Change in fine structure constant

[lark]

What would be the consequences of slightly changing the fine structure constant, i.e. changing the strength of the electromagnetic interaction - but not changing gravitation or the strong force? In the everyday world?

You might imagine that the strength of chemical forces etc. would change relative to the strength of gravitation, so gravity would feel weaker or stronger to us.

Laura

 

[VortexLattice]

Well, according to http://en.wikipedia.org/wiki/Fine-structure_constant#Definition there are 3 main definitions for it, but in all of them it's defined by several other variables... So if you were to change it, it seems like you'd have to choose which ones in its definition you'd be changing.

Not to be a buzzkill, but "what if xyz variable was changed" questions are normally kind of silly, I think...

 

[krome]

The more pertinent sections of the wikipedia article on the fine structure constant are "Is the fine-structure constant actually constant?" and "Anthropic explanation". The cited paper by Barrow, "Cosmology, Life, and the Anthropic Principle", was a good read as well.

It's probably silly to argue over whether or not this type of question is silly. However, since considering what would happen if the various fundamental constants were to change their values slightly essentially led to the fine tuning problem, I can't help but think that lark's question is actually quite important.

 

[mfb]

"what if xyz variable was changed" is fine for dimensionless constants (and only for them).
It would change the energy levels of electrons and nucleons. This could make stable nuclei unstable and vice versa, influence stellar fusion (and our fission reactors), and change the periodic system.

 

[lark]

"what if xyz variable was changed" is fine for dimensionless constants (and only for them).
It would change the energy levels of electrons and nucleons. This could make stable nuclei unstable and vice versa, influence stellar fusion (and our fission reactors), and change the periodic system.

Good point that it would change nuclear physics, because the ratio of electromagnetic force to strong force would change.
Why would the periodic table change? Looking at the wavefunction for the 1s orbital of atomic hydrogen, it looks like if the fine structure constant is multiplied by a factor [itex]F[/itex], the length scale of the wavefunction is divided by [itex]F[/itex]. The energy of that wavefunction would be multiplied by [itex]F^2[/itex], so the time scale of the wavefunction is divided by [itex]F^2.[/itex]
So perhaps the length scale of matter would be divided by [itex]F[/itex] also. I wonder what would happen to the rates of chemical reactions.
There are some disputed claims that the fine structure constant might vary in space and time, from astronomical observations.
Which brings up the question of how much the fine structure constant could be tweaked, and still leave a basically similar world and still permit life.
I'm sure people have thought about this, but I don't know who.
And maybe there are theories where the fine structure constant has an uncertainty, just as momentum / position are uncertain ...
Laura

 

[mfb]

The fine-structure would change, and influence the relative energy levels for different angular momentum. This does not simply scale with powers of alpha as the whole system does.

 

[lark]

The fine-structure would change, and influence the relative energy levels for different angular momentum. This does not simply scale with powers of alpha as the whole system does.

Looking at the Schroedinger equation you can see that if [itex]\alpha[/itex] is multiplied by [itex]F[/itex], then the potential [itex]V[/itex] is multiplied by [itex]F^2[/itex]; so if [itex]\Psi[/itex] is a solution before changing the fine structure constant, then if you divide the length scale of [itex]\Psi[/itex] by [itex]F[/itex], and divide the time scale of [itex]\Psi[/itex] by [itex]F^2[/itex], you would have a solution to the Schroedinger equation with the new fine structure constant. So this simple scaling ought to apply pretty generally.

So why would the fine-structure change? Is that because the Schroedinger equation isn't Lorentz invariant? It seems like with the relativistic version, this simple scaling with [itex]\alpha[/itex] ought to persist in some form.

I wonder how important the fine structure is, in everyday chemistry, the chemistry of life?

thanks
Laura

 

[mfb]

Energy levels are in first order proportional to (Z alpha)^2, but the fine-structure is the next order, and scales with (Z alpha)^4. As you can see, for large Z the fine-structure can become important, and it is different from the overall scaling.
The source of this expansion comes from relativistic corrections: E ~ p^2 (which would allow a perfect scaling) is a nonrelativistic approximation.

