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 x1 (x subscript 1) while x^2 means x2 (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 high energy physics - theory, while the 9501078 is the number of the paper submitted to the archive in January (the 01) of 1995.
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 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 m (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 was convenient because fm for 10-15 metres coincides with the old symbol which was short for fermi. 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 because they would not confuse with other symbols. Other than that they are roughly modelled on previous prefixes.