" Atoms are held together by electric forces. There is electrical attraction between the positively charged atomic nucleus and the negatively charged electrons. Let's imagine that we could turn off the electric forces. There would still be gravitational attraction. How tightly could gravity hold the nucleus and electrons together? How big would a gravitationally bound atom be? As big as a flea?
No. A mouse? No. A skyscraper? No, keep going. Earth? Not even close. An atom held together by gravity would have a hundred times the radius of the visible Universe. "

― Frank Wilczek , The Lightness of Being: Mass, Ether, and the Unification of Forces