 

[lark]

Here are a couple of references about effects on chemistry of changing the fine structure constant:
http://pra.aps.org/abstract/PRA/v81/i4/e042523

http://ned.ipac.caltech.edu/level5/Hogan/Hogan3_1.html

at least so far it seems like consequences for everyday chemistry aren't huge unless the fine structure constant varies a lot.
I don't have an account to download the Phys. Rev. paper, if anyone does & would send it to me, thanks
Laura

 

[mfb]

Hmm, those seem to discuss light elements. I would be interested how heavy elements are changed, but this is more difficult to calculate as they have so many electrons.

 

[Tweedle]

I did some research into this. Most consequences of changes of alpha are either linear, or small powers of alpha. Some are larger powers. I have some conclusions.

To begin with, an instantaneous change of alpha by even a tiny amount would immediately kill you. Typical atomic bonds are about 2x10^-10m long and have spring constants around 7x10²⁹Nm^-1; n identical springs with constant k in series have spring constant k/n. If we have a chain of atoms joined by bonds whose length is dm we get n = 5x10⁹d and the spring constant of the chain is 1.4x10²⁰d^-1Nm^-1.

An instant change of alpha by one part in 10^x will not instantly change the length of the chain, but will instantly change the length that would be in equilibrium by one part in 10^x. The result is a displacement of 10^xd. The spring force that instantly arises is then 10^xdm*1.4x10²⁰d^-1Nm^-1 = 1.4x10^{20 + x}N. Even a part-per-million change in alpha results in forces in the petaNewtons, independently of the size of the chain, acting on an atom-sized mass for a seriously ginormous acceleration.

If we momentarily ignore all contraction transverse to the length of a beam of material, the material may be modeled as chains like the above in parallel attached to a thin sheet of atoms at its end. If there are N atoms in an atom-thick cross-section there are N springs with the above constant in parallel attached to the sheet and N atoms in the sheet. Parallel springs are additive, so the spring constant, and the force, is multiplied by N. The mass it acts on is also, obviously, multiplied by N. So, with our simplifying assumptions, that ginormous acceleration is unchanged whether the beam is an atom thick or macroscopic.

Transverse contraction, bonds at angles other than straight to the surface from the center of mass, and other complications exist, but if they don't cause many-order-of-magnitude changes the accelerations experienced by any material object will be enormous for even very small changes in alpha -- divided by a factor of alpha squared for the changed timescale of electromagnetic phenomena, of course. Which is going to be minuscule.

Upshot: an instant change in alpha by more than parts per quadrillion is instantly lethal to everything, everywhere. Also, those huge restoring forces from tiny changes explain why commonplace solid materials are so darn incompressible.

A slower change could produce tolerable forces and accelerations. I calculate that changing alpha by one part per million over a period of one second would result in Earth shrinking by roughly seven meters in radius in a similar time, with accelerations similar to that due to gravity. The damage would then be that from everything freefalling two storeys, plus accompanying turbulence, earthquakes, atmospheric storms, and other consequences. It's enough to be a dino-killer event even then, especially when you note that for part of that second there'd be enough underpressure in magma chambers to "uncork the champagne", so to speak, and cause numerous massive eruptions around the world. A pretty drastic consequence for such a tiny tweak.

The energy released by the contraction would presumably end up as heat. Potential energy in a spring is 0.5kd². For a typical atomic bond, and a length change of 10^x, that's 0.5*7x10²⁹Nm^-1*(2x10^{x - 10}m)² = 1.4x10^{2x + 10}J. For x = -6 that's 0.014J per molecular bond; an order of magnitude estimate for the energy released in a material object is thus 10²²J/g -- exajoules released from every grain of sand! (I'm actually somewhat skeptical of this number; for reference, the Fat Man nuke yielded about 10<sup>14J, and annihilation of that same gram of matter to energy would yield a comparable amount, so that "gram" actually gets 108 times more massive from its potential energy at the moment alpha changes, suggesting Earth wouldn't even nuke, but implode into a black hole -- seems excessive).

Some of the energy ends up as sound, but that'll turn into heat eventually; accelerating charges emit light, but only the object's surface could shed energy this way, so all the energy in the interior would be converted into heat unless it had some way to become, or get transferred to, weakly-interacting particles of some kind.

