Abraham (Avi) Loeb: New Search Methods for Primitive and Intelligent Life Far from Earth

TL;DR

Astronomers define life as chemical reactions in liquid water that produce gases like oxygen or methane at abundances far out of equilibrium, while intelligent life is defined as producing artificial signals highly improbable under natural circumstances. New telescope techniques aim to detect both primitive and intelligent life, from the solar system to nearby stars and back to early cosmic times.

Transcript

MELISSA FRANKLIN: Welcome to Science Center Public Lecture Series given by Harvard Science professors. This is the first this year-- there's one every month, and I hope you'll come to all of them. And this will be videotaped and then it will be online. So you'll be able to see it. If you didn't understand one part, you can play it over and over and... Read More

Key Insights

• Life, for astronomers, is defined as chemical reactions in liquid water that produce gases like oxygen or methane at abundances vastly out of equilibrium, a definition that lets researchers search for these signatures in planetary atmospheres.
• Intelligent life is defined as a form of life that produces artificial signals highly improbable under natural circumstances, so anything unusual on the sky that physics cannot explain naturally would be alarming evidence.
• There are more planets like Earth in the visible universe than there are grains of sand on all the beaches on Earth, a scale that Loeb argues should teach humanity modesty rather than arrogance.
• The search for life is described as the ultimate interdisciplinary frontier, involving astronomy, planetary science, chemistry, biology, statistics, physics, and engineering, with implications for sociology, economics, theology, and philosophy.
• Even the bright flash from a nuclear war on a planet around the nearest stars to the solar system would not be detectable by our largest telescopes, showing the difficulty of spotting distant civilizations.
• The Kuiper Belt is a collection of relatively small objects orbiting the sun at roughly 100 times the Earth-sun distance, and Pluto is one of them, which is why some demoted it as a planet.
• Artificial light on a solar system object could be distinguished from reflected sunlight because reflected light declines as one over distance squared twice over, while artificially produced light would follow a different fall-off.
• Loeb coined the frontier 'cosmobiology' or 'biocosmology' after writing the first paper on whether life was possible at early cosmic times, addressing when life started in the universe and when it will end.

Questions & Answers

Q: How do astronomers define life when searching other planets?

For astronomers, life is associated with chemical reactions in liquid water, just like life on Earth, which produce gases such as oxygen or methane at abundances that are vastly out of equilibrium. Loeb says this is a useful definition because it gives researchers something concrete to search for: they can look for these out-of-equilibrium gas abundances in the atmospheres of planets, treating unusual chemistry as a potential biosignature of living processes.

Q: What is the definition of intelligent life used in this search?

Intelligent life is defined as a form of life that produces artificial signals which are highly improbable under natural circumstances. Loeb explains that if astronomers see something completely unusual on the sky that they cannot explain through the laws of physics under natural circumstances, that would be alarming and could indicate life out there. This definition focuses on detecting technology-produced signatures rather than biological chemistry alone.

Q: Why does Avi Loeb say astronomy teaches modesty?

Loeb notes there are more planets like Earth in the visible universe than there are grains of sand on all the beaches on Earth, so the pride of an emperor conquering the entire Earth is like the pride of an ant hugging a single grain of sand on a huge beach. He argues people are arrogant because they look down at Earth, but looking up at the sky reveals how insignificant we are, teaching modesty.

Q: Could there be intelligent life on Kuiper Belt objects like Pluto?

Loeb raises this as a real question. The Kuiper Belt is a collection of relatively small objects orbiting the sun at roughly 100 times the Earth-sun distance, and Pluto is one of them. He proposes searching for artificial light on such objects. While most astronomers assume solar system objects only reflect sunlight, Loeb asks whether artificial light produced on one of these objects could be detected and distinguished from reflected light.

Q: How can artificial light be distinguished from reflected sunlight on distant objects?

Loeb explains that when an object is illuminated by the sun, the flux impinging on its surface declines as one over the object's distance from the sun squared. Then observers on Earth see that light diminished by another factor of one over distance squared because the object is far from us. Artificially produced light would not follow this same double fall-off pattern, so the difference in how brightness scales with distance could reveal an artificial source.

Q: Why is the search for life called an interdisciplinary frontier?

Loeb calls it the ultimate interdisciplinary frontier because it involves astronomy for observing the sky, planetary science because life as we know it exists on planetary surfaces, chemistry to get reactions going, biology, statistics to estimate likelihoods, physics, mathematics, and engineering. It also has implications for sociology, economics, government, philosophy, psychology, linguistics for communication, art, history, and theology, since finding intelligent beings could require reinterpreting religious texts.

Q: Where in the solar system are scientists looking for life?

Loeb describes several solar system targets. Scientists are addressing whether there was liquid water on the surface of Mars. They question whether there is bacteria on Enceladus, a satellite of Saturn, and whether there is fish swimming on Europa, a satellite of Jupiter, where people believe liquid water exists under the ice. He notes these places are, in principle, ones we can actually visit, unlike systems beyond the solar system.

Q: What is cosmobiology and why did Avi Loeb create it?

Cosmobiology, which Loeb also calls biocosmology, is a new cosmological frontier he named after writing the first paper on whether life was possible at early cosmic times. He says the field started earlier this year with that paper. It addresses questions such as when life started in the universe and when it will end, extending the search for life beyond individual planets and galaxies into the deep cosmological past and long-term future.

