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What's up with gravity wave detection?



 
 
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  #1  
Old August 16th 04, 12:00 AM
dkomo
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Default What's up with gravity wave detection?

I found an old PBS documentary on VHS from 1991 called _The Astronomers_
at the local public library. One of the programs in the series was
"Waves of the Future" about gravitational waves. In the program Kip
Thorne was shown making a bet with one of his collaborators on gravity
wave theory that these waves would positively be detected by 2000.

I found this both humorous and a touch sad. The program described some
of the early planning for LIGO (Laser Interferometer Gravitational Wave
Observatory). Curious, I went to the LIGO web site to see what was
going on. I found nothing of substance there -- just a lot of slick PR.

So my question is, what are the prospects that gravity waves will be
detected anytime soon? Is LIGO still having technical problems or what?
It is now 2004, after all. Other detection labs are being built around
the world. Are these labs going to have any better luck?

Also, what are people's opinions about gravity waves? Is it possible
that these are a scientific dead end like the decay of the proton turned
out to be? If gravity waves are never detected, what are the
implications for the general theory of relativity?




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  #2  
Old August 16th 04, 12:19 AM
Sam Wormley
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dkomo wrote:

I found an old PBS documentary on VHS from 1991 called _The Astronomers_
at the local public library. One of the programs in the series was
"Waves of the Future" about gravitational waves. In the program Kip
Thorne was shown making a bet with one of his collaborators on gravity
wave theory that these waves would positively be detected by 2000.

I found this both humorous and a touch sad. The program described some
of the early planning for LIGO (Laser Interferometer Gravitational Wave
Observatory). Curious, I went to the LIGO web site to see what was
going on. I found nothing of substance there -- just a lot of slick PR.

So my question is, what are the prospects that gravity waves will be
detected anytime soon? Is LIGO still having technical problems or what?
It is now 2004, after all. Other detection labs are being built around
the world. Are these labs going to have any better luck?


Most likely LIGO will detect gravitational waves.
See: http://www.ligo.caltech.edu/
http:/www.edu-observatory.org/eo/cosmology.html

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 632 April 9, 2003 by Phillip F. Schewe, Ben Stein, and James
Riordon

FIRST LIGO SCIENTIFIC RESULTS. With two controlling partners, MIT and
Caltech, and two branch offices (two completely independent detectors)
located in Washington State and Louisiana, the Laser Interferometer
Gravitational-Wave Observatory (LIGO) is essentially a giant strain gauge.
In the LIGO setup laser light reflects repeatedly in each of two
perpendicularly oriented 4-km-long pipes. A passing gravity wave will
distort the local spacetime, stretching very slightly one of the paths while
shrinking the other, causing the interference pattern of the two merging
laser light beams to shift in a characteristic way. LIGO does not measure
static gravitational fields, such as those from the sun or the Earth itself.
Rather it strives to see ripples in spacetime radiated by such events as
the inspiral of two neutron stars toward each other, a phenomenon which
would typically produce a strain in the LIGO apparatus as large as one part
in 10^20. That is, a passing gravity wave is expected to change the
distance between mirrors some 4 km apart by about 10^-18 meters, a
displacement 1000 times smaller than a proton. Such a measurement
represents a physics and engineering feat of great delicacy. But at long
last the LIGO team has prepared its instrument and at this week's APS
meeting, reported its first official results from the initial "science" run
conducted over 17 days in September 2002.

In this first run no gravitational wave events were observed, but palpable
knowledge was gained as to what the sky should look like when viewed in the
form of gravity waves. So great is LIGO's sensitivity that it has been able
to set the best upper limit on the output of gravitational waves from three
of the four prime source categories. These four expected waveforms are as
follows: bursts from sources such as supernovas or gamma bursters; chirps
from inspiraling objects such as coalescing binary stars; periodic signals,
perhaps from sources like spherically asymmetric pulsars; and a stochastic
background source arising from gravity waves originating from the big bang
itself. LIGO deputy director Gary Sanders (Caltech,
) said that in three of these four categories,
had set new upper limits on the rate at which gravitational waves were being
produced. In the coalescing binary category, for instance, LIGO has
established an upper limit of 164 per year from the Milky Way, a factor of
26 better than the previous limit. Erik Katsavounidis (MIT,
) said that LIGO could establish an upper limit on
periodic signals from bright pulsars with a sensitivity of about 10^-22.
Sheila Rowan (Stanford Univ and Univ Glasgow) spoke of future operations at
LIGO. First of all, the second scientific run currently underway will be
some ten times more sensitive than the first run, the one being reported at
the meeting. If in the first science run LIGO was essentially sensitive to
gravity waves from the whole of the Milky Way, then in the second science
run (conducted Feb-Apr 2003), featuring a ten-times improvement in
sensitivity, the region of space patrolled would effectively reach out to
about 15 million light years, a realm that includes the nearby Andromeda
galaxy. (For more information about LIGO and a complete collaboration list,
see
www.ligo.caltech.edu ) In its search for gravity waves, LIGO (which with
about 440 scientists is as big as the large particle physics experiments
underway at accelerators) is also collaborating with other interferometer
devices such as GEO (in Germany, www.geo600.uni-hannover.de ) and TAMA
(Japan).
  #3  
Old August 16th 04, 04:44 AM
Greysky
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"dkomo" wrote in message
news
I found an old PBS documentary on VHS from 1991 called _The Astronomers_
at the local public library. One of the programs in the series was
"Waves of the Future" about gravitational waves. In the program Kip
Thorne was shown making a bet with one of his collaborators on gravity
wave theory that these waves would positively be detected by 2000.

