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Science

Renewed Gravity Research Could Soon Yield Results 89

Posted by timothy from the but-gravity-is-everywhere dept.
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.""
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Renewed Gravity Research Could Soon Yield Results More

Renewed Gravity Research Could Soon Yield Results

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  • I didn't know gravity was renewable. Heck, I didn't even know it wore out!

  • 30 years and still no results? (Score:5, Funny)

    by Zemrec ( 158984 ) on Wednesday September 24, 2003 @04:15PM (#7048740)
    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.

  • Maligning Einstein?? (Score:5, Interesting)

    by WTFmonkey ( 652603 ) on Wednesday September 24, 2003 @04:52PM (#7049167)
    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.
    • 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, si

  • And another thing (Score:4, Interesting)

    by WTFmonkey ( 652603 ) on Wednesday September 24, 2003 @05:06PM (#7049317)
    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 (Score:5, Interesting)

      by Yokaze ( 70883 ) on Wednesday September 24, 2003 @05:23PM (#7049479)
      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.
      • Space happens. Shit comes later.

      • Re:And another thing (Score:3, Informative)

        by rwaldin ( 318317 )
        Well maybe, or maybe not. From Parallel Universes [scientificamerican.com]

        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?" [scientificamerican.com] by Jean-Pierre Luminet, Glenn D. Starkman and Jeffrey R. Weeks; Scientific American, April 1999]. So far, however, the evidence is against them. Infini

        • I like your thoughts of there being infinite number of parallel universes. I belive there are infinite times that each time is a branching point for unlimited posible futures. In the end only one is chosen, but all are done. Though in this world only one action was taken in a parallel universes another event took place. So in the end all acions and reactions that are posible happen. And this will branch of agine and agine cousing limmitless posibilitys. *so the next time you deside to stop at a red li
          • I like to think that in a parallell universe, the other me is getting it on with this incredibly hot Spanish girl I keep running into...
            • in a parallell universe, the other me is getting it on with this incredibly hot Spanish girl...

              The good news is that in an an infinite number of parallel universes, everything that CAN happen DOES happen somewhere. The bad news is that you are telepathetic in all universes, so it never happens anywhere. :)

              -

      • Re:And another thing (Score:2, Interesting)

        by Nyphur ( 514992 )
        "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
      • I'm not very familiar with this subject...but...

        Was space a result of the big bang or something? Was distance? If not, then what do you call the stuff 10 miles from the first moments of the big bang? I'm sure it would have a name, even if it were nothing.

        Or, do you mean space, as in this definition?
        "The infinite extension of the three-dimensional region in which all matter exists." [dictionary.com].

        And, I'm confused by this your quote,
        "The point is there was no space in which the explosion happened and n
        • First of, I'm stating it like it is the truth. But in fact, it is a theory, which AFAIK is (or at least was) the most accepted one. Remember all what I say is limited by my lay-mans knowledge.

          > Was space a result of the big bang or something? Was distance?

          Excactly. So, at one point in time, 10 miles from anywhere could mean 10 times through the universe and back to where you started through a universe with a mile diameter.

          That is why there is a uniform background radiation, which are a reminiscence fr
          • > IRC doesn't explain some other thinks
            IRC doesn't explain some other things.

            For example, my spelling mistakes. I know there others left, but this one makes the text hard to understand.
          • Thanks for the good explanation :)

            >> Was space a result of the big bang or something? Was distance?

            >Excactly. So, at one point in time, 10 miles from anywhere could mean 10 times through the universe and back to where you started through a universe with a mile diameter.

            I find this hard to understand. Why wouldn't 10 miles be in the nothingness that is next to the big bang? Why would it have to be limited to within the bigbang/growing universe(?)?
            • > Why wouldn't 10 miles be in the nothingness that is next to the big bang? Why would it have to be limited to within the bigbang/growing universe(?)?

              If you walk for 10 miles, how far will you get? And what if you go on a circle of 1m diameter? Probably not farther than 1m. And what is if the circle has no diameter?

              It is similar with space. It has a diameter (the largest distance of any two points in it), because it is wrapped around.

              Except that the "circle" is 3 dimensional (or even more) and the dia
              • Again, I think I'm visualising the "big bang" as a "big bang" of matter...just a ball (or whatever shape) of matter/energy with some amount of volume. It then expanded, increasing it's volume (relative to what it was before). So, outside the big bang would be a point that it would expand to a couple moments later.

                I probably have some conceptual flaw that's keeping me from even slightly understanding. Even if you are considering the universe as only what was contained in the big bang...but if so, I would st
            • I find this hard to understand. Why wouldn't 10 miles be in the nothingness that is next to the big bang? Why would it have to be limited to within the bigbang/growing universe(?)?

              For much the same reason that 'north' and 'south' are restricted to the Earth's surface, '10 miles' is restricted to the Universe. To speak of something as being '10 miles outside the Universe' is as meaningless as to speak of something being '10 miles north of the North Pole'.

              Warning: the analogy in this post is under tension

              • >"To speak of something as being '10 miles outside the Universe' is as meaningless as to speak of something being '10 miles north of the North Pole'."

