Why are gravitons so sparse?

Question

LIGO and LISA are set up to detect gravitons as if they were very sparse. If all masses are interacting via gravitons, shouldn't there be a lot of them?

Maybe what I'm asking is: is this just a matter of weeding them out among the effects of other things (which would explain why LISA is waiting for a massive event)? or are they actually that spread out (then why?)?

Please refrain from the excuse that gravitons are hypothetical. They will remain that way if you continue to dismiss them.

And I guess I might have gotten LIGO and LISA confused with something else. Still I'm wondering why these events seem so rare.

Answer 1

gravitons are so weak in relation to the other forces that detection of them becomes more of a sensitivity issue than a collection issue compared to the EM, large, and small forces gravity is so weak that detection becomes very problematic.You can overcome the gravity of the entire earth with a 2 oz. magnet and light up a city with the energy of a speck of nuclear fuel ...gravity doesnt stack up
its by a matter of LARGE exponents that gravity is weakest(i think it might be just a fluke that we have it at all)and that is why i believe gravitons are so hard to detect

Answer 2

Nope. They are looking for gravity waves, not gravitons. A graviton is a quantized unit of gravity and likely unobservable with any detector imaginable. A gravity wave is a quasi-classical low field solution of Einstein's equations. A gravity wave can be thought of as the superposition of an enormous number of gravitons, but the individual gravitons can not be resolved with a low energy experiment like LIGO or LISA.

LIGO is an experiment which is on the limits of experimental art AND the limits of a theoretically expected gravitational wave spectrum. You can think of it as a marginal attempt to see things that we can be pretty sure off for theoretical reasons. I would expect that there will be results from LIGO over the next few years ( I have to see what their publication schedule is) and that steady upgrades and additions will allow to push it into the realm where it will be more than just a null experiment (which is should be by now).

LISA has to be built first (I don't know what the current state of funding is) and will measure lower frequencies than LIGO.

Answer 3

Unambiguous detection of individual gravitons, though not prohibited by any fundamental law, is very hard with any physical detector. The reason is simply the extremely low level of interaction of gravitons with physical matter. For example, a detector designed to measure the mass of Jupiter with 100% efficiency, placed in close orbit around a neutron star, would only be expected to observe one graviton every 10 years, even under the most favorable conditions. It would be impossible to discriminate these events from the background ocean of neutrinos.

So the answer to your question is yes, it is a question of weeding them out amongst the effects of other particles and forces.

Answer 4

Gravitons are not sparse, they are non-existant...at least until someone observes one. To date, gravitons, messenger particles carrying the attraction message from mass to mass, are strictly hypothetical.

On the other hand, bent space as the cause of gravitational effects (like attraction and accleration) has been observed...it's the source of the so-called gravitational lenses. So bent space, stemming from relativity, is a true theory since validating observations have been made.

Physicists have invented gravitons because they seem to make sense; after all, the three other fundamental forces (strong and weak atomic, and electro-magnetic) do have observed messenger particles: gluons, bosons, and photons. So why not gravitons for gravity? [See source.]

These hypothetical gravitons are hard to find because they are very very weak. In fact they are orders of many magnitudes weaker than any of the other three forces. And you know how hard it is to pick up a weak radio signal, just imagine picking up something 10^36 times weaker than a weak radio signal....that's the graviton. So they're not sparse so much, as they are very very..........very weak.

One WAG for why they are so weak, from String Theory, is that much of each graviton actually lies in higher dimensions. And the little bit of strength we do see comes from the little bit of each graviton that is in our universe; while the rest of each graviton lies in another, parallel universe. [See source.]

Answer 5

I think they're looking for gravitational waves. E.g. abnormalities in the space from stuff like supernovas.