How do we say that the universe we live is 3 dimensional?

[Altamash]

i opine that the universe is not 3 dimensional at all. its not build up of 3 coordinates at all. it is because, we humans could see 3 dimensions it doesn't mean the space metric is of 3 dimensions. suppose there's a super being living on an Earth like planet of some other galaxy whose viewing capacity is of say a complex dimension(i don't want to use the term multi-dimensions or something else), for that being, the whole physics is completely different, may be because of dimensional power of observing objects and their motion, the physics for him would be more simple and elegant.

 

[Drakkith]

Remember that science is all about what we can observe. What some alien or higher-dimensional being can or cannot see is irrelevant, as we are stuck firmly here in the 3-dimensional world. For information on why we say the universe is 3-dimensional, see here: https://en.wikipedia.org/wiki/Dimension#Spatial_dimensions

 

[Altamash]

okay, what about string theories then, string theorists say we live in a 3 dimensional membrane of the multidimensional space of universe.

what my point is, 3 dimensional analysis is not the only reality but there's something else beyond our 3 dimensional physics. also, as string theories rely on extra dimensions, it could mathematically reconcile general relativity and quantum physics...

 

[Drakkith]

okay, what about string theories then, string theorists say we live in a 3 dimensional membrane of the multidimensional space of universe.

Indeed but it is nothing like what you're imagining and there is no evidence supporting string theory over any other physical theory.

what my point is, 3 dimensional analysis is not the only reality but there's something else beyond our 3 dimensional physics.

I'm not sure where you're getting this from. There are exactly zero mainstream, accepted theories used to model things in real life that have more than 3 spatial dimensions. There are certainly other theories out there with more than 3 spatial dimensions, but they are not accepted as of yet (mainly because we have yet to find a situation where they describe space better than GR).

 

[e.bar.goum]

i opine that the universe is not 3 dimensional at all. its not build up of 3 coordinates at all. it is because, we humans could see 3 dimensions it doesn't mean the space metric is of 3 dimensions. suppose there's a super being living on an Earth like planet of some other galaxy whose viewing capacity is of say a complex dimension(i don't want to use the term multi-dimensions or something else), for that being, the whole physics is completely different, may be because of dimensional power of observing objects and their motion, the physics for him would be more simple and elegant.

Since this is a topic marked "Advanced", then you should be able to understand classical mechanics. Thus, this link will be of interest: http://usersguidetotheuniverse.com/index.php/2013/12/03/a-technical-post-on-more-than-3-dimensions/

Essentially, Bertrand's theorem: https://en.wikipedia.org/wiki/Bertrand's_theorem tells us that dimensionality >3 means that there are no closed orbits. Which I'll think you'd agree, is fairly essential us to be here.