# I need help in understanding space-time and space?

i know space-time has 4 demensions and space has 3. i know the deminsions but my question is this: do scientists prefer space or space-time? and does the universe have 4 or 3 demionsion based on what we know?

Relevance
• 1 decade ago

Space/Time as 4 dimensional space is *not* the same thing as 4-dimensional space. It is 3-dimensional space with time as a 4th dimension. When they speak of 11-dimensional space in String Theory they mean 11 spatial dimensions.

Think of it like this. When defining a point in space you use three numbers on a grid (X, Y & Z axis). So, with a given starting point you could say the location you want is 100 feet north, 200 feet east and 500 feet up. Those three numbers define a point in space from your starting point.

However, there can also be a time dimension to it. Say you are in New York standing on a street corner and I give you those directions which would take you into the Empire State building to the 45th floor where I will meet you. That is fine except you are missing a piece...*when* will I meet you there? So that gives us four data points: how far north, east and up and when.

Now, you do not always need that 4th data point. Maybe I am not meeting you and just telling you how to get where you are going from some starting point. However, the time dimension can also be critical. Say I am launching a probe to Mars. I need to know where Mars will be at some point in the future so when my probe arrives Mars is there too.

So sometimes you need it and sometimes you don't. Depends what you are doing.

• 1 decade ago

It depends on what you need it for. For physicists, many astronomers and people dealing with relativity, space-time is required, but for the rest of us, space will usually suffice.

According to the theories, there are about 11 dimensions by now. It has even been hypothesized that time is 2-dimensional.