Summary

In this video, Professor Avi Loeb discusses the search for life beyond Earth and the various techniques astronomers are using to find evidence of extraterrestrial intelligence. He explains the different distance scales at which life could exist, from the solar system to galaxies outside our own. He talks about the importance of searching for biomarkers, such as oxygen, in the atmospheres of exoplanets. He also discusses the possibility of using industrial pollution as a signature of intelligent civilizations. Professor Loeb concludes by highlighting the importance of the search for extraterrestrial life and how it could impact our society and culture.

Questions & Answers

Q: How does astronomy teach us modesty?

Astronomy teaches us modesty by giving us a perspective of how insignificant we are in the grand scheme of the universe. Looking up at the night sky and realizing the vast number of planets and galaxies out there, we gain a sense of humility and realize that Earth is just a tiny speck in a vast expanse.

Q: What is the definition of life according to astronomers?

Astronomers define life as chemical reactions occurring in liquid water that produce gases like oxygen or methane at abundances that are vastly out of equilibrium. This definition allows us to search for these indicators of life in the atmospheres of exoplanets.

Q: Why is the search for extraterrestrial life an interdisciplinary frontier?

The search for extraterrestrial life involves various fields including astronomy, planetary science, chemistry, biology, statistics, physics, mathematics, and engineering. It also has implications for sociology, economics, government, philosophy, psychology, linguistics, art, history, and theology. Therefore, it requires collaboration and knowledge from multiple disciplines to understand and explore this frontier.

Q: How does the search for life progress from the solar system to galaxies?

The search for life progresses from the solar system to galaxies in several steps. Firstly, we investigate the possibility of life within our own solar system, studying planets like Mars, Saturn's moon Enceladus, and Jupiter's moon Europa for evidence of liquid water and potential microbial life. Next, we broaden our search to exoplanets and analyze their atmospheres for biomarkers. Lastly, we consider the existence of intelligent life within our own galaxy and even in the entire universe.

Q: How can we search for artificial light on objects in the solar system?

The reflection of sunlight on objects in the solar system usually produces a specific signature of flux decline with distance. To detect artificial light on these objects, we can observe their emitted light and compare it with the expected flux decline. If the flux decline follows a different pattern, it suggests the presence of artificial light on the object.

Q: Why haven't we detected extraterrestrial signals through SETI programs?

The lack of detection through SETI programs raises Fermi's paradox, which questions why we haven't seen evidence of intelligent civilizations if they exist. One possibility is that intelligent civilizations are rare, and we may indeed be alone in the universe. Another possibility is that our search methods are limited or insufficiently sensitive to detect extraterrestrial signals. Further advancements in technology and improvements in search techniques may help resolve this question.

Q: How can we search for biomarkers in exoplanet atmospheres?

By observing exoplanets during transit events, where they pass in front of their host stars, we can analyze the composition of their atmospheres. By studying the spectral fingerprints of different molecules in the atmosphere, such as oxygen and methane, we can search for biomarkers that indicate the presence of life.

Q: What are the challenges in detecting habitable planets around stars similar to the sun?

The primary challenge in detecting habitable planets around stars similar to the sun is the contrast between the brightness of the star and the faint signal from the planet. The star is about 10 billion times brighter than the planet, making it difficult to observe the planet directly. However, upcoming telescopes like the James Webb Space Telescope and starshade technologies are being developed to overcome this challenge.

Q: How can we search for industrial pollution as an indicator of extraterrestrial civilizations?

Industrial pollution can be identified by looking for specific molecular signatures, such as pollutants produced by human industrial activities, in the atmospheres of exoplanets. By comparing the spectral fingerprints of pollutants with the Earth's atmosphere, we can detect potential evidence of industrialized civilizations outside of our solar system.

Q: How can we explore the early beginnings of the universe?

By studying the light emitted from distant objects in the universe, we can look back in time, seeing the universe as it was in its early stages. This allows us to investigate the formation of stars and galaxies and gain insights into the conditions that allowed life to emerge. Through computer simulations and observations, we can reconstruct the history of the universe from its early beginnings to the present day.

Takeaways

Professor Avi Loeb's lecture highlights the search for extraterrestrial life and the various techniques astronomers are using to detect signs of life beyond Earth. From searching for biomarkers in exoplanet atmospheres to looking for industrial pollution as an indicator of intelligent civilizations, these approaches offer hope for finding evidence of extraterrestrial intelligence. However, the search for life is not limited to our solar system or galaxy, but extends to the entire universe. The exploration of the early universe provides insights into the conditions that allowed life to emerge. The discovery of extraterrestrial life would have profound implications for our society, culture, and our understanding of our place in the universe.

Summary & Key Takeaways

• Avi Loeb frames the central question as whether we are alone or the universe is teeming with life, arguing the answer would dramatically change society and culture. He notes most colleagues simulate the universe assuming it is lifeless, but he sees this as an opening for a new Copernican revolution about our place in the biological universe.

• For astronomers, life means chemical reactions in liquid water producing out-of-equilibrium gases like oxygen or methane, while intelligent life produces artificial signals improbable under natural laws. The search spans distance scales: the solar system (Mars water, bacteria on Enceladus, fish on Europa), extrasolar planets via astrobiology, and intelligent life in the galaxy.

• Loeb describes novel detection techniques, noting even a nuclear war flash on the nearest stars would evade our largest telescopes. Closer to home, artificial light on Kuiper Belt objects like Pluto could be distinguished from reflected sunlight by its different fall-off with distance, and he introduces the cosmological frontier he calls cosmobiology.