Obviously, for even the slow version not to nuke everything with sheer heat output the vast majority of this energy would have to be radiated or absorbed by some mechanism.

One possibility is quantum mechanical: if alpha ever actually changes out from under us, then alpha was a quantum scalar field which decayed to a lower energy level. The energy released by a tiny drop may not be especially huge, and the decay itself, to have waited until now before happening, would have to have an energy barrier -- picture a potential with two wells, one slightly lower than the other, and a hill between them. The decay could take energy from the shrinking bonds it sweeps over to enhance its ability to tunnel through the hill, and then release that energy in some weakly-interacting form, depending on the precise nature of the quantum scalar field at issue. Since it's presumably linked to the electroweak force, it's not ridiculous that it could release energy in a weak form -- possibly by pair-creation of dark matter or neutrinos -- that would flee with the decay wavefront and help fuel its propagation, along with the direct energy of the released field potential.

Another is that to an electromagnetically-constructed object there has been a change in energy and temperature scales. In particular, the thermal energy carried by microscopic particles' motions doesn't instantaneously change, but the energy an EM-based observer sees is different by α-2, and, in particular, smaller if alpha increased, because their energy "yardstick"'s length changes as α2. The energy loss in that case is one part in 102x. The thermal energy per atom in typical materials is a few
times 1.38x10-23J/K, however, so the shortfall at temperatures of a few hundred K from a part-per-million change in alpha will be on the order of 10-32J per atom, far lower than the spring energy release and unable to absorb more than the merest fraction of it (like, one part in 1030 or so). Further, the ordinary heating from compression would recover the shortfall (exactly!) all on its own, without the spring energy release.

Long story short: anything not very gradual will cook or even explode you, absent some exotic physics related, presumably, to how alpha itself was able to change. Anything faster than a sizable fraction of a second will splat you with g-forces on top of nuking you to some ridiculously huge temperature or imploding you into a black hole.

What about long-term effects, such as from a very gradual change?

Absent highly nonlinear effects in, say, the chemistry and electrophysics of heavier elements (which could affect e.g. the structural strength of steel, the mechanical stability of UF₆ fuel elements, semiconductor physics, and other possibly sensitive technological systems) there are surprisingly few for alpha changes less than a percent or so.

At that point, there are increasingly major consequences to planetary habitability because of changes to stars.

http://deepblue.lib.umich.edu/bitstream/2027.42/64225/1/jcap8_08_010.pdf

The above paper contains a mathematical model of a(n ideal, perfectly spherical) star as a function of alpha, G, and a few other constants. It's a bit hairy to pick through it to see what the effects are of changing a constant while keeping the star's mass fixed, but it can be done, and the upshot is that luminosity scales as α-3 and radius as α-1 -- yep, the latter says a star changes size with alpha the same way a material object does, despite a star being supported by nuclear rather than just electromagnetic phenomena. (Exception: neutron stars. Degeneracy pressure of neutrons is presumably independent of alpha and depends solely on the strong force.)

A planet sees a bigger luminosity change, though. An observer, or an acre of photosynthesizing plants, or a square km of heat-absorbing ocean, changes size as α-2 and so receives an immediate change in solar energy flux by the same factor. Long term, as the changes in the star's core work their way out to the surface, that becomes α-5. (The observer perceives the areas as unchanging, but the sun as having become α times as far away, and thus α-2 times its apparent luminosity, consistent with the calculation from an outside viewpoint that didn't change its size units.)

The sun is anticipated to become about 5.5 percent more luminous in the next 600 million years for hydrogen shell migration reasons. At around that time, maintaining a tolerable temperature on Earth (assuming Earth's orbit is undisturbed after all that time) requires atmospheric CO2 to go to zero, suffocating plant life of its carbon source. Leaving CO2 for the plants makes Earth too hot. Therefore, we can consider that the threshold for long-term lethal luminosity increase. Alpha decreasing by about one percent would kill everything with heat, then, as the apparent luminosity would jump by that amount eventually. The immediate increase of just two percent would be sufficient to cause severe climate disturbances, and after the core nuclear burning increase worked its way to the surface, the further increase would spell the end of the planet's biosphere.

