Science news “Becoming Human,” 3 part series by NOVA, began last Tuesday night and continues for 2 more weeks on Tuesdays. One hypothesis considered as an explanation of evolution of human mental capacities/brain size: climate change.
“Becoming Human,” 3 part series by NOVA, began last Tuesday night and continues for 2 more weeks on Tuesdays.
One hypothesis considered as an explanation of evolution of human mental capacities/brain size: climate change.
Earlier hypothesis emphasized bidpedalism, but that was before we found fossils of other hominids with relatively small brains.
Prediction? NY Times review: If we go through another period of increasingly hot and dry climate, our descendants might be much smarter … and have heads the size of basketballs
Signs of early Homo sapiens in China?
Fossils over 100,000 years old found in southern China
Taken by Chinese scientists to challenge the hypothesis that the species originated in Africa and spread from there
Critics: Far too little evidence
A fragment of a lower jaw bone and some teeth
Complicating the logic of falsification
‘If H, then I’ is really ‘If [H & (A1… An)], then I’
More from Hempel:
‘I’ in ‘If H, then I’
is itself shorthand for ‘If C, then E’
where ‘C’ symbolizes some condition, and ‘E’ some event or phenomenon.
And ‘if C, then E’
is understood as “if some condition is brought about, then we will observe E .”
If this is correct, then the actual logic of falsification, on Hempel’s model, is
If [H & (A1… & An)], then (if C then E)
Either not H & (A1… & An) or not C
On the left side, H may be incorrect – but it could be correct and one or more of the auxiliary assumptions is the problem (Brahe).
Or (as indicated by the right side), it may be that the conditions weren’t brought about (med students didn’t wash their hands...)
Duhem/Quine thesis: It is bodies of theory (or systems of theories), not individual hypotheses, that entail predictions.
If T (for some body of theory), then (if H, then I)
Not some one or more statements of Tor notH
Pierre Duhem: a bench physicist writing in the 1930s
W.V. Quine: philosopher of science writing from the mid twentieth century to its end
If T, then (if H, then I)
Not some part of T or not H
Given what actually follows logically and empirically from ‘not I’, one needs to decide that ‘not H’ follows, rather than some part or whole of T; i.e., one has to choose to hold T firm and H infirm.
Are the choices arbitrary? Made on the basis of self-interest?
What are the consequences for objectivity?
Duhem’s examples (you do not need to memorize the details… just what he uses them to illustrate):
Neumann assumed a hypothesis that, if correct, was taken to predict that in an experiment involving a light beam reflected at a particular degree of angle, there ought to appear alternatively dark and light interference bands
Weiner, who challenged Neumann’s hypothesis, performed a test in which the predicted interference bands did not appear.
Had he, in fact, falsified, Neumann’s hypothesis?
No, according to Duhem, because Weiner had notonly used Neumann’s hypothesis to get the prediction and design the experiment: instead he brought and joined a lot of hypotheses to do both.
So what he actually demonstrated was that either Neumann’s hypothesis is incorrect, or one or more of the assumptions Weiner himself made, was/were incorrect.
In the case concerning whether light would travel faster in water than in air or vice versa as a test of Newton’s hypothesis that light consists of tiny projectiles vs. that light consists of waves moving through a medium:
It was the whole system Newton proposed that was under test, not the hypothesis that light is made up of projectiles
So, the moral is the same:
Nothing, logically or experimentally, stops us from accepting the hypothesis allegedly falsified and shifting the weight of the experimental contradiction to some other hypothesis or part of the larger theory that the experimenter assumes.
Both experiments Duhem cites had been taken as among the most decisive ones in optics; he is challenging this.
The model of Falsificationism as how scientists do or should reason, reflects “unfamiliarity with physics’ actual functioning”
Such people assume that “each one of the hypotheses employed in physics can be taken in isolation, checked by experiment, and then when many varied tests have established its validity, given a definitive place in the system of physics.”
“In reality, this is not the case. Physics is not a machine which lets itself be taken apart… physical science is a system that must be taken as a whole… If something goes wrong, if some discomfort is felt it, the physicist will have to ferret out … which “organ” needs to be remedied or modified without the possibility of isolating this organ and examining it apart.”
