Movement in Physical Space and Through Time is Shared

I just began reading the book “The Elegant Universe” by Brian Greene as suggested by E and Nikki.  I’ve really enjoyed it so far and it’s allowed me to get my head around some aspects of Einstein’s Theory of Relativity that I’ve understood only fleetingly before.  I’m still early in the book (I read many books at the same time and very slowly) and already I’ve had a really revelatory moment and I’d like to share that with everybody.

As we all know time moves more slowly the faster we move.  This has been experimentally proven and has been something I’ve always just accepted but never understood.  In his book Brian Greene does an exceptional job of explaining this phenomenon…  and it goes a little something like this, hit it:

There are three physical dimensions (up-down, left-right and forward-back).  Time represents a fourth dimension, for example if I want to meet you somewhere not only do I have to tell you where (physically) but also when (where in time).  Of course we all know what speed we travel through our physical universe 75 mph is common on a highway, but Einstein said we are also moving at a particular speed through time and that speed is the speed of light (I don’t think there is experimental evidence for this but there may be).  So as I sit here typing this and as you sit there reading this we are shooting from second to second at the speed of light.  Einstein also told us that nothing can move faster than the speed of light (there is experimental evidence for this) which means that as we sit zipping through time we are traveling at maximum speed.  If we get our heads back into our more easily understood three dimensions we know that moving in one particular dimension (left-right) at five miles an hour gives us a speed of…  five miles per hour.  If we start moving in another direction at five miles per hour (forward-back) we have to add both speeds together to get our total speed which would be ten miles an hour.  Since time is a dimension as are our other directions we need to consider the speed at which we travel in that direction (forward through time) and add that to the speed at which we are traveling through the other dimensions.  So now we’re moving five miles per hour in one dimension (left-right) and we’re moving at the speed of light in another dimension (through time).  To calculate how fast we’re moving we’d need to add the two speeds together which gives us the speed of light plus 5 miles per hour.  Here’s the rub:  We can’t move any faster than the speed of light (there is experimental evidence for this) so there is no way to add that 5 miles per hour to it.  Therefore we have to slow down a little bit from our light speed travel through time, thus we move the speed of light minus five miles per hour through time, or we could say that we are moving through time more slowly than someone not moving five miles per hour.  Of course the faster we go the more we need to subtract from our speed of travel through time all the way up to moving at the speed of light in which case we would have to subtract the speed of light from our travel through time which would mean that we would cease traveling through time and for us moving that fast time would stop.

That’s the big thing that I’ve learned from this book so far.  I’m curious to know if any more sciencey-minded people than me find this to be a solid characterization of what occurs.  Also, I’d like to know if there is any experimental evidence for the speed in which we move through time or if that’s something Einstein deduced and we just accept.