Open Questions:
Physics and Astronomy

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High-Energy Physics
Particle physics, the standard model, superstrings, quantum theory.
The big bang, inflation, large scale structure of the universe, inflation, galaxy formation, dark matter.
Relativity and Gravitation
Black holes, the cosmological constant, gravity waves, quantum gravity.
Astronomy, Astrophysics, and Space Science
Quasars and active galactic nuclei, gamma ray bursts, stellar formation and evolution, extraterrestrial life, extrasolar planets.

Recommended references: Web sites

Recommended references: Magazine/journal articles

Recommended references: Books

There was a time not so long ago when physics and astronomy were largely independent sciences. There was also a time fairly recently when cosmology, the study of the origin and evolution of the universe, was more a branch of philosophy than of science. Now, however, all of these studies are deeply intertwined, so we must almost necessarily consider them together.

The connection will become even closer in the future as physicists and cosmologists work jointly towards a "theory of everything", attempt to unify the still stubbornly incommensurable theories of relativity and quantum mechanics, and even search for the preconditions out of which the universe as we know it came into existence.

If and when a "theory of everything" is constructed, it will underlie almost everything in the sciences currently known as high-energy physics, cosmology, relativity, and astrophysics. Logically, then, we should consider it at this level, where all of those fields are present. However, the references listed on this page are mostly not about the "theory of everything" per se, but instead are simply so general in nature that they cover more than one of these closely related fields. (References to the "theory of everything" as it's currently emerging will be found as a topic under High-Energy Physics, since it is an extrapolation of the successes of particle physics in the last few decades.)

Recommended references: Web sites

Site indexes

Open Directory Project: Physics
Categorized and annotated physics links. A version of this list is at Google, with entries sorted in "page rank" order. May also be found at Netscape.
WWW Virtual Library: Physics
A directory of physics Web sites.
The Net Advance of Physics: Annotated Physics Encyclopedia
Maintained by Igor Ivanov. Good collection of links with useful annotations. Very good categorization.
Physics Internet Resources
Good directory of resources on the Web and elsewhere, provided by the American Physical Society. Categories include specific fields of physics, publications, organizations, societies, reference sites, and other directorise of physics resources.
Physics News Links
Maintained by the American Institute of Physics, this page provides key links to physics sites in a variety of areas (not just news).
PAM Resources in Physics
Good quality, mostly unannotated list of links, maintained by the Special Libraries Association.
Yahoo Physics Links
Annotated list of links.
Galaxy: Physics
Categorized site directory. Entries usually include descriptive annotations.
The Telson Spur: Physical Sciences
Part of a large directory of Web sites, dealing with physics, chemistry, relativity and cosmoloty.
Geometry.Net: Physics
Provides results of Web searches for many physics topics.
Martindale's Reference Desk: Physics Center
Extensive annotated list of links.
More About Particle Physics
Selected external links provided by Fermilab. Main categories are particle physics, astrophysics, and general physics.
The Net Advance of Physics
Excellent collection of links to online review articles and tutorials. Primarily organized alphabetically with some categorization. Maintained by Norman Redington.
The Net Advance of Physics: Philosophy and Foundations
An index of tutorial and research articles located at the physics preprint archive. Topics include CP violation, interpretation of quantum mechanics, spacetime structure.
The Net Advance of Physics: Theoretical and Mathematical Physics
An index of tutorial and research articles located at the physics preprint archive. Cateogrized into more specific topics.
Theoretical Physics Reviews and Lectures
A large collection of links to survey and review articles located at the physics preprint archive. Most of the articles are beyond the beginner stage and cover topics in black holes, cosmology, string theory, M-theory, D branes, supersymmetry, mathematical physics, and particle physics. List provided by The Official String Theory Web Site.

