If we’re to imagine an alien civilization with the interest in and ability to communicate with other civilizations, even those as (presumably) far-flung as Earth, then we have to imagine that those civilizations are pretty well dedicated to scientific research, particularly physics research. The aliens will want to understand all of the exotic varieties of matter and forces as much as we do, and maybe much more than we do (perhaps skipping the military trillions in favour of research).
This likelihood of distant very high-energy physics research might open up new possibilities in alien detection, according to new calculations by Princeton physicist Brian Lacki.
The idea is this: In order to completely explore physics, it may be required to search for particles at increasingly enormous high energies. While the particles of the current physics Standard Model mostly exist at reasonable, producible (as in the Large Hadron Collider) energy levels, it’s possible that searches beyond the model—for things like dark matter, missing antimatter, and what’s behind flip-flopping neutrinos—won’t be found anywhere near this range. And there’s an enormous energy gap between the picture we have now and the Planck energy, which is the boundary line where the smooth, continuous sheet of space-time as described by Einstein’s theories of relativity becomes the granular, discrete world of quantum physics.
If it turns out there’s no new physics, or physics beyond the Standard Model, left in our energy neighborhood, things get tricky really fast. Consider what it took to achieve the energies of the LHC; that’s a puff of smoke compared to what might be required. This is what physicists call the “nightmare scenario,” where new physics becomes seemingly out of reach. As accelerators achieve higher and higher energies, the electromagnetic fields required will become so great that the devices themselves risk becoming their own black holes. If we could even build them.
How does any of this have to do with the hunt for aliens? “I propose curiosity as a motivation for cosmic engineering,” Lacki writes in a preprint article posted to arXiv. That is, we might be able to detect aliens by their own efforts to understand physics at its deepest.
“In discussions of the Nightmare Scenario and the physics desert,” Lacki continues, “the idea of probing Planck scale physics directly is generally dismissed because it would require a particle accelerator that is ‘as big as the Solar System,’ ‘the size of the Galaxy,’ or ‘the size of the whole Universe.’ But starfaring ETs conceivably could build an accelerator the size of a galaxy over a few million years. If ETs are interested in fundamental physics, they may resort to such engineering. So why not look for artificial particle accelerators that are literally the size of a galaxy?” And such an alien endeavour might then be detectable by humans on Earth.
It sounds a bit batty because it is. But it’s also illustrative of, first, the difficulties in the whole alien-hunting enterprise—e.g. what constitutes a legitimate detection “channel”—and, second, the whole mess of potential scientific doom that lies between our current myopic snapshot of particle physics and the mythic Planck particle, which would lie at the boundary between quantum and classical physics, existing as a the tiniest conceivable black hole in existence.
But back to the detector. Lacki says it would have to be several times the radius of our own Sun to reach the required energies, yet even if such a thing were possible, there really aren’t any materials that can be imagined to withstand the ensuing forces. So, he suggests that it may be possible to harness the energy of a black hole for the task of accelerating particles and, as he shows in his calculations, the resulting neutrino waste might pack enough energy to make the trip to Earth, where we might be able to detect it (using vast arrays of suboceanic hydrophones, but that’s another story).
Meanwhile, in comments to Physics World, physics personality Paul Davies, current chair of the SETI: Post-Detection Science and Technology Taskgroup of the International Academy of Astronautics, notes one potential fatal flaw. Why would the aliens keep their accelerator running? Assuming the device achieved its goals, it seems reasonable that it would be abandoned (however one abandons a black hole). We’d then be hunting for just a single peak.
“Why do it?,” Davies asks. “Perhaps to create a baby universe or some other exotic space–time sculpture. Why do that? Perhaps because this hypothetical civilization feels it faces a threat of cosmic dimensions. What might that threat be? I have no idea! However, a civilization that knows a million times more than humanity might perceive all sorts of threats of which we are blissfully unaware.” Fair enough.