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?

[Mr. McGibby]

Complaining about teaching undergraduate classes.

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.

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!

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.