or why Vera Rubin and Albert Bosma deserve a Nobel Prize Natural Law: a concise statement describing some aspect of Nature. In the sciences, we teach about Natural Law all the time. We take them for granted. But we rarely stop and think what we mean by the term. Usually Natural Laws are items of textbook knowledge.
I promised more results from SPARC. Here is one. The dynamical mass surface density of a disk galaxy scales with its central surface brightness. This may sound trivial: surface density correlates with surface brightness. The denser the stars, the denser the mass. Makes sense, yes? Turns out, this situation is neither simple nor obvious when dark matter is involved.
OK, I’m not even going to try to answer that one. But I am going to do some comparison exploration. A complaint often leveled against MOND is that it is not a theory. Or not a complete theory. Or somehow not a proper one. Sometimes people confuse MOND with the empirical observations that display MONDian phenomenology. I would say that MOND is a hypothesis, as is dark matter.
I find that my scientific colleagues have a variety of attitudes about what counts as a theory. Some of the differences amount to different standards. Others are simply misconceptions about specific theories. This comes up a lot in discussions of MOND. Before we go there, we need to establish some essentials. What is empirical? I consider myself to be a very empirically-minded scientist. To me, what is empirical is what the data show. Hmm.
I’m just back from the World Science Festival where I participated in the discussion shaking up the dark universe. It was an interesting experience, and mostly positive despite some offstage diva behavior. One thing it drove home to me was how hard it is to communicate across a gulf of different training and experience. Not just from scientists to the public, but between scientists.
Cosmology used to be called the hunt for two numbers. It was simple and elegant. Nowadays we need at least six. It is neither simple nor elegant. So how did we get here? The two Big Numbers are, or at least up till the early-90s were, the Hubble constant H 0 and the density parameter Ω. These told us Everything. Or so we thought. The Hubble constant is the expansion rate of the universe.
There has been some debate of late over the role of falsifiability in science. Falsifiability is the philosophical notion advocated by Popper as an acid test to distinguish between ideas that are scientific and those that are not. In short, for a theory to be scientific, it has to be subject to falsification.
I travel to Cambridge, MA tomorrow to participate in the workshop Rethinking the Dark Matter Paradigm (I had nothing to do with the choice of title). I went to college at MIT in the ’80s, so is a bit back to the future for me in space as well as time. There is a lot to rethink, or nothing at all, depending on who you ask.
A beginning is the time for taking the most delicate care that the balances are correct. … take care that you first place him in his time… And take the most special care that you locate [him] in his place… – Princess Irulan ( Dune ) A human being is complex beyond the knowledge of any other individual. Identifying oneself is not a simple matter. Professionally, I am a scientist.
