This question may be either trivial to answer and I just don‘t get it, or it may be highly controversial. I am trying to pose my problem as shortly as I can.

What is responsible for my subjective experience of the present moment (or rather, the immediate past, taking information processing into account)? Why is now actually now?

Under the premise of spacetime being a static and eternal thing, doesn‘t any line of thought trying to answer this question necessarily make any intuitive notions of identity and the passing of time illusionary?

The only answer that I can come up with is that every conscious moment exists, despite any causal connections, for itself in some eternal sense. In this sense, „I“ right now am just existent at some specific point in spacetime, and before and after that there are, with regard to consiousness, separated and slightly different „mes“ which just happen to be in the closest proximity possible to the „me“ in that moment. Is there any more intuitive way of thinking about this?

Probably relates to timeless physics and quantum immortality.

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Lucius Bushnaq

Jun 18, 2023


Under the premise of spacetime being a static and eternal thing, doesn‘t any line of thought trying to answer this question necessarily make any intuitive notions of identity and the passing of time illusionary?

Illusory in what sense? The underlying laws of our universe are time symmetric[1], but the second law of thermodynamics means that entropy increases as you move away in time from a set low-entropy point (the big bang). This means that predicting bits at  from bits at  tends to be a much more difficult exercise than predicting bits at  from bits at . Large amounts of detailed information (entropy) about  can, with some tricks, often be read off from  with little computational effort. "Memory" is one way to do this. 

There are fewer ways to read off lots of information about  cheaply from . It is only possible in some very specific situations. You could, for example, look at a couch in a windowless room at time , and commit to look at that exact couch from that exact position at that exact angle again one week later. This would let you pretty reliably infer a large batch of future visual bits. But such techniques do not tend to generalise well, you can't do this for arbitrary future visual information the way you can use "memory" to do so for a wide class of past visual information. Thermodynamics means the trick only works one way, for bits that are closer in time to the big bang. To do the same for future bits is theoretically possible, but it typically requires different techniques and a far, far larger compute investment.

For an observer operating under such physics, it is useful to conceptualise the world as consisting of a "past" that has "already happened", and is thus amendable to inference through techniques like memory, a "future" that has "yet to happen" and is more uncertain, and a kind of "present", where these regimes meet, close to which techniques for inference from both regimes tend to be most efficient, and where information can be processed directly, because physics is local in time as well as space. Thus memory from  with  tends to be easier to protect from degradation than memory at , computing bit predictions for  tends to cost way less than for , and so on.

If you look at an intelligence inside such local physics, you will see that its internals at any point in time  tend to be busy computing stuff about , the "present moment" which the computation can locally operate on and affect, and which can often take in information from the "past", especially the "recent past" fairly easily, but has a harder time taking in information from the future, to the point that doing so usually involves totally different algorithms which feel totally different. So it feels to the computation at  that "it exists", "now".

I wouldn't really call this an illusion, except in the sense that "trees" are an illusion. A tree is fundamentally just some quantum field[2] excitations from a particular class of excited states inside a finite 4D volume. But its medium scale, medium-range interactions with baryonic matter are often pretty well described by the human concept of "tree".

 Likewise, dividing time into a "future", which has "yet to happen", a "past", which "has happened", and a "present", which "is happening", is a leaky abstraction of the underlying laws about performing inference and decision computations in a physics with locality, the second law of thermodynamics, and a low-entropy state at some  (big bang). It's not precise, but a good approximation under many circumstances. 

Imagine someone in the desert thinks they see an oasis. If it is actually a mirage, I'd say it makes sense to call the oasis an illusion. If it is an actual oasis, I don't think the moniker illusion is apt just because oases are really an imperfect abstraction of particular quantum field configurations.

  1. ^

    Well, actually CPT symmetric, but the distinction doesn't matter for the intuition here.

  2. ^

    Or, if you don't believe in asymptotically safe quantum gravity, it might not really be quantum fields either. Substitute whatever your favoured guess for the true fundamental physical theory is.


There is no one theory of time in physics.

The underlying laws of our universe are time symmetric[1], but the second law of thermodynamics means that entropy increases as you move away in time from a set low-entropy point (the big bang).

All that gives you is an asymmetry, a distinction between the past and future, within a static block universe. It doesn't get you away from stasis to give you a dynamic "moving cursor" kind of present moment.

