Detector Watch S6 V1

ML1
ML1
Joined: 20 Feb 05
Posts: 337
Credit: 66,344,190
RAC: 31,900

RE: RE: Bad vibrations

Message 93794 in response to message 93793

Quote:
Quote:
Bad vibrations aside, did the interferometer gravitationally 'see' the helicopter?

Yes, probably. But not in an immediately appreciable sense. What effect the chopper has will enter into all the other effects on the interferometer arms. To attribute a particular helicopter flyby, say, would require pretty well what we are doing here at E@H. Signal analysis. Trying to find that effect in amongst all the others. Like attempting to hear one 'off' note from a single instrument within a large orchestra, and while they are playing the 1812 Overture! Or Mamma Mia. :-) ...


Has LIGO been directly tested to see if it can 'see' what we would expect it to see for such as detecting the presence of the moon? Or could such as a large aircraft quietly passing low overhead generate a good gravitational test signal?

Ask the military to fly a fully laden C130 (or bigger) low overhead and throttled back to be as quiet as possible?

Or set up a holding tank nearby to hold and then release a few hundred tons of water into a pipeline and away into the distance?

Or would all such physically induced effects be at too low a frequency to be picked up?

Can any gravitational turbulence/burps from our own sun be detected directly gravitationally?

Or even such as the recent tsunami here on earth be detected gravitationally rather than seismically?

Or will only vastly mega-stellar upheavals do?

Regards,
Martin

(You asked for it! ;-) )

See new freedom: Mageia Linux
Take a look for yourself: Linux Format
The Future is what We all make IT (GPLv3)

Mike Hewson
Mike Hewson
Moderator
Joined: 1 Dec 05
Posts: 6,125
Credit: 126,944,457
RAC: 12,907

RE: (You asked for it! ;-)

Message 93795 in response to message 93794

Quote:
(You asked for it! ;-) )


Indeed! I'll have a crack at it!! :-)

Quote:
Has LIGO been directly tested to see if it can 'see' what we would expect it to see for such as detecting the presence of the moon?


Yes, such an effect has been seen. Tidal movements of the Earth's continents has been factored into a program that slightly adjusts the interferometer mirror positions on a continuous basis to account for arm length changes that are induced. The ground under the interferometers actually changes shape to a degree that corrections are needed, or the interferometer would lose lock within a short period of time ( about an hour I think ). So if anything we don't want the interferometer to 'see' the Moon! Actually I think there are GR studies of the moon, but they are using laser ranging ( bouncing off arrays left during Apollo times ).

Quote:
Or could such as a large aircraft quietly passing low overhead generate a good gravitational test signal? Ask the military to fly a fully laden C130 (or bigger) low overhead and throttled back to be as quiet as possible?


Hasn't been tried but I guess could be. I think they've accepted that it will take a space array ( LISA ) to look at that lower frequency band and below rigorously. The more noise there is in a band then the longer are the 'integration times' required to pick up a given signal. In which case you'd need longer un-interrupted stretches of interferometer lock, with correspondingly more analysis work ( that translates to the work units here at E@H ). For the type of search here at E@H ( which is only one aspect of LIGO work - hunting for continuous waves from pulsars ) most of the signal searching is a 'matched filtering' technique. This requires data that remains coherent in phase - you don't miss any wavelengths - for extended periods. A typical data segment could potentially contain tens of thousands of gravitational wave cycles of interest, at some frequency, and the analysis method will return a low statistic ( sort of a signal to noise ratio ) if there's even a half wavelength shift over that time. Indeed because E@H does an all sky search, the signal templates we try to match with the data are of many varieties corresponding to sky position, source frequency and frequency change per Doppler shifting. Because the Earth rotates and orbits around the Sun, in addition to whatever motion the source has way out there. The point is there is already an enormous calculation load, which is why E@H exists, for the better frequency reception bands. I haven't read of anyone getting especially excited or expecting detections from LIGO below about 50Hz, say.

Quote:
Or set up a holding tank nearby to hold and then release a few hundred tons of water into a pipeline and away into the distance?


Not exactly. But for a good laugh I'll tell you of what they have been up to with testing the seismic instrumentation system ( from this article ):

Quote:
A simple, but effective, impulsive seismic source was made using a 2 liter plastic soda pop bottle partially filled with liquid nitrogen. A steel weight was attached to the bottle with duct tape prior to filling to insure that the bottle would not float. Once a bottle was filled approximately one-third full of liquid nitrogen and the cap was tightly secured, it was thrown into the center of the erosion control pond immediately north of the LVEA. The water depth at this location is approximately eight feet. Figure 1 indicates the location of the seismic array relative to other features on the LLO site. When the soda bottle ruptured at the bottom of the pond, the water above it served as a reaction mass, making it possible to couple a relatively large amount of energy into the soil as a result of the explosion. Also, because the gas explosion is in water, the initial propagation through water is via a compressional wave and vertical “gravity†water wave motion. Vertical and horizontal shear modes result from the coupling at the soil-water interface at the pond boundary.


