In Which I Compare the Slashdot Commentariat to the 17th-Century Catholic Church

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:

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.

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.

Yay for phlogiston [] and aether []. 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

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?

23 responses so far

  • Zombie says:

    People still read Slashdot?

    After getting my physics degree I ended up in the computer software industry for various reasons (largely financial). Unfortunately, its one of those places where the practitioners are flattered that they're clever people, and some of them think they're a lot cleverer and better informed than they really are. They think they're computer scientists (which are far fewer and further between than industry people think), and therefore they get to be experts in everything.

    I've run into a couple people who "didn't believe quantum mechanics" because, well, basically, they didn't understand it, and if their clever selves couldn't understand it, it must be because its wrong. I've run into creationists and (plenty of) global warming deniers as well, and of course being a computer programmer also makes you an expert in economics and political philosophy, so of course there are a lot of libertarians.

    (I shouldn't rant too much - most people are fine. But I sometimes do regret going into private industry and having to deal with some of these tools.)

  • rknop says:

    Heh -- of course, physicists are also very frequently guilty of believing that since they're experts in physics, they're experts in everything else too....

  • Roger says:

    You say that the luminiferous aether does not exist, but relativity merely proved that it was Lorentz invariant. A medium for light is still today very much essential to modern understandings of quantum electrodynamics.

  • rknop says:

    QED needs no medium to wave. It just waves the electromagnetic field itself; there's no underlying aether or any other sort of similar medium needed.

  • Roger says:

    QED requires a quantum vacuum for light to propagate, and that has a structure that is very much different from empty space. That is what every textbook says.

  • rknop says:

    The vaccum state is not at all the same thing as the luminiferous aether. The aether was supposed to be the stuff that EM waves were waving. The vacuum state is just the lowset state of all the various quantum fields that exist. The ather was something external to the electromagnetic field, just as the water that water waves wave is something separate from the waves themselves. However, the vacuum state is just a property of the quantum fields.

  • Roger says:

    The modern terminology is slightly different, but there is no functional difference. The aether is also the lowest state of the fields. You could think of the aether as a property of the fields, just like the vacuum state. I would be interested if you could find some difference based on what some aether advocate like Maxwell actually said.

  • Anna says:

    (Hi! New reader! Love your blog etc.!)

    Maxwell's idea of the aether was something entirely different from zero-point energy. Of course there are functional similarities, because it tries to explain the same thing and Maxwell was a pretty smart guy. But his aether was mechanical (he had even drawn models for it with all kinds of turning wheels and moving parts) and thus came with freebies like a preferred "resting" frame of reference which is incompatible with relativity.

    They're fundamentally different concepts.

  • Ethan Siegel says:

    Rob, I love your take on this. You do an excellent job illustrating the parallels between dark-matter-deniers and geocentrists; 100 years from now this take will be mainstream, but it should be that way *today*. I liked it so well that I wrote up a take on it as well.

    Roger, Rob is correct. The quantum vacuum is the definition of what empty space is, while the aether was something else entirely. (The Michelson-Morley experiments thoroughly disproved it.) Mixing semantic terminologies between the two does not make them physically -- or functionally -- equivalent.

  • Bryan Kilian says:

    What are the theories on why dark matter forms "clouds" and doesn't clump and form dark matter bodies? It interacts with gravity, right? so shouldn't it behave the same way as other particles that interact with gravity?

    Would we ever expect to find dark matter "solar" systems? (I used quotes since dark matter would never form a star, that requires interaction with the other forces as far as I remember)

  • rknop says:

    Bryan, without saying any more why, I want to recommend that you read "Starplex" by Robert J. Sawyer.

    To answer your question: there are two answers to it. To get clumps of matter like dust grains, asteroids, and (many) planets, you actually need more than just gravity. You need other forces to stick particles together and allow them to build clumps. While Jupiter, for instance, is mostly held together by gravity, and while all of the gas on it was just gravitationally swept in, the original nucleation of the plant that allowed something to start gravitationally collecting the gas around it happened with particles clumping together using other forces.

    However, stars do entirely form gravitationally, so why is it that dark matter doesn't clump to form bodies like that? Again, there are a couple of answers. The first is temperature. What we call dark matter today is "cold dark matter", in contrast to "hot dark matter" (two competing ideas for dark matter; even by the late 20th century, the "cold" version was doing much better reproducing a wide range of observations). However, this "cold" is relative. All it means is that the dark matter particles are moving about at speeds very small compared to the speed of light. However, their effective temperature still is quite high. That means that those little particles are zipping around quite a bit. The result of that is that they can clump into things that are the size of a galaxy (although dark matter theories are still struggling to really reproduce the kinds of sizes of clumps when you get down to sub-galaxy scale, and observers look for signatures of sub-galaxy dark matter clumps), but they don't clump down to star sized (as awesome as that would be).

