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This is a linkpost for https://medium.com/p/a6988b94ca2d

Confusion about the reality of time comes from the fact that there are three entirely different things we call “time.” When we ask a physicist if time is real, we would get an answer about an entirely different phenomenon compared to the answer to the same question of a philosopher.

The aim of this article is to reduce confusion when tackling the question of reality of time. It turns out that each of the three things we call "Time" can be compared with other more familiar things, giving us better intuition about the reality of each of them.

# Dimension of Time

Spacetime is a four-dimensional manifold in which an observer perceives three dimensions as “space” and one as “time.” All four spacetime dimensions can be either fundamental themselves or emergent from some more fundamental phenomena. We know from experiments that the exact direction in the four-dimensional manifold an observer perceives as “time” depends on the observer’s velocity and gravity in the vicinity. So, we are confident that the Dimension of Time is as real as the other three Dimensions of Space.

# Arrow of Time

All the dimensions of space are isotropic, meaning that the laws of physics are the same in all possible directions in space. Dimension of Time, on the other hand, is anisotropic, meaning that there are some laws of physics that are different, when you look from the past into the future, compared to when you look from the future into the past. For example, entropy of a closed system increases as you move from the past into the future. We suspect that the Arrow of Time is at least as real as the lack of any special direction in space.

# Cursor of Time

There is a privileged moment in time we call “now,” and we perceive the privilege constantly moving from moment to moment from the past into the future.

It naїvely feels like “now” moves synchronously for all observers in the universe, i.e., all the observers would agree that today is Tuesday all across the entire universe. We know from experiments this is not true. We know that for causally disconnected events, it is possible to have observers who would disagree about the order of these events. In other words, the consistent for all observers notion of “now” is incompatible with general relativity.

Privileged moment called “now” doesn’t show up in any formulas or models in physics. Moreover, in order to move from the past to the future, “now” would need its own separate Dimension of Time, Arrow of Time, and Cursor of Time to move in, making any conceivable mathematical models of Cursor of Time infinitely recursive.

## Cursor of Time is an illusion

We suspect that Cursor of Time is one out of the multitude of Qualia. If true, Cursor of Time is as illusory as subjective redness of color red. We can also compare the problem of Cursor of Time with the problem of Personal Identity saying that they both are equally hard, and one can be presumably reduced to the other. We can think of Personal Identity as separating different subjects of Qualia in space, and Cursor of Time as separating different subjects of Qualia in time, undermining the stronger notions of Presentism. Today's You would be seeing as a different subject of Qualia compared to Yesterday's You.

We don't have any physical explanation for the phenomenon of Qualia yet, hence, Cursor of Time is the only one out of three that lacks physical ground, and thus is more likely to be an illusion than the other two.

It is also worth mentioning that Qualia, as a phenomenon we observe, requires a physical explanation starting with its definition. Right now, we don't have any better definition of Qualia than pointing out our finger at it and saying: “O! This is Qualia!” While it is a valid definition for an unexplained phenomenon, due to its limited nature this definition doesn't prevent anybody from disagreeing that they see anything unusual where we point our finger at and suggesting that the very existence of this phenomenon questionable.

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Yeah, I think presentism vs. non-presentism in time is an interesting example of how to reason from experience.

Like, obviously we're starting from our experience of the present. And so a qualiaphile might say "And so the buck has to stop there - there's something special about the present. If you come up with a theory of physics where there's nothing special about the present, you've missed something - you've failed to address the Hard Problem of the Present." Whereas a quale hunter might say "Of course I'm starting from my experience of the present. Which is why it's important that the theory of physics explains why the beings living within it would think there's something special about their presents, even if there isn't."

There's a possibility that there might be nothing special about the present at all. I don't feel like there's something special about the region of space I occupy, and the illusion of time flow comes from the fact that I cannot say the same about the time.

My point is that difference between presentism vs. non-presentism might be purely linguistical and difference between "this thing existed in the past, but it doesn't exist any longer" might be just similar to "this thing is there, but it doesn't stretch all the way to here."

[-]TAG10

Privileged moment called “now” doesn’t show up in any formulas or models in physics.

But we don't know the map is 100% accurate.

Moreover, in order to move from the past to the future, “now” would need its own separate Dimension of Time, Arrow of Time, and Cursor of Time to move in, making any conceivable mathematical models of Cursor of Time infinitely recursive.

That depends on how literally you take the metaphors of cursors and movement. The Growing Block Universe theory perhaps needs only one extra dimension.

illusion We suspect that Cursor of Time is one out of the multitude of Qualia. If true, Cursor of Time is as illusory as subjective redness of color red.

Qualia are not necessarily illusory. If you put your hand on a hot (objectively) stove, it feels hot subjectively.

But we don't know the map is 100% accurate.

Moreover, we know that it is certainly not 100% accurate, because we still have multiple gaps in our understanding. My point here is that we haven't encountered any physical process which would require "now" to be somehow special. It does not mean we won't encounter it in the future, but it is worth mentioning that we haven't encountered it yet.

That depends on how literally you take the metaphors of cursors and movement. The Growing Block Universe theory perhaps needs only one extra dimension.

For each point  in th-dimensional universe to be special, there must exists a point  in th-dimension of Growing Block Universe for which  would be special.

I.e., if Growing Block Universe grows in th dimension, we can say that and at the point  it grew all the way up to , making  special only from the perspective of , but not globally special across the entire Growing Block Universe.

In turn, in order to make the point  special, we need a non-special point in th dimention, and so on up to infinity.

I.e., if Growing Block Universe is  -dimensional, the "Growing" part would be only th-dimensional, and th-dimension part would be static.

Qualia are not necessarily illusory. If you put your hand on a hot (objectively) stove, it feels hot subjectively.

I'm not claiming that Qualia is illusory. On the contrary, Descartes's "Cogito, ergo sum" suggests that qualia might be the only thigh for which we can claim with certainty that it is not illusory.

I suggest entertaining the possibility that Cursor of Time itself might be illusory, making us think at every point in time that this moment is somehow special and that the time "flows".

I.e., if (and that's a big if) Cursor of Time is indeed an illusion, it would mean that "now" is no more special than "here."

[-]TAG10

but not globally special across the entire Growing Block Universe.

The phenomenon you are trying to explain is itself subjective and local.

Agree.

But I want to show that the phenomenon I try to explain cannot be reduced to Growing Block Universe, unless the Growing Block Universe is infinitely dimensional, which is not something totally unimaginable, but isn't parsimonious either.