Renewed Gravity Research Could Soon Yield Results

t482 writes "Dr. Michelle Thaller has a nice article describing the current thoughts on gravity. Why is it so weak? Detecting gravity waves has turned into a bit of a cottage industry. "We are close," says MIT physicist Rainer Weiss, a pioneer in gravity wave research for more than 30 years. "I think sometime in the next two or three years we will see something.""

Comments

30 years and still no results?

[Zemrec]

Damn...that's gotta be depressing.

(at the water cooler, 1973)
"Hi, Bob, seen any gravity waves lately?"
"Nope, but we're real close now."

(in an instant message, 2003)
"Hi, Bob, seen any gravity waves lately?"
"Nope, but we're real close now."

You gotta wonder what gets these people out of bed day in and day out.

Re:30 years and still no results?

[BobGarcia]

The problem is that you can get too close. Get closer and you have to deal with other forces: weak, strong, midic(h)lorian, and IWOMM ("It works on my machine" -- the most mysterious and pissoffingous force of them all.)

Re:30 years and still no results?

[Jahf]

There should be a "+.5 Almost Funny" rating :)

Re:30 years and still no results?

[Mr. McGibby]

Complaining about teaching undergraduate classes.

Re:Heavy!

[Anonymous Coward]

Gravity waves are bread and butter on Slashdot

Maligning Einstein??

[WTFmonkey]

Right, because it was Einstein's Theory of General Relativity, published in 1916, that proposed the existence of gravity waves -- ripples in the fabric of space-time that LIGO scientists hope to measure for the first time.

Wrong, because even the greatest genius of the 20th century never dreamed that humans would build something sensitive enough to actually detect a passing gravity wave.

Did Einstein ever actually say "We can never build a machine to detect these?" If not, then that's like saying that Plato was wrong because he never wrote about moon colonies. It just doesn't make sense. If he actually said, "We can never detect these things" then he's wrong. Otherwise he just didn't get around to thinking about it. Bad journalism.

Re:Maligning Einstein??

[TRACK-YOUR-POSITION]

Heh, do you know the kind of things Plato said? Plato, like perhaps all great philosophers, is judged to be great by the originality of his ideas and arguments rather than how well such arguments correspond to either today's thinking or reality. Unless you think that everything is made of earth, air, fire, and water, or that slavery and fascism are good.

Not that I'm arguing with the point your making, (I might not go so far as Bad journalism, though), but Plato struct me as a really humorous example, since he spent an awful lot of time saying things we now judge to be false.

And another thing

[WTFmonkey]

At those levels, scientists say they should be able to detect gravitational radiation from the first moments of the universe -- relic signals from the first second of the Big Bang.

I must be physics challenged. If there were waves created by the big bang, wouldn't they have moved away from the center much faster than the stuff that makes up our planet? Like 2 (3-d) ripples in a pond, one moving faster than the other? Or is this one of those "The universe is infinite and everything is moving away from everything else so there was no 'central location of the universe' because at the time of big bang the universe was only as big as the stuff was expanding" things. But.. but... if it's expanding, how is it infinite? If it's infinite, how is it expanding?

I wish I could wrap my mind around these things, because it's fascinating as hell, I just can't quite fit it.

Re:And another thing

[Yokaze]

Space is finite, but has not borders and is expanding.

The best likening I've heard of is the surface (2D) of a baloon.

The surface of the baloon has no borders, you can go around it like you want. Still, its space is finite. And if you pump it up, the space is expanding.

The mistake most people make in imagining the Big Bang is taking it literally. An explosion of material in space.
The point is there was no space in which the explosion happened and neither was material. Space happened. Material came even later.

Re:And another thing

[rwaldin]

Well maybe, or maybe not. From Parallel Universes

Space could be finite if it has a convex curvature or an unusual topology (that is, interconnectedness). A spherical, doughnut-shaped or pretzel-shaped universe would have a limited volume and no edges. The cosmic microwave background radiation allows sensitive tests of such scenarios [see "Is Space Finite?" by Jean-Pierre Luminet, Glenn D. Starkman and Jeffrey R. Weeks; Scientific American, April 1999]. So far, however, the evidence is against them. Infinite models fit the data, and strong limits have been placed on the alternatives.

Personally, I prefer to think that this universe may not be infinite, but an infinite number of the infinitely many parallel universes are!

