Re: Proof for atoms?

[Joseph Bellina <jbellina@SAINTMARYS.EDU>]

I think you might discuss two ideas with the student.
1) conservation of mass in chemical changes
2) Avogadroes principle (not number) that equal volumes of gases at the
same temperature and pressure have the same number of particles, and how
it provides such a good understanding for the gas laws.

There are other phenomena that point to non-continuum of matter, but
they are more technical...STM comes to mind.  Oh yes, you might also
talk about the Rutherford scattering experiments.

cheers,

joe

On Wed, 17 Apr 2002,
Savinainen Antti wrote:

> Hello,
>
> 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! Th=
> e doubter
> asked experiments which could provide convincing evidence for the exi=
> stence 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 n=
> ice
> explanations and predictions in thermal physics.
>
> The question is interesting from the point of view of philosophy of s=
> cience.
> Einstein said that it is the theory that determines what can be obser=
> ved (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 ex=
> perimental
> 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 wou=
> ld 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 tea=
> ching as
> well. It forces students (and me) to think critically. Late Arnod Aro=
> ns has
> written about this issue in his marvelous "Teaching Introductory Phys=
> ics" book.
>
> Regards,
>
> Antti
>
> Antti Savinainen
> Physics Teacher
> Kuopion Lyseo High School/IB
> Finland
>
> Homepage: <http://personal.inet.fi/tiede/physics/>

Joseph J. Bellina, Jr.               219-284-4662
Associate Professor of Physics
Saint Mary's College
Notre Dame, IN 46556