(I will be traveling for a few weeks and rather than put this blog on hiatus, thought that I would continue with my weekday posting schedule by reposting some of the very early items, for those who might have missed them the first time around.)

A commenter to a previous posting raised an interesting perspective that requires a fresh posting, because it reflects a commonly held view about how the validity of scientific theories get established.

The commenter says:

A scientist cannot be certain about a theory until that theory has truly been tested, and thus far, I am unaware of our having observed the evolution of one species from another species. Perhaps, in time, we will observe this, at which point the theory will have been verified. But until then, Evolution is merely a theory and a model.

While we may have the opportunity to test Evolution as time passes, it is very highly doubtful that we will ever be able to test any of the various theories for the origins of the Universe.

I would like to address just two points: What does it mean to “test” a theory? And can scientists ever “verify” a theory and “be certain” about it?

Verificationism as a concept to validate scientific theories has been tried and found to be wanting. The problem is that any non-trivial theory generates an infinite number of predictions. All the predictions cannot be exhaustively verified. Only a sample of the possible predictions can be tested and there is no universal yardstick that can be used to measure when a theory has been verified. It is a matter of consensus judgment on the part of scientists as to when a theory becomes an accepted one, and this is done on a case-by-case basis by the practitioners in that field or sub-field.

This means, however, that people who are opposed to a theory can always point to at least one particular result that has not been directly observed and claim that the theory has not been ‘verified’ or ‘proven.’ This is the strategy adopted by ID supporters to attack evolutionary theory. But using this kind of reasoning will result in every single theory in science being denied scientific status.

Theories do get tested. Testing a theory has been a cornerstone of science practice ever since Galileo but it means different things depending on whether you are talking about an experimental science like chemistry and condensed matter physics, or a historical science like cosmology, evolution, geology, and astronomy.

Any scientific theory is always more than an explanation of prior events. It also must necessarily predict new observations and it is these predictions that are used to test theories. In the case of experimental sciences, laboratory experiments can be performed under controlled conditions in order to generate new data that can be compared with predictions or used to infer new theories.

In the case of historical sciences, however, observations are used to unearth data that are pre-existing but as yet unknown. Hence the ‘predictions’ may be more appropriately called ‘retrodictions’, in that they predict that you will find things that already exist. For example, in cosmology the retrodictions were the existence of a cosmic microwave background radiation of a certain temperature, the relative abundances of light nuclei, and so forth. The discovery of the planet Neptune was considered a successful ‘prediction’ of Newtonian theory, although Neptune had presumably always been there.

The testing of a historical science is analogous is to that of the investigation of a crime where the detective says things like “If the criminal went through the woods, then we should be able to see footprints.” This kind of evidence is also historical but is as powerful as those of futuristic predictions, so historical sciences are not necessarily at a lower level of credibility than experimental sciences.

Theories in cosmology, astronomy, geology, and evolution are all tested in this way. As Ernst Mayr (who died a few days ago at the age of 100) said in What Evolution Is (2001): “Evolution as a whole, and the explanation of particular evolutionary events, must be inferred from observations. Such inferences must be tested again and again against new observations, and the original inference is either falsified or considerably strengthened when confirmed by all of these tests. However, most inferences made by evolutionists have by now been tested successfully so often that they are accepted as certainties.” (emphasis added).

In saying that most inferences are ‘accepted as certainties’, Mayr is exaggerating a little. Ever since the turn of the 20th century, it has been accepted that scientific knowledge is fallible and that absolute certainty cannot be achieved. But scientists do achieve a remarkable consensus on deciding at any given time what theoretical frameworks they have confidence in and will be used to guide future research. Such frameworks have been given the name ‘paradigms’ by Thomas Kuhn in The Structure of Scientific Revolutions (1970).

When scientists say they ‘believe’ in evolution (or the Big Bang), the word is being used in quite a different way from that used in religion. It is used as shorthand to say that they have confidence that the underlying mechanism of the theory has been well tested by seeing where its predictions lead. It is definitely not “merely a theory and a model” if by the word ‘merely’ the commenter implies a theory that is unsupported or untested.

So yes, evolution, like all the other major scientific paradigms, both historical and experimental, has been well tested.

(I will be traveling for the next few weeks and rather than put this blog on hiatus, thought that I would continue with my weekday posting schedule by reposting some of the very early items, for those who might have missed them the first time around.)

Mike Godwin coined a law (now known as Godwin’s Law) that states: “As an online discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches one.”

This makes sense. As the discussion drags on, people start running out of fresh or relevant arguments, begin repeating themselves, lose their tempers, reach for something new to say, and Hitler/Nazi comparisons inevitably follow.

