Two good friends of mine, Orad Reshef and Jesse Corbeil, have just started putting together a series of podcasts about science, which I think is a great initiative. I put a lot of effort into making philosophy accessible, but philosophy is far from the only discipline that needs a good dose of accessibility, so I'm very glad to see new efforts in that direction. (LFD fans will of course recognize the names and voices of the hosts, and keep your ears open during their theme song!) Anyway, it's nice not only because the show is good, clean, stimulating entertainment, but also because it wanders into my philosophical territory, which allows me to give some response, so it's a nice way to get back to work with some old friends while enriching both their endeavour to popularize science and mine to popularize philosophy. Good stuff all around.
So, without any further ado, let's talk about their first episode, which you can listen to here. The first episode of their show, which is called Yet Another Science Show, is entitled "The Metre and Friends," and it's all about the sordid and wonderful history of measurement. We often think of measurement as something very objective: you take a ruler, put it up to the object you want to measure, and the ruler tells you how long/wide/deep the object is. Objects just have length; we play no role in it; any subjective element is removed when it comes to measurement; measurement just gives you the clean, cold, hard, objective facts of the universe. Most scientific realists (and that probably means you too, casual reader: even if you don't know what scientific realism is, you probably believe in it anyway) believe that reality is defined by what you can measure. If you can measure it, it's real; if you can't, it ain't. Interestingly, Einstein believed no such thing: "“Not everything that counts can be counted, and not everything that can be counted counts," said the great physicist of the early 20th century. So if measurement plays such an important role in determining what's real (and neither Einstein nor I believes that), then we'd better be damned sure that measurement itself is sitting on a rock-solid foundation of objectivity.
Orad and Jesse do a wonderful job of tracing the history of measurement, and the fact that each unit of measure relies on others. In the early days when one foot was actually the measure of a human foot, our units of measure were very anthropocentric, relying heavily on our bodies and our practical concerns. Over time, we've moved away from those concerns towards a completely systematic definition of our units of measure: rather than defining the metre by a platinum-iridium bar in Paris, we now define it relative to the second and the speed of light. Actually, the speed of light defines both our measurements of space and of time. The two are interdefined, that's what the move to relativity a century ago was all about. And light is a good measuring rod because it's invariant across lots and lots of circumstances. In other words, no matter where and when you are, light is going to act in pretty much the same way all the time, so it's a good standard for measurement. However, the constancy of light across frames of reference is not something that we've demonstrated; it's one of the postulates of our science.
In other words, this whole systematic arrangement is a house of cards. Each piece relies on the other pieces or on our decisions to accept something as axiomatic. Once you've used the speed of light to define the length of a metre or the duration of a second, how could you ever discover that the speed of light wasn't what you thought it was? Suppose that you use your best clock and your best metre stick and you find out that the value of the speed of light wasn't what you thought it was. What then? Well, the problem is that you used light to define space and time, and therefore you'd be forced to say that the metre stick or the clock must be wrong. The speed of light is the metre stick of your metre stick, or so we've decided to believe as a first postulate of physics.
So how is our science not arbitrary? History. We didn't just select the number 299 792 458 m/s as the speed of light. Rather, we used to have a definition of a metre (remember the platinum-iridium bar in Paris) and a definition of time. Using those old definitions, we figured out the speed of light. In those days, the speed of light was an empirical matter, something you could get right or wrong. But not anymore: now that we've used the speed of light to define metres and seconds, if you claimed that the speed of light were different than it is, you wouldn't be making a claim about how fast light moves. Actually, you'd be giving a re-definition of the metre and the second. (Be wary about doing that sort of thing, because remember that all of our other units of measure are also connected to space and time, metres and seconds, so you'd be redefining our measures for everything. That can be a time-consuming task to sort out.) So the non-arbitrarity comes from the fact that we're never just choosing a whole system at a time. We're always operating in some moment or another in history, where things already have a definition, and all we ever need to consider at a given moment is the possibility of redefining one corner of our set of measures, knowing that this will have minor effects on the others that will then need to be worked out. We never need to build Noah's Arc the first time; we're just constantly patching the hull on the high seas.
Science is always historically situated, and our measures and the revisions thereof are constantly building on the history of science. But all of these measures are interdependent rather than objective: they're not picking out the real structure underlying the world. It's not like the speed of light, measured in metres/second, is a fact out there in the world that we can get right or wrong. Light moves at a certain speed, but (at least at the moment) we use that speed to define the metre and the second, to stipulate what they mean. We choose bases for measurement that are invariant across lots of different contexts so that we don't have one metre and a different metre on Mars. Such a situation wouldn't be very helpful (though few outside the science community would really notice a difference in the day-to-day world, except that their cell phones wouldn't work).
What measurement gives us is not a way of minimising the subjective element of experience: what it gives us is a set of instructions for making something an object. The measured length of an object is not an objective fact out there in the world, independent of us, because measurement itself is a human construct, a very powerful and systematically complex one that allows us to cut the world up into objects with lengths in metres. But if we'd decided to define the metre differently, if we'd decided to "force" the speed of light to be 300 000 000 m/s for instance, then our definition would be different, as would the lengths of all objects. If you want a good example of how much we use our interrelated sets of definitions to "cut up" the world into usable chunks, you need listen no further than the comment at the 28th minute of "The Metre and Friends," when Jes says that he thinks in inches. That's exactly what these definitions do for us: they give us a framework with which to grasp the world.
But clearly science advanced importantly when we started defining the metre by the speed of light rather than the bar in Paris (we also passed through an intermediate stage of defining it by the wavelength of a certain colour of light). So if these tools are what we use to cut up the world, and they are "just" definitions that we stipulate, how could we be progressing? How could we be moving away from the anthropomorphic definitions of these terms and toward something "objective"? Recall the big leap forward (not a quantum leap, cause quanta are actually ridiculously small) we made when we started to interdefine space and time. What we did there was not to strip away the subjective elements of our measures: what we actually did was to increase the systematic interdependence of those measures. We used to define metres one way and seconds another, and used those definitions to measure the speed of light. Then we started to use the speed of light to define metres and seconds with respect to one another. Metres and seconds were not independent phenomena any longer. They spring from a common source now.
Anyway, I've tried to give an argument here that measurement is not objective; rather, it's objectivizing. We never "discovered" what the metre was by walking through the world and looking at stuff. Rather, we stipulated a definition of a metre and that allowed us to interact with objects in a radically new fashion, a fashion that is improved drastically when those measures start to be defined more and more with respect to one another rather than based on objects we encounter in our day-to-day practical lives. Progress in measurement does not remove subjectivity: it actually provides the conditions of us as subjects to create a world for ourselves that has a particular structure.
Anyway, that's all I've got to say on the topic for now. Hopefully this will inspire not only some interesting feedback, but will also inspire you to start following their show. They've just released their second episode, "Black Holes Don't Suck," so give that a listen too!
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