Hostname: page-component-848d4c4894-nr4z6 Total loading time: 0 Render date: 2024-05-22T20:22:58.411Z Has data issue: false hasContentIssue false

Planck frequencies as Schelling points in SETI

Published online by Cambridge University Press:  07 September 2020

Jason T. Wright*
Department of Astronomy & Astrophysics and Center for Exoplanets and Habitable Worlds and Penn State Extraterrestrial Intelligence Center 525 Davey Laboratory, The Pennsylvania State University, University Park, PA16802, USA
Author for correspondence: Jason T. Wright, E-mail:


In SETI, when searching for ‘beacons’ – transmissions intended for us and meant to get our attention – one must guess the appropriate frequency to search by considering what frequencies would be universally obvious to other species. This is a well-known concept in game theory, where such solutions to a non-communicative cooperative game (such as a mutual search) are called ‘Schelling points’. It is noteworthy, therefore, that when developing his eponymous units, Planck called them ‘natural’ because they ‘remain meaningful for all times and also for extraterrestrial and non-human cultures’. Here, I apply Planck's suggestion in the context of Schelling points in SETI with a ‘Planck Frequency Comb’, constructed by multiplying the Planck energy by integer powers of the fine structure constant. This comb includes a small number of frequencies in regions of the electromagnetic spectrum where laser and radio SETI typically operates. Searches might proceed and individual teeth in the comb, or at many teeth at once, across the electromagnetic spectrum. Indeed, the latter strategy can be additionally justified by the transmitter's desire to signal at many frequencies at once, to improve the chances that the receiver will guess one of them correctly. There are many arbitrary and anthropocentric choices in this comb's construction, and indeed one can construct several different frequency combs with only minor and arbitrary modifications. This suggests that it may be fruitful to search for signals arriving in frequency combs of arbitrary spacing. And even though the frequencies suggested here are only debatably ‘better’ than others proposed, the addition of the Planck Frequency Comb to the list of ‘magic frequencies’ can only help searches for extraterrestrial beacons.

Research Article
Copyright © The Author(s), 2020. Published by Cambridge University Press

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)