Nice work if you can get it! Depth charging the local flood retarding pond. The 'gravity' wave mentioned here is older unrelated terminology from hydrology. It's simply the bulk up/down motion of the water.

Quote:
Or would all such physically induced effects be at too low a frequency to be picked up?


Yep, see above.

Quote:
Can any gravitational turbulence/burps from our own sun be detected directly gravitationally?


The Sun doesn't burp in a way that would be realistically detected. Or if it did, we would all be in mortal strife. This is a deep issue that goes to the heart of the difference between gravity and the other forces. If I grab some charge and push it around I can generate emission of waves easily. Indeed we are communicating now using technology based upon that. For gravitational wave production it is not simply enough to accelerate some mass ( which is the gravitational 'charge' ). The pattern of movement must have particular geometric characteristics, related to conservation of mass/energy/momentum/angular-momentum and that there are no negative masses ( or anti-gravity if you like ). While the Earth-Sun system may have such characteristics, the effect is small due to relatively low masses and speeds. There is also another issue of distinguishing/detecting effects in the 'near' and 'far' fields. General Relativity is non-linear, so close in to the source there are all sorts of 'higher order' effects which rapidly diminish with distance - like an inverse cube law say. Whereas we ( hopefully! ) see waves from distant sources because the strength in the far field goes like a simple single inverse power.

Indeed one goal of this GW detector business is to verify whether any of our above understandings of the consequences of GR are true. I am currently re-reading a book called "Traveling at the Speed of Thought : Einstein and the Quest for Gravitational Waves" by Daniel Kennefick. It outlines quite well the history of GR research. The themes of all of your questions were/are/will-be the object of discussion amongst researchers. In the end experiment will decide and guide ( Hello? Anyone doing string theory listening? ). The most dramatic result from GW experiments would be we looked, no waves were found, and if they were there we would have heard them.

Quote:
Or even such as the recent tsunami here on earth be detected gravitationally rather than seismically?


Nowhere near enough mass/energy/velocity to achieve that. Unless possibly if the tsunami was real close to the interferometer. It'd be along the lines of the holding tank above. But then there'd be other issues.

Quote:
Or will only vastly mega-stellar upheavals do?


This is the key point. Order of magnitude calculations rule out any method of generating waves here on Earth. You have to have mass/energy/velocities far out of even solar system scale to even begin to wiggle spacetime significantly. That's a result of high speed of light ( or that to higher powers actually ) and the slightness of G. The frequency band that a space array would detect refers to really, really big things like multi-million stellar mass black hole mergers ( ie. colliding galaxies ), whole universe oscillations from the ( well, alleged ) inflationary epoch etc.

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

MAGIC Quantum Mechanic
MAGIC Quantum M...
Joined: 18 Jan 05
Posts: 1,304
Credit: 418,703,377
RAC: 102,041

We try to keep things

We try to keep things balanced up here by having the Columbia River on the east and south side and Mount St Helens on the west side and Mount Ranier on the nw side just to make sure.

And of course the Columbia Generating Station so we have the reactor giving us 8,109 GWh's of electricity.

That should take care of the "Ring of Fire" earthquakes and plate techtonics.

 

Mike Hewson
Mike Hewson
Moderator
Joined: 1 Dec 05
Posts: 6,125
Credit: 126,944,457
RAC: 12,907

RE: We try to keep things

Message 93797 in response to message 93796

Quote:

We try to keep things balanced up here by having the Columbia River on the east and south side and Mount St Helens on the west side and Mount Ranier on the nw side just to make sure.

And of course the Columbia Generating Station so we have the reactor giving us 8,109 GWh's of electricity.

That should take care of the "Ring of Fire" earthquakes and plate techtonics.


Ah, Feng Shui for LIGO! Well done. :-)

[ The astronomers keep raving about the solar system barycentre. The place to be. It's inside the Sun .... ]

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

ML1
ML1
Joined: 20 Feb 05
Posts: 337
Credit: 66,344,190
RAC: 31,900

RE: ... solar system

Message 93798 in response to message 93797

Quote:
... solar system barycentre. The place to be. It's inside the Sun ...


Not always...

Via wikipedia:

Aside and wild conjecture: Might that have some indirect influence on the solar cycles?...

