Here's one example, where they measure the separation of spectral features from the OH molecule in a fairly distant galaxy and use that information to put a limit on how much variation there could be in the fine structure constant over the past 2.9 billion years: https://ui.adsabs.harvard.edu/abs/2018PhRvL.120f1302K/abstra...
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I'm confused - is this essentially saying we haven't ruled out fluctuations but we are putting a tighter bound on the variance? But not that we actually detected variation right?
My curiosity led me down the rabbit hole of all the eras that happened before the first microsecond and to consequently learning about when the forces diverged. What is the intuition on the four forces being unified? What does that mean? Is this even a question that makes sense to ask?
Yes. If there are no variations, it's impossible to rule them out. You can only put tighter and tighter constraints on them.