                So, the universe was only the space inside the big bang, and as it grew, the space within that?
      • And that's something I've always wondered - if every point of the universe is expanding relative to every other point, does that mean everything is getting bigger?

        Or if it's that the points are getting further away, then is everything getting less dense?

    • 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?

      My impression is that at the moment of the "big bang" the universe was not a point-- it had some sort of volume-- there was a distance between two points inside it, and as it grew, that distance got bigger. Some light or gravity waves or whatever that was generated at the moment of the big bang has not yet gotten here from where it started-- it continues to arri

    • 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
      • Thanks for the answers. I guess the hardest part for me to grasp is the radiation part.

        Let's say I'm immortal for a minute. And let's say that we know how far it is from here to the furthest edge of teh universe, call it a godzillion light years. Will I stop seeing this radiation in a godzillion years (life age of the universe notwithstanding)? Seems like you would, because that initial whumph of radiation from that godzillion light years away, well there was nothing beyond that when

        *head explodes*

        • Well, see, the big bang is reall the result of what's referred to as the reheating phase after the inflationary phase (in the current cosmology - let me not discuss the evidence for that right now). In the early universe, it is believed to be twisted and contorted and very irregular. Then some dynamics takes over a small patch an inflates it, expands it exponentially, fast enough, even, that two points that had been in causal contact before (i.e., capable of exchanging a light signal within the age of the u
      • I'm confused. If it was seen 14billion light years away, then what created it? If the whole universe was hot like you mention, then wouldn't there not be a specific point that you are talking about? What would create that point?
    • Space might be infinite - AFAIK, we don't know yet; general relativity doesn't help (it tells us about local properties of space, from which we can deduce some global properties, but both finite and infinite spaces are mathematically possible). For a simple finite analogy, the standard blowing-up-a-balloon thing works. For infinite space with expansion: what's meant isn't that space-now is bigger than space-past, if you look at the 'total area' (infinite, and infinite) but that wherever you look from, you f

  • My curious cat (Score:5, Funny)

    by NanoGator ( 522640 ) on Wednesday September 24, 2003 @05:15PM (#7049415) Homepage Journal
    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.
    • This is very, very true. I have always had suspicions that cats were put on the earth to test gravity by pushing things off desks, counters, tables and staying immobile in one spot for long periods of time.

  • Gravity waves != gravitational waves (Score:5, Informative)

    by ControlFreal ( 661231 ) <niek@@@bergboer...net> on Thursday September 25, 2003 @04:06AM (#7053062) Journal

    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 [physics.uwo.ca]

    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 [caltech.edu] 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 [physicspost.com]/

    A primer on gravitational waves can be found here [uiuc.edu]. A more detailed description here [lanl.gov].

  • I have a question. (Score:2, Interesting)

    by Mac73117 ( 122267 )
    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.

    • 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

    • 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.
    • We could. It'd help. Do you have $many-billion to spare putting equipment up that needs to be quite big?

    • Why couldn't we put this lab in orbit?

      The main reason is that the effect is so weak. A mission concept called LISA [caltech.edu] 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 lo

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

      Because "microgravity" does not mean "a minimum of gravity".

  • Lost me towards the middle (Score:1, Interesting)

    by Anonymous Coward
    The thrust of these new developments in gravity research implicates multiple dimensions as the cause for the relative weakness of gravity.

    And if they can make this idea self consistant and conform to measurements, good for them.

    But this has a feeling of sloppiness to it. ie: we cannot explain this coherently with 4 dimensions, so we take what we can't figure out and hide it within the complexities of additional dimensions.

    Could it be possible that explaining gravity is beyond the scope of our current mod
    • Let's be clear about something: there are two issues relating to gravity which involve extra dimensions:

      1) How does one combine quantum mechanics and gravity?

      2) what is gravity so weak compared with the other forces?

      The first has only ever had one consistent theory, and that is string theory (or more recently the still somewhat ill-defined m-theory). superstring theory is the only current stable string theory and it is only a consistent quantum theory in 10 dimensions. (M-theory is a limit where you see
    • Could it be possible that explaining gravity is beyond the scope of our current models, and no amount of tap dancing is going to make it fit with their contexts? Probably. But you can't do that, no no no! Don't even bother pondering alternative models or colleagues will jump up and down on your skull, screaming "Crackpot!" String theory? Branes? No-one got seriously attacked over them. Everyone accepts that if current_model isn't working, you need a new model. Of course, if you're just spouting crap whic
  • Now wait a minute .. how can these guys be sure that when their mirrors are distorted, that the laser emitters they're using to measure them are not also distorted .. therefore giving them whacky data?
  • Yes, I've noticed that PSU is doing some very good work with LIGOS as well.. there's a mysterious little nondescript door on the 2nd floor of my physics dept, a little brown door with the words 'Center for Gravitational Wave Research' stenciled neatly in old-fashioned letters on the frosted glass.. asked my physics prof about it and he confirmed that PSU is indeed one of the forefront institutions working on it.. I'm going to have to find a way to wiggle my way into helping them out with it ;)

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