Photons carry energy and so have equivalent mass due to e=mc^2.
Therefore photons are affected by and effect ambient gravitational fields as they travel through the universe.
In other words, if a photon passes by a star, the gravitational field of the star alters the course of the photon. Despite the fact that the masses of these two objects are vastly different, we can still consider them as two particles influencing each other with their relative masses in a form of transaction between the two particles.
So, as in all such gravitational transactions, the photon also alters the course of the star. Even though this is a minute effect, it still exists.
Also, since gravity is an inverse square law, its effect never totally disappears no matter what the distance between the two interacting masses (although it might be that there is some kind of quantum cut-off once the field forces become weak enough).
So as a photon travels, it is subject to gravity fields from several sources, such as:
* virtual particles (pairs of particles which pop into and out of existence again apparently spontaneously in so called "empty" space, predicted by quantum theory)
* Other photons also traversing the universe
* atomic particles such as protons, neutrons, electrons, neutrinos, etc
* atoms and molecules in the surrounding space (maybe one hydrogen atom per cubic meter?)
* Larger masses such as stars, planets, moons, asteroids, dust, comets, galaxies, black holes, etc
* Possibly dark matter whatever that turns out to be
Now, here is the key point of this idea:
Lets imagine a photon passing close by a neutron.
As the photon approaches, its path is bent towards the neutron, and its energy increases as it "falls" along a changing vector past and towards the neutron. It is effectively blue shifted in the same way it would be when falling towards a star.
At the same time, the neutron is attracted towards the photon and increases its energy by "falling" towards the photon.
As the photon passes the neutron, it starts loosing energy again through gravitational red shift, just as it would lose energy when leaving a larger mass such as a star.
One might assume that the energy gained from blue-shifting on the inbound path exactly equals the energy lost by the red-shifting on the outbound path.
But this seems not to be the case, because during the transaction, the neutron has moved towards the photon in the mutual attraction. This introduces an asymmetry between the inbound and outbound paths of the photon. When the photon leaves the neutron it is nearer to the neutron on average than it was on approach.
Due to this asymmetry, the photon appears to experience a small net red-shift, as it is red-shifted a bit more than blue-shifted during the transaction.
This may well be an absolutely minor effect, but it does seem to exist. And since it is affected by the gravitational effect of every mass in the universe, the effect is multiplied by some large factor.
There may one or more experiments or simulations that could verify this idea.
I invite comment on this topic, you can also email me at jjalexand@yahoo.com
Thanks for reading this far :)
