Astrobiology and SETI

A Neutrino Beam Beacon

If you want to look for potential artifacts of superior civilizations, as do those training what’s now being referred to as Dysonian SETI, then it pays to take heed to the daddy of the sector. My good friend Al Jackson has achieved so and presents a Dyson quote to steer off his new paper: “So the first rule of my game is: think of the biggest possible artificial activities with limits set only by the laws of physics and look for those.” Dyson wrote that in a 1966 paper that repays research immediately (citation under). Its title: The Search for Extraterrestrial Know-how.” Dysonian SETI is an enormous, brawny zone where speculation is coin of the realm and the imagination is inspired to be pushed to the limit.

Jackson is intrigued, as are so many people, with the thought of utilizing the Solar’s gravitational lens to make observations of different stars and their planets. Our current e-mail dialog brought up the identify of Von Eshleman, the Stanford electrical engineer and pioneer in planetary and radio sciences who died two years ago in Palo Alto at 93. Eshleman was writing about gravitational lensing prospects at a time once we had no applied sciences that would take us to 550 AU and past, the world the place lensing results begin to be felt, however he saw that an instrument there might make observations of objects immediately behind the Sun as their mild was targeted by it.

Claudio Maccone has been working this terrain for a very long time, and the entire concept is laid out in his seminal Deep Area Flight and Communications: Exploiting the Sun as a Gravitational Lens (Springer Praxis, 2009). There’s much to be stated about lensing and area missions, and it’s heartening to see curiosity in scientists inside the Breakthrough Starshot undertaking — a sail shifting at 20 % of lightspeed gets us to 550 AU and beyond relatively shortly. By my back of the envelope figuring, journey time is just a bit in need of 16 days.

There can be no want for Starshot to strategy 550 AU at 20 % of c, in fact. The focal line runs to infinity, but as Jackson explains when operating by means of gravitational lensing’s calculations, we will assume beam intensity regularly diminished by absorption within the interstellar medium, although all of this with little beam divergence. Just find out how to use the Solar’s gravity lens (a relay for returning knowledge from a star mission, I assume) and easy methods to configure mission parameters to get to the lensing area and use it are beneath debate.

Transmitting Via a Gravitational Lens

However back to Al Jackson’s paper, which presents us a take on gravitational lensing that I have by no means earlier than encountered [see my addendum at the end of this post for a correction]. What he’s proposing is that a complicated civilization of the type Dyson is occupied with would have the potential of utilizing a gravitational lens to transmit knowledge. He’s turned the method round, from remark to beacon or different type of communication. And he’s working with neutrinos, the place attenuation from the interstellar medium is negligible.

A gravitational lens does not, in fact, have to be a star, but could possibly be a better mass object like a neutron star. In Jackson’s considering, a KII civilization might place a neutrino beam transmitting station around a neutron star. We make neutrino beams at this time by way of the decay of pi mesons, because the writer reminds us, when giant accelerators increase protons to relativistic energies that strike a goal, producing pions and kaons that decay into neutrinos, electrons and muons. What counts for Jackson’s functions is that pions and kaons could be targeted to supply a beam of neutrinos.

For a stellar mass gravitational lens and 1 Gev neutrinos, the wavelength is about 10-14 cm, the achieve is roughly 1020! The characteristic radius of foremost region of concertation is about one micron; nevertheless there’s an effective flux out to about one centimeter.

And as talked about above:

This beam intensity extends to infinity only diminished by absorption within the interstellar medium, encounters with an enormous object like a planet or star and a very small beam divergence.

Picture: That is Determine 6 from the paper. Caption: A schematic illustration of a attainable neutrino accelerator-transmitter, the accelerator and lens (nothing to scale). Credit score: A. A. Jackson.

A one-centimeter beam creates the problem of specializing in a selected goal, one whose phenomenal pointing accuracy might only be left to our putative advanced civilization. Even so, improve the variety of transmitters and detection becomes easier. Thus Jackson:

Suppose that a K2 sort civilization capable of interstellar flight can reach a neutron star it should have the technological capability to build a beacon consisting of an array of transmitters in a constellation of orbits concerning the neutron star. Let this constellation include 1018 ‘neutrino’ transmitters 1 meter in attribute measurement ‘covering’ the world of a sphere 1000 km in radius with 1018 particle accelerators in orbit… This present day there’s the development of plasma Wakefield particle accelerators which might be meters in measurement [21, 22]. It’s probable that a K2 civilization might construct Wakefield electron accelerators of very small measurement.

Jackson has heeded Dyson, that’s for positive. Keep in mind the latter’s injunction: “…think of the biggest possible artificial activities with limits set only by the laws of physics and look for those.”

What emerges is a ‘constellation of neutrino beam transmitters,’ 1018 in orbit at 1000 neutron star radii, growing the chance of detection, in order that the detection fee at 10,000 mild years becomes roughly 5 per minute. The transmitters have to be configured to seem as point sources to the gravitational lens, again one other leap demanding KII ranges of performance. But when a civilization is making an attempt to be observed, a neutrino beam that takes neutrino detection properly out of the range produced by means of stellar events within the galaxy ought to stand out.

