What is the ``scientific method''?
The scientific method is the best way yet discovered for winnowing the truth from lies and delusion. The simple version looks something like this:

• 1. Observe some aspect of the universe.
  
• 2. Invent a tentative description, called a hypothesis, that is consistent with what you have observed.
  
• 3. Use the hypothesis to make predictions.
  
• 4. Test those predictions by experiments or further observations and modify the hypothesis in the light of your results.
  
• 5. Repeat steps 3 and 4 until there are no discrepancies between theory and experiment and/or observation.
  

The great advantage of the scientific method is that it is unprejudiced: one does not have to believe a given researcher, one can redo the experiment and determine whether his/her results are true or false. The conclusions will hold irrespective of the state of mind, or the religious persuasion, or the state of consciousness of the investigator and/or the subject of the investigation. Faith, defined as belief that does not rest on logical proof or material evidence, does not determine whether a scientific theory is adopted or discarded.
A theory is accepted not based on the prestige or convincing powers of the proponent, but on the results obtained through observations and/or experiments which anyone can reproduce: the results obtained using the scientific method are repeatable. In fact, most experiments and observations are repeated many times (certain experiments are not repeated independently but are repeated as parts of other experiments)

If the original claims are not verified the origin of such discrepancies is hunted down and exhaustively studied.
When studying the cosmos we cannot perform experiments; all information is obtained from observations and measurements. Theories are then devised by extracting some regularity in the observations and coding this into physical laws.
There is a very important characteristic of a scientific theory or hypothesis which differentiates it from, for example, an act of faith: a theory must be ``falsifiable''. This means that there must be some experiment or possible discovery that could prove the theory untrue. For example, Einstein's theory of Relativity made predictions about the results of experiments. These experiments could have produced results that contradicted Einstein, so the theory was (and still is) falsifiable.
In contrast, the theory that ``the moon is populated by little green men who can read our minds and will hide whenever anyone on Earth looks for them, and will flee into deep space whenever a spacecraft comes near'' is not falsifiable: these green men are designed so that no one can ever see them. On the other hand, the theory that there are no little green men on the moon is scientific: you can disprove it by catching one. Similar arguments apply to abominable snow-persons, UFOs and the Loch Ness Monster(s?).
A frequent criticism made of the scientific method is that it cannot accommodate anything that has not been proved. The argument then points out that many things thought to be impossible in the past are now everyday realities. This criticism is based on a misinterpretation of the scientific method. When a hypothesis passes the test it is adopted as a theory it correctly explains a range of phenomena it can, at any time, be falsified by new experimental evidence. When exploring a new set or phenomena scientists do use existing theories but, since this is a new area of investigation, it is always kept in mind that the old theories might fail to explain the new experiments and observations. In this case new hypotheses are devised and tested until a new theory emerges.
There are many types of ``pseudo-scientific'' theories which wrap themselves in a mantle of apparent experimental evidence but that, when examined closely, are nothing but statements of faith. The argument , cited by some creationists, that science is just another kind of faith is a philosophic stance which ignores the trans-cultural nature of science. Science's theory of gravity explains why both creationists and scientists don't float off the earth. All you have to do is jump to verify this theory - no leap of faith required.

In popular usage, a theory is just a vague and fuzzy sort of fact and a hypothesis is often used as a fancy synonym to `guess'. But to a scientist a theory is a conceptual framework that explains existing observations and predicts new ones. For instance, suppose you see the Sun rise. This is an existing observation which is explained by the theory of gravity proposed by Newton. This theory, in addition to explaining why we see the Sun move across the sky, also explains many other phenomena such as the path followed by the Sun as it moves (as seen from Earth) across the sky, the phases of the Moon, the phases of Venus, the tides, just to mention a few. You can today make a calculation and predict the position of the Sun, the phases of the Moon and Venus, the hour of maximal tide, all 200 years from now. The same theory is used to guide spacecraft all over the Solar System.
A hypothesis is a working assumption. Typically, a scientist devises a hypothesis and then sees if it ``holds water'' by testing it against available data (obtained from previous experiments and observations). If the hypothesis does hold water, the scientist declares it to be a theory.

Experiments sometimes produce results which cannot be explained with existing theories. In this case it is the job of scientists to produce new theories which replace the old ones. The new theories should explain all the observations and experiments the old theory did and, in addition, the new set of facts which lead to their development. One can say that new theories devour and assimilate old ones (see Fig, 1.2). Scientists continually test existing theories in order to probe how far can they be applied

When a new theory cannot explain new observations it will be (eventually) replaced by a new theory. This does not mean that the old ones are ``wrong'' or ``untrue'', it only means that the old theory had a limited applicability and could not explain all current data. The only certain thing about currently accepted theories is that they explain all available data, which, if course, does not imply that they will explains all future experiments!