A larger magnitude is needed for an alpha increase to cause problems: Earth's near the inner edge of the habitable zone of the Sun, and a CO2 increase could compensate for a fairly large luminosity drop. The Earth may have been largely frozen over repeatedly before about 700 million years ago; back then the Sun was maybe 90% its present luminosity. A 10% drop in apparent luminosity requires a roughly 2% increase in alpha to cause.

Alpha changes larger than a couple of percent will shift nuclear energies enough to kill off the resonances that enable the triple-alpha fusion process in red giant stars. Without this, synthesis of most heavy elements is liable to stop, limiting the future supply of "metals" for planet formation to the present supply.

Colors of stars are also changed. Surface luminosity goes as the square of radius and the fourth power of surface temperature, and also as α-3; radius goes as α-1. If the surface temperature changes as αy then the surface luminosity formula gives α-3 = α-2α4y, which is easy to solve for 4y = -1, so the surface temperature changes as the inverse fourth root of alpha. Wien's Displacement Law says that the product of wavelength peak of blackbody radiation and temperature is a constant, so if that constant is independent of α the wavelength of sunlight changes as the (direct) fourth root of α, i.e. reddens if α increases. The derivation of Wien's Displacement Law appears to be independent of α. So, star color changes with changing alpha, but quite weakly; a very large change (such as an actual doubling of alpha) would be needed to see a pronounced reddening or bluing of stars.

These stellar effects stem from changing alpha (while leaving the strong force alone) making the nuclear fusion Coulomb barrier higher. The effect is similar to shifting the mass-scale of stars up or down as some increasing function of the change in alpha. The nuclear reactions take more energy to cause and release less energy, but the latter effect is actually very slight for even sizable alpha changes (for H->He fusion, anyway -- there, doubling alpha reduces the He nuclear binding energy by only about 5%). The main consequential change is a lower reaction rate for a given temperature, pressure, and density.

Fission reactions are not very sensitive to alpha, as they depend solely on binding energy per nucleon, which as we saw isn't very sensitive to alpha. Very big increases might noticeably increase the energy from uranium fission by making the uranium nucleus less stable, and humongous ones might spontaneously destroy all uranium. A fission reactor would change size, though, with effects similar to a change, varying with α2, in neutron luminosity. Any decently self-regulating reactor wouldn't react to small perturbations but large ones would shut it down (smaller alpha) or make it melt down or even explode (larger alpha) (assuming the alpha change's associated spring energy release somehow disappeared down a hole in the first law of thermodynamics instead of vaporizing it to QGP first).

Alpha changes larger than about 10 percent will have an additional, benign but highly visible, consequence: changes in the colors of butterfly wings. I kid you not.

As alpha changes, the time scale of EM based structures (e.g. your eyes, photospheric plasma emitting light, etc.) and the energy scale of same vary with α2 (energy up, frequency up, duration down). In particular, to an observer the frequency spectrum of light from 5500K plasma doesn't change. However the wavelength does. The observer changes size with α-1, so the observed product of wavelength and frequency, and thus speed, of any wave based on EM phenomena (so, light, water waves, sound waves) is proportional to α. From the observer's perspective, in particular, the speed of light changes with α and the wavelength of a fixed frequency of light changes with it. Light absorption by pigments, including in green leaves and in the retina's green cone cells, is governed by energy, and therefore by frequency; to the observer, then, green leaves are still green and the frequency of 520nm green light is still 1014s-1. But the wavelength seems to be shifted to α*520nm. The color of anything whose color depends on wavelength instead of on frequency therefore shifts, and because their colors come from diffraction gratings, that includes butterfly wings. The observer sees the diffraction gratings in the wings at their usual size, but the wavelength of green light as shifted; once the shift gets up to 10% that's a noticeable change in color (doubling/halving alpha would shift red all the way to blue, or vice versa, as the whole visible spectrum spans only about one factor of two change in wavelength). (In unvarying units, the light wavelength is unchanged but the butterfly wing nanostructure changed size, with the same shift in its response to light.)

