Twighlight
Quantum Scribe
I'd define an entity as something that has a discreet existence of it's own....such as an atomic particle.
However it's not as simple as that....as most particles only 'exist' relative to others via exchange of other particles ( such as virtual photons ). A particle that does not exchange in such manner quite literally does not exist !
It's a concept that is right at the heart of quantum mechanics. There is no absolute 'existence'. Everything exists relative to everything else, in a complex web of interchange of particles. Dark matter, for example, is almost on the boundaries of non-existence......if it did not interact gravitationally then relative to our universe it would not 'exist' at all ( but could still exist relative to other particles we know nothing of ).
The complicating factor is that all this exchange of particles takes time. Even gravity is mediated by exchange of virtual particles, gravitons, which travel at the speed of light. So gravity is not an instantaneous force. In fact, if any of the forces of nature were instantaneous......the entire history of the universe would be over in a split second. We rely on the relatively 'slow' speed of light for the universe lasting billions of years. In a sense, the speed of light......which is the speed of exchange of virtual particles....is the speed of time.
That is why one cannot seperate time from physical entities. Those entities only exist by exchange of particles, and that exchange takes time.
On a much deeper level, this means that the entire universe has no absolute 'existence', but we see only that much of it that interacts with us at any one moment. So 'the universe' keeps popping into existence every split second via particle interchanges as the exchanged particles reach us......and this is smudged over a period of time as different objects have different distance. So the idea of a single discreet 'universe' out there is very illusory indeed.