Astropy Collaboration, Price-Whelan, AM, Sipőcz, BM, Günther, HM, Lim, PL, Crawford, SM, Conseil, S, Shupe, DL, Craig, MW, Dencheva, N, Ginsburg, A, Van der Plas, JT, Bradley, LD, Pérez-Suárez, D, de Val-Borro, M, Aldcroft, TL, Cruz, KL, Robitaille, TP, Tollerud, EJ, Ardelean, C, Babej, T, Bach, YP, Bachetti, M, Bakanov, AV, Bamford, SP, Barentsen, G, Barmby, P, Baumbach, A, Berry, KL, Biscani, F, Boquien, M, Bostroem, KA, Bouma, LG, Brammer, GB, Bray, EM, Breytenbach, H, Buddelmeijer, H, Burke, DJ, Calderone, G, Cano Rodríguez, JL, Cara, M, Cardoso, JVM, Cheedella, S, Copin, Y, Corrales, L, Crichton, D, D'Avella, D, Deil, C, Depagne, É, Dietrich, JP, Donath, A, Droettboom, M, Earl, N, Erben, T, Fabbro, S, Ferreira, LA, Finethy, T, Fox, RT, Garrison, LH, Gibbons, SLJ, Goldstein, DA, Gommers, R, Greco, JP, Greenfield, P, Groener, AM, Grollier, F, Hagen, A, Hirst, P, Homeier, D, Horton, AJ, Hosseinzadeh, G, Hu, L, Hunkeler, JS, Ivezić, Ž, Jain, A, Jenness, T, Kanarek, G, Kendrew, S, Kern, NS, Kerzendorf, WE, Khvalko, A, King, J, Kirkby, D, Kulkarni, AM, Kumar, A, Lee, A, Lenz, D, Littlefair, SP, Ma, Z, Macleod, DM, Mastropietro, M, McCully, C, Montagnac, S, Morris, BM, Mueller, M, Mumford, SJ, Muna, D, Murphy, NA, Nelson, S, Nguyen, GH, Ninan, JP, Nöthe, M, Ogaz, S, Oh, S, Parejko, JK, Parley, N, Pascual, S, Patil, R, Patil, AA, Plunkett, AL, Prochaska, JX, Rastogi, T, Reddy Janga, V, Sabater, J, Sakurikar, P, Seifert, M, Sherbert, LE, Sherwood-Taylor, H, Shih, AY, Sick, J, Silbiger, MT, Singanamalla, S, Singer, LP, Sladen, PH, Sooley, KA, Sornarajah, S, Streicher, O, Teuben, P, Thomas, SW, Tremblay, GR, Turner, JEH, Terrón, V, van Kerkwijk, MH, de la Vega, A, Watkins, LL, Weaver, BA, Whitmore, JB, Woillez, J, Zabalza, V and Astropy Contributors (2018) The Astropy project: building an open-science project and status of the v2.0 core package. Astronomical Journal 156, 123.Google Scholar
Astropy Collaboration, Robitaille, TP, Tollerud, EJ, Greenfield, P, Droettboom, M, Bray, E, Aldcroft, T, Davis, M, Ginsburg, A, Price-Whelan, AM, Kerzendorf, WE, Conley, A, Crighton, N, Barbary, K, Muna, D, Ferguson, H, Grollier, F, Parikh, MM, Nair, PH, Unther, HM, Deil, C, Woillez, J, Conseil, S, Kramer, R, Turner, JEH, Singer, L, Fox, R, Weaver, BA, Zabalza, V, Edwards, ZI, Azalee Bostroem, K, Burke, DJ, Casey, AR, Crawford, SM, Dencheva, N, Ely, J, Jenness, T, Labrie, K, Lim, PL, Pierfederici, F, Pontzen, A, Ptak, A, Refsdal, B, Servillat, M and Streicher, O (2013) Astropy: a community Python package for astronomy. Astronomy and Astrophysics 558, A33.Google Scholar
Blair, DG and Zadnik, MG (1993) A list of possible interstellar communication channel frequencies for SETI. Astronomy and Astrophysics 278, 669672.Google Scholar
Blair, DG, Norris, RP, Troup, ER, Twardy, R, Wellington, KJ, Williams, AJ, Wright, AE and Zadnik, MG (1992) A narrow-band search for extraterrestrial intelligence (SETI) using the interstellar contact channel hypothesis. Monthly Notices of the RAS 257, 105109.CrossRefGoogle Scholar
Borra, EF (2012) Searching for extraterrestrial intelligence signals in astronomical spectra, including existing data. Astronomical Journal 144, 181.CrossRefGoogle Scholar
Cocconi, G and Morrison, P (1959) Searching for interstellar communications. Nature 184, 844846.CrossRefGoogle Scholar
Drake, FD and Sagan, C (1973) Interstellar radio communication and the frequency selection problem. Nature 245, 257258.CrossRefGoogle Scholar
Enriquez, JE, Siemion, A, Foster, G, Gajjar, V, Hellbourg, G, Hickish, J, Isaacson, H, Price, DC, Croft, S, DeBoer, D, Lebofsky, M, MacMahon, DHE and Werthimer, D (2017) The breakthrough listen search for intelligent life: 1.1–1.9 GHz observations of 692 nearby stars. Astrophysical Journal 849, 104.CrossRefGoogle Scholar
