You Only Exist In The Moment
The moment is all there is.
Relativity makes this kind of confusing when applied to everything, but let's do what we do best and focus on ourselves:
You only exist in the moment. You are an instantiation of the most complex (per unit of volume) thing in the universe. While obviously you need a ton of bits to specify a galactic cluster, if we do this on a per-litre basis, you need the most bits to specify a hominid.
And that's seemingly obvious! We aren't just a complicated, three-dimensional structure of cells, with an incredibly dense and interconnected compute unit (the brain), we also exhibit interesting behaviors across time: weddings, technical interviews, the olympics, and speaking in tongues are a quick sample of the diverse set of sequences we can take part in, each of which really require a lot of information to pin down fully.
To be coherent across time, we leverage memory and imagination. We plan for the future and recall the past. However we don't have much depth in the moment. Verify this yourself:
Quick Experiment:
Go back and read the last paragraph. How many words are you saliently latching onto as your eyes go across the screen? It feels like more than one, but it's not something as large as ten. It's like we are the head of a record player with some width, but we obviously can't read off the entire record at once and work with that information. Instead we have faculties that allow for us to take in small slices of moments and build structures to reason about larger temporal objects. Kind of like building more records on the fly and then playing them back.
But what are you? You could answer this in a number of ways. You could be a self-reference, so some sort of reflexive concept in the brain that has interesting properties when it appears in your phenomenological context window. Arguably, you could also be the tape head which has some very narrow temporal width, or put more precisely, the cohesive set of qualia that keeps appearing at each moment in time.
I would argue the latter is a much better answer, as it's an actual answer: If you are just the thing referred to when "I" or "me" appear in your context window, then it's pretty reasonable to ask, well, what are they referring to? And I think if you unravel that question you quickly come to said set of qualia.