So-called crucial experiments:
Assume the logic of Reductio ad absurdum, an argument form that works in mathematics
But not, Duhem argues, in empirical science
Either P or Q 1. Either H1 or H2
Not P 2. Not H2
Recall Paley’s reasoning…
Reductio ad absurdum only works if one can list all the hypotheses that can account for some phenomena and then by experimental contradiction, eliminate all except one.
If you could do this, the resulting hypothesis would look like a certainty.
But you cannot. One can never be sure one has identified every possible hypothesis that might account for the phenomena.
An example: In the late 1980’s, researchers developed a drug predicted to be capable of thwarting the replication of the HIV virus implicated in AIDS.
H: “All things being equal … the drug will be effective”
In experiments, one group was given the drug and the other a placebo.
The initial trials (running over 2 years) confirmed the drug’s predicted success. But in the 3rd year, it stopped being effective.
Initial results (showing effectiveness) were taken to be mistaken
And the hypothesis was rejected by some
Then current theories suggested that it didn’t matter if the drug was stored and delivered in glass or plastic containers.
After the initial 2 year period, the drug was stored and delivered in plastic rather than glass containers.
Thus the conclusion that not H presumed the truth of this background knowledge – and it was wrong.
Storing the drug in plastic containers did affect it.
Critics of the Quine/Duhem (or Duhem/Quine) thesis argued that if correct, theories could never be refuted by evidence – but only by decisions made by scientists in the relevant field
This, they argued, leads to relativism and/or degrees of subjectivity that challenge scientific objectivity
Duhem and Quine: not so. It just means that science isn’t a machine.
Duhem: the physicist is more like a doctor making a diagnosis with available information, than a watchmaker who fixes a watch.
Later in the full chapter, Duhem argues that there are values (epistemic or cognitive) that guide the scientist’s choice
A list many cite includes:
Empirical adequacy and/or success
First published in 1962, Kuhn’s SSR was named one of the 50th most important books of the 21st century by many lists (including The New York Times)
Kuhn: a bench physicist who became interested in the history of science (actual history) and argued that it did not match the reconstructions philosophers and historians of science, and scientists themselves, offered
While historians and philosophers of science (as well as scientists) emphasized revolutions in science as models of how science works, Kuhn emphasized what he called “Normal Science” – the kind of science most scientists engage in all of their lives that does not look what philosophers or historians of science, or even working scientists, hold up as “scientific method”
From “pre-science” to “normal science” to “crisis” to “revolution
Pre-science Lots of “schools” arguing over fundamentals
No agreement over what is the most important phenomena to be explained
No agreement on a basic theory or how the most basic phenomena are to be explained
The emergence of a “paradigm”
The beginning of a “normal science” (as opposed to a pre- science”) tradition
The emergence of a “paradigm” which
Solves a lot of puzzles (or promises to solve
puzzles) that need to be solved
Is open-ended enough to leave lots of work to do…
Is like a “judicial decision” in that it invites further articulation
Brown v. Board of Education
“Separate but equal” is internally inconsistent
Originally about racially-segregated schools
But articulated to apply to other apparently “separate but equal” laws and practices
And other laws that cite “separate but equal” standards”
Once a science community accepts a paradigm (Copernican astronomy, Newtonian physics, Darwinian natural selection, Relativity, Quantum physics…) the paradigm itself is unquestioned and work begins on
Puzzle solving: the paradigm indicates what problems are important (nature of the orbits of the planets, how natural selection works….) and this results in a
Normal science (everyday, most of the time science) involves puzzle solving
Assume that any puzzle suggested by a paradigm is intrinsically important and
Has a solution that the paradigm, itself, supplies
Can be solved with sufficient ingenuity and/or creativity
Any failure to solve the puzzle is due to the researcher (her or his understanding of the puzzle, appropriate tests… but not the paradigm.
Normal science (everyday, most of the time, science) is a closed-minded enterprise
Is not looking for anomalies
Seeks only confirming evidence of the Paradigm and any subsidiary hypotheses it suggests
Is an attempt to “fit nature into the boxes the Paradigm supplies”
Will only pay attention to anomalies (counter-examples) when
It is no longer reasonable to blame the individual researcher/test or
To wait for scientists of the next generation to find a solution or
there is a “competing paradigm”
Kuhn’s “diagnosis” of how Popper “went wrong”
Not because (as Duhem article would suggest) that Popper didn’t know the history of science
But because he focused his attention on episodes of revolution
These, according to Kuhn, are rare and not “typical” of how science proceeds