The galactic year depends on how far out you are (similarly to how solar system years do.) To a good approximation, circular orbit velocity is independent of distance from the center of the galaxy (about 220 km/s), but the distance to travel is proprotional to the radius of the orbit, so the 'year' length is proportional to distance from galactic center. (This approximation fails within a few kiloparsecs of galactic center.)
The spiral pattern is misleading - it is a wave, rather than a group of bright stars that stay together as the galaxy rotates. As time passes stars enter and leave the spiral arms. There is a modest increase in stellar density in the arms, but most of the increased brightness is because the sprial arm triggers star formation, and the very bright stars live for a very short time - so they mostly occur in the arms.
Yes, the rate of star formation in the galaxy is declining, and the abunance of heavy elements increasing (although mass locked up in white dwarfs, neutron stars and black holes is probably more significant for this decline than the change in elemental abundance.) However, new, very bright stars are still being formed, so we won't entirely run out of these for some time yet.
You've got it a bit mixed up. From memory, the elemental abundances after the big bang (prior to stars forming) was about 80% hydrogen, 20% helium, and largish fraction of 1% heaver elements.
Current composition depends on where you are (how much of the gas has been cycled through stars) but solar abundance is I think about 70% hyrdogen, 27% helium and 3% heavy elements.
Warning - all the above was from memory, and may not be accurate.
Basically, non-uniform gravitational forces on an extended cloud will give it some (very slow) spin. If the cloud then collapses, conservation of angular momentum greatly speeds up the spin. If you make a very small object (such as a white dwarf, neutron star or black hole) then it will tend to spin very quickly.
So essentially the answer is - random perturbations, greatly magnified.
As another poster aludes to, this spin acts to reduce the ability of the objects to collapse to very small sizes. The more angular momentum there is in the initial gas, the less massive (and more numerous) you expect the results of the collapse to be - whether galaxies, star clusters or stars.
"but really, wtf could hold an entire GALAXY together but a black hole?"
I am (or rather, was) an astrophysicist. The answer is the rest of the galaxy holds it together, a bit like the gravity of the Earth is what holds the Earth together. The galaxy has the mass of billions of stars - so any stars not at the center are being pulled towards the center.
In answer to the original poster, the 'size' of a black hole is its event horizon radius:
R = 2GM/c^2 where G = universal gravitational constant M = mass of the black hole c = speed of light.
Very good. I translate the last two as 'freedom and generousity.' Not having my dictionary handy, I can't say if 'courtesy' is also legitimate, but it seems likely. (Actually, I might even prefer 'courtesy'.)
Incidentally, I think my comment above was overrated by the moderators.
I too have scientific training (astronomy) although I'm no longer active in science.
I agree with all of this - falsification of data is the ultimate scientific crime. The analogy with recent accounting fraud is quite a good one - not only will nobody hire this guy as a scientist again (as nobody would hire some ex-CEO/CFOs from fraudulant companies) but he has destroyed much that was good (as many employees and shareholders of the bad companies had their livelyhoods destroyed) - any work based on what he did is now worthless, and old and possibly correct work he did is worthless, because nobody knows what they can trust.
For the scientist, this is like a child-molestation conviction for a teacher - it makes him completely unhirable. I think that because of the seriousness of fraud charges, scientists are very unwilling to bring them. I suspect that, like child-molestation a generation or two ago, that it very often gets swept under the carpet.
Following the 'non-swamped' press release link, I have now doubled the number of web sites I know of that pay attention to your browser language preferences.
Some time ago, I set my preferences to (1) Latin, (2) French, (3) English (despite being monolingual) just to see what sites would notice. Until a few minutes ago, the exhaustive list of sites I had found that did so was: Google*. (Not even the Quebec government site noticed!)
With my alledged French preference, Mandrakesoft came up with a little message saying (in English!) that the release was not available in my prefered language, and gave me a link to the English version.
* Except that I generally get there via bookmark with a URL demanding Google in Sweedish Chef instead - which overrides the language preference.) Occasionally a link somehow looses the URL-supplied preference, and then Google switches to Latin for me.
