Re: What is the Current Status of the Graviton?

Aaron Denney wrote:
On 2006-02-22, Mark Fergerson <nunya@xxxxxxxx> wrote:

sharp@xxxxxxxxxxx wrote:

We haven't even detected gravity waves yet. There are reasons to
believe we may never be able to detect individual gravitons, assuming
they exist. Speculations about this involve things like detectors the
size of Jupiter parked near neutron stars, and trying to get a
detection within the lifetime of the universe.

OK, so tell me why Robert L. Forward's work with coupled rotating gravity gradiometers doesn't count as generating and detecting gravitational radiation?

Because it works just fine for a static field. His "rotating cruciform
gravity gradiometer" (AKA Forward Mass Detector) was inspired by
thinking of how to detect mass by using GR effects and thinking:
"Hmm, gravity waves would be strong enough to detect easily if I could
move that mountain really quickly. Hmm. Relativity. What if I move
the detector really quickly?"

The idea, as with all great inventions, is simple, yet hard to come up
with. Attach two beams at their centers, and put in springs holding
them at right angles. Attach large masses to the ends. Spin up.
Measure the angle they make. If it changes with a period half as long
as that of the rotation, you've got yourself a nearby mass. Fourier
trickery and under and over driving can extract a bit more information.

The specific experiment(s) I'm thinking of involve two such detectors, except one is used as a "transmitter" by feeding signals to the piezo benders on the four arms, modulating the arm angles. The detector (analyzes voltages produced by the piezo benders) some distance away presents an output following the input. Since Forward went to a lot of trouble to eliminate EM and mechanical coupling, how'd the signal get from here to there if not via something strongly resembling gravitational radiation?

And no, I can't find that paper on the net either. While he was alive his website had lots of his stuff as d'l'able PDFs but since his death they went away. AFAIK they're now only available in dead tree form:

http://www.robertforward.com/UAH.htm

I have it archived somewhere on an old HD. If I ever find it I'll be happy to tell you which paper references it.

Gravity is an incredibly weak force. There are two things that make it
significant. It has an infinite range which allows the contributions of
a lot of mass to add up. And it only has one kind of "charge", so
there are no opposite charges whose effects can cancel each other out.

Yep, no dipole waves; lowest order possible is quadrupole.

AIUI, that's true, but not due to infinite range or one kind of charge,
but rather that gravity is a tensor field / is mediated by a spin-2
particle. One can, for example, use only positive electric charges to
create dipole radiation, and E&M also has infinite range (apart from
shielding).

Yep. I should have clarified.


Mark L. Fergerson

.

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