Regards,
Martin

See new freedom: Mageia Linux
Take a look for yourself: Linux Format
The Future is what We all make IT (GPLv3)

ML1
ML1
Joined: 20 Feb 05
Posts: 337
Credit: 66,344,190
RAC: 31,900

RE: RE: (You asked for

Message 93799 in response to message 93795

Quote:
Quote:
(You asked for it! ;-) )

Indeed! I'll have a crack at it!! :-) ...


Thanks for some good comments.

And it's amazing how useful liquid nitrogen can be! Hope there were no fish in the pond...

So... Is all this primarily a practice for learning how to set up a space based version of LIGO? Or is there still a good hope of seeing something from the presently known possible sources?

Is there a particular stellar binary that is going to be the target of special analysis?

Regards,
Martin

See new freedom: Mageia Linux
Take a look for yourself: Linux Format
The Future is what We all make IT (GPLv3)

ML1
ML1
Joined: 20 Feb 05
Posts: 337
Credit: 66,344,190
RAC: 31,900

RE: RE: ... solar system

Message 93800 in response to message 93798

Quote:
Quote:
... solar system barycentre. ...

Aside and wild conjecture: Might that have some indirect influence on the solar cycles?...


Will the shape of the sun be affected by where the solar system barycentre is at that time? Or even reshape how the Coriolis forces shape circulation in the sun?

Do the planets impart a significant tidal force on the sun? Anything significant happen when we get planetary alignments?...

Enough to comment on for a new thread?

Regards,
Martin

See new freedom: Mageia Linux
Take a look for yourself: Linux Format
The Future is what We all make IT (GPLv3)

Mike Hewson
Mike Hewson
Moderator
Joined: 1 Dec 05
Posts: 6,125
Credit: 126,944,457
RAC: 12,907

The barycenter is the centre

The barycenter is the centre of mass - a computed position based upon our knowledge of positions and masses of bodies in the solar system. There isn't anything unusual in space or time at the barycentre on account of it being that. If I choose a different set of objects to calculate for I'll get another answer. Given that it varies, that suggests a number of possibilities like inaccuracy in our knowledge, or influences unaccounted for. Note that the Sun also is in orbit too, though we often think of it as fixed. Being rather larger than other bodies it just doesn't move as much. Indeed the extrasolar planet detections have been based upon the slight apparent wobbles in motions of stars due to the presumed/deduced presence of planets.

The use of the barycentre is to convert our observations/results to that reference frame. It is probably the closest to an inertial frame ( un-accelerated ) that we would have sufficient knowledge of here-abouts. Alot of the workload at E@H is to unwrap the effects of Earth's accelerated motions- the varying Dopplering of the signals due to rotation about axis and orbit around Sun. As your diagram shows any change in this barycentre frame is very slow, so only low acceleration and hence nearly inertial.

The Earth's surface is not inertial, witness the Coriolis effects on weather systems. I have found that even light aircraft need to account for non-inertial effects when travelling significant distances. So if you go Northward, in the Southern Hemisphere, then effectively the ground under you is moving faster towards the East the more North you go. Zero at the South Pole and about 1000 mph at the equator. It'd go like the cosine of latitude, I think. The aircraft's course may seem to deviate to the West without even trying! So you have to point the aircraft more eastward than you would otherwise calculate, to ensure that you 'catch up' with the earth and nullify the effect. But that depends upon the basis of navigation one uses. I think these types of effects were first discovered with cannonballs!! :-)

I'm not aware of any conjecture of the energy production or transport within the Sun being affected by planetary positions. But that may well be my ignorance. One wonders what planetary rhythm(s) would produce eleven-ish year cycles. That's the right order of magnitude for the gas giants' orbital periods.

LIGO and LISA are distinct efforts. Probably the LISA people are taking an interest in the current GW efforts. There is quite a range of possible GW sources to 'view'. Roughly speaking things bigger in size and mass go to lower frequencies. So the various methods are going to be better ( generally ) at picking up different types of objects. Ultimately all of the stellar binary variants are going to be searched for.

One particular method I rather like is the use of high precision pulsar timings over many years. This may detect a subtle change in the rate of time passing here on Earth compared to the field of pulsars. So our atomic clocks may slow, say, due to a very low frequency gravity wave passing by. We would see that as the pulsars speeding up. So low in GW frequency that it takes years to do so, it's wavelength is humungous.

Cheers, Mike.

