To determine wether an egg is fresh, immerse it in cool water. If it sinks, it's fresh, if not, toss it.
So it got me thinking...I have used this trick for years, but wondered what causes them to float. I found the info here. When the egg is laid, an air pocket forms as it cools. As an egg ages, fluid evaporates through the porous eggshell and gas and oxygen filter in causing the egg to be more buoyant and float!
There! You got a science lesson for the day as well as a tip! Time for me to go make some scrambled eggs.