This is a standard semiclassical motivation as to why gravitons most probably exist (I think from Steven Weinberg “gravitation and cosmology” but I have since long lost the book so I am not sure): In the limit of weak gravitation GR looks similar to the Maxwell equations. In particular there should exist gravitational waves.. (Have not yet been detected experimentally but if GR is (at least approximately) correct they should exist.) This means that you could in principle build a gravitational wave microscope. Say you want to measure the position of a test particle using this microscope. Now if gravitational waves were actually classical you could use arbitrarily feeble waves and thus arbitrarily small recoil on the test particle. And thus measuring position and momentum of the test particle with lower unaccuracy of position times momentum (along a given direction) than allowed by the Heisenberg uncertainty relation. But if gravitational waves are quantized in gravitons of energy = h times oscillation frequency Heisenberg uncertainty relation will be satisfied (Heisenberg’s original semiclassical derivation goes through for any wave quantised like this).
I do agree with you that GR cannot be a fully correct description of reality on a quantum level (because of this and other issues, especially many worlds). I was saying that we should take the structure of GR into account when building a unified theory, rather than just starting off with the assumption that gravity works exactly like all the other forces.
This is what the proponents of the loop approach usually stress—demand that the theory be background independent, or general covariant (I am not sure whether there is some important difference between the use of these terms).
This is a standard semiclassical motivation as to why gravitons most probably exist (I think from Steven Weinberg “gravitation and cosmology” but I have since long lost the book so I am not sure): In the limit of weak gravitation GR looks similar to the Maxwell equations. In particular there should exist gravitational waves.. (Have not yet been detected experimentally but if GR is (at least approximately) correct they should exist.) This means that you could in principle build a gravitational wave microscope. Say you want to measure the position of a test particle using this microscope. Now if gravitational waves were actually classical you could use arbitrarily feeble waves and thus arbitrarily small recoil on the test particle. And thus measuring position and momentum of the test particle with lower unaccuracy of position times momentum (along a given direction) than allowed by the Heisenberg uncertainty relation. But if gravitational waves are quantized in gravitons of energy = h times oscillation frequency Heisenberg uncertainty relation will be satisfied (Heisenberg’s original semiclassical derivation goes through for any wave quantised like this).
I do agree with you that GR cannot be a fully correct description of reality on a quantum level (because of this and other issues, especially many worlds). I was saying that we should take the structure of GR into account when building a unified theory, rather than just starting off with the assumption that gravity works exactly like all the other forces.
This is what the proponents of the loop approach usually stress—demand that the theory be background independent, or general covariant (I am not sure whether there is some important difference between the use of these terms).