# Reality and Relativity

by Moneer81
Tags: reality, relativity
 P: 153 hey, so most of us understand special relativity, and I also understand it and appreciate it. However, most people understand it from a mathematical point of view. But come to think about it, what is actually happening in relativity? there are many examples we can look at. for instance the two observers, one on a fast train and another on the ground: a certain event's time will be shorter for the one on the train. Another example, the twin paradox, where one of the twins travels to a distant planet on a very fast spaceship and returns to find his twin brother has aged many more years than himself. Or for a more realistic example, the 1975 experiment where an atomic clock flown on an airplane showed a different reading than an identical one on the ground. When I explain relativity to friends or other students, people tell me: this is all BS! They keep asking me about what is happening to these clocks, and whether the velocity at which they're moving has anything to do with they way these clocks function. I also wonder about those twins: does the one twin actually age more? i.e. does he show signs of older age like wrinkles and stuff before his brother does? any comments? thanks
 Sci Advisor P: 1,883 In SR, there is absolutely NOTHING happening to clocks/people when they move at high speeds, as speed is relative. Itīs always the others that age slower or get contracted. Only when people meet again and compare clocks the one with the straighter way to the meeting point will turn out to be older. Nevertheless none of them will experience anything unusual. Itīs not that one twin is "ageing faster" in some weird way, itīs that he is actually older because he experienced more time elapsed.
 P: 352 Preview Ewo -------------------------------------------------------------------------------- Hi. I am new to physicsforums. I have tried to tell many people about relativity, and what I have learned is that relativity contradicts common sense to the point of disbelief. Although, scientist do accept it as true, many cannot grasp concepts of space and time. When I was first introduced to relativity, it was hard for me to perceive time as an actual entity (dimension), let alone imagine that it can be relative. I was suggest these links to your friends. http://science.howstuffworks.com/time-travel.htm http://science.howstuffworks.com/relativity.htm try to get them to grasp the general concepts of relativity first, then you can tell them about the lorenz transformation $sqr(1- \frac {v^2} {v^2} )$ PS, sorry for my poor latex skill
P: 90

## Reality and Relativity

There is an old paperback by David Bohm called Relativity that developes Bondi's K-calculus (really just space-time diagrams) and worries about why the concepts of special relativity appear so strange at first sight. He talks about Piaget's experiments with developing children and points out that our "common sense" Newtonian ideas are really hard won. For instance, very young children presented with a brightly coloured object from behind one side of a screen, moved in front of the screen in full view, and then hidden at the other side of the screen, look to the source of the object rather than where the object disappeared. This is supposed to indicate that the notion of invariance or permanence has to be learned.

From my own experience, I don't know how many times I stood in front of a class and told them of the symmetric dilation and contraction between inertial frames, before it dawned on me that something had to give if all inertial frames had the same maximum speed. Now it is perfectly obvious to me. However I notice that if I teach a topic in a way that is obvious to me I like to think I have taught well, but lord knows what the students think. A confident presentation is certainly better than a fumbling one, but some fumbling around is required for learning.

I remember one prof who got all kinds of awards for teaching excellence. An excited anticipation would build as the class assembled as today would be the day that we would see a great technique or theorem. He would carefully lead us down the path, making sure that every 2 pi i had the right sign and that each line followed meticulously from the last. As the class ended and he disappeared, we would awake from our reverie and with puzzled faces would ask each other "Just What did he show???" The guy could have sold refrigerators to Inuit. None of these concepts are obvious or trivial and learning them requires hard work. There is no royal road to learning.
 Sci Advisor Emeritus P: 7,204 Bondi himself wrote a book on relativity from the k-calculus point of view, called "Relativity and common sense". I have a certain fondness for this book, and for the k-calculus approach, because it was one of the very first books I read on relativity back in high school. It's not very demanding mathematically, one needs only basic algebra (not calculus) to follow his derivation of the Lorentz transforms from the basic premise that the doppler shift depends only on the relative velocity between two bodies. Amazon.com reviews on this book were not so favorable, many apparently found the exposition a bit tedious
 P: 1,441 Like Dingle - When I first understood SR a really didn't. After pondering it more I puzzled more. What I think I have come to understand is why those that are not disturbed by its consequences claim to understand it. On the other hand, if I don't understand that, the whole effort has been wasted.
 PF Patron Sci Advisor Emeritus P: 16,094 For me, the light didn't click until I started drawing space-time diagrams, and realized geometrically how to make measurements in reference frames other than the one I had drawn.
 P: 1,441 Hurkyl - well put
 P: n/a I thought the twin paradox was flawed because there's acceleration involved.
PF Patron