprint archive, feel free by all means. Just wait until its not getting lots of hits from a story on the front page of
This is a good point that really doesn't get made often enough -- namely, that every time a proprietary software company takes action to combat illegal sharing, they open the door a little wider to Free software. Usually this argument shows up when antipiracy measures are adopted to increase the cost of copyright infringement. One hopes that some of those who can no longer afford (or, as in this case, will no longer be able) to illegally acquire a given piece of proprietary software will turn to Free alternatives.
Mind now, I don't fundamentally care how many users gFoo has. Userbase is important to Free software in a couple of indirect ways: some of those users will submit bug reports or patches, or help in other ways with development; also, many users of Free software make it difficult for proprietary vendors to lock users into their products through closed formats, much less force new users to their product by making such formats into de facto standards.
Should Adobe go through with this withdrawal, I forsee (or at least hope for) benefits to Free software in that some former unlicensed users will go on to help make real Free substitutes for Adobe products -- e.g. Gimp has potential, but it ain't Photoshop yet -- or help i18nize various packages to their native locale.
And as everyone knows, if you put 5900 randomly chosen (American, normally distributed) women in a room, you have to wait roughly 18 days for one of them to have a kid. You actually need 2.5 million to get a kid in an hour, and not even MS employs that many programmers. Though to hear some tell, the Open Source Movement might. Of course, they're predominantly male geeks, so you'd probably have to wait several years before 5900 open source programmers produced offspring, and even then it might just be a replicant.
"That basic fact immediately discounts and proves impossible any compressibility of random data, absolutely and non-refutably."
Well, that's a little harsh for talking about a statistical phenomenon. Since random numbers are randomly distributed in state space as well as numerically, it is true that roughly 50% of N-bit numbers will contain N bits of entropy; the other 50% will contain less. 25% will contain N-2 bits of entropy, and so on. In fact, one randomly chosen number in every 2^(N-1) will contain only one bit of entropy (you have to pick all 1's sooner or later)!
You don't.
Specifically, the immutable sections are intended to be a place to put stuff
to quote from the Free Documentation License, section 1.
Because the invariant sections (which are specially designated Secondary Sections) cannot contain information that the work is primarily about, it shouldn't go out of date in any way that is meaningful to the work in question. And anyway, if the author really screwed up and put something totally wrong in such a section, you can feel free to add your own errata.
At least in the sense you are talking about, the fate of the universe is already sealed. The result of interest was discovered about four years ago now, but I'm too lazy to look up the exact reference.
It turns out that you can calculate the absolute brightness of a type Ia supernova from its light curve (how quickly it fades away). By measuring the apparent brightness of a bunch of these events at large distances, we can find their physical distance. By measuring the redshift of the light arriving here, we can find out how long the light has been traveling (sorta; general relativity makes it slightly more complicated to explain what I'm talking about here. Look up "comoving distances" for yourself.).
The thing is, up until then everyone assumed that the universe is expanding but slowing down. Not so! Turns out, it is accelerating. We know from GR that only a vacuum energy density could produce this effect, and that is a constant per *physical* volume, while everything else in the universe spreads out with the increasing size of the comoving volume. As a result, the amount of vacuum energy can only increase, barring some kind of phase transition. Therefore, the acceleration can only increase with time.
So the answer is -- no, the universe will never collapse back on itself, but will expand forever at an ever increasing rate. The only thing that could change this would be a vacuum decay event, which would unfortunately probably destroy all matter in the universe.
The term "dark matter" has wound up being overloaded in astrophysical discussions, because it has been used to name the solution to a number of different problems.
First, people noticed that we cannot observe enough luminous matter to either produce a flat universe, or account for the dymanical behavior of large-scale systems. This was long assumed to consist of halos of cold gas, dust, brown dwarfs, etc.
However, cosmological considerations (especially primordial nucleosynthesis) rules out this scenerio, because we can use the deuterium mass fraction to calculate the ratio of photons to baryons in the early universe. We know how many photons there are (per comoving volume, as usual), and it turns out that there are only enough baryons to account for about 4% of the density needed to produce a flat universe. Since the universe is not noticably non-flat, we can assume there is "a lot" of non-baryonic matter out there, in axions, massive neutrinos, or something more exotic. This stuff is called non-baryonic dark matter, unsurprisingly, and often gets confused with the other kind.
