>
> A lot of the math tricks were originally developed for radio, but LIGO is
> taking them much further. A lot of the things (like aiming) that radio could
> mostly do in hardware and merely "top up" in software have to be done all or
> almost all in software for gravitational wave detectors. There are some
> tantalizing similarities to radio, but it's really a different game.
>
> Hope this helps,
> Ben
>
It certainly does Ben, thanks.... and it only makes me even more interested in learning more of the mathematical details.
So the "aiming" is done strictly within the data, and the key to the aiming or "filtering out" the surroundings from a detection within the data is the correlation of an expected Doppler shift with a known time interval of gravity wave measurment. Since you determine the values of the Doppler and the interval of time as an iterative function of the total computation, the expected signatures that would emerge in each calculation are therefore known to come from a predetermined area.
Did I earn my beer for the night?
And ok... so the cross hair isn't eye candy. But does the rate at which it appears to moves across the celestial sphere have a basis in truth, too?
Glenn
"No, I'm not a scientist... but I did stay at a Holiday Inn Express."
> - Movement of the earth relative to the source doesn't only mean its own rotation, but it also movement around the sun in the solar system, and this solar system also moves relative to the center of our galaxy. These movements, btw., are described in the "earth" and "sun" files you downloaded.
does not it means that there must exist an absolute frame of reference which is at rest relative to the frame of empty space time in which gravitational waves propogate ?
what is our earth movemenet relative to that empty space-time grid, our Sun's movement, our galaxy center movement ?
> And ok... so the cross hair isn't eye candy. But does the rate at which it
> appears to moves across the celestial sphere have a basis in truth, too?
Yes. When your machine is done analyzing all the data in the current work unit for a particular spot on the sky, the orange marker moves to the next spot and your machine starts analyzing for that spot (that Doppler shift). If you have a fast machine it zips around - my home machine is very new and the orange marker moves as fast as the star sphere, so it looks like it's staying in place on the screen. My old laptop is much slower and you have to watch a while to see the orange marker shift locations.
> When your machine is done analyzing all the data in the current work unit
> for a particular spot on the sky, the orange marker moves to the next spot
> and your machine starts analyzing for that spot (that Doppler shift). If you
> have a fast machine it zips around - my home machine is very new and the
> orange marker moves as fast as the star sphere, so it looks like it's
> staying in place on the screen. My old laptop is much slower and you have to
> watch a while to see the orange marker shift locations.
>
> Hope this helps,
> Ben
Fantastic... there is light at the end of the tunnel, and in that light sits a whole six-pack.
Last set of questions, and I'll can it for at least a week. I AM learning a lot, though. Thanks.
Ok.... the cross hair is moving pretty quickly on my computers, too. And so BOINC is performing a calculation and getting a result at each point (with a pre-determined Doppler based on sun/earth/time FOR that point.) I haven't sat down for a full 4 hour stretch to watch the screen saver, but it appears that it's moving fast enough to make more than one complete trip around the sphere during the CPU time required to complete the WU.
1. Is that my imagination?.. Does the crosshair only make one pass around the celestial sphere for each WU?
2. If so/If not... What variables are changing between each WU/complete sweep? Or is each WU just a new slice of time to be processed?
3. The work units are not "pieces of a single gigantic puzzle", per say, to be reassembled into the grand result after enough have been reported. Rather, they are each new and unique measurements that require a result to be calculated... and these WUs are being generated very rapidly by the LIGOs.... ergo, the need for distributed processing to handle the rate (vice volume) of data generated.
Finito.
Glenn
"No, I'm not a scientist... but I did stay at a Holiday Inn Express."
Actually the current WUs consist of three steps or passes: Two almost identical ones, in which they perform an all-sky search on two different data sets (currently two different time stretches from the same detector), and a third coincidence step, in which the results of the first two passes are compared. So with the current WUs, the crosshair should make two passes around the sphere.
> > - Movement of the earth relative to the source doesn't only mean its own
> > rotation, but it also movement around the sun in the solar system, and this
> > solar system also moves relative to the center of our galaxy. [...]
> does not it means that there must exist an absolute frame of reference which
> is at rest relative to the frame of empty space time in which gravitational
> waves propogate ?
>
> what is our earth movemenet relative to that empty space-time grid, our Sun's
> movement, our galaxy center movement ?
If relativity is right, and if in addition gravity waves move at the speed of light, then there is no meaningful 'frame of empty space'. This is because, contrary to intuition, a wave that moves at the speed of light in one inertial frame of reference also moves at the same speed of light in any other inertial frame of reference.
However, even though there is no frame of 'empty space', at any one point in the universe there is a frame that is almost as good, which is the cosmic microwave background. If we are at rest wrt (with respect to) the backgrond, we will observe the same temperature in every direction. If we are moving wrt the background, then there will be a steady variation of temperature from the hottest (dead ahead in our direction of movement) to the coolest 180deg away from that.
When these measurements are made it is found that our motion wrt the background is (if I remember rightly) about 200km/sec, a bit smaller than our rotation round the galaxy and in a different direction. This means we can tell that our galaxy as a whole has its own motion wrt the background.
There is some debate about what this motion means philosophically: most physicists will say it is not a fundamental frame of the universe (becasue, amongst other things we expect the background seen by anonther galaxy to be moving wrt the background seen by us, each of us seeing a slightly different set of photons from the early universe).