Re:And another thing

[edgar_is_good]

The point is that the big bang happened everywhere at once - at least insofar as we're causally aware right now. The entire universe was incredibly hot, and then the space itself expands, so the universe becomes dilute, cools, galaxies form, etc. There was a recent result - the WMAP experiment - which sees the relic radiation from the big bang. But the light we see was emitted from 14 billion light years aware (14 billion years being the age of the universe) and is just getting here now. In another billion years, we'll still be seeing this radiation, but it will be sourced 15 billion light years away, but just getting here then. The fact that this radiation is isotropic to one part in 100000 is the best evidence that the _whole_ universe was hot and expanded. The gravity waves travel just like the light - we'll see the waves produced 14 billion light years away now. But the big bang wasn't a point in space, in which case you would have been right. This is a common misinterpretation (even among people who ought to know better)

Re:And another thing

[Nyphur]

"Space in finite, but has not borders and is expanding."

Think in terms of energy levels. If we take a perfect vacuum, a space in which nothing exists, there is no energy. Of course, even space isn't a perfect vacuum. Such a vacuum would be expected to be found somehwere outside the measurable distance of the universe. "Beyond the edge," as it were. Thinking in terms of energy levels, we can percieve matter to be the highest energy level. Matter being thought of as energy condensed and slowed to a stable coactive form is not a new idea, but it has been one of the most important principals of Quantum Phyiscs on such issues.
Taking this as true, matter cannot exist as an energy level without energy levels bneath it being full, otherwise the matter would drop down to the lower energy level and release a tremendous ammount of energy in the process. This again, is not that new of a way of thinking. "Zero point" energy, as it is called, is the lowest order of energy. It has been proposed that if we could tap into zero point energy, we could effectively get limitless energy for free, zero point energy being essentially everywhere since if there is a place for anything to exist, that place must have energy levels higher than the zero point and thus the zero point energy levels must be there. Even in a total vacuum, zero point energy exists. However, the potential of "mining" zero point energy is not in the energy you get yourself from removing it. Indeed, it would probably require a tremendous input of power in order to remove zero point energy from an area of space. The theoretical potential which exists for mning zero point energy is the fact that once it is removed, all energy levels above it must drop to fill in the space. Thus, if you took some matter and in the space in which the matter existed, mined out the zero point energy, the matter would convert into a lower energy form than matter, having no energy level to be based on as matter itself. This would, in essence, convert the matter to energy, releasing a tremendous ammount of energy. It is said that the resulting explosion from removing a small potion of zero point energy from matter filled space would make the largest nuke look like a firecracker.

This all said, we have to consider what exists at the "edge" of the universe. With amtter existing based on higher energy levels in places and no matter existing in others, it is reasonable to assume that the energy levels are concentrated towards some kind of central point and thus fade, the further you get from that point. The edge of the universe would then be an area which has few higher energy levels, eventually fading out into a point of having not even zero point energy. This point of not having zero point energy would result in a lack of space existing in the sense that we know it, making a final edge to the expanse of the universe. However, any matter approaching this edge would be converted to energy slowly as it passes the point where there is no energy level below matter in order that the amtter can remain matter. This means we can't actually send matter to the edge of the universe since it is of too high an energy order.
The energy levels diffusing and expanding from the central point of highest energy level (the big bang point, if you like) to lower points of lower energy levels, which is essentially, the universe expanding.

It's all just a theory of mine though.. pieced together from this and that. It works right in my head and I'll probably change it some time if I find out more on the subject.

My curious cat

[NanoGator]

My cat performs gravitic experiments all the time. He's even discovered anti-gravity. He pushes my cell phone off the desk, and within minutes it levitates back up to the desk.

Gravity waves != gravitational waves

[ControlFreal]

Allright, IAAP (I Am A Psysicist), and I think it's good two debunk a common misconception here:

Gravity waves are not the same as gravitational waves

Gravity waves are matter density waves in fluidi (fluids or gases) caused by the interaction of two forces: bouyancy and gravity. Here, bouyancy is the upward-driving force, and gravity is the downward-driving force. The essence is that these waves require a medium to propagate (e.g. air).

Gravity waves can be found in the atmosphere, e.g. clouds which form in regular bands of cloud and clear sky, where the gravity waves carry momentum and energy from the troposphere to the middle and upper atmosphere Gravity waves can also be found on the surface of fuilds: think of the waves behind a boat. A good primer on gravity waves can be found here

Gravitational waves are a whole different ballgame! These waves have got nothing to do with matter densities as they don't require a medium to progagate: it is not matter that moves, and in that respect gravitational waves are like light (which, contrary to beliefs held at the beginnning of the century, don't require a medium such as "ether"). Gravitational waves are wacves in the spacetime-metric.

