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

Gravitational waves

  1. Mar 15, 2005 #1
    If the advanced LIGO will not detect gravitational waves then is the theory dead?
     
  2. jcsd
  3. Mar 15, 2005 #2

    ohwilleke

    User Avatar
    Gold Member

    Theories don't die. They just get remodeled.
     
  4. Mar 15, 2005 #3
    Do you have any idea what could be remodeled?
     
  5. Mar 15, 2005 #4

    SpaceTiger

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    We haven't confidently reached the threshold where we can be sure we should have detected gravitational waves. One of several things could happen:

    1) LIGO detects something and everybody believes it. This is looking less and less likely with time.
    2) LIGO is a bust, but LISA (a planned space interferometry mission) detects gravitational waves. This is where my money is at the moment.
    3) LISA is a bust because of some failed instrumentation and we have to wait for the next generation.
    4) LISA registers a non-detection of gravitational waves down to the threshold where theory definitely predicts them.

    Rather than "killing" anything, that last option would likely excite the community. The least interesting result would be a complete verification of current theory.
     
  6. Mar 15, 2005 #5
    In a chance when both LIGO and LISA will fail, we would have to wait for Constellation-X (after 2016) i guess. If they don't exist this would be a big lesson.

    Of course there are some theories which postulate that we'll never detect gravitational waves, such as MLET.
     
    Last edited: Mar 15, 2005
  7. Mar 15, 2005 #6

    SpaceTiger

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Constellation-X is an X-ray mission....
     
  8. Mar 15, 2005 #7
    But isn't it part of the 'Beyond Einstein project'? The project has nothing to do with gravitational waves though...
     
    Last edited: Mar 15, 2005
  9. Mar 15, 2005 #8

    ohwilleke

    User Avatar
    Gold Member

    Well, and to be clear, I'm talking about a situation where the experiment disproves with undisputed accuracy the presence of gravity waves which theory predicts, you have a number of options:

    (1) The wave length of gravity waves is different, probably longer, than expected.
    (2) Gravity waves are slower than expected.
    (3) Contrary to theory, gravity is particle-like and not wave-like.
    (4) Contrary to theory, gravity is instananeous.
    (5) The instrument is part of the system in an unexpected way which makes it incapable of detecting gravity ways.
    (6) It's all the Dolphins' fault.
     
  10. Mar 15, 2005 #9
    I think that if all matter has a wave structre than GR is probably correct about gravitational waves.
     
  11. Mar 16, 2005 #10

    Phobos

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    As ohwilleke notes, it may be that the system is not sensitive enough to detect gravitational waves (i.e., the experiment produces a "false negative" result). I don't know the details of the experiment, but presumably it was designed to detect gravity waves as they are best understood via the current theory of general relativity. If gravity waves are weaker than we expected, then we may need to tweak the theory accordingly and a more sensitive detector would need to be built. Any detector has a "detection limit" below which it cannot see, so it's hard/impossible to prove that there are zero gravity waves (an experiment may say there are no gravity waves detectable at X meters...and we can keep lowering X with better detectors).

    In order to totally scrap general relativity, we would first need to develop a new theory that explains everything GR can and more (GR has already been shown to be very accurate on a broad range of tests). A scientific "theory" has already passed experimental tests. It's a hypothesis that you can keep/drop based on (essentially) one experimental result.
     
  12. Mar 16, 2005 #11

    ohwilleke

    User Avatar
    Gold Member

    Of course, I think that either an inconclusive result or a LIGO confirmation of gravity waves is much more likely, than a definitive contraindication of gravity waves from LIGO.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Gravitational waves
  1. Gravitational Waves (Replies: 12)

  2. Gravitational Waves (Replies: 37)

  3. Gravitational Waves (Replies: 6)

Loading...