Item 23.

Open Questions                                  updated 01-JUN-1993 by SIC
--------------                                  original by John Baez

        While for the most part a FAQ covers the answers to frequently
asked questions whose answers are known, in physics there are also plenty
of simple and interesting questions whose answers are not known. Before you
set about answering these questions on your own, it's worth noting that
while nobody knows what the answers are, there has been at least a little,
and sometimes a great deal, of work already done on these subjects. People
have said a lot of very intelligent things about many of these questions.
So do plenty of research and ask around before you try to cook up a theory
that'll answer one of these and win you the Nobel prize!  You can expect to
really know physics inside and out before you make any progress on these.

        The following partial list of "open" questions is divided into two
groups, Cosmology and Astrophysics, and Particle and Quantum Physics.
However, given the implications of particle physics on cosmology, the
division is somewhat artificial, and, consequently, the categorization is
somewhat arbitrary.

        (There are many other interesting and fundamental questions in
fields such as condensed matter physics, nonlinear dynamics, etc., which
are not part of the set of related questions in cosmology and quantum
physics which are discussed below.  Their omission is not a judgement
about importance, but merely a decision about the scope of this article.)

Cosmology and Astrophysics

1.  What happened at, or before the Big Bang?  Was there really an initial
singularity?  Of course, this question might not make sense, but it might.
Does the history of universe go back in time forever, or only a finite

2.  Will the future of the universe go on forever or not?  Will there be a
"big crunch" in the future?  Is the Universe infinite in spatial extent?

3.  Why is there an arrow of time; that is, why is the future so much
different from the past?

4.  Is spacetime really four-dimensional?   If so, why - or is that just a
silly question?  Or is spacetime not really a manifold at all if examined
on a short enough distance scale?

5.  Do black holes really exist?  (It sure seems like it.)  Do they really
radiate energy and evaporate the way Hawking predicts?  If so, what happens
when, after a finite amount of time, they radiate completely away?  What's
left?  Do black holes really violate all conservation laws except
conservation of energy, momentum, angular momentum and electric charge?
What happens to the information contained in an object that falls into a
black hole?  Is it lost when the black hole evaporates?  Does this require
a modification of quantum mechanics?

6.  Is the Cosmic Censorship Hypothesis true?  Roughly, for generic
collapsing isolated gravitational systems are the singularities that might
develop guaranteed to be hidden beyond a smooth event horizon?  If Cosmic
Censorship fails, what are these naked singularities like?  That is, what
weird physical consequences would they have?

7.  Why are the galaxies distributed in clumps and filaments?  Is most of
the matter in the universe baryonic?  Is this a matter to be resolved by
new physics?

8.  What is the nature of the missing "Dark Matter"?  Is it baryonic,
neutrinos, or something more exotic?

Particle and Quantum Physics

1.  Why are the laws of physics not symmetrical between left and right,
future and past, and between matter and antimatter?  I.e., what is the
mechanism of CP violation, and what is the origin of parity violation in
Weak interactions?  Are there right-handed Weak currents too weak to have
been detected so far?  If so, what broke the symmetry?  Is CP violation
explicable entirely within the Standard Model, or is some new force or
mechanism required?

2.  Why are the strengths of the fundamental forces (electromagnetism, weak
and strong forces, and gravity) what they are?  For example, why is the
fine structure constant, which measures the strength of electromagnetism,
about 1/137.036?  Where did this dimensionless constant of nature come from?
Do the forces really become Grand Unified at sufficiently high energy?

3.  Why are there 3 generations of leptons and quarks?  Why are there mass
ratios what they are?  For example, the muon is a particle almost exactly
like the electron except about 207 times heavier.  Why does it exist and
why precisely that much heavier?   Do the quarks or leptons have any

4.  Is there a consistent and acceptable relativistic quantum field theory
describing interacting (not free) fields in four spacetime dimensions?  For
example, is the Standard Model mathematically consistent?  How about
Quantum Electrodynamics?

