A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Astronomy and Astrophysics » Astronomy Misc
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

What's up with gravity wave detection?



 
 
Thread Tools Display Modes
  #11  
Old August 16th 04, 04:55 PM
Dave Houseman
external usenet poster
 
Posts: n/a
Default

Sure, the planets would have a big gravity wave signal, in the same
way that jupiter appears brighter than P Centauri in the night sky.
But surely LIGO can tell what direction a wave is coming from - that's
the whole point, isn't it?

Dave

"Androcles" wrote in message ...
....snip...
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.

  #12  
Old August 16th 04, 05:21 PM
The Last Danish Pastry
external usenet poster
 
Posts: n/a
Default

"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?

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?


For the LIGO weekly report, see:
http://www.ligo.caltech.edu/~weekly/weekly.htm

For a "LIGO-in_space", see:
http://lisa.nasa.gov/

For the Louisiana LIGO as seen from space, see:
http://www.terraserver-usa.com/image...=1056&z=15&w=1

--
Clive Tooth
http://www.clivetooth.dk


  #13  
Old August 16th 04, 05:52 PM
Androcles
external usenet poster
 
Posts: n/a
Default


"Dave Houseman" wrote in message
om...
| Sure, the planets would have a big gravity wave signal, in the same
| way that jupiter appears brighter than P Centauri in the night sky.

No comparison whatosever. Jupiter is reflecting sunlight. You cannot observe
any planets in orbit about Proxima Centauri. You are comparing soldier ants
to eleph ants.


| But surely LIGO can tell what direction a wave is coming from - that's
| the whole point, isn't it?
| Dave

Can it? I don't think so.
As dkomo said, all he's seen is PR hype, not results.

Androcles.



| "Androcles" wrote in message
...
| ...snip...
| 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.
|


  #14  
Old August 16th 04, 06:55 PM
Eric Flesch
external usenet poster
 
Posts: n/a
Default

On Sun, 15 Aug 2004 23:58:58 -0800, Eric Gisse
wrote:
No, EM radiation gravitates too.


No, that's just an error in the practice of current models -- which
themselves don't require such gravitation, which has never been
observed. Note this is a separate issue from travelling along null
geodesics.

Do you know what the stress-energy tensor is? How about the
theoretical construct called a geon?


Not relevant to observation.

  #15  
Old August 16th 04, 07:37 PM
Mike
external usenet poster
 
Posts: n/a
Default

"Australopithecus Afarensis" wrote in message news:zQXTc.100010$sh.86278@fed1read06...
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.


They will detect nothing but thermal noise and geo vibrations. Signal
to noise ratio will be too low to make anything out of that. Any
signal processing applied will open the room to subjectivity.

Another one bites the dust. Gravity will always stay a mystery.

Mike
  #16  
Old August 16th 04, 10:00 PM
external usenet poster
 
Posts: n/a
Default

In sci.astro Eric Flesch wrote:
On Sun, 15 Aug 2004 23:58:58 -0800, Eric Gisse
wrote:
No, EM radiation gravitates too.


No, that's just an error in the practice of current models -- which
themselves don't require such gravitation


Certainly they do. In general relativity, the right-hand side of the
field equations must include the stress-energy tensor for all matter.
Otherwise, the vanishing covariant divergence of the left-hand side is
inconsistent.

More generally, electromagnetic radiation observably responds to
gravitational fields. If it does not itself gravitate, you get an
immediate violation of basic Newtonian physics. Just trap a bunch
of radiation in a mirrored box and glue it next to a mass. The
radiation will be attracted toward the mass, but if the radiation
doesn't gravitate, the mass won't have an equal attraction toward
the radiation. So the whole system will self-accelerate.

which has never been observed.


That's true. It *has* been observed that electrostatic energy,
specifically the electrostatic binding energy of nuclei, gravitates,
but there's been no such observation for electromagnetic radiation.
(Gravity is weak, and it's hard to trap enough radiation in one place.)