Finally, in the last five years or so we have received a couple of cool new data points: the angular size of the first harmonic mode of perturbations in the cosmic microwave background, and the distance scale to various redshifts, as seen using type Ia supernovae. The CMB data tells us that the universe really is flat, to high accuracy; otherwise, the perturbations -- we know how big they should be after all -- would be "lensed" by the curvature of spacetime. The supernovae data tells us that -- BIG surprise! -- the universe's expansion is accelerating, not slowing down at all. This implies that there is actually more vacuum energy than matter and energy combined. Best guess, the universe is roughly 70% vacuum energy, 30% matter. For some bizarre reason, people have been calling this the "dark energy" lately. Thus, even more confusion about what you mean when you say "dark matter".
The world has already got anonymous, untraceable email in the cypherpunk and mixmaster remailer networks. If you really want to help out, set up one of these servers and announce yourself on alt.privacy.anon-server. If you want to know more about these systems, the best web page these days is probably here.
Of course, you should be aware that doing so will get you a lot of flames, a lot of network abuse, and such. Why? Because a lot of people don't know how to deal with real, hardcore anonymity. The people who run the remailers are dedicated privacy advocates who believe in the right to speak without fear, even if that enables some evils (spam, harassment, etc) and even if they have no control whatsoever over the data flowing through their servers.
Think about that: would you be comfortable providing an encrypted, anonymous service so powerful that neither you nor the FBI/NSA/etc would ever know about the kiddie porn and terrorist plots that could be flowing through your computer if, in return, you helped dissidents and human rights workers communicate without fear of reprisals from hostile governments and corporations? It's a tough call, but I'm certainly glad that at least a few people have the guts to publicly answer that one in the affirmative.
Indeed. As far as I can tell, nearly everyone here missed this juicy little tidbit from the article:
Hmm ... now why on Earth would they do that? Everyone knows that the chemical industry has always had the best interests of the citizenry and the environment at heart. Obviously, if this operational data is removed from public view, these industries will just work that much harder to police themselves with respect to public health and the like.
Next information-restriction order that comes down, ask yourself: who could possibly have lobbied for that?
Erm ... nope. Sez the article:
So if by "yanked" you mean that a copy may still exist somewhere in the massive archives of the Government Printing Office, then I can't really argue. But from a public perspective, the disks have been smashed with no particular reason to believe that they will be made available again.
On the other hand, I'd be curious to know how many of those librarians quietly burned copies of those disks first, for safe keeping. Don't underestimate librarians: they are some of the most tenaciously pro-first amendment types you'll ever meet, and they are surprisingly technically sophisticated to boot. Corporate publishers have hated them for years; I guess now its the government's turn.
This is more or less how software patents are supposed to work over here in the U.S., too. However, because the PTO has pathetically little software expertise, the result is that you can patent pretty much any stupid idea that is obvious to everyone else if your patent description ends with "...on a computer!"
The other big problem with this is that the patent system is explicitly not supposed to cover algorithms or mathematical formulae, because these are deemed fundamental properties of nature. However, patenting software is a surprisingly easy backdoor to patenting algorithms. E.g. RSA Data Security and the RSA patent which held back public key cryptography by a decade or more, and would have been worse if RSA had succeeded in convincing the PTO that their patent actually covers all forms of PK crypto.
Strictly speaking, there's always the revised steady-state model people -- many of whom are accomplished scientists who are IMHO mostly just being tenured and perverse.
I believe that their current model states that we live in an infinitely expanding universe filled with a false vacuum, out of which condenses a slow, steady stream of new matter at a just sufficient rate to keep the universe looking forever as it does now. Since this relies on some very poorly understood physics, they can just barely get away with this on a purely intellectual level, although nobody really takes them seriously.
I do occasionally find it kind of creepy that there isn't much (any?) solid evidence that PROVES them wrong, except for the bit that their version of the universe it totally constructed and assumes some pretty big coincidences. On the other hand, they're dead on in pointing out that in an expanding universe, time-translation symmetry is broken and thus conservation of mass-energy is no longer required.
