Fundamental Constants: How Do We Know They're Constant?

[PumpkinCougar95]

How do we know that constants in nature like the Gravitational constant or plank's constants are actually "constant" and don't actually change over time? What sorts of experiments have been done which verify these things?

 

[sophiecentaur]

You could try Googling "Measuring G" or "measuring h" and see that such quantities are frequently 'checked'. Somebody could make a real name for themselves if they managed to find that G is increasing. Dark Matter was introduced to explain weird recession speeds of distant galaxies.

 

[Dale]

How do we know that constants in nature like the Gravitational constant or plank's constants are actually "constant" and don't actually change over time? What sorts of experiments have been done which verify these things?

You can just check the BIPM definitions of the SI. These constants are not “in nature” they are in the SI. In other unit systems they may or may not even exist.

 

[sophiecentaur]

The gravitational constant of earth is roughly 9.81m/s2.

That's not the gravitational constant. It's the gravitational acceleration g (lower case) on Earth and it depends on the Mass of the Earth and the radius.
G (upper case) is constant in
g = MG/d²

Source: This is common, undisputed knowledge.

Whoops! That was really sticking your neck out to say something like that on PF.

 

[Dadface]

How do we know that constants in nature like the Gravitational constant or plank's constants are actually "constant" and don't actually change over time? What sorts of experiments have been done which verify these things?

Only time will tell if some constants change over time.

 

[Vagn]

Only time will tell if some constants change over time.

Precise measurements of the gravitational constant G using pulsars suggest that such a change is consistent with zero. The measured value is found to be (−0.6 ± 1.1) × 10−12 yr^-1 within a 95% confidence limit.
http://iopscience.iop.org/article/10.1088/0004-637X/809/1/41/meta
https://arxiv.org/abs/1504.00662