Lead sinks for the same reason. This tendency is seen for every state of mass and energy. In classical mechanics this is called thermodynamics. Thermodynamics explains the properties of heat and how it affects mass. Heat is an energy level just under the octave we call light.
Every octave is twice as high as the one before it, and half as long.
A two to one ratio in both directions. Using what is called the blackbody radiation signature, scientists can tell what temperature an object is by looking at the level at which it stops absorbing energy and begins to glow - emits energy. In the case of the big bang, the background temperature of the whole cosmos glows at a wavelength seven millimeters in length. This puts it in the microwave - radio octaves in the spectrum of energy. The temperature for an object that glows at that level is a scant 2.7 degrees above absolute zero.