Quora question: Do physical constants change?

Potentially too many ways to answer this question.

What kind of change for instance? A corrected value as a result of more precise experiments? Sure, almost every constant has “changed” in this way. Famously, the first estimate of the Hubble constant was so far off that it implied a universe younger than the age of the earth.

A better predicted value from a more complete theory, perhaps? Yep, we got that too. The gyromagnetic ratio of the electron was at one point thought to be exactly 2, then loop corrections came along.

Or constants can “change” due to updated definitions. The charge-to-mass ratio of the electron used to be a “constant” independent of velocity before we understood relativity.

Or maybe you mean some change driven by underlying physics. The rate of expansion of the universe is accelerating, for instance, is a physical statement. Likely, even the true value of the Hubble constant has never not changed, though our lifetimes are definitely not long enough to measure the difference. And there’s potentially spatial variation, too. What would we measure for G outside the observable universe? It’s hard to be sure what’s going on where we have no causal contact.

And then there’s the matter of what kind of constant you are talking about. There are an insane number of constants. Does this constant have dimensions? If so, the speed of light can be considered differently “valued” depending on if you’re measuring in meters per second or knots.

Physic’s relationship with its constants is honestly pretty complex. On the one hand, they’re constants of proportionality. Dimensional constants like c, which relate space and time, or h, connecting frequency with energy of light, or k, relating temperature and energy, all of which just basically tell us that we’re using the wrong system of units, that these things that we measure in all these different ways are fundamentally the same. Change into the “right” system of units and we can make them go away.

But then you look at the standard model, and it’s full of straight up completely arbitrary dimensionless constants: ratios of masses, coupling strengths (like alpha), whole tables of interaction parameters that we don’t get to choose at all. That we’re totally stuck with defining by explicit measurement only. Our very existence is based sensitively on the values of these parameters- “change” any of these and our universe is unrecognizable. Yet even our current, incomplete field theory predicts these constants to “run” as we go to higher energy scales.

Is constant just a bad word? Are we confused because we don’t have the whole picture?

This is a subject I definitely wouldn’t mind exploring further. Maybe I’ll do a “fundamental constants and our lives” series.

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3 thoughts on “Quora question: Do physical constants change?

  1. Guillermo says:

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    • Lulu says:

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