Monday, 19 May 2014

It's "Just a Theory"

     Quite often you hear people say that the theory of evolution is "just a theory", and not an established fact, or a law of nature. When you hear this, you know two things about the speakers:
  1. They are absolutely correct; and
  2. They haven't a clue what they are talking about.
     Their problem is that they don't understand what these terms mean, or the scientific method. In science, the observations, or data are the facts. A theory, hypothesis, or model - the terms are interchangeable - is a proposed explanation. Once a theory appears plausible research is undertaken to obtain further observations, which will either support or invalidate the theory. To the critics, the word "theory" implies a lack of certainty, and in a sense this is correct. Science regards the truth as a destination which can be approached infinitely closely, but never reached. In other words, you can be 99.99% sure that the theory is correct, but not 100%, for there is always the slight possibility that new information will arrive to invalidate it. In practice, of course, once it has been established long enough, explaining everything in its path, nobody seriously doubts it. Instead, they are more interested in delving deeper into the theory. In other words, if A is caused by B, we start looking for the cause of B.
     Let us take an example no-one will dispute. You no doubt believe that the earth revolves around the sun, and no doubt you are right. But the fact remains, no-one has ever observed it. Not even from outer space has anyone ever seen the earth move around the sun. What they have observed is the heavenly bodies moving across the sky. Note that these were not laboratory observations. It is a fallacy that science is solely concerned with the laboratory. There are a great many observations which can never be made in the laboratory.
     At any rate, the observations of the cosmos lend themselves to a couple of hypotheses. The first is the apparently self-evident assumption that the earth stands still and everything moves around it. The trouble was, the movements of these heavenly bodies is very complex, especially those of the planets, which tended to double back on themselves. The best hypothesis was the Ptolemaic one, which postulated each planet moving in a cycle within a cycle, a model so successful that it was able to predict the position of all of the heavenly bodies, within a small margin of error, for 1,400 years, and which is still used today by planetariums to depict the night sky. The trouble was, it was very complicated.
     It was not until 1543 that Copernicus came up with a rival theory. The data could be explained more simply, and more accurately, if you make four basic assumptions: that the earth rotates on its axis once a day, the moon revolves around the earth, and the earth and the other planets revolve around the sun, while the stars can be considered as fixed in position. What is often overlooked is that this was not the only heliocentric theory. Tycho Brahe proposed a rival hypothesis that all the planets revolved around the sun, but that the sun revolved around the earth. This explained all the data available at the time just as well as Copernicus' theory, but further observations supported Copernicus. (See here for a very detailed history of the way these theories were developed. They were not self evident.)
     Next came Kepler, who showed that the observations can be best explained by his three laws of planetary movement. Here we have another conceptual misunderstanding. A lot of people think of natural "laws" as something mystical, and set in stone. A law is just an hypothesis which can be expressed in a simple mathematical fashion. The concept belongs to an early period in the history of science, but it still has it uses. Essentially, it means that, if we do not understand the natural processes, at least we can work out the rules by which they operate. Kepler's three laws were:
  1. The orbit of each planet follows an ellipse, with the sun at one focus.
  2. The planets move faster when closer to the sun, such that an imaginary line between the sun and the planet sweeps out equal areas in equal times.
  3. For any two planets, the square of their periods, or years, is proportional to the cubes of their average distance from the sun.
     Note that Kepler could not explain why this happened. This was left to Newton with his theory of gravity, which said, basically, that every object in the universe is attracted to every other object with a strength directly proportional to the product of their masses, and indirectly proportional to the square of the distance between them. This hypothesis had the advantage of explaining two phenomena at once: the movement of the heavenly bodies, and why everything on earth falls downwards. It is also incorrect to say that Newton's theory of gravity has been invalidated by Einstein's. Einstein fine-tuned the theory, but the basics still stand.
      Note, too, that Newton's theory does not explain why objects attract each other. And, if the truth must be known, scientists have given up trying to find the answer; they just hide behind words and mathematics. Modern phrases, such as the "gravitational gradient" or the "curvature of space-time" are just new words used to describe the phenomenon or, if you like, terms to add a visual conception to the reality of arithmetic calculations. But how any object can attract or repel another at a distance is one of the deepest mysteries of the universe.
     A theory is considered to have been supported if predictions based on it prove accurate. The fact that we have been able to send spaceships to the moon and other planets using  gravitation theory is a good reason to believe it is correct. Note, too, that when a theory has been established for a long time, we do not, willy-nilly reject it as soon as some adverse data turn up. When the orbit of Uranus behaved in a way not predicted by the theory, astronomers did not reject the theory, they assumed that there was some other body affecting the orbit, and went looking for it. That was how Neptune was discovered - as was Pluto at a later date.
     What has all this got to do with evolution? It has merely been quoted to show how the scientific method works - because gravity is "just a theory", just as evolution is "just a theory".
     And now for the flies in the ointment: dark matter and dark energy. The theory of gravity predicts very accurately what is happening in our galaxy, but when astronomers took a broader view of the movement of galaxies in the aggregate, they have found that it can only be explained by the influence of something invisible and undetectable to any of our instruments. By all accounts, 95% of the universe consists of dark matter and dark energy. Our knowledge of the universe must be very incomplete if we can account for only 5% of it. And yes, maybe the theory itself needs amending.
     If I had an ideological objection to the theory of gravity the way some people object to the theory of evolution, I would ignore all the data it explains, and shout: What a load of rubbish! There is no objective evidence for dark matter and dark energy. They are hypothesizing enormous quantities of undetectable material merely to protect their precious theory. There is no such thing as gravity! The whole theory is a hoax!
     I cannot see how this approach is any less appropriate than the attitude of those who pounce on perceived difficulties in the theory of evolution. Indeed, it is more appropriate. The problems involved in gravitational theory are real, and admitted by the experts. The things which the critics claim cannot be explained by evolution, in the vast majority of cases, can be explained by it. They are just not knowlegeable enough to understand it.
     The theory of evolution is "just a theory", just like the theory of gravity, and heliocentrism is. It also cannot be proved - if you mean reaching 100% rather than 99.99% certainty. It is just very, very good at explaining the diversity of life in the world: the natural classification of animals and plants, the uniformity of the genetic code, vestigial organs, the jerry-built structure of most life forms, embryology, biogeography, the fossil record, the actual observed changes over time, to name just a few. In popular books these are asserted as evidence for evolution, but that is really putting the cart before the horse. It is better to say that these are the observations for which evolution is the best explanation. It is even effective in prediction - in this case, the prediction that transitional forms would be found, which they have been, in great numbers.
     Anyone interested in the truth about the most common criticisms of the theory might wish to check the FAQ of the excellent Talkorigins site.
     A couple of other points need to be raised. Firstly, a theory is valid only for the data which it seeks to explain. Gravitational theory does not explain electro-magnetism, nor the quantum theory the movement of planets. Similarly, the theory of evolution seeks to explain only the differentiation of life forms over time. It is not intended to explain the origin of life itself, let alone the origin of the earth, or of the universe. The only reason some people think it should is that they the imagine the theory is some sort of conspiracy to get rid of the Creator. On the contrary, it is the antievolutionists' silly arguments which are a stumbling block to belief by educated people.
     Ironically, this might have something to do with a second phenomenon I have noticed: some recent evolution websites have been captured by militant atheists. We never used to have to deal with this nonsense. I don't know how many of my lecturers and fellow students were believers when I was at university - I know there were some - because it was not considered an issue. Indeed, I remember some discussion during a field trip when one of the students, not known to be religious, stated, "I don't think this is inconsistent with the Bible," and nobody contradicted her. It would have made an interesting discussion if someone had.