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| Karl Popper |
As I have said in other posts, quoting Popper, a scientific theory can never be considered utterly confirmed. In other words, we can never be completely sure that it is true. But some people try to rely on this (and on Kant’s philosophy) to reach the conclusion that we cannot know anything about reality, that scientific knowledge is relative, and that science is no different from other human activities, such as arts or fashion, whose productions cannot be said to be true or false.
Against this position, in an article published in 1990 in defense of realism, Martin Gardner wrote the following paragraph, which in my opinion hits the center of the bull’s eye:
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| Martin Gardner |
Although all scientific statements are
corrigible, it does not follow that they can’t be placed in a continuum of
probabilities that range from virtual certainty to almost certain falsehood. No
one doubts, for instance, that the earth is shaped like a ball, goes around the
sun, rotates, has a magnetic field, and has a moon that circles it. It is
almost certain that the universe is billions of years old and that life on
earth evolved over millions of years from simple to more complex forms. The big
bang origin of the universe is not quite so certain. The inflationary model of
the universe is still less certain. And so on. Science at present lacks any
technique for applying precise probability values, or what Rudolf Carnap liked
to call “degrees of confirmation,” to its statements. That doesn’t mean, however,
that a scientist is not justified in saying that evolution has been strongly
confirmed or that a flat earth has been strongly disconfirmed.
In his 1956 popularization
book The Modern Universe, the
British astronomer Raymond A. Lyttleton wrote that every scientific theory can
be assigned a probability value, a number between zero and one, where zero
corresponds to impossible ideas, and one to fully confirmed theories. However,
he added this warning:
Never let your estimate of the probability
of a theory reach the values zero or one.
In other words, no
theory should be considered utterly proven (probability equal to one) or utterly
excluded (probability equal to zero). Of course, in our estimation of their probability
we can approach zero and one as much as we want. This is exactly the same thing
that Gardner says at the end of the quoted paragraph. However, I would add the
following consideration:
If we have no reason to assume that a theory is true or false, its
probability should be close to 0.5.
As I explained in another post,
a scientific theory must be adjusted to what we already know, but
it cannot be considered validated until it makes one or more surprising accurate predictions. On the other
hand, although they can still be used in certain fields of application, I won’t
consider here those scientific theories refuted by some surprising wrong prediction, such as Newton’s
Mechanics, which was refuted by the wrong prediction of the existence of planet
Vulcan. With this in mind, I would propose this probability scale for
scientific theories:
- Almost certain theories: their probability will be higher than 0.9, without
reaching 1.0. Among these theories I will cite the statements in the first
half of Gardner’s paragraph; and the assertion that the species of living
beings evolve and the history of life was (and is) a process whose development
is reflected in the
tree of life.
- Theories validated and not refuted, with a probability between 0.8 and 0.9. Among
them I will cite the Big Bang theory, General Relativity, Quantum Mechanics,
and the standard model of particle physics.
- Theories not validated, but adjusted to
what we know, with a probability
between 0.6 and 0.8. Among them, with varying probabilities, I will cite
the theory of cosmic inflation, the standard cosmological model with its
appendages (the existence of dark matter and dark energy), and the anthropogenic
origin of climate change.
- Theories about which we have no
information, for or against, with a probability between 0.4 and 0.6. I will cite the existence of
extraterrestrial intelligence, the possibility of building strong
artificial intelligence, or the various theories of the multiverse. Some
of these theories could perhaps be confirmed, others are probably forever
out of our reach.
- Probably wrong theories, with a probability less than 0.4. Among them I
will cite the possibility of time travel, and all the pseudosciences, of
which some are close to a probability of 0.5, and if they exceed it, they
could become scientific. Others (such as the flat Earth, the hollow Earth,
and Velikovsky’s theory) have a probability very close to zero.
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| Sheldon Glashow |
I end with a quote
from Sheldon Glashow, Nobel Prize in Physics, which was published in 1989 in
the New York Times and is quoted in Martin Gardner’s article:
We believe that the world is knowable,
that there are simple rules governing the behavior of matter and the evolution
of the universe. We affirm that there are eternal, objective, extrahistorical,
socially neutral, external and universal truths and that the assemblage of
these truths is what we call physical science. Natural laws can be discovered
that are universal, invariable, inviolate, genderless and verifiable. They may
be found by men or by women or by mixed collaborations… Any intelligent alien
anywhere would have come upon the same logical system as we have, to explain
the structure of protons and the nature of supemovae.
This quote is a declaration of faith in
the real existence of the world and its intelligibility, and against scientific
relativism.
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