Furlanetto, SR, Oh, SP and Briggs, FH (2006) Cosmology at low frequencies: the 21 cm transition and the high-redshift Universe. Physics Reports 433, 181301.CrossRefGoogle Scholar
Gindilis, L, Davydov, V and Strelnitski, V (1993) New Magic Frequencies for SETI. In Shostak, GS (ed). Third Decennial US-USSR Conference on SETI. Astronomical Society of the Pacific, pp. 161163.Google Scholar
Horowitz, P and Sagan, C (1993) Five years of project META - an all-sky narrow-band radio search for extraterrestrial signals. Astrophysical Journal 415, 218235.CrossRefGoogle Scholar
Kardashev, NS (1979) Strategy for the search for extraterrestrial intelligence. Acta Astronautica 6, 3346.CrossRefGoogle Scholar
MacMahon, DHE, Price, DC, Lebofsky, M, Siemion, APV, Croft, S, DeBoer, D, Enriquez, JE, Gajjar, V, Hellbourg, G, Isaacson, H, Werthimer, D, Abdurashidova, Z, Bloss, M, Brandt, J, Creager, R, Ford, J, Lynch, RS, Maddalena, RJ, McCullough, R, Ray, J, Whitehead, M and Woody, D (2018) The breakthrough listen search for intelligent life: a wideband data recorder system for the Robert C. Byrd Green Bank telescope. Publications of the ASP 130, 044502.Google Scholar
Morrison, I (2017) constraining the discovery space for artificial interstellar signals.Google Scholar
Narusawa, S-y., Aota, T and Kishimoto, R (2018) Which colors would extraterrestrial civilizations use to transmit signals?: the ‘magic wavelengths’ for optical SETI. New Astronomy 60, 6164.CrossRefGoogle Scholar
Planck, M (1900) Ueber irreversible Strahlungsvorgänge. Annalen der Physik 306, 69122.CrossRefGoogle Scholar
Planck Collaboration, Aghanim, N, Armitage-Caplan, C, Arnaud, M, Ashdown, M, Atrio-Barandela, F, Aumont, J, Baccigalupi, C, Banday, AJ, Barreiro, RB, Bartlett, JG, Benabed, K, Benoit-Lévy, A, Bernard, JP, Bersanelli, M, Bielewicz, P, Bobin, J, Bock, JJ, Bond, JR, Borrill, J, Bouchet, FR, Bridges, M, Burigana, C, Butler, RC, Cardoso, JF, Catalano, A, Challinor, A, Chamballu, A, Chiang, HC, Chiang, LY, Christensen, PR, Clements, DL, Colombo, LPL, Couchot, F, Crill, BP, Curto, A, Cuttaia, F, Danese, L, Davies, RD, Davis, RJ, de Bernardis, P, de Rosa, A, de Zotti, G, Delabrouille, J, Diego, JM, Donzelli, S, Doré, O, Dupac, X, Efstathiou, G, Enßlin, TA, Eriksen, HK, Finelli, F, Forni, O, Frailis, M, Franceschi, E, Galeotta, S, Ganga, K, Giard, M, Giardino, G, González-Nuevo, J, Górski, KM, Gratton, S, Gregorio, A, Gruppuso, A, Hansen, FK, Hanson, D, Harrison, DL, Helou, G, Hildebrandt, SR, Hivon, E, Hobson, M, Holmes, WA, Hovest, W, Huffenberger, KM, Jones, WC, Juvela, M, Keihänen, E, Keskitalo, R, Kisner, TS, Knoche, J, Knox, L, Kunz, M, Kurki-Suonio, H, Lähteenmäki, A, Lamarre, JM, Lasenby, A, Laureijs, RJ, Lawrence, CR, Leonardi, R, Lewis, A, Liguori, M, Lilje, PB, Linden-Vørnle, M, López-Caniego, M, Lubin, PM, Macías-Pérez, JF, Mandolesi, N, Maris, M, Marshall, DJ, Martin, PG, Martínez-González, E, Masi, S, Massardi, M, Matarrese, S, Mazzotta, P, Meinhold, PR, Melchiorri, A, Mendes, L, Migliaccio, M, Mitra, S, Moneti, A, Montier, L, Morgante, G, Mortlock, D, Moss, A, Munshi, D, Naselsky, P, Nati, F, Natoli, P, Nørgaard-Nielsen, HU, Noviello, F, Novikov, D, Novikov, I, Osborne, S, Oxborrow, CA, Pagano, L, Pajot, F, Paoletti, D, Pasian, F, Patanchon, G, Perdereau, O, Perrotta, F, Piacentini, F, Pierpaoli, E, Pietrobon, D, Plaszczynski, S, Pointecouteau, E, Polenta, G, Ponthieu, N, Popa, L, Pratt, GW, Prézeau, G, Puget, JL, Rachen, JP, Reach, WT, Reinecke, M, Ricciardi, S, Riller, T, Ristorcelli, I, Rocha, G, Rosset, C, Rubiño-Martín, JA, Rusholme, B, Santos, D, Savini, G, Scott, D, Seiffert, MD, Shellard, EPS, Spencer, LD, Sunyaev, R, Sureau, F, Suur-Uski, AS, Sygnet, JF, Tauber, JA, Tavagnacco, D, Terenzi, L, Toffolatti, L, Tomasi, M, Tristram, M, Tucci, M, Türler, M, Valenziano, L, Valiviita, J, Van Tent, B, Vielva, P, Villa, F, Vittorio, N, Wade, LA, Wandelt, BD, White, M, Yvon, D, Zacchei, A, Zibin, JP and Zonca, A (2014) Planck 2013 results. XXVII. Doppler boosting of the CMB: Eppur si muove. Astronomy and Astrophysics 571, A27.Google Scholar