Sites with general resources

Institute of Physics
UK-based international physics professional society. Publishes many technical journals and magazines, including Physics World. Also provides a wide range of online services, mostly free, such as, PhysicsWeb, CERN Courier, and the New Journal of Physics.
Online version of Physics World magazine, published by the Institute of Physics. Latest news stories and magazine contents. Various other resources, including Web links.
The Internet Pilot to Physics
Outstanding collection of physics resources, including links to other sites, calendar of physics events, physics software, and communication services.
Physics Today
This is the leading publication on physical sciences for a general audience. The entire contents of all issues since July 2000 is now online. The feature articles, focus stories on recent research findings, and book reviews are especially good.
Usenet Physics FAQ
General Q & A about physics, from the Usenet sci.physics group. Many of these address some of the principal open questions. Also contains some good external links, including related FAQs.
Physics FAQ
Another version of the Usenet sci.physics FAQ.
The site is sponsored by the Institute of Physics and is intended to provide access to educational resources for all of physics and all educational levels. The search facility is especially useful for finding information at other sites on specific topics, but there are additional features as well, especially a question/answer service.
Nature Physics Portal
Excellent portal/gateway for physics. Provides general news on physics, library of original research papers, external links, and other services for professionals.
Europhysics News
Feature articles in this bimonthly publication of the European Physical Society provide good technical surveys of important developments in all branches of physics and related fields. The articles are accessible to non-specialists. Articles are available online dating back to January/February 2000.
High Energy Astrophysics Science Archive Research Center
A portal to all kinds of data and information from NASA's research program in astrophysics. The Images section contains various short tutorial articles in addition to impressive imagery. Additional educational resources can be accessed through the Education and Outreach section.
NASA's Origins Program
The program is concerned with the origins of the universe, the solar system, and life. Essentially all of the major questions of cosmology and related high-energy physics will be investigated by one or another of the missions planned in thie program. The existing and planned missions are described in some detail. There is an archive of press releases related to the program.
ESA Space Science
Provides general information and resources related to scientific activities of the European Space Agency. These include images, videos, animations, press releases, a glossary, frequently-asked questions, and brief articles on relevant scientific topics.
Carnegie Mellon Physics Department News
The department publishes an online newsletter with news stories and brief overview articles on discoveries in which department staff are involved. The archives go back to 1996.
BBCi Space Homepage
High-quality collection of accessible information on astronomy, cosmology, and space science. It is most easily navigated through the site map.
Sci.Physics.Research Archive
This Usenet newsgroup is for heavy-duty professional discussions of research-level physics. The archives go back to 1998 and can be searched by keyword or browsed by date. General information about the newsgroup is here.
NASA Astrophyics Data System
Search system for astrophysics, planetary sciences, and solar physics abstracts.
Theoretical Physics
Web site of a group of physics enthusiasts to provide services to the physics community. The site includes a member database, online discussion group, glossary of physics terms (with Web links for most entries), news articles, and links to related Web sites.
Level 5: A Knowledgebase for Extragalactic Astronomy and Cosmology
Very extensive site sponosred by NASA to collect research, reference, and tutorial material pertaining to extragalactic astronomy and cosmology. Also includes material on particle physics. See the table of contents for access to articles.
Physics at
Extensive site covering all areas of physics. Includes news articles, physics dictionary, and a subject library.
PhysNet: the Worldwide Physics Departments and Documents Network
Links to physics departments, documents, journals, conferences, and other resources for the physics community.
Erik Max Francis' Physics Pages
Assorted physics reference information, but most importantly, the Laws List, which is more like a dictionary/glossary of important concepts in physics.