In some cases new theories provide not only extensions of old ones, but a completely new insight into the workings of nature. Thus when going from Newton's theory of gravitation to Einstein's our understanding of the nature of space and time was revolutionized. Nonetheless, no matter how beautiful and simple a new theory might be, it must explain the same phenomena the old one did. Even the most beautiful theory can be annihilated by a single ugly fact.

Saturn devouring his sons (by F. Goya). A paradigm of how new theories encompass old ones.

Scientific theories have various degrees of reliability and one can think of them as being on a scale of certainty. Up near the top end we have our theory of gravitation based on a staggering amount of evidence; down at the bottom we have the theory that the Earth is flat. In the middle we have our theory of the origin of the moons of Uranus. Some scientific theories are nearer the top than others, but none of them ever actually reach it.
An extraordinary claim is one that contradicts a fact that is close to the top of the certainty scale and will give rise to a lot of skepticism. So if you are trying to contradict such a fact, you had better have facts available that are even higher up the certainty scale: ``extraordinary evidence is needed for an extraordinary claim''.

In 1666 Isaac Newton proposed his theory of gravitation. This was one of the greatest intellectual feats of all time. The theory explained all the observed facts, and made predictions that were later tested and found to be correct within the accuracy of the instruments being used. As far as anyone could see, Newton's theory was ``the Truth''.
During the nineteenth century, more accurate instruments were used to test Newton's theory, these observations uncovered some slight discrepancies. Albert Einstein proposed his theories of Relativity, which explained the newly observed facts and made more predictions. Those predictions have now been tested and found to be correct within the accuracy of the instruments being used. As far as anyone can see, Einstein's theory is ``the Truth''.
So how can the Truth change? Well the answer is that it hasn't. The Universe is still the same as it ever was. When a theory is said to be ``true'' it means that it agrees with all known experimental evidence. But even the best of theories have, time and again, been shown to be incomplete: though they might explain a lot of phenomena using a few basic principles, and even predict many new and exciting results, eventually new experiments (or more precise ones) show a discrepancy between the workings of nature and the predictions of the theory. In the strict sense this means that the theory was not ``true'' after all; but the fact remains that it is a very good approximation to the truth, at lest where a certain type of phenomena is concerned.
When an accepted theory cannot explain some new data (which has been confirmed), the researchers working in that field strive to construct a new theory. This task gets increasingly more difficult as our knowledge increases, for the new theory should not only explain the new data, but also all the old one: a new theory has, as its first duty, to devour and assimilate its predecessors.
One other note about truth: science does not make moral judgments. Anyone who tries to draw moral lessons from the laws of nature is on very dangerous ground. Evolution in particular seems to suffer from this. At one time or another it seems to have been used to justify Nazism, Communism, and every other -ism in between. These justifications are all completely bogus. Similarly, anyone who says ``evolution theory is evil because it is used to support Communism'' (or any other -ism) has also strayed from the path of Logic (and will not live live long nor prosper).

When a new set of facts requires the creation of a new theory the process is far from the orderly picture often presented in books. Many hypothses are proposed, studied, rejected. Researchers discuss their validity (sometimes quite heatedly) proposing experiments which will determine the validity of one or the other, exposing flaws in their least favorite ones, etc. Yet, even when the unfit hypotheses are discarded, several options may remain, in some cases making the exact same predictions, but having very different underlying assumptions. In order to choose among these possible theories a very useful tool is what is called Ockham's razor.
Ockham's Razor is the principle proposed by William of Ockham in the fourteenth century: ``Pluralitas non est ponenda sine neccesitate'', which translates as ``entities should not be multiplied unnecessarily''.
In many cases this is interpreted as ``keep it simple'', but in reality the Razor has a more subtle and interesting meaning. Suppose that you have two competing theories which describe the same system, if these theories have different predictions than it is a relatively simple matter to find which one is better: one does experiments with the required sensitivity and determines which one give the most accurate predictions. For example, in Copernicus' theory of the solar system the planets move in circles around the sun, in Kepler's theory they move in ellipses. By measuring carefully the path of the planets it was determined that they move on ellipses, and Copernicus' theory was then replaced by Kepler's.
But there are are theories which have the very same predictions and it is here that the Razor is useful. Consider form example the following two theories aimed at describing the motions of the planets around the sun

• The planets move around the sun in ellipses because there is a force between any of them and the sun which decreases as the square of the distance.
  
• The planets move around the sun in ellipses because there is a force between any of them and the sun which decreases as the square of the distance. This force is generated by the will of some powerful aliens.
  

Jose Wudka
9/24/1998
http://phyun5.ucr.edu/~wudka/Physics7/Notes_www/