Cosmo 101

So I went to my first cosmology class today and it was amazing. I am very much looking forward to walking through all of this with you. And guess what! All of the things we’ve been talking about up to now have been almost a perfect introduction to where we started off in class today. But there are some things I didn’t mention, so I would like to take today and explain what an inertial reference frame is. Ok so whenever I think of this topic I always picture people in bubbles floating around in spacetime and it always makes me think of this commercial. But anyway inertial means that the bubbles aren’t accelerating, they’re just floating along at a constant velocity looking at events that take place. The other thing I wanted to cover today way the units that I couldn’t remember from before. So when dealing with spacetime in any sort of relativistic way you have to make a choice. Both time and distance either have to be in meters or in seconds. The book we are using picks meters. So whenever you have a time 12 seconds for example you multiply by the speed of light, 3x10^8 m/s and you get an answer in meters. The units of everything else change too, for example velocity is unitless, it’s just a number.