    Another wrinkle: for a gas cloud to collapse to make a star, it actually has to lose a lot of energy. For a star's worth of mass to collapse from gas cloud size down to star size, it must get rid of a whole lot of gravitational potential energy. How does it lose that energy? Electromagnetically! It radiates it away. Indeed, it turns out that pure hydrogen (or 75%-Hydrogen 25%-Helium by mass) gas has a hard time radiating away enough energy to efficiently form stars. This is one reason why we believe that the very first generation of stars (when pretty much the only atoms out there were Hydrogen and Helium) were really massive-- the relative inefficiency of radiating away energy while collapsing meant that smaller stars just couldn't formed. However, once you throw in an admixture of heavier elements that forms even less than 1% of the mass, that provides additional avenues for radiating away energy allowing smaller stars to form.

    Dark Matter, as far as we know, has none of this available to it. It certainly doesn't have the ability to radiate away electromagnetically the way regular matter does. *If* Dark Matter were to condense down to star sized, and it had to get rid of all that gravitational potential energy, it would need another way to do it. It is possible that the "Dark Sector" is more complicated, and dark matter isn't all one thing. There might be a whole spectrum of "dark" particles, including, say, "photoffs", particles that can carry away energy from dark matter the way photons do from regular matter, but that don't interact with our detectors and as such can't be observed by us. However, there's no observational evidence for that. As far as the actual evidence goes, we don't have good reason right now to postulate any more than a single additional particle to be Dark Matter. But it could be out there.

  • One of the problems with the public perception of "dark" stuff is the confusion between dark energy and dark matter. Since they are both mentioned together, it seems much like we just dream up dark stuff as we go along - tomorrow maybe dark force? I have thus started to tell my readers first of all that dark energy is actually not like dark matter at all, see here
    Now, this article is rather promoting dark energy than dark matter, but to clear up one of them as clearly not being a fudge factor may just be an important step in bringing light into the whole issue. Hmm, looking at it again, I should rewrite that article, adding some thoughts I had recently when answering comments directed against "all that dark stuff". Please have a look and tell me what you think about this approach.

  • Actually - this is an important subject. Your and Ethan's posts today have let me to chime in once more with a different thought on how to get people over to the dark side.
    Let me know what you think:

  • Mike says:

    Why would you pay any attention to slash-dot? With a few exceptions the comments get very little right about computer programming, and especially not about computer science.

  • rknop says:

    Mike : that's an excellent question for which I fear I have no good answer.

  • Dennis Des Chene says:

    Learn some history so that next time you’ll get it right.

    • rknop says:

      I have to admit I find thonyc's blog post rather curious. Am I painting over a much more complicated Galileo Affair with too broad a brush? Yes.

      But... if you read his blog post, he argues that Galileo's evidence wasn't enough to convince other scientists, says that the Church celebrated Galileo's discvoery and had a banquet in his honor, and stops there.

      No mention of the fact that Galileo was convicted for heresy.

      Honestly, thonyc's portrayal sounds like a whitewashing written by somebody who doesn't like the Church being painted in a bad light! I don't fully understand what his motivation is. If you look back on the Galileo affair, a lot happened, but in the end he was in fact convicted for heresy and spent the last decades of his life in house arrest. Any extremely broad depiction of that affair that doesn't focus on that is missing the ultimate point of what happened.

    • Roger says:

      No, Galileo was not convicted of heresy, and he only spent 8.5 years in house arrest, not "decades". You can read the details on Wikipedia/Galileo_affair. Your analogies to the aether and Galileo are complete nonsense to anyone who knows the historical facts.

  • rknop says:

    Roger -- if you read the page you linked to, you will find the following:

    Galileo was found "vehemently suspect of heresy,"

    in the section "Trial", listing what Galileo was found guilty of.

    So much for supporting your argument there!

    Galileo was put in house arrest in 1632, and spent the rest of his life there. He died in 1642. So, yes, I'm wrong to say "decades"... it was just "decade". But it was the rest of his life.

    As for your assertion about the aether, that has been dismantled above in the comments. Your ideas of what the "aether" is, and what the quantum vacuum is, are, shall we say, not generally shared by people who know what they're talking about.

  • Roger says:

    Yes, Galileo was found "vehemently suspect of heresy," but he was not convicted of heresy. Your statement was incorrect. It has never been considered heresy to propose heliocentric models of the solar system. If you are going to criticize the Church, then cite what it actually said and did.

    Frank Wilczek knows what he is talking about a lot more than you do. He explains the aether this way: "Quite undeservedly, the ether has acquired a bad name. There is a myth, repeated in many popular presentations and textbooks, that Albert Einstein swept it into the dustbin of history. … the truth is more nearly the opposite … At present, renamed and thinly disguised, it dominates the accepted laws of physics."

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