Is spacetime just a mathematical trick or is it the actual physical reality?

[martinbn]

Hm yes what is space and what is time separately are tough questions...But does the fact that one exist with the other mean they are the same thing ?

No, I meant. What is space? What is time?

 

[DoobleD]

In particular, when you go to GR, space-time is a fundamental concept...

Yes, I was wondering if that could be a "proof" that the world is "really" spacetime. The thing that annoys me is that the fact GR is expressed using spacetime, does still not prove it can't be correctly expressed via a different model. But yeah it kind of says "there's a huge change that reality is spacetime indeed and nothing else".

No, you are right. Minkowski spacetime is one possible geometrical interpretation of SR, that was proposed after SR has been already published.

But note that in Minkowski spacetime, time is not "just like space", that why it is pseudo-Euclidean. There is another, less common geometrical interpretation of SR by Epstein, where proper time is more like another space dimension, and (coordinate)time is the Euclidean path integral.

Thank you for the information ! At least that is clearer now. EDIT : can you explain why, in Minkowski spacetime, time is not actually treated "just like space" ?

No, I meant. What is space? What is time?

Honestly I think any attempt I'd do to define space, and define time, would fail. :D

 

[A.T.]

can you explain why, in Minkowski spacetime, time is not actually treated "just like space" ?

The time term has the opposite sign of the 3 space terms in the Minkowski metric:
https://en.wikipedia.org/wiki/Minkowski_space#Minkowski_metric

 

[Herman Trivilino]

Experiments confirm SR, they do not confirm our world is a Minkowski spacetime where time is just like space. I distinguish those two things, SR and Minkowski spacetime. This might be wrong, from what everybody says.

Spacetime doesn't mean space is just like time.

 

[DoobleD]

The time term has the opposite sign of the 3 space terms in the Minkowski metric:
https://en.wikipedia.org/wiki/Minkowski_space#Minkowski_metric

Ok, thanks.

Spacetime doesn't mean space is just like time.

That's what I've just learned indeed (see post above).

 

[alw34]

No, I meant. What is space? What is time?

Space is what keeps everything from happening to you.

Time is what keeps everything from happening all at once.

 

[Dale]

Experiments confirm SR, they do not confirm our world is a Minkowski spacetime where time is just like space. I distinguish those two things, SR and Minkowski spacetime.

Nature does not distinguish those two things. All interpretations are experimentally indistinguishable.

 

[PeterDonis]

a Minkowski spacetime where time is just like space

Time is not "just like space" in SR/Minkowski spacetime (which are the same thing, as DaleSpam says). There is a fundamental difference between timelike intervals and spacelike intervals (and there is also a third type, null intervals, which is fundamentally different from the other two). Physically, the difference shows up as, for example, the fact that you can't measure timelike intervals and spacelike intervals the same way; you use a clock for the former and a ruler for the latter. Mathematically, the difference shows up as a difference in signs in the metric.

 

[DoobleD]

Thanks for the answers !

 

[industry7]

Nature does not distinguish those two things. All interpretations are experimentally indistinguishable.

How do you measure spacetime?

 

[HallsofIvy]

How do you measure spacetime?

s^2= t^2- x^2- y^2- z^2

 

[Dale]

This thread is closed