I am regularly struck, when giving public outreach talks, or when hearing the topic of Dark Matter discussed amongst the general non-Astronomer public, at the separation between acceptance of Dark Matter between astronomers and the general (informed) public. (The general public at large probably doesn't have enough of a clue about Dark Matter even to have a wrong opinion, alas!) Most astronomers know the evidence, and accept that non-baryonic dark matter is a real component of our Universe. Many in the public, however, seem to view Dark Matter as a horrible kludge, an ex-rectum fudge factor that astronomers have invoked in order to explain discrepancies between observation and theory. Indeed, topics related to this will be the subject of my upcoming August 16 365 Days of Astronomy podcast.
For a popular level discourse on the evidence for dark matter, I shall point you to two sources:
- "How We Know That Dark Matter Exists", an hour-long lecture I gave in Second Life a couple of years ago, and which was recorded for posterity.
- "Convincing a Young Scientist that Dark Matter Exists", a 2010 post from Ethan Siegel's excellent blog Starts With A Bang
And now I can get to the snarky bits of this post. Yesterday, on Slashdot there showed up a post entitled CERN Physicists Says Dark Matter May Be An Illusion. In the paper indirectly referenced by the Slashdot article, a theoretical physicists explores the idea of negative gravitationally charged antimatter and the polarization of the vacuum as an explanation for the rotation speeds of galaxies (the mainstream explanation for which is, yes, Dark Matter).
What's interesting is the tone of the Slashdot comments. Some are informative, and ask exactly what I ask: what about the Bullet Cluster? However, a fair number of the comments show the same tenor as these excerpts:
I hope so. Dark matter is the ugliest kludge to the standard model ever.
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Agreed. I have always had a hard time stomaching the theory that dark matter and dark energy exist. It seems far too much like aether, i.e. something made up to fill a gap in knowledge without much evidence backing it up.
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Yay for phlogiston [wikipedia.org] and aether [wikipedia.org]. Dark matter might end up on the list of ideas that physcists turned to in order to explain things that had other explanations. La plus ca change
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Dark matter, too, has never been observed, and possesses properties of matter previous unseen or indeed thought impossible, and exists solely to bridge a gap between our model of how things should behave, and how things actually behave. This does not bode well for it.
There is a strong general sense among a large (majority? hard to tell) subset of the Slashdot commentariat that astronomers are all on the wrong track and propping up a failing theory, and that dark matter is a kludge that just can't be right.
The thing is, they're wrong. They just know that Dark Matter can't be real, because they are not comfortable with the idea that a substantial fraction of the Universe is made up with stuff that we can't see, that doesn't even interact with light. Much as... the 17th century Catholic church just knew that Galileo (and others) were wrong about Heliocentrism, because it's obvious to everyday observation that the Earth is still and the Sun is going around it. (Also, the Bible says so.) And, just as the leaders of the Catholic church completely discounted (and indeed refused to look at) Galileo's observation of Jupiter's moons orbiting Jupiter (and, crucially, not the Earth), armchair pundits completely ignore (probably mostly through ignorance!) the wide range of evidence for Dark Matter that goes beyond the "accounting error" represented by the motion of stars in galaxies, and galaxies in galaxy clusters. (Those motions are indeed one part of the evidence for Dark Matter, and historically formed the first evidence for it, but they're far from all of the evidence nowadays.) They cling to notions of how science ought to work, and how the Universe ought to be made up in a familiar way that seems natural to us humans, and use this to assert that an entire field full of scientists must all be on the wrong track for having a different model.
Specifically with regard to comparisons to the luminiferous aether, I would point you to my June 2010 podcast: "Dark Matter: Not Like the Luminiferous Ether". (And, yes, I'm conscious that I've spelled aether two different ways in this paragraph!)
Indeed, I would say that the comparison between denial of Dark Matter and denial of Heliocentrism goes deeper than that. The Copernican Principle is that the Sun, not the Earth, is at the center of... well, today we would say the Solar System, but in Copernicus' day that was also what was thought to be the whole Universe (the stars not at the time being understood to be things like the Sun). An extension of this is the Cosmological Principle, which stated succinctly says "you are nowhere special". We're not at a special center of the Universe, we're just at a typical random place in the Universe pretty much like any other. Observations (of galaxy distributions, of the Cosmic Microwave Background, and so forth) bear up this assumption or postulate, which is why we call it a principle. Think about it in broader terms, though. We are made up of "baryonic matter", which is Physicist for "stuff made of protons, neutrons, and electrons". In light of the Cosmological Principle, however, why should we expect that most of the Universe is made up of the same general kind of stuff as we are? In the face of evidence otherwise, many still insist that most of the Universe must be made up of baryonic stuff that interacts with other baryons and our familiar photons. Is this not just as much hubris as insisting that the Earth, where we live, must be the center about which all the other Solar System bodies orbit?
This is Rob Knop's blog about physics, astronomy, science & society, general geekery, and anything else he is inspired to rant about. Rob Knop is a member of the faculty of