What would we notice if the fine structure constant started to increase?

Wikipedia says:

For instance, were α to change by 4%, stellar fusion would not produce carbon, so that carbon-based life would be impossible. If α were greater than 0.1, stellar fusion would be impossible, and no place in the universe would be warm enough for life as we know it.

So if the fine structure constant started to increase today, stars would soon stop creating carbon. But what else would happen and when? When would the sun's output change? When would our biological systems fail due to e.g. chemical reaction rates changing? (By "when would", I just mean the order of events, not when in time).

  • $\begingroup$ I don't know what effect this would have on biological/chemical systems on Earth, but "the Sun stops fusing carbon" is certainly no big deal as it hardly fuses any carbon now. OTOH I have to wonder what happens to nearby stars that are further along in their evolution (and have no light elements left to fuse). If a star can't fuse any matter at all, then it will likely undergo some sort of rapid restructuring or death. $\endgroup$ – Kevin Apr 6 at 18:10
  • $\begingroup$ Apart from being probably unanwserable with existing science (at least in the way the hard-science requires), it is extremely broad. Also not that when something would happen would require some statement of (at least) how quickly the value would change and where - is it local to some place or universally (which is hard to imagine). $\endgroup$ – StephenG Apr 6 at 18:37
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    $\begingroup$ Fine structure constant is tied up with Planck units. So some of those will have to change - do you have a preference regarding which ones? $\endgroup$ – Alexander Apr 6 at 18:45
  • $\begingroup$ @Kevin more supernovae? Although IIRC if a star is burning carbon, it doesn't have much left anyways, so maybe not $\endgroup$ – John Dvorak Apr 6 at 19:17
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    $\begingroup$ As a rule, the answer to "what happens if <fundamental constant> starts to change" is "rocks fall, everyone dies". The constants don't operate in a vacuum, and changing them violates the weak anthropic principle. We live in a universe that suits our form of life because the rules of that universe suit our form of life. If the rules change, life as we know it is no longer favoured. $\endgroup$ – jdunlop Apr 6 at 19:18

Let's assume that we're standing on a normal Earth in a normal universe, and suddenly the fine-structure constant changes. What would happen? My answer is based largely on Adams (2019). As a note on notation, I'll let $\alpha_0\equiv1/137$ be the value of the fine structure constant in our universe.

  • We need $\alpha\gtrsim7\times10^{-5}$. If it was lower, the Coulomb barrier would be quite low and quantum tunneling would lead to stellar fusion happening extremely quickly. The Sun would begin run out of fuel - though not before increasing its luminosity, raising the surface temperature of Earth to presumably inhospitable levels.
  • We need $\log\alpha/\alpha_0\lesssim1.5$. If it was higher, the electromagnetic force would dominate over the strong force and nuclei would suddenly become unstable to fission; atoms would break apart. Adams also says (if I understand correctly) that for $\alpha/\alpha_0\gtrsim2$ (!), protons and neutrons would be unstable to inverse beta decay.
  • We need $-2\lesssim\log\alpha/\alpha_0\lesssim2$. This is a constraint arising from the equations of stellar structure and is too complicated to fit in a succinct answer, but the gist is that a change of more than two orders of magnitude in $\alpha$ would lead to unstable stars. (This is also close to the constraint listed in the question!)
  • We need $\log\alpha/\alpha_0\lesssim1$. At higher values of $\alpha$, the surface temperature of a star would be too low to allow for habitable planets (effectively, the habitable zone must be outside the star!).
  • We need $\alpha\ll1$ (Adams equates this with, roughly, $\alpha\lesssim1/3$, i.e. $\log\alpha/\alpha_0\lesssim3.8$). This is for several reasons, including that electrons must be nonrelativistic and bulk matter must be stable.

Your question postulates the $\alpha$ increases. We'd notice instabilities on the atomic scale, as nuclei become unstable and then as chemical energy scales become comparable to nuclear energy scales, leading to fission. Shortly before this, the Sun would have begun to cool, although this would likely take some time. Eventually, temperatures on Earth would drop, and as we approached $\alpha=1$, the Sun would become unstable.

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    $\begingroup$ Note to self: don't screw with the fine structure constant, especially while drunk. $\endgroup$ – John O Apr 6 at 20:42
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    $\begingroup$ Impressive answer. I'm a little dubious our biochemistry would be robust to changing $\alpha$ by much at all - many energy levels would shift to perhaps the wrong side of balance sheet - anyhow a great answer and thanks for the link to the paper. $\endgroup$ – StephenG Apr 6 at 21:44
  • $\begingroup$ @StephenG: Indeed, I find it hard to believe that none of this would bugger up the Calvin/Krebs cycles, and if those break down you effectively don't have a biosphere any more. Sure, some other form of life would probably still be possible, based on a new and different biochemistry, but in the meantime, everything would die out. $\endgroup$ – Kevin Apr 6 at 22:41
  • $\begingroup$ @StephenG Thanks - and I should clarify that it seems like things would get quite difficult biologically before we get to the stellar cooling stage. $\endgroup$ – HDE 226868 Apr 6 at 22:45
  • $\begingroup$ Could you include two more parts? One where you look at chemistry (which might be the most immediate thing we notice) and one where you look at the notion of 'life' - i was always under the impression that it was 'any putative form of life' that was endangered by changes in the fine constant, i.e. that the questions revolved around 'is there matter accretion, is there C, is there warmth' and less 'is there homo sapiens on planet earth' $\endgroup$ – bukwyrm Apr 7 at 5:46

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