http://sciencebulletins.amnh.org/astro/f/gravity.20041101/essays/44_2.php

You can see a close-up of the central region here.
http://sciencebulletins.amnh.org/astro/f/gravity.20041101/

Lots of info at the link the BA provided in the article. From here:
http://sciencebulletins.amnh.org/astro/f/gravity.20041101/essays/45_2.php
—–
No Noise, Please!
If only it were so easy. Many, many types of competing vibrations, or noise, can jostle the test masses enough to mask the effect of a true gravitational wave.

Loggers felling trees nearby cause noise. The crash of ocean waves produce noise. “Even the motion of the atoms inside the mirrors are making the mirrors move,” says Gabriela González, a physicist at nearby Louisiana State University.

Scientists have taken painstaking precautions to reduce the impact of noise on LIGO. The mirrors are suspended on a single thin metal wire to reduce the effects of forces other than gravity. To dampen competing vibrations, investigators constantly adjust the mirrors with the ultraprecise equivalent of a car suspension system.

Still, how do you detect a gravitational wave and not a rabbit jumping nearby? “That’s the $300 million question,” laughs González. One way is by checking if a suspected wave coincided with a disturbance registered by other instruments on site, which look for changes in ground motion, magnetic field, power line voltage, and other aspects. Another way, González explains, is by double-checking results with LIGO’s twin—a complete duplicate facility constructed in a barren scrub desert in Hanford, Washington. At 3,030 km away, it’s distant enough that seismic and other disturbances won’t affect both observatories simultaneously.
—–

So the scientists are definitely thinking of the noise problem and doing everything they can to eliminate mechanical vibrations so that the gravitational wave distortions of space-time can be separated out.

And then here is a page that discusses what causes gravitational waves and why the effects we can detect come from supermassive space objects far away instead of nearby tiny objects, like people.
http://sciencebulletins.amnh.org/astro/f/gravity.20041101/essays/46_1.php
———-
Why do all those massive, exploding outer-space events get all the fun? Why is it that only they can create a gravitational wave? The truth is, anything with an accelerating mass has a gravitational effect. Detecting it? Well, that’s another matter entirely.
…
You: “Every time you accelerate—say by jumping up and down—you’re generating gravitational waves,” says Rainer Weiss, Professor Emeritus of Physics at MIT. “There’s no doubt of it.” But just standing there won’t cut the mustard. To make a wave, your mass has to both move (have velocity) and have acceleration (change the rate of motion, direction, or both).

Still, don’t get your hopes up. No matter how fast you jump, sprint, or cartwheel, the resulting warp your waves make on space is so weak that it’s utterly unmeasurable—perhaps 100,000,000,000,000,000,000,000 times less so than the warp made by massive exploding space objects. And LIGO has a tough enough time measuring those.

Spinning Aircraft Carrier: Only enormous amounts of motion at enormous speeds from enormous masses can produce a ripple that LIGO could detect. “To rival here on Earth the strength of gravitational waves from a supernova in the center of our galaxy,” suggests Mike Zucker, the head of LIGO’s Livingston facility, “you’d need to take an aircraft carrier and spin it, end over end, a thousand times a second.” Not very likely.
———-

I also think that sometimes the ones using the metaphor don’t fully grasp the intent of the metaphor, and misuse it. That doesn’t help anyone, either. Part of the problem is one of memory. We hear this brilliant metaphor that helps us grasp a concept, but we don’t commit the full details of the metaphor to memory, only the concept. Later we try to share that metaphor with someone else because it was so meaningful to us, but our lack of grasping the fullness of the metaphor leads us to miss some of the details and thus misdirect the person we are trying to help.

I don’t know what the fix is, other than trying to pay more attention ourselves when we hear good metaphors to the actual context and intent, and trying to remember those elements along with the concept. Also, helping correct others when we hear them misunderstand or misuse a metaphor.

