Usenet Relativity FAQ

This is the web version of the Usenet Relativity FAQ (Frequently Asked Questions). Its purpose is to provide good answers to questions which have been discussed often in sci.physics.relativity and related Usenet newsgroups. The articles in this FAQ are based on those discussions and on information from good reference sources. That does not mean that they are always perfect and complete. If you have corrections, updates or additional points to make please send E-mail to the editors at relfaq@corepower.com. You can also raise the subject in the newsgroups if you really think you have something new to say. If you want to write up an article following a discussion about a subject not yet covered here then feel free to send it to us, but please do not use this address to ask new questions. Ask them in the appropriate newsgroup instead.

If you are new to this newsgroup, please read "Welcome! to sci.physics.relativity", "An Introduction to the Physics Newsgroups", and "Possible Topics for Discussion on sci.physics.relativity". They will help you find the right newsgroup for your questions and will give you other crucial advice about appropriate netiquette for these groups. Above all you should check carefully to see if your questions are answered in this FAQ before posting.

This FAQ was originally part of the Physics FAQ which was created by Scott I. Chase in 1992. The web version was created by Michael Weiss, and has been maintained and enlarged by Michael Weiss, Philip Gibbs, and Chris Hillman. The present maintainer is Nathan Urban. Others who have written for the FAQ are credited at the top of the items they submitted while many more who have made smaller contributions have been thanked privately.

This FAQ is currently available at these web sites:

USA:

http://www2.corepower.com:8080/~relfaq/relativity.html

http://math.ucr.edu/home/baez/physics/relativity.html

http://www.public.iastate.edu/~physics/sci.physics/faq/relativity.html

http://www.weburbia.com/physics/relativity.html

UK:

http://hepweb.rl.ac.uk/ppUK/PhysFAQ/relativity.html

http://www.weburbia.demon.co.uk/physics/relativity.html

Netherlands:

http://www.xs4all.nl/~johanw/PhysFAQ/relativity.html

Germany:

http://www.desy.de/user/projects/Physics/relativity.html

Australia:

http://www.phys.unsw.edu.au/physoc/physics_faq/relativity.html

Taiwan:

http://www.phy.ncku.edu.tw/mirrors/physicsfaq/relativity.html

Thanks go to John Baez, Philip Gibbs, Alan Cairns, Dave Edsall, Chung-rui Kao, Matthew Parry, Jon Butterworth, Harald Falkenberg, Johan Wevers and the various organisations for hosting us! If any other non-commercial sites would like to mirror this FAQ in countries not listed above, please contact relfaq@corepower.com.

The full Physics and Relativity FAQ in HTML form can be downloaded as a single large archive file by FTP from ftp://ftp.corepower.com/pub/relfaq/. You can install it on your local disk and view it from there with a suitable web browser.

This document is copyright. Please read the copyright notice for copyright details and archival information

Index of Subjects

Administrivia and Reference

• An Introduction to the Physics Newsgroups
• New: Possible Topics for Discussion on sci.physics.relativity
• The Care and Feeding of Kill Files
• Useful Physics Resources on the Web
• Notation and Abbreviations used in the FAQ and newsgroups
• New: A Guide to Relativity Books
• A Physics Booklist

Speed of Light

• Why is c the symbol for the speed of light?
• Is the speed of light constant?
• Updated: How is the speed of light measured?
• Why is the speed of light so high?
• Is there an equivalent of the sonic boom for light?
• Is it possible to go faster than light?
• I am going at the speed of light and I turn on my headlights...?

Special Relativity

• How do You Add Velocities in Special Relativity?
• Does a Clock's Acceleration Affect its Timing Rate?
• Can Special Relativity Handle Acceleration?
• What are the Equations for the Relativistic Rocket?
• The Barn and the Pole
• The Twin Paradox
• The Superluminal Scissors
• Can You See the Lorentz-Fitzgerald Contraction?
• The Rigid Rotating Disk in Relativity
• Relativity in Chemistry: The Color of Gold
• Bell's Spaceship Paradox
• Apparent Superluminal Velocity of Galaxies
• Does mass change with velocity?
• Does light have mass?
• What is the experimental basis of special relativity?

General Relativity and Cosmology

• What Causes Gravity?
• Is pi Constant in Relativity?
• What is Gravitational Radiation?
• Does Gravity Travel at the Speed of Light?
• Is Energy Conserved in General Relativity?
• Olbers' Paradox
• What is Dark Matter?
• Do Atoms Get Bigger as the Universe Expands?
• What Causes the Hubble Redshift?
• Updated: Where is the centre of the universe?
• Mercury's Orbital Precession
• Time Travel - Fact or Fiction?

Black Holes

• What is a black hole, really?
• How does the gravity get out of the black hole?
• What happens to you if you fall into a black hole?
• If you go too fast do you become a black hole?
• What is Hawking Radiation?
• The Black Hole Information Loss Problem
• Is the Big Bang a Black Hole?

If you do not find your question answered here you may find it in one of these related FAQs.

• Physics FAQ
• sci.astro FAQ
• Space FAQ
• Jason Hinson's Relativity and FTL Travel FAQ
• Ted Bunn's Black Holes FAQ
• Ned Wright's Cosmology FAQ
• Douglas Scott's Cosmic Microwave Background FAQ
• Sten Odenwald's Ask The Astronomer
• John Simonetti's Astronomy and Physics FAQ
• Chris Hillman's Relativity on the WWW
• Wayne Throop's Relativity
• Scientific American's Ask The Experts (Astronomy)