Web edition: February 7, 2013
Print edition: February 23, 2013; Vol.183 #4 (p. 31)
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.
Dennis Blanchard, San Jose, Calif.
About 72 percent of the total mass plus energy content of the universe is dark energy; nearly all of the remaining 28 percent is matter of some form, either ordinary atomic matter or the mysterious dark matter, which is distinct from dark energy. By the latest calculations, about 4.6 percent of the total mass-energy is ordinary matter, which comes to a little less than 17 percent of the total amount of matter. — Tom Siegfried
Why is it assumed that dark matter exists in our part of the galaxy? If WIMPs cause the edges of galaxies to rotate much faster than predicted by gravity, wouldn’t that imply that they are distributed differently than ordinary matter? For example, they might be confined to a halo surrounding the galaxy.
Bob Eramia, Seattle, Wash.
Scientists have assumed Earth should have more interactions with WIMPs when moving in the direction of the constellation Cygnus. I assume that is because our solar system is moving in that direction within the Milky Way and not simply because of our revolution around the center of the galaxy.
Sam Scrutchins, Benicia, Calif.