KnightDelight wrote:You know I never have found a good explanation of how that extra mass is actually manifested as an object gets near the speed of light. Apparently the energy used to propel the thing forward is converted to mass instead of forward momentum, thus creating inertia and keeping it from going faster, in a continuous loop.
That's a pretty good intuitive description, as to how the situation appears from the point of view of an outside observer.
But, how does that extra mass manifest itself? Do the individual components of each atom get more massive? Or do new atoms just pop into existence, adding to the number of atoms in the thing itself? And how does the process know what kind of atoms to create? And then there is this thing about the object getting flatter, as if it is being smashed into an unseen wall. A wall that travels just ahead of the object.
Well, a big part of the answer is in the term used to describe it: "relativity". The things that we see, depend on where we're looking from.
The changes in a fast-moving object (its increase in mass, the fact that it shortens, the fact that time slows down) are things which "appear" from the point of view of an external observer - one which hasn't been accelerated.
To an observer in the (e.g.) accelerated spaceship... nope. These changes don't exist. The pilot of the spaceship that's been accelerated, doesn't notice any increase in the mass of his/her ship... it behaves just as before. No physical shortening. Clocks on-board run as they seem they ought to.
What the pilot does see, is that the whole remainder of the universe warps in strange ways. For example, if you travel to a star ten light-years from here, the trip can't take less than 10 years... from our point of view. If the spaceship accelerates at about 1 G (which would accelerate to light-speed in about a year), the total trip will seem to to the pilot to take only a couple of years - one year to accelerate and one year to decelerate. The pilot will never see him/herself exceed light-speed as measured around the ship - instead, it will appear to him/her as if the space ahead of the ship "squashes flat" so that the distance to the star is shortened.
Neither the pilot, nor anybody else, sees new atoms (or other new particles) created. Instead, from the external observer's point of view, every individual particle "measures out" as having a higher mass, and a slower-running clock, than would be the case if it were moving slowly. From the pilot's point of view, the particles' masses are normal, as is their "clock" behavior.
Things really are screwy... two observers passing one another at high speeds, and observing events off at a distance, can't agree on when those events occurred. In fact, they often won't be able to agree on what order those events happened in - each can see a different thing "happen first".
Space-time is
weird (from the point of view of our normal intuition).
... or even laughing. 
Even if the little 'star' meant the hitting the ground may have hurt. 
She needs to show that the collision WAS an Accident. 
LOL
