Friday, 12 March 2010

Fudging your model

As an ecosystem modeller, part of my job is fudging our model so that it better fits observations. Said fudging occurs because the model is a highly inadequate representation of the real world, but one which captures some first order features, and one which can capture them just a little bit better if I tweak this specific rate and that half-saturation constant ...

So it was with a degree of sympathetic leniency (or perhaps schadenfreude) that I watched this week's Horizon entitled "Is Everything We Know About The Universe Wrong?", which concerned itself with the creeping modification of the so-called Standard Model.

While this model is an evolving, lumbering beast dealing with, well, everything, it is still relatively simple, and it both agrees well with current observations and informs cosmologists about the history of the universe. The most familiar part of this history, the Big Bang, was originally proposed in the 1930s and has come to be the prevailing view of the universe's evolution.

But the relative homogeneity of the universe (i.e. that it looks pretty similar in all directions) did not seem a likely outcome of a cosmic explosion, which led to the development of cosmic inflation in the late 1970s. This posits that, at very early stage of its evolution when it was still homogeneous, the universe rapidly expanded exponentially, allowing this same-ness to persist and ultimately give rise to the current appearance of the universe. Inflation explains the smoothness of the cosmic microwave background and got a big boost from its predictions of the "wobbles" measured by the WMAP mission.

However, subsequent work on the motion of stars within galaxies has found those at the periphery are inexplicably orbiting galactic central point too quickly for theory to permit. This strongly implies the presence of extra matter, but of a kind that is neither visible to conventional astronomy nor interacts with the regular matter with which we're familiar. But since the evidence strongly points to its existence, dark matter has been postulated to augment the Standard Model.

Meanwhile, work studying the expansion of the universe has found that, instead of expanding at a constant or declining rate, the rate of expansion is actually accelerating. This violates the expectations of Hubble's Law, suggests a different future for the universe than previously expected, and poses another problem for the Standard Model. Clearly some force is operating to accelerate expansion, but as it too is imperceptible, the moniker dark energy has come into use to describe it.

Finally, even more recent work (which is still a little current to be widely accepted) has found that a portion of the observed universe is moving in an unexpected manner. In keeping with the ominous naming convention of earlier developments, this has become known as dark flow, and it hints at yet other unknown processes or factors that the Standard Model needs to accommodate. The discoverers of this phenomenon have suggested that this anomalous movement is a consequence of some distant portion of the universe that lies beyond what is visible to us (i.e. because of inflation).

What the programme did very well was to convey the evolutionary nature of science, as well as (in spades!) the provisional nature of developments. Admittedly, the incremental embellishment of the Standard Model with successively more ropey postulations was not exactly science at its most edifying. One definitely formed the view that astronomy may be on a highway to nowhere with all of the "dark X" additions, none of which have convincingly provided anything tangible concerning their existence. Each of them may well improve the predictions of the Standard Model (inflation being a particularly clear example), but none appear to be more of demonstrable substance than a few lines of mathematics. I suspect that each development has been made with the hope that, somewhere down the line, a deeper understanding of reality will clear things up. But with this advance still nowhere in sight (and even the critics on the programme were less than forthcoming on this point), our understanding of cosmology seems increasingly precarious. Still, leaving the viewer with an open-ended finale to the story is a useful corrective to the done-and-dusted school which paints a rather static portrait of how science works.

What the programme did very badly was the repetitive use of footage to convey each of the facets of the story. So, for the big bang there was an explosion; for inflation a red balloon repeatedly expanding; dark matter became magnetised metal balls attracting one another; dark energy was bizarrely represented as a slowly spreading slick of tar; while dark flow was an odd star-motion graphic that looked suspiciously like stock footage for a black hole documentary. Using each of these images once or twice would have been acceptable, especially since they were at least a partially imaginative attempt to convey difficult concepts, but bludgeoning the viewer time and time again was stupid. From now on I'm not going to be able to imagine cosmic inflation without thinking of a big red balloon. Thanks for that Horizon.

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