Perhaps here is a method to weed out folks that should take a different career path. Maybe people that can’t grasp the concept(s) will be better served and serve in fields and areas in which such concepts are not relevant. I remember reading somewhere that intelligence is comprised of maybe a hundred different abilities, and we all have varying combinations and degrees of them.
I had the same problem trying to explain to some people about the “Flatlanders”. Some readers here may have heard of ‘em. A 2D world containing 2D people that have no experience of 3D reality. It’s a tool to show how we, in our 3D universe, have trouble visualizing other dimensions that may be around us. A fellow might try to argue with the Flatlander’s concept, saying something to the effect of “that’s impossible because they couldn’t have a circulatory system because they would be cut to pieces”. Please, ignore details irrelevant to the concept.

You raise a difficult issue, something inherent to using metaphors and models to represent effects that aren’t directly observable. Bending of space time is such a difficult thing for us to conceptualize, thus the need for a model. The problem is that the model or metaphor is constrained by the rules of our everyday life, but it is those rules that make conceptualizing the effect so difficult in the first place. Those rules define our common experience. They are “how the world works” at the level we experience it. So when we look at something beyond everyday experience, such as gravity bending space-time, or the expanding universe, we’re dealing with effects that doesn’t conform to everyday rules that we can easily see. Metaphors and models are attempts to explain it, conceptualize it, put it in a context that we can conceptualize. Of course, that’s the inherent flaw, that the model or metaphor is inherently misleading and therefore, maybe our understanding is flawed. Certainly, if you scrutinize the metaphor too closely you can find flaws. The trick is to understand what you’re trying to get out of the model and ignore the details that detract when they don’t conflict with the elements you’re trying to grasp.

That is what makes the bending sheet metaphor and the expanding balloon metaphor and the expanding raisin cake metaphor so difficult to use. People who don’t accept the premise will argue the periphery of the metaphor, the details that are irrelevant to the concept that is the intent of the model. That’s also why it’s hard to teach with those models, because some people can’t grasp the concept you’re trying to convey out of the extraneous details.

What the metaphor is attempting to explain is the warping of the fabric caused by mass. More mass causes a larger depression. The depression affects the path of objects rolling in a straight line nearby. Yes, this model is using external gravity to provide a downward force against a 2-D plane of fabric of “space-time”, bending into a 3rd dimension. The reality is a 3-D space-time, and the warping is not caused by an external force, but by the object itself compressing space-time around it. We might think of it as a 3-D space being curved in a 4th dimension. But humans can’t very well see 4 dimensions, so we have to simplify and then extrapolate. The problem is I can’t come up with any other example that demonstrates a curvature caused by a presence, at least nothing that can be visualized any easier. And nobody else seems to be able to, either.

Here’s a thought. Think of a large magnet in the center of a table. Now roll a small iron sphere across the table near the magnet. In this example, gravity is only constraining the sphere to move in the plane of the table, not affecting the pull in any way. Now the magnet is having an effect on the sphere without touching the sphere. That is the magnetic field lines. The sphere gets effected because as it passes through the field lines, the iron molecules try to align, and thus wiggle the field lines. But what are magnetic field lines? Can you see them? Does this example help you visualize the mass making the change to the surroundings? Or is this such an imaginary game itself that it needs its own metaphor to explain it?

Our school participates in the Einstein@home project which uses “computer’s idle time to search for spinning neutron stars…using data from the LIGO and GEO gravitational wave detectors…” School computers as well as student personal computers contribute CPU time to the project.

The quote is from http://einstein.phys.uwm.edu where there’s also linked a nice pdf of Bruce Allen’s talk at the the 10th annual Gravitational Wave Data Analysis Workshop:

http://www.phys.utb.edu/GWDAW10/other/files/BA0001_BruceAllen.pdf

That is, what did the universe look like before x-rays “existed” compared with now?

If they pull this off (gravity wave detection), what will the universe “look like” if we could “see” gravity waves?!

As for other astronomical sources, it turns out that you can calculate how big a gravity wave affect would be for lots of possibilities (2 asteroids colliding 0.5 AU away, binary stars a few light years way, etc.). It turns out that the biggest signals are likely to come from very rare objects like colliding black holes, even though the nearest such event is probably going to be in a distant galaxy many millions of light years away.

