Science and Stamp Collecting

Musing over the comments posted on my (slightly ironic) blog item about exoplanetary ennui, I remembered a piece I wrote for the Times Literary Supplement last summer so I dusted it off, chopped it up, and updated it for presentation here because it expands a bit on the earlier contribution.

If the Sun were the size of a golf ball, then the Earth would be a speck of dust a few metres from it and the nearest star would be hundreds of kilometres away. And this is what it is like in the relatively crowded environment of the Milky Way. The unimaginable scale of our Universe means that astronomy has never really become an experimental science, but has largely remained an observational one, having more in common with, say, archaeology than chemistry or other laboratory-based disciplines. Consequently, even though it is perhaps the oldest science, it is also in some respects the least mature. The absence of the traditional interplay between theory and experiment, the inability to perform repeated experiments under slightly different conditions, and the sheer difficulty of measuring anything at all have stunted its development compared to younger fields. For this reason, one often finds in astronomy certain tendencies that other subjects have largely grown out of, such as an unhealthy mania for classification and nomenclature.

Taxonomy has its place within the scientific method: modern chemistry owes much to Dmitri Mendeleev‘s periodic table; botany could not have progressed without Linnaeus; and the theory of evolution was founded on Charles Darwin‘s painstaking studies on the Galapagos Islands. But arranging things in groups and giving them names does not in itself constitute scientific progress, no matter how systematically it is done. The great experimental physicist Ernest (Lord) Rutherford dismissed this kind of activity as not science but “stamp collecting”.

This brings us to the grand debate that took place in Prague in the summer of 2006 under the auspices of the International Astronomical Union. One of the problems before the IAU’s 26th General Assembly was what to do about the fact that recent investigations have revealed the presence of a number of objects orbiting the Sun that are ostensibly at least as worthy of the name “planet” as Pluto, which in our current textbooks is the ninth one out. Obviously, which objects should be called planets depends on how you define what a planet is. The solar system contains objects of all shapes and sizes, from tiny asteroids to immense gas giants such as Jupiter and Saturn. Where should one draw the line? The original proposal was to increase the number of planets to twelve by admitting some lowly new members to the club, but in the end the IAU decided to demote Pluto to the status of a “dwarf” planet thus restricting the number of true planets to eight. This was a controversial decision, at least in the United States, because the vital vote was taken on the last day of the meeting when most of the US delegates had to take flights home. Pluto was discovered by an American, Clyde Tombaugh, in 1930, so the decision deprived the nation of its only planet-discoverer.

The “no” decision hinged on the adoption of three criteria: that the object be round, i.e. have a shape determined by internal gravitational forces; that it should have cleared its own orbit of debris; and that it should be orbiting our own star, the Sun. None of these has any special scientific value; the resulting decision was therefore pretty arbitrary. Moreover, deep-space observations have led to the discovery of literally hundreds of planetlike objects orbiting other stars. These exoplanets offer much greater prospects for scientific progress into the general theory of planet formation than the few objects that happen to have formed in our particular vicinity, so why are they excluded from the definition? In any case, what have we learned scientifically from the new nomenclature? Pluto is still the same object that it was before August 2006, and astronomers still don’t understand what one can infer from its own particular properties about the general process of planet formation.

So is Pluto a planet?

Who cares? In this case there really is nothing in a name. When I was asked this question on the telephone by a reporter I gave precisely that answer and he was shocked. I’m sure he thought that all that astronomers do is look at things and give them names. There are some that do that, of course, but most of us prefer doing proper science.

In the field of exoplanet research we are seeing real signs of maturity, although current studies are still firmly rooted in the “discovery” and “classificatuion” stage. Witness last weeks press interest in the first directly imaged exoplanets. I am well aware of the immense potential that those pictures have for stimulating interest in science, but there is still a long way to go before this field reaches its prime. That probably makes it an excellent area for young scientists to work in. But ultimately this youthful exuberance should give way to something a bit more serious, which is to go beyond what these discoveries are in themselves and ask what deeper questions they might answer.

One can see many other parallels in the history of astronomy, such as the discovery of quasars in the late 1950s. The first few of these must have generated a huge amount of excitement because they were not at all understood. Within a few years hundreds had been detected by radio observations but their nature remained unknown. The subsequent identification of redshifted hydrogen emission lines in the spectra of these objects led to them eventually being identified as very distant extragalactic sources of immense intrinsic power. By the 1980s quasars were identified as a particular type of active galaxy and placed within a general classification scheme that also involved blazars, Seyfert galaxies, and so on. Nowadays we have samples of tens of thousands of quasar spectra and the interest evolves around how the activity in their nucleus relates to the process of galaxy formation in an expanding Universe and how we can use these objects to map out the large-scale distribution of matter. To an outsider these tasks may seem less glamorous that the early days of quasar research, but that’s what science is like.

At the extreme end of the distance scale of astronomical investigation lies my own field of cosmology, the scientific study of the Universe as a whole. The scale of the solar system is challenging enough, but the cosmos is really big. Until recently, cosmology was so lacking in reliable observational input that it was thought of as a flaky offshoot of astronomy, more a branch of metaphysics than a proper scientific discipline, a paradise for theoreticians whose wildest speculations stood no chance of ever being tested with real measurements. Over the past twenty years or so, however, staggering advances in astronomical instrumentation have allowed astronomers to probe the darkest depths of space, capturing light that has travelled for almost 14 billion years on its way towards us. Theories are now so tightly constrained by these observations that there is very little room for manoeuvre. From this interplay between conjecture and refutation has emerged a cosmological framework that accounts, at least in a broad-brush sense, for how the Universe is constructed and how it is evolving.

