Updated PEG March 1997.

Original by Philip Gibbs May 1996.

In this FAQ and in the sci.physics newsgroups we usually manage to avoid getting too
deeply into detailed mathematics but physics is a very mathematical subject and it is
impossible to avoid a few equations from time to time. At present there is no
universally accepted mechanism for writing equations in the newsgroups. Indeed
Usenet is one of the last bastions of pure ASCII text and many would like to see it stay
that way. So when it is not possible to write equations using simple computer
characters on one line, most people resort to using either *ASCII art* or
TeX/LaTeX.

*ASCII art* means constructing symbols using the ASCII characters suitably
placed on consecutive lines. With some care it is possible to do integral and
summations signs in this way. Here are some examples.

oo 2 --- 1 __ \ --- = || / 2 --- --- n 6 n=1 / 1 | - dx = log(x) + C / x

Diagrams can be produced in a similar way. With skill you really can be artistic!

*TeX/LaTeX* are a system used to produce mathematical documents with equations
and diagrams. It is not really very readable in ASCII. If you see things like. . .

$ \int{e^{\mu x} dx} $

. . . then it is TeX.

The only part of TeX that we use in the FAQ is the notation for subscripts and
superscripts. x_1 means x_{1} (*x subscript 1*) while x^2 means
x^{2} (*x squared*). This is often preferred to ASCII art when you
don't want to break the flow of text.

Sometimes people try to use special characters that extend the ASCII character set. Sadly, these give different characters on different systems so they must be avoided.

By the way, it is possible to write some mathematical equations correctly in HTML web pages but traditionally we have stuck to ASCII art and TeX so that extracts can be conveniently cut and pasted from the web browser straight into sci.physics when someone asks a FAQ. Many of the pages now use proper subscripts and superscripts to improve readability. Images will also be used where ASCII art becomes impossible for figures and equations in the FAQ .

There are a lot of unexplained acronyms used as abbreviations in Usenet. They are not a terribly good thing because it means that people who are not familiar with the territory don't understand what is being said, and all for the sake of a little brevity.

Here are a few of the more common ones used in the physics groups and throughout Usenet. These are listed to help you understand them, not to encourage you to over use them. If you do want to use them think about including a key to those you use in your signature. OTOH the ones I use in this FAQ are OK and need no explanation :-)

AE Albert Einstein BB Big Bang BH Black Hole c speed of light CBR Cosmic Background Radiation CMB Cosmic Microwave Background E-M Electromagnetic EP Equivalence Principle EPR Einstein-Podolsky-Rosen paradox FOR Frame Of Reference FTL Faster Than Light GR General Relativity GUT Grand Unified Theory HST Hubble Space Telescope HUP Heisenberg Uncertainty Principle LET Lorentz Ether Theory LNH Dirac's Large Number Hypothesis M&M Michelson–Morley experiment MMX Michelson–Morley experiment MTW Misner, Thorn, Wheeler, ("gravitation" a common reference) MWI Many Worlds Interpretation NM Newtonian Mechanics PEP Pauli Exclusion Principle PMT Photon Multiplier Tube PR Principle of Relativity QCD Quantum Chromo Dynamics QED Quantum Electrodynamics QFT Quantum Field Theory QM Quantum Mechanics SM Standard Model SOL Speed Of Light SR Special Relativity TP Twin Paradox TT Time Travel

AFAIK As Far As I Know BTW By The Way DYOH Do Your Own Homework FAQ Frequently Asked Question FWIW For What It's Worth FYI For your Information IIRC If I Remember Correctly IMHO In My Humble Opinion IOW In Other Words OTOH On The Other Hand ROTFL Rolls On The Floor Laughing TIA Thanks In Advance WRT With Respect To :-) happy face :-( sad face :-| straight face

Sometimes people cite papers which are available as electronic pre-prints (e-prints). You may come across something like. . .

*. . . see Dr Underwood in hep-th/9501078 . . . *

This is a reference to an e-print which can be found on the web at http://xxx.lanl.gov/abs/hep-th/9501078.
The **hep-th** is the name of an e-print archive for papers in **h**igh
**e**nergy **p**hysics **-** **th**eory, while the **9501078** is the
number of the paper submitted to the archive in January (the 01) of 19**95**.

There are other e-print archives apart from hep-th and most of the ones covering areas of physics can be found at http://xxx.lanl.gov. If you want to read the papers you will need to install software on your system to read TeX, Postscript or PDF.

Large and small numbers and quantities are often described by using *scientific
notation*. For example 3*10^20 eV means three times ten raised to the power of
twenty electron volts. We may also say 300 EeV. E stands for exa, which is the
Systeme International (SI) prefix for 10^18.

Prefix value symbol date example etymology yotta 10^24 Y 1991 yottajoule from otto, eight Italian zetta 10^21 Z 1991 zettamole from sette, seven Italian exa 10^18 E 1975 exaweber from hex, six in Greek peta 10^15 P 1975 petahertz from pente, five in Greek tera 10^12 T teracandela teras, monster in Greek giga 10^9 G gigawatt gigas, giant in Greek mega 10^6 M megakelvin megas, huge in Greek kilo 10^3 k kilovolt khilioi, thousand in Greek hecto 10^2 h hectoradian hekaton, hundred in Greek deca/deka 10 D (or da) dekapascal deka, ten in Greek deci 10^-1 d decisievert decimus, tenth in Latin centi 10^-2 c centimetre centum, hundred in Latin milli 10^-3 m milliampere mille, thousand in Latin micro 10^-6 μ (Greek mu) microohm mikros, small in Greek nano 10^-9 n nanosecond nanos, dwarf in Greek pico 10^-12 p picofarad pico, little bit in Spanish femto 10^-15 f 1964 femtonewton femten, 15 in Danish or Norwegian atto 10^-18 a 1964 attogram atten, 18 in Danish or Norwegian zepto 10^-21 z 1991 zeptohenri from sept, seven Greek yocto 10^-24 y 1991 yoctolitre from okto, eight Greek

The etymology of the SI prefixes is quite interesting in itself. Many came from Greek and Latin via the
French but a few are from other European languages. The choice of femto aligns with the fact that "fm" for
10^{-15} metres is often called a "fermi", in honour of Enrico Fermi, a giant of early nuclear
theory. Peta and exa were apparently modelled on tera by imagining that it came from tetra (four in Greek)
with the r dropped. Hence peta is penta with the n dropped and exa is hexa with the h dropped. In the
cases of yotta, zetta, zepto and yocto the initial letters were obviously required to avoid confusion with other
symbols. Other than that, they are modelled roughly on previous prefixes.