His opinion pieces are carried on PBS' website. Does he have a show on PBS? I've searched the TV schedules for all the nearby PBS stations but no one seems to carry a show entitled "I, Cringely." Is it a show that's carried somewhere? Or does he have a show of some other name, and as a result gets to do this opinion piece on their web site as well? If so, what's the other show? What's it about? Is it any good at all?
And one of Maxwell's Laws ("the divergence of the magnetic field equals zero") has, as a direct consequence, an absolute law: NO MAGNETIC MONOPOLES EXIST. NO OPEN MAGNETIC FIELD LINES EXIST.
So if Maxwell's Laws are wrong and relativity is built heavily on Maxwell's Laws, then there's a tantalizing chance relativity is wrong.
Or if Maxwell's Laws are right and monopoles are conclusively proven not to exist, then there's a tantalizing chance quantum mechanics is wrong.
You have to be careful here. Your first paragraph is a correct statement of what's implied by one of the four Maxwell Equations. It's a bit misleading, though, to say that "relativity is built heavily on Maxwell's Laws." That seems to imply that relativity somehow depends upon Maxwell's Equations being true. That isn't correct. A better way of putting it is that Maxwell's Equations can be shown to incorporate special relativity within them, in the sense that the laws of electromagnetism stay the same ("Lorentz covariance") after changing relativistic reference frames (through a Lorentz transformation).
In fact, we already know that the Maxwell Equations are wrong. We know that they're wrong because they fail to explain behavior on the quantum scale. For that, we turn to quantum electrodynamics (QED), which, again, incorporates special relativity. Maxwell's Equations are thus seen as an excellent approximation on macroscopic scales. The failure of such an approximation to allow for magnetic monopoles doesn't seem like much of a failure.
That said, I've forgotten enough of my field theory that I don't remember how monopoles fit into QED. But I do know lots of field theorists, and most of them believe that monopoles are around (they'd be produced by the breaking of certain fundamental symmetries that many theorists expect to have been present in the early universe; although any inflationary epoch in the history of the Universe would be expected to make monopoles very very rare); and they don't seem to be stressing about the implications of monopoles for QED. So my suspicion is that QED is OK.
Oh, and just as a brief defense of string theorists . ..I don't much like string theory myself, and I echo your reluctance to take it seriously on the basis of the difficulty in making comparison to experiment. But I think most string theorists would take exception to your statement
that string theories "literally cannot be experimentally tested at any realistic energy level." To we who are not string theorists, that's what it looks like, yes; but a string theorist would simply reply that string theorists haven't yet been clever enough to figure out how to extract observable predictions. In other words, I don't think many string theorists would disagree with the principle that for a theory to be interesting, it must be testable. In fact, they would claim that that's their goal with string theory -- to figure out how to make realistically testable predictions -- and they just haven't yet been successful. The Planck scale is a long way from observable energy scales, to be sure. But people explore ideas that allow the examination of classes of models, e.g. the "one large dimension" stuff from a few years ago that would have had observable consequences.
Seriously, I've been on the debian-users mailing list for a long time, and it's made up almost exclusively of nice, outgoing, helpful people. I've never seen a newbie with a legitimate question get an RTFM from the regulars.
Well, be careful. I have seen newbies with legitimate questions get RTFMs there; just not in that form. Rather, they're typically delivered in a less mean-spirited way. For example, someone posting "I got this error message: _______. What does it mean? What do I do?" might get a response of "Google is your friend for this sort of thing. I googled on that error message and got this webpage (________), which has an explanation and a solution." Sometimes a link to Eric Raymond's "How To Ask Questions The Smart Way" will be provided, as well. Much kinder than an RTFM, but in the same vein.
Not that I think that's a bad thing. To me, part of being helpful is to help people learn how to help themselves in the future . ..so long as one does so kindly (which, for the most part, debian-user does, and #debian@freenode doesn't).
But at the same time, I didn't want what you wrote above to give the impression that no one is ever encouraged to do some work themselves.
It kind of sucks to read about all the great ideas and ideals that Debian represents and then get a dose of the real Debian community in #debian.
There are a fair number of assholes and jerks in #debian@freenode, it's true. But that sort of thing happens in any community. No matter what the subject, there will be people who get their entire sense of self-worth from treating those less-far-along like crap.
The key is to realize that there are other avenues for help. The
debian-user mailing list,
in contrast to #debian, is almost always friendly (even when someone does something stupid, the response may be stern, but almost never *mean*); and it's tremendously more informative/educational/useful. I highly recommend it.
IIRC, the smallest scale at which antimatter can dominate is galactic superclusters, but even that may now be ruled out.
I just wanted to respond to back this up; at least as of the mid-90's, you'd have to go out beyond the Local Supercluster. I haven't followed this since then, unfortunately, so I don't know what the implication of the current (GRO?) data is.
Here's something to think about that follows: light emitted by antimatter, because the electric and magnetic fields are generated in reverse, would be inverted in frequency/wavelength.