Price, DC, Enriquez, JE, Brzycki, B, Croft, S, Czech, D, DeBoer, D, DeMarines, J, Foster, G, Gajjar, V, Gizani, N, Hellbourg, G, Isaacson, H, Lacki, B, Lebofsky, M, MacMahon, DHE, Pater, Id, Siemion, APV, Werthimer, D, Green, JA, Kaczmarek, JF, Maddalena, RJ, Mader, S, Drew, J and Worden, SP (2020) The breakthrough listen search for intelligent life: observations of 1327 nearby stars over 1.10–3.45 GHz. Astronomical Journal 159, 86.CrossRefGoogle Scholar
Reid, MJ, Menten, KM, Brunthaler, A, Zheng, XW, Dame, TM, Xu, Y, Wu, Y, Zhang, B, Sanna, A, Sato, M, Hachisuka, K, Choi, YK, Immer, K, Moscadelli, L, Rygl, KLJ and Bartkiewicz, A (2014) Trigonometric parallaxes of high mass star forming regions: the structure and kinematics of the milky way. Astrophysical Journal 783, 130.CrossRefGoogle Scholar
Schelling, T (1960) The strategy of conflict. Galaxy book. Cambridge, MA: Harvard University Press.Google Scholar
Schönrich, R, Binney, J and Dehnen, W (2010) Local kinematics and the local standard of rest. Monthly Notices of the RAS 403, 18291833.CrossRefGoogle Scholar
Sheikh, SZ, Wright, JT, Siemion, A and Enriquez, JE (2019) Choosing a maximum drift rate in a SETI search: astrophysical considerations. Astrophysical Journal 884, 14.CrossRefGoogle Scholar
Sheikh, SZ, Siemion, A, Enriquez, JE, Price, DC, Isaacson, H, Lebofsky, M, Gajjar, V and Kalas, P (2020) The breakthrough listen search for intelligent life: a 3.95–8.00 GHz search for radio technosignatures in the restricted earth transit zone. Astronomical Journal 160, 29.CrossRefGoogle Scholar
Siemion, APV, Demorest, P, Korpela, E, Maddalena, RJ, Werthimer, D, Cobb, J, Howard, AW, Langston, G, Lebofsky, M, Marcy, GW and Tarter, J (2013) A 1.1–1.9 GHz SETI survey of the Kepler field I. A search for narrow-band emission from select targets. Astrophysical Journal 767, 94.CrossRefGoogle Scholar
Tarter, JC, Cuzzi, J, Black, D and Clark, T (1980) A high-sensitivity search for extraterrestrial intelligence at lambda 18 CM. Icarus 42, 136144.CrossRefGoogle Scholar
Tellis, NK and Marcy, GW (2015) A search for optical laser emission using Keck HIRES. Publications of the ASP 127, 540.Google Scholar
Tellis, NK and Marcy, GW (2017) A search for laser emission with megawatt thresholds from 5600 FGKM stars. Astronomical Journal 153, 251.CrossRefGoogle Scholar
Weber, A (1995) A Biochemical Magic Frequency Based on the Reduction Level of Biological Carbon. In Shostak, G. S., (eds), Progress in the Search for Extraterrestrial Life., vol. 74 of Astronomical Society of the Pacific Conference Series, p. 479.Google Scholar
Wright, JT (2017) Exoplanets and SETI. Handbook of Exoplanets. In Deeg, Hans J., Belmonte, Juan Antonio (eds), Springer Living Reference Work, p. 186, Springer, ISBN: 978-3-319-30648-3, 2017, id.186.Google Scholar
Wright, JT and Eastman, JD (2014) Barycentric corrections at 1 cm s1 for precise Doppler velocities. Publications of the ASP 126, 838852.Google Scholar
Wright, JT, Kanodia, S and Lubar, E (2018 a) How much SETI has been done? Finding needles in the n-dimensional cosmic Haystack. Astronomical Journal 156, 260.CrossRefGoogle Scholar
Wright, JT, Sheikh, S, Almár, I, Denning, K, Dick, S, Tarter, J (2018 b) Recommendations from the Ad Hoc Committee on SETI Nomenclature. arXiv e-prints, page arXiv:1809.06857.Google Scholar