Does an egg have to boiled float?

Here's why:

* Fresh eggs sink. This is because the air pocket inside the egg is small, and the egg's density is higher than water.

* Older eggs float. As an egg ages, the air pocket inside gets bigger. This makes the egg less dense than water, causing it to float.

So, while boiling an egg can make it float (because the heat expands the air pocket), it's not the only way.