Scientific-Integrity Theft by Artificial Intelligence
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By Avi Loeb Medium
An image of the city of Dubai from the International Space Station in 2012. (Image credit: NASA)In 2010, I attended the official inauguration conference of a new campus of New-York University in Abu Dhabi, along with my Princeton colleague, Ed Turner. As we were touring Abu Dhabi and Dubai, the tour guide bragged that Dubai’s city lights at night time can be seen all the way from the Moon.
Ed and I were instantly inspired to consider the question: How far away can city lights be observed in the Solar System? In particular, we Googled Tokyo which had its official luminosity listed online, and calculated during some of the boring talks at the conference that Tokyo would detectable at the distance of Pluto by deep exposures of the Hubble Space Telescope. In other words, if a city like Tokyo existed on Pluto, then the Hubble Space Telescope could detect its lights!
But detecting a source of light from an unknown object is insufficient. How can we infer that the light originates from an artificial source rather than the reflection of sunlight from a rock or iceberg? In principle, this can be done by taking a spectrum, namely studying the intensity of the light source as a function of wavelength. Artificial light would typically have a different spectrum than sunlight. However, it is challenging to obtain a spectrum of a faint source of light. Is there another way?
A self-luminous source behaves like a light bulb. It fades inversely with distance squared. However, an object illuminated by a lamppost fades inversely with distance to the fourth power. Ed and I reckoned: all we need to do is measure the change in the source brightness as a function of its distance from the Sun in order to infer whether it reflects sunlight or produces its own light. This was the idea conveyed in a paper that we published in 2012 here.
A few years earlier, I published another original idea here with Ed Turner and Amaya Moro-Martin, where we were first to predict quantitatively that interstellar objects could be detected with survey telescopes, like the NSF-DOE Rubin Observatory. This idea is coming to fruition right now, although the first paper to suggest it is forgotten. This appears to be the fate of pioneering ideas ahead of their time. In 1952, the astronomer Otto Struve suggested in a paper published here the practical methods for discovering Jupiter-mass planets in close-proximity to Sun-like stars. His idea was ignored for 43 years until the first discovery was reported here in 1995 by Michel Mayor and Didier Queloz who won the Nobel Prize for it. Their discovery paper does not reference Struve’s paper. Why is science so inefficient?
The application of the Loeb-Turner test to interstellar objects allows us to distinguish between natural interstellar rocks which reflect sunlight and technological objects which produce their own light. But a much larger population of objects is known to reside inside the Solar System. Have we actually checked whether all known objects beyond Neptune, the so-called trans-Neptunian objects, only reflect sunlight?
When Mike Brown from Caltech, who pioneered the discovery of trans-Neptunian objects, visited my Harvard office a decade ago, I asked him: Did you check whether their brightness declines as expected for the reflection of sunlight? Mike replied: “Why should I check? They are obviously just reflecting sunlight.” His response explains why Struve’s idea in 1952 did not translate to the discovery of a hot-Jupiter decades earlier than 1995. Observers assumed that they understood why Jupiter is far from the Sun and so they chose not to waste observing time searching for Jupiter-mass planets in close proximity to their host star. This led me to wonder: How many scientific discoveries end up as “unborn babies” because of prejudice?
And so today, my brilliant new postdoc, Omer Eldadi, completed a detailed paper in collaboration with me, studying all existing data on the brightness variation of trans-Neptunian objects with distance from the Sun. By applying the Loeb-Turner test to all objects, we have found that the current data available in the Minor Planet Center archive is of insufficient quality to conduct the test. Of all trans-Neptunian data bins, 53 consistent with reflected sunlight, 24 with self-luminous emission, and 109 appear anomalous. The anomalous bins exhibit slopes outside the expected range, consistent with uncorrected instrument calibration offsets rather than any particular physical mechanism. However, we find that the NSF-DOE Rubin Observatory’s ten-year survey will deliver uniform single-instrument calibration on a tenfold larger sample and resolve the Loeb-Turner test with a statistical confidence better than 10 standard deviations on hundreds of trans-Neptunian objects.
Here’s hoping that thanks to the NSF-DOE Rubin Observatory, we will be able to know within the coming years whether there are any spacecraft with city-scale lights within the Solar System.
ABOUT THE AUTHOR
(Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
Professional website:
https://lweb.cfa.harvard.edu/~loeb/
Social media:
https://avi-loeb.medium.com/
https://www.youtube.com/@ProfessorAviLoeb
https://open.spotify.com/show/1zhndXkvSY2b8FdjspFpCd
https://x.com/ProfAviLoeb
View the full article
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By Avi Loeb Medium
(Image credit: ScienceDirect)The four astronauts on Artemis II were in space for 9 days and did not suffer any significant medical problems from the low gravity environment that they experienced. But for space journeys lasting years, it is necessary to produce an analog of Earth’s gravity in order to protect astronaut health. Without gravity, bones lose mineral density at a rate of about 1.5% per month and muscles atrophy rapidly. Bodily fluids move towards the head, potentially causing eye damage and brain swelling.
