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afterburner
2006-Mar-18, 12:42 AM
this post was inspired by iantresman's post about black holes...

how far away is the closest known black hole? for experimental purposes...

also photons dont have mass right? and photons are particles that behave like waves...gravitons communicate the force of gravty...

so the idea that gravity is a whole bunch of gravitons would suggest that there is some kind of interaction between photons and gravitons near a black hole or any object for that matter..matter causes light to bend right?...is this correct?

would this then suggest that there are more gravitons than photons in the universe? because photons get influenced by gravitons? (if you shine a laser beam near a black hole to observe the bending of light...every singe photon in that beam would be affected ...right?)

GOURDHEAD
2006-Mar-18, 03:31 AM
If "for every action there is an equal but opposite reaction" holds then photons influence gravitational attractors in a way equal to but opposite from the gravitational effect on them.

Eroica
2006-Mar-18, 04:49 PM
how far away is the closest known black hole? for experimental purposes...
V4641 Sagittarii is the closest candidate that I know of. It's about 1600 light-years away.

Ken G
2006-Mar-18, 05:11 PM
In terms of the number of photons versus gravitons, one must distinguish between real and virtual particles. We usually think of photons as real, but those that are mediators of electromagnetic attraction are virtual. I don't think you count the virtual particles. Similarly, gravitons, as mediators of gravity, are virtual particles and again I'm not sure you can count them. Real gravitons, on the other hand, would be manifestations of gravitational radiation, which even now is trying to be detected by LIGO. I imagine there is about the same number of gravitons as photons in the cosmic background (if they were ever thermalized to each other during the Big Bang), but we'd never detect the background gravitons.

Nereid
2006-Mar-18, 06:07 PM
Gravitons are speculative particles - the theory (or theories) in which they exist haven't any experimental or observational support (other than that for GR and QM separately). They would be the 'carrier' particle of gravity, if a quantum theory of gravity were to be experimentally or observationally verified.

Gravitational radiation ("waves") is predicted in GR, and those predictions match observations very nicely (that's what got Hulse and Taylor their Nobel prize). They are also what LIGO, LISA, and other gravitational wave detectors will find, if their search is successful.

As has already been noted, photons are the carrier of the EM force. While it is nice to be able to say 'photons behave like both waves and particles' or 'photons behave sometimes like waves and sometimes like particles', it is far more accurate to say that 'photons behave like photons', or 'photons behave like {insert quantum theory description here*}. The behaviour of photons is counter-intuitive, at many levels and in many ways, and you cannot really describe that behaviour in words, or the (mathematical) language of classical physics (unless you are very, very careful to enter all the necessary caveats).

This is, of course, exceedingly weird; however, the best tests we have done to date - and physicists have been doing these tests for over a century now - predict exactly what is observed. So in some sense the universe is truly as weird (and magical?) as quantum theory says it is.

*there are many excellent websites that will provide the (mathematical) description. Be warned though that the math is more advanced that what you will learn at high school.

afterburner
2006-Mar-20, 09:19 PM
Photons have wave lengths, which determine their energy level...
Do gravitons have a similar idea? do they even have wavelengths?
if they do, could we theoretically give them more energy so that the gravitational effect appears to be greater...or less?

trinitree88
2006-Mar-20, 11:52 PM
:D
Photons have wave lengths, which determine their energy level...
Do gravitons have a similar idea? do they even have wavelengths?
if they do, could we theoretically give them more energy so that the gravitational effect appears to be greater...or less?

