Dark matter enlightened
Tom Siegfried’s article on dark matter “Light in the Dark,” (SN: 1/12/13, p. 18) reminded me of the 19th century search for the luminiferous ether. One can only wonder if history will repeat itself in the 21st century search for dark matter.
Jeffery Miller, Los Angeles, Calif.
The difference is that the ether was only surmised; attempts to observe its effects failed. There is abundant observational evidence for the existence of dark matter. Its actual identity could still, of course, turn out to be very surprising. — Tom Siegfried
Where did the figure that 17 percent of the universe is composed of ordinary matter come from? The data I have seen is that ordinary matter constitutes less than 5 percent of the universe, 23 percent is dark matter and 72 percent is dark energy.