Okay, here’s the concept. Is it just “empty space” or something else? But since relativity; we know that space cannot, and does not exist without time, And it’s a continuum "spacetime" rather than space and time. So does it means that vacuum is just “empty spacetime” There arises a logical contradiction. Vacuum should be “empty spacetime” as its concept started after big bang. We say there was nothing before big bang; we don’t say there was vacuum before big bang. (But wait! “The nothing” is what we say vacuum. So does that mean there was vacuum before big bang?) So, according to this concept vacuum should be just "empty spacetime". let's take the other one. If vacuum were to be “empty spacetime”, and then let’s say we have a region of spacetime, where there is “nothing”. Let’s pass a ray of light form this region, the regions is still in vacuum, as we know that light can travel thru vacuum. But spacetime is no more “empty” as we’ve got an event “the passage of light ray from that region” that is in occurrence. So, as spacetime is no emptier any more but vacuum is still there, this implies that empty spacetime cannot be a vacuum. IS not this a contradictory result? Also if vacuum is none of these, then what else?