SETI at Planck Energy: When Particle Physicists Become Cosmic Engineers

Abstract

What is the meaning of the Fermi Paradox -are we alone or is starfaring rare? Can general relativity be united with quantum mechanics? The searches for answers to these questions could intersect. It is known that an accelerator capable of energizing particles to the Planck scale requires cosmic proportions. The energy required to run a Planck accelerator is also cosmic, of order 100 M ⊙ c 2 for a hadron collider, because the natural cross section for Planck physics is so tiny. If aliens are interested in fundamental physics, they could resort to cosmic engineering for their experiments. These colliders are detectable through the vast amount of "pollution" they produce, motivating a YeV SETI program. I investigate what kinds of radiation they would emit in a fireball scenario, and the feasibility of detecting YeV radiation at Earth, particularly YeV neutrinos. Although current limits on YeV neutrinos are weak, Kardashev 3 YeV neutrino sources appear to be at least 30-100 Mpc apart on average, if they are long-lived and emit isotropically. I consider the feasibility of much larger YeV neutrino detectors, including an acoustic detection experiment that spans all of Earth's oceans, and instrumenting the entire Kuiper Belt. Any detection of YeV neutrinos implies an extraordinary phenomenon at work, whether artificial and natural. Searches for YeV neutrinos from any source are naturally commensal, so a YeV neutrino SETI program has value beyond SETI itself, particularly in limiting topological defects. I note that the Universe is very faint in all kinds of nonthermal radiation, indicating that cosmic engineering is extremely rare.

The Log Log Prior for the Frequency of Extraterrestrial Intelligences

“…SETI has sought evidence for extraterrestrials through many programs and an increasing number of methods, from the traditional surveys for radio broadcasts (e.g., Tarter 1985;Blair et al 1992;Horowitz & Sagan 1993;Anderson et al 2002;Gray & Ellingsen 2002;Siemion et al 2010), to searches for laser light (Shvartsman et al 1993;Reines & Marcy 2002;Howard et al 2004;Hanna et al 2009;Borra 2012), high energy radiation (Harris 2002; see also Learned 1994;Corbet 1997;Lacki 2015), extraterrestrial technology in the Solar System (Freitas 1983;Steel 1995), artificial "megastructures" the sizes of planets (Arnold 2005;Wright et al 2016;Boyajian et al 2016) or star systems (Slysh 1985;Timofeev et al 2000;Jugaku & Nishimura 2004;Carrigan 2009;Villarroel et al 2016), and the engineering of entire galaxies (Kardashev 1964;Annis 1999;Wright et al 2014a;Griffith et al 2015;Zackrisson et al 2015;Lacki 2016). But so far, no alien societies have been found yet, and there is no consensus about what that means (Brin 1983;Ćirković 2009).…”

Type III Societies (Apparently) Do Not Exist

“…Or perhaps we could abandon the waste heat idea entirely. But as I pointed out in Lacki (2015), there are no signs of non-thermal emission from Type III societies either. The quietness of the cosmic radio background, for example, implies that less than 10 −5 of the Universe's luminosity is converted into radio broadcasts.…”

“…Reasons for a relatively high f after -I think there are plausible motives for cosmic engineering, suggesting a relatively large f after . Aside from sheer expansionism, some scientific experiments might require cosmic engineering to be carried out, in particular building particle accelerators to test Planckscale physics (Lacki 2015). Although very esoteric now, Planck-scale physics could determine the ultimate limits of technology, like whether traversable wormholes can be built (e.g., Morris & Thorne 1988), which might become an especially pressing issue as the cosmic expansion accelerates and most of the Universe falls out of contact.…”

“…SETI also tends to examine underexplored regions of parameter space, as noted by Harwit (1981). For example, it provides a motivation for searching for very brief pulses of radio emission (Siemion et al 2010;Messerschmitt 2014) and visible light (Howard et al 2004;Borra 2012), photon orbital angular momentum (Harwit 2003), and YeV neutrinos (Lacki 2015). From a purely commensal point of view, SETI brings the possibility of finding unexpected natural phenomena.…”

Sunscreen: Photometric Signatures of Galaxies Partially Cloaked in Dyson Spheres

“…First, they can use large amounts of power to produce non-thermal radiation that we can detect. The typical example is the radio beacon designed to be found by astronomers within millions of light years (Horowitz & Sagan 1993), but this can also take the form of high energy radiation from pulsars or X-ray binaries, modulated to act as a beacon, or even as pollution from particle accelerators (Chennamangalam et al 2015;Lacki 2015). Second, they can move stars and gas around within galaxies, making the galaxy look strange to us (Badescu & Cathcart 2006;Carrigan 2012;Voros 2014).…”