> Umm, World War III was planned to happen back in the 60's. That's what these things were built to withstand.
Sigh. Another project way over deadline, and with massive scope changes.
A quote from an early-80's British TV skit comedy show:
"Experts have finally understood American foreign policy. Having been late for the last two world wars, they want to make sure they're really prompt for the next one."
Notice I said I read while *walking* through town. And I do stop reading to cross the road. (Books are more forgiving of interuptions than cellphones.)
Anyway, I've always thought that getting hit by a car while deep in thought was a proper Geek way to go - like Piere Curie.
I would expect post-cremation ashes to contain very little carbon - the ash is what won't burn*, and carbon burns - so it is perhaps unrealistic to use ashes as a starting point.
There's also a potential trust problem - how do you know your diamond is Grandma's carbon, not chimney sweepings? (One could say something similar of ordinary cremation ashes, of course.)
* More technically, the ash is what was didn't a gas when chemically combined with air. Unless some other atom is holding onto it very tightly, the carbon will form CO or CO2.
They're going to have a hell of a cooling problem: all the inefficiencies in the conversion of laser to electricity and in the drive train will turn to heat.
Dialect output. Soon, you won't have to listen to some Croatian nun discussing free will translated into Bostonian English, you'll be able to listen to a Croatian nun discussing free will translated into Jive.
This reminds me of a story told to me long ago by a friend of the family. She was of Dutch descent, and the story is about a well bred Englishman who went on a working holiday to Holland. He got work on the docks, and that is where he learned to speak Dutch. The result was that in a refined English accent he spoke obscenity-laden gutter Dutch, apparently unaware that he was doing so.
If true, there should be some very large custom-built hangers for these things that would show up in commercially available satellite photos. Do these exist? (For that matter, the craft themselves should have been imaged multiple times, but in the flood of data, it could be hard to find them.)
On a side line - how are the 'Aurora' rumours coming along? ('Aurora' is supposedly a deep black hypersonic reconnosance airplane, replacing the SR-71.)
I was a graduate student at Princeton. Each year at admissions time, the student newspaper would trumpet that once again Princeton was the 'most exclusive' university in the country. The justification for this was that they had accepted a smaller percentage of their applicants than any other university. This always struck me as a bizare measure of merit, as it is only loosely correlated to the quality of students.
I can offer Princeton some advice on how to increase their exclusivity:
1) Slash the application fee. Someone with a 1 in 1000 chance of being accepted will be more inclined to apply if it costs $10 than if it costs $50.
2) With many more applications at a much lower fee, there will be problems with budget blow-out on evaluating them. No problem - save costs by heavy handed use of randomness in the selection process. This has the additional benefit if increasing the chances for borderline applicants to be accepted, which will even further increase applications.
The ultimate extension of this is that you raffle off admissions places, and count everyone who bought a ticket as an applicant. This could push your exclusivity from about 1 in 6 to 1 in 10,000.
It said 1am on the article. I couldn't be bothered figuring out what part of the USA that applied to, as the front page didn't specify the time zone. It was mid afternoon for me.
Re:No... a 64bit chip doesn't have to be 'slower'
on
AMD's 64-Bit Chip
·
· Score: 3, Interesting
"AMD came up with a simple solution... when this mode bit is set..."
I'd note that this is not a new solution, and possibly not a desirable one. The book "The Soul of a New Machine" describes the engineering effort at Data General c1980 to develop a new mini computer. I think it was a 32 bit design, and needed to be backwards compatable with the older 16 bit design. The chief engineer insisted that the compatability *not* be done by a 'mode bit'. I can no longer remember what the objections to a mode bit were. Can anyone comment?
The article talks about constant linear velocity (used in the original audio standard) and constant angular velocity drives. It comments how manufacturers like to have CAV drives to quote impressive speeds compared to the CD (audio) standard, but doesn't mention a much more important reason for using CAV: if you used CLV you'd need to wait for a long time (probably seconds) for the spin rate to change and stabalize whenever you seeked from one part of the disk to another.
There will always be close call borderline cases. If you say 'any doubt - toss it out' then you have borderline cases over whether there is any doubt.
