> Is there anyone on the forum or on Bad Astronomy, if anyone has a contact there, that can explain what Neville meant when he said that the theory of special relativity states that a clock must be running faster and slower at the same time as another clock? > > Jack Jack, I believe Dr. Jones was referring to what I have read about called the "Twins Paradox". I asked the BA directly about this, and really don't agree with the response I received. Anyway, my recap of that problem is that relativity supposedly says that there is nothing absolutely still. There is only motion relative to other things, the only "stillness" (ie.,constant) being the speed of light. That is, if you fall and hit your nose on the ground, it should be equally true that the ground came up and hit your nose. So the famous story about astronaut Peter leaving twin brother Paul on earth and flying away at the speed of light says that astronaut Peter returns in one year of his time only to find brother Paul aged to 80 years or better. This is due to the fact, I understand, that time slows down dramatically when going speeds approaching "c". But wait. If relativity says you have no absolute stillness, and that it is equally true that the ground hit my nose, as I hit it, then why isn't Paul aging just as slowly relative to astronaut Peter since he is separating from Peter at the same rate as Peter is separating from him and relativity says both frames are equally valid. Peter should be both old and young when he returns, and Paul should be both old and young when Peter returns. This is my understanding of the problem in a nutshell, and I believe what Dr. Jones was referring to. I'd forward you the BA response if you're interested. Sincerely, Gary