Thus we have now a way for producing directed neutrino sign transmission. Why provide you with such? Reminiscent of Dyson, we will think about the necessity to look at the range of attainable ETI applied sciences, hoping to create a catalog that would clarify future anomalous observations. Jackson’s beam might be used as what he calls a ‘honey pot’ to draw attention to an electromagnetic transmitter broadcasting extra refined info. But we might not essentially be capable of perceive what makes use of a complicated civilization would make of such capabilities. We’d should content ourselves merely with the potential for observing them.

As Jackson points out, a KII civilization “…would likely have the resources to finesse the technology in a smarter way,” so what we’ve got here’s a demonstration that a thing may be potential, while we’re left to marvel in what different methods a neutrino supply can be utilized to supply detections at cosmic distances. Going deep to take a position on applied sciences far beyond our attain right now should, as Dyson says, remind us to stay inside the realm of recognized physics whereas simultaneously asking about phenomena that advanced engineering might produce. We hope by way of the labors of Dysonian SETI to recognize such signatures if we see them.

Appreciating Von Eshleman

And a digression: When Al introduced up Von Eshleman in our conversations, I began considering back to early gravitational lensing work and Eshleman’s paper, written back in 1979 however prescient, certainly, of what was to return within the type of critical examination of lensing capabilities for area missions. Let me quote Eshleman’s conclusion from the paper, cited under. I’ve a lot more to say about Eshleman’s work, however let’s get into that at one other time. For now:

It has been pointed out that radio, tv, radar, microwave hyperlink, and other terrestrial transmissions are expanding into area at 1 light-year per yr (2). One other technological society close to a neighboring star might obtain the strongest of these immediately with substantial effort and could study an excellent deal concerning the earth and the know-how of its inhabitants. The ideas introduced here recommend that on an imaginary display sufficiently far behind that star, the short-wavelength end of this terrestrial activity is now being played out at substantial amplifications. Properly positioned receivers with antennas of modest measurement might in principle scan the earth and discriminate between totally different sources, mapping such exercise over the earth and studying not solely concerning the know-how of its inhabitants, but in addition about their thoughts. It’s potential that several or many such targeted stories about different worlds at the moment are operating their course on such a big display surrounding our solar, however nobody in this theater is observing them…

I discovered about Eshleman’s work originally via Claudio Maccone and sometimes mirror on the tenacity of concepts as we go from a concept initially recommended by Einstein to a SETI alternative realized by Eshleman to a mission concept detailed by Maccone, and now a possible actual mission critically discussing using gravitational lensing as a relay alternative for knowledge return from Proxima Centauri (Breakthrough Starshot). As it all the time has, the interstellar area demands long-term considering that crosses generations in help of a wide ranging aim.

[Addendum]: Although I hadn’t heard of discussions on using gravitational lensing for transmission, an e-mail just now from Clément Vidal points out that both Claudio Maccone and Vidal himself have appeared into this. In Clément’s case, the reference is Vidal, C. 2011, “Black Holes: Attractors for Intelligence?” at In the direction of a scientific and societal agenda on extra-terrestrial life, Four-5 Oct, Buckinghamshire, Kavli Royal Society International Centre. Summary here. This quote is to the purpose:

“For a few decades, researchers have proposed to use the Sun as a gravitational lens. At 22.45AU and 29.59AU we have a focus for gravitational waves and neutrinos. Starting from 550AU, electromagnetic waves converge. Those focus regions offer one of the greatest opportunity for astronomy and astrophysics, offering gains from 2 to 9 orders of magnitude compared to Earth-based telescopes…It is also worth noting that such gravitational lensing could also be used for communication…Indeed, it is easy to extrapolate the maximal capacity of gravitational lensing using, instead of the Sun, a much more massive object, i.e. a neutron star or a black hole. This would probably constitute the most powerful possible telescope. This possibility was envisioned -yet not developed- by Von Eshleman in (1991). Since objects observed by gravitational lensing must be aligned, we can imagine an additional dilating and contracting focal sphere or artificial swarm around a black hole, thereby observing the universe in all directions and depths.”

The writer of The Starting and the Finish: The Which means of Life in a Cosmological Perspective (2014), Vidal’s considering is examined in The Zen of SETI and elsewhere within the archives.

I’m glad Clément wrote, particularly as it stroke a chord in my memory about Claudio Maccone’s paper on using lenses as a communications software, where the chances are hanging. See The Gravitational Lens and Communications for more. I wrote about this again in 2009 and thus haven’t any good excuse for letting it slip my thoughts!

The paper is Jackson, “A Neutrino Beacon” (preprint). The Dyson paper is “The Search for Extraterrestrial Technology,” in Marshak, ed. Perspectives in Trendy Physics: Essays in Honor of Hans Bethe, New York: John Wiley & Sons 1966. The Eshleman paper is “Gravitational Lens of the Sun: Its Potential for Observations and Communications over Interstellar Distances,” Science Vol. 205 (14 September 1979), pp. 1133-1135 (summary).