But Godwin’s rule has been extended beyond its original intent and is now used as a decision rule to indicate that a discussion has ceased to be meaningful and should be terminated. In other words, as soon as the Hitler/Nazi comparison is brought into any discussion where it is not relevant, Godwin’s rule can be invoked to say that the discussion is over and the person who introduced the Hitler/Nazi motif has lost the argument.
[Read more…]

(I will be traveling for the next few weeks and rather than put this blog on hiatus, thought that I would continue with my weekday posting schedule by reposting some of the very early items, for those who might have missed them the first time around.)

In an <a href=http://blog.case.edu/mxs24/2005/02/09/evolution_ii_science_is_not_a_smorgasbordearlier posting, the question was posed as to whether it was intellectually consistent to reject the findings of an entire modern scientific discipline (like biology) or of a major theoretical structure (like the theory of evolution) while accepting all the other theories of science.

The short answer is no. Why this is so can be seen by examining closely the most minimal of creationist theories, the one that goes under the label of ‘intelligent design’ or ID.

ID supporters take great pains to claim that theirs is a scientific theory that has nothing to do with religion or God, and hence belongs in the school science curriculum. (This particular question whether ID can be considered a part of science or of religion will be revisited in a later posting. This is becoming a longer series than I anticipated…)

ID advocates say that there are five specific biochemical systems and processes (bacterial flagella and cilia, blood clotting, protein transport within a cell, the immune system, and metabolic pathways) whose existence and/or workings cannot be explained by evolutionary theory and that hence one has to postulate that such phenomena are evidence of design and of the existence of a designer.

The substance of their arguments is: “You can claim all the other results for evolutionary theory. What would be the harm in allowing these five small systems to have an alternative explanation?”

Leaving aside the many other arguments that can be raised against this position (including those from biologists that these five systems are hardly intractable problems for evolutionary theory), I want to focus on just one feature of the argument. Is it possible to accept that just these five processes were created by a ‘designer,’ while retaining a belief in all the other theories of science?

No you cannot. If some undetectable agent had intervened to create the cilia (say), then in that single act at a microscopic level, you have violated fundamental laws of physics such as the law of conservation of energy, the law of conservation of momentum, and (possibly) the law of conservation of angular momentum. These laws are the bedrock of science and to abandon them is to abandon some of the most fundamental elements of modern science.

So rejecting a seemingly small element of evolutionary theory triggers a catastrophe in a seemingly far-removed area of science, a kind of chaotic ‘butterfly effect’ for scientific theories.

Scientific theories are so interconnected that some philosophers of science have taken this to the extreme (as philosophers are wont to do) and argued that we can only think of one big scientific theory that encompasses everything. It is this entire system (and not any single part of it) that should be compared with nature.

Pierre Duhem in his The Aim and Structure of Physical Theory (1906) articulated this position when he declared that: “The only experimental check on a physical theory which is not illogical consists in comparing the entire system of the physical theory with the whole group of experimental laws, and in judging whether the latter is represented by the former in a satisfactory manner.” (emphasis in original)

Of course, in practical terms, we don’t do that. Each scientific subfield proceeds along its own path. And we know that there have been revolutions in one area of science that have left other areas seemingly undisturbed. But this interconnectedness is a reality and explains why scientific theories are so resistant to change. Scientists realize that changing one portion requires, at the very least, making some accommodations in theories that are connected to it, and it is this process of adjustments that takes time and effort and prevents trivial events from triggering changes.

This is why it usually requires a major crisis in an existing theory for scientists to even consider replacing it with a new one. The five cases raised by ID advocates do not come close to creating that kind of crisis. They are like flies in the path of a lumbering evolutionary theory elephant, minor irritants that can be ignored or swatted away easily.

In my previous post, I suggested that in science, the burden of proof lies with the proponent for the existence of some thing. The default assumption is non-existence. So if you propose the existence of something like electromagnetic radiation or neutrinos or N-rays, then you have to provide some positive evidence that it exists of a kind that others can try to replicate.

But not all assertions, even in science, need meet that positive evidence standard. Sometimes negative evidence, what you don’t see, is important too. Negative evidence is best illustrated by the famous Sherlock Holmes story Silver Blaze, in which the following encounter occurs:

Gregory [Scotland Yard detective]: “Is there any other point to which you would wish to draw my attention?”
Holmes: “To the curious incident of the dog in the night-time.”
Gregory: “The dog did nothing in the night-time.”
Holmes: “That was the curious incident.”

