Strange things can happen when you move FAST...things you won't learn about in high school courses, and won't experience while driving down the road in your pick-up. But these things are still very real, and definitely WEIRD!
 

Light rays travel very quickly...they cover about 300,000 kilometers every SECOND. This is as fast as anything can travel; nothing can move as fast as light particles.
But if it were possible to build a very powerful vehicle that could move almost as fast as light...perhaps 200,000 km every second...then anyone observing this vehicle as it flashed past would notice some extremely peculiar things happening to it.
The vehicle would appear shorter than normal, and in fact, it would be shorter. If the vehicle were ordinarily 3 meters long, it might now be only 2 meters in length.
If you were able to weigh the vehicle, you would discover that it weighed much more than normal. Anybody riding in it would weigh many times their normal weight.. However, the people in the vehicle would not FEEL any heavier, or any thinner. They would feel and look normal to themselves...but if they looked out the window, they would see the rest of the world moving by, and IT would appear to be shrunk.
 

If the vehicle were to move faster and faster, getting closer and closer to the speed of light, it and the people in it would continue to get thinner and thinner, while at the same time getting heavier and heavier!
These strange occurrences, as described by Albert Einstein, can actually be observed. It is not yet possible to build a vehicle that will go this fast, of course...the fastest spacecraft only cover about 15-20 kilometers in a second. But tiny particles called 'cosmic rays' that are given off by the sun...the ones that cause the Northern Lights when they hit earth's magnetic field...move almost as fast as light, and their mass can be measured. When they move that fast, their mass IS much heavier than normal.
 

A much more dramatic effect of moving fast is what happens to time. It seems that the faster you move, the more slowly time runs!
At normal, every-day speeds (airplane speed, for instance), the effect of 'time slowing down' is just barely measureable. You could fly nonstop around the world in an airplane, and because of your increase in speed, time would run slower for you. Everyone on the plane, all the watches and clocks, the plane itself...all would be a small fraction of a second YOUNGER than if they had not gone anywhere!
That experiment has been done. Want to live longer? Spend lots of time on high-speed planes, and time will move more slowly for you. You might live 2 seconds longer than you would have if you'd stayed on the ground.
 

Things get much more interesting if you fly off in a spacecraft that can go REALLY fast...perhaps 200.000 km per second. Now time is really slowing down. Suppose you and a friend are both exactly 16 years old. He stays on earth, but you go off for a trip in our very fast spacecraft.
Fifty years go by on earth. (It's a long way to the nearest stars!) You return to find your friend is now 65 years old.
You, however, have experienced a phenomenon known as time dilation. Time has been running more slowly for you, in the fast-moving spacecraft. According to you, the trip took only TEN years...and you are just 26 years old!
 

This effect would seem impossible...yet it has been demonstrated to be a fact. Once again, small particles can be observed and measured. Many are radioactive, which means they disintegrate with clockwork precision. The time it takes them to disintegrate can be accurately measured.
When these particles are accelerated to high ('relativistic') speeds as in our example above, they live longer before disintegrating!

It has been almost 100 years since these theories were first put forward by Einstein and others, and since then they have become accepted as fact by scientists world-wide. More evidence of their validity is also apparent from studies of objects in far distant space.