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Dear Ben,
Is it true that every time anything moves --times slows down for it , its' length shortens and its' mass increases? Is it true that this effect is for everything even a dust mite - everywhere, everytime in any given frame of reference?
And that when said movement stops---is it so that  the relativity effects vanish and you are back to square one - your starting length, mass and time ?
I know, after much time and adoo,  i am not capable of understanding relativity but if I could just get past this one question I could see a little clearer and could pass it on to some curious people I know for them  to take further because if I can see a little-- ANYONE can and can  go further.  These people regret now, as is often so, (late twenties) they didn't learn more in school and I (real old) am trying to help.  

thank you,


Joan, I am sorry to be late in answering you.

The truth is a little more complicated that what you say. Suppose you are on a bicycle riding past me. I am sitting on a park bench. Now is the park bench moving?

It is not moving relative to me but it is moving relative to you.  And it is likely moving with respect to the moon and to the sun. All at different speeds.

So how do I answer your question?  Is the bench moving or not moving?  You can see the problem.

We say that motion is relative, not absolute.  The number of pennies in your pocket is absolute. Your motion is not.

The phenomena you ask about do occur, but you can see that the length of the park bench is, believe it or not, relative. I could say that it has more than one length, but that might be a little misleading. Still, it has one length relative to me and another to you at the same time.

If that sounds mysterious, it is, but we believe it to be true. I can't explain it, nor can anybody else, but it works!


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Uncle Ben


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.


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.

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

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

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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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