E.g. you have to put an X in a box. Someone puts an X just next to one of the boxes. Count it or not? What if it was right on the edge of the box, or 1/3 of the way to the nearest other box?
Others have mentioned white spots on black background that need to be blackened to vote. How much of the white needs to be covered to count it as a vote? Wherever you draw the line, you will get borderline cases.
This is not to say that all systems are equally good - a better system will have far fewer borderline calls.
We have a sample size of only one, and that this sample resulted in intelligent life is a given (else we wouldn't be here to make observations on it.) We do however have some timing information. From this we see:
1) Life evolved on Earth pretty much as soon as conditions were stable enough to allow it. This suggests that bacterial life is highly likely.
2) It took at least hundreds of millions of years to develop Eukariotic life (big cells with a nucleus, such as we are made of, as opposed to bacteria.) This means that this step might be rare.
3) It took about 3 billion years to evolve differentiated multicellular life. This means that this step could be exceedingly rare.
4) Multicellular life evolved into a vast array of designs in a just a few million years (the 'Cambrian explosion'.) This means that once multicellular life starts, it will quickly produce complex forms.
5) From the Cambrian explosion to us is something like 500 million years. This is an intermediate time scale that makes it hard to judge how likely intelligent life is.
Disclaimer: I'm not 100% sure of some of the timescales above. It is all from memory.
Disclaimer 2: The Edicara fauna complicate the picture above on the origin of multicellular life, depending on how you interpret them.
Disclaimer 3: All the above is merely probabilistic. E.g. if the evolution of bacterial life is very rare, there is still a 5% chance that it will have occurred during the first 5% of the available time. Therefore we can't strongly exclude the possiblity that the evolution of bacterial life is hard.
Slashdot Mirror
The galactic year depends on how far out you are (similarly to how solar system years do.) To a good approximation, circular orbit velocity is independent of distance from the center of the galaxy (about 220 km/s), but the distance to travel is proprotional to the radius of the orbit, so the 'year' length is proportional to distance from galactic center. (This approximation fails within a few kiloparsecs of galactic center.)
The spiral pattern is misleading - it is a wave, rather than a group of bright stars that stay together as the galaxy rotates. As time passes stars enter and leave the spiral arms. There is a modest increase in stellar density in the arms, but most of the increased brightness is because the sprial arm triggers star formation, and the very bright stars live for a very short time - so they mostly occur in the arms.
Yes, the rate of star formation in the galaxy is declining, and the abunance of heavy elements increasing (although mass locked up in white dwarfs, neutron stars and black holes is probably more significant for this decline than the change in elemental abundance.) However, new, very bright stars are still being formed, so we won't entirely run out of these for some time yet.
You've got it a bit mixed up. From memory, the elemental abundances after the big bang (prior to stars forming) was about 80% hydrogen, 20% helium, and largish fraction of 1% heaver elements.
Current composition depends on where you are (how much of the gas has been cycled through stars) but solar abundance is I think about 70% hyrdogen, 27% helium and 3% heavy elements.
Warning - all the above was from memory, and may not be accurate.
Basically, non-uniform gravitational forces on an extended cloud will give it some (very slow) spin. If the cloud then collapses, conservation of angular momentum greatly speeds up the spin. If you make a very small object (such as a white dwarf, neutron star or black hole) then it will tend to spin very quickly.
So essentially the answer is - random perturbations, greatly magnified.
As another poster aludes to, this spin acts to reduce the ability of the objects to collapse to very small sizes. The more angular momentum there is in the initial gas, the less massive (and more numerous) you expect the results of the collapse to be - whether galaxies, star clusters or stars.
"but really, wtf could hold an entire GALAXY together but a black hole?"
I am (or rather, was) an astrophysicist. The answer is the rest of the galaxy holds it together, a bit like the gravity of the Earth is what holds the Earth together. The galaxy has the mass of billions of stars - so any stars not at the center are being pulled towards the center.
