Why do we consider time as the 4th dimension?

In summary, time is not the fourth dimension, but it is a dimension like space and mass. It is necessary to specify an event in space/time using 4 numbers. These numbers are the spatial coordinates and the time at which the event occurred.
  • #1
TheDonk
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Time is not the 4th dimension. Well... depends on perspective. Why do people say time is the 4th dimension? I know you can say it's a dimension and there are already 3. But why not say mass is a dimension? Each point in space has a certain mass. What's the difference? Einstein said it and it became convention? That better not be the reason :mad: :rolleyes:.
I think it would be best when describing time with space and need to call it a dimension to say something like, "If you use time as a dimension then..."
 
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  • #2
I've said thsi before to say time is the foruth diemsnion is is some ways menaingless as your not saying what it is a dimensions of.

Of course the reason people say this is that we do physics in spacetime which has four dimensions and we may view time as one of them.
 
  • #3
if time isn't a dimension, then what do you put in place of it when you describe an event?
 
  • #4
It is a simple matter of mathematics. It requires 4 numbers to specify an event in Space/time. 3 spatial coordinates and the time at which the event occurred. It is not necessary to specify the mass. Notice that I am specifying a SPECIFIC type of problem, one dealing with SPACE/TIME events. In a different problem, one NOT dealing with space/time the meaning and number of dimensions may be entirely different.

If you were dealing with problem where mass was changing with position, you may well need a set of equations were mass is the forth dimension, but that would be a different problem, if fact if you were track your mass and position through out your life you would need 5 dimensions, 3 for your position,1 for the time and 1 for your mass.

Once again the number of dimensions of a system is the minimum number of points required to completely specify the state of that system.

To say that time is not a dimension of space/time is simply ludicrous.
 
  • #5
Calling space 3 dimensional implies that the three quantities used to describe a point are similar. Thus 1 metre North is thought to be the same as 1 metre East - if you have a metre rule pointing North then you can turn it to point East. Equivalently, different observers may have different meanings for 'forwards' and 'sideways'. What special relativity says is that time is similar to space - although different observes will agree on the spacetime distance between events, they may not agree on how this splits up between time and space.
 
  • #6
TheDonk said:
Time is not the 4th dimension. Well... depends on perspective. Why do people say time is the 4th dimension? I know you can say it's a dimension and there are already 3. But why not say mass is a dimension? Each point in space has a certain mass. What's the difference? Einstein said it and it became convention? That better not be the reason :mad: :rolleyes:.
I think it would be best when describing time with space and need to call it a dimension to say something like, "If you use time as a dimension then..."

Time and space mix together. What is a pure space-like separation for one observer is a mixture of space and time separation to another moving relative to the first.

It's this mixing together of space and time by the equations of relativity that that makes space-time a unified concept, usually called the space-time continuum.
 
  • #7
TheDonk said:
Time is not the 4th dimension. Well... depends on perspective. Why do people say time is the 4th dimension? I know you can say it's a dimension and there are already 3. But why not say mass is a dimension? Each point in space has a certain mass. What's the difference? Einstein said it and it became convention? That better not be the reason :mad: :rolleyes:.
I think it would be best when describing time with space and need to call it a dimension to say something like, "If you use time as a dimension then..."
If you use time as a fourth dimension you will find the theory of relativity, which makes predictions that have been verified by experiments. If you use density as a fourth dimension you get nothing interesting. That's why we say that time is the fourth dimension. What that really means is that time is the fourth dimension of spacetime, which is a useful concept. You could say that density is the fourth dimension of "spacedensity", but that seems kind of pointless doesn't it?

(It doesn't really make sense to speak of the mass at a certain point. That's why I replaced mass with density).
 
  • #8
Without time, spatial dimensions are meaningless. As Integral said, you cannot quantify distance [or force for that matter] without time.
 
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FAQ: Why do we consider time as the 4th dimension?

Question 1: What is meant by "Time is not the 4th dimension?"

The concept of time being the 4th dimension is a common misconception. In physics, dimensions refer to the spatial coordinates that are needed to describe the position of an object. Time is not a spatial coordinate, therefore it is not considered a dimension in this context.

Question 2: Why is time not considered a dimension?

Time is not considered a dimension because it does not behave in the same way as spatial dimensions. Unlike spatial dimensions, time is not fixed and can vary depending on the observer's frame of reference. Additionally, time only moves in one direction, while spatial dimensions can move in multiple directions.

Question 3: Can time be measured in the same way as spatial dimensions?

Time can be measured, but not in the same way as spatial dimensions. Spatial dimensions can be measured in units of length, such as meters or feet. However, time is measured in units of seconds, which is a measure of duration rather than distance.

Question 4: How is time incorporated into the concept of spacetime?

The concept of spacetime combines the three dimensions of space with the dimension of time to create a four-dimensional framework for understanding the universe. This concept was developed by Albert Einstein in his theory of general relativity, which describes how gravity affects the curvature of spacetime.

Question 5: What are the implications of time not being the 4th dimension?

The implications of time not being the 4th dimension are mainly theoretical. It challenges our understanding of the universe and raises questions about the nature of time and its relationship to space. It also has implications for the study of physics, as it suggests that time may need to be described by a different framework than spatial dimensions.

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