I found this both humorous and a touch sad. The program described some
of the early planning for LIGO (Laser Interferometer Gravitational Wave
Observatory). Curious, I went to the LIGO web site to see what was
going on. I found nothing of substance there -- just a lot of slick PR.

So my question is, what are the prospects that gravity waves will be
detected anytime soon? Is LIGO still having technical problems or what?
It is now 2004, after all. Other detection labs are being built around
the world. Are these labs going to have any better luck?

Yep. And the AI folks had predicted machine intelligence by now, too. We do
have Fritz8...


Also, what are people's opinions about gravity waves? Is it possible
that these are a scientific dead end like the decay of the proton turned
out to be? If gravity waves are never detected, what are the
implications for the general theory of relativity?


The implications of conservation of baryon number as you allude to when you
say proton decay detection represents a dead end has not yet been truly
absorbed in the greater schema of thought. Something very wrong is occuring
and we are just now obtaining proof that the last 30 years of thought is
wrong. The first run of gravity wave detection has determined a baseline for
event detection that can only get larger (read worse) the longer they run
the interferometers..... if no gravity waves are detected out to theoretical
limits - as has happened with proton decay- then there will be none but the
blind who will say our interpretation of the universe is dead wrong and is
wrong in such a way that theoreticians will not be able to fix, or modify,
current theory to make it even seem to work on a bad day. There are already
rumblings coming from unnamed sources that the first run should have found
*something*.... believe me, there are many careers at stake on the result of
this project, as well as many fingers crossed...

We may even have to rip the "Big Black Book" in half and throw it, along
with substantial portions of geometrodynamics in the trash can on this one
if it should go wrong.

Greysky

www.allocations.cc
Learn how to build FTL radio.



  #4  
Old August 16th 04, 06:44 AM
Australopithecus Afarensis
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Most likely LIGO will detect gravitational waves.
See: http://www.ligo.caltech.edu/
http:/www.edu-observatory.org/eo/cosmology.html


It is very interesting how institutions would spend millions of dollars
trying to detect something that has not been thoroughly understood. As I
read in Scientific American a year or two ago, LIGO was chosen to be built
in places where noise generated by human activities are at near maximum.
This means LIGO's detection of gravitational waves is subjected to broad and
creative interpretations of data which can easily be explained by something
else.


  #5  
Old August 16th 04, 08:05 AM
Androcles
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"dkomo" wrote in message
news | I found an old PBS documentary on VHS from 1991 called _The Astronomers_
| at the local public library. One of the programs in the series was
| "Waves of the Future" about gravitational waves. In the program Kip
| Thorne was shown making a bet with one of his collaborators on gravity
| wave theory that these waves would positively be detected by 2000.
|
| I found this both humorous and a touch sad. The program described some
| of the early planning for LIGO (Laser Interferometer Gravitational Wave
| Observatory). Curious, I went to the LIGO web site to see what was
| going on. I found nothing of substance there -- just a lot of slick PR.
|
| So my question is, what are the prospects that gravity waves will be
| detected anytime soon?

