# What is the 4th dimension? [closed]

I have heard before that the 4th dimension is time, however, another theory makes a lot more sense to me. This is that the 4th dimension is the third dimension stacked on top of each other in a similar in which 3d objects are just many 2d planes.

I have seen many articles related to the 4thdimension being time, but how do we know this?

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## closed as off topic by Tim van Beek, sb1, space_cadet, Marek, dbraneFeb 12 '11 at 13:35

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Dear Cameron, this question will be answered in any introductory class to physics, which means that it is not appropriate for this site, which is for students and researchers (see faq). In case you are not a student of physics: there are a lot of nice introductions to special relativity for non-experts, like N. David Mermin:"Space and Time in Special Relativity". I'm voting to close. – Tim van Beek Feb 12 '11 at 11:44
This is too elementary and I believe it does not belong here. I have voted to close. – user1355 Feb 12 '11 at 12:11
Thank you Tim, I will think about that, I am a student but only at high school. – Cameron Feb 12 '11 at 18:59
don't get discouraged at using this site. If you can formulate your questions (including this one) in some better way, I am sure you will receive some good answers. – Marek Feb 13 '11 at 2:51
After knowing your age, I came to think that you are quite intelligent. You may edit this question and it may be reopened. – user1355 Feb 13 '11 at 16:57

It is all in what you want to describe mathematically. You can have an N dimensional space and yes, you could "visualize" the analogue of two dimensions going into three. These are Euclidean spaces , i.e. the metric is ds*2=dx*2+dy*2+dz*2+.... up to N terms.

Time is the fourth dimension in current physics because we are attempting to describe and predict motions and interactions of matter and light in a mathematical manner, and the equations are such that they simplify when time is assumed to be the fourth dimension in what is called a pseudo Euclidean space., and in our case dt**2 has a negative sign. It is what the physics comes out with that makes time the fourth dimension.

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If the question is silly, the answer is sillier. – user1355 Feb 12 '11 at 12:14
Why, thank you sb1. I was just trying to relate to the level of the question, which was evidently by someone who knew no physics. Sorry for offending your sensibilities, or not reaching your level of intellgence. – anna v Feb 12 '11 at 14:36
@anna: I don't see how you related to the level of question. You are still talking about metric and such. Moreover, you talk about simplifying some equations (which ones?) which has nothing to do with the question. The reason time is included is simply because it's a requirement for special relativity. Nothing more or less. – Marek Feb 12 '11 at 15:32
@Marek, I took the trouble to look at the questioner's profile, and though he is unfamiliar with physics he seems familiar with maths. For somebody unfamiliar with physics general descriptions should be enough. Does one have to write a dissertation when answering such vague questions? Or should one bite the head off the unfortunate questioner, ( how silly how stupid etc) as some seem prone here? Not many students will dare ask questions in such an environment. ( and I would think that special relativity is some equations, no?) – anna v Feb 12 '11 at 16:15
Sorry to have caused a debate, I do "understand" physics however on a very small scale. I am only at high school (13, as it says on my profile) and although I am one of the top in my class it is obviously a very low level compared to the people on this site. Oh and @anna why do you think I am fammiliar with mathamatics? Again, I am high for my level in high school (you are probably laughing now!) but I can't find where it says on my profile that I am good at maths. – Cameron Feb 12 '11 at 18:55