So to continue with Einstein and his theory of Special Relativity, there are problem with classical physics that seem to be problematic. As we said last time, light is a constant. It onlychanges when it passes through different mediums. Keep this in mind.
Now picture a moving walkway. The wide, flat ecalator that moves in one direction (can be seen in airports). If you step on it and stand still while it moves, you are moving at the same speed as it is. but if you decide that you want to go faster, you walk, and the 2 speeds are added to give your new speed.
Classical Physics Failure #1
This is not true when you decide to shine a light while you are moving. When you shine a light while in a rocket moving at the speed of light (only hypothetical right now), then the light does not shoot ahead of you, but is matching your speed. You don't get to see any light.
In this paradox we will show how 2 referance frames mystically can be right even though the conculsions are different.
Imagine a train with a passenger in the middle is moving at a constant velocity. There is another observer in the middle of a platform. As the train passes, lightening strikes both the front and tail of the train simultaneously. This occurs when the passenger and the platform observer (Joe for short) are lined up. They are both in the middle of the train.
The light reaches Joe at the same time, because he knew they were equal distances apart, he concludes that they happened at the same time.
Classical Physics Failure #2
Joe thinks that the train observer, Jane, will see the front flash first because of the speed of the train. And she does. But she has a totally different conclusion, the flash in the front occured first. If she sees it first, the event happened first.
Who is right?
Einstien said that if there are different frame of referances (perspectives) than there will never be agreement about simultaneousness of events. Therefore, both Jane and Joe are correct, in their own prospective.
This property is also involved with Length Contraction. This is the property where 2 measurments can be accurate because of the frame of referance. When I say measurements, I mean measuring anything in 1D, 2D or 3D space. NOT SPACETIME.
If you measure a desk, and you are at rest, you get an accurate measurement of the desk. Because both you and the desk are at rest. Now think of a small rocket that is able to take measurements. If it flew by with a high speed, would it get an accurate measurement? No! How could it? It can't just whip out a meter stick and measure.
Ahh.. But Time can measure distances, so is this accurate? Nope! The rocket actually is going to pass it faster than it can get an accurate measurement. The rocket will not get a proper length even though it will get a proper time for 2 event to occur.