It seems too fantastic to me that they can extrapolate the data more than 7 orders of magnitude into the past (15 years into 250 million years). At this extreme, usually the error terms and list of assumptions swamp the usefullness of the projections.
That's definitely true... and if you asked what the error in the trajectory of any individual star is, you'd find it's pretty high. But the aggregate distribution should be pretty well constrained... you know what fraction are moving outwards, what fraction are moving inwards, what fraction are moving up, what fraction are moving down, etc...
They imply they are measuring the change in both relative position and brightness of the stars. From their conclusion and simulation showing that stars appear closer now (than from 15 years ago), I guess this means the change in relative brightness was the dominating statistic in the extrapolations. I seem to remember that this is very difficult to measure accurately, let alone precisely - especially with land-based telescopes.
You're mis-interpreting the article... what you're suggesting would be impossible to measure, as you suggest (quick numbers: let's say a star 1pc away was moving towards us at 100 km/s, which are ridiculously extreme numbers... then in 15 years it would be 0.15% closer, so 0.3% brighter. About the best photometric accuracy you can get is 1% and that requires a hell of a lot of work).
The way they get the velocity toward/away from us is using the Doppler shift of lines in the spectrum of the star... that's actually quite a bit easier than getting the proper motion (change of position). You only need one observation to get it! (though it sounds like they have multiple observations if they've catalogued the fraction of multiple systems).
Weird... I was just noticing the other day how good a year 2003 was for music. Among the better releases of the year:
Afro Celt Sound System - Seed
Aghast View - drifter.ep
Blue Man Group - The Complex
Collide - Some Kind of Strange
The Cruxshadows - Ethernaut
F-Space - Preliminary Impact Report
God Module - Empath
Incendio - Incendio
Pzycho Bitch - The Day Before
Tanzwut - Ihr Wolltet Spass
T.Raumschmiere - Radio Blackout
v/a - 2003 Hands
Of course, out of those only the Afrocelts and T.Raumschmiere are on RIAA labels... I'm not sure which labels report to the IFPI - the article says "The IFPI represents hundreds of the world's independent and major music labels including Warner Music, Sony Music, Universal Music, EMI and BMG", but there are thousands of independent labels, so it makes a difference!
Ah, here's a list: http://www.ifpi.org/site-content/directory/member_ sites.html
Looks like Tanzwut and Incendio are also on reporting labels... but still, most of the best releases of the year aren't in those stats.
There's no phonetic similarity... it's pronounced "Throatwarbler Mangrove".;-)
[TMB]
Re:Plotting Ahead?
on
Unruly Milky Way
·
· Score: 2, Informative
It's possible to trace the orbits for the stars they have forward about as well as they can trace them backwards.
The problem, though, is that getting good enough kinematical information to do this is hard for stars that aren't near the Sun. You notice that all of the stars end up right near the Sun - that's not a coincidence! Those are the ones whose orbits we can get a handle on precisely because right now they're close enough that it's easy to get their kinematics.
You can imagine that if you waited 220 million years (one orbit) and did the same exercise, you'd find the same thing - the stars came from a broader range of radii "220 million years ago" (i.e. now). So right now, most of them are too far away for us to get good proper motions and/or good distances, and therefore good spatial velocities.
[TMB]
Re:Plotting Ahead?
on
Unruly Milky Way
·
· Score: 2, Informative
Stars do collide - I'm sure quite frequently given the number of them.
Rather than just asserting that blindly, why don't we work out the numbers?
The only place in the Milky Way that stars collide are inside globular clusters, where they form "blue stragglers". There are about 3000 known blue stragglers in the Milky Way (Piotto et al. 2004). The rate is probably higher now than in the past (it should increase with time as more clusters undergo core collapse), but averaging over the 13.7 billion year history, that's an average rate of one every 4.5 million years
Now, whether you consider that "quite frequently" or not depends on your perspective.;-)
I've never tried sending email to an MP, but I have written on paper before, and at least the office of the Minister of Justice (under Martin Cauchon), and Foregin Affairs (under Bill Graham) are quite good about actually reading letters and replying to them.
Couldn't gravitational lensing be a possible means for testing frame dragging?
