Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Gravity Waves?

  1. Nov 27, 2004 #1
    I understanding there is some effort to detect a “Gravity Wave”
    What kind of event are looking for that could produce one?

    Assuming we are starting from a base of gravitation “tension” being exerted on us like rubber bands from all directions. I assume the wave to be detected would be in line – like someone pulling back and forth on the rubber band.
    And if detected it would likely be a highly damped single Square Wave. A sudden change in the number of gravitons coming our way up or down.

    So this wouldn’t be just be something moving around out in the Cosmos.
    We must be looking for some significant change is Mass to generate such a wave.

    The question is – What is it that we expect to be happening out there that should have such a dramatic affect. A massive release energy though the sudden elimination of mass on a scale large enough that we hope detect a G wave?

    Do we have an idea of what this predicted event should “Look” like?
    Should be disappointed if such an event is seen but G wave is not detected?

    Randall B
  2. jcsd
  3. Dec 1, 2004 #2
    There is expectation to detect two classes of events, continuous sources and gravitational waves bursts. Continuous sources are for example binary pulsars, in fact the indirect detection of gravitational waves in a binary pulsar granted a Nobel prize to Taylor. GW bursts are produced for example, in the explosion of a supernova
    The search for gravitational waves is not new, there is an effort of years to detect them, but our current technology has proven primitive to detect them.
    There's a laser interferometer called LISA that will be launched in 2012 that possibly will detect such events
    Another possible device to detect gravitational waves is a matter wave interferometer, as proposed here
    Last edited: Dec 1, 2004
  4. Dec 1, 2004 #3


    User Avatar
    Science Advisor
    Gold Member

    Thanks for the link, meteor. Hadn't seen that one. In addition to LISA, the Square Kilometer Array is promising and may provide some results useful for the LISA project:
    Science with the Square Kilometer Array: Motivation, Key Science Projects, Standards and Assumptions
  5. Dec 1, 2004 #4


    User Avatar
    Science Advisor
    Gold Member

    Just about any astrophysical event will generate gravity waves, however a well-known theorum on gravitational radiation is that spherically symmetric systems do not generate graviational waves, so for example (I guess) when a star collapses into a black hole (which is often cited as one of the best possible sources of g. waves), the amount of graviational wvaes will strongly depend on the degree of spherical asymmetry of the star/black hole. Binary systems of dense objects such as neutron stars orbiting each other closely should also be a copius form of graviational waves.

    We are never going to see strong graviational waves from the Earth, as the waves will be string only tclose to the source, an object 'hit by a gravitional wave will appear to move to some remote observer, but from the object's point of view it stays still!
  6. Dec 1, 2004 #5
    I remember from the Elegant Universe DVD that gravity waves could be used to communitcate with intellgient life in other universe that were // with our own. Let me see if I can find the clip about it from the streaming video
  7. Dec 1, 2004 #6
  8. Dec 2, 2004 #7


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The LIGO website has lots of good resources and links to answer all your questions RandallB.

    The two key expected soures (for LIGO detection) are colliding neutron stars (or black holes) and asymmetric supernovae. Some feel that colliding SMBH (galaxy or quasar nuclei) might also be detected, even to the edge of the universe, but the expected rate of occurrance is very low.

    If you're into this kind of thing, click on the Einstein@Home link on the LIGO page ... your own PC can take part in data reduction, perhaps leading to the discovery of the first gravitational wave detection!
  9. Dec 5, 2004 #8
    What might be the relationship, coincidence or symmetry, of the fact that light and gravity travel at the same speed?
  10. Dec 5, 2004 #9


    User Avatar
    Staff Emeritus
    Gold Member
    Dearly Missed

    That's as fast as anything can go. And if gravity turns out to be carried by gravitons, they are massless, which means they travel at c.
  11. Dec 6, 2004 #10
    Thanks Nererd and others, LIGO has a lot of great material on how they are hopefully of see something. I’ll keep looking it over.
    I just have a lot of doubt about detecting anything from orbital or explosive events even if they appear “asymmetric” when you look at it. Seems to me when you get down to it gravitationally they will likely present “symmetric”. Doesn’t seem to me that a “wave” should be expected from mass just moving about.

    However the idea that the center of a couple of galaxies could collide Super Massive Black Holes scoring direct hits on each other, that might have the potential for releasing/creating a massive amount of energy converted from disappearing mass.
    If enough mass disappeared that I can understand could create a true liner G wave.

    Got to be impressed with the effort to even look, two SMBH’s finding each other – that would be rare.

    Randall B
  12. Dec 7, 2004 #11


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The (experimental) detector design aspects of Gravity Wave detectors is quite an intersting area too. The Q-factors on some of the low-frequency vibration isolation systems built by these people are nothing short of mind-blowing. I remember being particularly impressed by some of the isolators built by a group in Australia (either U of New South Wales or U of S. Australia) - don't recall which one, but I have the paper saved somewhere.

    I brought this up because detector design is often the make or break issue in gravity wave measurements and the people that do this incredibly (and I cannot sufficiently describe how technically challenging this job is) difficult work seldom receive recognition.

    <just sticking up for my fellow experimenters :biggrin:>
    Last edited: Dec 7, 2004
  13. Dec 7, 2004 #12


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Rare, but nonetheless sure to happen. The best example I've seen is 3C75, two radio galaxies (they have their own pairs of jets and bright nuclei) on death spiral, at the heart of Abell 400.
  14. Dec 7, 2004 #13


    User Avatar
    Science Advisor
    Gold Member

    All a gravitional wave is doing is telling an objects gravitational field taht the stae of an object has changed and to change itself to reflect this (infact in some sense all it is is the changes in the field). It's specifically spherically symmetric objects that do not produce graviational waves as long as spherical symmetry is maintained. To get somne clue as to why this might be you might remember the well known theorum that a spherically symmetric object behaves like a point mass, therefore under any changes that do not alter the fact that it's spherical symmetry it will go on behaving like a point mass and there will be no changes to it's gravitatioanl field (actually to be clear we're strictly talking about the field outside of the object).
  15. Dec 8, 2004 #14

    What about gamma ray bursts emitting possibly detectable gravity waves? Nothing as yet has been found to emit more energy in a short period of time as they do. They are thought to be on the edge of the universe and it is unlikely that black holes would collide there, as they would have had no time to form.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Gravity Waves Date
B LIGO gravity waves Oct 24, 2017
Stargazing New Radio Telescope is World's Largest Jul 4, 2016
B LIGO detects second gravity waves Jun 16, 2016
LIGO discovery on gravitational waves. Feb 12, 2016
Question on the new gravity wave discovery Feb 11, 2016