( edit ) Darn the difference b/w 'centre' and 'center' spellings. Divided by a common language we are! :-)

( edit ) And that leftward deviation DownUnda gives the North - > West and South -> East rule for here. If you go south then the ground is travelling less fast towards the east and hence you will 'overtake' it comparatively. This behaviour is the converse in the Northern Hemisphere where southward movement puts you to the west of where you expected, and northward movement to the east. Just think of it like a cannonball, a ballistic movement that begins with a certain eastward velocity from the point of firing. That is : what is the eastward speed of the ground in the direction you are firing towards - is it greater than or less than where you began? So more generally expressed : movement away from the equator makes you go eastward, and toward the equator you go westward. [ We know the earth rotates toward the East 'cos the Sun rises there! ]

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Mike Hewson
Mike Hewson
Moderator
Joined: 1 Dec 05
Posts: 6,125
Credit: 126,944,457
RAC: 12,907

Well, at least they're not

Well, at least they're not letting the weather get them down at Hanford :

Quote:

Sci Mon Summary (no science mode this shift)
Summary: Lots of wind meant there were no Science Segments this shift! We got a couple of locks, but IFO quickly dropped out of it again before getting to high power. Couple of earthquakes and spikes in seismic, but as we werent locked not really looked into them.

You can stop reading here, or purely because I had gone through the effort of making notes you can read comments on the wind:

15:00 UTC I managed to make my way to LHO despite the very apocalyptic looking morning (strong wind picking up loads of dust and a strange smell of burning in the air) and arrived to find it out of lock. Daniel and Patrick were both trying their best to get the IFO in lock but, with winds of over 30 Mph buffeting the arms and stations, this is proving to not be an easy task.

17:00 UTC We are still feeling the wrath of the Greek God Boreas. Couple of hours into shift and wind is still increasing, regularly blowing over 40 Mph. Got the IFO briefly in lock but it was quickly blown back out by the wind.

19:00 UTC Its fair blowing a gale oot there!
(It is a little breezy outside)

20:00 UTC Yon wind is still gien' it laldy!
(The wind is still strong.)

21:00 UTC The gale's still kicking up a load o stoor!
(The wind is still bringing a lot of dust)

22:00 UTC Had a keek ootside and it's still minging.
(I had a look outside, and it's still not very nice)

23:00 UTC Totally Scunnered Man!
(I am a little fed up)

Here endeth today's Scottish lesson...


The good news is that prior to the above, they were getting 18 - 19 Mpc at 14W for decent stretches.

At Livingston they are getting 13 - 14 Mpc but at 7W.

I'm still reading to define what it is that is upsetting the locks. So far it seems the new setup - higher input power, output mode cleaner and TCS - make the control systems more twitchy.

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Mike Hewson
Mike Hewson
Moderator
Joined: 1 Dec 05
Posts: 6,125
Credit: 126,944,457
RAC: 12,907

After some further thought

After some further thought about the barycenter, it occurred to me that the barycenter is not truly inertial. And thus that can't be the reason for it's use. If I bung a small test mass in there it will fall inward toward the Sun's centre. To keep it from moving away from the barycenter I'd have to apply some other force to stop that - hence breaching the concept of an inertial frame. Or put another way, the centre of mass is not the point of force equilibrium in an inverse square field *. For instance the point where the attractions from the Sun and Jupiter are equal ( and opposite as vectors ), say, is going to be way out near Jupiter and nowhere near the barycenter.

So I looked up what the International Astronomical Union has to say and came up with the definition of barycentric radial-velocity measure that includes this phrase :

Quote:
"by a hypothetical observer at zero gravitational potential, located at, and being at rest with respect to, the solar-system barycenter"


note the 'zero gravitational potential' component. All in all it seems the idea is to construct a fictitious reference frame and convert various different observations to it, for the purpose of comparison between the research efforts. So when a pulsar Doppler measurement ( 'radial velocity measure' ) is made by a radio astronomer, say, we may compare that with some gravitational wave Doppler measurement by transforming both to this standard view. They no doubt would have made their measurements at quite different circumstances of the Earth's motion. It's fictitious because the gravitational potential at the barycenter is certainly not zero - that's why a test mass would actually wander off fairly quickly. So you want a motionless observer ( no velocity with respect to the barycenter ) which is at the barycenter, but ignoring the actual gravitational forces there! And we are ignoring things like being evaporated by the high temperature of course! :-)

It would appear that the value in doing this is to separate those Doppler effects caused by distant behaviours - at the source, stuff like lensing on the way, cosmic expansion, whatever - from what are obviously 'local' ones. And I'm guessing that because the position of the barycenter varies relatively slowly, one can make a reasonably sensible comparison of observations when they are transformed to the barycenter if the time of said observations is suitably close.

I suspect there are further subtleties however, and of course I may be spouting rubbish! :-) :-)

Cheers, Mike.

( edit ) * - except in the special case where one has only the two masses, and they are equal. Or generally, the centroid of an equilateral polygon of equal masses .....

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.