Time in a timeless universe
A conversation between Alice & Bob
(3:18 PM) Bob: Alice, tell me again about this 'timeless view' of physics. I don't think I get it.
(3:20 PM) Alice: Well, in the 'timeless view', the future, past and present of any system are equally real. For example, in general relativity, the fundamental objects of the theory are worldlines – a worldline is the path an object traces over 4-dimensional spacetime. The state of an object at a particular time is but a point in the object's worldline.
(3:22 PM) Bob: So why does my consciousness pick out this particular moment to exist in?
(3:24 PM) Alice: It doesn't: you have conscious experiences in the past and future too. But this version of you exists in 'the present' (i.e. 3:24 PM). The other versions of you that exist at different times are equally conscious, but you are not them.
(3:26 PM) Bob: But why does it feel like my consciousness jumps from moment to moment?
(3:28 PM) Alice: It doesn't jump. The state of your brain at this moment includes memories of things that happened in the past. But nothing physical 'jumped' from the past to the future. The fact that you are asking that question shows you are thinking about the present as something with a preferred status, whereas the universe treats all moments as equally real.
(3:32 PM) Bob: And yet, my consciousness has flowed from the past to the present because, at this moment, I have a conscious experience.
(3:34 PM) Alice: You do, but the version of Bob at timestamp 3:24 PM also had a conscious experience. A hypothetical observer who possessed a script of our conversation could return to that moment in the script, reread it, and conclude that Bob is also conscious at 3:24 PM.*
Moreover, for such a hypothetical observer, no part of the script is more real than any other part because the script already exists in full as the observer reads it.
(3:36 PM) Bob: So why do I experience being conscious now?
(3:38 PM) Alice: That's like asking, 'why am I Bob and not Alice?' You are Bob at 3:38 PM, and therefore you have the experience of Bob at 3:38 PM.
(3:40 PM) Bob: So I feel conscious now because ... I happen to exist now?
(3:42 PM) Alice: Yes. You exist 'now' – i.e. at 3:42 PM. Note that the present time (3:42 PM) seems unique to you at 3:42 PM, just as 3:24 PM seemed special to you at 3:24 PM, but neither is more special than any other time.
(3:44 PM) Bob: OK, I think I can go along with that for the moment. But this script you mentioned must have timestamps, right? Otherwise, you cannot tell the hypothetical observer reading the script to go back to a particular time. What are those timestamps physically? They seem to be something outside of our universe.
(3:46 PM) Alice: Good observation. In our universe, the timestamps are physical: they represent the state of some clock, which is a physical system within the universe – for instance, the cosmic microwave background functions as a kind of clock, as does the solar system. Hence, if one were given a complete description of the universe, it would include a description of the clock and the timestamps it represents.
(3:48 PM) Bob: So about this whole script thing – are you saying we are living in a script?
(3:49 PM) Alice: LOL. As if.
*modulo the philosophical issue of how to observe that people are conscious.
(3:25 PM) Bob: If "me at 3:24" is one of my versions, then I am not just one of these cuts or versions, but something that is identified as permeating all of them. Now, where and in what time is this universal "I" located?
Very helpful! But what’s still a bit unclear to me is the status of all possible future states of the multiverse. Are they all already part of the “script”, all the way into an infinite future ?