Likewise, dividing time into a “future”, which has “yet to happen”, a “past”, which “has happened”, and a “pres

... (read more)
2Lucius Bushnaq10mo
There are many popular hypotheses with all kinds of different implications related to time in some way, but those aren't part of standard textbook physics. They're proposed extensions of our current models. I'm talking about plain old general relativity+Standard Model QFT here. Spacetime is a four-dimensional manifold, fields in the SM Lagrangian have support on that manifold, all of those field have CPT symmetry. Don't go asking for quantum gravity or other matters related to UV-completion.[1] Combined with locality, the rule that things in spacetime can only affect things immediately adjacent to them, yeah, it does. Computations can only act on bits that are next to them in spacetime. To act on bits that are not adjacent, "channels" in spacetime have to connect those bits to the computation, carrying the information. So processing bits far removed from t at t is usually hard, due to thermodynamics, and takes place by proxy, using inference on bits near t that have mutual information with the past or future bits of interest. Thus computations at t effectively operate primarily on information near t, with everything else grasped from that local information. From the perspective of such a computation, that's a "moving cursor". (I'd note though that asymmetry due to thermodynamics on its own could presumably already serve fine for distinguishing a "present", even if there was no locality. In that case, the "cursor" would be a boundary to one side of which the computation loses a lot of its ability to act on bits. From the inside perspective, computations at t would be distinguishable from computations at t+1 and t−1 in such a universe, by what algorithms are used to calculate on specific bits, with algorithms that act on bits "after" t being more expensive at t≤t1. I don't think self-aware algorithms in that world would have quite the same experience of "present" we do, but I'd guess they would have some "cursor-y" concept/sensation. I'm not sure how hard construct
Along a worldline, you have a bunch of activity at time T0 that is locally affecting stuff, a bunch of stuff at time T1 that is locally affecting stuff, and so on. They're all present moments. None is distinguished as the present moment, even from the perspective of a single worldline.. There could be any number of such approximate "boundaries" along a worldline. Assuming you mean collapse -- the Born rule is a just a timeless relationship between probability and amplitude -- there could be one in reality as well. That's one of the reasons there isn't a single model of time in physics. Collapse actually is a moving cursor.

Thank you, this has clarified the issue a lot for me regarding the time aspect of my problem, but the identity part still remains very elusive.


Jun 18, 2023


State of mind that describes the experience of 11:28 AM exists in my mind at 11:28 AM, that's what the brain does, it prepares this state of mind using its structure, preceding states of mind, and observations. At 11:30 AM, the state of mind is different, and describes the updated experience of 11:30 AM.

A device that instantiates my state of mind of 11:28 AM at 10:28 AM would result in a me that experiences 11:28 AM at 10:28 AM. With this device, there are two mes of 11:28 AM that exist at different times, both at 10:28 AM and at 11:28 AM. If I'm aware of the device, the me of 11:28 AM knows that now is both 10:28 AM and 11:28 AM. It's a foothold for controlling the past.

Charlie Steiner

Jun 18, 2023


It's a hard job, but someone's gotta do it.


Jun 18, 2023


I suspect it is creation of memories. You don't experience time when you're not creating memories, and they're some kind of very subtle object that lasts from one moment to (at least) the next so they leave a very subtle trace in causality, and the input that goes into them is correlated in time, because it is (some small selection from) the perceptions and representations you had simultaneously when you formed the memory.

I even believe you experience a present moment particularly intensely when you're creating a long-term memory - I use this to consciously choose to create long-term memories, and it subjectively seems to work.

Carl Feynman

Jun 17, 2023


You have a subjective distinction between “now” and all earlier times.  Evolution made you that way.  At any given moment, much of the maximally informative information about what do now will have arrived in the past fraction of a second.  Information from a minute ago, or last week, may be useful, but our mind makes a distinction between the freshest information and the old stuff.  The freshest information is called “now”.  We feel like we’re deciding things and doing things “now” because the upcoming fraction of a second is the time over which we have the most influence.

”Now” is not a fundamental fact about the universe, it’s a useful abstraction in an algorithm that has to steer a body through a difficult world.  Its subjective salience is what it feels like to be that algorithm.


Jun 17, 2023


"Now" is the time at which you can make interventions. Subjective experience lines up with that because it can't be casually compatible with being in the future, and it maximizes the info available to make the decision with. Or rather, approximately maximizes subject to processing constraints: things get weird if you start really trying to ask whether "now" is "now" or "100 ms ago".

That's sort of an answer that seems like it depends on a concept of free will, though. To which my personal favorite response is... how good is your understanding of counterfactuals? Have you written a program that tries to play a two-player game, like checkers or go? If you have, you'll discover that your program is completely deterministic, yet has concepts like "now" and "if I choose X instead of Y" and they all just work.

Build an intuitive understanding of how that program works, and how it has both a self-model and understanding of counterfactuals while being deterministic in a very limited domain, and you'll be well under way to dissolving this confusion. (Or at least, I've spent a bunch of hours on such programs and I find the analogy super useful; YMMV and I'm probably typical-minding too much here.)


