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Asked by Pikachu 2000 to Frank, Ian, Isabel, Jared, Zena on 9 Mar 2015.
Question: What is Spacetime?
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Frank Longford answered on 9 Mar 2015:
I’m no physicist but I guess the simplest way of thing of spacetime is just the mathematical combination of our 3 dimensions of space (x, y, z) and time as a 4th dimension (t). Mathematically you can see the relationship between space and time by using a right angled triangle relationship: h^2 = a^2 + b^2 (^2 just means “squared”). If you think of “change in space” as one side of the triangle (dR) and “change in time x speed of light” as the other (cdT), then the hypotenuse is just a spacetime vector (S) that explains the link between the two:
S^2 = dR^2 + (cdT)^2
In this way we can mathematically explain how things affects the fabric of the universe. However, it’s still quite difficult to “see” what spacetime is and interpreting these equations can be a difficult task even for expert physicists! Maybe this video will give a clearer explanation (hopefully!):
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Zena Hadjivasiliou answered on 9 Mar 2015:
Hmmm I think this is one of the most challenging concepts to understand in physics and I have to admit I don’t understand it very well at all!
We are used to thinking about space as being three-dimensional. Think about it: we can move forwards/backwards (1st dimension), right/left (2nd dimension) or up/down (3rd dimension). The idea of spacetime (as far as I understand), brings in time as a fourth “dimension” and so a thing that we can perceive in different ways. The dimension of time depends on the other three dimensions (so the dimensions of space). So where something is or (most importantly) how fast it moves can affect the way in which time changes. According to the theory of relativity for example, time changes more slowly for something that moves very, very fast! But like Frank said, understanding these concepts is a real challenge even for experts on this field!
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