I have no idea what you mean by "inverted in frequency/wavelength." However, the truth is that light would be perceptibly unaffected. As correctly noted by several people here, the photon is its own antiparticle. Or, if you wish to think in terms of E-M waves, changing the sign of the E- and B-fields in an electromagnetic wave is simply equivalent to a 180-degree phase change (remember those sin/cos waves), which we wouldn't notice.
Would antimatter tend to absorb high-frequency light (uber-ultra-violet) and permit low-frequency (infrared) to pass through, rather than the reverse with matter?
We don't have a whole lot of experience at this point studying the atomic structure of anti-atoms.
However, there's nothing at this point to cause one to expect that their atomic physics would be dramatically different from theoretical expectation: that they'd be the same as regular atoms.
The only thing that I'm having trouble with is the microwave background radiation. Light and matter decoupled when the universe was extremely compact - the parts emitting the background radiation we see would have been very close indeed to our location. Space must have been growing fast enough for points this close to still be moving apart at or very close to the speed of light.
Well, not as compact as you might think. The surface of last scattering, and matter-radiation decoupling, are at a redshift of about 1000. That means that distance scales have expanded by a factor of 1000 between decoupling and the present.
That seems like it'd make things pretty small.
However, for flat universes (which appears close to correct, and more importantly is the only case for which I can remember the equations off the top of my head right now, books not being handy), the coordinate distance out to a redshift of 1000 is basically 97% of the way out to the particle horizon (the edge of the theoretically observable universe). A factor of 1000 is a lot of compression, to be sure; but we're also talking a big distance scale.
On reflection, the relation you provided does give an expansion velocity between any two points that tends towards infinity as time tends towards zero. It's just a change in how I'd viewed the early universe.
Right -- although obviously, in the case of the microwave background, we don't go back to that close to t=0; just something like
a factor of 3e-5 of the current age of the universe. The Hubble parameter is basically just (da/dt)/a; for any power law form for a(t), H will scale as 1/t. In terms of the scale factor a, H scales as a^(-3/2) for a matter-dominated universe; a factor of 1000 smaller scale factor makes for a Hubble constant larger by over four orders of magnitude at that time than at present.
> They also said that the number may actually be too small, given that light
> from some parts of the Universe hasn't had time to reach us yet. So it may
> be impossible to determine the total size of the Universe.
The total size of the universe may even be infinite. At any given time, we can only see the parts close enough for light emitted in the past to reach us, but to the best of my knowledge there is no restriction on the dimensions of the universe as a whole (perhaps an astrophysicist can enlighten me if I'm mistaken?).
Right now, we have no good data suggesting the Universe has finite volume (there's one group that thinks they may see a signature of finite volume in the microwave background data, but it's a very speculative claim). The most straightforward theoretical model of how a Universe of finite volume could be true -- a closed universe model -- appears to be ruled out by a variety of observations. So, if you want a Universe of finite volume, it appears that you have to appeal to new physics in the early Universe for which we have no current experimental evidence (see, e.g. the work of some particle theorists on so-called "small universe models"). That doesn't make it wrong, of course; but it does make most people lean towards infinite volume.
> One question I've always had is: when we look back in time to the
> creation of the Universe, we see light from that time. So the light has
> been traveling for 15 billion years to get to us. But if that light
> has been traveling that whole time toward us, how did we get here
> first?
[ snip ]
As the universe expands, more space is added between any given points in the universe. Thus, light emitted from an object that was initially quite close to us could find itself traversing a surprisingly large distance before finally reaching us. This is why light from the very early universe took so long to reach us, if I understand correctly.
You do understand correctly (yay!). As just one example, it's pretty straightforward to show with some simple algebra that a universe where the expansion is described by
a(t) proportional to t^(2/3),
where "a(t)" is the scale factor of the universe (an increase in "a" by a factor of two means distance scales have doubled) and "t" is time, results in the most distant objects we can theoretically see being three times more distant than the speed of light times the age of the Universe. The functional form of a(t) is expected to be more complicated than that, of course; but data suggests that that power law is a good approximation for most of the history of the Universe. And the reason for such a surprising result, as you say, is that when we observe light from a distant source, its distance away is now larger than it was at the time it emitted.
The universe expands by growing empty space everywhere, not just at its edges. This is why you measure the Hubble constant as speed per distance, (ie. kilometers per second per Megaparsec).
. ..is that I would change your description of the Hubble parameter to apparent recession velocity per distance. This is a subtle but important change, because it addresses one of the most common misconceptions about the expansion of the Universe -- namely, that we think the galaxies are flying apart from each other in space, when what's actually going on (as you note in your post) is an expansion of space itself. There are a kajillion analogies people use -- dots on a stretching rubber sheet or inflating balloon, raisins in a loaf of baking (and thus expanding) raisin bread. In all such analogies (which are ultimately bad analogies in full, but still serve to illustrate this point), the dots/raisins/whatever are getting farther apart, but not because they're moving compared to the medium in which they're embedded (the rubber sheet/bread/whatever). Rather, it's simply because of an expansion in the medium.
