"Our Universe does not have a real cosmic medium". "Light is fundamentally dual, comprising a wave aspect and a
particle aspect". These two statements are jointly present in most physics textbooks, but they are logically incompatible.
The argument against mediation is based on the outcome of the Michelson-Morley experiment. It only works under the
assumption that light is a running wave in the ether, similar to a sound wave in the air. Without such an assumption,
invariance only proves that the speed of light is not the speed of a wave. If light has a dual nature, then the speed of light
is the speed of the particle aspect. In quantum mechanics, it can be described as the speed of the photon. Classical
models would suggest that the speed of light is equal to the rate of mutual generation of electric and magnetic fields
across space. Alternatively, the speed of light can be described as the speed of a train of fields, propagating like a stream
of particles. There is no room for running waves in these models, except as a constituent element of static fields. For a
coherent account of our knowledge, the second statement should be preserved, and the first one should be rejected.
We have performed several original experiments, in order to investigate the nature of optical interference. In some
contexts, the assumption that light beams suffer perturbations during their interaction is the most plausible. In others, the
assumption that they do not is more appealing. Yet, the observable outcomes of both models are compatible with each
other, in theory as well as in experiment. We conclude that they work equally well for the purpose of making physical
predictions, and that each of them is logically valid. However, their interpretive value is not equal. If we assume that
light beams cross each other unperturbed (even at the microscopic level), then we run into theoretical complications and
even paradoxes that are not otherwise present.
In quantum mechanics, light cannot be described in terms of waves and particles at the same time. However, the
question about light "as it really is" implies a description that is independent from the constraints of measurement. It is
rather preferable to incorporate both aspects in a causal ontological theory, especially if it simplifies explanation and
improves predictions. Hence, the photon can be described as an extended longitudinal association of discrete indivisible
constituents, which are held together by the effect of their own waves on each other. The same waves can then be used to
interpret the force of interactions between different pulses of light, or between light and matter. The concept of wavemediated
interaction between sub-photonic entities is entirely consistent with the observations of quantum mechanics.
The key is to assume that elementary sources of waves never collide, and that they have constant parameters. Novel
experimental implications follow from this approach. For example, the speed of propagation of changes within magnetic
or electrostatic fields may not be equal to the speed of light. Also, interference fringes should be detectable beyond the
volume of overlap of two non-entangled beams, but only in special experimental settings.