Minkowski (1908) posited a structure of four dimensional (4D) spacetime that treats time as another dimension just like the three dimensions of space. One way to think about spacetime is that everything that has happened, is currently experienced by someone as happening, or is ever going to happen, has a location in this 4D structure. Past, present, and future exist in spacetime as a frozen block. This realist interpretation of Minkowski spacetime is known as eternalism or the block universe.
Assuming that conscious experience is real and part of the physical world, there is an interesting problem to solve of where it is, in particular where now is, and how we experience the passage of time. Even those who argue that the experience of time is an illusion have to explain what enables the illusion (Prosser, 2012).
Consider a 2D toy model of spacetime: one dimension of time, one dimension of space. You could imagine this as a model of a universe in which it is only possible to jump up and down and not move in any other direction. Also suppose there are only three points in this spacetime. The figure below illustrates three example scenarios of where phenomenal experience could be. The black points denote where someone is and the orange blobs denote where their conscious experience of now is occurring.
Scenario a consists of a multitude of experiences scattered across spacetime. In this toy universe, there are three experiences at three nows. It doesn’t seem to work, at least not according to my experience of the world. As I type this, I see my fingers dance across the keyboard. There is movement. But in scenario a, each of the three individual experiences is frozen. Another way to think of the universe of a is as an animated flip book which, in the example above, has three pages. The problem is that there is nobody and nothing to flip the book to bring the animation to life. There is no way to travel between the nows.
I first spotted scenario b in a chapter by Natalja Deng (2019, p. 12). The idea is that conscious experience is temporally extended across spacetime rather than located at multiple individual points in spacetime. Using the flip book analogy, imagine threading a string through the pages of the book, passing through the points where and when someone having an experience is located. That piece of string is where conscious experience is. So in our universe, conscious experience would be some kind of 4D structure. This is compatible with the view of objects (such as us) as 4D spacetime “worms”. It is very appealing as it allows information flow across time, though it’s unclear to me why there would be an experience of the passage of time, rather than simultaneous experience of all times past, present, and future. The now is rather over-extended.
Scenario c is another logical possibility that I haven’t yet found in the literature, illustrating that consciousness does not have to be spatially or temporally close to the action being experienced. The idea is that the information required for temporal experience is accumulated over time, along the spacetime worm, until finally you get a burst of experience covering your whole life at the moment you die. Or perhaps this happens at the very end of time down one end of the block universe. In any case, according to this possibility, if you are having a conscious experience then either time has ended or – at this end of the universe – you are dead (but worry not, most of your spacetime worm is still alive). Note the absence of orange left of the final blob: for most of your existence you are living as a zombie. Scenario c again doesn’t explain how the burst is experienced as passage of time.
So much for that exercise!
There are very many other ways to think about the passage of time. One is to reject the notion of a block universe. Physicist Avshalom Elitzur really doesn’t like it at all (Falk, 2016):
“I’m sick and tired of this block universe. I don’t think that next Thursday has the same footing as this Thursday. The future does not exist. It does not! Ontologically, it’s not there.”
Another is to keep the block universe but conjecture the existence of a moving spotlight in which particular regions of spacetime “glow” and become experienced (Skow, 2009). I don’t understand the details of this yet, e.g., it seems to require another dimension of time to index what regions glow, and consequently another problem to solve.
Yet another is to conceive of the universe as a growing block, so the past and present exist; however, the future doesn’t yet (Perović, 2021, reviews different versions of the theory). Time passes as the universe grows and “now” is at the newly created edge of the block. This seems compatible with Muller and Maguire’s (2016) theory that the universe expands in 4D by Hubble expansion:
“We postulate that the increase in space is accompanied by an increase in time, by the creation of new moments of time. […T]he future does not yet exist; we are not moving into the future, but the future is being constantly created. The moment we experience as ‘now’ can be identified as the instant of new time that was just created.”
References
Deng, N. (2019). One Thing After Another: Why the Passage of Time Is Not an Illusion. In The Illusions of Time (pp. 3–15). Springer International Publishing.
Falk, D. (July 19, 2016). A Debate Over the Physics of Time. Quanta Magazine.
Minkowski (1908). Space and time. Lecture given at the 80th Meeting of the Natural Scientists in Cologne on September 21, 1908.
Muller, R. A., & Maguire, S. (2016). Now, and the Flow of Time. arXiv.
Perović, K. (2021). Three Varieties of Growing Block Theory. Erkenntnis, 86, 623–645.
Prosser, S. (2012). Why Does Time Seem to Pass? Philosophy and Phenomenological Research, 85, 92–116.
Skow, B. (2009). Relativity and the Moving Spotlight. Journal of Philosophy, 106, 666–678.