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Relativity/Regarding GPS and relativity

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Question
Hi Ben,

Thanks for your reply.

I read that atomic clocks run differently throughout the different surfaces of the earth. Please see the link below.

http://en.wikipedia.org/wiki/International_Atomic_Time

If the atomic clocks runs differently in earth itself, how could the relativity be the explanation of time variation when we are dealing with a single body (earth). Isn't the difference in atomic clock running due to the difference in their surface's gravity?. Could the same reason be applicable in satellite clock slowing?. Also I read that satellite clocks are already running 16 seconds ahead of UTC,(pls see link: http://en.wikipedia.org/wiki/Global_Positioning_System#Leap_seconds ), how could 38 nano seconds adjustment due to relatvity matter?. I read that some top physicists, ex: Herbert Dingle (http://en.wikipedia.org/wiki/Herbert_Dingle ) opposed relativity. pls see below:

http://blog.hasslberger.com/Dingle_SCIENCE_at_the_Crossroads.pdf

Answer
First, relativity tells us that time is relative.  

If you are on a speeding train and I am at home, the rate of a single clock will be different with respect to you than with respect to me.
That is one effect.  

If you are on a mountain top and I am in a valley, the same atomic clock will run at different rates with respect to each of us.  That is a second effect. General Relativity teaches us that.

How can one clock run at different rates for different observers? It just does. We have to accept that as a fact because experiments have verified it.

It is not like numbers of things.  If there are three marbles in a box, that number is absolute:  it is three for everybody.  

Time is like position. Where is the Panama Canal?  For me is  south;  for my Bolivian nephew it is north. The same Canal has different positions relative to different observers.

That is what "relative" and "absolute" mean.  It seems impossible that time can be relative, but it is.  Time is as relative as position. It is not absolute, like numbers of marbles.

Herbert Dingle was at work many years ago. Today, nobody takes him seriously. The evidence for relativity is overwhelming.  

Nature does not care what we think;  we have to figure out what Nature already knows. Experiment is the only judge of what is true.

To go further in relativity, Ameen, you need to take a university course. You will learn the experimental evidence that shows that time is relative.

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Uncle Ben

Expertise

I can answer questions regarding Einstein's Theory of Relativity, particularly in Special Relativity. I will not answer homework questions or mathematical problems that require special symbols.

Experience

I have taught physics at the college level, undergraduate and graduate, for many years including Special Relativity. I have taught at Johns Hopkins, Case-Western, and MIT. I have also served as a staff member of the Commission on College Physics, which was supported by the National Science Foundation to recommend improvements in the curriculum of college physics departments in the US. I am also the author of a textbook titled Vector Calculus, which was used at MIT in the teaching of electromagnetic theory and relativity. My research interests were mainly in solid state physics, especially the properties of metals at low temperatures. I am listed in the publication known as American Men of Science.

Publications
I have dozens of papers published in the Physical Review and in the American Journal of Physics.

Education/Credentials
I hold a Ph.D. degree in physics from the Johns Hopkins University.

Past/Present Clients
Johns Hopkins University, Case-Western Reserve University, Massachusetts Institute of Technology, Empire State College, Georgetown University, Commission on College Physics, and UNESCO.

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