So to speak. How would you measure the velocity of the expansion of space, anyway? You can't measure the velocity of objects that aren't at your exact location (cosmically speaking) in GR. You could take the mean velocity (distance they end up away from you divided by the time elapsed on your watch) but that is a function of how far away they started. The best units for this sort of thing are those of the Hubble constant, which is something like 68 (km/s)/Mpc (megaparsec). But this sort of unit isn't really amenable to saying "And now, space is expanding faster than light!" And anyway, this value has some serious fudge factors included that hinge on our assumptions about the geometry and evolution of the universe.
One thing you can say is that, in some regions, space is contracting faster than the speed of light -- it's called a black hole. Of course, objects (falling) inside a black hole can't tell that this is the case, although they can infer that this is the case based on the distribution of photons arriving from outside (being able to see the back of your head, etc).
It's sort of a similar statement to say that, in the absense of photons arriving from elsewhere in the universe (for elsewhere defined to be cosmically large), we could not tell that the universe is expanding. Of course, during the period of rapid inflation, the horizon would have been on the order of femptometers or less, meaning that unles you were significantly smaller than an atomic nucleus, you would definitely notice the expansion, as neighboring atoms went flying off at nearly the speed of light and dissapearing from your observable universe!
In reality, general relativity doesn't have a concept of relative velocity for objects that are separated by nonzero distance. In an expanding universe, it isn't the objects that are moving, for any sensible definition of motion. Instead, the space between them is getting bigger on its own. In the same sense, there isn't a well-defined concept of time across distances -- the elapsed time for a photon to traverse any path is identically zero. Thus, as far as GR is concerned, those stars are shining right now.
The best you can really do is measure the redshift, solve the Friedman equation, and say that our local chunk of space looked like that stuff over there about X years ago.
However, your classical approximation is correct for stuff that's merely moving, in the fictitious God's Eye View reference frame at least -- which is good enough for plenty of things.
Bingo! The article mentioned that this star cluster was found at a redshift of z=5.58 I believe. The formula of interest here is that
1+z=(Lamda_em - Lamda_ob)/Lamda_ob
This means that the light we observe from this star cluster is arriving at a bit less than a quarter of its original wavelength -- the red light seem in the picture was emitted as hard ultraviolet radiation from young massive stars! Yes, young stars are really hot.
If you think that's impressive, consider the quasars the Sloan Digital Sky Survey keeps finding out at z>6. We see them as faint red dots, but they are actually outshining entire galaxies, mostly in the form of hard X-rays. And then there's the cosmic microwave background, sitting out there at z~1300. That was once a sea of energetic photons, just slightly too cool to ionize all the hydrogen in the universe; now it is a 2.7 degree Kelvin hiss in your radio.
Executive summary: you'd better believe you can see cosmological redshifts.
Oh, and PS -- don't ever call it a "doppler shift", that really pisses off cosmologists (or at least the ones in my department). Doppler shifts are the result of objects moving toward/away from you emitting photons that are a different wavelength in your rest frame. In the case of cosmological redshifts, the objects in question are not only not moving away from us, but general relativity doesn't even have a concept of "relative velocities" on these scales. Instead, the photons are actually arriving with a different wavelength, because space expanded underneath them en route.
If you aren't sure there is a difference, try this thought experiment: an observer and an emitter are at relative rest in a static universe, when a photon is emitted. While the photon is in transit, the observer and emitter move farther apart, then come to rest again. The observer sees the photon at its original wavelength, since the motion occurred totally independantly of the photon. Now imagine that, while the photon was en route, the universe expands for a little while. The observer and emitter are in the same end state (i.e. farther apart and at relative rest), but the photon arrives with a reduced wavelength, because this time space expanded underneath the photon.
Lessee now ... the article estimated the kinetic energy released at around 75 Ktons for 2 million kids. So bounce ~10^9 people with an average mass slighly greater than a British schoolkid and you should manage in the neighborhood of 50 Mtons or so. Of course, this would be dispersed over the whole of China (mostly the coastal regions, really).
.5-5 Mtons of energy to the remoter parts of Mongolia or ships docked on their east coast. Not too shabby, actually.
On the other hand, if you could synchronize them, taking into account the propogation velocity of the leading compression wave, you might have a hope of delivering 1-10% of that energy to a target. So, they can deliver