A few questions to ponder and discuss:
Does the past exist?
Yes, as a set of occupied space and abstract relationships the present
Yes, however only based on best understanding the nature of occupied space's eternal existence, flow of time --Observed -reality- Time { OT } via our experiences of the latter
Yes. Ex unicorns exist as occupied space drawings pixels on a screen etc, that were conceived via human experience, and that humans access to Meta-space mind/intellect/conceptual abstractions.
I think about an occupied space experience ergo I exist as an occupied experience with access to Meta-space mind/intellect/concepts and ego.
If something will never be observed, does it exist?
Does not exist for humans, until we have quantised it. I remains speculative until quantization occurs
If you have heard that something has been observed, but never observe it yourself, does it exist?
It exists as Meta-space mind/intellect/concept via an occupied space humans experience and passed on to another human via communication in whatever method of occupied space transfer of information.
There exists three, primary kinds of cosmic existence, with the #2 being a moot point of existence:
1} eternally existent, Meta-space mind/intellect/concepts aka abstractions,
---------------conceptual line of demarcation------------------------
2} eternally existent, macro-infinite and truly non-occupied space, that surrounds/embraces the following,
3} eternally existent, finite, occupied space Universe.
It does not get any simpler than this Cosmic Trinary Set, however, there exist subsets of Meta-space truth, and greater number of subsets of occupied space Universe, if we discount all of the complementary Meta-space aspects of those differrentiated subsets of occupied space Universe.