# B Is the time dimension more fundamental?

1. Feb 14, 2018

### thermia

If we do the thougt experiment to delete one of the three spacedimentions we end up with a flat-land universe, which is fully possible to imagine (while probably not existing)
But if we delete the time dimesion it becomes inpossible to imagin. Whithout time there is no existence.
Could that mean that the time dimension is more fundamental than the other three?

2. Feb 14, 2018

### phinds

Personally, I don't think it's more fundamental, just different. Flatland is an interesting mathematical construct but not, I believe, a possibility for actual existence.

3. Feb 14, 2018

### Ibix

It's just a Euclidean space. I don't see the problem imagining it - we have been doing so since Euclid's time.

4. Feb 14, 2018

### thermia

Thanks for your reply. Of course flatland is highly improbable. My thought came from my inability to imagine a universe without time.

5. Feb 14, 2018

### thermia

Well, I was tryiing to imagine physical universes. Euclidian space is just math.

6. Feb 14, 2018

### itfitzme

If you examine the measures of time in detail you will find that time is simply a measure of distance, more specifically a measure of cyclical distance. For instance, we measure time by counting the number of instances that the Sun moves around the Earth (celestial sphere).

7. Feb 14, 2018

### PeroK

I'm not sure I would use the word fundamental, but your point seems trivially true. We can study motion and systems in 1, 2 or 3 spatial dimensions, but we always need a time dimension to get physics, as we know it.

8. Feb 14, 2018

### thermia

Yes, of course. But physisists have thught a lot about why the so called "time arrow" seem to be forced to go in just one direction, which may indicate that there is a fundamental difference between time and other dimensions.
I have been thinking that maybe all the dimensions are not created in exactly the same moment. I'm probably wrong but it is interresting to speculate about

9. Feb 14, 2018

### thermia

Thanks for reply. I understand you see my point :-)

10. Feb 14, 2018

### Grinkle

Also, I can imagine exactly one time dimension and I can imagine not moving at all or moving forward in that one dimenion. I have no idea what is implied by multiple time dimensions. I also don't have any intuitions that I trust at all regarding time travel to the past.

I can easily imagine 0, 1, 2 or 3 space dimensions, and I have intuitions that I trust regarding the implications of more than 3 spatial dimensions even if I can't make a mental picture of them.

But I don't know if that is anything more than an observation of human brain evolution.

11. Feb 14, 2018

### thermia

Well, that's the wall we allways are running into, aren't we? :-)

12. Feb 14, 2018

### jbriggs444

Suppose that I lay out a two dimensional coordinate system with axes labelled x and t. Suppose further that I draw a graph that satisfies the equation: $xt=1$

What grounds do I have for considering t more "fundamental" than x? Why am I forced to consider that position x evolves over time t. Why can I not with equal rigor declare that time t evolves over position x?

13. Feb 14, 2018

### thermia

Of course that's correct but only in Eucledian mathematics. My question is about physical dimentions i.e.the "real" world.

14. Feb 14, 2018

### jbriggs444

Lacking a measurement procedure, both are equally hypothetical. It is a distinction without a difference.

15. Feb 14, 2018

### Staff: Mentor

It's different.
Does that mean that it's more fundamental? There's no answering that question unless someone provides a definition of "fundamental" that we can use to determine how fundamental something is and compare that with the "fundamentalness" of something else - and I'm not seeing that happening.

16. Feb 14, 2018

### itfitzme

And there's the problem, this imagined "time arrow" which supposedly might run in some other way. At it's core, physics is simply correlating on property with another. "Time" is label we give to one of these correlations. Fundamentally, physics is a study of how things change. There are cyclical changes that we recognize, the magnitude of voltage going up and down, the point end of the hand of a clock passing a mark "12" on its face, the change of a pulse of light as it goes down and back, reflecting off some distant mirror. The standards of weights and measures was devised so that we have a common reference for correlation. When we get down to the root of it, "time" is a measure of distance. A light year is the distance light travels compared to some other reference we have chosen as a cyclical distance. Time isn't some real property of space, it is the change of an object's position in space which we mark by correlating those positions to the swing of a pendulum that cycles in position in space.

17. Feb 14, 2018

### Grinkle

That remark is not physics, whatever else it may be. General Relativity models spacetime and gives very specific attributes to space and time.

18. Feb 14, 2018

### thermia

A clever answer, well worth to consider, thank you.

19. Feb 14, 2018

### itfitzme

I find it an interesting think to wonder. The single observation that come close to the arrow of time is entropy. But this, as far as I know, is simply that things tend towards spreading out evenly across space. Again, we're down to that fundamental point of measure of distance, whatever changed position.

I have made some effort at finding some fundamental measure of time that doesn't involve a measure of distance and haven't. Always, in there, is that requirement of comparison to some other thing displaced in a spatial dimension, by convenience a cyclical displacement.

20. Feb 14, 2018

### Grinkle

Does it make less sense to claim that a universe containing only a single static particle is getting older than to claim that same universe is expanding? For either case, I can't think of an experiment to define either older or bigger. My point is that I don't see how time is different from space in requiring some anchor points if one is to actually measure.