Why Have We Not Found Any Aliens? - with Keith Cooper

The speaker begins by expressing gratitude for being present at a venue where famous Christmas lectures have been held, highlighting Carl Sagan's influence. The topic of discussion is SETI (Search for Extraterrestrial Intelligence), which is described as a scientific endeavor to find intelligent life in outer space, contrasting with popular misconceptions of UFOs and alien abductions. The speaker emphasizes the importance of SETI, referencing the film 'Contact' and the scientific basis for using radio signals in the search, including a historical account of why radio waves were chosen as the primary method of detection.

The speaker delves into the Drake Equation, a mathematical framework used to estimate the number of extraterrestrial civilizations that might exist. The factors considered include the rate of star formation, the fraction of stars with planets, the number of habitable planets, the likelihood of life developing on those planets, the presence of intelligent life, and the lifetime of a transmitting civilization. The speaker also discusses the potential for detecting alien signals through radio waves, given their ability to penetrate interstellar dust, and the limitations of our current technology in sampling the universe for signs of life.

The speaker talks about the evolution of SETI, from its early days with Project Ozma to the present, highlighting the technological advancements that have allowed for the observation of billions of radio channels simultaneously. Despite the scientific community's initial skepticism and lack of funding, the speaker mentions the Breakthrough Listen project, a 10-year initiative funded by billionaire Yuri Milner, which aims to revolutionize SETI by observing a million stars in detail and scanning the entire sky for signals. The speaker emphasizes the importance of patience in the search for extraterrestrial intelligence and the potential for future discoveries.

The speaker discusses the possibility of extraterrestrial communication through means other than radio, such as lasers. While lasers have advantages over radio, including not being affected by dispersion, their range is limited by interstellar dust. However, infrared light, which can penetrate dust, offers a new avenue for SETI. The speaker mentions the work of Professor Shelley Wright, who is developing an instrument to search for infrared laser pulses. Although no signals have been detected yet, this represents a promising new direction in the search for extraterrestrial intelligence.

The speaker explains the method of detecting exoplanets through transits, where a planet passes in front of its star and causes a temporary dip in the star's brightness. This method allows astronomers to infer the size of the planet and, when combined with other data, its composition. The speaker also discusses how analyzing the starlight that passes through a planet's atmosphere during a transit can reveal the presence of certain gases, which may indicate the existence of life. The search for biosignatures in planetary atmospheres is a key focus of current and future missions, such as the European Space Agency's PLATO and CHEOPS missions.

The speaker recounts the discovery of the Wow Signal in 1977, a strong radio signal that was detected for 72 seconds and has not been detected since. Despite various hypotheses, including the possibility of an extraterrestrial source, the origin of the signal remains unexplained. The Wow Signal serves as a reminder of the tantalizing nature of the search for extraterrestrial intelligence and the need for continued exploration and funding for SETI projects.

The speaker discusses the assumptions underlying SETI, such as the belief that intelligent life forms will develop technology and the idea that they will be able to detect us or choose to communicate. The speaker challenges these assumptions, pointing out that they are based on our own human experience and may not apply to alien civilizations. The speaker introduces the concept of the 'contact paradox,' which suggests that while we actively search for extraterrestrial life, we may also be hesitant about the potential consequences of making contact. The speaker argues for a more cautious approach, advocating for further reconnaissance and understanding before attempting to establish contact.

The speaker expresses optimism about the future of space exploration and the potential for discovering extraterrestrial life. Mentioning upcoming missions like TESS and the European Space Agency's PLATO and CHEOPS, the speaker highlights the advancements in technology that will allow us to study exoplanets and their atmospheres in greater detail. The speaker also discusses the possibility of launching our own messages into space to provoke a response from other civilizations, while acknowledging the potential risks and the need for careful consideration.

The speaker concludes by reiterating the concept of the 'contact paradox,' emphasizing the need for caution and preparation before attempting to make contact with extraterrestrial civilizations. The speaker argues that SETI is an important part of scientific inquiry, as it not only seeks to understand the existence of alien life but also reflects on human life and our place in the universe. The speaker calls for a better future for humanity, suggesting that by addressing current threats and building a more sustainable and peaceful world, we may one day become an advanced civilization capable of engaging with others in the galaxy.