Have the values of constants ever changed before?

Question

Example sub-questions:

Was the speed of light always that value?
Was the acceleration due to gravity always been 9.8m/s/s?
Etc

By "change" I mean both actual change in the physical world because of multiple factors and "change" in the numerical value (because the initial value discovered was not precise or accurate).

9.8 m/s only applies at the earth's surface. It is different everywhere else. In fact it goes down as you climb up a mountain. The Oklo nuclear reactor indicates there has been no change in the strength of electromagnetic forces (the fine structure constant) in the last 2 billion years. See http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor — hdhondt, Feb 06 '14 at 09:53
There has obviously been change in the measured values of constants. For example the first measurement of $c$ was 26% too low, which was actually pretty good given the measurement was made in 1676. — John Rennie, Feb 06 '14 at 10:08
Related, possibly a duplicate: Cases of any known fundamental physical constants changing within our locality?. — John Rennie, Feb 06 '14 at 10:11
Possible duplicates: http://physics.stackexchange.com/q/21721/2451 and links therein. — Qmechanic, Feb 06 '14 at 10:12
Futurama GAVE you the answer - "Speed of light was maximum speed until scientist increased it". — Asphir Dom, Feb 06 '14 at 11:20

score 3 · Answer 1 · answered Feb 06 '14 at 17:09

Look to large redshift values with the Hubble telescope. Then do spectroscopy. Primary physical constants have not changed within visible time within experimental error - more than 14 significant figures for the hydrogen atom hyperfine transition. Look up the half-life of that spin flip, then Heisenberg for slop in the gears.

Terrestrial acceleration due to gravity is not a constant,

http://www.splung.com/content/sid/2/page/gravitation
http://www.typnet.net/Essays/EarthGrav.htm
bottom

Big G is a universal constant. It is the worst-measured physical constant, upon which all gravitation hinges. Even worse, the very modest accuracy values substantially diverge - and don't grow better over the years,

http://iopscience.iop.org/0957-0233/10/6/001
1999
http://www.nature.com/news/2010/100823/full/4661030a.html
2010

Have the values of constants ever changed before?

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