Theoretically, yes.... there's a recent paper that works out the numbers for lensing from a spiral galaxy, and it's roughly on the order of a few micro-acroseconds. Possibly detectable by SIM or GAIA.
What's wrong with the CRIA obtaining subpoenas against people that they can positively identify as file uploaders of the member companies' copyrighted material? It's not outrageously hard to have somebody at minimum wage sit behind a terminal and try to download music from Canadian ip addresses. And once you have that, it's a known act of copyright infringement anyway, which as we all know, is illegal.
I'm pretty sure that paying someone to commit an illegal act is illegal.;-)
Matching that data with activity on the OpenNap file-sharing network, they concluded that file sharing actually increases CD sales for hot albums that sell more than 600,000 copies. For every 150 downloads of a song from those albums, sales increase by a copy, the researchers found.
...
For albums that fail to sell well, the Internet may contribute to declining sales. Oberholzer-Gee and Strumpf found that albums that sell to niche audiences suffer a "small negative effect" from Internet piracy.
This is the exact opposite trend to what I'd expect. I think we all agree that filesharing has both a positive effect, due to advertising/finding new bands, and a negative effect, due to people downloading a song and not buying the album when they otherwise would have. So filesharing should increase CD sales when the former effect outweights the second, and decrease them when the latter effect is more important.
The advertising effect of filesharing should be much stronger for unknown bands than for known bands. Everyone's heard the mainstream hits; not many people have heard Random Unknown Cool Band. I see no reason why people's desire to buy a CD when they already have an MP3 should depend on how big the artist is. So small bands should do better under filesharing than big bands, whether or not the net effect integrated over all CD sales is positive, negative, or neutral.
But... this study says that the situation is exactly opposite. Which suggests that people's desire to buy a CD from a mainstream band once they have the MP3 is greater than their desire to do so from a small band... or that P2P is only increasing the status quo, in sharp contrast to "conventional" wisdom and really fucking depressing if true.
Funny, as I read this I'm listening to Velvet Acid Christ's Between The Eyes Vol 1, which I bought this afternoon. Why? Because I once grabbed the Nazi Bastard mix of Futile on Audio Galaxy (ah, those halcyon days of yore) and have been looking for a CD copy ever since.:) Glad he finally found a good way to release it.
But don't these people test the damn machines with the pens they are handing out? Or did someone bring their own pen or something?
These were absentee ballots. Unless they send out mandatory pens along with the absentee ballot (which I guess they don't, since this problem arose... might not be a bad idea), there's no control over what kind of pen the voters use.
Just to clarify... in the imaging data, the stars outnumber galaxies by a lot. They purposely target likely galaxies for spectroscopy, which is why there are more galaxies than anything else in the spectroscopic data.
That's in contrast with the Hubble Ultra Deep Field, where almost every object is a galaxy, because they purposely chose a patch of sky with very few stars.
But, yes, there are an incredible number of stars in the observable universe.:)
Someone who values the principles of democracy more than they do freedom for the next N years of their life ought to go in and do it. Make it absolutely blatant that it was done. Leave Diebold standing there saying "We really think that this county of 100,000 people produced 5 million votes for Ralph Nader in the Republican primary. That's what the machine says." Preferably during as minor an election as possible.
Now's the time to show what you're made of. I admit I'm too chicken to do it (besides, it's not my country - we still use paper and pen).
This comes as a great shock to exactly no one.;-) Postulating anything else is like introducing epicycles when you've only just figured out that there are orbits.
Piece of advice... don't post both as an AC and non-AC in the same thread when you have a very distinctive post style if you really want the AC post to be anonymous.;-)
(I am an astrophysicist. I am not a cosmologist, but I do galaxy evolution... we hang out with cosmologists)
There are quite a few pieces of evidence for dark matter:
- internal dynamics of galaxies: when you look at how fast the outer parts of galaxies move around the central parts, you find that the amount of mass necessary is much more than what you see
- dynamics of galaxies in clusters: when you look at how fast galaxies move around in galaxy clusters, you find the amount of mass necessary is much more than what you see
- non-linear growth of primordial perturbations (sounds complicated, isn't really): the universe used to be almost completely smooth. now it's filled with clumps of matter like galaxies and clusters and big voids without much matter. the structures collapsed because of their mass. if there were only as much mass as you can see, there hasn't been enough time for galaxies to have collapsed
The amazing thing about all of these measurements is that they all give you the same answer for how much mass is really out there.
