People are less dense than water? explain how you could test this idea

You can place various people into pools of water, and see if they will spontaneously float like "less dense" objects will. ... Since most of the human body is made of water, the margin of difference is so close that you get these kind of outcomes

Explanation:

Archimedes' Law. A human submerged in water weighs less (and is less 'dense') than the water itself, because the lungs are full of air like a balloon, and like a balloon, the air in lungs lifts you to the surface naturally.

3. dark matter

empty space could also be a simple vacuum