‘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 Uncle Al said was that space was not just, well, space, but actually a thing, a framework in which matter and energy exist. As such, it could be affected by matter, bent, distorted, like a tightly stretched sheet can be bent by placing a heavy weight on it.
But he made another astonishing prediction: if two massive objects were to collide, they would send out ripples, or waves, through space. These ripples bend the fabric of space, something like the ripples on a pond surface when a rock is dropped into it. In the case of Einstein, these are called gravitational waves.
When two black holes or superdense neutron stars collide, they can send out these ripples (in reality, the movement of anything generates gravitational waves, but the more sudden the movement and the more massive the objects, the sharper and easier to detect the waves are).
LIGO was built to listen to these waves. When a wave passes through space, it distorts objects within it. For your typical black hole collision way off in the distant Universe, this distortion is smaller than the size of a proton, so you’d never notice it in your daily life. But the engineers at LIGO have been struggling for years to fine tune their machine so that they can actually see this tiny ripple. The setup is a bit complicated, but basically they use a laser beam to measure the distance between two mirrors.
Last November, they finally got the detectors sensitive enough to hear astronomical sources. They can measure a ripple so small that if the mirror move by 10-18 meters — 1/1000th the size of a proton! — they can detect it. This means that if two neutron stars collide, and they’re less than about 40 million light years away (basically, our local galactic neighborhood), they’ll catch it.
This may seem all pretty weird and esoteric, but what this means is that LIGO may be opening a door on the Universe that was previously shut. If it works– and it could make its first astronomical detection any time now — then bigger projects are waiting down the line. More sensitive detectors would increase the range of LIGO, and NASA, along with the European Space Agency, are planning a space-based version called LISA, which would be able to hear two neutron stars colliding anywhere in the Universe.
These are still in the future. In fact, the first real detection from LIGO is sometime in the future, but probably not too much longer. I’ve been reading about LIGO for many years, and it’s exciting to see it’s online and ready to start its life as a research instrument.’
January 9th, 2006 at 8:19 am
Detecting proton-scale changes in the spacetime continuum really does seem a bit wicked and out of this realm… But if it really does work, then it’s a huge achievement and I can only congratulate.
January 9th, 2006 at 8:31 am
How long do these waves stay detectable? What I mean is, can we detect the ripple before it reaches us and observe it on the way, or do we have to wait for it to reach and pass us by to observe it?
January 9th, 2006 at 9:04 am
I would think if it’s a ripple like a wave, we would detect it only as it is passing by. You can’t see it coming, because the only way to see it is to actually see it. Er, if you understand.
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.
January 9th, 2006 at 10:37 am
David Letterman had a joke a few years ago: “Scientists recently discovered that stars are not massive objects trillions of miles away, but instead are extremely tiny objects only a few feet away.” OK, so if this proton bounces a little, how will we know it’s from two neutron stars halfway across the galaxy, or from a baseball being hit on Earth? Also, as big as the universe is, aren’t there probably a LOT of things crashing together? Isn’t this going to mean a lot of noise in the detector? You can’t shield it, can you? You’d need a whole planet to shield it, wouldn’t you? So maybe you’re going to need hundreds of them around Earth, to see if Earth is casting a gravity-shadow. Even then, you’ve got the baseball question. As sensitive as this thing is, if the scientists, in their joy at getting a signal, toasted each other with cocktail glasses, the glasses clicking together would drive it off scale. Are people working in the lab going to have to talk in hushed tones? Wear tennis shoes?
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
January 9th, 2006 at 10:48 am
Why mention Britney Spears? She’s on my mind a lot.
Ick. that can cause brain cancer.
January 9th, 2006 at 11:05 am
the Laser Interferometer Gravitational Wave Observatory
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
January 9th, 2006 at 11:15 am
That’s not listening to the universe, it’s feeling the universe.
“Why mention Britney Spears? She’s on my mind a lot.”
Yuck!
January 9th, 2006 at 11:46 am
Agreed on Spears – yuck!
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?
January 9th, 2006 at 11:53 am
If the gravity wave is the distortion of space itself, why isn’t light also affected by the ripple? In other words, if space is “compressed” in that thousandth of a proton diameter, wouldn’t light change its speed to compensate as it passed through the ripple? I don’t understand how distance can be changed because of the ripple but light still travels at the same speed through the ripple.
January 9th, 2006 at 12:14 pm
I’m curious what the wavelength of the ripple is and as blizno ask about the speed of light travelling through the ripple. If the wavelength is incredibly long it would take a significant period for the ripple to pass. Lets say the wavelength is on the order of a light-year – then the ripple would take a year to go from normal to crest to normal to the opposite crest and back to normal.
