Relativity

According to Einstein,  if an observer gets on a bus on Courtney Place and gets off an Manners street, the bus they get off will be the same as the bus they got on to, but the shops nearby will be quite different, except for MacDonalds, which is constant. However, the clock on the bus will be entirely random in relation to a clock that you carry with you onto the bus- for example, the clock on the bus may say 7.04 and the clock on your phone will say 2.55. These numbers exist entirely independent of one another, and there is no way to predict what the difference between these numbers will be before entering the bus. 

According to Einstein, if I am standing at one end of the bus, and the bus is travelling at speed a fraction of the speed of light, and I walk back down the bus while observing both the clock on my phone and clock at the front of the bus, I am likely to fall over and hurt myself. The same applies if I don't sit down fast enough as the bus accelerates from the stop. No-one knows why this is.