Why not consider the biggest "wave" or pulse in our galaxy imaginable?
That would correspond to ALL the mass of a star entirely disappearing, as
could just conceivably happen if the star were converted to entirely to
energy
in one enormous supernova. We'd see a brilliant flash of EM radiation,
brighter than daylight, but the entire gravity would be gone. This would
correspond to a negative going pulse radiating outward, which for the sake
of argument we'll allow to be at velocity c (although we have no evidence of
that), and ask if we could detect it. Next, we ask if this cataclysm were to
occur at the nearest star (other than the sun, of course), since that would
provide the strongest negative pulse obtainable to any instrument capable of
detecting it. So... how much gravity do we at present detect from Proxima
Centauri that would disappear?
In reality, even a supernova leaves a considerable remnant, so at best we
could expect 1/10th of a full pulse.
There is a gravity 'wave' we can detect. As our planet turns upon its axis,
it passes through the lunar gravity and causes the tide to rise and fall,
which is clearly detectable as a sinusoidal wave. Take the moon away, and
this would vanish. Also, a lesser tide is produced by our own sun, and this
is superimposed on the oceans. We have spring and neap tides depending on
the relative positions of the moon and sun with respect to the earth. Take
the sun away and this too would vanish, but so would we.
The highest tides we know of are in the Bay of Fundy,
"Every 12 hours 25 minutes 100 billion tonnes of water surges out of the NE
Atlantic and slams into a 70 mile wide funnel between Nova Scotia and New
Brunswick. When it reaches this point, 100 miles in, the channel narrows and
divides into two narrow prongs. The bottom one, Minas Channel, is only 10-15
miles wide. All that lunar-driven water has nowhere to go but up. Near
Wolfville in the Minas Channel high tide is about 16 metres above low tide,
the highest on earth." - http://www.tvnature.com/obh/bald-eagle.htm

and that channel tells we could artificially duplicate our own miniature Bay
of Fundy anywhere in the world, passing the water through a narrow tube and
measure it's velocity and volume as the Earth turns with considerable
precision, since we can measure the height of the water in the tube with
great precision using the wavelength of light.
So... how much does the tide rise and fall as a result of Proxima Centauri
being nearby? I'll leave you to do the trigonometry of Earth, Moon, Sun and
Proxima Centauri and the numbers, you'll have more luck detecting the pull
of Jupiter, Mars, Venus and Saturn, and you'll be looking for the effect of
something far less than the miniscule tug of Phobos or Deimos.
I'm going to say LIGO was doomed to failure at the outset, and it will not
detect a darned thing. That is not the same as saying there is nothing to
detect, just that the effect is so miniscule it cannot be measured. The
inverse square law totally precludes any possiblity of detecting anything
with a source of gravity as far away as Proxima Centauri.

So the answer to your question is... zilch.
Androcles.



Is LIGO still having technical problems or what?
| It is now 2004, after all. Other detection labs are being built around
| the world. Are these labs going to have any better luck?
|
| Also, what are people's opinions about gravity waves? Is it possible
| that these are a scientific dead end like the decay of the proton turned
| out to be? If gravity waves are never detected, what are the
| implications for the general theory of relativity?
|
|
|


  #6  
Old August 16th 04, 08:58 AM
Eric Gisse
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Posts: n/a
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On Mon, 16 Aug 2004 07:05:56 GMT, "Androcles"
wrote:


"dkomo" wrote in message
news | I found an old PBS documentary on VHS from 1991 called _The Astronomers_
| at the local public library. One of the programs in the series was
| "Waves of the Future" about gravitational waves. In the program Kip
| Thorne was shown making a bet with one of his collaborators on gravity
| wave theory that these waves would positively be detected by 2000.
|
| I found this both humorous and a touch sad. The program described some
| of the early planning for LIGO (Laser Interferometer Gravitational Wave
| Observatory). Curious, I went to the LIGO web site to see what was
| going on. I found nothing of substance there -- just a lot of slick PR.
|
| So my question is, what are the prospects that gravity waves will be
| detected anytime soon?

Why not consider the biggest "wave" or pulse in our galaxy imaginable?
That would correspond to ALL the mass of a star entirely disappearing, as
could just conceivably happen if the star were converted to entirely to
energy
in one enormous supernova. We'd see a brilliant flash of EM radiation,
brighter than daylight, but the entire gravity would be gone.


[snip]

No, EM radiation gravitates too.

Do you know what the stress-energy tensor is? How about the
theoretical construct called a geon?
  #7  
Old August 16th 04, 11:16 AM
Igor
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"Australopithecus Afarensis" wrote in message news:[email protected]
Most likely LIGO will detect gravitational waves.
See: http://www.ligo.caltech.edu/
http:/www.edu-observatory.org/eo/cosmology.html


It is very interesting how institutions would spend millions of dollars
trying to detect something that has not been thoroughly understood.



The theory of gravitational radiation has been well established for
several decades. Details can usually be found in any GR textbook.
Weinberg's book is probably the best in this regard.


As I
read in Scientific American a year or two ago, LIGO was chosen to be built
in places where noise generated by human activities are at near maximum.
This means LIGO's detection of gravitational waves is subjected to broad and
creative interpretations of data which can easily be explained by something
else.



