No need for google, I see this every time I have them hard boiled. I have not compared boiled eggs air space with age of egg. I think I will mark my eggs and see next time.
I found a hidden nest in my yard with 9 eggs! I floated them and they all laid flat on the bottom. Went to use them, 8 were fine but one was blue/green and so funky I had to air out the house.
THAT ROTTEN @$$ EGG DID NOT FLOAT AT ALL