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Posts Tagged 'Pluto'



Scientific Debates Are (Mostly) a Waste of Time

The fake table of contents from the April 1, 1986 issue of the Astrophysical Journal. (Click for larger version.)

The fake table of contents from the April 1, 1986 issue of the Astrophysical Journal. (Click for larger version.)

Recently, I acquired a stack of books, papers, conference proceedings, and other scientific memorabilia, including the fake journal table of contents on the right. Though the material varied a lot in content and tone, I noted a lot of things in common: nearly every set of items emphasized a debate that was very significant at one time, but now is pretty much dead and buried. Though it’s intended to be humorous, the first three items in the Astrophysiological Journey (a parody of the prominent Astrophysical Journal) table of contents highlighted a real conflict in the cosmology community.

That conflict was over the rate of the expansion of the Universe. Since the 1920s, we’ve known that most galaxies are moving away from us, and the farther they are, the faster they seem to be receding. Though it took decades for many cosmologists to accept, eventually the evidence convinced the community that these galaxies aren’t actually “moving” in the usual sense, but being carried by the tide of cosmic expansion. The debate highlighted in the first three items of the Astrophysiological Journey was over the rate of that expansion, encapsulated in the Hubble parameter (sometimes known as the Hubble constant).

The Hubble parameter isn’t a speed as such. Instead, it tells how fast a galaxy would appear to be moving away from us as, if we know its distance (or vice versa). Today, the value of the Hubble parameter is approximately 71.2 km/s/Mpc (with some variation in estimates depending on what data you use). That means a galaxy 1 million parsecs away (1 megaparsec, or Mpc) appears to be moving away from us at a speed of 71.2 kilometers per second (km/s), while a galaxy 10 Mpc away would appear to be moving 712 km/s.

However, it took decades to settle the value of the Hubble parameter, and the authors of the first two “papers” in the Astrophysiological Journey were real astronomers striving to be the first to get it right. Alan Sandage was the heir apparent of Edwin Hubble, who (along with the awesomely named Vesto Slipher) first attempted to measure cosmic expansion; Gerard deVaucouleurs’ work was largely with galaxies, so he thought he had a better method than Sandage’s. They each had their partisans and students; the story is told in Dennis Overbye’s excellent book Lonely Hearts of the Cosmos. Conferences were devoted to the debate over the Hubble parameter, with Sandage and his camp advocating a relatively low value (in the 50 km/s/Mpc range), while deVaucouleurs and his partisans pushed for a higher value (100 km/s/Mpc or thereabouts). I find it amusing that the value established in part by the Hubble Space Telescope was roughly halfway between the earlier estimates, meaning both of them were wrong.

The gamma ray burst GRB 100621A, discovered in 2010. GRBs are some of the brightest objects in the entire Universe, outshining everything else put together during their brief periods of brightest activity. For many years, however, astronomers debated whether they were local objects in our galaxy, or very distant. The latter answer turned out to be correct, based on many years of hard work. [Credit:  NASA/Swift/Stefan Immler]

The gamma ray burst GRB 100621A, discovered in 2010. GRBs are some of the brightest objects in the entire Universe, outshining everything else put together during their brief periods of brightest activity. For many years, however, astronomers debated whether they were local objects in our galaxy, or very distant. The latter answer turned out to be correct, based on many years of hard work. [Credit: NASA/Swift/Stefan Immler]

For a long time, the debate was ascendent, but it seems pretty silly now—at least to me. Similarly, some of the other papers in the stack I got involved the debate over the nature of gamma ray bursts (GRBs), specifically whether they were local bright sources of gamma rays, or objects located much farther away in space. The consensus is strongly in favor of the latter: GRBs are some of the brightest objects in the Universe, corresponding to extraordinarily violent cosmic phenomena like collisions between neutron stars, or explosions of extremely massive stars. These debates only persisted as long as the data was incomplete or ambiguous; once the evidence strengthened, the issues that caused virtual hair-pulling and real conflict in the community more or less evaporated.

That’s not to say the issues weren’t real at the time. Science isn’t magical: new types of measurements may require many years of hard work to become accurate, and in some cases can require entirely new technology before they can be done properly. To measure the Hubble parameter, astronomers need to know distance and velocity accurately, and independently of each other. For best results, both of these measurements require knowledge of the intrinsic spectrum of an object (galaxy, supernova, or what have you). Additionally, galaxies are moving relative to cosmic expansion, due to gravitational interactions with each other; that needs to be corrected for to get an accurate number for the Hubble parameter. In other words, this stuff isn’t intrinsically easy to do.

However, any number of debates didn’t settle the matter. Today’s debates in cosmology are over the nature of dark matter, the substance of dark energy, and different models of inflation. Even though some of the debaters will be right and others wrong by necessity, it’s not the debate that will determine that—it’s the evidence. Some of these challenges are very difficult: inflation in particular is something we can only study indirectly, and particle colliders have ruled out many of the simplest options for the composition of dark matter. If the past is any guide, ingenuity and persistence will eventually pay off, perhaps in ways we don’t currently anticipate.

Of course, most scientists recognize and acknowledge all of this. However, even we tend to overemphasize the role of debate, centering conferences around it and playing it up for the public. (I’m not even going to get into the “debate” over Pluto‘s planetary status, which is mostly an embarrassment, with emotions overriding the scientific content.) I think it’s a human tendency: we love controversy, and love to argue. I’m no different, though I’m not as into it as some people I can think of, who really seem to thrive on conflict. Who doesn’t want to be right?

On the other hand, I won’t debate Creationists or climate-change deniers, even though the evidence is on my side. I’m not a good debater, and a skilled opponent could trash me. I’m aware of that fact, so I find it better to lay on the evidence in my writing and avoid direct confrontation. In fact, framing science as being about debates can make every issue seem equally important. After all, if there is legitimate conflict over the nature of dark matter and we debate about it publicly, maybe to the public there’s something to the “debate” over climate change—even though there isn’t. The jury has ruled on the Hubble parameter, evolution, climate change, and the origin of birds, all things that were debatable at one time, but are no longer controversial.

Returning to the Astrophysiological Journey: the fourth, fifth, and sixth items are also telling. Halton “Chip” Arp built his reputation around an excellent catalog of interacting galaxies, which helped astronomers characterize the role of mergers and collisions in galactic evolution. However, he staked that reputation on a misguided attempt to prove that the Big Bang didn’t happen, and that the apparent motion of distant objects (such as quasars) due to cosmic expansion was actually due to an intrinsic effect. There was no real debate on the subject, but many astronomers participated in a bit of a pile-on—understandably since Arp’s ideas were so blatantly incorrect. However, from the parody table of contents, it might even look like the Arp-vs.-nearly everyone else conflict was coequal to the real challenge of determining the Hubble parameter.

True debate is only possible when the evidence isn’t in, and only profitable when it spurs us toward innovation and the collection of better data. I think we would do well to remember that. If a jokey journal cover is what it takes to remind us, I say bravo.

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