Yes, eggs are porous and as they age an air pocket forms in the eggs causing it to float. At the same time water vapor and gases are leavening the egg. This difference in mass will cause the egg to float.
If the egg stay at the bottom - it is fresh. If the egg is at an angle on the bottom - it is still fresh and good to eat. If the egg stands on its pointed end at the bottom - it is still safe to eat...