rcain wrote:interestingly, i can't see any news from LIGO since about 2002! what have they been doing with all that time and money? you'd have thought they'd have picked up something, the sun, the moon, anything... anyone heard of any results?
They didn't find anything.
The system is now dismantled and they are proceeding with a general upgrade. The works should be completed around 2015.
rcain wrote:there have got to be pretty strong predictions on 'scale' in such an experiment - i don't see the logic in having both LIGO and LISA. where's it justified?
LISA should have scanned for gravitational waves at much lower frequencies than LIGO.
rcain wrote:interestingly, i can't see any news from LIGO since about 2002! what have they been doing with all that time and money? you'd have thought they'd have picked up something, the sun, the moon, anything... anyone heard of any results?
They didn't find anything.
The system is now dismantled and they are proceeding with a general upgrade. The works should be completed around 2015.
rcain wrote:there have got to be pretty strong predictions on 'scale' in such an experiment - i don't see the logic in having both LIGO and LISA. where's it justified?
LISA should have scanned for gravitational waves at much lower frequencies than LIGO.
thanks. kind of expected that.
re: wavelengths - surely though, that would be much to do with the receiving equipment and filtering - which could as well be ground-based, and using a smaller scale beam (ie. the existing facilities). if the effects are so small that they 'need' an arial/beam millions of times longer, then surely there's something wrong with the theory that they can detect anything that way.
rcain wrote:. if the effects are so small that they 'need' an arial/beam millions of times longer, then surely there's something wrong with the theory that they can detect anything that way.
I don't think that this comes as a surprise either
If it is, I still don't see how it can "detect" gravity waves.
Same concept but LISA should operate at a much lower frequency to detect gravitational waves from black holes.
That is, provided that Gravitational Waves actually exist.
The idea would be to see if changes in the electrical field as measured on the moons can be detected in conjuntion with changes in orbit, and if these deviate from what would be expected.
If it is, I still don't see how it can "detect" gravity waves.
Same concept but LISA should operate at a much lower frequency to detect gravitational waves from black holes.
That is, provided that Gravitational Waves actually exist.
The idea would be to see if changes in the electrical field as measured on the moons can be detected in conjuntion with changes in orbit, and if these deviate from what would be expected.
is that right?
i always thought it was a relativistic effect they were measuring - space bending causes minute deformation of the beam/refraction/delay of the signal.
don't know if they're using polarized beams. anyone know?
we may not have a terribly long beam line on terra firma, but we sure have some strong gravitational fields swinging about - enough to lift the oceans. i thought it was already pretty much agreed that grav-waves cannot propagate at greater than 'c' (if they exist - which i suppose they must).
so, what else do they hope to show? it seems to be just the black holes they are after.
Basically my idea is that instead of measuring changes in a beam of light try to find changes in an electric field, plus the gravitational field of the small moons has a substantial effect when they come within such close proximity, enough to switch orbits.
ah, i seem to recall, one of the problems with the ground based LIGO was vibrations and noise through the ground... (some bbc/ch4 TV documentary... need to check wiki) ... but why not filterable?
rcain wrote:ah, i seem to recall, one of the problems with the ground based LIGO was vibrations and noise through the ground... (some bbc/ch4 TV documentary... need to check wiki) ... but why not filterable?
it's filterable of course to some extent. but any noise even after being filtered is going to degrade the signal. at the end of all the filtering what you have is white noise - noise that by definition cannot be predicted and therefore can't be filtered - and then the only 2 steps you got left is blind source separation and a kalman filter. the final product is still "blurry" and it's a bluriness that mathematically cannot be removed via signal processing. the only way to remove it is to remove the source of noise in the first place, and that means insulating the equipment from vibrations as much as possible. yes, the periodic vibrations can be mathematically removed no problem, but it's the aperiodic ones are a different story, and the white noise component can at best be diminished, but never fully removed through signal processing.
EDIT: at bottom, any detection and signal processing problem is a source separation problem. and the more sources you have mixed together the tougher it is.
rcain wrote:ah, i seem to recall, one of the problems with the ground based LIGO was vibrations and noise through the ground... (some bbc/ch4 TV documentary... need to check wiki) ... but why not filterable?
it's filterable of course to some extent. but any noise even after being filtered is going to degrade the signal. at the end of all the filtering what you have is white noise - noise that by definition cannot be predicted and therefore can't be filtered - and then the only 2 steps you got left is blind source separation and a kalman filter. the final product is still "blurry" and it's a bluriness that mathematically cannot be removed via signal processing. the only way to remove it is to remove the source of noise in the first place, and that means insulating the equipment from vibrations as much as possible. yes, the periodic vibrations can be mathematically removed no problem, but it's the aperiodic ones are a different story, and the white noise component can at best be diminished, but never fully removed through signal processing.
EDIT: at bottom, any detection and signal processing problem is a source separation problem. and the more sources you have mixed together the tougher it is.
true. but by all accounts, the wavelengths of 'change' associated with heavenly bodies, must be several orders of magnitude longer, (lower frequency), than terrestrial ground noise. various movements of the crust, plate tectonics, etc, perhaps. (perhaps that is indeed a problem - or part of a solution?).
there are also ample 'unambiguous' signatures to look for - eg: sun, moon, eclipses, alignments, etc, that should be unequivocally detectable by similar earth-bound arrays.
rcain wrote:
true. but by all accounts, the wavelengths of 'change' associated with heavenly bodies, must be several orders of magnitude longer, (lower frequency), than terrestrial ground noise. various movements of the crust, plate tectonics, etc, perhaps. (perhaps that is indeed a problem - or part of a solution?).
there are also ample 'unambiguous' signatures to look for - eg: sun, moon, eclipses, alignments, etc, that should be unequivocally detectable by similar earth-bound arrays.
also remember this is _gravity_ we're talking about. the signal is very very weak. you're listening for a whisper on a scream.
and even if you just amplify it right off the bat - well then the screams are going to saturate the channel and you'll just get an aperiodic square wave.