. GR predicts gravitational waves and QM requires that every kind of wave is associated with a particle. So if we have gravitational waves we must have gravitons.

Steve, Why do we believe that it must be transmitted by some sort of 'particles'?

I look at it as a field in three dimensions observed in time.

The interactions we see by gravity will be 'ripples' in the field propagating at 'c'.

You could see it as the ocean, if you allow for waves/ripples to move in any direction they choose in this 3D-medium.

Perhaps one could think of it as a unlimited amount of 'surfaces' 360 degrees (3D).

Although some insist on photons containing invariant mass I still differ between matter and photons.

We use the expression 'invariant mass', as I see it, for that 'ultimate' definition of matter.

To my eyes this definition is not as clear as I would have wished.

Maybe I'm just not getting it:)

Photons contains something 'styled' as momentum which is a force expressed in the velocity (direction & speed) of the photon.

We know through experiments that momentum is there, there is no experiments proving any invariant mass though, that I know of.

You say "Photons are always moving so they have no rest mass"

Rest mass is a definition exclusively pertaining to a single particles invariant mass.

Anything larger than that is nowadays defined as 'proper mass' or 'invariant mass'.

You are definitely correct in that they do not have any rest mass, but I will presume that you meant it this way:)

The reason why a photon can move at 'c' in a vacuum is to me that it is a truly 'mass less' particle.

Am I correct in assuming that it was so you thought?

Then you said that "since they are always moving they have energy and energy and mass are in principle interchangeable. Therefore the graviton can interact with photons because, to a graviton, a photon looks like mass."

Here you touch several points of interest for me.

1. Does photons come in different energy quanta?

2. Or is its energy levels created by comparisons done between different 'frames of reference'.

If we look on a flashlight with variable 'strength' we can produce different types of waves from red to blue shifted. And that we observe being 'at rest' with this flashlight (proofs obtained relative being in the same 'reference frame' as our flashlight:)

So it seems that light quanta can come in different energies.

If we want to dispute that we seem to end in a 'place' with an unlimited number of reference-frames.

Or it could be seen as if we let every peak in a wave represent the particle aspect of a photon then one could say that blue shifted light is represented of a larger amount of photons inside a 'time slice' as compared to a lesser amount when 'red shifted'.

I'm not sure if there is any experiments proofing which is correct here.

There should be:)

But red/blue shift is also a direct result from our reference-frames interaction with any other.

And it's not possible to proof whose frame that is moving relative the other.

As long as we are talking about uniformly moving frames.

From within an accelerating frame you would be able to define a certain gravity well displaced from your object of acceleration.

Still, without a knowledge of your objects 'mass' you would be hard pressed to guess how much of that would be 'expressed' in the 'blue shift' of the light coming at you from the outside.

Seen this way we can't be sure on whether any light coming at us, from outside our own reference-frame, will be as we perceive it.

Although the light leaving our reference-frame will be at rest with us and therefore seen as it , more or less, internally 'is'.

But, in a accelerating 'reference frame' as a spaceship, the light even when seen from inside will be perceived as red--blue shifted.

One could see that as an unlimited amount of 'reference-frames' inside that one 'reference-frame' :) I think.

And the photon does not, to my eyes, contain any mass, only momentum, and so seen they are not 'interchangeable' entities (gravitons/photons).

Gravitons is still an unproven idea, even if we succeed to proof the Higgs particle.

"the Higgs is a postulated particle. It was born as a mathematical trick in order to solve some problems concerning symmetry in quantum field theory. The Higgs has mass because we defined it like that. The Higgs particle gives mass to elementary particles via it's interaction with these particles. This interaction can be expressed in terms of a coupling between the Higgs field and the elementary particle field.

The coefficient of the product of these fields is the mass of the elementary particle. This is just how the QFT formalism works. This is all very nice but the question remains as to whether this is true. This is why many scientists await the first experimental verification of this system of spontaneous breakdown and mass generation. Also, elementary particles need to be massless when in gauge theory because of symmetry reasons."

"The Standard Model falls short of being a complete theory of fundamental interactions because it does not include gravity and because it is incompatible with the recent observation of neutrino oscillations."

From that statement to assume that it therefore craves to be included

"In particle physics, the Higgs boson is a massive scalar elementary particle predicted to exist by the Standard Model."

Is a rather great jump to me.

So far I know it there was no Higgs boson 'predicted' by Einstein?

There is an absence of explanation for gravity as a 'force'.

But that's not the same to my eyes.

" Einstein tried to form a generalized theory of gravitation that would unify the gravitational and electromagnetic forces (and perhaps others), guided by a belief in a single origin for the entire set of physical laws. These attempts initially concentrated on additional geometric notions such as vierbeins and "distant parallelism", but eventually centered around treating both the metric tensor and the affine connection as fundamental fields. (Because they are not independent, the metric-affine theory was somewhat complicated.) In general relativity, these fields are symmetric (in the matrix sense), but since antisymmetry seemed essential for electromagnetism, the symmetry requirement was relaxed for one or both fields. Einstein's proposed unified-field equations (fundamental laws of physics) were generally derived from a variational principle expressed in terms of the Riemann curvature tensor for the presumed space-time manifold.

In field theories of this kind, particles appear as limited regions in space-time in which the field strength or the energy density are particularly high. Einstein and coworker Leopold Infeld managed to demonstrate that, in Einstein's ultimate theory of the unified field, true singularities of the field did have trajectories resembling point particles. However, singularities are places where the equations break down, and Einstein believed that in an ultimate theory the laws should apply everywhere, with particles being soliton-like solutions to the (highly nonlinear) field equations. Further, the large-scale topology of the universe should impose restrictions on the solutions, such as quantization or discrete symmetries."

He also predicted gravitational waves.

See here.

http://www.ligo-wa.caltech.edu/ligo_overview.htmlhttp://en.wikipedia.org/wiki/Gravitational_waveBut the Higgs field is a rather cool idea if it is correct.

http://www.hep.yorku.ca/what_is_higgs.html---------

Looking at Karens original question:)

My answer would be that we need to look from the right perspective here.

Otherwise it gets very complicated:)

The photon does not bend to mass, the photon just follows the energy-wise 'shortest/cheapest' path.

Space is a 360 degrees in -3D- roller coaster with an unlimited amount of peaks and dips (gravity-wise:)

Created by and adapting too mass (and acceleration), seen by us in time.