# What is a constant exactly?

1. Nov 19, 2004

### DB

I know a constant is a fixed number, but what is a constant exactly? What does it mean when you have an equation that equals a constant?

Ty

Last edited: Nov 19, 2004
2. Nov 19, 2004

### Sirus

3. Nov 21, 2004

### FrankMak

As Sirus noted there are different kinds of constants, physical science versus mathematical constants.

There are official physical science constants defined as Universal at the following URL:
http://physics.nist.gov/cgi-bin/cuu/Category?view=html&Universal.x=82&Universal.y=7

It should be noted that the universal constants are dimensioned, that is, described using units which are themselves defined values (meters, seconds, temp., etc.). None of the physical science constants are "dimensioned" by a unit that is in itself a physical science constant.

There are a number of physical science constants that are dimensionless, usually ratios, like the neutron-electron mass ratio. The numeric value of dimensioned physical science constants are predicated upon the "value" of the defined units. I would say all constants are not created equal.