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Space Science

A Galaxy-Sized Observatory For Gravitational Waves 190

KentuckyFC writes "Gravitational waves squash and stretch space as they travel through the universe. Current attempts to spot them involve monitoring a region of space several kilometers across on Earth for the telltale signs of this squeezing. These experiments have so far seen nothing. But by monitoring an array of pulsars throughout the galaxy, astronomers should be able to see the effects of gravitational waves passing by. They say such an array of pulsars should effectively shimmer as the gravitational waves wash over it, like a grid of buoys bobbing on the ocean. That'll create an observatory that is effectively the size of the entire galaxy. These observations should be capable of monitoring how galaxies and supermassive black holes evolve together, and shed light on the physics of the early universe. Best of all, the next generation of radio-telescope arrays should be capable of making these observations at a cost of around $66 million over ten years. That's a small fraction of the hundreds of millions that Earth-based observatories have already cost."

A Galaxy-Sized Observatory For Gravitational Waves

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  • Usefulness (Score:3, Funny)

    by JustNiz ( 692889 ) on Tuesday September 15, 2009 @06:12PM (#29432507)

    >>> "Gravitational waves squash and stretch space as they travel through the universe

    Gravitational waves are very useful in the kitchen. I use them for juicing oranges.

    • Re:Usefulness (Score:4, Insightful)

      by A beautiful mind ( 821714 ) on Tuesday September 15, 2009 @06:34PM (#29432859)
      Detecting or not detecting gravitational waves validates* or invalidates part of Einstein's theory of general relativity. That's a pretty big deal. It means that we have found the first flaw in a theory whitstanding constant attacks on it since 1915 if we would not find gravitational waves.

      *take "validates" in this context to mean that there is no experiment or information in disagreement with the theory, therefor going by science's falsification requirement, science considers the theory to be currently valid.
      • Every time someone finds something that Einstein "may have gotten wrong", we just end up with more evidence that he was right.

        Personally, I don't believe in something like gravitational waves, but I'm more inclined to trust his intelligence more than mine.
    • I use them to make binary neutron stars swirl into each other and explode. They remove energy from the system so you can pack those stars in there real good... and rapidly spinning black holes make great gifts for the kids.
  • that is could falsify the theory? if so then go for it.

    I mean, they don't have to exist, there are other theories out there.

    • Re: (Score:2, Insightful)

      Is thisntest desing in such away

      Is your title designed in such a way that could falsify your hopes of being taken seriously?



    • Re: (Score:3, Funny)

      by rts008 ( 812749 )

      Is thisntest desing in such away that is could falsify the theory?

      What language is this written in?
      What does it translate to in English?

      • Drink a few tins of hobo beer and you'll be able to understand it, no problem.

        It says "GAHHHHH FUGGIN PIGEONS GET OFF MY HAT... I love you."
  • by beanyk ( 230597 ) on Tuesday September 15, 2009 @06:17PM (#29432569)

    Just wanted to point out that the pulsar timing array approach will cover a completely different frequency range (~ 10^-9 to 10^-7 Hz) to existing ground-based detectors (LIGO, Virgo and friends), which operate in the 10^1 to 10^4 Hz range. In between are projects like LISA (http://lisa.jpl.nasa.gov/).

    The different frequency ranges mean different astrophysical sources of gravitational waves; generally speaking, the more massive the system, the lower the GW frequency. LISA, for instance, would see the radiation produced by the supermassive black holes at the centres of galaxies, while the other detectors would be targetting much smaller systems.

    • by TropicalCoder ( 898500 ) on Tuesday September 15, 2009 @06:31PM (#29432813) Homepage Journal
      Thank you for your interpretation of the meaning behind today's article. It was a revelation for me to consider gravity waves as an analogue of electromagnetic waves. On the The North American Nanohertz Observatory for Gravitational Waves web site [arxiv.org] there is more information. They say "The timing precision of today's best measured pulsars is less than 100 ns. With improved instrumentation and signal-to-noise it is widely believed that the next decade could see a pulsar timing network of 100 pulsars each with better than 100 ns timing precision." I thought it interesting that they only get 100. Then if you did a long term integration of these signals, you may get down to pico-second timing. Such a timing base may be used to correct atomic clocks in GPS satellites and have many other uses. This is all just pure speculation by a non-physicist, so take it with a grain of salt.
    • by electrostatic ( 1185487 ) on Tuesday September 15, 2009 @07:03PM (#29433265)
      If the pulsars under observation are, say, 100-1000 light years apart, then the time necessary to notice a gravitational wave perturbation would seem to be on the order of 100-1000 years, respectively.

