Original Usenet Physics FAQ
Version Date: June 2023
This list of answers to frequently asked questions in physics was created by Scott Chase in 1992. Its purpose was to provide good answers to questions that had been discussed often in the sci.physics and related Internet news groups. The articles in this FAQ are based on those discussions and on information from good reference sources. They were later maintained and enlarged by Michael Weiss and Philip Gibbs. 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.
Most of the entries that you'll find here were written in the days when the Internet was brand new. But rather than showing their age, this means that they were written in a time when most contributions to the Internet came from authors who had a lot of knowledge of their subject. The same is no longer true of the modern-day Internet, where a vast number of authoritative-looking wiki-type pages are written by anyone who wants to, regardless of their knowledge.
So because of their age, the FAQ entries that you'll find here have a great deal of academic credibility—but they are not always perfect and complete. If you have corrections, updates or additional points to make, please send an email to the editor, (his CV is here). If you want to write an article on a frequently asked question in physics, feel free to suggest it to the editor.
This document is copyright. Please read the copyright notice for copyright details and archival information.
Index of Subjects
General Physics
- What is Occam's Razor?
- Hot water freezes faster than cold!
- Why are golf balls dimpled?
- What is a dippy bird, and how is it used?
- Why do mirrors seem to reverse left and right, but not up and down?
- Which way will my bathtub drain?
- How does a light-mill work?
- Why do stars twinkle whereas planets do not?
- Is glass liquid or solid?
- I know a place where things can roll uphill!
- What do you call the rate of increase of acceleration?
- Is magnetic levitation possible?
- Why is the sky blue?
- Open questions in physics
- Does centrifugal force hold the Moon up?
- What is weight?
- What is a leap second?
- Is force measured in newtons or Newtons?
- Can all the natural numbers be summed? (or, does 1 + 2 + 3 + ... equal −1/12?)
- Can you take the logarithm of a dimensioned quantity?
- What is 1 / 2 (3 + 4)?
Particle and Nuclear Physics
- What is negative temperature?
- How to change nuclear decay rates
- Have physical constants changed with time?
- Do tachyons exist?
- The particle zoo
- Does antimatter fall up or down?
- Baryogenesis: why are there more protons than antiprotons?
- The solar neutrino problem
- What is the mass of a photon?
- Why are there eight gluons?
- What are half lives and mean lives?
Quantum Physics
- The EPR Paradox and Bell's Inequality
- Some frequently asked questions about virtual particles
- What is the Casimir Effect?
- Can the human eye detect a single photon?
Relativity and Cosmology
Speed of Light
- Why is c the symbol for the speed of light?
- Is the speed of light everywhere the same?
- 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. . .
- Apparent superluminal speed of galaxies
- I saw two events at the same time/different times. Were they simultaneous?
Special Relativity
- What is the experimental basis of special relativity?
- Attacking relativity: what was Herbert Dingle's argument?
- How do you add velocities—relativistically and otherwise?
- Can special relativity handle acceleration?
- Where is the boundary between special and general relativity?
- Does a clock's acceleration affect its timing rate?
- Do moving clocks always run slowly?
- What are the equations for a relativistic rocket?
- The barn and the pole
- The rigid rotating disk in relativity
- The twin paradox
- Bell's spaceship paradox
- The superluminal scissors
- Can you see the Lorentz contraction?
- Are the Lorentz contraction and time dilation real?
- Relativity in chemistry: the color of gold
- What is relativistic mass?
- What would a relativistic interstellar traveller see?
- Rotating coordinates in 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?
- Where is the centre of the universe?
- Mercury's orbital precession
- Time travel: fact or fiction?
- Is the cosmological constant nonzero?
Black Holes
- What is a black hole, really?
- How does the gravity get out of a 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?
Reference Topics
- An introduction to the physics news groups
- The care and feeding of kill files
- Accessing and using on-line physics resources
- Useful physics resources on the internet
- Notation and abbreviations used in the FAQ and news groups
- A physics book list
- The Nobel Prize for physics
- Possible topics for discussion in the news groups
- A guide to relativity books
Related FAQs
There are many other places where you may find answers to your question. Here is a list of other FAQs and answer archives that might be useful.
- sci.astro FAQ
- Space FAQ
- David Stern's Science Overviews (astronomy)
- Scientific American's Ask The Experts
- Sten Odenwald's Ask the Space Scientist
- John Simonetti's Astronomy and Physics FAQ
- Cornell University's Ask an Astronomer
- 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
- Arnold Neumaier's Theoretical Physics FAQ
- Measurement in quantum mechanics FAQ
- sci.chem FAQ
Mirror sites
This FAQ is currently available from these web sites:-
Netherlands:
- http://www.xs4all.nl/~johanw/PhysFAQ USA:
- http://math.ucr.edu/home/baez/physics
- http://www.edu-observatory.org/physics-faq
- http://www.ronen.net/physics
Thanks go to John Baez, Ronen Ben-Hai, Philip Gibbs, Chris Hillman, Chung-rui Kao, Matt McIrvin, Joe Mirando, Matthew Parry, Han-Tzong Su, Nathan Urban, Johan Wevers, Sam Wormley, and the various organisations for hosting us! If any other non-commercial sites would like to mirror this FAQ, please contact the editor.