Unfortunately, alpha changes slow enough for you or a butterfly to survive will take longer than your life time, and indeed long enough for the butterfly to evolve in response by changing its nanostructures to maintain apparently-unchanged colors, assuming that some selective pressure is operating on those colors and that it's frequency-dependent (the opposite sex butterfly's visual pigments, or a predator's visual pigments, would be -- though the response of those could evolve to shift instead, within bounds set by the sun's color, which also would change in the event of an alpha change that big, reddening for an increase and bluing for a decrease, but only with the fourth root of alpha).

Alpha changes much larger than that, e.g. doublings and more, begin to wreck the periodic table: besides strewing the energy levels on which chemistry depends all over the place, increases make successively lighter nuclei violently unstable, while decreases make successively heavier ones stable and allow more and more isotopes with fewer and fewer neutrons. Past a certain point with increasing alpha, metals are destroyed and fusion becomes impossible as even helium fusion consumes more energy than it releases. Decreasing alpha accelerates nuclear burning in stars, with possibly a fairly sharp breakpoint when 2He becomes sufficiently long-lived. At that point, proton-proton chain fusion becomes vastly faster and more efficient, and every main sequence star very rapidly burns through its fuel and explodes, dousing the universe in helium gas.

One last note on stellar physics. You might object to increasing alpha making stars smaller and fainter, on two grounds: one, higher temperatures are needed to make fusion work and prop the star up against gravity, and two, aren't helium-burning stars, which have double the Coulomb repulsion and less released energy per fusion, red giants, so shouldn't doubling alpha turn hydrogen-burning main-sequence stars into red giants, and smaller alpha increases cause smaller amounts of luminosity and size increase?

1: No, because the mass isn't enough to support such high temperatures. The rate drops, the star shrinks, and gas pressure increases relative to radiation pressure as a mechanism of support. Past a certain point, the star couldn't exist (falls off the bottom of the shifted stellar mass ladder/main sequence) as the gas becomes degenerate before it fuses -- alpha increasing that much halts fusion, results in a core collapse and micro-nova, and leaves a helium white dwarf behind; larger stars go supernova immediately and leave neutron stars.

2: No, because what makes a red giant big and bright isn't the helium burning in the core (which can even switch off for long periods) but the continued hydrogen burning in a shell that is expanding towards the surface of the star. A pure-helium star would be small and faint compared to a normal main sequence star of the same mass, with about half the size and 1/8 the luminosity, similar to how the main sequence star would be if alpha were doubled.</sup>

 

[haael]

In addition to the excellent post of Tweedle I want to say one thing.

The Kaluza-Klein theory claims the existence of fifth compact dimension and the fine structure constant is the length of that dimension. This dimension may bend just like any other dimension. Oscillations of the fine structure constant produce a new scalar particle, the dilaton.

 

[mfb]

@Tweedle: I think you have to be careful here.

- to change the fine-structure constant, you have to define in which way this is done. How does "current distance" relate to "distance after the change"? The definition of a meter is arbitrary, of course, so saying "1m stays 1m" does not help. You can try to express it in Planck units, but if you change c or hbar, you change those (relative to current setups), too.
- interatomic bonds are way weaker than the bonds of electron orbitals. You can compress water (=human) by 1 part in a million with a pressure of just ~2kPa=2kN/m^2. This is small compared to everyday forces (~10kPa at your feet if you are standing on both feet).

 

[Tweedle]

The model I'm using assumes that, if the dimensioned constants that effectively determine units of time and distance (e.g. c) are regarded as constant, all particles remain in the same locations. The electromagnetic forces among them, however, change in magnitude. If the elementary charge is treated as being what changed that might give similar results (though, that model locally violates charge conservation; if the universe as a whole is electrically neutral the alpha-change-wave might be regarded as transporting charge and local conservation can then be restored).

Basically, I'm not so much saying "1m stays 1m" as "particle positions stay put". Nothing instantly teleports or instantly changes velocity, no matter what units are used.

