I don’t think it’s an illusion, it’s just not a constant and can be perceived in different ways.
Think of it like animation.
I can draw a bunch of frames of Mickey Mouse running, but he’s not running. I just have a bunch of frames that when played look like he’s moving.
So you the viewer of the movie see him as running, but the dude drawing it or filming it has a different perspective, he saw it all happen much slower…or you can spread all the frames out and see all of it at once.
So its basically just the the idea of time moving forward in the same way isn’t true for all observers and you could also look at it very differently.
This is based on Julian Barbour’s idea of timeless physics.
Imagine one person, playing a game of Snakes and Ladders. This game will represent the universe, and each square will represent a possible state, a possible configuration of all the particles in the universe. The rules of Snakes and Ladders are then like the laws of physics, they tell you how to move from one square to another, from one configuration of the universe to another. This is, in a sense, timeless, because all the squares, all the possible configurations, all exist, and never change. However, we can recover a notion of time, by considering the moves of the game. Each move of the game is like the tick of some cosmic clock that takes the universe from one configuration to another, so even though the configurations themselves are static, we can still construct a notion of time by tracking the location of our counter.
The issue arises when we bring in quantum mechanics. In quantum mechanics, we don’t have definite states any more, just probabilities for each square, and these probabilities can’t change with time because the individual squares are supposed to be static. The probability of a square then has to represent the probability that we land on that square *at some point* during the game. For example, the probability of the first square is 1, because we always start there, and the probability of the second square is 1/6, because the only way to get there is to roll a 1 on the dice.
Since we now just have the probabilities on each square, we no longer have a notion of time. The different states, the different configurations of the universe, all just sit their with their own unchanging probabilities in some timeless existence. Barbour argues, then, that the high-probability states are the ones that *appear* to have a consistent history, but this is just an illusion. The states don’t have a history at all, because they all exist independently and nothing ever changes.
It’s a bit like Zeno’s paradox of the arrow, which says that at any fixed instance, an arrow in flight is stationary, so how can it be moving? If a fixed arrow and a moving arrow look the same at any point in time, how can you tell the difference?
I don’t find it a very compelling argument, I have to say. The solution to Zeno’s paradox is to consider momentum. Momentum can’t be seen from just a snapshot, because it describes how things change from one snapshot to the next. Momentum describes the transitions from one state to another.
We can think of a similar idea in Barbour’s timeless universe of unchanging configurations, by considering not the probability of ever landing on a square, but the probability of going from one square to another. These are still timeless, in the sense that the probability of e.g. going from square 41 to square 45 doesn’t change, no matter whether you make it as your 10th move, your 20th, or your 100th, but with transition probabilities, you can construct possible sequences of states, and bring the time back into the physics. The most probable sequences are then those with the most probable squares, which Barbour argues are those that look most like they have a consistent history, so the most probable sequences are those that look like time is passing in the usual way. If we have a timeless universe, then, we can still invent a notion of time that works the way we expect, so it’s not *really* timeless.
Alright kiddo, let’s talk about time! Imagine you have a favorite toy that you like to play with, and you can only play with it for a certain amount of time before you have to go to bed. That’s because we have something called “time,” which helps us keep track of when things happen and how long they last.
But here’s the tricky part: some people believe that time isn’t really a “thing” that exists on its own. Instead, they think that time is just something that our brains make up to help us understand the world around us.
It’s kind of like a game of pretend. We pretend that time is real, even though it might not be. And just like how you can pretend to be a superhero or a princess, we can pretend that time exists, even if it’s not really there.
So when people say that time is an illusion, what they mean is that it might not be real in the way that we think it is. It’s just something that we imagine in our heads to make sense of the world