In answer to the original poster, the 'size' of a black hole is its event horizon radius:
R = 2GM/c^2
where
G = universal gravitational constant
M = mass of the black hole
c = speed of light.
i like to listen to cd's on my computer. sadly enough, my monitor is larger than my TV, so i watch movies on there too.
You have a TV???
Very good. I translate the last two as 'freedom and generousity.' Not having my dictionary handy, I can't say if 'courtesy' is also legitimate, but it seems likely. (Actually, I might even prefer 'courtesy'.)
Incidentally, I think my comment above was overrated by the moderators.
I too have scientific training (astronomy) although I'm no longer active in science.
I agree with all of this - falsification of data is the ultimate scientific crime. The analogy with recent accounting fraud is quite a good one - not only will nobody hire this guy as a scientist again (as nobody would hire some ex-CEO/CFOs from fraudulant companies) but he has destroyed much that was good (as many employees and shareholders of the bad companies had their livelyhoods destroyed) - any work based on what he did is now worthless, and old and possibly correct work he did is worthless, because nobody knows what they can trust.
For the scientist, this is like a child-molestation conviction for a teacher - it makes him completely unhirable. I think that because of the seriousness of fraud charges, scientists are very unwilling to bring them. I suspect that, like child-molestation a generation or two ago, that it very often gets swept under the carpet.
Following the 'non-swamped' press release link, I have now doubled the number of web sites I know of that pay attention to your browser language preferences.
Some time ago, I set my preferences to (1) Latin, (2) French, (3) English (despite being monolingual) just to see what sites would notice. Until a few minutes ago, the exhaustive list of sites I had found that did so was: Google*. (Not even the Quebec government site noticed!)
With my alledged French preference, Mandrakesoft came up with a little message saying (in English!) that the release was not available in my prefered language, and gave me a link to the English version.
* Except that I generally get there via bookmark with a URL demanding Google in Sweedish Chef instead - which overrides the language preference.) Occasionally a link somehow looses the URL-supplied preference, and then Google switches to Latin for me.
> Umm, World War III was planned to happen back in the 60's. That's what these things were built to withstand.
Sigh. Another project way over deadline, and with massive scope changes.
A quote from an early-80's British TV skit comedy show:
"Experts have finally understood American foreign policy. Having been late for the last two world wars, they want to make sure they're really prompt for the next one."
No - real, 100% genuine dead-trees book.
Notice I said I read while *walking* through town. And I do stop reading to cross the road. (Books are more forgiving of interuptions than cellphones.)
Anyway, I've always thought that getting hit by a car while deep in thought was a proper Geek way to go - like Piere Curie.
People who walk and talk on cell phones are crazy. They should instead do what I do when walking through town - read a book.
I would expect post-cremation ashes to contain very little carbon - the ash is what won't burn*, and carbon burns - so it is perhaps unrealistic to use ashes as a starting point.
There's also a potential trust problem - how do you know your diamond is Grandma's carbon, not chimney sweepings? (One could say something similar of ordinary cremation ashes, of course.)
* More technically, the ash is what was didn't a gas when chemically combined with air. Unless some other atom is holding onto it very tightly, the carbon will form CO or CO2.
They're going to have a hell of a cooling problem: all the inefficiencies in the conversion of laser to electricity and in the drive train will turn to heat.
Dialect output. Soon, you won't have to listen to some Croatian nun discussing free will translated into Bostonian English, you'll be able to listen to a Croatian nun discussing free will translated into Jive.
This reminds me of a story told to me long ago by a friend of the family. She was of Dutch descent, and the story is about a well bred Englishman who went on a working holiday to Holland. He got work on the docks, and that is where he learned to speak Dutch. The result was that in a refined English accent he spoke obscenity-laden gutter Dutch, apparently unaware that he was doing so.
If true, there should be some very large custom-built hangers for these things that would show up in commercially available satellite photos. Do these exist? (For that matter, the craft themselves should have been imaged multiple times, but in the flood of data, it could be hard to find them.)
On a side line - how are the 'Aurora' rumours coming along? ('Aurora' is supposedly a deep black hypersonic reconnosance airplane, replacing the SR-71.)
Hello, Police?
Somebody broke into my car. I'd only left it for a few minutes.