Slashdot Mirror
> Any technology distinguishable from magic is insufficiently advanced.
;-)
:-)
> That way it's a pure rearrangment.
I bow to your better judgement.
> Now I can't help wondering your post derives from an independant source, or if it's a misquote of my own creation a few years ago.
I think a colleague said it to me about a year ago... I can't claim any knowledge of where they picked it up from.
[TMB]
That's definitely true... and if you asked what the error in the trajectory of any individual star is, you'd find it's pretty high. But the aggregate distribution should be pretty well constrained... you know what fraction are moving outwards, what fraction are moving inwards, what fraction are moving up, what fraction are moving down, etc...
You're mis-interpreting the article... what you're suggesting would be impossible to measure, as you suggest (quick numbers: let's say a star 1pc away was moving towards us at 100 km/s, which are ridiculously extreme numbers... then in 15 years it would be 0.15% closer, so 0.3% brighter. About the best photometric accuracy you can get is 1% and that requires a hell of a lot of work).
The way they get the velocity toward/away from us is using the Doppler shift of lines in the spectrum of the star... that's actually quite a bit easier than getting the proper motion (change of position). You only need one observation to get it! (though it sounds like they have multiple observations if they've catalogued the fraction of multiple systems).
[TMB]
Corollary: "Any technology distinguishable from magic is not sufficiently advanced." ;-)
[TMB]
Weird... I was just noticing the other day how good a year 2003 was for music. Among the better releases of the year:
_ sites.html
Afro Celt Sound System - Seed
Aghast View - drifter.ep
Blue Man Group - The Complex
Collide - Some Kind of Strange
The Cruxshadows - Ethernaut
F-Space - Preliminary Impact Report
God Module - Empath
Incendio - Incendio
Pzycho Bitch - The Day Before
Tanzwut - Ihr Wolltet Spass
T.Raumschmiere - Radio Blackout
v/a - 2003 Hands
Of course, out of those only the Afrocelts and T.Raumschmiere are on RIAA labels... I'm not sure which labels report to the IFPI - the article says "The IFPI represents hundreds of the world's independent and major music labels including Warner Music, Sony Music, Universal Music, EMI and BMG", but there are thousands of independent labels, so it makes a difference!
Ah, here's a list: http://www.ifpi.org/site-content/directory/member
Looks like Tanzwut and Incendio are also on reporting labels... but still, most of the best releases of the year aren't in those stats.
[TMB]
There's no phonetic similarity... it's pronounced "Throatwarbler Mangrove". ;-)
[TMB]
It's possible to trace the orbits for the stars they have forward about as well as they can trace them backwards.
The problem, though, is that getting good enough kinematical information to do this is hard for stars that aren't near the Sun. You notice that all of the stars end up right near the Sun - that's not a coincidence! Those are the ones whose orbits we can get a handle on precisely because right now they're close enough that it's easy to get their kinematics.
You can imagine that if you waited 220 million years (one orbit) and did the same exercise, you'd find the same thing - the stars came from a broader range of radii "220 million years ago" (i.e. now). So right now, most of them are too far away for us to get good proper motions and/or good distances, and therefore good spatial velocities.
[TMB]
Rather than just asserting that blindly, why don't we work out the numbers?
The only place in the Milky Way that stars collide are inside globular clusters, where they form "blue stragglers". There are about 3000 known blue stragglers in the Milky Way (Piotto et al. 2004). The rate is probably higher now than in the past (it should increase with time as more clusters undergo core collapse), but averaging over the 13.7 billion year history, that's an average rate of one every 4.5 million years
Now, whether you consider that "quite frequently" or not depends on your perspective. ;-)
[TMB]
I've never tried sending email to an MP, but I have written on paper before, and at least the office of the Minister of Justice (under Martin Cauchon), and Foregin Affairs (under Bill Graham) are quite good about actually reading letters and replying to them.
I also recommend cc:ing your MP.
[TMB]
Theoretically, yes.... there's a recent paper that works out the numbers for lensing from a spiral galaxy, and it's roughly on the order of a few micro-acroseconds. Possibly detectable by SIM or GAIA.
