3 ms·

I can't see why the article would say the effect is not measurable. We are trying to contrast two explanations: In one, galaxies are receding and the expansio

I can't see why the article would say the effect is not measurable. We are trying to contrast two explanations: In one, galaxies are receding and the expansion of space in the intervening distance red shifts the spectra. In the other masses are changing (globally?) as some rate, changing the spectra. The best modern atomic clocks depend on atomic spectra, a shift in which would be evidence for or against this model. Given the precision of modern atomic clocks (<10^-17)[1] and the fact that the galactic spectral shifts are significant at large distances this seems plausible. I don't have precise #'s to do the calculations at hand so maybe I've made an error. [1] https://en.wikipedia.org/wiki/Quantum_clock https://en.wikipedia.org/wiki/Quantum_clock

deleted 8y ago
[deleted]
AnimalMuppet 8y ago
But if our atomic clocks' frequency is changing, how would you tell? You can't use a more precise clock; we don't have one. You'd have to do something like measure how far light travels in the same time. But if our length measurements are changing too... do they cancel? Or could we still tell?
- jepler 8y ago
  What you would need to determine is whether a dimensionless quantity is changing. https://en.wikipedia.org/wiki/Fine-structure_constant#Is_the_fine-structure_constant_actually_constant https://en.wikipedia.org/wiki/Fine-structure_constant#Is_the...? If the fine structure constant α is found to change, then would only be able to say that the relationship among the speed of light c, the elementary charge e, and the Planck constant ħ are changing, but IMO if we discovered that (say) α changed from .007300… to its present value of .007297…, we would not be able to then say "the speed of light changed (and the elementary charge and Planck constant remained the same)" …but as a matter of practicality, scientists could feel free to use a different value for c in the past (and the present value for the elementary charge and Planck constant), if that is the most convenient way to accommodate a change in α. It wouldn't surprise me in the least if holding c and ħ constant is better for astronomers and holding e and ħ constant are better for particle physicists. (Saying that ħ changes would be similar to saying that mass changes, or at least, the units of ħ include mass, and the Planck constant "is the basis for the definition of the kilogram." in the SI system [well, technically, this is not the case until next month. Right now the kilogram is still defined by the physical "international prototype kilogram" object, but the above quote is from wikipedia]) However, while the best experiments are consistent with changing α, the change in α is constrained to be WAY less than it would need to be to explain cosmological red shift observations.

deleted 8y ago

[deleted]

AnimalMuppet 8y ago

But if our atomic clocks' frequency is changing, how would you tell? You can't use a more precise clock; we don't have one. You'd have to do something like measure how far light travels in the same time. But if our length measurements are changing too... do they cancel? Or could we still tell?

jepler 8y ago
What you would need to determine is whether a dimensionless quantity is changing. https://en.wikipedia.org/wiki/Fine-structure_constant#Is_the_fine-structure_constant_actually_constant https://en.wikipedia.org/wiki/Fine-structure_constant#Is_the...? If the fine structure constant α is found to change, then would only be able to say that the relationship among the speed of light c, the elementary charge e, and the Planck constant ħ are changing, but IMO if we discovered that (say) α changed from .007300… to its present value of .007297…, we would not be able to then say "the speed of light changed (and the elementary charge and Planck constant remained the same)" …but as a matter of practicality, scientists could feel free to use a different value for c in the past (and the present value for the elementary charge and Planck constant), if that is the most convenient way to accommodate a change in α. It wouldn't surprise me in the least if holding c and ħ constant is better for astronomers and holding e and ħ constant are better for particle physicists. (Saying that ħ changes would be similar to saying that mass changes, or at least, the units of ħ include mass, and the Planck constant "is the basis for the definition of the kilogram." in the SI system [well, technically, this is not the case until next month. Right now the kilogram is still defined by the physical "international prototype kilogram" object, but the above quote is from wikipedia]) However, while the best experiments are consistent with changing α, the change in α is constrained to be WAY less than it would need to be to explain cosmological red shift observations.