holograms
Identity is like a hologram.
The holograms I've made are just extremely complex lenses: the 3D image itself is a visual phenomenon made of light reflecting off of ridges produced by light in a photosensitive emulsion (which is then developed, like camera film). It does not exist without the light waves hitting it, and it is composed of them.
The hologram as a concept is best described as a perfect recording of the way that light was reflecting off of an object at one point in time.
When a person goes away, we lose an entire universe: the way the cosmos was viewed from those angles, in those contexts, at those points in time.
Your idea of someone else is a hologram of them. You carry in your mind the way you perceived the world reflecting off of them.
There's a popular conceit that each part of a hologram (in the sense of "3D image in a glass plate", like I used to make) contains all of the image information of the entire thing. If you break it, each shard will still contain the information of the entire object. That's not strictly true: the hologram is like a window looking out at a brick wall. Depending on how close the wall is, and how large your window (shard) is, the amount of wall that you can see by changing your viewing angle varies.
A person you don't know very well is super-low-res. A person you've lived with for years is much clearer, and you have a much bigger window to work with. And you get to observe them from different vantage points by interacting with them in different environments. But you still only see the sides that are shown to you.
This is sort of what the dream tarot project was about: I was asked to create a family portrait, but was studying abroad. So, I built a set of cards that attempted to convey the archetype that each of my family members (and some other symbols) became, when reduced to rough, high-contrast icons by my sleeping brain. These are not nearly as complex as my actual mental image of each person/thing, but they follow the same concept: the "aunt" that I carry around in my brain is not the same as the actual person out there, not by a long shot, and portrays only the sides of her (like the moon) that I see from my vantage point in the world.