      IOW, because gravitational waves travel at light speed (general theory of relativity), then a "stretch and squeeze" at one pulsar would reach the more distant pulsar many years later. The observed delay is of course a function of the distance between the pulsars, the angle of the wave and the angle of them to earth.

      OTOH, a gravitational wave train with a wavelength much shorter the the distance between the pulsars could also be observed if a lot of pulsars were involved -- and if the observation period was at least one cycle. The 10^-9 frequency mentioned equates to a 31.7 year period.
  • by davidwr ( 791652 ) on Tuesday September 15, 2009 @06:18PM (#29432595) Homepage Journal

    Will beings in larger galaxies taunt us because their gravity-wave detectors are bigger than ours?

  • If there are no gravitational waves to be found? If we search the entire spectrum, and we don't find any, then I assume that falsifies the grav-wave theory (and the entire Honorverse). At that point, what is the next step/theory? In a related note, does gravity pull, or push? I think I remember reading somewhere that Einstein said gravity pushed, rather than pulled.
    • Re: (Score:3, Interesting)

      I think that is an excellent question. It's the classic divide between Einstein and Bohr. For Einstein, gravity is geometric, for Bohr et al, it is a product of Stuff and Stuff exists as particles, waves, and/or both.

      If they don't find gravity waves in this attempt, I would suspect the following to happen:

      A: One bunch, the Einsteins of the lot will say "Well, I toldja so..."

      B: The Quantum types will simple demand more money for an even bigger test that will look at clusters of Galaxies or some such co

    • Re:So what happens (Score:5, Interesting)

      by dido ( 9125 ) <dido@@@imperium...ph> on Wednesday September 16, 2009 @01:35AM (#29436415)

      If gravity waves didn't exist, you'd have to find some other explanation for PSR B1913+16 [wikipedia.org], which is a pulsar in orbit around another star. The pulsar and its companion are spiraling in together, losing energy in exact agreement with the phenomenon of gravitational radiation predicted by General Relativity. This binary pulsar system has been hailed as sufficiently convincing indirect evidence for the existence of gravity waves that Russell Alan Hulse and Joseph Hooton Taylor Jr. were awarded the 1993 Nobel Prize in Physics for its discovery.

      No, it doesn't seem that the existence of gravitational waves is in any question here. The only thing is that there might be much yet we don't understand about gravity that is stifling our ability to observe them directly. It's obvious that General Relativity is far from being the final word on gravitation.

  • by mosb1000 ( 710161 ) <mosb1000@mac.com> on Tuesday September 15, 2009 @06:44PM (#29432993)
    "Gravitational waves squash and stretch space as they travel through the universe."

    Does anyone else find these words to be a little presumptuous. It's not like they've ever detected any. Might I suggest the following wording instead:

    "Gravitational waves would squash and stretch space as they travel through space, if they exist"
    • Re: (Score:3, Insightful)

      by nstlgc ( 945418 )
      Technically speaking, no. They squash and stretch space by definition. If they don't exist, space obviously won't be squashed and stretched by them, but that won't change their definition. They just won't exist. It's like saying "a unicorn has wings". The fact that it allegedly doesn't exist doesn't mean it doesn't have wings when someone draws one.
      • No, the article is making a claim about space, which is real. It would be like me saying "Unicorns are eating my lawn," which is obviously not true. What I should say is "Unicorns might eat my lawn, if they exist."
    • Re: (Score:3, Insightful)

      by kindbud ( 90044 )

      Space itself is a theoretical construct and gravitational waves passing through it are part of the same theory. So it is more correct to say:

      "Gravitational waves, if they exist, would squash and stretch space, if it exists, as they travel, if travel is possible, through the universe, if it exists."

      But that's retarded, so they don't.

      Anything else I can help with, just ask.

    • by blueg3 ( 192743 )

      It's not like they've ever detected any.

      If only the summary had said so! Wait...

      Might I suggest the following wording instead

      No, that would be presumptuous.

      Perhaps the summary author assumed a level of reading comprehension. It might be presumptuous if we knew there were gravitational waves, but not what their behavior was. However, we know their behavior, but not if they exist.

    • Gravitational waves are found as a 'natural solution' from Einstein's General Relativity, more or less like electro-magnetic waves are a solution to Maxwell's equations. Since GR so far seems to be solid as a rock (supported by many experiments [wikipedia.org]), there is little doubt among theoreticians that GWs exist. Moreover, a binary system containing a pulsar observed by Hulse and Taylor is spinning down at exactly the rate that you would expect if the system loses energy by gravitational waves. This is not a direct o
  • So, stop me if I'm way off base, but might it be impossible to detect gravity waves? If a gravity wave is a change in the gravitational constant of a finite space, then wouldn't that affect the mass, and the space-time qualities of a sensor within that space, rendering its observations relative, and useless?