I could not really make sense of your comment, though I had actually done what you proposed a couple of years ago, until I had read Lucius Bushnaq‘s comment. Did that imply what you were trying to tell me or is there another aspect to what you call an intuitive understanding?

Rob Dost

Jun 21, 2023


I don't have precise answer to your question, but have some question which can prehaps be useful in answering it. 

Namely: what about space? I mean, you talk here about time, something along the lines of "We can imagine our Universe as a solid eternal block of spacetime, so why do I experiencing present moment instead of all moments at once?" But what about "We can imagine our universe as a solid eternal block of spacetime, so why I am experiencing 'here' locality instead of all places at once?". I think these are very similar questions. 

We can go even further and ask "We can imagine Multiverse of self-consistent mathematical objects (among which is, of course, our Universe) as one eternal blob, so why do we experience present, local moment instead of everything existent?". 

It seems, the key to confusion here is that we imagining ourself as an outside observer of arbitrary high level and then we ask "why our experience difers from experience of such an observer". But this is exactly because we are not this observer. What we are is a different question, of course. I personally havn't yet found a satisfactory answer to the hard problem of consciousness, but it seems this specific in experience (space/time locality) tells us about something about which consciousness is certainly not.


Related to this idea of space, is maybe asking "why am I me, and not someone else?".

The question in quotes is obviously nonsense, but I think it can get quite confusing, especially if we start assuming that people can be replicated (perhaps using digital copies). If you are one of 5 copies of a digital personality, does it make sense for you to be grateful you are not a different one of those copies? The world would not in any mechanical way be different if you were one of the copies and they were you. So it becomes complicated to think about because it se... (read more)


Jun 18, 2023


Time, change, and continuity through change, are all real. A life is not a constellation of static experiences in eternity, disconnected but imagining that they are connected; it is the history of the changes experienced by one awareness as it transforms. The phenomenological study of experienced time will tell you about its nature, not the current guesses of physicists and neuroscientists. 


I cannot see how your last sentence holds. My subjective experience of time was, up to now, everything from the usual feeling of continuous time and total disarray during psychosis up to a feeling of complete timeless eternity during transcendental meditation. Instead if knowing how time feels like - I have had my share - I would like to understand how consciousness relates to time in the light of physics. Subjective experience can be deceiving in infinitely many ways, but there must be (at least I hope so) some objective underlying physical foundation for it. At least my inclination towards realism tells me that.

Do the disarray of psychosis or the timelessness of meditation lead you to think that the "usual feeling of continuous time" is illusory?  My own experience of altered states comes from psychedelics, and from dreaming and sleeping. The usual feeling of continuous time leads to a certain ontology of subjective time, and one's relationship to it: continuity of time, reality of change, persistence of oneself through time, the phenomena of memory and anticipation. The altered states don't lead me to doubt that ontology, because I can understand them as states in which awareness or understanding of temporal phenomena is absent, compared to the usual waking state.  I cautioned you against using scientific ontology as your touchstone of reality, because so often it leads to dismissal of things that are known from experience, but which aren't present in current theory. For example, in your post you suppose that "spacetime is a static and eternal thing". My problem here is with the idea that reality could be fundamentally "static". It seems like you want to dismiss change or the flow of time as unreal, an illusion to be explained by facts in a static universe.  On the contrary, I say the way for humanity to progress in knowledge here, is to take the phenomena of experience as definitely real, and then work out how that can be consistent with the facts as we seem to know them in science. None of that is simple. What is definitely real in experience, what we have actually learned in science, it's easy to make mistakes in both those areas; and then synthesizing them may require genius that we don't have. Nonetheless, I believe that's the path to truth, rather than worshipping a theoretical construct and sacrificing one's own sense of reality to it. 


Jun 18, 2023


I pretty much agree with your hypothesis. Each 'moment' of conscious experience is a distinct, unique -- something. Our subjective stream of consciousness is simply the most likely path through all possible spacetime states that lead to the 'present' -- sort of like a Feynman sum-of-paths integral.

Not sure how to fit quantum mechanics in there...

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How would you know if you were experiencing the "wrong" time?

I'm inclined to agree with your theory about all states existing "simultaneously" but I'm not sure how to reconcile this with the continuous-feeling nature of experience.


Continuity is mostly an artifact of memory, I expect. The "you" of 11:30 remembers the experiences of 11:29 quite well, remembers 11:20 (often lesser in fidelity), but the experiences of 11:31 and other future times not at all. Frequent vivid memories of particular past experiences can break this feeling of continuity to some extent, though the directionality remains and establishes some ordering.

This would predict that people who have frequent vivid delusions of future experiences probably have a much weaker feeling of continuity of experience, if any such people exist.