It's clear from your post that you know this; I just wanted to emphasize it for anyone else who might be reading, because it's such a common misconception, and because some of the questions/comments in this thread have indicated that "galaxies moving apart through space" is what people think is going on.
IANAPhysicist, but I'm pretty sure I can answer some of your questions. It has been theorized that the speed of light has changed in the past, and therefore can continue to change. However, if light used to be slower, then matter could still not travel faster than the slower speed, following all the current known laws.
And it doesn't really matter anyway, since we have no good evidence at present that the speed of light has changed significantly over the history of the Universe, and (especially) since an appeal to a changing speed of light is not necessary to answer the question (of how we could have gotten so far away from the stars whose light has been travelling to us almost since the Big Bang).
Nobody's reading this thread anymore, but I still feel like responding to this . . .
Yes, but it's always possible that that 7-8% error over the visible universe is actually only part of a much larger structural inconsistency that we simply can't observe (yet).
Sure. It's also possible that tomorrow, someone will do an experiment or observation that overturns the principle of conservation of momentum or energy, or the 2nd Law of Thermodynamics. I doubt it, but it's possible.
Nothing you would use to make predictions is ever known to be 100% true in science; that's not how science works. You do experiments/observations, collect data, construct your best theories/models, and compare them to new data. As you collect more data, you either invalidate your theory/model, or you bolster its support.
Right now, the data shows a gradual convergence towards homogeneity at larger and larger scales.
We know from microwave background observations that the level of mass inhomogeneity on really huge scales, out to redshifts of 1000 or so, is at less than 1e-5. Furthermore, we've had a lot of success with the relativistic hot Big Bang model; the success of the model makes us feel good about the assumptions upon which it's based, and one of those assumptions is that of homogeneity and isotropy on sufficiently large scales (the so-called "Cosmological Principle").
Maybe in the end, this all turns out to be wrong -- maybe there is some large-scale inhomogeneity out there, on scales so large we haven't yet observed them; but right now, lots of data and ways of looking at things suggest that large-scale homogeneity is a good way to think, so that's what people work with.
By calculating the population of my neighborhood and assuming that my neighborhood has average distribution...
From the article:
> That number was then multiplied by the number of similar sized strips
> needed to cover the entire sky, Driver said, and then multiplied again
> out to the edge of the visible universe.
I wonder if this sort of "science" is how hardware manufacturers get their numbers?
Be careful. Do you have a reason to believe that your neighborhood is typical? Do you have data indicating such?
The astronomers in question didn't use such an approach because they're idiots; they used such an approach because we already have a heck of a lot of data about the galaxy distribution. The RMS (fractional) fluctuation in galaxy number count in a random volume the size of the one they surveyed is expected to be tiny; and it's expected to be tiny because of surveys we've already done which indicate such a convergence towards homogeneity as scale increases.
One issue is essentially with the ability of authors to define "invariant sections" of their documents, the subsequent modification of which would violate the GFDL. This conflicts with the requirement of the DFSG that licensing must allow modifications, and must permit the modifications to be distributed under the same licensing terms as the original, as e.g. the GPL does.
Other people have
raised the concern
that the GFDL's restrictions on the use of
"technical measures to obstruct or control the reading or further copying of the copies you make or distribute" -- a restriction that, on the surface, makes sense in that it prevents attempts to limit the freedom others have to read the distributed copies -- could have the unintended consequence of forbidding putting documents covered by the GFDL on devices which are encrypted for personal security.
I'm curious whether FSF folks speaking about licenses plan to discuss this at the seminar(s).
> I am so sick of this infinitely repeated bullshit claim.
The only "bullshit" is what you posted. Why don't you try reading the material at the links you provided:
You missed his/her point completely. The original poster asserted that copyright is covered by civil law rather than criminal law. The respondant to whom you replied gave counterexamples, to show that in the U.S. copyright comes under both civil and criminal law. You assert that the counterexamples don't cover p2p file swapping; that's true, but utterly irrelevant to his/her point: to whit, "is the assertion that copyright is solely the province of civil law correct?" The answer, as demonstrated, is no, it isn't correct.
"Theft" is a crime. "Copyright infringement" is a civil offense.
Again, it ain't necessarily so. Copyright law is mostly civil law, true; but there are already laws in the books that criminalize certain types of copyright infringement. The DMCA is one example. For another, commercial copyright violation involving more than 10 copies and monetary value over $2500 is a federal felony.
It's true that the particular type of copyright infringement in question here is not (yet) a felony; but since in this subthread we're trying to be careful about our use of terminology, it's incorrect to make the blanket assertion that copyright infringement is solely the province of civil law. This law wishes to expand the types of copyright infringement that are considered federal felonies, beyond what they currently are.
Theft is a criminal offence. Copyright violation is a civil offence. That is a very big difference, and one the media don't seem to have noticed.
