I had an interesting discussion about atoms with a doubter who asked if there
is any proof for existence of atoms. The argument was that of course physicists
find atoms because the idea of atoms is their very starting point! The doubter
asked experiments which could provide convincing evidence for the existence of
atoms without having initially decided that idea of atoms is used to analyze
the data.
What would you answer?
In a way I think that the doubter would have been quite right in the 19th
century. At the time atoms were used as an hypothesis which allowed nice
explanations and predictions in thermal physics.
The question is interesting from the point of view of philosophy of science.
Einstein said that it is the theory that determines what can be observed (I
don't have an exact citation here; I read it from an issue of Physics Today a
year or two ago). I also recall that Hawking said that there is no experimental
data on cosmology which would be independent on theory (again this is not exact
citation). OTOH it is not easy at all to construct theories which would provide
correct predictions even in previously unkonown phenomena. It is very
convincing if a theory is capable of doing that.
I think that these "how do you know" questions could be useful in teaching as
well. It forces students (and me) to think critically. Late Arnod Arons has
written about this issue in his marvelous "Teaching Introductory Physics" book.
Regards,
Antti
Antti Savinainen
Physics Teacher
Kuopion Lyseo High School/IB
Finland