Gravitons must couple to all the other particles. That's known as a universal coupling. They couple to all the quarks, and all the other leptons...otherwise trying to make QM match GR is impossible. In GR the "curvature" of empty space affects the passage of all particles, both massive, and massless (including photons).
The trick in assigning energy to gravitons, is identifying their characteristics. They must be bosons, with integral spin, like photons, and gluons. They must obey Bose-Einstein statistics, allowing an infinite number in a confined region. They must not only act on matter, but through matter as well (the gravitational attraction of the Earth-Sun system is unaffected by a solar eclipse with a transient intermediary present...the moon...the moon adds it's effect but doesn't diminish the sun's).
As yet there is only one QM fit....the intermediate vector boson...or Z0...in the form of a neutrino/antineutrino pair proposed by Nobel laureate George Gamow in his text "Gravity", Doubleday, 1964. It fits on the diagonal of the Standard Model's SU(5) symmetry published in Scientific American, April, 1981, by Howard Georgi of nearby Boxford, Mass. Neutrinos may have any energy, without limit, as a photon does, according to E=hv....unless you're going to post the minimum wavelength at~ the arbitrary Planck Scale...~10-31cm. Interestingly, at energies less than 1.022 Mev, the Z0, can only take two forms.....photon/anti-photon where it is it's own anti-particle....and a neutrino/antineutrino pair, or graviton.
As every neutrino can interact universally with all the matter, and all the energy in the universe this way, through the neutral current, both on the massive objects and through them...i.e..undiminished effects for solar eclipses...the quantitative modeling of the ambient neutrino sea enables predictions of fluctuations of local gravitational gradients, that is ...gravitational waves.:shifty: Been there. Done that. (On a Unified Field Theory, copyright April 1982, Grav. Research Foundation competition paper, Babson College, Wellesley, MA ).:D Pete

afterburner
2006-Mar-21, 01:44 AM
:D

As every neutrino can interact universally with all the matter, and all the energy in the universe this way, through the neutral current, both on the massive objects and through them...i.e..undiminished effects for solar eclipses...the quantitative modeling of the ambient neutrino sea enables predictions of fluctuations of local gravitational gradients, that is ...gravitational waves.:shifty: Been there. Done that. (On a Unified Field Theory, copyright April 1982, Grav. Research Foundation competition paper, Babson College, Wellesley, MA ).:D Pete

if this is so...the part where every neutrino can interact with all matter and all enery...why is this interaction not the same for objects that are near and that are distant? how does that get explained?

p.s great post :D

Nereid
2006-Mar-21, 01:56 AM
trinitree88, this is the Q&A section of BAUT, where we require that answers be taken from established, mainstream science (= physics, in this case).

As any 'graviton' must, by definition, be consistent with both GR and QM, and as these two highly successful theories are mutually incompatible, any comments on the properties of any such hypothetical particle must be speculative, and must also be described in terms of the theory which incorporates both GR and QM in a way that their mutual incompatibility is aleviated.

If you wish to talk about 'gravitons', please be very clear about your premises especially the unified theory (or theories) within which domain you are mentioning 'gravitons'. Makes sure that any such theory is a mainstream one (the only two I know of are LQG and M-Theory/String-Theory).

Further, promoting ATM ideas (in this case, "On a Unified Field Theory, copyright April 1982, Grav. Research Foundation competition paper, Babson College, Wellesley, MA") outside the ATM section is explicitly a violation of BAUT rules (http://www.bautforum.com/showthread.php?t=32864). You have been warned.

trinitree88
2006-Mar-22, 11:56 PM
trinitree88, this is the Q&A section of BAUT, where we require that answers be taken from established, mainstream science (= physics, in this case).

As any 'graviton' must, by definition, be consistent with both GR and QM, and as these two highly successful theories are mutually incompatible, any comments on the properties of any such hypothetical particle must be speculative, and must also be described in terms of the theory which incorporates both GR and QM in a way that their mutual incompatibility is aleviated.

If you wish to talk about 'gravitons', please be very clear about your premises especially the unified theory (or theories) within which domain you are mentioning 'gravitons'. Makes sure that any such theory is a mainstream one (the only two I know of are LQG and M-Theory/String-Theory).

Further, promoting ATM ideas (in this case, "On a Unified Field Theory, copyright April 1982, Grav. Research Foundation competition paper, Babson College, Wellesley, MA") outside the ATM section is explicitly a violation of BAUT rules (http://www.bautforum.com/showthread.php?t=32864). You have been warned.



Nereid. My apologies, I'll move there. I was merely answering his speculative question on gravitons. Fair enough. Pete.