This point (that copyright is a civil offence) used to be fair, but isn't anymore.
There are already laws in place making certain types of copyright offenses criminal acts in the U.S, the DMCA for example.
Trade secrets, copyrights, and patents, are three different things, covered by three different sets of legislation and case law, and typically suggest three different approaches for relevant IP management. Most of Linus' comments in the article are about copyright. The LKML entry you reproduce is about patents. Patent issues have nothing to do with the dispute over RCU.
You say that you've "reported this....to the appropriate people." Has that been in private conversation, or has that been through the LKML?
I mean, it's hard to believe that only one person would have ever noticed this; but if so, I would expect that lots of people would care. And the more people on the LKML that know about it, the more likely it is for something to happen . . .
This is off-topic, I know; but based on the story author's question, I'm curious what scientific field he/she is in. And maybe other people here can comment on this question too. I come from the physical sciences (specifically, physics and astronomy) and academia, and I know of no one in the field who uses Word. Or Windows, for that matter. The Physical Review, the Astrophysical Journal, etc. etc., go out of their way to discourage submission of papers using Word, and encourage (and, to some extent, facilitate) the use of TeX/LaTeX instead.
Drop in on xxx.lanl.gov/arxiv.org, and nearly all of the papers in the physics and astrophysics sections will have been submitted in TeX/LaTeX.
So I'm curious -- what scientific fields use Word documents as the principle medium for authors?
Reading this a couple of days ago when the article about the timeline of space discorveries came on/. said that :
In addition, the new portrait precisely pegs the age of the Universe at 13.7 billion years old, with a remarkably small one percent margin of error.
So I'm not really all that sure what "humble" is trying to find out...
There are different ways of estimating the age of the Universe. We can, for instance, measure the ages of the oldest stars in the Universe, which then sets a lower bound on the Universe's age. Or, we can measure cosmological parameters (such as the Universe's expansion rate, geometry, and energy content) that theory tells us should be related to the age of the Universe in a certain way that one can calculate mathematically.
None of these, by itself, is adequate for estimating the age of the Universe for the simple reason that we astrophysicists might be wrong. We might be wrong in our understanding of old stars, and thus in our techniques for determining their ages. We might be wrong in our theoretical cosmological models, and thus in our equations relating the age of the Universe to observed cosmological parameters. But if we try several independent approaches, and they all say pretty much the same thing, that makes us more confident that we're on the right track -- not only about the age of the Universe, but about the sets of assumptions that go into the different methods (since then they'd all be either close to correct, or all wrong in just such a way as to produce the same wrong answer for the age of the Universe, which is very unlikely).
So, despite the fact that cosmic microwave background observations have produced a very precise estimate of the age of the universe, it's still important to look at it from other directions.
I don't have a lot other than my (very faulty) memory to back this up, but I seem to remember a Scientific American article that most of our heavy elements were formed in the shock waves of supernovas of the first round of stars.
But most of us was not inside a star at one type, hydrogen possibly excepted. Most of us was most likely formed in a shock wave.
The references I gave earlier in this discussion are good sources for more on this. You're correct that I was careless in my wording in the initial post, in that inside the star (through standard stellar thermonuclear processes), you can't get any higher than iron; stuff more massive than iron gets produced through supernovae. But I don't believe the incident nuclei in such reactions are merely in the vicinity of the SN; the incident nuclei are part of the SN itself, and the reactions in question take place in or nearby. (I really wish I had my copies of Bethe's reviews around) So the stuff heavier than iron is still processed through stars; just at the very end of the life cycle for those stars that SN.
Not only that, but the progress of the supernova shock wave creates large clumps of specific types of elements.
I'm not sure what this means, so I dunno. It's certainly true that different types of SN (carbon deflagration on a white dwarf surface vs. the classic scenario of collapse of a massive star) have different heavy element production ratios (the second type producing more r-process elements like oxygen and neon and so forth). I'm not sure if that's what you're referring to, though.
The remnants from the Big Bang are only hydrogen, helium, and maybe a little lithium (I'm not sure about that).
You synthesize nuclei up to carbon in Big Bang Nucleosynthesis, but the mass fractions produced above helium are *very* small. The hydrogen mass fraction is about 0.76, the helium mass fraction is about 0.24, and the lithium mass fraction is about 1e-6. Beryllium, boron, and carbon are significantly less than that.
But despite the low abundances above helium, observers do go hunting for these relic abundances (of lithium, anyway); see e.g. papers by Doug Duncan's group at the University of Chicago on lithium abundances in old halo stars.
Slashdot Mirror
His opinion pieces are carried on PBS' website. Does he have a show on PBS? I've searched the TV schedules for all the nearby PBS stations but no one seems to carry a show entitled "I, Cringely." Is it a show that's carried somewhere? Or does he have a show of some other name, and as a result gets to do this opinion piece on their web site as well? If so, what's the other show? What's it about? Is it any good at all?
