*Reference: Fundamentals of Physics*

Newton defined momentum as the product of mass and velocity. But then we find that light has quanta (amount) in addition to velocity, and it also has momentum. Light has no mass, but the light quanta must have some property very similar to mass. The property common to mass and quanta has to be inertia (resistance to motion). In the absence of inertia, the velocity would be infinite. The finite velocity of light tells us that it must have inertia.

Let’s call the mass-like property of light quanta as its “consistency”. The English dictionary defines “consistency” as a degree of density, firmness, viscosity, etc. For example, we notice honey to have a thick consistency. The light quanta is not made of atoms like honey is. So, its consistency is extremely small. But the light quanta can coalesce with each other much like the drops of honey can. Therefore, photons will act much like fluid in that they can split and coalesce together as we see them do in the double-slit experiment.

Momentum provides us with the feeling of impact. It is this impact that underlies our sensations. Sensations make up our sense of reality. In Newton’s time we associated momentum with mass only because Newton mostly dealt with matter. But since then, we have been able to detect the momentum of light through very fine instruments. We have found that light can exert pressure. Even though this pressure is too small to be sensed by us; still, it puts light in the category of substance like matter.

In case of electrons, the consistency is much higher than that of light. In the atom, the consistency of electrons has been measured as 1/1836 of the mass in the nucleus. Up to this point, we have defined all the sub-atomic properties mathematically only. Now the concept of consistency brings all those mathematical interpretations closer to reality. We can visualize the electrons within the atom as forming layers of thin shells of slightly different consistencies.

We can now identify mass as the property of very high consistency. We can now see nuclear material, electrons, radiative energy and gravity forming a spectrum of decreasing consistency. We may find a direct relationship between consistency and frequency on this spectrum. We may call this spectrum—the spectrum of substance.

On this spectrum, momentum may now be defined as the product of consistency and velocity, rather than mass and velocity. This explains the momentum of light in the absence of mass.

On this spectrum, inertia may be associated with consistency in a more generalized sense. This explains why the speed of light is large but still finite. Absence of inertia will inevitably lead to infinite velocity.

On the spectrum of substance, we notice that the lighter (thinner) is the consistency, lesser is the inertia, and the higher is the natural velocity. There is an inverse relationship between the consistency of substance and its velocity. So there is an undiscovered universal constant that is more basic than the speed of light.

We may form a hypothesis that the speed of light ‘c’ varies infinitesimally with frequency of light, but it is virtually a constant when viewed in the inertial frame of reference of mass. Similarly, the inertial mass of objects changes infinitesimally with changes in their acceleration, but it is impossible to detect.

The “rest mass” of an object is measured when it is moving at a constant velocity (zero acceleration). This applies to material objects only. Subatomic particles and light quanta of all consistencies are always accelerating because their paths are always curved. They all are part of whirlpools, at the center of which are the nuclei of atoms.

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