[Phys-L] so-called "modern" physics

[John Denker <jsd@av8n.com>]

On 02/21/2014 11:12 AM, Larry Smith wrote:

> P.S. Isn't it interesting that we still call stuff that is over 100 years old "modern"?

Yeah, that's weird.  On the other hand, art from the same 
period is still called "modern art".  Maybe we are moving
toward a post-modern definition of "modern".

=====================

That started me thinking of various ways of improving the 
terminology, which was a colossal waste of time, until I 
remembered the rule that should have been the starting point:  
IMHO the rule should be: ideas first, terminology later.

So I made a list of ideas, and them played with it to come 
up with some possible names.  How about this:  4PTH Physics, 
pronounced FourPTH.  That stands for 4D, probabilistic, tiny,
huge physics.  The next level of detail is given in the 
following chart:

4D, probabilistic, tiny, huge
 |         |        |     |
 |         |        |     |
 |         |        |     |
 |         |        |     \-- 6+ orders of magnitude bigger stuff
 |         |        |
 |         |        \-- 5+ orders of magnitude smaller stuff
 |         |            (atoms, nuclei, X-rays, radioactivity, etc.)
 |         |
 |         \-- statistical mechanics, then QM
 |
 \-- spacetime, then general relativity


On alternate Tuesdays I'm tempted to call this Progressive
Era physics, because in US history the Progressive Era is 
considered to have run from the late 1890s to the early 1920s, 
which more-or-less corresponds to the emergence of 4PTH physics.
This makes an amusing mnemonic but nothing more, because 4PTH 
physics had very little influence on politics, and vice versa.

Taking yet another step toward more detail:  The realm of physics
grew by /at least/ 12 orders of magnitude during this era.  The
estimated size of the Milky Way went up by an order of magnitude,
and then the size of the universe increased from galaxy-size to
5+ orders of magnitude more than that.

At the other end, the atomic hypothesis was not taken seriously
until this era.  Folks "should" have known the size of atoms
since 1865 (Loschmidt) but mostly they didn't know and/or
didn't care.  Almost nobody /did anything/ that depended on
knowing the size of atoms until around the turn of the century.
Then, not long after atoms showed up, nuclei showed up, five 
orders of magnitude smaller.

Physicists seemed to think that all of this stuff belonged to 
physics, and was subject to the laws of physics ... on the
scale of 10^-15 meters and 10^25 meters and everything in 
between.

Statistical physics (including applications to transport theory)
goes back a long ways, but other than Loschmidt most people 
didn't do very much with it.  Then Boltzmann came along.  It's 
not every day that somebody redefines entropy.  This includes
the idea of microstates, which IMHO is at least as fundamental
and at least as revolutionary as the idea of atoms.  One of
the guys who noticed was Planck, who used statistical mechanics 
as a springboard into quantum mechanics, which involves
probability in yet another, even-more-intimate way.

It's also not every day that somebody redefines the most
fundamental notions of "space" and "time" (Minkowski, 1908).
Initially Einstein said he didn't understand what Minkowski 
had done.  However, before long he figured it out, and used 
it as the basis of future work, including general relativity
aka gravitation.  This connects to the aforementioned
large-scale cosmology.

=================

IMHO it is a mistake to assume 4PTH physics is arcane 
physics, irrelevant to ordinary life.  I say some of
it is arcane, but a lot of it isn't.

For starters, even today there are some chemistry books
that introduce the subject in terms of 19th-century
macroscopic notions such as "element" and "compound"
... and even today according to the official definition 
the "mole" is the SI base unit for "amount of substance"
whatever that means.  I say the 19th century has been
over for a while now;  wake up and smell the atoms.
The modern concepts of atom and molecule and number
of particles are vastly simpler than the archaic
notions of "element" and "compound" and "amount of
substance".

Similarly, IMHO it is a monumental mistake for teachers
to say that relativity is weird and paradoxical.  IMHO
the point of learning relativity is not to make life
more complicated, but rather to make it more simple.
I see it mostly as a framework for unifying stuff you
already know:  Unifying electricity and magnetism,
unifying space and time, unifying rotations and boosts,
unifying energy and momentum, unifying mass and momentum 
and kinetic energy, et cetera.........

Last but not least, if you're going to talk about
entropy at all, the modern (post-1898) statistical
definition Σ p_i log(1 / p_i) is vastly simpler and
in every way better than the archaic definition.
Yeah, it requires knowing some probability, but 
that is part of the Common Core standards starting 
in 6th grade, so I reckon if students get to high 
school (or college!) and don't know how probability
works, it's high time they learned.

Maybe I'm overlooking something, but it seems rare for 
somebody to need to know about entropy but not need to 
know about probability.