And one of Maxwell's Laws ("the divergence of the magnetic field equals zero") has, as a direct consequence, an absolute law: NO MAGNETIC MONOPOLES EXIST. NO OPEN MAGNETIC FIELD LINES EXIST.
So if Maxwell's Laws are wrong and relativity is built heavily on Maxwell's Laws, then there's a tantalizing chance relativity is wrong.
Or if Maxwell's Laws are right and monopoles are conclusively proven not to exist, then there's a tantalizing chance quantum mechanics is wrong.
You have to be careful here. Your first paragraph is a correct statement of what's implied by one of the four Maxwell Equations. It's a bit misleading, though, to say that "relativity is built heavily on Maxwell's Laws." That seems to imply that relativity somehow depends upon Maxwell's Equations being true. That isn't correct. A better way of putting it is that Maxwell's Equations can be shown to incorporate special relativity within them, in the sense that the laws of electromagnetism stay the same ("Lorentz covariance") after changing relativistic reference frames (through a Lorentz transformation).
In fact, we already know that the Maxwell Equations are wrong. We know that they're wrong because they fail to explain behavior on the quantum scale. For that, we turn to quantum electrodynamics (QED), which, again, incorporates special relativity. Maxwell's Equations are thus seen as an excellent approximation on macroscopic scales. The failure of such an approximation to allow for magnetic monopoles doesn't seem like much of a failure.
That said, I've forgotten enough of my field theory that I don't remember how monopoles fit into QED. But I do know lots of field theorists, and most of them believe that monopoles are around (they'd be produced by the breaking of certain fundamental symmetries that many theorists expect to have been present in the early universe; although any inflationary epoch in the history of the Universe would be expected to make monopoles very very rare); and they don't seem to be stressing about the implications of monopoles for QED. So my suspicion is that QED is OK.
Oh, and just as a brief defense of string theorists . . .I don't much like string theory myself, and I echo your reluctance to take it seriously on the basis of the difficulty in making comparison to experiment. But I think most string theorists would take exception to your statement
that string theories "literally cannot be experimentally tested at any realistic energy level." To we who are not string theorists, that's what it looks like, yes; but a string theorist would simply reply that string theorists haven't yet been clever enough to figure out how to extract observable predictions. In other words, I don't think many string theorists would disagree with the principle that for a theory to be interesting, it must be testable. In fact, they would claim that that's their goal with string theory -- to figure out how to make realistically testable predictions -- and they just haven't yet been successful. The Planck scale is a long way from observable energy scales, to be sure. But people explore ideas that allow the examination of classes of models, e.g. the "one large dimension" stuff from a few years ago that would have had observable consequences.
Actually, that's not true anymore. Things have changed and Debian is not the best example of free software or GNU. Check out GNU/Linex instead.
You'll not see a link to Debian from the FSF/GNU sites for this reason.
You mean, like the one on this page, found by following "Links to other sites" from the main page?
Seriously, I've been on the debian-users mailing list for a long time, and it's made up almost exclusively of nice, outgoing, helpful people. I've never seen a newbie with a legitimate question get an RTFM from the regulars.
Well, be careful. I have seen newbies with legitimate questions get RTFMs there; just not in that form. Rather, they're typically delivered in a less mean-spirited way. For example, someone posting "I got this error message: _______. What does it mean? What do I do?" might get a response of "Google is your friend for this sort of thing. I googled on that error message and got this webpage (________), which has an explanation and a solution." Sometimes a link to Eric Raymond's "How To Ask Questions The Smart Way" will be provided, as well. Much kinder than an RTFM, but in the same vein.
Not that I think that's a bad thing. To me, part of being helpful is to help people learn how to help themselves in the future . . .so long as one does so kindly (which, for the most part, debian-user does, and #debian@freenode doesn't).
But at the same time, I didn't want what you wrote above to give the impression that no one is ever encouraged to do some work themselves.
It kind of sucks to read about all the great ideas and ideals that Debian represents and then get a dose of the real Debian community in #debian.
There are a fair number of assholes and jerks in #debian@freenode, it's true. But that sort of thing happens in any community. No matter what the subject, there will be people who get their entire sense of self-worth from treating those less-far-along like crap.
The key is to realize that there are other avenues for help. The debian-user mailing list, in contrast to #debian, is almost always friendly (even when someone does something stupid, the response may be stern, but almost never *mean*); and it's tremendously more informative/educational/useful. I highly recommend it.
that's odd, it shows on every browser I've tried.
Yeah, it's there now.
I would have complained to them directly, to get them to add the submit button; but . . . .
The comment form would be a lot more useful if it had a "submit" button, so that you could actually give them the comment.
Unless it's not showing up because my browser is broken. But in that case, I'd like to comment on that, since I'm using Galeon.
IIRC, the smallest scale at which antimatter can dominate is galactic superclusters, but even that may now be ruled out.
I just wanted to respond to back this up; at least as of the mid-90's, you'd have to go out beyond the Local Supercluster. I haven't followed this since then, unfortunately, so I don't know what the implication of the current (GRO?) data is.
