Special Relativity Introduction Introduction

Our senses understand the world in which we live. Displacements, velocities, and acceleration are all calculated a certain way. If we decided to meet up at Subway 15 minutes from now, we'd have an approximate idea of when that would be. When we meet up, we'll all agree that we made that decision 15 minutes ago. And if we order a 12-inch sub, we'd also agree that our sub measures 12 inches and weighs the same number of grams. Time flows at a constant rate. Objects have definite lengths and has specific masses. You could measure, or we could we measure; these properties won't suddenly change.

Right? Wrong.

Welcome to the world of Einstein. In this world, all of our instincts and notions of reality crumble to pieces. What if we told you that our trip to Subway could be measured to last different times depending on whom was looking at the clock? On top of that, what if our 12-inch sub might not always be 12 inches and change weight too? You'd look at us in the face and laugh.

Laugh away. Please. Get it out of your system. We had to. Seems crazy, right?

Sir Isaac Newton would've probably said so. He believed time was absolute, that everyone would agree on how long an event, like a trip, lasted. Was he wrong? Well, not quite. As we will learn in this mystifying module, time is relative. There, we said it. Now, we're about to find out exactly what that means, relatively speaking, of course.

We don't see changes in mass, length, or time on a daily basis just because we're not traveling anywhere near the speed of light,.The speed of light is always constant and nothing can travel faster. This has a lot more implications, ramifications, complications, and lots of other "-tions" than it sounds. Objects contract or expand, time flows faster or slower, and masses increase and decrease based on speed. Keep on reading: this unit is fascinating and mind-boggling at the same time.

Back to Newton. He's correct, provided we're not moving at anywhere close to the speed of light. Since high speeds were impossible in his day, he was correct as far as he knew. Nor do our daily activities around town change with relativity. We can all sigh with relief that our 12-inch Subway orders are unaffected by relativity.