Matter
= Matter
{wiki}
Material constituents such as <particles> and their composites. In <cosmology>, the narrower phrase <pressureless matter> usually refers to nonrelativistic components whose <rest energy> dominates their random <kinetic energy>, giving negligible <pressure> and density proportional to the inverse cube of the <scale factor>. This usage distinguishes the matter contribution from relativistic <radiation in cosmology> and <vacuum energy>.