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Register a new userSETI strategy with FAST fractality
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We applied the Koch snowflake fractal antenna in planning calibration of the Five-hundred-meter Aperture Spherical radio Telescope (FAST), hypothesizing second-order fractal primary reflectors can optimize the orientated sensitivity of the telescope. Meanwhile, on the grounds of NASA Science Working Group Report in 1984, we reexamine the strategy of Search for Extraterrestrial Intelligence (SETI). A mathematical analysis of the radar equation will be performed in the first section, aiming to make it convenient to design a receiver system that can detect activities of an extraterrestrial civilization, according to the observable region of the narrowband. Taking advantage of the inherent potential of FAST, we simulate the theoretical detection of a Kardashev Type I civilization by a snowflake-selected reflecting area.
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As our ability to undertake more powerful Searches for Extraterrestrial Intelligence (SETI) grows, so does interest in the more controversial endeavour of Messaging Extraterrestrial Intelligence (METI). METI proponents point to the SETI Paradox - if all civilisations refrain from METI then SETI is futile. I introduce Mutual Detectability as a game-theoretic strategy aimed at increasing the success potential of targeted SETI. Mutual detectability is embodied by four laws: mutuality, symmetry, opportunity and superiority. These laws establish how SETI participants can engage each other using game theory principles applied to mutual evidence of mutual existence. The law of superiority establishes an onus to transmit on the party whom both SETI participants can judge to have better quality evidence, or common denominator information (CDI), thus avoiding the SETI Paradox. I argue that transiting exoplanets within the Earth Transit Zone form a target subset that satisfies mutual detectability requirements. I identify the intrinsic time-integrated transit signal strength as suitable CDI. Civilisations on habitable-zone planets of radius $R_{rm p}/R_{oplus} lesssim (L_*/L_{odot})^{-1/7}$ have superior CDI on us, so have game-theory incentive (onus) to transmit. Whilst this implies that the onus to transmit falls on us for habitable planets around $L_* > L_{odot}$ stars, considerations of relative stellar frequency, main-sequence lifetime and planet occurrence mean such systems are likely a small minority. Surveys of the Earth Transit Zone for Earth-analogue transits around sub-solar luminosity hosts, followed up by targeted SETI monitoring of them, represent an efficient strategy compliant with mutual detectability. A choice to remain silent, by not engaging in METI towards such systems, does not in this case fuel concerns of a SETI Paradox.
The Search for Extraterrestrial Intelligence (SETI) attempts to address the possibility of the presence of technological civilizations beyond the Earth. Benefiting from high sensitivity, large sky coverage, an innovative feed cabin for Chinas Five-hundred-meter Aperture Spherical radio Telescope (FAST), we performed the SETI first observations with FASTs newly commisioned 19-beam receiver; we report preliminary results in this paper. Using the data stream produced by the SERENDIP VI realtime multibeam SETI spectrometer installed at FAST, as well as its off-line data processing pipelines, we identify and remove four kinds of radio frequency interference(RFI): zone, broadband, multi-beam, and drifting, utilizing the Nebula SETI software pipeline combined with machine learning algorithms. After RFI mitigation, the Nebula pipeline identifies and ranks interesting narrow band candidate ET signals, scoring candidates by the number of times candidate signals have been seen at roughly the same sky position and same frequency, signal strength, proximity to a nearby star or object of interest, along with several other scoring criteria. We show four example candidates groups that demonstrate these RFI mitigation and candidate selection. This preliminary testing on FAST data helps to validate our SETI instrumentation techniques as well as our data processing pipeline.
In the spirit of Trimbles ``Astrophysics in XXXX series, I very briefly and subjectively review developments in SETI in 2020. My primary focus is 74 papers and books published or made public in 2020, which I sort into six broad categories: results from actual searches, new search methods and instrumentation, target and frequency seleciton, the development of technosignatures, theory of ETIs, and social aspects of SETI.
Much work in SETI has focused on detecting radio broadcasts due to extraterrestrial intelligence, but there have been limited efforts to transmit messages over interstellar distances. As a check if such messages can be interpreted once received, we conducted a blind test. One of us coded a 75-kilobit message, which the other then attempted to decipher. The decryption was accurate, supporting the message design as a general structure for communicating with aliens capable of detecting narrow-band radio transmissions.
The ability to walk in new scenarios is a key milestone on the path toward real-world applications of legged robots. In this work, we introduce Meta Strategy Optimization, a meta-learning algorithm for training policies with latent variable inputs that can quickly adapt to new scenarios with a handful of trials in the target environment. The key idea behind MSO is to expose the same adaptation process, Strategy Optimization (SO), to both the training and testing phases. This allows MSO to effectively learn locomotion skills as well as a latent space that is suitable for fast adaptation. We evaluate our method on a real quadruped robot and demonstrate successful adaptation in various scenarios, including sim-to-real transfer, walking with a weakened motor, or climbing up a slope. Furthermore, we quantitatively analyze the generalization capability of the trained policy in simulated environments. Both real and simulated experiments show that our method outperforms previous methods in adaptation to novel tasks.
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