Tuesday, February 17, 2009

Why does science change over time?

Anyone who has studied the history of science cannot disagree that science changes over time. As just one example, just a couple of centuries ago science was firmly convinced that a “Luminiferous aether” pervaded all of the heavens. That was the medium through which light propagates. They thought that light could not move through space without such a medium. That is now known to be untrue.

What causes science to change its views?

In order to answer this question, you need to first understand how science works in the 21st century.

It took a very long time for the idea that the universe was governed by some understandable principles (or laws) to take root. Very little was done before the inventions of agriculture and writing. Most of the initial work in what we could call “science” involved time-keeping and calendars. Quite obviously, agricultural success, more than anything else, depended on knowing about the seasons, when they occurred, how long they lasted and so on.

Over time people started to contemplate other parts of the natural world, particularly astronomy and anatomy (most generally in an attempt to devise medical procedures).

Plato and Aristotle were among the first philosophers who expanded the human desire to understand the world by asking and attempting to devise answers to the question: "How did the ordered cosmos in which we live come to be?"[1]

Aristotle felt that such answers could be discovered solely through contemplation and debate with others. In essence he felt that what we would call biology, physics and other sciences were nothing but alternative fields of philosophy similar to ethics or politics. Because of that, Aristotle’s work in science was largely qualitative rather than quantitative.

As Wikipedia describes his contributions to science:

“Beginning in the sixteenth century, scientists began applying mathematics to the physical sciences, and Aristotle's work in this area was deemed hopelessly inadequate. His failings were largely due to the absence of concepts like mass, velocity, force and temperature. He had a conception of speed and temperature, but no quantitative understanding of them, which was partly due to the absence of basic experimental devices, like clocks and thermometers.”[2]

The best illustration of the flaws in Aristotle’s methods is his hypothesis about how fast bodies fell to Earth. Aristotle closely reasoned that heavier things would fall faster than less heavy things. In fact he made a specific prediction: a body will fall at a speed proportional to its weight. For example, if Body A weighed ten times as much as Body B, then Body A would fall ten times faster than Body B.

The idea that heavier things fall faster than lighter things is probably an intuitive belief for many people. But there is probably nothing that would be easier to test. You simply need to put two different weights in your two hands, let them go at the same time and see which one hits the ground first. An observer with a stopwatch would help, but if one of the weights was ten times heavier than the other and you dropped them from a substantial height, confirmation of Aristotle’s hypothesis wouldn’t really need any instrumentation. Anyone would be able to observe the noticeable difference which should occur. (Note that because of air friction, the two weights should be made of the same or similar materials and have the same shape. Or, better yet, the experiment should be performed in a vacuum. A subtlety such as that might escape an early experimenter. But in general a test of how fast weights that were dropped fell to the ground should be trivially easy to set up and perform.)

Amazingly, for many centuries, no one performed that experiment. Everyone simply accepted Aristotle’s advice in the matter.

That is, everyone accepted Aristotle’s ideas until Galileo came along. Galileo tried dropping two weights (supposedly from the Leaning Tower of Pisa) and found that they hit the ground at the same time.

Because of such things, science changed.

In the 21st century, as we have already discussed in this chapter, for something to be “scientific” it must be “falsifiable”.

Note that even continued confirmation of a scientific hypothesis can never prove a hypothesis. This confuses people who are unfamiliar with how science works. Many people, instead, feel that science is like mathematics and concepts like gravity can be and have been proven.

Of course if you were to drop something like your car keys and it was to hang in mid-air, you would not immediately reject gravity. You would instead expect some sort of anomalous circumstance. Maybe, if the thing you let go of was made of metal, your first thought would be that some giant magnet was affecting its fall. Or you might suspect some sort of optical illusion. With all of the confirmation of gravity that we have experienced during our lives the idea that gravity is not working under any circumstances seems intuitively absurd. Even a dog will look down, rather than up, if it lets go of a bone. Surely the idea of gravity is indisputable and has been proven!

But, in fact, it hasn’t. Instead it has merely been confirmed innumerable times. Though it would be an incredibly remote possibility, scientists must always consider the possibility that gravity doesn’t work as we believe that it does.

Anyone who is the least bit familiar with science knows that Sir Isaac Newton developed the first hypotheses about gravity. An equally, or possibly even more familiar name is Albert Einstein.

What many people don’t know is that Einstein’s General Theory of Relativity showed that Newton’s ideas about gravity weren’t completely accurate. Newton’s hypotheses were really only approximations.

Scientists had known for a while that something was amiss with Newton’s ideas. Their strongest clue was the orbit of the planet Mercury around the sun. Newton’s Law of Gravity predicted an elliptical orbit – which Mercury has – but the perihelion of Mercury’s elliptical orbit precessed. What that means is that the ellipse moves around the sun as its focal point such that the furthest point of the orbit is not always in the same direction from the sun.

Newton could explain some of this variation, but not all of it. General relativity completed the model so that it matched the measured data.

Effectively Newton was wrong about gravity (if only by a small amount). Yet gravity was, and remains, probably the single most well-accepted scientific idea of all. It’s easy for anyone to understand and we see it around us all of the time. If gravity can’t be proven, then what in science can be?

In fact, nothing in science can be proven.

To be scientific, an idea must be falsifiable. Once it has been falsified, it must change.

That is why science changes over time.

[1] F. M. Cornford, Principium Sapientiae: The Origins of Greek Philosophical Thought, (Gloucester, Mass., Peter Smith, 1971), p. 159.
[2] http://en.wikipedia.org/wiki/Aristotle, referenced on November 9, 2007.

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