So what the hell does that mean? Well, in gravity waves, there is a wave in space (and time) in which the thing that changes over space and time is the density of matter. In gravitational waves, there also is a wave in space and time, but the thing that "wiggles" is not the density of matter (or the strength of electric and magnetic fields, like in light or EM radiation in general), but the properties of the fabric of space and time itself. You can think of it as if the coordinate system itself wiggles, so to speak. This "wiggling" results in the length of the arms of e.g. the LIGO interferometer to change ever so slightly, causing a phase shift between light beams send through both arms, which can (hopefully) be detected.

In more mathematical terms, the exact properties of space and time are called the metric. In a portion of space without any matter, the metric is flat (called the Minkovski metric), which means that the usual laws of geometry apply. In any circumstances with matter (and thus gravity) present, these laws to do hold up!

What?!, I hear you think. Yes sir, you've been lied to in geometry class! However, you've been lied to only very, very slightly. Example: if you measure the radius of a sphere (say: R), you expect to find a surface area of exactly 4/3 * pi * R^3. If the earth would be a perfect sphere (which it isn't), and you would be able to measure its radius and surface very accurately, you would find that the surface area is ever so slightly smaller than expected. Or, in other words, the radius seems to be a bit too large (in the order of 3 cm or 30 cm IIRC). Read more about space time curvature here/

A primer on gravitational waves can be found here. A more detailed description here.

Re:Gravity waves != gravitational waves

[Anonymous Coward]

What?!, I hear you think. Yes sir, you've been lied to in geometry class! However, you've been lied to only very, very slightly. Example: if you measure the radius of a sphere (say: R), you expect to find a surface area of exactly 4/3 * pi * R^3.

When I finished geometry, I expected to find the surface area of a sphere to be exactly 4*pi*R^2.

Re:Gravity waves != gravitational waves

[pyrrho]

man, I HATE it when you subconsciouly do an integration! Arg!

I have a question.

[Mac73117]

Why couldn't we put this lab in orbit? That way we wouldn't have to compensate for so much extraneous gravitational noise. Or am I missing that fact that this equipment needs the Earth's gravity well to function.

Disclaimer: I am not a physicists, just a guy who likes science.

Re:I have a question.

[Patrik_AKA_RedX]

Why couldn't we put this lab in orbit? That way we wouldn't have to compensate for so much extraneous gravitational noise.

That wouldn't matter. The amount of gravity affecting a orbiting spacecraft isn't much lower than on earths surface. The whole concept of orbiting requires gravity (the craft falls around the planet).
Even far away from the planet the lab would still be inside the gravitational field of the sun.
So to compensate for gravity you would need to place the lab in interstellar space, however it's much more practical to leave the lab on earth and compensate for the planet's gravity in the equations.

Re:I have a question.

[edgar_is_good]

There actually is a plan to put it in space called LISA. It would consist of satellites to study the waves. Different setups make you sensitive to different sources of gravitational waves and LISA will detect different sources than LIGO will.

Re:I have a question.

[Stuntmonkey]

Why couldn't we put this lab in orbit?

The main reason is that the effect is so weak. A mission concept called LISA is being studied by ESA and NASA. The idea is to have 6 spacecraft orbiting the Sun, which together form a interferometer several million kilometers in size. The catch: Because the waves are so weak, the distances between these spacecraft would need to be controlled to within about a nanometer (!) to have any hope of detecting a signal. Needless to say a VERY challenging mission.

A lot of other interesting missions would be enabled by good formation flight technology. Look at NASA's Terrestrial Planet Finder mission, or the ESA's similar Darwin mission.

Re:Gravity doesn't effect me

[charlesbakerharris]

Effect is a verb. He just used it incorrectly. To effect = to do, as in "he effected a change", whereas to affect = to alter.

Re:Gravity what it is and what it is not.

[DoctorRad]

The eminent professor asked the Batchelor student to explain General Relativity. The student thought for a moment before replying "Well, I'm sure I understood it at some point, sir, but I appear to have forgotten".

The professor looked startled: "This is an unfortunate turn of events. It appears that of the two people in the world ever to have understood General Relativity, one of them has forgotten".

Anyway, thing is, General Relativity is all about the fact that the presence of mass causes the curvature of space-time. What we call gravity is a consequence of that curvature.

Get your head around that one, and we'll talk some more.

Matt...

Re:Gravity what it is and what it is not.

[edgar_is_good]

No, no, gravity is just spacetime curvature and spacetime curvature holds us on the Earth.