5.  Is QCD a true description of quark dynamics?  Is it possible to
calculate masses of hadrons (such as the proton, neutron, pion, etc.)
correctly from the Standard Model?  Does QCD predict a quark/gluon
deconfinement phase transition at high temperature?  What is the nature of
the transition?  Does this really happen in Nature?

6.  Why is there more matter than antimatter, at least around here? Is
there really more matter than antimatter throughout the universe?

7.  What is meant by a "measurement" in quantum mechanics?  Does
"wavefunction collapse" actually happen as a physical process?  If so, how,
and under what conditions?  If not, what happens instead?

8.  What are the gravitational effects, if any, of the immense (possibly
infinite) vacuum energy density seemingly predicted by quantum field
theory?  Is it really that huge?  If so, why doesn't it act like an
enormous cosmological constant?

9.  Why doesn't the flux of solar neutrinos agree with predictions?  Is the
disagreement really significant?  If so, is the discrepancy in models of
the sun, theories of nuclear physics, or theories of neutrinos?  Are
neutrinos really massless?

The Big Question (TM)

This last question sits on the fence between the two categories above:
 How do you merge Quantum Mechanics and General Relativity to create a
quantum theory of gravity?  Is Einstein's theory of gravity (classical GR)
also correct in the microscopic limit, or are there modifications
possible/required which coincide in the observed limit(s)?  Is gravity
really curvature, or what else -- and why does it then look like curvature?
An answer to this question will necessarily rely upon, and at the same time
likely be a large part of, the answers to many of the other questions above.

Item 24.                                        updated 24-MAY-1993 by SIC

Accessing and Using Online Physics Resources

(I) Particle Physics Databases

        The Full Listings of the Review of Particle Properties (RPP), as
well as other particle physics databases, are accessible on-line.  Here is
a summary of the major ones, as described in the RPP:

(A) SLAC Databases

PARTICLES   - Full listings of the RPP
HEP         - Guide to particle physics preprints, journal articles, reports,
              theses, conference papers, etc.
CONF        - Listing of past and future conferences in particle physics
HEPNAMES    - E-mail addresses of many HEP people
INST        - Addresses of HEP institutions
DATAGUIDE   - Adjunct to HEP, indexes papers
REACTIONS   - Numerical data on reactions (cross-sections, polarizations, etc)
EXPERIMENTS - Guide to current and past experiments

Anyone with a SLAC account can access these databases.  Alternately, most
of us can access them via QSPIRES.  You can access QSPIRES via BITNET with
the 'send' command ('tell','bsend', or other system-specific command) or by
using E-mail.  For example, send QSPIRES@SLACVM FIND TITLE Z0 will get you
a search of HEP for all papers which reference the Z0 in the title.  By
E-mail, you would send the one line message "FIND TITLE Z0" with a blank
QSPIRES is free.  Help can be obtained by mailing "HELP" to QSPIRES.

For more detailed information, see the RPP, p.I.12, or contact: Louise

(B) CERN Databases on ALICE

LIB         - Library catalogue of books, preprints, reports, etc.
PREP        - Subset of LIB containing preprints, CERN publications, and
              conference papers.
CONF        - Subset of LIB containing upcoming and past conferences since 1986
DIR         - Directory of Research Institutes in HEP, with addresses, fax,
              telex, e-mail addresses, and info on research programs

ALICE can be accessed via DECNET or INTERNET.  It runs on the CERN library's
VXLIB, alias ALICE.CERN.CH (IP#  Use Username ALICE (no
password required.)  Remote users with no access to the CERN Ethernet can
use QALICE, similar to QSPIRES.  Send E-mail to QALICE@VXLIB.CERN.CH, put
the query in the subject field and leave the message field black.  For
more information, send the subject "HELP" to QALICE or contact CERN
Scientific Information Service, CERN, CH-1211 Geneva 23, Switzerland,

Regular weekly or monthly searches of the CERN databases can be arranged
according to a personal search profile.  Contact David Dallman, CERN SIS
(address above) or E-mail CALLMAN@CERNVM.CERN.CH.