Steve Carlip
  #17  
Old August 16th 04, 11:18 PM
vonroach
external usenet poster
 
Posts: n/a
Default

On Mon, 16 Aug 2004 07:07:28 -0700, "N:dlzc D:aol T:com \(dlzc\)" N:
dlzc1 D:cox wrote:

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


Or which are well known but denied by an advocacy group?
  #18  
Old August 16th 04, 11:19 PM
vonroach
external usenet poster
 
Posts: n/a
Default

On 16 Aug 2004 11:37:51 -0700, (Mike) wrote:

They will detect nothing but thermal noise and geo vibrations.


Then maybe they can be applied to earthquakes or volcanic eruptions.
  #19  
Old August 17th 04, 05:50 AM
Eric Flesch
external usenet poster
 
Posts: n/a
Default

On Mon, 16 Aug 2004 21:00:24 +0000 (UTC),
wrote:
In sci.astro Eric Flesch wrote:
On Sun, 15 Aug 2004 23:58:58 -0800, Eric Gisse wrote:
No, EM radiation gravitates too.


No, that's just an error in the practice of current models -- which
themselves don't require such gravitation


Certainly they do. In general relativity, the right-hand side of the
field equations must include the stress-energy tensor for all matter.
Otherwise, the vanishing covariant divergence of the left-hand side is
inconsistent.


You're missing the point. The stress-energy tensor is a classical
description which assumes continuous motion. But QED shows that the
photon path is the summation of all possible paths (diffraction
gratings are an application of this) and the delayed-choice experiment
shows explicitly that the travelling photon cannot be pinpointed to
any particular location in its presumed path(s). The point is that
the "travelling photon" can be modelled only by a quantum description,
and the classical stress-energy tensor does not apply.

More generally, electromagnetic radiation observably responds to
gravitational fields. If it does not itself gravitate, you get an
immediate violation of basic Newtonian physics.


No, the equivalence principle shows that relative acceleration is
achieved by just one of the two bodies accelerating -- they do not
both need to. Travel on the null geodesic is the default -- a
non-gravitating body would not choose a different path.

Just trap a bunch
of radiation in a mirrored box and glue it next to a mass. The
radiation will be attracted toward the mass


No it won't be. The mass might have some miniscule effect on the
local geometry, that is all.

which has never been observed.


That's true. It *has* been observed that electrostatic energy,
specifically the electrostatic binding energy of nuclei, gravitates,
but there's been no such observation for electromagnetic radiation.
(Gravity is weak, and it's hard to trap enough radiation in one place.)


Let's keep in firm view that observation is far more real than theory,
especially theory which is mis-applied.

Eric

  #20  
Old August 17th 04, 09:49 PM
Joseph Lazio
external usenet poster
 
Posts: n/a
Default

"A" == Androcles writes:

A "Dave Houseman" wrote in message
A om...
Sure, the planets would have a big gravity wave signal, in the same
way that jupiter appears brighter than P Centauri in the night sky.


A No comparison whatosever. Jupiter is reflecting sunlight. You
A cannot observe any planets in orbit about Proxima Centauri. You are
A comparing soldier ants to eleph ants.

Actually, the planets do not produce a gravitational wave signature
(or if they do, it is incredibly small).

But surely LIGO can tell what direction a wave is coming from -
that's the whole point, isn't it? Dave


A Can it? I don't think so. As dkomo said, all he's seen is PR hype,
A not results.

In principle it can, crudely. There are two of them. So by timing
when the signal gets to one versus when it gets to the other, one gets
a rough sense of the direction from which the signal came.

--
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
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Beyond Linear Cosmology and Hypnotic Theology Yoda Misc 0 June 30th 04 07:33 PM
Empirically Refuted Superluminal Velocities. EL Astronomy Misc 22 October 31st 03 05:07 PM
Oceanographers Catch First Wave Of Gravity Mission's Success Ron Baalke Science 13 August 7th 03 06:24 AM


All times are GMT +1. The time now is 02:17 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.