Now I thought of another way to model an object that's suddenly one part in 10^x different in size from what it wants to be; along each dimension it could be regarded as containing a portion of an acoustic wave with a wavelength large in comparison to the object. We take the wavelength as some D large in comparison to the object, and then the particle displacement ξ for the sound wave is D10^x. Displacement relates to acoustic energy density via E = (2πfξ)²ρ. The frequency f = v/D where v is the speed of sound in the medium, and ρ is the density of the medium. Plugging in ρ = 2.7g/cm³ = 2.7x10^-3kg/m³ (typical of granite) and v = 6km/s = 6x10³m/s for a P-wave in Earth's crust gives E = (2π*6x10³m/s*10^x)²*2.7x10^-3kg/m³ = 3.83x10^{6 + 2x}J/m³. This represents the energy along one axis only, so the full energy density calculated this way is 1.15x10^{7 + 2x}J/m³.

For the previously-contemplated value of x = -6 that gives 1.15x10^-5J/m³, which is a vastly smaller energy density (in rock) than the spring constant calculation suggested. (For reference, the spring constant I used was for a deuterium-deuterium bond, picked more or less at random; I expected that would be good enough for an order of magnitude estimate.)

At least one of the energy density calculations is wrong -- one gives a gram of rock yielding 10⁸ times the rock's own rest mass worth of energy and the other gives something that seems much more reasonable. :)

The particle velocity calculation using the acoustic model gives a peak velocity of 2πfξ = 3.77x10^{4 + x}m/s = 3.77x10^-2m/s for x = -6; particle acceleration is to be 2πv/D and for x = -6 that's 1.421x10³m/s² for D = 1m. This calculation indicates that larger objects have smaller surface accelerations, so shrink or expand more slowly than smaller objects after alpha changes, in stark disagreement with the spring model in which surface accelerations were larger for larger objects.

Any further insights into this would be appreciated, as would any insights into the likely effects of changing alpha on metals, semiconductors, and other technologically-relevant materials. For example how likely are small alpha changes to cause sudden jumps (up or down) in conductivity of metals and semiconductors, changes in common materials' strengths, and other things like that?

 

[mfb]

"particle positions stay put"

Relative to what?
How do you define an absolute measurement for your particle positions to define "stays at the same place"?

one gives a gram of rock yielding 10⁸ times the rock's own rest mass worth of energy

That is obviously wrong ;)

Density, bulk modulus and the speed of sound are related, so it is not surprising to see similar (small) results with both approaches.

 

[Tweedle]

Yeah. Is the acoustic-energy-based approach giving the right result? At least to within an order of magnitude or so.

 

[mfb]

Well, at least it uses the relevant quantities. I have some doubts about the quadratic dependence on x - this would imply that the material behaves like a spring and not as the compression module would suggest.

 

[Tweedle]

I calculated the thermal energy per degree Kelvin in granite at 2.2J/m³, so the acoustic energy density noted above for x = -6 seems to represent an unnoticeable heat increase even in a rock near absolute zero. For larger x it can become noticeable; at normal temperatures the added heat is one part in 10^{2x - 7} or so, so x = -3 (a .1% change in alpha) gives a ten percent warming -- room temperature to sauna-warm, or thereabouts.

There'd also be heat released from the decay of the scalar field itself. If we assume that that energy is presently visible as the mysterious "quintessence" causing cosmic acceleration, there's almost no change -- the energy density of dark energy is a joke, compared to typical thermal energy densities in typical materials, at 10^-29g/cm³ = 10^-29*10¹⁴J/cm³ = 10^-9J/m³, four orders of magnitude smaller than the mechanical heat release calculated for x = -6.

Assuming, of course, that the acoustic model is the correct one and I didn't bork up the math. :)

 

[Tweedle]

The vacuum energy release of 10^-9J/m³, incidentally, is about the energy density of the emitted light within one meter of a one-watt power-indicator LED. If the energy was released as light (and since it's the EM field-strength-deciding scalar field this seems plausible) and the wavelength was in the visible range, it would be a fairly mild flash of light; in a hundred-cubic-meter room, equivalent to a few bright lights briefly switching on.