There are two simple ways to produce artificial gravity. One is by accelerating astronauts on a rocket or any other propulsion system. The artificial linear acceleration would be indistinguishable from gravity for the passengers, for the same reason that gravity is not experienced in a free-falling elevator.
The challenge with this method is to have sufficient fuel for a prolonged acceleration phase. Steady acceleration at 1-gee for a full year brings a payload to the speed of light. This means that the required energy for a year-long journey equals the rest-mass of the payload. Chemical rocket fuel only converts a billionth of its rest mass to pure energy. Nuclear fusion of deuterium-tritium fuel converts 0.37% of the fuel rest mass to energy. In order to accelerate at 1-gee for a year and reach the speed of light, a rocket must carry anti-matter fuel that would annihilate a mass of matter comparable to that of the payload. CERN produces about a billionth of a gram of antimatter per year. To accelerate a lightweight 140-kilogram human at 1-gee for a full year would require CERN to produce antimatter for 140 trillion years, a period ten thousand times longer than the current age of the Universe.
The more practical method for generating artificial gravity is to spin a large structure so that the centripetal force would push passengers against the outer walls away from the rotation axis with a force that feels like gravity. This can be realized in a torus or a wheel-like structure or with two modules connected by a long tether and rotated around a common center.
To create the Earth-like gravity of 1-gee, equal to 9.8 meters per second squared, without causing dizziness for human passengers from high rotation speeds, the radius of the rotating structure needs to be larger than the Artemis II Space Launch System. A system with a radius of 100 meters needs to rotate three times per minute in order to generate a centripetal acceleration of 1-gee. A system with a radius of 1-kilometer needs about one rotation per minute. The centripetal acceleration scales as the radius divided by the square of the rotation-period.
The surface gravity on the Moon is 16.6% of the 1-gee on Earth. On Mars the value is 38% of gee. The health hazard for astronauts spending extended periods time on a permanent human base on the Moon needs more attention from NASA or space corporations like SpaceX or Blue Origins.
If humans will need to stay on the Moon or Mars for extended periods of time, one could imagine creating “artificial gravity health centers” for them, equipped with huge centrifuges measuring a kilometer in radius and rotating once per minute. Local residents will visit these rotating giant structures periodically to get the “1-gee experience” and rejuvenate their bodies. This is the kind of infrastructure that nobody talks about.
Other health risks on the Moon involve the exposure to energetic cosmic rays with 200 more radiation intensity than on Earth, enhancing the rates of cancer, central nervous system damage, and degenerative tissue effects. In addition, the lunar surface is covered with fine dust from asteroid impacts. Unlike dust on Earth, lunar dust was never eroded by wind or water, leaving it sharp like shattered glass.
There is no place like home.
***
Progress report on my first bronze sculpture: “The Alien”
Five months ago, the accomplished artist Greg Wyatt gifted me two bronze sculptures of Galileo Galilei and 51 watercolors which transformed my Harvard office into a mini-museum. But Greg’s biggest gift was a chunk of plastelina for me to create an original sculpture, which I chose to name: “The Alien”.
In crafting this sculpture, I imagined what an ideal alien body might include, supplementing the human body with a third eye, a third leg, wings, and technological devices. I shipped my creation to Greg three months ago. By now, my sculpture progressed to the next phase and was cast in red wax.
Greg informed me of the wonderful news in an email and added that once the Alien sculpture is casted in bronze with a beautiful patina, he will make sure that it is mounted on an appropriate size cherrywood pedestal. I responded:
“Dear Greg,
This is amazing. The alien sculpture is becoming a reality. I will do my best to discover a real alien for comparison before the sculpture is cast in bronze.
With deep gratitude.
Avi”
Below are three perspectives of the red wax phase of the sculpture.
(Image credit: Greg Wyatt)ABOUT THE AUTHOR
(Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, former director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics (2005–2026), and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
Professional website:
https://lweb.cfa.harvard.edu/~loeb/
Social media:
https://avi-loeb.medium.com/
https://www.youtube.com/@ProfessorAviLoeb
https://open.spotify.com/show/1zhndXkvSY2b8FdjspFpCd
https://x.com/ProfAviLoeb
View the full article
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By Avi Loeb Medium
(Image credit: Greg Wyatt)The fundamental difference between artificial intelligence (AI) and extraterrestrial intelligence (ETI) is in their training data sets. Whereas AI is trained on data limited to Earth, most of the real estate lies beyond Earth.
