TL;DR

I'd propose that weak force life has a tiny change of existing in environments where particles travel at high speeds. A possible example is the jets produced by an active galactic nucleus. At the high energies (and high speeds) particles reach in these jets, the range of the weak force could be sizably extended to the point where it is less negligible than for a low-energy environment, because at high speeds, the $W$ and $Z$ bosons' lifetimes can be dramatically extended. While it's difficult to speculate as to what structures and processes - let alone life - could coherently arrive, I would bet that proton-antiproton collisions and the decay of charged leptons (muons and tau particles) might be potential sources of the $W$ and $Z$ bosons.

The decay problem

The weak force is mediated by three particles: The charged $W^{\pm }$ bosons and the neutral $Z$ boson. Unlike the photon, their cousin, these bosons have mass, approximately 80.4 GeV and 91.2 GeV, respectively. Also unlike the photon, the bosons decay. The $W^{+}$ boson has several decay paths, including hadronic paths (dominated by quark-antiquark pairs) and leptonic paths (a positively charged lepton and its associated neutrino); the $W^{-}$ decays involve the corresponding antiparticles. For the $Z$ bosons, hadronic decays to quarks are also the main contributors, although pairs of charged leptons and their antiparticles may also be produced.

Both particles have half-lives of $\tau \sim {10}^{-25}$ seconds, and so the range of the weak force is approximately $r\approx \tau c\sim {10}^{-17}$ meters, even in the case of relativistic particles. Another way of expressing this uses the derivation of the half-life from Heisenberg's uncertainty principle: $$r\approx \frac{\hslash }{2mc}\propto \frac{1}{m}$$ where $m$ is the mass of the boson. Therefore, by decreasing the mass of the $W$ and $Z$ bosons, you could of course extend the range of the weak force. That said, changing the mass would involve changing weak force coupling constant across the universe, which would cause serious issues.

Time dilation

Changing our fundamental constants seems to be right out, then, so let's stay away from those. Instead, let's see what happens if we try to extend the lifetimes of these bosons through time dilation. Time dilation comes in two flavors: gravitational and special relativistic. It turns out that to dilate time enough to significantly extend $r$, you need to be in a steep gravitational field, quite close to a black hole; this seems an unlikely and unsafe (certainly short-lived) setup.

However, we could extend the range of the weak force by instead having these bosons travel quickly, as happens with muons in Earth's atmosphere. The boson's lifetime should be $\tau =\gamma {\tau }_0$, where $\gamma$ is the Lorentz factor and ${\tau }_0\sim {10}^{-25}$ seconds, from before. The highest Lorentz factors we've seen come from ultra-high energy cosmic rays; the Oh-My-God particle had a kinetic energy of $3.2\times {10}^{20}$ eV, and thus (as you can determine by calculating the relativistic kinetic energy, $T\approx m\gamma c^2$) a Lorentz factor of $\sim {10}^{11}$, corresponding to a speed that differs from $c$ by less than one part in ${10}^{23}$. The boson's lifetime is then $\tau \sim {10}^{-14}$ seconds, and the weak force's range is a surprising $r\sim {10}^{-6}$ meters.

There are some caveats:

• Propelling a particle to this energy requires an active galactic nucleus, and therefore, ambient $W$ and $Z$ bosons can only survive in the jets emitted from such an AGN.
• The jets should be dense with leptons and hadrons, an extreme environment that produces gamma rays and cosmic rays. Interactions should be frequent, and it seems that bosons could very quickly interact with these ambient particles, limiting their range. There could be a limit similar to the GZK limit for cosmic rays, albeit involving these ambient fermions.
• The bosons presumably can't be accelerated to these speeds in the same manner as normal cosmic rays, but they could be produced by high-energy particles in the jets. Proton-antiproton interactions can produce both $W$ and $Z$ bosons; if these interactions transferred the majority of the progenitor's energies to the bosons, we might well see the bosons reach the required energies. This is guesswork on my part, though.

While I would propose AGN jets as an alternative to a4android's neutron star suggestion, simply because they're the only energy sources that could create these Lorentz factors, it seems clear that only these extreme environments could host anything akin to life based on the weak force.

What particle(s) would life be based on?

As you might have guessed, you likely won't see elements per se in these jets. Nuclei, yes, primarily protons. What you will see is, as I mentioned before, a messy soup of hadrons and leptons, producing synchrotron radiation and gamma rays. These particles will make up your building blocks of life.

How will these bosons be produced, then? There are two basic types of weak force interactions: charged current interactions (involving the $W$ bosons) and neutral current interactions (involving the $Z$ boson). Examples include:

• Quark-antiquark interactions from proton-antiproton collisions, as I mentioned above. We see these occur in colliders. Typical pathways involve up and down quarks ($u$ and $d$) and their antiparticles ($\overline{u}$ and $\overline{d}$): $$\overline{d}u\to W^{+},d\overline{u}\to W^{-},u\overline{u}\to Z,d\overline{d}\to Z$$
• Lepton decay, e.g. a muon decaying to a muon neutrino and a $W^{-}$ boson, which then decays to an electron and an electron antineutrino: $$\mu \to {\nu }_{\mu }+W^{-}\to {\nu }_{\mu }+e^{-}+{\overline{\nu }}_e$$

There are other hadronic decay processes, of course (e.g. pion decay); I list the above just as examples. The dominant production processes depend on the ambient fermions and hadrons.

A note on WIMPs

I'd like to second Spencer's suggestion of weakly interacting massive particles, or WIMPs, which remain prime dark matter candidates. They're high-mass particles that interact only via gravity and the weak nuclear force, and hence would be excellent candidates for a creature that primarily uses the weak force insofar as it really couldn't interact in any other way. It does seem unlikely that they would combine in high densities, as dark matter doesn't clump quite like normal matter does, but they remain an interesting possibility.

posted almost 6 years ago

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