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Naming time the "fourth dimension" is a misnomer, it's not a dimension in the usual sense of the. Hence the spacetime of relativity, formulated in Minkowski spa

by Jun8 17y ago

Naming time the "fourth dimension" is a misnomer, it's not a dimension in the usual sense of the. Hence the spacetime of relativity, formulated in Minkowski space, is different than standard 4-ED Euclidean space (see http://en.wikipedia.org/wiki/Minkowski_space http://en.wikipedia.org/wiki/Minkowski_space). As Einstein says, "Make things as simple as possible, but not any simpler." The time as fourth dimension thing, I think, is an example of a wrong analogy pushed to make it easy for people to understand what in effect is quite hard to grasp.

mattheww 17y ago
While you're right that it's not a dimension in the sense that most people are used to, I think that it appropriately conveys the fact that time and space are intertwined. When you start traveling very quickly your sense of distance and time change in a way that is exactly proportional to each other. The fact that space and time need to be treated as a single entity was in fact one of the key conceptual advances that Einstein made.
lutorm 17y ago
They said "4th dimension", not "4th Euclidean dimension" so I don't see that there was anything incorrect there.
aero142 17y ago
I always understood a dimension as "a variable that you can change to avoid occupying the spot." In 3d space, two objects cannot be in the same spot so either their x,y, or z coordinate must be different. If I add time as a fourth dimension then two objects can be at the same x,y and z, but not at the same time. You are right that time is a special dimension, but there are many things it has in common with the 3 spacial dimensions as well, my example being one.
- derefr 17y ago
  I've always heard dimensions being referred to as "timelike" or "spacelike", similar in vein (though not in concept) to the difference between "flat" and "rolled up" dimensions.
- Jun8 17y ago
  You're right, in an intuitive sense. In math, especially dealing with weird stuff like extra dimensions, intuition may break down, though. For example, in the 4D Minkowski space you can have a unit sphere with a radius of -1! One has to understand what is meant when we say that "time is a special dimension". otherwise teh analogies we draw may fail. The Wikipedia article I linked explains these in a simple way.
jeffbradberry 17y ago
-1 (if I in fact had the points to do it), for assuming that changing the metric space obviates calling a dimension a dimension.
- Jun8 17y ago
  Of course it doesn't :-) However, I wonder how many people reading this article in the Guardian know about different metric spaces. Hawking's presumed audience here is "laymen".

by Jun8 17y ago

mattheww 17y ago

While you're right that it's not a dimension in the sense that most people are used to, I think that it appropriately conveys the fact that time and space are intertwined. When you start traveling very quickly your sense of distance and time change in a way that is exactly proportional to each other. The fact that space and time need to be treated as a single entity was in fact one of the key conceptual advances that Einstein made.

lutorm 17y ago

They said "4th dimension", not "4th Euclidean dimension" so I don't see that there was anything incorrect there.

aero142 17y ago

I always understood a dimension as "a variable that you can change to avoid occupying the spot." In 3d space, two objects cannot be in the same spot so either their x,y, or z coordinate must be different. If I add time as a fourth dimension then two objects can be at the same x,y and z, but not at the same time. You are right that time is a special dimension, but there are many things it has in common with the 3 spacial dimensions as well, my example being one.

derefr 17y ago
I've always heard dimensions being referred to as "timelike" or "spacelike", similar in vein (though not in concept) to the difference between "flat" and "rolled up" dimensions.
Jun8 17y ago
You're right, in an intuitive sense. In math, especially dealing with weird stuff like extra dimensions, intuition may break down, though. For example, in the 4D Minkowski space you can have a unit sphere with a radius of -1! One has to understand what is meant when we say that "time is a special dimension". otherwise teh analogies we draw may fail. The Wikipedia article I linked explains these in a simple way.

jeffbradberry 17y ago

-1 (if I in fact had the points to do it), for assuming that changing the metric space obviates calling a dimension a dimension.

Jun8 17y ago
Of course it doesn't :-) However, I wonder how many people reading this article in the Guardian know about different metric spaces. Hawking's presumed audience here is "laymen".