DK

I don’t know if this is how LIGO works, but imagine this scenario. If you were to split a beam of light with a diagonal mirror and create two identical copies of the laser at right angles to each other.

Then a gravity wave passes through. One beam will be closer to inline with the axis of the wave and will be affected more strongly by the warping effect. The other beam will be closer to a right angle to the axis of the gravity wave and will be affected less strongly by the warping effect.

By recombinging the laser beams at the other end you will get an interference pattern which gives you information about the magnitude and direction of the passing gravity wave.

As series of lasers at various angles would give you even more axis with which to fine tune your detection ability.

And Bill… I imagine that if our instruments were sensitive enough to detect the gravity waves of a baseball then we would simply have conducted the measurements in a lab on Earth, make the observation, and declare successful observation of gravity waves right then and there. Obviously, our instruments aren’t sensitive enough to do that. We can’t even get a reading on our Moon as it orbits our own planet, I think it safe to say that movements on Earth aren’t likely to interfere. If anything, heating of the components will be a much more serious consideration. I think you underestimate the incredibly powerful nature of these cosmic collisions.

If the speed of light decreases in the ripple as it does passing through water, air, or transparent matter then the ripple would still be invisible.

So the question is, what does theory say the expected wave length is and how does it respond to compressed space?

jbs

The question about multiple possible sources of gravitational waves and therefore huge problems identifying them is a good one and makes me wonder too, whether it won’t be needed to add hellova these devices all around the Solar system to make the results at least valid and a bit useful?

“Why mention Britney Spears? She’s on my mind a lot.”
Yuck!

Just read this from Bad Astronomy:I just attended a press conference for LIGO, the Laser Interferometer Gravitational Wave Observatory. This is a new way of observing the Universe, and it depends on a very odd prediction by Einstein. Basically, what

Ick. that can cause brain cancer.

Cleve Backster set up a polygraph with a plant years ago and said it detected human emotions. But he said it was sensitive at a great distance. Within a great distance there are a lot of people having emotions. I replicated his experiment, and it did seem to respond to strong emotions of people in the room. One was during an evening watching a talk show/comic, and laughing hard at one of his jokes, possibly David Letterman about the stars. But seriously, isn’t this a no-brainer? Noise, distance, selectivity etc. I don’t get it.

Also a comment on the stretched sheet example. It always comes with gravity. A ball rolls along the sheet and when it comes to the depression, it rolls in. Duh! GRAVITY made it roll in. How about an example of space being warped by mass, that does NOT involved gravity in the explanation? Putting gravity into the explanation is circular. Or so it seems to me

Thanks for the chance to express my views. This blog is cool. I’m an amateur amateur astronomer and very interested in these topics. I recently read Karen Fox’s book on black holes, and talked with her at a bookstore. Brian Greene was on Stephen Colbert’s show a few weeks ago. What a neat guy. Talked about strings. Karen Fox talks about strings and branes (membranes) (in the 11th dimension). Branes “splat” together, as she puts it. The Big Splat. She’s a neat person too. Also Phil Plait is a neat guy. We’ve corresponded before. Maybe on my question about why the Big Bang worked, why wasn’t it a black hole, why didn’t it just sit there, annoyed like Alexander, “no more worlds to conquer”? And inflation, well, that’s very fishy. Temporary suspension of the faster than light limit. No way. OK that’s enough. Don’t want to get off topic.

But the topic is listening to the universe. WHAT is it we are listening to, with these esoteric instruments? A few degrees above absolute zero, we get readings. Of WHAT? The Big Splat inflating? Spare me! Maybe it’s sunlight splatting off of space dust! Cosmic rays! Britney Spears! WHAT is being detected?!

Now, cosmic rays, there’s something you can quantify and vectorize. There are more at different altitudes, coming from a certain direction. Why mention Britney Spears? She’s on my mind a lot.

Bill34543@yahoo.com

We detect the waves by the wiggle of the mirrors. We can’t see them coming because the only way we see them is by the effect they cause, the wiggle of the mirrors. But that mirror wiggle is pretty definitive.