Einstein and Relativity: Part 2

When you are courting a nice girl an hour seems like a second. When you sit on a red-hot cinder a second seems like an hour. That's relativity. - Albert Einstein

Now we come to the much more interesting - yet challenging - Special Theory of Relativity (STR). Lets focus on the first point we should keep in mind.

Imagine a juggler on a pier (Adam), and imagine another juggler in a boat traveling 5 mph away from the pier (David). Suppose they are both juggling eggs. We thus have two frames of reference: the one on the pier and the one on the boat. What is interesting is this: ‘relative’ to both frames of reference, Adam and David’s eggs are moving in the same way. Even though the boat is ‘moving’ and the pier is ‘stationary’, both Adam and David can both say they are stationary. Why? Because Adam and David are in different frames of reference. And the laws of physics stay the same in any and every moving frame of reference.

Look at it this way. You’re driving down a superhighway going 80 mph. You look out the window as the asphalt and the trees race by. But then your attention shifts to inside the car: everything seems to be at rest relative to inside the car. Suppose you have a quarter and you drop it in your lap. Relative to the frame of reference ‘outside’ the car, the quarter actually traveled 80 mph! But relative to the frame of reference ‘inside’ the car, the quarter didn’t go anywhere - it just gently landed on your lap. But if you roll down the window and put the quarter an inch outside the window, it doesn’t any longer fall straight down (as it is did on your lap, and as it would do if it was just an inch inside the window): it is sucked outside the car, careening along the side of the road.

All of this is really cool, and it’s been known since Galileo. But Einstein asked a very simple question: how does ‘light’ play into all this? Remember, that light travels 186,000 miles per second! Lets put Adam and David in a rocket ship. Suppose Adam raced along at 60% the speed of light; and David sped along at 90% the speed of light. According to Einstein, both Adam and David would still measure light passing by them at a constant rate of 186,000 milers per second! No matter how fast you go (and even if you're standing still), light goes by you at the same speed. Isn’t that strange? How is this possible?

Lets look at this more closely. What is speed, exactly? It’s a measure of the amount of distance you cover in a certain time. Since the speed of light is constant, something else has got to give, something else has got to change. And what is it that has to change? TIME! Time, according to Einstein, begins to actually change. A paradox is this: if Adam is traveling in his rocket ship 80% the speed of light, and David is traveling in his rocket ship 50% the speed of light, the time for Adam and David would be different!

To test this groundbreaking hypothesis, Einstein began asking questions about something called ‘simultaneity’. What does it mean for two events to happen at the same time? Can two events happen at the same time for David, and yet those exact same two events NOT happen at the same time for Adam? Yes! Einstein concocted a really cool thought-experiment that is now very famous. Lets explore it!

In our minds, lets imagine a railroad track with two poles erected on one side (an equal distance away: lets say 20 feet away from each other), and another pole placed at their midpoint. Suppose Adam stands at the midpoint with what is called a ‘right-angle mirror’. This mirror allows Adam to see both the left and the right poles at the same time (without having to turn his head!). Next, imagine that a bolt of lightening strikes both of the poles at the same time, and Adam is able to see this using his handy-dandy right-angle mirror. To Adam, the light (from the lightening) travels toward him over the same distance (he is at the midpoint) at the same speed (185,000 miles per second). So far so good.

But now Einstein wants us to focus on David, who is coming down our railroad track on a train. Einstein asks: how would David experience the bolt of lightening hitting the two poles? Does the lightening hit both the poles at the same time to David, like they did with Adam? Hanging out of the train window, David is also armed with his handy-dandy right-angle mirror. As the train passes by the midpoint (where he can wave to Adam who is on the ground), David sees the bolt of lightening hit the pole he is moving toward first (pole A), and then he sees the bolt hit the pole he moving away from (pole B). Why? According to Einstein, it’s a matter of distance - the light coming from A doesn’t have to travel as far as the light coming from B: the train is moving toward A!

Einstein picks the point of view of David who is on the train. Remember, everything is relative to a frame of reference. To Adam, he is stationary and the train is moving past him. But to David, he is stationary and the poles are moving past him. So, Einstein ponders: the lightening would have needed to strike A first and then B (to David) ‘in order that’ Adam see the lightening strike A and B at the same time. This allows the light time to catch up to Adam in time, in time for Adam to see the poles struck at the same time.

To Adam’s frame of reference, the poles WERE struck at the same time; to David’s frame of reference, the poles WERE NOT struck at the same time. But to Einstein, there is no privileged frame of reference! And therefore Einstein concluded: TIME IS RELATIVE (play the soundtrack from 2001: A Space Odyssey in the background!).

Here we come full circle. According to STR, the faster you move, the slower time moves. So what follows! The faster your movement (the closer you got to the speed of light), the slower your clock would tick. But remember what Einstein said in his General Theory of Relativity! Space and Time aren’t two separate realities: there’s just one - space/time. Therefore, not only would time go slower (in your frame of reference), you would actually begin to SHRINK, relative to an observer outside your frame of reference.

All this begs the most fascinating question in the theory: what exactly would occur, what would it be like, to ride a beam of light? This is impossible - at the speed of light, there is no length! You’d shrink to nothing, and time itself stops ‘flowing’ (but don't tell that to Captain Kirk!).

Einstein’s fame exploded when he applied STR to Mass and Energy: E=MC2. So, what does that mean? If you take any object, there is contained in that object ‘energy’. That ‘Energy’ is equal (=) to that object’s Mass multiplied by the speed of light ‘squared’ - that’s a lot of Energy! After all, the Energy that explodes from an Atomic bomb is just the energy exploding from one teeny tiny atom! And, thus, if Mass contains Energy, then Energy has Mass! For example: this means the Earth is struck by 4 and 1/2 ‘pounds’ of sunlight every second!

Summary: Einstein was a beast!