I am just taking about SPACETIME. The physical quality of space is 3D extension.

The concept of space-time originates from multiplying time times the speed of light turning time into distance. Time is a dimension of space in the Theory of relativity.

Time is the "fourth" dimension in actual fact.

Here is an excellent answer with regards to the reality of spacetime.

https://www.quora.com/Is-spacetime-... is no absolute frame,yeah space-time is real.

Most, if not all, scientific theories are behavioral in nature as opposed to existential. By this I mean

**theories are models of behavior. **They describe how things behave they do not describe what things are. Einsteins General Relativity Theory provides exceptionally high resolution predictions of experimental and observational outcomes. As such it is a powerful theory that exhibits a strong and useful relationship to underlying reality. His “Elevator” thought experiments reveal much about the relationship between inertial and gravitational mass and the nature of their equivalency. While they do provide deep insight into some very important experiments they do not explain why a static mass has the same properties as an inertial frame under acceleration.

Here is where Einstein’s real genius comes in. He realized that Euclidean geometry could not accommodate this relationship but a geometry with additional dimensions could. He turned to Riemann geometry and Minkowsky space and incorporated these concepts into his field equations, and it worked!

So here is the rub.

**The mathematics of curved space-time provides a testable strategy to validate Einsteins theory and when tested the results are consistent with his predictions.** So what does that mean? At the very least it means that his theory bears, as I said,

** “a strong and useful relationship to underlying reality.” **Does that mean these extra dimensions are real in a physical sense or that something else is going on? The honest answer is “Nobody knows”. So far the tests of actual hypergeometries are inconclusive

**but the observational and experimental results are consistent with their reality.**

Another answer by a physicist......

In the 18th Century Bishop Berkeley promoted his idea that our world of experiences is an illusion, and that the “true reality of God and his creation” was immaterial, more or less the philosophy we would today call Idealism or even Solipsism.

The philosopher Samuel Johnson, after a talk with the Bishop, stood up in front of a large stone, kicked it as hard as he could with his foot and famously said “Bishop, I refute your theory thus”. The stone was real enough to injure his foot.

What is “real”?. It’s real enough for us, so we need to account for it. Obviously it’s also a concept, as so many other things are. Spacetime is what makes our physical world possible, what causes the singularity of events. Without spacetime all events would (in principle, read below) be one and only one.

Of course you can also say that spacetime is just a useful system of coordinates which we use to make the distinction between events.

Several respected scientists have however developed and are developing theories in which spacetime is not fundamental but it is a sort of emerging property. The most famous is probably the holographic principle developed by Juan Maldacena, in which a 2D surface encodes all the information of the events which we perceive as a 3D universe. Other approaches propose similar concepts, that spacetime is simply a sort of relationship between events which can be seen as simply a mathematical relationship, which to our perception takes the shape of a 3D geometry. Some similar theories propose that spacetime is a relationship which fundamentally describes the entanglements between quantum particles. Depending on the details of all the entanglements all the particles appear to us as spatially and/or temporally separated when they are not in the “true real underlying mathematical world”. This could explain the famous quantum “spooky action at a distance”.

Now in the times of virtual reality we can see that the appearance of a 3D spacetime can indeed be generated by a computation system.

**So yes, all possibilities are open, but spacetime does exist for us, that much is clear. Whether it is a fundamental “4D volume in which events unfold” or not, that’s another story.**