What it shows:
According to present accepted theory the Universe came into existence some 17 billion years ago as a Big Bang and is currently expanding. You can model the expansion of space in two dimensions using a balloon.
How it works:
We use an 8ft weather balloon 1 connected to Daedalon Air Source™ blower. 2 The galaxies in the Universe are represented by galaxy shapes cut in sticky tape and stuck on the balloon. When the balloon expands, the galaxies move apart. This demo shows clearly that the galaxies aren't themselves racing apart through space, but that the space itself is expanding.
figure 1. galaxies racing apart
Setting it up:
Lay the balloon out on the floor off to one side, because when it inflates it will obscure the blackboard. For the stick on galaxies, use fluorescent orange tape (galaxies drawn on the balloon will themselves expand). Consult the lecturer as to whether they want the galaxies already attached, or if they want to do it. The balloon inflation time with the Air Source pump is about 10 minutes.
Any size balloon will do of course, but let's face it, this is the Universe we're talking about. Edmund also make a 16ft balloon (R72,151) but it's expensive and some professors think it's neat to go for a big bang of their own.
1 Edmund Scientific R60,568
2 Daedalon EA22