Simple answer: we have no way of knowing in absolute terms...at least as far as what we understand to be life.
Thus we can only truly understand everything in relative terms.
Fundamentally because we cannot even answer the question, do we even perceive the same? i.e does the colour red look the same to me as it does to you?
Those that accept the need for absolutism to exist, often fill it with a creator/deity/force of some kind....since only an absolute can even answer this question....from which stems everything else.
When you talk of virtual reality, simulation etc, these are also relative constructs we have conceptualised. In the end it would depend on whether the reality is an open set or closed set (i.e does reality have bounds).
If its an open set....chances of it being understood (any fundamental aspect of it e.g. existence/non-existence) is always going to be zero. Since with it being unbounded, we accept there are infinite possibilities (thus always an infinite unknowns)....given any finite number/infinity = 0. Even if we last billions (or some finite) number of years, the relative sum total (knowledge ratio) of what we know in the end is going to be zero in that case. Even if we last an infinite number of years, it will still be 0 because that time infinity by set theory is not mapped one to one with the knowledge infinity (multiple infinities theory - ref. Georg Cantor).
If the reality on the other hand is a closed set, the drop in an ocean analogy prevails. We just over time expand the drop to be the ocean. Provided there is enough time, it can be done (drop = ocean itself)...and we can potentially answer what reality is in the end (if is in deed answerable by having all information in the bounds). But even then we only answer it for what exists within those bounds. Could we ever answer for whats outside the bounds? Do the bounds even matter in the first place? Are there other realities? Are there essentially 0? Or something completely foreign to our approach and understanding potential? It again boils down to the concept of infinity. Thus I don't think we can ever know in the absolute sense.
It is talked about, quite hauntingly, in one verse of the Vedas:
Then even nothingness was not, nor existence,
There was no air then, nor the heavens beyond it.
What covered it? Where was it? In whose keeping?
Was there then cosmic water, in depths unfathomed?
Then there was neither death nor immortality
nor was there then the torch of night and day.
The One breathed windlessly and self-sustaining.
There was that One then, and there was no other.
At first there was only darkness wrapped in darkness.
All this was only unillumined water.
That One which came to be, enclosed in nothing,
arose at last, born of the power of heat.
In the beginning desire descended on it -
that was the primal seed, born of the mind.
The sages who have searched their hearts with wisdom
know that which is kin to that which is not.
And they have stretched their cord across the void,
and know what was above, and what below.
Seminal powers made fertile mighty forces.
Below was strength, and over it was impulse.
But, after all, who knows, and who can say
Whence it all came, and how creation happened?
the gods themselves are later than creation,
so who knows truly whence it has arisen?
Whence all creation had its origin,
he, whether he fashioned it or whether he did not,
he, who surveys it all from highest heaven,
he knows - or maybe even he does not know.