DIR is available in Filemaker PRO format for Macintosh.  Contact Wolfgang

(C) Particle Data Group Online Service

        The Particle Data Group is maintaining a new user-friendly computer
database of the Full Listings from the Review of Particle Properties. Users
may query by paper, particle, mass range, quantum numbers, or detector and
can select specific properties or classes of properties like masses or
decay parameters. All other relevant information (e.g. footnotes and
references) is included. Complete instructions are available online.

        The last complete update of the RPP database was a copy of the Full
Listings from the Review of Particle Properties which was published as
Physical Review D45, Part 2 (1 June 1992). A subsequent update made on 27
April 1993 was complete for unstable mesons, less complete for the W, Z, D
mesons, and stable baryons, and otherwise was unchanged from the 1992

Login to: PDG_PUBLIC with password HEPDATA.

Contact: Gary S. Wagman, (510)486-6610.  Email: (GSWagman@LBL.GOV).

(D) Other Databases

Durham-RAL and Serpukhov both maintain large databases containing Particle
Properties, reaction data, experiments, E-mail ID's, cross-section
compilations (CS), etc.  Except for the Serpukhov CS, these databases
overlap SPIRES at SLAC considerably, though they are not the same and may
be more up-to-date.  For details, see the RPP, p.I.14, or contact:
Dick Roberts (RGR@UKACRL.BITNET).  For Serpukhov, contact Sergey Alekhin
(ALEKHIN@M9.IHEP.SU) or Vladimir Exhela (EZHELA@M9.IHEP.SU).

(II) Online Preprint Sources

There are a number of online sources of preprints: (algebraic geometry)           (astrophysics)           (condensed matter)           (functional analysis)            (computational and lattice physics)                 (high energy physics phenomenological)                 (high energy physics theoretical)              (liquid crystals, optical materials)                  (general relativity, quantum cosmology),               (nuclear physics theory)               (nonlinear science)

        To get things if you know the preprint number, send a message to
the appropriate address with subject header "get (preprint number)" and
no message body. If you *don't* know the preprint number, or want to get
preprints regularly, or want other information, send a message with
subject header "help" and no message body.

(III) The World Wide Web

        There is a wealth of information, on all sorts of topics, available
on the World Wide Web [WWW], a distributed HyperText system (a network of
documents connected by links which can be activated electronically).
Subject matter includes some physics areas such as High Energy Physics,
Astrophysics abstracts, and Space Science, but also includes such diverse
subjects as bioscience, musics, and the law.

* How to get to the Web

        If you have no clue what WWW is, you can go over the Internet with
telnet to (no login required) which brings you to the WWW
Home Page at CERN. You are now using the simple line mode browser. To move
around the Web, enter the number given after an item.

* Browsing the Web

        If you have a WWW browser up and running, you can move around
more easily. The by far nicest way of "browsing" through WWW uses the
X-Terminal based tool "XMosaic". Binaries for many platforms (ready for use)
and sources are available via anonymous FTP from in directory
Web/xmosaic.  The general FTP repository for browser software is
(including a hypertext browser/editor for NeXTStep 3.0)

* For Further Information

        For questions related to WWW, try consulting the WWW-FAQ: Its most
recent version is available via anonymous FTP on in
/pub/usenet/news.answers/www-faq , or on WWW at

        The official contact (in fact the midwife of the World Wide Web)
is Tim Berners-Lee, For general matters on WWW, try or Robert Cailliau (responsible for the "physics"
content of the Web,

(IV) Other Archive Sites

        There is an FTP archive site of preprints and programs
for nonlinear dynamics, signal processing, and related subjects on node ( at the Institute for Nonlinear Science,
UCSD.  Just login anonymously, using your host id as your password. Contact
Matt Kennel ( for more information.