Yeah, they smashed the window and took the seat.
No, NOT the CD - the seat.
I was a graduate student at Princeton. Each year at admissions time, the student newspaper would trumpet that once again Princeton was the 'most exclusive' university in the country. The justification for this was that they had accepted a smaller percentage of their applicants than any other university. This always struck me as a bizare measure of merit, as it is only loosely correlated to the quality of students.
I can offer Princeton some advice on how to increase their exclusivity:
1) Slash the application fee. Someone with a 1 in 1000 chance of being accepted will be more inclined to apply if it costs $10 than if it costs $50.
2) With many more applications at a much lower fee, there will be problems with budget blow-out on evaluating them. No problem - save costs by heavy handed use of randomness in the selection process. This has the additional benefit if increasing the chances for borderline applicants to be accepted, which will even further increase applications.
The ultimate extension of this is that you raffle off admissions places, and count everyone who bought a ticket as an applicant. This could push your exclusivity from about 1 in 6 to 1 in 10,000.
It said 1am on the article. I couldn't be bothered figuring out what part of the USA that applied to, as the front page didn't specify the time zone. It was mid afternoon for me.
"AMD came up with a simple solution ... when this mode bit is set ..."
I'd note that this is not a new solution, and possibly not a desirable one. The book "The Soul of a New Machine" describes the engineering effort at Data General c1980 to develop a new mini computer. I think it was a 32 bit design, and needed to be backwards compatable with the older 16 bit design. The chief engineer insisted that the compatability *not* be done by a 'mode bit'. I can no longer remember what the objections to a mode bit were. Can anyone comment?
The article talks about constant linear velocity (used in the original audio standard) and constant angular velocity drives. It comments how manufacturers like to have CAV drives to quote impressive speeds compared to the CD (audio) standard, but doesn't mention a much more important reason for using CAV: if you used CLV you'd need to wait for a long time (probably seconds) for the spin rate to change and stabalize whenever you seeked from one part of the disk to another.
Several minutes after it got posted, after 1am in the USA, only 6 comments so far, and I still can't get to the page. Sigh.
There will always be close call borderline cases. If you say 'any doubt - toss it out' then you have borderline cases over whether there is any doubt.
E.g. you have to put an X in a box. Someone puts an X just next to one of the boxes. Count it or not? What if it was right on the edge of the box, or 1/3 of the way to the nearest other box?
Others have mentioned white spots on black background that need to be blackened to vote. How much of the white needs to be covered to count it as a vote? Wherever you draw the line, you will get borderline cases.
This is not to say that all systems are equally good - a better system will have far fewer borderline calls.
We have a sample size of only one, and that this sample resulted in intelligent life is a given (else we wouldn't be here to make observations on it.) We do however have some timing information. From this we see:
1) Life evolved on Earth pretty much as soon as conditions were stable enough to allow it. This suggests that bacterial life is highly likely.
2) It took at least hundreds of millions of years to develop Eukariotic life (big cells with a nucleus, such as we are made of, as opposed to bacteria.) This means that this step might be rare.
3) It took about 3 billion years to evolve differentiated multicellular life. This means that this step could be exceedingly rare.
4) Multicellular life evolved into a vast array of designs in a just a few million years (the 'Cambrian explosion'.) This means that once multicellular life starts, it will quickly produce complex forms.
5) From the Cambrian explosion to us is something like 500 million years. This is an intermediate time scale that makes it hard to judge how likely intelligent life is.
Disclaimer: I'm not 100% sure of some of the timescales above. It is all from memory.
Disclaimer 2: The Edicara fauna complicate the picture above on the origin of multicellular life, depending on how you interpret them.
Disclaimer 3: All the above is merely probabilistic. E.g. if the evolution of bacterial life is very rare, there is still a 5% chance that it will have occurred during the first 5% of the available time. Therefore we can't strongly exclude the possiblity that the evolution of bacterial life is hard.
>> I'm no scientist, but it seems to me ...
... kettle ... black.
> That's why you're not a scientist.
[...]
> Gasoline fumes are lighter than air
Pot