More Things in Heaven and Earth, Horatio

For late night thoughts, the New Scientist offers 13 problems for science.

From ultra-energetic cosmic rays to Martian methane, from tetraneutrons to the placebo effect, a baker’s dozen places where the gaps in our scientific knowledge may be openings for some very interesting learning.

For example:

5. Dark matter

TAKE our best understanding of gravity, apply it to the way galaxies spin, and you’ll quickly see the problem: the galaxies should be falling apart. Galactic matter orbits around a central point because its mutual gravitational attraction creates centripetal forces. But there is not enough mass in the galaxies to produce the observed spin.

Vera Rubin, an astronomer working at the Carnegie Institution’s department of terrestrial magnetism in Washington DC, spotted this anomaly in the late 1970s. The best response from physicists was to suggest there is more stuff out there than we can see. The trouble was, nobody could explain what this “dark matter” was.

And they still can’t. Although researchers have made many suggestions about what kind of particles might make up dark matter, there is no consensus. It’s an embarrassing hole in our understanding. Astronomical observations suggest that dark matter must make up about 90 per cent of the mass in the universe, yet we are astonishingly ignorant what that 90 per cent is.

Maybe we can’t work out what dark matter is because it doesn’t actually exist. That’s certainly the way Rubin would like it to turn out. “If I could have my pick, I would like to learn that Newton’s laws must be modified in order to correctly describe gravitational interactions at large distances,” she says. “That’s more appealing than a universe filled with a new kind of sub-nuclear particle.”

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About Doug Merrill

Freelance journalist based in Tbilisi, following stints in Atlanta, Budapest, Munich, Warsaw and Washington. Worked for a German think tank, discovered it was incompatible with repaying US student loans. Spent two years in financial markets. Bicycled from Vilnius to Tallinn. Climbed highest mountains in two Alpine countries (the easy ones, though). American center-left, with strong yellow dog tendencies. Arrived in the Caucasus two weeks before its latest war.

1 thought on “More Things in Heaven and Earth, Horatio

  1. Dark matter is plausible as an explanation simply because if you suppose that dark matter exists, then you can measure where the dark matter must be on the basis of its gravitational force. If dark matter didn’t exist, you would expect that following this method would give you nonsense (the Michaelson-Morley experiment is the obvious historical analogy). Since it doesn’t, it would be strange if general relativity turned out to be wrong in such a way that made it look like there were particles in specific locations that turned out not to exist.

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