An Introduction to String Theory

Slide 5 of 37
<<   [Outline]   >>

I decided to start with something that everyone in the audience was familiar with: the first example is all of them, listening to this talk.

I wan to focus on two "events" during the talk. One is when the fellow on the left (I call him Rhett) leans over and whispers to his friend Gary, and the other is when Violet (sitting to the right) gets up to leave the room. From my perspective, those events happen simultaneously, as shown in the middle picture on the left.

On the right side of the slide is drawn a schematic picture of what this looks like over time. In the diagram, each person traces out a path through time. The slices show my perception of time as I stand at the front of the lecture hall: each slice is a set of events that I see as simultaneous, and these slices correspond to the "snapshots" on the left. You can see in the diagram that a single slice passes through both events.

Note that we are treating time as just another direction in the picture. For now, that's just a convenient way to draw these diagrams, but in Relativity we learn that it is literally true. In these pictures, time increases from bottom to top: that's the usual physics convention; it's a bit like a geological column. If that's confusing for you, don't worry about it: the laws of physics that we'll talk about work pretty much the same regardless of which direction time goes.)

However, unbeknownst to us, we are not alone in the universe. In fact, even now, an alien being is watching us in this very room. ...His name is Hank, and to be honest he's pretty bored: he took string theory back in high school.