What made the universe have 3 dimensions, instead of some other number?

[Jack21222]

The fact that m-theory or other types of string theory require extra dimensions mathmatically to me means that, while we are not arbitrarily adding constraints ala Newton/einstein, our theory needs to be improved so that it does not mathmatically require these extra dimensions in the first place.

I could be wrong though.

Is time a dimension? What makes Einstein's addition of time as a dimension any different from adding other dimensions?

 

[arkajad]

Is time a dimension? What makes Einstein's addition of time as a dimension any different from adding other dimensions?

Arrow of time.

 

[nismaratwork]

Is time a dimension? What makes Einstein's addition of time as a dimension any different from adding other dimensions?

Well, he redefined something that's been in our common experience. Nobody disputes that time exists, and defining it as a dimension actually makes a lot of sense, never mind the good physics we get from that. Recognizing that time and 3 spatial dimensions are subject to warping by mass is what makes Relativity.

schteev: I have issues with string theory, but what you're talking about isn't one of those issues nor do you make sense. You're acting from a biased point of someone experiencing 3 spatial and one temporal dimension, much as people were skeptical about time as a dimension and not some absolute measure. The issue with string theory is confirmation of a prediction, not extra dimensions. If that confirmation ever comes out, then the dimensions would naturally follow... no more or less, much as with GR. Is this any odder than the notion of quantum behaviour at small scales?

 

[closet mathemetician]

In my opinion, dimensions are simply a theoretical degree of freedom. There is no reason why there shouldn't be an infinite number of possible degrees of freedom. However, actual geometrical structures don't generally have an infinite number of dimensions. They have some finite number of dimensions that places boundaries and limitations on things.

The geometrical object you happen to inhabit forms the "space" in which you live, along with its limiting dimensional structure. If you live on a line, your space is one-dimensional, if you live on a plane your space is two-dimensional. If you live in spacetime, you have four dimensions. You can't assume that the geometrical object is embedded in a higher "space".

 

[arkajad]

If you live on a line, your space is one-dimensional, if you live on a plane your space is two-dimensional. If you live in spacetime, you have four dimensions. You can't assume that the geometrical object is embedded in a higher "space".

But physics is not about my space or your space. It is about the objective reality. And the objective reality may well be different from the subjective one experienced by our senses.

 

[schteev]

But physics is not about my space or your space. It is about the objective reality. And the objective reality may well be different from the subjective one experienced by our senses.

Yes our senses are limited, which makes it hard for the average human to get their head around these sorts of concepts, just like it's hard for the average flatlander to comprehend a three-brane world.

I tend to think a simple explanation is a better fit than something that is needlessly complicated. Yes, in the language of our universe string theory (all of them) makes sense and goes a long way to at least trying to unify our great theories.

I just think that we should spend time trying to explain what's happening in our own brane world first before getting too far ahead of ourselves. Let's work out what is keeping stars in galaxies, and where all this unexplained energy is coming from first. Let's work out dark matter with a simple explanation.

 

[Kevin_Axion]

The extra-dimensions to some extent simplify the mathematics. Also possibly the answers to your questions such as dark energy and dark matter will be discovered in superstring theory.

 

[schteev]

The extra-dimensions to some extent simplify the mathematics. Also possibly the answers to your questions such as dark energy and dark matter will be discovered in superstring theory.

I hope so, but I think we are a long way from answering these questions.

It certainly doesn't hurt to try though.