Why does time flow at different rates for different people? Isn't it constant?

Question

I understand the light cone analogy, but aren't we all sharing it at the same time on earth? Why do we travel at different rates?

Answer 1

In any practical senses, yes, we all share the same light-cone. The differences would be measured in the trillionths - a millisecond or so over a lifetime.

Anyway, picture an extension of the Pythagorean equation determining the distance between two points.
c^2 = a^2 + b^2

You can extend this into multiple dimensions - including time-
d^2 = x^2 + y^2 + z^2 + t^2
(this isn't entirely correct but will suffice for explaining this)

The equation always equals one. That is:
1 = x^2 + y^2 + z^2 + t^2
In other words, either you perceive something moving through space, or through time, but not both. If something is moving at 80% of c away from you-
1 = .8^2 + 0^2 + 0^2 + t^2

t must equal .6 - meaning, you see it move through six 'seconds' for every ten that you experience. Things stationary to you will move along with you at an identical rate of time, but things moving will seem to progress at a slower rate. This only becomes noticible at extreme velocities, however.

Answer 2

Time is subjective to people.
To a 4 year old 1 hour to wait is forever, to a 70 year old a year is a flash in the pan.

Answer 3

As the analogy is meant to point out, everything depends on perception.

Answer 4

time is time. It is only your perception of time that changes. Just like the old watched pot never boils, kind of thing.