Time and Local Frames of Reference
Dear Physics Professors:
I am a graduate accounting student and astronomy is a big hobby of mine,
so I like to occasionally study physics. I have been reading
"The Fabric of the Cosmos" by Greene and I rather enjoyed this book's
explanation of Einstein's time dilation theory. The book indicates that
"stationary" objects (such as a car) have 100% motion through time, and 0%
motion through space; therefore time progresses at "normal" speed for the
stationary car. Furthermore, when the car is in motion speeding down the
highway at 60 mph, some of its motion through time is diverted to motion
through space. Therefore time for the car and it's passengers "slows
down" relative to the observer on the sidewalk. My question is as
follows: The earth is moving along it's orbit AND rotating at extremely
high speeds, so no object on earth is really "stationary". How does this
fact figure into all of this? Does this impact the entire planet's
perception of time? Is the passage of time different for us than it would
be for a colony on Mars, since Mars is moving at a different relative
speed? I hope this question is clear.
The "key" to relativity is that there is no such thing as one real time. As
measured by someone riding in the moving car, the car has 100% motion
through time. It is the ground that "slows down". For the person on the
sidewalk, the ground is going through normal time and the car's clock slows
down. Both observers are correct. A man in the car sees a clock on the
sidewalk as moving too slowly. A man on the sidewalk sees a clock in the
car as moving too slowly. Of course, this time dilation is much too small
to even try to measure when the speed is only 60 mph.
What you measure is all that there is. The universe does not have one
absolute truth that everyone measures differently. What is actually true
about space and time does not just look different for different observers.
It IS different.
For those of us on the Earth, things on the Earth happen in normal time.
For someone "riding a comet", things on the Earth are dilated in time.
Dr. Ken Mellendorf
Illinois Central College
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Update: June 2012