Here's something to think about that follows: light emitted by antimatter, because the electric and magnetic fields are generated in reverse, would be inverted in frequency/wavelength.
I have no idea what you mean by "inverted in frequency/wavelength." However, the truth is that light would be perceptibly unaffected. As correctly noted by several people here, the photon is its own antiparticle. Or, if you wish to think in terms of E-M waves, changing the sign of the E- and B-fields in an electromagnetic wave is simply equivalent to a 180-degree phase change (remember those sin/cos waves), which we wouldn't notice.
Would antimatter tend to absorb high-frequency light (uber-ultra-violet) and permit low-frequency (infrared) to pass through, rather than the reverse with matter?
We don't have a whole lot of experience at this point studying the atomic structure of anti-atoms. However, there's nothing at this point to cause one to expect that their atomic physics would be dramatically different from theoretical expectation: that they'd be the same as regular atoms.
The only thing that I'm having trouble with is the microwave background radiation. Light and matter decoupled when the universe was extremely compact - the parts emitting the background radiation we see would have been very close indeed to our location. Space must have been growing fast enough for points this close to still be moving apart at or very close to the speed of light.
Well, not as compact as you might think. The surface of last scattering, and matter-radiation decoupling, are at a redshift of about 1000. That means that distance scales have expanded by a factor of 1000 between decoupling and the present. That seems like it'd make things pretty small. However, for flat universes (which appears close to correct, and more importantly is the only case for which I can remember the equations off the top of my head right now, books not being handy), the coordinate distance out to a redshift of 1000 is basically 97% of the way out to the particle horizon (the edge of the theoretically observable universe). A factor of 1000 is a lot of compression, to be sure; but we're also talking a big distance scale.
On reflection, the relation you provided does give an expansion velocity between any two points that tends towards infinity as time tends towards zero. It's just a change in how I'd viewed the early universe.
Right -- although obviously, in the case of the microwave background, we don't go back to that close to t=0; just something like a factor of 3e-5 of the current age of the universe. The Hubble parameter is basically just (da/dt)/a; for any power law form for a(t), H will scale as 1/t. In terms of the scale factor a, H scales as a^(-3/2) for a matter-dominated universe; a factor of 1000 smaller scale factor makes for a Hubble constant larger by over four orders of magnitude at that time than at present.
> They also said that the number may actually be too small, given that light
> from some parts of the Universe hasn't had time to reach us yet. So it may
> be impossible to determine the total size of the Universe.
The total size of the universe may even be infinite. At any given time, we can only see the parts close enough for light emitted in the past to reach us, but to the best of my knowledge there is no restriction on the dimensions of the universe as a whole (perhaps an astrophysicist can enlighten me if I'm mistaken?).
Right now, we have no good data suggesting the Universe has finite volume (there's one group that thinks they may see a signature of finite volume in the microwave background data, but it's a very speculative claim). The most straightforward theoretical model of how a Universe of finite volume could be true -- a closed universe model -- appears to be ruled out by a variety of observations. So, if you want a Universe of finite volume, it appears that you have to appeal to new physics in the early Universe for which we have no current experimental evidence (see, e.g. the work of some particle theorists on so-called "small universe models"). That doesn't make it wrong, of course; but it does make most people lean towards infinite volume.
> One question I've always had is: when we look back in time to the
> creation of the Universe, we see light from that time. So the light has
> been traveling for 15 billion years to get to us. But if that light
> has been traveling that whole time toward us, how did we get here
> first?
[ snip ]
As the universe expands, more space is added between any given points in the universe. Thus, light emitted from an object that was initially quite close to us could find itself traversing a surprisingly large distance before finally reaching us. This is why light from the very early universe took so long to reach us, if I understand correctly.
You do understand correctly (yay!). As just one example, it's pretty straightforward to show with some simple algebra that a universe where the expansion is described by
a(t) proportional to t^(2/3),
where "a(t)" is the scale factor of the universe (an increase in "a" by a factor of two means distance scales have doubled) and "t" is time, results in the most distant objects we can theoretically see being three times more distant than the speed of light times the age of the Universe. The functional form of a(t) is expected to be more complicated than that, of course; but data suggests that that power law is a good approximation for most of the history of the Universe. And the reason for such a surprising result, as you say, is that when we observe light from a distant source, its distance away is now larger than it was at the time it emitted.
The one thing I would add to your post . . .
The universe expands by growing empty space everywhere, not just at its edges. This is why you measure the Hubble constant as speed per distance, (ie. kilometers per second per Megaparsec).
. . .is that I would change your description of the Hubble parameter to apparent recession velocity per distance. This is a subtle but important change, because it addresses one of the most common misconceptions about the expansion of the Universe -- namely, that we think the galaxies are flying apart from each other in space, when what's actually going on (as you note in your post) is an expansion of space itself. There are a kajillion analogies people use -- dots on a stretching rubber sheet or inflating balloon, raisins in a loaf of baking (and thus expanding) raisin bread. In all such analogies (which are ultimately bad analogies in full, but still serve to illustrate this point), the dots/raisins/whatever are getting farther apart, but not because they're moving compared to the medium in which they're embedded (the rubber sheet/bread/whatever). Rather, it's simply because of an expansion in the medium.
