Scientific Terminology

I often express numbers in scientific notation where the superscript represents the number of decimal places moved to the right, if positive, or the number of decimal places moved to the left, if negative. Some examples: 2.125 x 10⁵ is, therefore, 212,500. 2.125 x 10^-5, on the other hand, is 0.00002125. This gets important when trying to express really large or small numbers.

I use the short scale numbering system that increases from a million by factors of 1,000. Thus, one billion is 1,000 million or 10⁹, and one trillion is 1,000 billion or 10¹². Beyond those two, I always use the exponent numbering system described above. The US has always used the short scale, and the UK officially moved to it in 1974. The long scale is used in most of Europe, however. I have used the American unit system; miles, feet, inches etc. I mile is about 1.6 km, and one foot is about 30.5 cms. I plan to add metric unit system equivalents, which is quite an extensive change and will take a while.

Astronomical distance is expressed in either Light-Years, or Parsecs. 1 light-year is 5,878,630,000,000 (just under 6 trillion or 6 x 10¹²) miles. Light-years are used generally only for intragalactic measurements. On larger intergalactic scales, astronomers generally use the parsec, megaparsec or gigaparsec. The word parsec comes from the parallax of one arcsecond, and is the distance from the Earth to a star or other astronomical object that subtends a parallax angle of one arcsecond when viewed from Earth. 1 parsec is approximately 3.26156 light-years or 19.174 trillion miles (19,174,000,000,000 miles) or 30.857 trillion kilometers. It first came into use in 1913, and is abbreviated to "pc". A Kiloparsec (Kpc) is 1,000 parsecs, Megaparsec (Mpc) is a million parsecs and a Gigparsec (Gpc) is one billion parsecs.

The Universe is approximately 13.75 billion years old. However, due to the "stretching" of space, the radius of the observable universe, is approximately 14 Gpc (46.5 billion light-years or nearly 2.7 x 10²³ miles!), although no one knows how far the universe extends beyond that. Note that all distances quoted here assume a value of ~71 km/sec/Mpc for the Hubble Constant, although the latest WMAP figure is 70.5± 1.3 km/sec/Mpc.

Most temperatures are quoted in degrees Kelvin (°K). Zero Kelvin, also call Absolute Zero, is -273.15 Celsius (°C) and -459.67 Fahrenheit (°F). A change of 1°K equals a change of 1°C or 1.8°F. Thus 0°C = 32°F = 273.15°K, or 500°C = 932°F = 773.15°K.

Particle masses are generally quoted in electron volts (eV). MeV is 1 million electron volts, GeV is a billion electron volts and TeV is a trillion electron volts. An electron volt is defined as the amount of kinetic energy gained by an electron when it accelerates through an electrostatic potential difference of one volt. As a unit of energy, to use it to define mass, it should be divided by c²; that is eV/c²(where c is the speed of light). This is just a derivation of E=Mc², but usually the c² is left off, and taken as understood. The kinetic energy of a flying mosquito (not its mass; just the kinetic energy of its flight) is approximately 1TeV. The Large Hadron Collider at CERN is planned for an energy level of 14TeV, 7TeV for each of the two beans, but the LHC concentrates the energy into a pair of protons, which are a lot smaller than a mosquito!.

Within the scientific community, what is a Theory? Or a Hypothesis? Essentially, a hypothesis is an educated guess, generally resulting from observing phenomena. Over time, additional observations or experiments could support or disprove it. A theory generally derives from a hypothesis, or series of hypotheses, that has been supported by experiment or repeated observation by a number of people. If evidence is found to disprove a theory, it is no longer considered a valid theory, or it may be altered to define the limits within which it applies. Thus, saying, for example, that Quantum Physics is "just a theory" implies a lack of credibility whereas Quantum Physics is supported by a huge body of experimental verification. The same is true for Relativity. In both these examples, limits are placed around the degree of applicability of the theory; for example, it is generally understood that general relativity breaks down around the Planck energy and Planck length scales. BUT; theories are NOT guesses or fanciful notions plucked from the air.

Science - Terminology & Information Sources

Terminology