Percent Milkfat
Percent Milkfat
[Ponytail, raising her palm, and Cueball are talking.] Ponytail: "2% milk" is 2% milkfat. But "whole milk" isn't 100% milkfat–it's 3.5%. Cueball: Weird. What's the rest of it? Ponytail: About 27% is dark matter. The remainder is dark energy.

While cow milk contains a variable amount of fat (about 4.2%), whole milk from the store generally contains about 3.5% milkfat by weight according to the comic and some sources; other sources list similar but not identical numbers such as 3.25%.
Dairies commonly sell whole milk as well as products with less fat produced by removing milkfat. In the United States , there are three common products with less fat: 2% or "reduced fat" milk, 1% or "lowfat" milk, and "fat-free" or "skim" milk with 0 to 0.5% milkfat.
Since whole milk is labeled as "whole" milk and not as "3.5% milk," one might naively assume that whole milk is 100% milkfat, although this is not the case; 100% would be a product which is entirely milkfat (also known as butterfat), such as clarified butter or ghee. In milk, the remainder is mainly water along with proteins, lactose (a sugar), and other substances.
The comic analogizes this difference to the fact that physicists believe that "ordinary" matter constitutes only 5% of the actual mass-energy of the universe. Scientists predict the existence of another kind of matter known as " dark matter ," invisible to our current instruments but exerting gravitational force on ordinary matter, which would constitute 85% of total matter and 27% of the universe's mass-energy, with the remainder an even less detectable and more mysterious " dark energy " accounting for the increasing speed of expansion of the universe .
Ponytail uses these quantities to "explain" the "missing" percentage in whole milk between the actual 3.5% and a potential 100% "whole." She actually uses the 27% as mentioned above for dark matter. She thus indicates that dark energy takes up the remaining 69.5% of the whole milk.
Ponytail is assuming that dark matter and dark energy are distributed uniformly throughout all pockets of the universe, no matter how small. This assumption is common in statistics and may have seemed appropriate since no one knows the proportion of dark matter or dark energy of an object as small as a milk carton (though a more sensible argument is that all matter is accounted for when considering the milk and the carton; no additional "dark" matter is necessary to explain the weight of the milk carton).
Cosmologists are working to better understand dark energy or another reason for the universe's accelerating expansion. The title text supposes that both cosmologists and the Food and Drug Administration (FDA), which regulates milk and other food items in the United States, are trying to understand the dark energy of the whole milk. In real life, the work of cosmologists and FDA scientists does not overlap at all. [ citation needed ]
Dark energy was recently mentioned in 2113: Physics Suppression , but before that milkfat and dark energy were actually mentioned in the same sentence in 2063: Carnot Cycle from almost a year before this comic, so the idea behind this comic is not new for Randall. Dark matter was mentioned back in 1758: Astrophysics .
[Ponytail, raising her palm, and Cueball are talking.] Ponytail: "2% milk" is 2% milkfat. But "whole milk" isn't 100% milkfat–it's 3.5%. Cueball: Weird. What's the rest of it? Ponytail: About 27% is dark matter. The remainder is dark energy.