It's clear from your post that you know this; I just wanted to emphasize it for anyone else who might be reading, because it's such a common misconception, and because some of the questions/comments in this thread have indicated that "galaxies moving apart through space" is what people think is going on.
IANAPhysicist, but I'm pretty sure I can answer some of your questions. It has been theorized that the speed of light has changed in the past, and therefore can continue to change. However, if light used to be slower, then matter could still not travel faster than the slower speed, following all the current known laws.
And it doesn't really matter anyway, since we have no good evidence at present that the speed of light has changed significantly over the history of the Universe, and (especially) since an appeal to a changing speed of light is not necessary to answer the question (of how we could have gotten so far away from the stars whose light has been travelling to us almost since the Big Bang).
Nobody's reading this thread anymore, but I still feel like responding to this . . .
Yes, but it's always possible that that 7-8% error over the visible universe is actually only part of a much larger structural inconsistency that we simply can't observe (yet).
Sure. It's also possible that tomorrow, someone will do an experiment or observation that overturns the principle of conservation of momentum or energy, or the 2nd Law of Thermodynamics. I doubt it, but it's possible. Nothing you would use to make predictions is ever known to be 100% true in science; that's not how science works. You do experiments/observations, collect data, construct your best theories/models, and compare them to new data. As you collect more data, you either invalidate your theory/model, or you bolster its support.
Right now, the data shows a gradual convergence towards homogeneity at larger and larger scales. We know from microwave background observations that the level of mass inhomogeneity on really huge scales, out to redshifts of 1000 or so, is at less than 1e-5. Furthermore, we've had a lot of success with the relativistic hot Big Bang model; the success of the model makes us feel good about the assumptions upon which it's based, and one of those assumptions is that of homogeneity and isotropy on sufficiently large scales (the so-called "Cosmological Principle"). Maybe in the end, this all turns out to be wrong -- maybe there is some large-scale inhomogeneity out there, on scales so large we haven't yet observed them; but right now, lots of data and ways of looking at things suggest that large-scale homogeneity is a good way to think, so that's what people work with.
By calculating the population of my neighborhood and assuming that my neighborhood has average distribution...
From the article:
> That number was then multiplied by the number of similar sized strips
> needed to cover the entire sky, Driver said, and then multiplied again
> out to the edge of the visible universe.
I wonder if this sort of "science" is how hardware manufacturers get their numbers?
Be careful. Do you have a reason to believe that your neighborhood is typical? Do you have data indicating such?
The astronomers in question didn't use such an approach because they're idiots; they used such an approach because we already have a heck of a lot of data about the galaxy distribution. The RMS (fractional) fluctuation in galaxy number count in a random volume the size of the one they surveyed is expected to be tiny; and it's expected to be tiny because of surveys we've already done which indicate such a convergence towards homogeneity as scale increases.
Debian has moved a large amount of documentation licensed under the GNU Free Documentation License into the non-free section of its software archive, out of concerns that the GFDL is not free, at least as far as "free" is defined by the Debian Free Software Guidelines.
One issue is essentially with the ability of authors to define "invariant sections" of their documents, the subsequent modification of which would violate the GFDL. This conflicts with the requirement of the DFSG that licensing must allow modifications, and must permit the modifications to be distributed under the same licensing terms as the original, as e.g. the GPL does.
Other people have raised the concern that the GFDL's restrictions on the use of "technical measures to obstruct or control the reading or further copying of the copies you make or distribute" -- a restriction that, on the surface, makes sense in that it prevents attempts to limit the freedom others have to read the distributed copies -- could have the unintended consequence of forbidding putting documents covered by the GFDL on devices which are encrypted for personal security.
I'm curious whether FSF folks speaking about licenses plan to discuss this at the seminar(s).
> I am so sick of this infinitely repeated bullshit claim.
The only "bullshit" is what you posted. Why don't you try reading the material at the links you provided:
You missed his/her point completely. The original poster asserted that copyright is covered by civil law rather than criminal law. The respondant to whom you replied gave counterexamples, to show that in the U.S. copyright comes under both civil and criminal law. You assert that the counterexamples don't cover p2p file swapping; that's true, but utterly irrelevant to his/her point: to whit, "is the assertion that copyright is solely the province of civil law correct?" The answer, as demonstrated, is no, it isn't correct.
"Theft" is a crime. "Copyright infringement" is a civil offense.
Again, it ain't necessarily so. Copyright law is mostly civil law, true; but there are already laws in the books that criminalize certain types of copyright infringement. The DMCA is one example. For another, commercial copyright violation involving more than 10 copies and monetary value over $2500 is a federal felony.
