© NASA, WMAP Science Team.
The figure above shows how the abundance of the light elements deuterium, helium, and lithium, would change if the amount of ordinary matter in the universe were different. The red line shows the value for the density of ordinary matter we believe to be correct (see Unit 10), and the red circles show the expected abundance of the different elements we should observe. Experimental values are in excellent agreement with this prediction, falling within the red circles on the plot. This agreement supports the notion that the density of ordinary matter is only 4 percent of the critical density. The remainder is made up of dark matter and dark energy. (Unit: 11)