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How would one look for and confirm existence of a graviton?

Someone was speaking to me about perhaps one day discovering the graviton, but to me it seems unlikely, although I'm young and essentially quite naive, so am coming to you physicists to ask

  1. What actually is the likelihood of finding it?
  2. How would we find it?
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If you like this question you may also enjoy reading this post. –  Qmechanic Aug 13 '12 at 22:44
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2 Answers

up vote 8 down vote accepted

Unfortunately, no physically reasonable detector could ever detect gravitons. For example, a detector with the mass of Jupiter placed in close orbit around a neutron star would only be expected to observe one graviton every 10 years (see the below paper). The few that would be detected would be indistinguishable from the background 'noise', i.e. neutrinos.

See here:

http://arxiv.org/abs/gr-qc/0601043

Even though we can't detect individual gravitons, gravitational wave detectors may shed some light on them, since the graviton is the quantum of the gravitational wave (similar to how early 20th century physicists studied the nature of the photon based on properties of light, such as the photoelectric effect.).

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Thanks, are there any experimental physicists that are currently working on any such projects? Or have they pretty much all ruled it out? –  Olly Price Aug 13 '12 at 22:33
    
We certainly haven't ruled gravitational waves out, because we have seen their effects through the Binary Pulsar 1913+16 (astro.cornell.edu/academics/courses/astro201/psr1913.htm) for which the 1993 Nobel Prize in physics was awarded. So, we know they exist (and therefore have very strong confidence gravitons exist in some form). In order to detect GWs, detectors such as LIGO (astro.cornell.edu/academics/courses/astro201/psr1913.htm) have been constructed. LISA (lisa.nasa.gov) is also being planned, which should certainly detect GWs. –  Mark M Aug 13 '12 at 22:52
    
Does not detection of gravitational waves actually amount to detection of gravitons? –  Anixx Aug 13 '12 at 22:58
    
@Annix In my answer, I was referring to direct detection of gravitons. Of course, you may argue that since quantum mechanics requires waves to have quanta with energy proportional to their frequencies (Planck's law, $E = hf$), and since gravitational waves exist, then so must gravitons. –  Mark M Aug 13 '12 at 23:01
    
To me the possibility of detection is highly dependent on graviton's energy. Possibly natural gravitons are difficult to detect but given a source of high-energy gravitons, they would not be that difficult to detect. –  Anixx Aug 13 '12 at 23:06
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This depends on graviton energy and wavelength.

Given a source of a beam of high-frequency gravitons with high luminocity, it would not be difficult to detect one.

The problem is that nature has little sources of high-energy gravitons.

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