tj444 wrote:I would like to take the thread in a different direction. Do temporal parts exists. If I am not mistaken that means that a 4d object must exist. Does the past exist? If the past does not exist does that mean that an individual human doesn't have persistence and doesn't have temporal parts ? What about from a scientific answer to the question does the past exist?
Can you try to keep the answers simple, thanks.
You can not say the street behind you has vanished and you can not say the street ahead doesn't exist yet. The whole street exists (all at the same time) and you are merely a traveler (observer) heading down that street. The sum of your knowledge tells you where you are presently located and allows you to guess at what may lay ahead. I would call that Conventional Time, or Case (C)
Since there exists in this four dimensional structure [space-time] no longer any sections which represent "now" objectively, the concepts of happening and becoming are indeed not completely suspended, but yet complicated. It appears therefore more natural to think of physical reality as a four dimensional existence, instead of, as hitherto, the evolution of a three dimensional existence.
Just one more question when you describe Presentism above the quoted part. Were you adding your own thoughts or is that the exact definition of Presentism?
We live in 4 dimensions (minimum). All 4 are just directions. Up-Down, Left-Right, Closer-Further and Before-After. So that's called 3D space with Time, or Space-Time.
So let's just start with 2D space only. Imagine a super thin canvas, so thin it has no real thickness. But it has height and width. So I cast a shadow on it of a ball. The flat view (shadow) would be a simple circle. Now imagine the shadow is of a person. This person's shadow has height and width only. I tell him I can reach inside his body and grab his heart without breaking his skin. He says that's impossible. So I walk up to the canvas and give his heart a squeeze. I can do this because I can come at him from an angle that he can't understand. I tell him I am going to pass a ball in front of his face and push the ball through the canvas. He told me that he saw a circle, but it started out small and got bigger and bigger, then got small again and disappeared. He asked where the ball went and I said it's just a few inches from his face. But he can't reach it because it's not touching the canvas and he can't leave the surface of the canvas.
Ok, so that's two dimensions and he's flat. Not too hard to understand. Now, and I'm sorry for this, I gave him an extra dimension I shouldn't have, just for the sake of this previous example. I gave him Time. So let's take back Time and give him another dimension. I take the thin canvas and make copies of it and push them together. Now that circle looks like a cylinder to me and he looks 3D to me, but I see no motion anymore.
When he bounces the circle up and down like a ball, I only see a cylinder that looks like a roller coaster track. The cylinder bends up and down as I float along and look at it. But it's not moving. I have given him "Time" as a dimension of Depth. When I added Time to his dimension, to take him from 2D to 3D, I still don't get the impression of "Time" as we think of it. Just a long stretched out statue that, like the cylinder, goes back as far as I can see and forward as far as I can see, depth wise.
If that's hard to imagine then think about when a cartoon character runs through a wall and leaves a hole with his shape. Now imagine it's a very thick wall, such that the hole looks more like a long tunnel. A very, very long tunnel. Now fill this tunnel with cement and get rid of the wall. I now have a long cast, or sort of stretched out statue, in the shape of the cartoon character. If the cartoon guy was flapping his arms as he went through the wall, then imagine how this would affect the shape on the cast part of his arms. Now you may have some idea of how this flat guy looks to me, now that I have given him depth. It's not moving but I can see where the cylinder rises to his hands and falls to the floor, over and over, and realize he was bouncing this circle (ball) at that point in his life.
If I follow his shape all the way back to one end, I see him being born. If I go all the way to the other end, then I see him getting buried because he died of old age. So this 3D world has Time, at least as far as the flat guy is concerned, but to me the whole place has no motion. Nothing moves, it's all frozen still. Like it's all one solid piece of Geometry.
Just one more thing I wanted to add when David_Oblad discusses A and B theory is he just referring to what most people consider the A and B theory of time?
Another question which theory on time is correct?
The past can exist but it exists in the past.
How can individual persist if only the present exists?
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