It's true that the particular type of copyright infringement in question here is not (yet) a felony; but since in this subthread we're trying to be careful about our use of terminology, it's incorrect to make the blanket assertion that copyright infringement is solely the province of civil law. This law wishes to expand the types of copyright infringement that are considered federal felonies, beyond what they currently are.
Theft is a criminal offence. Copyright violation is a civil offence. That is a very big difference, and one the media don't seem to have noticed.
This point (that copyright is a civil offence) used to be fair, but isn't anymore. There are already laws in place making certain types of copyright offenses criminal acts in the U.S, the DMCA for example.
Oh brother, not this again.
Trade secrets, copyrights, and patents, are three different things, covered by three different sets of legislation and case law, and typically suggest three different approaches for relevant IP management. Most of Linus' comments in the article are about copyright. The LKML entry you reproduce is about patents. Patent issues have nothing to do with the dispute over RCU.
You say that you've "reported this....to the appropriate people." Has that been in private conversation, or has that been through the LKML?
I mean, it's hard to believe that only one person would have ever noticed this; but if so, I would expect that lots of people would care. And the more people on the LKML that know about it, the more likely it is for something to happen . . .
This is off-topic, I know; but based on the story author's question, I'm curious what scientific field he/she is in. And maybe other people here can comment on this question too. I come from the physical sciences (specifically, physics and astronomy) and academia, and I know of no one in the field who uses Word. Or Windows, for that matter. The Physical Review, the Astrophysical Journal, etc. etc., go out of their way to discourage submission of papers using Word, and encourage (and, to some extent, facilitate) the use of TeX/LaTeX instead. Drop in on xxx.lanl.gov/arxiv.org, and nearly all of the papers in the physics and astrophysics sections will have been submitted in TeX/LaTeX.
So I'm curious -- what scientific fields use Word documents as the principle medium for authors?
Thanks.
Reading this a couple of days ago when the article about the timeline of space discorveries came on
In addition, the new portrait precisely pegs the age of the Universe at 13.7 billion years old, with a remarkably small one percent margin of error.
So I'm not really all that sure what "humble" is trying to find out...
There are different ways of estimating the age of the Universe. We can, for instance, measure the ages of the oldest stars in the Universe, which then sets a lower bound on the Universe's age. Or, we can measure cosmological parameters (such as the Universe's expansion rate, geometry, and energy content) that theory tells us should be related to the age of the Universe in a certain way that one can calculate mathematically.
None of these, by itself, is adequate for estimating the age of the Universe for the simple reason that we astrophysicists might be wrong. We might be wrong in our understanding of old stars, and thus in our techniques for determining their ages. We might be wrong in our theoretical cosmological models, and thus in our equations relating the age of the Universe to observed cosmological parameters. But if we try several independent approaches, and they all say pretty much the same thing, that makes us more confident that we're on the right track -- not only about the age of the Universe, but about the sets of assumptions that go into the different methods (since then they'd all be either close to correct, or all wrong in just such a way as to produce the same wrong answer for the age of the Universe, which is very unlikely).
So, despite the fact that cosmic microwave background observations have produced a very precise estimate of the age of the universe, it's still important to look at it from other directions.
I don't have a lot other than my (very faulty) memory to back this up, but I seem to remember a Scientific American article that most of our heavy elements were formed in the shock waves of supernovas of the first round of stars.
But most of us was not inside a star at one type, hydrogen possibly excepted. Most of us was most likely formed in a shock wave.
The references I gave earlier in this discussion are good sources for more on this. You're correct that I was careless in my wording in the initial post, in that inside the star (through standard stellar thermonuclear processes), you can't get any higher than iron; stuff more massive than iron gets produced through supernovae. But I don't believe the incident nuclei in such reactions are merely in the vicinity of the SN; the incident nuclei are part of the SN itself, and the reactions in question take place in or nearby. (I really wish I had my copies of Bethe's reviews around) So the stuff heavier than iron is still processed through stars; just at the very end of the life cycle for those stars that SN.
Not only that, but the progress of the supernova shock wave creates large clumps of specific types of elements.
I'm not sure what this means, so I dunno. It's certainly true that different types of SN (carbon deflagration on a white dwarf surface vs. the classic scenario of collapse of a massive star) have different heavy element production ratios (the second type producing more r-process elements like oxygen and neon and so forth). I'm not sure if that's what you're referring to, though.
The remnants from the Big Bang are only hydrogen, helium, and maybe a little lithium (I'm not sure about that).
You synthesize nuclei up to carbon in Big Bang Nucleosynthesis, but the mass fractions produced above helium are *very* small. The hydrogen mass fraction is about 0.76, the helium mass fraction is about 0.24, and the lithium mass fraction is about 1e-6. Beryllium, boron, and carbon are significantly less than that.
But despite the low abundances above helium, observers do go hunting for these relic abundances (of lithium, anyway); see e.g. papers by Doug Duncan's group at the University of Chicago on lithium abundances in old halo stars.