Surveys, overviews, tutorials

Quantum Universe: The Revolution in 21st-Century Physics
A 58-page report prepared for the U. S. National Science Foundation and the U. S. Department of Energy. Though somewhat long, it is a pleasure to read, and one of the best places to start for an overview of the connection between high energy physics and cosmology.
John Baez's Stuff
Research papers, short elementary articles, and a weekly column called This Week's Finds in Mathematical Physics
Open Questions in Physics
A list from John Baez and the Physics FAQ
Unsolved problems in physics
Article from Wikipedia. Covers astrophysics, cosmology, technology as well. Links to separate articles for each topic.
Unsolved Problems in Physics and Astronomy
Useful list of over 30 unsolved problems, by Joseph Pedersen
Article from Wikipedia. See also List of physics topics.
Physics Problems for the Next Millennium
A list of ten questions compiled at the Strings 2000 Conference.
Unanswered Questions in Physics
Commentary and elaboration on the Strings 2000 questions by several physicists at Queen's University.
Hitoshi Murayama
Home page of a U. C. Berkeley physicist. Contains a variety of survey, overview, and tutorial materials dealing with high-energy physics, especially related to collider physics, supersymmetry, neutrino physics, and particle cosmology.
Stephen Hawking's Universe
Site offered by PBS covering many topics in cosmology and relativity. Good overview material. See especially Strange Stuff Explained and Unsolved Mysteries.
Cambridge Relativity Public Home Page
Tutorial/overview material on cosmology, black holes, cosmic strings, inflation, and quantum gravity.
21st Century Science
A series of lectures by James Schombert covering the history of the universe, from the point of view of cosmology and physics. Topics include basic physics, relativity, quantum theory, elementary particles, cosmology, and the origins of life.
Violence in the Cosmos
By Mike Guidry.
What is the Future of Cosmology?
Excellent overview by Lee Smolin that ties many things together.
Astronomy and Cosmology
Variety of pages in both areas, including links and a discussion forum, but information is rather sparse.
Andrew Hamilton's Home Page
Astronomy, cosmology, relativity and black holes

Ask an expert
A general physics education portal which includes a question/answer service.
Ask a High Energy Astronomer
Good service provided by NASA's High Energy Astrophysics Science Archive Research Center. Questions may be submitted by email. Questions that have already been answered are archived under a number of topics.
Ask the Physicist!
A service provided by the Department of Physics and Astronomy at the University of Georgia. Questions may be submitted by filling in a form. Answers are archived.
Ask a Physicist
At the University of Texas at Dallas. Questions may be submitted by email. No archives.
Ask the Experts
Accepts questions on physics and astronomy. Answers may be offered by anyone, but are reviewed for accuracy. Past questions may be searched or browsed by category. Hosted at
Galaxy: Ask-A-Physicist
Categorized site directory. Entries usually include descriptive annotations.

Online books and lecture notes

MIT OpenCourseWare: Physics
Course materials provided by the MIT OpenCourseWare project. New courses are continually added. Detailed lecture notes and additional materials such as problem sets are provided for some, but not all, courses. Courses in astronomy, relativity, astrophysics, and cosmology are also in this area.
Eric Weisstein's World of Physics
Extensive collection of encyclopedia-style articles.
A Radically Modern Approach to Introductory Physics
Lecture notes from an introductory physics course, by David J. Raymond. In addition to standard material such as waves, optics, etc., there are a number of sections on relativity, symmetry in quantum mechanics, and the standard model of particle physics.
Astronomy Notes
Detailed introductory course in astronomy, by Nick Strobel. In addition to standard material on astronomy, the site deals with stellar structure, stellar life cycles, galactic structure, active galaxies, and galaxy clusters, and cosmology. There's also a good glossary and selected external links.

Recommended references: Magazine/journal articles

Universe on a String
Edward Witten
Astronomy, June 2002, pp. 40-45
Superstring theory holds out the prospect of being able to unify quantum theory and gravitation through the concept of supersymmetry. If it is successful, we would also have answers to cosmological questions such as the nature of dark matter and dark energy, the explanation for cosmic inflation, and even a theory of the origins of space and time.
The 11 Greatest Unanswered Questions of Physics
Eric Haseltine
Discover, February 2002, pp. 36-42
A committee of the U. S. National Research Council has produced a report describing the most significant unanswered questions of physics and cosmology. Questions range from the nature of dark matter to the origin of the universe.
A Unified Physics by 2050?
Steven Weinberg
Scientific American, December 1999, pp. 68-75
Experimental results by 2050 should fill out the details of the Standard Model of the electromagnetic, weak, and strong forces. Unification of the gravitational force into the model may be much more difficult.
The Nature of Space and Time
Stephen W. Hawking, Roger Penrose
Scientific American, July 1996, pp. 60-65
The authors are two of the leading contemporary theoretical physicists with differing views on various fundamental questions of relativity and quantum theory. In 1994 they gave a series of lectures to contrast these views. The lectures were published in 1996 in a book from which this article is a brief excerpt.

