[extropy-chat] the future of ...

[Hal Finney]

Scerir pointed to:

> http://online.itp.ucsb.edu/online/kitp25/

But he didn't say what it is the future of...

It is a conference on The Future of Physics!  And it was held at UC
Santa Barbara, just a couple of miles from where I live.  I did not try
to crash it, but there was quite a bit in the local news about it this
weekend because the director of the UCSB Kavli Institute for Theoretical
Physics is David Gross, who just won the Nobel Prize for his work on
quantum theory.

The conference program has audio and video of the talks available to
download, as well as the slides in an easy-to-view format.  Most of them
appear to be very technical however.

I watched one of the first ones, Where do we Stand? by Steven Weinberg.
It was a summary of the current state of physics.  Most of it was over my
head but I was surprised that he spent about ten minutes on the anthropic
principle, its implications and applications.

Anthropic reasoning in physics is anything that is built around the
assumption that conditions have to be such that observers can exist
to observe them.  The example given by Weinberg is the size of the
cosmological constant, which is equivalent (or at least related) to the
inherent gravitational energy of the vacuum.  It turns out that this
energy density is about the same as the energy density of the matter of
the universe, but there is no known theoretical reason to explain this
rough match.  In fact current theory does little to constrain the vacuum
energy density and this would suggest that it would more plausibly be
extremely high, at black-hole density levels.  However, if it were much
higher than we observe it at, the universe as we know it could not have
existed for long enough for stars to form and life to evolve.

If you imagine that there are a lot of universes and they each have a
random vacuum energy density, then in most of them life will never form.
Only in the ones where it is about the size that we actually see could
life evolve.  This can be viewed as a sort of explanation of why the
cosmological constant is the size it is.

Weinberg went on to mention that many physicists hate anthropic reasoning,
including Gross, the Nobelist who runs the Institute.  They want to
hold out hope that physics will advance to the point that it can explain
exactly why the cosmological constant has the value it does, along with
other such values.  The idea of saying that it was essentially an accident
is not acceptable to them.

However Weinberg explained that physicists might have to lower their
sights and accept that some things just can't be explained by theory.
He pointed out that his had happened in the past.  At one time, European
scientists thought that the arrangement of the continents on the Earth
ought to follow some simple geometrical rules.  When Columbus was
planning his voyage to Asia there were those who tried to use simple
symmetry arguments to argue about the size of the oceans based on the
known size of Asia.  Another famous case was Kepler's attempt to explain
the sizes of the planetary orbits using regular solids of various types,
nesting solids and spheres together in different ways to try to make
them come out to the sizes of the orbits.

Today we know that the positions of the continents, and the spacings
of the planets, have no such simple explanations, and are essentially
accidental outcomes of complex processes.  It might be, Weinberg
suggested, that the cosmological constant and perhaps some other physical
constants could turn out the same.

I find anthropic reasoning fascinating because of its connection to
the possibility that other universes exist, and in particular the Many
Worlds Interpretation of quantum mechanics which suggests that these
other worlds include ones that have alternate versions of ourselves.
Cosmologists tend to be more open to the MWI than most physicists,
because they have to deal with an early universe that had no conscious
observers around to make measurements, which keeps them from using
certain alternative quantum interpretations.

If you look at the slides for James Hartle's talk at the conference,
<http://online.itp.ucsb.edu/online/kitp25/zee/oh/201.html>, you see
this laid out explicitly.  He concludes, "We are all Schrodinger Cats
in Hawking's wave function of the universe."  That's pretty cool!

Hal