Hi,
The whole question of whether we should base our understanding of the universe on rational observation or authoritarian superstition is something that I don't care to get into at the moment. So, let me instead address the smaller but still important question of just what a damn THEORY is when the word is used by scientists.
First, it is not a wild-assed guess, like when Linda says, "I've got a theory why Jane dumped Dick and is seeing Paul." This common usage is the interpretation that the anti-science community wants you to believe and apply. Since the spewing of any random neural firings can be called a 'theory' in this interpretation, it cheapens the whole concept of 'theory' and allows the fanatical and ignorant to claim the first round before the bell even rings.
Second, it is not enough even to be the well considered opinion of an expert in a field. While this is a valid usage of the word, unlike the bastardization above, it can cover things other than scientific. For instance, we can have musical theories, theories of artistic perspective (the projection, not the attitude -- artists have enough attitude without a theory to support them ;) ), theories of combat, and so on forever. But none capture what a scientist means when he uses the word 'theory'.
The first thing one needs to know is that the word 'theory' as used by a scientist is an acknowledgment that "the map is not the terrain". Until around the mid to late nineteenth century, scientific principles were often called laws. The "laws" where thought to apply exactly. They could be solved exactly for simple systems (say two bodies interacting gravitationally) but the solution had to be approximated for more complex systems (a flask full of gas). All nature was assumed to be described by a small number of exact, knowable interactions and the apparent complexity was just due to the great number of these interactions. But as it slowly became clear that in nature there was complexity in quality as well as quantity, the quiet arrogance of the early scientists was replaced by a more tentative approach, and the pronouncements became known as 'equations', or 'principles', and so on. I leave out 'theorem' because that is *not* a scientific concept, it is a mathematical one. It might be that under a set of axioms a theorem is true but that truth has no bearing on the theorem's applicability to the external (sorry, Kant) universe. But, to return to the main topic, the word 'theory' is now used as an acknowledgment of the fact that the statement so described may have to be modified or abandoned as our knowledge increases. That the only map that is perfectly accurate in describing nature is nature herself. Everything else is an abstraction and a simplification.
That tells us why 'theory' but that still does not define it. To a scientist, ideally a theory must be complete, compact, falsifiable, and predictive. 'Complete' simply means that the theory must describe everything about its subject. If there are any bits left sticking out, then the theory needs to be expanded somehow, even if it is in an ad hoc fashion (which, of course, has a negative impact on 'compact' -- a laundry list is not a theory). To some extent, the theory of evolution is in the state of expansion and development. Just how to extend and modify the theory as new information comes in is a matter that generates much argument among the researchers in a field. But note that the arguments are about details, and typically newly discovered or observed details, not about the underlying structure of the theory.
A 'compact' theory is one that contains no extraneous material. Of course, a theory of falling bodies that includes a recipe for poached eggs is clearly laughable to all ;) But further, to be 'compact' means to assume the least; to have the fewest number of 'fundamental' postulates, each as simple as it can be made; to be intellectually simple. And, of course, arguments go on constantly as to which formulation of a theory is preferable, since ultimately, if the formulations are isomorphic, it is a question of aesthetics. But, again, note that the people in these arguments are not questioning the underlying validity of the theory, but simply questioning the best way of expressing it.
It is commonly heard that a scientific theory should be 'testable'. To say that a theory should be 'falsifiable' is a more precise statement. Every experiment, every observation, every field discovery is a test of a theory. The result might be further confirmation, or an indication that the theory is incomplete, or that it is incorrect. Of the three, the first is the most satisfying to the technician and engineer and the least to the scientist -- just one of the ways in which not all 'technical' people are equal ;) The other two indicate that a modification of the theory is necessary, perhaps even an overthrow. The last case is extremely rare since modern theories have typically been well tested. Any new theory will have to reduce to (something isomorphic to) the old theory under the conditions the old theory was sufficient to explain. Again, both the necessity for change, and the type and extent of change necessary are matters of furious debate by the practitioners in a field. As Max Planck said, "A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it."
Many emerging theories start as observational summaries and classification schema. But as a theory develops, it should develop some 'predictive' powers. The predictions the theory makes then become both part of the theory and part of the means to test the theory. Lack of predictive powers in a theory is often nothing more than an indication of an immature field. However, there is some question if such a field can yet call itself a science. But then, as with all language, the definition of 'science' itself is somewhat in flux.
Now, not all theories are equally developed. Some had more of a head start; some treat of simpler subjects. All theories are 'works in progress' (a standing joke in physics is that progress is replacing a wrong theory with one more subtly wrong).
Now, with this better understanding (I hope) of just why evolutionary theory isn't just something a couple of stoned valley gals came up with one afternoon, perhaps the rest of the discussion can remain sensible. Or perhaps not. And if someone can tell me where the 'intelligence' for Intelligent Design originated other than from some form of god, then I'll allow the possibility it isn't superstition and ignorance trying, again, to get in the window after it was tossed out the door. And 'aliens' doesn't cut it unless they are eternal.
"E pur si move." -- G.G.
