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# Relativity/Time space continuum

Question
Dear Ben,

I wonder if you could give a quick synopsis of the concept of the space time continuum? This is not a homework question, just an older guy who didn't do well in physics many years ago. I have watched a utube that depicted relativity as slices in bread but I still can't wrap my mind around it.

Also, in another section, an expert (religious not scientific) said water is the only think that affects light and returns it to its natural form. Any idea what we was talking about and any truth to it?

Thanks once again

The idea of the space-time continuum is grounded in the fact that when you measure a moving rod's length with respect to you, you have to make your marks at the same time with respect to you.  But your clocks run at a different rate with respect to you than the rate that the moving clocks run, again with respect to you. Moving clocks run fine with respect to a person moving along with them, you but they run slow with respect to a person not moving with them.

All the "with respect to's" are needed because in Einstein's relativity, lengths and clock rates are relative to the frame of reference in which they are measured, no matter how mysterious that seems to be.  Without that, we could not say that the speed of light is the same with respect to every inertial frame of reference.  And without that, we could measure the speed of light in different frames and find one privileged frame of reference for the universe and could measure our own speeds with respect to THAT frame, which is ABSOLUTELY at rest.  The evidence says that that is not so, and something has to give, and the only candidates are length and time.

The fact that both length and rate are frame-dependent connects time to distance.  They both change so as to keep the speed of light constant.  Does that answer your question? It doesn't persuade anybody, but the statement is true none the less. Many fine physicists in the early twentieth century didn't believe it, but Nature doesn't care whether we believe her or not!

Ben

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.