There are times when the absence of evidence can be suggestive. This is true with the postulation of universal laws. The substance of such laws (such as that the total energy is conserved) is that they hold in every single instance. But we cannot possibly examine every possibility. The reason that we believe these types of laws to hold is because of negative evidence, what we do not see. If someone postulates the existence of a universal law, the absence of evidence that contradicts it is taken as evidence in support of the law. There is a rule of thumb that scientists use that if something can happen, it will happen. So if we do not see something happening, that suggests that there is a law that prevents it. This is how laws such as baryon and lepton number conservation originated.

Making inferences from absence is different from proving a negative about the existence of something, be it N-rays or god. You can never prove that an entity doesn’t exist. So at least at the beginning, it is incumbent on the person who argues for the existence of something to provide at least some evidence in support of it. The case for the existence of entities (like neutrinos or X-rays or god) requires positive evidence. Once that has been done beyond some standard of reasonable doubt, then the burden can shift to those who argue for non-existence, to show why this evidence is not credible.

This rule about evidence was not followed in the run up to the attack on Iraq. The Bush administration simply asserted that Iraq had weapons of mass destruction without providing credible evidence of it. They then (aided by a compliant media) managed to frame the debate so that the burden of proof shifted to those who did not believe the weapons existed. Even after the invasion, when the weapons did not turn up, Donald Rumsfeld famously said “There’s another way to phrase that and that is that the absence of evidence is not the evidence of absence. It is basically saying the same thing in a different way. Simply because you do not have evidence that something does exist does not mean that you have evidence that it doesn’t exist.” But he was wrong. When you are asserting the existence of an entity, if you have not provided any evidence that they do exist, then the absence of evidence is evidence of absence.

It is analogous to criminal trials. People are presumed innocent until proven guilty, and the onus is on the prosecution to first provide some positive evidence. Once that is done, the accused usually has to counter it in some way to avoid the risk that the jury will find the evidence sufficiently plausible to find the accused guilty.

So the question boils down to whether believers in a god have provided prima facie evidence in support of their thesis, sufficient to shift the burden to those who do not believe in god to show why this evidence is not convincing. Personal testimony by itself is usually not sufficient in courts, unless it is corroborated by physical evidence or direct personal observation by other credible sources who have observed the same phenomenon.

One of the common forms of evidence that is suggested is that since many, many people believe in the existence of god, that should count as evidence. My feeling is that that is not sufficient. After all, there have been universal beliefs that have subsequently been shown to be wrong, such as that the Earth was located at the center of the universe.

Has the evidence for god met the standard that we would accept in science or in a court of law? I personally just don’t see that it has but that is a judgment that each person must make. Of course, people can choose to not require that the evidence for god meet the same standard as for science or law, and if that is the case, then that pretty much ends the discussion. But at least we can all agree as to why we disagree.

As you can imagine, the world of science has been abuzz with the news yesterday of the release of a paper in the prestigious science journal Nature heralding the discovery of a 375-million year old transitional fossil between fish and land animal, which has been named Tiktaalik. The fossil seems to provide evidence of a key evolutionary idea that land animals evolved from fish.
[Read more…]

In response to an earlier post about the surprisingly high percentage of Americans who believe in the rapture and other things, there was some skepticism about how reliable the numbers and how they broke down depending on age, etc.

I have not been able to find further documentation to support the figure of 44% who are either certain or think it very likely that the rapture will occur in their lifetimes. But there are other interesting breakdowns.

For example, in this Harris poll from July 6, 2005, 47% do not believe that apes and humans have common ancestry, which is a key tenet of evolution, while 46% believe it. A similar number 45% do not believe plants and animals evolved from other species. So we can pretty much conclude that slightly less than half the population reject pretty much all of evolution.

Curiously, only 22% believe that humans evolved from earlier species, while 64% believe that humans were created directly by God. I am not sure how this squares with the above answers. Maybe people are interpreting the phrases “common ancestry” and “directly created” in ways that are different from me.
[Read more…]

I have been meaning to write about this for some time but got sidetracked by all the other topics. It formed the basis of an article by Robert Rosenberg in the December 2005 issue of Physics Today (pages 50-55).

How people respond to such a question can tell you a lot about their relationship to science in general. Some people will think that such an everyday question should have a simple answer that has been known for a long time. Others will answer that that is just the way ice is. Intelligent design and other types of creationists might respond that ice was made slippery for a purpose that we cannot comprehend. Yet others will say “who cares?” and wonder why we should bother with trying to answer such a question at all. But ask a group of scientifically-minded people this question and you will get a lively discussion going about the various possible explanations.
[Read more…]