Why do you think they built two of them in entirely separate
locations?
  #8  
Old August 16th 04, 12:28 PM
Eric Gisse
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On 16 Aug 2004 03:16:43 -0700, (Igor) wrote:

"Australopithecus Afarensis" wrote in message news:[email protected]
Most likely LIGO will detect gravitational waves.
See:
http://www.ligo.caltech.edu/
http:/www.edu-observatory.org/eo/cosmology.html


It is very interesting how institutions would spend millions of dollars
trying to detect something that has not been thoroughly understood.



The theory of gravitational radiation has been well established for
several decades. Details can usually be found in any GR textbook.
Weinberg's book is probably the best in this regard.


As I
read in Scientific American a year or two ago, LIGO was chosen to be built
in places where noise generated by human activities are at near maximum.
This means LIGO's detection of gravitational waves is subjected to broad and
creative interpretations of data which can easily be explained by something
else.


Either you or Scientific American are incorrect, look at the pictures
of the LIGO sites.




Why do you think they built two of them in entirely separate
locations?


Error checking, redundancy, and most importantly, so direction can be
discerned.


  #9  
Old August 16th 04, 02:38 PM
Joseph Lazio
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"d" == dkomo writes:

d I found an old PBS documentary on VHS from 1991 called _The
d Astronomers_ at the local public library. One of the programs in
d the series was "Waves of the Future" about gravitational waves. In
d the program Kip Thorne was shown making a bet with one of his
d collaborators on gravity wave theory that these waves would
d positively be detected by 2000.

d I found this both humorous and a touch sad. The program described
d some of the early planning for LIGO (Laser Interferometer
d Gravitational Wave Observatory). Curious, I went to the LIGO web
d site to see what was going on. I found nothing of substance there
d -- just a lot of slick PR.

You don't define "slick PR" but I see links for "Observational
Results," "Publications," "Research Bulletin Boards," "LIGO Email
Archives," .... At least some of these strike me as more than PR.

Of course, you've hit upon a problem not unique to LIGO. If the Web
site isn't slick and flashy, then it's derided as boring and useless.
If it is slick and flashy, then it's derided as just PR.

d So my question is, what are the prospects that gravity waves will
d be detected anytime soon? Is LIGO still having technical problems
d or what? It is now 2004, after all. Other detection labs are being
d built around the world. Are these labs going to have any better
d luck?

There are a host of other gravitational wave laboratories around the
world. The LIGO site has links to VIRGO, GEO600, TAMA300, ACIGA,
LISA, and IGEC.

As for prospects of detection, that's probably a good question to post
on sci.astro.research. In part that depends upon how kind Nature is
to us. I think if a supernova went off in our part of the Galaxy
tomorrow, LIGO would (or should!) detect it. Right now, of course, it
has not detected anything, so the best that one can do is say that the
density of fill in your favorite gravitational wave source is no
larger than some upper limit.

Some will, of course, decry this as adjusting the theory. However,
getting a handle on potential gravitational wave sources is tough.
For instance, just last year the binary pulsar PSR J0737-3019 was
discovered. It's (probably) less than 2000 light years away from us
and yet had gone undetected for the first 35 years of pulsar
searching. Binary neutron star systems are thought to be a prime
candidate for gravitational wave sources as they spiral together.
Finding a binary neutron star system so close to us immediately
boosted the expected signal strength for gravitational waves from
binary neutron star systems.


d Also, what are people's opinions about gravity waves? Is it
d possible that these are a scientific dead end like the decay of the
d proton turned out to be? If gravity waves are never detected, what
d are the implications for the general theory of relativity?

What about PSR B1913+16? This is a binary neutron star system in
which one of the neutron stars is seen as a pulsar. The orbit is
decaying at a rate exactly consistent with that predicted by general
relativity, if gravitational waves are carrying away energy. In a few
years (if not sooner), the orbital decay of PSR J0737-3019 should also
be measurable. (PSR J0737-3019 is a much tighter system, a 2.4-hr
orbit, as compared to PSR B1913+16, an 8-hr orbit, so the rate of
orbital decay should be higher.)

The decay of the orbit of PSR B1913+16 is only an indirect
measurement, of course, but it is a powerful indicator that
gravitational waves do exist.

--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. |
http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html
  #10  
Old August 16th 04, 03:07 PM
N:dlzc D:aol T:com \(dlzc\)
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Dear Australopithecus Afarensis:

"Australopithecus Afarensis" wrote in message
news:[email protected]
Most likely LIGO will detect gravitational waves.
See: http://www.ligo.caltech.edu/
http:/www.edu-observatory.org/eo/cosmology.html


It is very interesting how institutions would spend millions of dollars
trying to detect something that has not been thoroughly understood.


Like AIDS? Money is spent to find out about things that are not yet known.

That is what research is for. That is what theories are about, predict and
test.

David A. Smith


 




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