# Spacetime, the Universe, the Present and the Future

1. Apr 18, 2007

### Seeker2K

At http://en.wikipedia.org/wiki/Spacetime#Historical_origin I read the following quote:
Wouldn't this imply that the universe (respectively spacetime) is actually static and that the present doesn't really exist except for our consciousness? And wouldn't this also imply that in such a universe the future would also be already determined, if time is only another dimension like space in the static construct of spacetime?

What is the general understanding regarding these issues in the field of physics today? Or is this more or less a matter of debate and/or personal interpretation of spacetime?

2. Apr 18, 2007

### pmb_phy

Since time plays the same role mathematically, but not physically, then there is a sense where one can say that space plays the same role as time but the fact still remains that this relationship is a role mathematically, but not physically. Either way the universe exist. If it didn't then I'd be hard pressed to say who posted this thread.

Pete

3. Apr 18, 2007

### pervect

Staff Emeritus

I would say that there is NOT a consensus whether the future is predetermined or not.

There are apparently some enthusiasts at the Wikipedia who have written and believe that there aren't any alternatives.

For some papers that take different views see the references in my post in PF

https://www.physicsforums.com/showpost.php?p=1176689&postcount=6

you may also find the thread of which this is a part of some interest (select view thread).

4. Apr 18, 2007

### Chris Hillman

Time and space are not completely equivalent

H. G. Wells didn't have it quite right, if you are trying to read that (anachronistically) as a description of Minkowski spacetime. You can turn around in space---your world line can describe a helical arc--- but you can't turn around in time--- your world line can't "turn over" and start heading into the past.

5. Apr 19, 2007

### rbj

besides that (the "arrow of time" vs. some "arrow of space" which i don't think exists outside of the event horizon of black holes), i don't think (from an amateurish read) that they have precisely the same role mathematically (responding to Pete). $t^2$ has a minus sign attached to it where $x^2, y^2, z^2$ all have plus signs.

6. Apr 19, 2007

### Seeker2K

Seems you are right...

Yes, I took a look at the thread and at the papers. Dieks' "Time in special relativity and its philosophical significance" sounds interesting, but unfortunately I can only access the abstract.
The paper by Mauro Dorato is interesting as well, but apparently he is supporting a kind of kantian point of view in which time is something purely mental and only exists in our consciousness. I wonder how objects are supposed to exist then, if time and space only exist in our minds - does spacetime only exist in our minds/consciousness as well then? I have to say that I am no expert regarding Kant though.
However, according to the author of that paper Kant’s view of time is actually vindicated by relativity.

Personally I have thought about all of these issues and currently think that it could be problematic to combine an objective, universal 'present' with the theory of relativity, as there would be problems with simultaneity. However I think that it should still be possible that there is something like a 'present' with an open future for every existing frame of reference in space. The existence of such a shifting 'present' doesn't directly follow from the concept of spacetime as all points in the time dimension appear to be equal there, but something has to be added to this concept anyway, as there surely is something as an 'experienced present' that moves through time from the past to the future in our consciousness. Everybody can surely say that there is a certain moment in time that he/she is experiencing right now (for him/her at least). The question remains if it only exists in our minds or if there is some general kind of 'flow of time' with a past, present and open future.

Last edited: Apr 19, 2007
7. Apr 19, 2007

### MeJennifer

Some might be interested in reading Julian Barbour's views on time. He wrote a book called "The End of Time".

His website is called Platonia.

" ... time is an illusion.
The phenomena from which
we deduce its existence are real,
but we interpret them wrongly.
My arguments are presented in
The End of Time."

- Julian Barbour.

Last edited: Apr 19, 2007