I have been told that: "time is an illusion. Rather than a chronological progression of events, all events occur simultaneously in space, and so right now, dinosaurs exist, WW2 just ended, you're eating breakfast eventhough you haven't eaten yet, etc". This is apparently eternalism (block universe)? Is there evidence against the claim that everything from the past, present and future is happening simultaneously and that time is an illusion?
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Is there evidence against the claim that everything from the past, present and future is happening simultaneously
Certainly. Using the standard meaning of simultaneous, anything that is within the future or past light cones of an event is not simultaneous with that event. So in a radar experiment the emission of the radar pulse is not simultaneous with the reflection nor the reception of the radar pulse.
Dale
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This question as stated contains a fallacy which pops up again and again in this context. I will try to identify it for you here by enlarging upon Dale's answer.
We imagine ourselves to exist as two-dimensional objects to make this answer easier to visualize. Those two dimensions, x and y, exist for example on the surface of a piece of graph paper, which we then inhabit. To include time, we put it on the z-axis, pointing straight up out of the x-y plane of the graph paper. As time marches on, the whole history of our world gets represented by a vertically-oriented "bread loaf" in which an instant in time is represented by a horizontal x-y slice (at a particular value of z, representing an instant in time). The whole set of slices then traces your movements in x-y space as time t (on the z-axis) marches onward and upwards into the future, leaving the past slices behind in the stack.
This situation also holds for all possible (x,y) points anywhere on that grid of graph paper, where each of those points represents "home" for some another inhabitant of that (x,y) grid at some distance from us.
Now we introduce the fact that if you are moving in (x,y) space while time is marching onward, your "bread slices" get transformed from flat planes into a cone shape, with you inhabiting the tip of the cone at that time instant. The faster you are moving, the pointier the cone shape becomes. Since that cone shape represents one instant of time for you, it represents that same instant for all other points in the evolving (x,y) world around you that touch that cone.
Then we notice that because you are at the tip of the cone and the surface of that cone slants backwards into your past, the cone surface (which represents exactly the same slice of time to any point it touches) intersects a circle of points in the (x,y) plane which exist in your past.
This means that far enough back into the past and far enough away from your (x,y) location, that cone will intersect a world in which dinosaurs are living and walking around- in your present. But if you are standing still in (x,y), your instantaneous bread slices of time flatten out again into completely flat planes.
To summarize, in this "toy world" of 2-dimensional space and one of time, events that are simultaneous to you are all mapped onto those slice surfaces in the bread loaf of history. And this means that if you are in motion, your present is simultaneous with events far away from you which are in your past.
This leads to the idea that the past isn't dead, it's happening simultaneously with events in your present-only if you are in motion. But that past is inaccessible to you in your present because it is far away from you in your (x,y) world.
niels nielsen
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In space, you occupy the point right here. But other points exist, even though you aren't using them now.
Time is more like space than classical physics and your intuition lead you to expect. You occupy the time right now. But other times exist, even though you aren't using them right here.
At your point (or any point) event occur in a particular order.
Classical physics adds the idea the time is absolute. At all points, everybody is checks on themselves and their neighbors. Everybody sees that everybody is using the same time right now. In a little while, they check again. Everybody is using a different time, but they still all are using the time one.
Relativistic physics has no universal way of matching up times like this.
My brother and I are sitting motionless some distance apart. A traveler and his brother pass by us, moving at the save velocity.
At one time, the traveler and I occupy the same point. At that time, the brothers also occupy the same point. A while later, the traveler's brother and I occupy the same point.
I see the travelers always occupying two different points. I always occupy the same point. Yet at one time my unchanging point is the same as the traveler's point. At another, it is the same as his brother's. There is no confusion here. We expect the points we consider to be the same to depend on how we are moving.
Time is more like space than you expect. The times we consider to be the same also depend on how we are moving.
There is a time where the traveler and I occupy the same point. We both agree that right now we are at the same point.
I see that right now the brothers also occupy the same point. My brother agrees with me.
However, the travelers match up right now at other points differently than we do. They say that the brothers meet after we have already passed each other. This is one of the most confusing counter-intuitive ideas in all of physics because it so badly violates our classical idea of what time is.
Classically, we think the present is all that exists. The future hasn't happened yet. The past is over and gone. The universe changes state. Time is a universal way of identifying different states of the universe. It is very difficult to understand how this idea can be wrong, and how things work if it is wrong.
The dinosaurs are all in my past. Even though we occupy different times and places in space-time, and our trajectories through space-time move with respect to each other, the dinosaurs are in my past, and I am in their future. I can dig up fossils of those dinosaurs.
In the past, a dinosaur and his brothers were standing in a line under different trees. The simultaneously bite a leaf. Off in that direction, there are a couple of very distant stars. At the same time as the dinosaurs take a bite, a sunspot erupts on each star.
If I move with respect to a dinosaur and his brother, I pick a way of matching up times so that the most distant brother is closer to my time than the others. One of the stars is just the right distance that the sunspot erupts right now, in my present. The other, being farther, has not yet erupted at this time.
Relativity guarantees that both stars are so distant that light from the sunspots has not yet reached me. The sunspots are neither in my past nor my future. Nor were they in the dinosaurs' past or future. They are so distant that it isn't possible for either of us to measure their eruption. We will have to wait for their light to reach us.
We can say that dinosaurs are in the my past because causes always come before effects. A dinosaur is the cause of a fossil. My finding it is an effect that must happen later.
So light traveling at the speed of light isn't the important thing here. Cause and effect travel at that speed. The sunspots cause light. We will have to wait until the effect (light and possibly other stuff) gets here. Until they do, they are elsewhere, the region we can't interact with yet.
All right nows that are so badly mismatched with our right now that they could cause time travel paradoxes are elsewhere, where we can't get at them.
mmesser314
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