There are some important gaps, including some puzzling anomalies, and the precise nature of many of its constituents is yet to be understood, but the establishment of the “concordance model” is a sign that cosmology really has come of age.


15 Responses to “Science and Stamp Collecting”

  1. Bryn Jones Says:

    Whether Pluto is a planet matters very much indeed. You are absolutely that it does not matter scientifically at all, but the status of Pluto matters to the public perception of science. That there were nine planets and that Pluto was one of them are two of the very few facts about science that were almost universally appreciated across society. Losing a planet confuses people. It damages the public view that science deals with precise, fixed concepts. The reclassification of Pluto so that it is not one of the “planets” is unfortunate because it does tarnish the image of science, even if there were very sensible reasons for needing to change definitions in the light of new discoveries. The broad public do not understand the complications inherent in the details of science: they only understand the headlines.
    (And the IAU’s opinion that a “dwarf planet” is not a “planet” is at odds with definitions in the rest of astronomy: a dwarf star is still a star, a dwarf galaxy is still a galaxy.)

  2. I second Bryn Jones statement, especially the last sentence about the linguistic nonsense that states a dwarf planet is not a planet at all. However, I don’t believe that there are sensible reasons for changing the defintiion of planet in the direction the IAU did, namely to artificially narrow it. At this time of new discoveries in both this and other solar systems, we should keep the term planet broad to encompass any non-self-luminous spheroidal object (one in hydrostatic equilibrium) orbiting a star. We can then distinguish between the many types of planets through use of subcategories. We do this with stars and galaxies, so why not with planets? What the IAU did only served to further confuse and alienate the public, especially since their definition is sloppy, was adopted by only four percent of its members, and is opposed by as many astronomers as those who support it.

  3. Michael Merrifield Says:

    Not so sure, Bryn. I think it would be a good thing if society recognized more widely that scientists do not deal with precise fixed concepts when working at the cutting edge. It would, for example, make discussion of real issues like climate change more informed if the conspiracy theorists could no longer get serious traction by arguing that the dissenting evidence “disproved” global warming.

    What was damaging in all the Pluto hysteria was the widely-held perception that the status of Pluto is viewed by scientists as being at the cutting edge of science, and that they have nothing more interesting and worthwhile to do with their time than spend extended periods arguing over it.

  4. But the field of exoplanet research was science from the beginning. The first “hot Jupiter” completely changed our preconceptions about the makeup and formation of solar systems. It forced people to explain how the hell planets managed to get so close to their stars, which spawned models of planetary formation and migration that made definite testable predictions. These predictions are being tested with the discovery of each new system, and the models are constantly being modified to make new, better predicitons.

    Now, as many organisations prepare to launch the next generation of planet-searching instruments, exoplanet theorists are developing models that predict how many terrestrial planets these missions should find. They’ve even had to answer questions about the theoretical ramiifications of a Null result!

    And although people in the field use jargon like “super-Earths” and the aforementioned “hot-Jupiters”, they spend very little if any time at all squabbling over which terms to apply to which objects.

    There is still a strong component of “discovery” for its own sake in the field, evidenced, for example, by those who are closely studying transiting planets to look for evidence (any evidence at all) of water and methane in planetary atmospheres. But right along side those who are making the discoveries are the ones who are trying to model their results, make predictions relevant to future work, and push the theoretical knowledge of planetary atmoshperes forward. They are not simply looking to classify some planets as “water containing” and some planets as “methane containing”, they are using the results to model exoplanetary atmospheres!

    So I think your comparison with the Pluto fiasco is off – the people I know working in exoplanets could not care less what the things are called. Their field is too exciting, too rapidly evolving to get bogged down in mindless stamp collection. They are constantly on to the next big question, trying to figure out how today’s results impact the whole field. In short, very little like those you portray as chasing press-releases.

  5. telescoper Says:

    Methinks you doth protest too much

  6. Anton Garrett Says:

    At this time of year I am pleased to present an extract from the astronomers’ Christmas pantomime, illustrating the high standard of the debate about whether Pluto is a planet:


    OH NO IT ISN’T!!

  7. Whether it’s a planet or not I think it’s a shame that they decided to name it after a Walt Disney cartoon character…

    ..and, please, no jokes about Mickey Mouse science!

  8. Michael Merrifield Says:

    No “they” about it, Peter — Pluto is a proper British choice of name!

  9. “They” is third person plural; no nationality implied.

  10. […] In the Dark A blog about the Universe, and all that surrounds it « Science and Stamp Collecting […]

  11. Michael Merrifield Says:

    Whereas “we” is a first person plural, accepting corporate ownership and finessing any possible misinterpretation of implication from a Disney reference that the other side of the Atlantic is somehow responsible (as many might think, given that Pluto was discovered by an American). I can do parts of speech, too.

  12. telescoper Says:

    I’d prefer if you didn’t “we” all over my blog.

  13. Actually, the Disney character was named after the planet, not the other way around.

  14. telescoper Says:

    Really? How astonishing. I never would have guessed. I’m glad you didn’t think my comment was meant to be ironic.

  15. You may have meant to be ironic, but there are a lot of people out there who actually believe the planet was named after the dog rather than the other way around. 🙂

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