> > A lot of the math tricks
)
>
> A lot of the math tricks were originally developed for radio, but LIGO is
> taking them much further. A lot of the things (like aiming) that radio could
> mostly do in hardware and merely "top up" in software have to be done all or
> almost all in software for gravitational wave detectors. There are some
> tantalizing similarities to radio, but it's really a different game.
>
> Hope this helps,
> Ben
>
It certainly does Ben, thanks.... and it only makes me even more interested in learning more of the mathematical details.
So the "aiming" is done strictly within the data, and the key to the aiming or "filtering out" the surroundings from a detection within the data is the correlation of an expected Doppler shift with a known time interval of gravity wave measurment. Since you determine the values of the Doppler and the interval of time as an iterative function of the total computation, the expected signatures that would emerge in each calculation are therefore known to come from a predetermined area.
Did I earn my beer for the night?
And ok... so the cross hair isn't eye candy. But does the rate at which it appears to moves across the celestial sphere have a basis in truth, too?
Glenn
"No, I'm not a scientist... but I did stay at a Holiday Inn Express."
> - Movement of the earth
)
> - Movement of the earth relative to the source doesn't only mean its own rotation, but it also movement around the sun in the solar system, and this solar system also moves relative to the center of our galaxy. These movements, btw., are described in the "earth" and "sun" files you downloaded.
does not it means that there must exist an absolute frame of reference which is at rest relative to the frame of empty space time in which gravitational waves propogate ?
what is our earth movemenet relative to that empty space-time grid, our Sun's movement, our galaxy center movement ?
> Did I earn my beer for the
)
> Did I earn my beer for the night?
Looks like.
> And ok... so the cross hair isn't eye candy. But does the rate at which it
> appears to moves across the celestial sphere have a basis in truth, too?
Yes. When your machine is done analyzing all the data in the current work unit for a particular spot on the sky, the orange marker moves to the next spot and your machine starts analyzing for that spot (that Doppler shift). If you have a fast machine it zips around - my home machine is very new and the orange marker moves as fast as the star sphere, so it looks like it's staying in place on the screen. My old laptop is much slower and you have to watch a while to see the orange marker shift locations.
Hope this helps,
Ben
> When your machine is done
)
> When your machine is done analyzing all the data in the current work unit
> for a particular spot on the sky, the orange marker moves to the next spot
> and your machine starts analyzing for that spot (that Doppler shift). If you
> have a fast machine it zips around - my home machine is very new and the
> orange marker moves as fast as the star sphere, so it looks like it's
> staying in place on the screen. My old laptop is much slower and you have to
> watch a while to see the orange marker shift locations.
>
> Hope this helps,
> Ben
Fantastic... there is light at the end of the tunnel, and in that light sits a whole six-pack.
Last set of questions, and I'll can it for at least a week. I AM learning a lot, though. Thanks.
Ok.... the cross hair is moving pretty quickly on my computers, too. And so BOINC is performing a calculation and getting a result at each point (with a pre-determined Doppler based on sun/earth/time FOR that point.) I haven't sat down for a full 4 hour stretch to watch the screen saver, but it appears that it's moving fast enough to make more than one complete trip around the sphere during the CPU time required to complete the WU.
1. Is that my imagination?.. Does the crosshair only make one pass around the celestial sphere for each WU?
2. If so/If not... What variables are changing between each WU/complete sweep? Or is each WU just a new slice of time to be processed?
3. The work units are not "pieces of a single gigantic puzzle", per say, to be reassembled into the grand result after enough have been reported. Rather, they are each new and unique measurements that require a result to be calculated... and these WUs are being generated very rapidly by the LIGOs.... ergo, the need for distributed processing to handle the rate (vice volume) of data generated.
Finito.
Glenn
"No, I'm not a scientist... but I did stay at a Holiday Inn Express."
Actually the current WUs
)
Actually the current WUs consist of three steps or passes: Two almost identical ones, in which they perform an all-sky search on two different data sets (currently two different time stretches from the same detector), and a third coincidence step, in which the results of the first two passes are compared. So with the current WUs, the crosshair should make two passes around the sphere.
BM
BM
> > - Movement of the earth
)
> > - Movement of the earth relative to the source doesn't only mean its own
> > rotation, but it also movement around the sun in the solar system, and this
> > solar system also moves relative to the center of our galaxy. [...]
> does not it means that there must exist an absolute frame of reference which
> is at rest relative to the frame of empty space time in which gravitational
> waves propogate ?
>
> what is our earth movemenet relative to that empty space-time grid, our Sun's
> movement, our galaxy center movement ?
If relativity is right, and if in addition gravity waves move at the speed of light, then there is no meaningful 'frame of empty space'. This is because, contrary to intuition, a wave that moves at the speed of light in one inertial frame of reference also moves at the same speed of light in any other inertial frame of reference.
However, even though there is no frame of 'empty space', at any one point in the universe there is a frame that is almost as good, which is the cosmic microwave background. If we are at rest wrt (with respect to) the backgrond, we will observe the same temperature in every direction. If we are moving wrt the background, then there will be a steady variation of temperature from the hottest (dead ahead in our direction of movement) to the coolest 180deg away from that.
When these measurements are made it is found that our motion wrt the background is (if I remember rightly) about 200km/sec, a bit smaller than our rotation round the galaxy and in a different direction. This means we can tell that our galaxy as a whole has its own motion wrt the background.
There is some debate about what this motion means philosophically: most physicists will say it is not a fundamental frame of the universe (becasue, amongst other things we expect the background seen by anonther galaxy to be moving wrt the background seen by us, each of us seeing a slightly different set of photons from the early universe).
~~gravywavy