--Pete
The whole question of whether we should base our understanding of the universe on rational observation or authoritarian superstition is something that I don't care to get into at the moment. So, let me instead address the smaller but still important question of just what a damn THEORY is when the word is used by scientists.
First, it is not a wild-assed guess, like when Linda says, "I've got a theory why Jane dumped Dick and is seeing Paul." This common usage is the interpretation that the anti-science community wants you to believe and apply. Since the spewing of any random neural firings can be called a 'theory' in this interpretation, it cheapens the whole concept of 'theory' and allows the fanatical and ignorant to claim the first round before the bell even rings.
Second, it is not enough even to be the well considered opinion of an expert in a field. While this is a valid usage of the word, unlike the bastardization above, it can cover things other than scientific. For instance, we can have musical theories, theories of artistic perspective (the projection, not the attitude -- artists have enough attitude without a theory to support them ;) ), theories of combat, and so on forever. But none capture what a scientist means when he uses the word 'theory'.
The first thing one needs to know is that the word 'theory' as used by a scientist is an acknowledgment that "the map is not the terrain". Until around the mid to late nineteenth century, scientific principles were often called laws. The "laws" where thought to apply exactly. They could be solved exactly for simple systems (say two bodies interacting gravitationally) but the solution had to be approximated for more complex systems (a flask full of gas). All nature was assumed to be described by a small number of exact, knowable interactions and the apparent complexity was just due to the great number of these interactions. But as it slowly became clear that in nature there was complexity in quality as well as quantity, the quiet arrogance of the early scientists was replaced by a more tentative approach, and the pronouncements became known as 'equations', or 'principles', and so on. I leave out 'theorem' because that is *not* a scientific concept, it is a mathematical one. It might be that under a set of axioms a theorem is true but that truth has no bearing on the theorem's applicability to the external (sorry, Kant) universe. But, to return to the main topic, the word 'theory' is now used as an acknowledgment of the fact that the statement so described may have to be modified or abandoned as our knowledge increases. That the only map that is perfectly accurate in describing nature is nature herself. Everything else is an abstraction and a simplification.
That tells us why 'theory' but that still does not define it. To a scientist, ideally a theory must be complete, compact, falsifiable, and predictive. 'Complete' simply means that the theory must describe everything about its subject. If there are any bits left sticking out, then the theory needs to be expanded somehow, even if it is in an ad hoc fashion (which, of course, has a negative impact on 'compact' -- a laundry list is not a theory). To some extent, the theory of evolution is in the state of expansion and development. Just how to extend and modify the theory as new information comes in is a matter that generates much argument among the researchers in a field. But note that the arguments are about details, and typically newly discovered or observed details, not about the underlying structure of the theory.
A 'compact' theory is one that contains no extraneous material. Of course, a theory of falling bodies that includes a recipe for poached eggs is clearly laughable to all ;) But further, to be 'compact' means to assume the least; to have the fewest number of 'fundamental' postulates, each as simple as it can be made; to be intellectually simple. And, of course, arguments go on constantly as to which formulation of a theory is preferable, since ultimately, if the formulations are isomorphic, it is a question of aesthetics. But, again, note that the people in these arguments are not questioning the underlying validity of the theory, but simply questioning the best way of expressing it.
It is commonly heard that a scientific theory should be 'testable'. To say that a theory should be 'falsifiable' is a more precise statement. Every experiment, every observation, every field discovery is a test of a theory. The result might be further confirmation, or an indication that the theory is incomplete, or that it is incorrect. Of the three, the first is the most satisfying to the technician and engineer and the least to the scientist -- just one of the ways in which not all 'technical' people are equal ;) The other two indicate that a modification of the theory is necessary, perhaps even an overthrow. The last case is extremely rare since modern theories have typically been well tested. Any new theory will have to reduce to (something isomorphic to) the old theory under the conditions the old theory was sufficient to explain. Again, both the necessity for change, and the type and extent of change necessary are matters of furious debate by the practitioners in a field. As Max Planck said, "A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it."
Many emerging theories start as observational summaries and classification schema. But as a theory develops, it should develop some 'predictive' powers. The predictions the theory makes then become both part of the theory and part of the means to test the theory. Lack of predictive powers in a theory is often nothing more than an indication of an immature field. However, there is some question if such a field can yet call itself a science. But then, as with all language, the definition of 'science' itself is somewhat in flux.
Now, not all theories are equally developed. Some had more of a head start; some treat of simpler subjects. All theories are 'works in progress' (a standing joke in physics is that progress is replacing a wrong theory with one more subtly wrong).
Now, with this better understanding (I hope) of just why evolutionary theory isn't just something a couple of stoned valley gals came up with one afternoon, perhaps the rest of the discussion can remain sensible. Or perhaps not. And if someone can tell me where the 'intelligence' for Intelligent Design originated other than from some form of god, then I'll allow the possibility it isn't superstition and ignorance trying, again, to get in the window after it was tossed out the door. And 'aliens' doesn't cut it unless they are eternal.
"E pur si move." -- G.G.
--Pete
How big was the aquarium in Noah's ark?