Did you know Albert Einstein wrote this letter to a grieving family when his lifelong friend Michele Besso died? He wrote a letter consoling Besso’s family: this piece here is very important “Now he has departed from this strange world a little ahead of me. That means nothing. People like us, who believe in physics, know that the distinction between past, present, and future is only a stubbornly persistent illusion.” Not exactly the best consoling words. But what's important is that he states that his best friend is still alive due to time being an illusion. But how can this be so? Well, according to Neil Degrasse Tyson, the Universe is under no obligation to make sense to us.
But let's try to ponder this anyway.
The DVD analogy helps us conceptualize or at least tries to.
This brings us to the block universe. What's a block universe? The past, present AND future all exist simultaneously in the block universe. There is a great analogy to this, that our experience of time is like that of a DVD. We know the future events exist on the DVD even whilst you're watching halfway through a movie, we know that the future events and the ending have already happened. It is just so the DVD player is making it so that we will watch the movie in a forward liner fashion from beginning to ending. So, our brains are doing something similar to the DVD player, constructing time passing linearly. On the DVD, we know the past, present and future of the movie exist within it and this is very similar to the nature of time within our block universe. Einstein says time is an illusion due to these things. Time only moves forward in a linear fashion due to our perceptions, just as the DVD spins to create a linear forward flow of illusion of the movie.
Essentially, what the block universe model is all about is that time exists just like the 3 dimensions. We wouldn't think of 3 dimensions flowing so we shouldn't think that the 4th dimension is flowing. This graph here shows time existing just like how three dimensions exist. And this graph here shows our perception of time, which is an illusion. The block universe graph allows us to grasp that past, present, and future exist simultaneously and that, all events no matter when or where they happen, exist and are equally real. I said where because time is a dimension. As just mentioned, every moment in time is equally real, so the whole of space and time must be laid-out in one unchanging spacetime block, hence the name. Essentially, this means that spacetime exists as an unchanging structure. If we go back to the DVD analogy and pause the movie; we can greatly conceptualize this because as soon as you pause the movie, the DVD just exists as an unchanging structure! So, it is merely our perceptions that make it so that we experience a linear flow in time! It is exactly how the illusion of a movie works, by playing different still images at a frame rate of 25 per second. You can now conceptualize how this works because we now know those individual images are merely played in such a way to appear to be changing, but we know they're just still images - it is only until the images.
Photographer Eadweard Muybridge put together this horse animation in 1878 in his chronophotographic works which is a photographic technique from the Victorian era which captures a number of phases of movements. There is not much difference in how this is done today with digital cameras, just that the number of still images per second has increased. Essentially what we see as motion, is simply not! This is a perfect analogy to use as this is occurring within our brains, albeit via the interpretations of the senses, the perceptions.
Then a perfect analogy, now a perfect diagram.
As you can see in this wee diagram, all past events, the current moment, and future events are already there. This is very different to the ordinary view of how we view time. Usually, we view time as the past ceasing to exist once it has passed, only existing as memories, only the current moment existing and the future developing. Well, what's interesting is that this view has a name, which is known as presentism.
Simply put, presentism is the view that only present entities exist, so it would look like this, rather than the block diagram above.
To be clear, the diagram shows that only the current moment exists, neither the past exists, nor the future does not happen yet. Nothing new here, that's the majority of everyone's view of the past, present, and future. But this is philosophy, the block universe is physics, which is the real view of time. Presentism could also be named Perceptionism due to how very similar it is to how our perceptions view time. Thankfully, we humans have a linear forward flow of time, it's good it is not like in the movie, Arrival, which shows aliens perceiving time radically differently, non linearly - sorry digressing there.
And here's a diagram of Eternalism, which is the same as the block universe. There are other names for it such as four-dimensionalism. Due to space-time being proven time and time again, eternalism has changed from philosophy to physics.
Here, an illustration of the concept of eternalism, shows a man walking his dog. Time progresses through the series of snapshots from the bottom of the page to the top. In a common-sense view of time, each of those four instants would exist one after another. According to eternalism, those four instants all equally exist, just like the block universe.
There's a different block universe, the growing block universe, that adds that the future does not exist already. The past and present both exist, and the future as yet does not. The present is an objective property, to be compared with a moving spotlight. With the passage of time, more of the world comes into being; therefore, the block universe is said to be growing.
More on this in the future.