    Or does my thought experiment lack a certain... Knowledge?


    • > So, stop me if I'm way off base, but might it be impossible to detect gravity
      > waves?

      Proving that they cannot be detected would be exactly the same as proving that they do not exist.

    • by Anti_Climax ( 447121 ) on Tuesday September 15, 2009 @07:46PM (#29433781)

      A gravity wave, as derived from the theory of relativity, doesn't specify that the gravitational constant would oscillate - simply that the shifting of large masses, like co-orbital black holes and such, will distort spacetime in wavelike manner. Those perturbations of spacetime would travel from their origin outward at the speed of light.

      It's best to think of it in terms of the bowling-ball-on-a-rubber-sheet analogy of space-time. If you take a large mass like a bowling ball and set it in the middle of a large rubber sheet, it will depress deeply nearby and taper off the further away from it you go on that sheet. If that bowling ball magically disappeared, there would be a wave that travelled across that sheet as well as if you had 2 bowling balls spinning around each other.

      The way we've been trying to detect gravity waves so far (LIGO) uses lasers set up at right angles so if space were to compress or stretch in one dimension, the beams the were previously in phase would shift apart. This can detect a stretching of spacetime equal to a fraction of the wavelength of light used in the lasers.

      In actuality, it is the change in the behavior of spacetime that lets us measure in that manner, but if the wave were to stretch spacetime in all dimensions, LIGO couldn't work. Hope that explains it.

      • You, I, and the lasers are inside the three-space being acted upon by the gravitational wave. How the hell are we supposed to measure this phenomenon from the "inside?"
        • Re: (Score:3, Informative)

          by Anti_Climax ( 447121 )

          Like I mentioned in the last sentence, it relies on the expectation that a gravity wave passing through an area would stretch one dimension of space while contracting another perpendicular to it.

          If it causes all dimensions (including time) to expand and contract simultaneously, it can't work.

          Of course, I have to defer my understanding of gravity waves to those who study this stuff for a living and have experimentally verified a large body of the predictions made by general relativity.

        • by Velex ( 120469 )


          Same way we'd measure the surface of a sphere changing if we were on the surface of the sphere. Just add an extra dimension.

    • by mbone ( 558574 )

      A gravity wave will change the distance to objects at right angles to its direction of propagation. This effect is biggest when the distance to an object is order the wavelength of the wave, or longer. (Since they travel at the speed of light, the relation between wavelength and frequency is the same as for light.) Likewise, the sensitivity is biggest when the period of the wave is between the frequency of measurement and the total duration of observations. So, pulsars are sensitive to waves with periods be

  • I believe that any theory of gravity where

    1. Energy is conserved

    2. Gravitational information propagates at a finite speed (most theories set this speed equal to the speed of light)

    will have gravitational waves of some sort.

    Is there any physicist who does not believe in both 1 and 2?

    Gravitational waves exit. The real problem is detecting them and interpreting the waveforms.

    • by mbone ( 558574 )

      The really interesting thing is that General Relativity predicts two and only two polarizations, while other theories (that cannot be distinguished from G.R. in the usual solar system tests) have more polarizations. If and when we get a good, high SNR, detection of gravitational radiation, a profound test of gravity should follow in short order.

  • by voss ( 52565 ) on Tuesday September 15, 2009 @11:07PM (#29435503)

    Doesnt mean its not true...Democritus 2400 years ago proposed the existence of the atom.

    He had no way testing this, he simply used logic to deduce it.

    • by volpe ( 58112 )

      Bear in mind that there's a big difference between a theory which cannot be tested in principle, and one which cannot currently be tested in practice due to limited technology. Actually, it's not even appropriate to use the word "theory" in this context. In the latter case, it's a hypothesis. In the former, it's metaphysics.

    • He might not have thought about, but there's actually a fairly simply way to measure the size of an atom.

      Take an oil drop and measure its weight. Then drop it on the surface of a very still lake, and leave it to spread it out. It will spread to be about 1 atom thick. Then you can simply look to see how big it spread out, divide by the volume by the area, and the result is the size of the atom.

      This gives a result to within an order, which amazing given its simplicity.

  • Why can't our great minds that are exploring the Galaxy construct their Observatories on the Moon? Maybe on both Poles? The clarity of their images, I believe, would be fairly difficult to equal across any collections of arrays on Earth.