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
January 9th, 2006 at 12:40 pm
Keep in mind that LIGO is an interferometer. While I’m not familiar with LIGO especially, I do know that the prime mechanism for the operation of an interferometer is that it uses two beams of light. One is a reference for the other.
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.
January 9th, 2006 at 12:47 pm
Why not a baseball?
That’s really a very good question, and it has a lot to do with why there are two LIGO facilities and why each one is set up in an “L” shape. Gravity waves from a great distance should be seen by both of them, whereas a local effect would only be seen at one facility. A detection at both facilities that has the right characteristics for a gravity wave is not that easy to fake.
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
January 9th, 2006 at 1:27 pm
Further to what HvP and DK said, the LIGO systems will work by comparing compression of one axis on the passage of the wave while the perpendicular beam remains the same and will indeed show as an interferance pattern. There’s a rumour of a space based system that will give greater accuracy using much longer distances but the technical problems in that one are huge. I think the project is called LISA.
If I remember my degree correctly the gravitational waves are supposed to not fade with distance like most waves do (eg the one over distance squared rule for light), but they should travel at the speed of light, or, depending on which damn weird multidimensional theory takes your fancy, faster than the speed of light in a non-energised vacuum (I’m a fan of 11 dim strings myself).
By the way, did you see that the European interferometer GEO600 is in a field in Saxony? We need more investment in science here in Europe.
Keep up the good astronomy Phil!
January 9th, 2006 at 1:44 pm
i really should read the articles a bit more fully shouldn’t I? Phil covered the LISA project so I apologise for being a muppet.
January 9th, 2006 at 3:04 pm
Regarding the problem of there being too many sources of graviational waves out there…think about how many sources of light waves are out there, too. We’re not overwhelmed with them because we can tell from which direction in space they are coming and can therefor identify individual objects/events. I assume we could also tell from which direction in space the gravitational waves were coming, and be able to identify the object or event responsible.
January 9th, 2006 at 6:35 pm
OK, I’l admit this is definitely an endeavor with a “cool factor” which educators must tend to as they attempt to introduce elements of contemporary science in the classroom.
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?!
January 9th, 2006 at 9:09 pm
LISA is wonderful, but it will not be able to detect neutron star inspiral anywhere in the universe. For one thing it will operate at too low a frequency.
LISA can see massive enough black holes coalescing anywhere in the universe, and neutron star binaries orbiting well before coalescence anywhere in the Milky Way.
January 10th, 2006 at 6:17 am
I believe the expanded SETI site has a program to detect these waves.
January 10th, 2006 at 10:22 am
Bill 34543 Said:
>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
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?
January 10th, 2006 at 6:32 pm
Irishman said:
>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.>
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.
January 11th, 2006 at 8:12 am
Maybe, but that’s not the limit of the use of the metaphor. These same examples are used to convey the information to anyone interested in the topic, be it someone trying to get a career in astronomy and cosmology, or just some layperson who has a hobbyist interest in knowing about the universe. So I don’t think that attitude is particularly helpful. Okay, maybe the answer is “you’re just not suited to understanding astronomy, pick a new hobby,” but somehow that’s dissatisfying to me. Anyone interested in learning should be taught to the best of our abilities to teach them. Sometimes that’s limited by their ability to learn, and sometimes their willingness to learn. But if we don’t make the effort, then it is our fault.
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.
January 11th, 2006 at 8:41 am
Bill 34543 Said:
>OK, so if this proton bounces a little, how will we know it’s from two neutron stars halfway across the galaxy, or from a baseball being hit on Earth? Also, as big as the universe is, aren’t there probably a LOT of things crashing together? Isn’t this going to mean a lot of noise in the detector?
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.
———-
January 11th, 2006 at 8:53 am
And here is a graphic representation showing an object warping space-time. This example is a 3-D representation and does not use external gravity.
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/
January 11th, 2006 at 6:08 pm
Irishman said:
>So I don’t think that attitude is particularly helpful. Okay, maybe the answer is “you’re just not suited to understanding astronomy, pick a new hobby,†but somehow that’s dissatisfying to me. Anyone interested in learning should be taught to the best of our abilities to teach them. Sometimes that’s limited by their ability to learn, and sometimes their willingness to learn. But if we don’t make the effort, then it is our fault.
January 13th, 2006 at 10:44 am
From what I know it is strictly speaking incorrect to say that space is warped by mass. Instead one should say that gravitational fields the spatiotemporal structure. After all, as Einstein himself remarked, if you remove all bodies and radiation from the universe nothing at all remains. This is a fundamental change vis-a-vis the Newtonian perspective where space and time *are* “stuffs”.