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# Relativity/Further on GPS and relativity

Question
Hi Ben,

Thanks for your time in answering my questions. You have not specifically answered the  questions regarding whether relativity is used in GPS or not.

The atomic clock is running differently in different places of the earth. The measurement in each place is absolute and that is why,"TAI as a time scale is a weighted average of the time kept by over 200 atomic clocks in over 50 national laboratories worldwide". The time measured in each of the place is absolute, yet we find that the time in each place is different. I don't understand how relativity comes into picture here.

I read that even Nikola Tesla, one of the greatest scientist denied relativity. Also there is an array of physicists who denied relativity. Some of them have PhDs too. Didnt they see the evidences which you were saying. pls see:

Herbert Dingle, Louis Essen, Petr Beckmann, Maurice Allais and Tom van Flandern denied relativity.

(http://en.wikipedia.org/wiki/Criticism_of_the_theory_of_relativity)

Louis Essen is the developer of first practical atomic clock
http://en.wikipedia.org/w/index.php?title=Louis_Essen&action=edit§ion=3

Ameen, GPS does use both special and general relativity.  If the didn't, the clocks would become de-synchronized within minutes after the are synchronized.

I cannot answer all your remaining questions without writing you a book.

I thought the thing that would help you the most was an explanation of how a clock can have more than one time rate when observed by more than one observer.  This is the thing that Dingle never understood.

I am sorry I could not be of more help. Relativity is deep.

Best of luck in your studies.

Relativity

Volunteer

#### 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.