Dear Constantin,
You haven't read my essay and comments very careful since I have repeatedly argued why there can be no Absolute Time, why we should discard any such notion in physics. Also I do not look solely through the 'eyes' of a photon where I said that A (a massive particle) sees B's state change as soon as it emits the photon, just as B likewise sees A change the moment it absorbs A's photon. Though to the observer these changes seem to be only randomly connected, as if the emission, voyage and absorption are three completely independent events, since A sees B's state change at the time it emits the photon, it certainly is a single event. If A sees B absorb the photon at the time of the emission, then a finite velocity would mean that since nothing is allowed to happen which might prevent B from absorbing that photon, time would have to stand still for as long as the photon is traveling. Though A sees its entire environment change as it emits a photon, if its voyage would take time, then the effect of B's absorption, its change of state on A would again take time to reach A, which seems equally unlikely. If in a Self-Creating Universe particles are informed about each other's state as they owe that state, their properties to their continuous energy exchange, then we cannot determine whether A wants to get rid of some energy, or if B incites A to produce the photon. If there's no absolute time, then it doesn't make sense to ask what causally precedes what, even though we see one event to happen before the other. This only would be possible if there would be an absolute clock, which, to prevent misunderstanding, does not exist as far as I'm concerned. This means that causality indeed requires the existence of just such an absolute time. If in a SCU particles have to create one another, then they are each other's cause and effect, so the change of state of A cannot causally precede that of B.
''The propagation of light never violates causality''
Indeed, it never violates causality but it doesn't obey causality either. We certainly can use light to cause events to happen elsewhere: my point is that by switching on the light, we do not cause a photon transmission but only facilitate the process, just like by switching on the light we don't cause the potential powering the current.
''According to your definition even massive particles cannot be the sources of gravity since their positions are not definite, according to Heisenberg.''
I should have made clear what I mean with this: At my site www.quantumgravity.nl in Chapter 1.2 'Mass, a quantum mechanical definition' I have defined the rest mass of a particle as being greater as its position is less indefinite, as it remains longer within the area corresponding to that indefiniteness, that is, as the probability to find it inside a smaller area is greater. This is why I in my essay I said that the rest energy of a particle depends on its ability to express that energy as gravity, on the definiteness of its position and vice versa. The less indefinite its position is, the greater its mass is, the stronger a source of gravity it is. Since at the 'speed' of light the position of a particle is completely indefinite, it cannot act as a source of gravity. So a beam of light cannot bend space time: only matter can, as you admit as you say:
''The curvature is caused by the energy-momentum of matter.''
This energy-momentum of matter refers to the continuous energy exchange between massive particles by means of which they express and preserve each other's mass. As the particles alternately borrow and lend each other the energy to exist so their energy in every cycle varies, at a rate equal to their energy, they continuously convert from mass to energy and back again, so you might say that it is this alternating in- and outflow of energy which powers the curvature as well as the mass associated with it.
''such events as the photon's emission and voyage never can be ''a single event''
Well, it is a single event in the sense that the change of state of A and that of B are coupled by the photon transmission, just like paying money for something is a single transaction. That the transmission leads to different events, effects at A and B does not mean that the transmission consists of separate, independent events. Since to a massive observer A and B are separated in space, to him the photon emission at A and its absorption at B are separated in time. As to the photon there is no distance between A and B, to the photon its transmission is instantaneous. The symmetry between A's point of view and that of B, that according to A, B changes at the time it emits the photon, whereas according to B the emission happens as B absorbs the photon, means that even though we certainly measure at duration, it doesn't make sense to ask what causally precedes what.
Regards, Anton