Medium of Light

There is no luminiferous aether but that doesn't mean that space is empty. It is made up something which provides medium to light. Einstein says any such things would slow down the light. Yes it is slowing down the light that is why light is limited to 3,00,000 Km/s.

Speed of a wave depends on the properties of its medium. Space is determining the speed of light and thus the scale of time that is why there is a sequence of events in the universe. In the absence of this limit to the speed of light, all events would have happened instantaneously.

Mass Space Equivalence

Let's take a hypothetical modal of the universe. In this modal we have two analogies:

1. Water is analogous to the space in real world.
2. Bubbles of water vapor analogous to the matter in the real world.

Now when water vapor will change into water; only the energy, being released; will be measurable because we have no way to measure space(water in this case). Nobody will say that water vapor (matter) is converting into water (space). People will say that water vapor (matter) is converting into energy.

Now let's talk about the real world. Same as the above example, the space is intangible to us, so when mass converts into space; we only see the energy getting released and thus we say that mass is convertible into energy.

Currently this is only my hypothesis, I want to research on this, if I could get a chance.

Relativity of Space

Perfect vacuum is just the origin of our reference frame of space. It is not the absolute zero. It means that space can be negative too. At least to some extent if not to the negative infinitive.