Are eggs ok if they stand on end in water?

I'm curious, can you clarify for me if it's normal for eggs to stand upright in water? I've heard some people say that it's an indication of freshness, but I'm not sure if that's true. Could you explain the science behind this phenomenon and whether or not it's a reliable way to test the quality of an egg? I'm particularly interested in how the air cell inside the egg affects its buoyancy and whether there are any other factors that might play a role.