In a large perfect vacuum, the light received every second by a surface would stay constant, as at any given time the volume of decaying field on the past light cone grew as t² but the distance grew as t and so that from a fixed-size volume dropped as t^-2. (This is similar to the Olber's Paradox calculation.) In actual outer space, the light would be absorbed and attenuated by dust and gas as well, so would grow dimmer over time, while the interstellar medium warmed up slightly with the absorbed energy. It would be reradiated by the warmed medium at longer wavelengths. In the (astrophysical) short run this release would warm the universe slightly and modify the CMBR. In the long run there'd be substantial cosmological effects from a vacuum pressure that had contributed negatively to gravitation converting to radiation pressure that contributes positively.

Note: if the released energy reached thermodynamic equilibrium with the CMBR immediately, we'd have 30,000 degrees in the shade. However, a very large proportion would be emitted in intergalactic space where the mean free path of a photon is pretty damn long, so it would take a long time (on human timescales) to reach thermodynamic equilibrium -- long enough for cosmic expansion to dilute the hell out of it, in all likelihood.

As for the long-term cosmological effects: the universe would stop accelerating and go from dark energy dominated back to radiation dominated, and eventually transition to matter dominated, unless it began to collapse before that could happen. Since the total energy density of the universe seems to be at exactly the critical density and wouldn't change, it seems likely it would become a flat, ever-slowing, non-collapsing lambda-less universe like we thought it was in 1980.

Well, except for one thing: if those quasar data are correct, something like this actually happened before and the dark energy came back. Perhaps because the scalar field potential has a series of peaks and valleys, and which is the lowest valley depends on some cosmological parameter that's evolving in time, so the field goes from global minimum to supercooled and awaiting a phase transition every so often.

Note that the foregoing applies no matter what the quintessence scalar field actually is. Maybe it's a Higgs-like field that would cause symmetry breaking among the three quark colors instead -- who knows? Until we have a working TOE, nobody does. :)

The curious thing is that, depending on what actually changed when the dark energy decayed, and what form of radiation it decayed into, it might be a survivable event; the direct energy release doesn't seem to be enough to cook everything. More like a camera flash going off (indoors) or some several extra full moons worth of light all night, every night for a while (outdoors). It seems it's the changed particle physics rules that might get you, not the direct energy release.

Of course, if it's been decaying every so often for the past few billion years, and was alpha changing by minute quantities each time, it's already happened without effects on Earth life worse than the odd mass extinction here and there. And, if that deadly, also isn't likely again any time soon, based on the only-every-few-tens-of-millions-of-years frequencies of those.

But even that is probably science fiction. The quasar data are more likely wrong than the Oklo data. Though the above is consistent with one set of quasar data being right, Oklo being wrong, the no-change-right-now data being right (if it changes in a quantized fashion every few tens or hundreds of millions of years or whatever rather than smoothly), and the we-don't-observe-a-really-low-mass-scalar-boson data being right (if, again, the field is stable between fairly abrupt changes rather than varying smoothly, the boson can be quite massive).

What form of radiation would be produced? The field decay would produce, first, heavy and presumably unstable scalar bosons, which would decay in turn. If each decayed into two photons they'd be gamma rays at any plausible boson mass. (Not healthy. Even if you were in a coffin-sized lead box some would be produced inside your own body.) A more complex decay mode might produce more, longer-wavelength photons, and possibly other particles (e.g. a dark matter particle plus a photon, or just dark matter, or electron-positron pairs which of course would give rise to more nasty gamma rays).

There is, of course, one way alpha could be changing smoothly and very slowly with no observed low-mass scalar boson. And that's if the scalar boson is the dark matter. In that case, the field decayed long ago (and dark energy is something else), producing dark matter, and the twin causes of alpha changes would be changes in dark matter concentration nearby and long-term dilution from cosmic expansion and dark matter annihilations. Any area with fewer of the scalar bosons would have a lower energy of the field in that area, and possibly a slightly different value of alpha. Of course the force associated with the bosons would push and pull on all electromagnetically-interacting particles, noticeably at lower masses, but this effect and that of the dark matter's gravity could, in principle, be difficult to tell apart -- only that something's pushing and pulling matter around that isn't the gravity of baryonic matter. (This might be ruled out, or not, by the actual data on dark matter. It would also suggest that the quasar observations point to a large-scale, shallow gradient in dark matter distribution that should be findable in a dark matter survey, with whatever cause.)