Searching For Gravitational Waves

[/caption]Colliding neutron stars and black holes, supernova events, rotating neutron stars and other cataclysmic cosmic events… Einstein predicted they would all have something in common – oscillations in the fabric of space-time. This summer European scientists have joined forces to prove Einstein was right and capture evidence of the existence of gravitational waves.

Europe’s two ground-based gravitational wave detectors GEO600 (a German/UK collaboration) and Virgo (a collaboration between Italy, France, the Netherlands, Poland and Hungary) are underway with a joint observation program which will continue over the summer, ending in September 2011. The detectors consist of a pair of joined arms placed in a horizontal L-shaped configuration. Laser beams are then passed down the arms. Suspended under vacuum at the ends of the arms is a mirror which returns the beam to a central photodetector. The detectors work by measuring tiny changes (less than the diameter of a proton), caused by a passing gravitational wave, in the lengths (hundreds or thousands of meters). The periodic stretching and shrinking of the arms is then recorded as interference patterns.

Much like our human ears are able to distinguish the direction of sound from being spaced apart, so having interferometers placed at different locations benefits the chances of picking up a gravitational wave signal. By placing receivers at a distance, this also helps to eliminate the chances of picking up a mimicking terrestrial signal, since it would be unlikely for it to have the same characteristics at two locations while a genuine signal would remain the same.

“If you compare GEO600 and Virgo, you can see that both detectors have similar sensitivities at high frequencies, at around 600Hz and above”, says Dr Hartmut Grote, a scientist at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute/AEI) and the Leibniz University in Hannover, Germany. “That makes it very interesting for us to search this band for possible gravitational waves associated with supernovae or gamma-ray bursts that are observed with conventional telescopes.”

Of all phenomena, gamma-ray bursts are expected to be one of the strongest sources of gravitational waves. As the most luminous transient event in the known Universe, this collapse of a supermassive star core into a neutron star or black hole may be the most perfect starting point for the search. As of now, the frequencies will depend on the mass and may extend up to the kHz band. But don’t get too excited, because the nature of gravitational wave signals is weak and chances of picking up on it is low. However, thanks to Virgo’s excellent sensitivity at low frequencies (below 100 Hz), it is a prime candidate for gathering signals from isolated pulsars where the gravitational wave signal frequency should be at around 22Hz.

And we’ll be listening for the results…

Original Story Source: Albert Einstein Institute News.

16 Replies to “Searching For Gravitational Waves”

  1. When I was in high school we took a trip to LIGO (LASER INTERFEROMETER GRAVITATIONAL-WAVE OBSERVATORY). Unfortunately, back then I liked physics but I was more into computer science — so I didn’t pay too much attention on the tour. Now I kick myself for not paying attention because now I really want to study physics and learn as much as I can. I wonder how these two in Europe compare to the one we have here in my own back yard (Louisiana)?

    1. you’ll be delighted to know the US detectors are equally up to the task – just down right now for major upgrades. all interferometers will soon be testing out new technologies as well!

  2. When I was in high school we took a trip to LIGO (LASER INTERFEROMETER GRAVITATIONAL-WAVE OBSERVATORY). Unfortunately, back then I liked physics but I was more into computer science — so I didn’t pay too much attention on the tour. Now I kick myself for not paying attention because now I really want to study physics and learn as much as I can. I wonder how these two in Europe compare to the one we have here in my own back yard (Louisiana)?

  3. I hope these detectors get gravity waves soon. It is one thing to get no Higgs at the LHC, but another not to be able to confirm a major consequence of general relativity.


  4. What if the problems in detecting gravitons, Higgs bosons and gravity waves is due to that there are no such phenomena? I mean that there are nothing propagating gravity, it just is. Many think that if you remove a massive object from the face of the universe, say the sun, it wouldn´t take 8 minutes for us to notice it was gone. We would feel the absence of its gravity instantly.

    I thought like that once but after learning more about physics I have learnt that gravity itself can not “travel” faster than the speed of light. Has the possibility that the effect is instant even at great distances actually been completely disproved by observations or experiments?

    1. Gravity for small masses or equivalently weak fields is similar to Maxwell’s equations of electromagnetism. A Newtonian gravity field is similar to the Coulomb law for an electric field. If that charge is displaced some the lines of force do not move instantaneously everywhere, but adjust along a wave with an induced magnetic field. With gravity, here in the weak field case, a similar physics holds. In this case the weak gravity wave is similar to an electromagnetic wave.


      1. Ok, that´s what I expected. Thanks for the links. Maybe gravity works differently than expected though. By other means than particles or waves I mean. If the LHC reaches it´s full capacity without having detected the Higgs boson people are going to have to think about making a new model for mass and gravity. According to the theories LHC should be able to reach the maximum energies predicted for the Higgs boson.

      2. As lcrowell comments, the wave nature falls out of the low-energy behavior of the force description. That has to happen, or the description would have been shown to be in error by now. Similar to when you see a liquid, expect waves.

        As for particles, you can always quantize a classical field, and a graviton falls out of quantizing a similar low-energy description of gravity.

        Since gravitons comes naturally out of string theory too, they likely exist as real particles even if the low-energy picture can’t be the whole physics of gravity.

  5. From the talk about frequencies, I assume there must be a gravitational-wave analog to the familiar “electromagnetic spectrum” we often see diagrammed in physics books, with different regions associated with different sources and detection methods. Has anyone seen one? Where can I find such a thing?

  6. Good luck to the teams. Although it seems like a lot of effort to go to to prove a part of Einstein’s theory. We know GR works in its own context. How much will this validation really delver to GR, Apart from a lot of; “in your face GR skeptics parties” the world over… 🙂

    Or more pertinently, what technological advantage would we gain if they are detected.?
    Gravitational telescope perhaps?

    Its often said that: “Detecting Gravitational waves will revolutionize our understanding of the universe.” But its rarely articulated exactly how it will do so.

    Wouldn’t the Suns heliosphere and gravitational influence shield us from such things in any case? Perhaps we should be looking for gravitational pond ripples in our solar helio-sheath?

    1. Well, you identify the two cases.

      First we must always test theories as much we can, because they can be wrong or we can discover deviations that hints at new physics and in best case larger theories.

      Second it is a new window for astronomy and cosmology. Detecting gravity waves from the early universe would help test _that_ theory (standard cosmology). Even better, new windows have always resulted in observation of new phenomena (and in cases better observation of old).

      FWIW, whenever “revolutionize” is mentioned, it is always an inflated description of newness. It’s a 100 $ word worth 1 $.

      1. I agree, a many times tested theory still needs testing with newer views as to the test.

        If gravity waves are anything like the EM counterpart we should expect to find the waves of those first gravity interactions of the early universe to have been affected by the initial rapid expansion, and the accelerated expansion which follows to some extent.

        As Damian suggested, there might be some type of spectrum to measure; along with some type of prism or means to focus or guide the shape of space-time without effecting changes which would mask the intended study resultant.


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