Recommended references: Books

Stephen Webb – Out of This World: Colliding Universes, Branes, Strings, and Other Wild Ideas of Modern Physics
Copernicus Books, 2004
Webb's book is a relatively short (compared to the books of Greene and (especially) Penrose) survery of some of the sexier and most recent concepts of cutting-edge physics. It's not a bad place to start if you're pressed for time. Topics include symmetry, the standard model, grand unified theories, supersymmetry, higher dimensions, superstrings, M-theory, branes, black holes, and the holographic principle. Whew.
Roger Penrose – The Road to Reality: A Complete Guide to the Laws of the Universe
Alfred A. Knopf, 2004
It's probably safe to say that this book is sui generis – there's nothing else like it and never will be. Penrose is a master of conteporary science. At heart, he's a mathematician, and his book is heavy with math. As almost an afterthought to all the mathematical goodness, he shows how it's the right language to express physics, gravitation, quantum theory, cosmology and all that. But the book isn't for the faint of heart.
Brian Greene – The Fabric of the Cosmos: Space, Time, and the Texture of Reality
Alfred A. Knopf, 2004
This may be the single best book available at the time of its publication for an overview of most of the important open questions of modern physics and cosmology. It deals with the issue of "reality", spacetime, the nature of time, the big bang, gravity, and string theory – to name only the main threads. Green is regarded as a very good expositor of these topics.
Connecting Quarks with the Cosmos: Eleven Science Questions for the New Century
The National Academies Press, 2003
This book is a report of the Committee on the Physics of the Universe of the U. S. National Research Council. (See link below for a table of contents and excerpts.) It provides, for general readers, the best summary available of the most important open questions in the intersection of particle physics and cosmology. It was prepared by a panel of leading experts in the subject, and you won't find a better explanation of what the most important question are or how they fit together.
[Book home page]
Jonathan Allday -- Quarks, Leptons, and the Big Bang
Institute of Physics Publishing, 2002
Here's the perfect volume for the reader who wants one book with plenty of substance on the big issues of modern physics and cosmology -- quantum theory, relativity, particle physics, cosmology, and their rich interrelationships. Hawking's book (The Theory of Everything) gives brief introductions, but this one offers a lot more depth and detail, while stopping short of using any mathematics to speak of.
Stephen W. Hawking -- The Theory of Everything: The Origin and Fate of the Universe
New Millennium Press, 2002
This brief volume presents transcripts of seven lectures by Hawking on all the key topics: the expansion of the universe, black holes, the big bang, the direction of time, and the (possible) "theory of everything".
John W. Bahcall; Jeremiah P. Ostriker, eds. - Unsolved Problems in Astrophysics
Princeton University Press, 1997
A collection of papers that could be used by graduate students in astrophysics as a guide to selecting thesis topics from the most important problems on which progress may be made in the next decade. Although not an introductory work, it is an excellent survey of the field - from the nature of dark matter to the large-scale structure of the universe.
Val L. Fitch, Daniel R. Marlow, Margit A. E. Dementi, eds. - Critical Problems in Physics
Princeton University Press, 1997
Proceedings of a 1996 conference that surveyed the complete range of open problems in physics. Subjects include computation and neurobiology, cosmology, gravity, and high-energy physics.
Stephen Hawking; Roger Penrose - The Nature of Space and Time
Princeton University Press, 1996
This short volume contains six lectures and a debate between the two distinguished authors. The subject, as described by the title, is our scientific understanding of the ultimate nature of physical reality. Specific topics include spacetime singularities, quantum black holes, quantum cosmology, and twistors.
[Book review - PDF format]
Paul Davies (ed.) - The New Physics
Cambridge University Press, 1989
Excellent collection of survey articles by leading physicists on all the main related areas of physics, astrophysics, and cosmology. Mathematics used where appropriate.
Stephen W. Hawking - A Brief History of Time: From the Big Bang to Black Holes
Bantam Books, 1988
Despite the book's fame, "brief" is a fair characterization of the sketchiness with which most of the topics are treated. Main topics are black holes, the origin and fate of the universe, and unification. It's not the whole story, just a place to start.
Frank Wilczek, Betsy Devine - Longing for the Harmonies: Themes and Variations from Modern Physics
W. W. Norton & Company, 1988
This is an impressive survey and synthesis of most of the ideas that are important in modern physics and cosmology. The themes include symmetry, field theory, and unification.


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