“The nightmare of particle physics is the dream of astronomers searching for extraterrestrials,” says astrophysicist Brian Lacki, at the Institute for Advanced Studies in Princeton, New Jersey, who proposes that advanced civilizations may want to build a black-hole-powered particle accelerator to study physics.
Astrophysicist Paul Davies at Arizona State told Hamish Johnston of Physics World, that he believes that it is very difficult for homo sapiens of Planet Earth today to understand why an advanced civilization would want to build a particle accelerator to study physics at “Planck-scale” energies.
“Why do it?” Davies asks. “Perhaps to create a baby universe or some other exotic space–time sculpture,” he conjectures. “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.”
Lacki’s study, SETI at Planck Energy: When Particle Physicists Become Cosmic Engineers, asks 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, Lacki writes. “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_sun 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 Lacki says 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.
Lacki contemplates 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. He notes that the Universe is very faint in all kinds of nonthermal radiation, indicating that cosmic engineering is extremely rare.
Lacki suggests that if electric fields are used for acceleration, the particle accelerator would have to be at least 10 times the radius of the Sun. However, a magnetic synchrotron-type accelerator could be somewhat smaller. Lacki adds that normal materials could not withstand the strong electromagnetic fields. But a natural solution already exists in cosmos — one of the few places where such a high energy density could exist is in the vicinity of a black hole, which he argues could be harnessed to create a Planck-scale accelerator.
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And if such a cosmic collider exists in a corner of the universe, could we detect it here on Earth? Yes, says Lacki, who has completed calculations that suggest that if such an accelerator exists, it would produce yotta electron-volt (YeV or 1024 eV) neutrinos that could be detected here on Earth.
As a result, reports Johnston, Lacki is calling on astronomers involved in the search for extraterrestrial intelligence (SETI) to look for these ultra-high-energy particles. This is supported by astrophysicist Paul Davies of Arizona State University, who believes that the search should be expanded beyond the traditional telescope searches.
Like humanity, writes Johnston, “it seems reasonable to assume that an advanced alien civilization would have a keen interest in physics, and would build particle accelerators that reach increasingly higher energies. This energy escalation could be the result of the ‘nightmare scenario’ of particle physics in which there is no new physics at energies between the TeV energies of the Standard Model and the 1028 eV Planck energy (10 XeV) – where the quantum effects of gravity become strong.”
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However, quantum physics suggests the density of electromagnetic energy needed to reach the Planck scale is so great that the device would be in danger of collapsing into a black hole. However, Lacki points out that a clever designer could, in principle, get round this problem and “reaching [the] Planck energy is technically allowed, if extremely difficult”.
Colliding particles at tens of XeVs is only half the battle, however. Lacki calculates that the vast majority of collisions in such a cosmic collider would be of no interest to alien researchers. To get useful information about Planck-scale physics, he surmizes that the total collision rate in the accelerator would have to be about 1024 times that of the Large Hadron Collider.
“As such, accelerators built to detect Planck events are extremely wasteful and produce vast amounts of ‘pollution’,” explains Lacki.
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While much of this pollution would be extremely high-energy particles, that in principle could reach Earth, it is unclear whether they could escape the intense electromagnetic fields within the collider. Furthermore, like colliders here on Earth, the builders of a cosmic machine would probably try to shield the surrounding region from damaging radiation.
Lacki’s analysis suggests that neutrinos are the only particles that are likely to reach Earth.
Read more at Physics World
The Daily Galaxy, Sam Cabot, via Physics World and arXiv
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