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# Relativity/Time

Question
I've studied in "A brief history of time" and in "The theory of everything" that we cannot go back to the past.. But fuure may be possible.. like that. Hawking told a simple example like "How will you born if you killed your mother in the past?". But my point of view like in some movies.. that if we move to past.. there can be 2 persons.. like one already present and the other is me the time traveler.. so there might be 2 shameems in the past. If it is "No", tell me why. And how do you know that speed of light is the limit of everything? And gravity traveling at speed of light? Gravity a form of light?

Whether there are 2 shameems in the past is a question that is for the proponents to answer, not the sceptics. Look up "Occam's Razor" in Wikipedia.

We believe that light travels at the fastest speed possible because it is the prediction of a theory that seems to be confirmed in many ways and is disconfirmed by nothing yet. The speed c is the speed limit for everything, not just light.  And no, gravity is not a form of light as far as we know. Light is an electromagnetic wave, and gravity seems to have nothing to do with electromagnetism. Gravity travels no faster than light because nothing travels faster than light. If something is found that travels faster, we will have to rethink the whole matter, but nothing so far does.

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.