[TMB]
I'm pretty sure that paying someone to commit an illegal act is illegal. ;-)
[TMB]
Quoth the article:
This is the exact opposite trend to what I'd expect. I think we all agree that filesharing has both a positive effect, due to advertising/finding new bands, and a negative effect, due to people downloading a song and not buying the album when they otherwise would have. So filesharing should increase CD sales when the former effect outweights the second, and decrease them when the latter effect is more important.
The advertising effect of filesharing should be much stronger for unknown bands than for known bands. Everyone's heard the mainstream hits; not many people have heard Random Unknown Cool Band. I see no reason why people's desire to buy a CD when they already have an MP3 should depend on how big the artist is. So small bands should do better under filesharing than big bands, whether or not the net effect integrated over all CD sales is positive, negative, or neutral.
But... this study says that the situation is exactly opposite. Which suggests that people's desire to buy a CD from a mainstream band once they have the MP3 is greater than their desire to do so from a small band... or that P2P is only increasing the status quo, in sharp contrast to "conventional" wisdom and really fucking depressing if true.
[TMB]
Funny, as I read this I'm listening to Velvet Acid Christ's Between The Eyes Vol 1, which I bought this afternoon. Why? Because I once grabbed the Nazi Bastard mix of Futile on Audio Galaxy (ah, those halcyon days of yore) and have been looking for a CD copy ever since. :) Glad he finally found a good way to release it.
(going to see IOC in about 2.5 weeks...)
[TMB]
I always thought Pluto was a bloodhound. ;-)
[TMB]
In what way?
I need to travel for work a lot. I'd rather that didn't affect my ability to vote.
[TMB]
These were absentee ballots. Unless they send out mandatory pens along with the absentee ballot (which I guess they don't, since this problem arose... might not be a bad idea), there's no control over what kind of pen the voters use.
[TMB]
Just to clarify... in the imaging data, the stars outnumber galaxies by a lot. They purposely target likely galaxies for spectroscopy, which is why there are more galaxies than anything else in the spectroscopic data.
That's in contrast with the Hubble Ultra Deep Field, where almost every object is a galaxy, because they purposely chose a patch of sky with very few stars.
But, yes, there are an incredible number of stars in the observable universe. :)
[TMB]
Unfortunately the MPEG compression makes it almost impossible to actually see the bubbles! Guess I'm going to have to go "experiment" on my own! ;-)
[TMB]
You've never seen Six Degrees of Separation, have you?
[TMB]
Damn, so that's why they keep losing...
[TMB]
Okay, who wants to be the fall guy?
Someone who values the principles of democracy more than they do freedom for the next N years of their life ought to go in and do it. Make it absolutely blatant that it was done. Leave Diebold standing there saying "We really think that this county of 100,000 people produced 5 million votes for Ralph Nader in the Republican primary. That's what the machine says." Preferably during as minor an election as possible.
Now's the time to show what you're made of. I admit I'm too chicken to do it (besides, it's not my country - we still use paper and pen).
[TMB]
w=-1
;-) Postulating anything else is like introducing epicycles when you've only just figured out that there are orbits.
This comes as a great shock to exactly no one.
[TMB]
Photocopiers are legal.
[TMB]
The last thing I hacked was Cowboy Neal.
Piece of advice... don't post both as an AC and non-AC in the same thread when you have a very distinctive post style if you really want the AC post to be anonymous. ;-)
[TMB]
A few minor quibbles...
(I am an astrophysicist. I am not a cosmologist, but I do galaxy evolution... we hang out with cosmologists)
There are quite a few pieces of evidence for dark matter:
- internal dynamics of galaxies: when you look at how fast the outer parts of galaxies move around the central parts, you find that the amount of mass necessary is much more than what you see
- dynamics of galaxies in clusters: when you look at how fast galaxies move around in galaxy clusters, you find the amount of mass necessary is much more than what you see
- non-linear growth of primordial perturbations (sounds complicated, isn't really): the universe used to be almost completely smooth. now it's filled with clumps of matter like galaxies and clusters and big voids without much matter. the structures collapsed because of their mass. if there were only as much mass as you can see, there hasn't been enough time for galaxies to have collapsed
The amazing thing about all of these measurements is that they all give you the same answer for how much mass is really out there.
[TMB]