That we fail to recognize this simple fact and focus on our immediate environment is testimony to the limitations of the human mind. Even just days before the Artemis II launch of humans to an orbit around the Moon, critics express concerns that money would be better spent on solving problems closer to home. Well, guess what … if we keep our focus only close to home, we may lose this home and everything in it to a future catastrophe.
Exploration of residential areas far from home can save our descendants from extinction. Sixty-six million years ago, non-avian dinosaurs were not smart enough to avoid an asteroid impact. Are we smarter than they were or are we doomed to extinction together with our digital mirrors?
(Image credit: Greg Wyatt)Earth went through many major catastrophes in the past 4.6 billion years. Its history started with the Moon-forming collision when a Mars-sized protoplanet named Theia is believed to have collided with proto-Earth. Subsequently, the Permian-Triassic Extinction, event, about 252 million years ago, eliminated about 96% of marine species and 70% of land vertebrates. Later, the Great Oxygenation Event, about 2.4 billion years ago, occurred as early bacteria began producing oxygen via photosynthesis, which was toxic to the anaerobic life that dominated the Earth at the time, leading to a massive die-off. The Earth also went through multiple snowball events during which it encountered “deep freezes” where glaciers may have reached the equator. One significant period occurred around 700 million years ago, likely triggered by changes in greenhouse gases or volcanic activity, turning the entire planet into a frozen wasteland for millions of years. The end of the Ordovician period, about 444 million years ago, was triggered by intense glaciation and falling sea levels, killing 85% of marine life. The late Devonian period, about 360 million years ago, was associated with a series of pulses over millions of years, likely caused by ocean oxygen depletion as land plants rapidly diversified. And the end of the Triassic period, about 201 million years ago, was associated with massive volcanic activity during the breakup of the supercontinent Pangaea which led to rapid climate change, allowing dinosaurs to dominate.
Existential risks are inevitable also in our future. Within about a billion years all liquid water will dry up on Earth as a result of the Greenhouse effect of the brightening Sun (as discussed here), and in 7.6 billion years the drag on the expanded envelope of the Sun will deliver Earth into its hot and dense center.
In the long run, the City of Jerusalem will not be within humanity’s Promised Land, because it will be consumed by the dense metallic remnant of the Sun, a white dwarf the size of Earth containing about 60% of the current mass of the Sun.
The actual Promised Land for humanity’s long-term future will be on a space platform that guarantees its long-term survival. Instead of relying on a natural fusion reactor, the Sun, we could build an artificial nuclear fusion reactor inside a city-size spaceship that produces artificial gravity through rotation or rocket acceleration.
(Image credit: Greg Wyatt)Our transition from the surface of a habitable natural rock to a space platform where the living conditions are manufactured technologically, is similar to the transition from the jungles of Africa where human needed to collect their food from scarce natural resources to a city where abundant food can be ordered through speech to an AI agent.
Currently, our most visionary space ambitions involve traveling to other natural rocks which happen to exist in our neighborhood, like the Moon or Mars. But a more uplifting vision would be to construct a space platform that will carry humans to interstellar journeys, a Noah’s spaceship of sorts, making our survival independent of Earth’s future calamities.
So far, we have not employed AI for our space missions, but future interstellar trips will likely be guided by AI, while the bodies of any human passengers will stay frozen through the boring and long parts of the journeys.
We might be inspired to become an interstellar species once we discover that ETI were successful in doing so. Finding their spacecraft would guide us in selecting the technologies that made their trips successful. The fact that they arrived at our backyard before we arrived to theirs would not be surprising, given that we only had one century of modern science and technology after discovering General Relativity and Quantum Mechanics, whereas most Sun-like stars formed billions of years before the Sun.
The best is yet to come. Here’s hoping that a new age of peace and prosperity will result from our encounters with ETI. Judging by the terrestrial news cycle every day, it appears likely that we are not at the top of the cosmic food chain.
Recently, Vice-President JD Vance noted that Unidentified Anomalous Phenomena (UAP) might be demons flying around Earth (as reported here). If the Galileo Project will discover UAP under my leadership, I would view them instead through the words of President Abraham Lincoln as the “better angels of our nature.”
(Image credit: Greg Wyatt)*******
In this essay, I featured four amazing watercolors from a series created by the celebrated artist, Greg Wyatt. These watercolors incorporate inspiring statements by Giordano Bruno and Marsilio Ficino. This is the ninth in a sequence of essays, where Greg and I collaborate on the interface between art and science. The first essay in this series, titled “Music of the Cosmic Spheres,” appeared here; the second essay, titled: “Cosmic Waterfalls in Spacetime Cliffs,” appeared here; the third titled “Missing Elements in the Cosmic Jigsaw Puzzle,” appeared here; the fourth essay, titled: “Why Do We Exist?”, appeared here, and the fifth titled “Inspiration from the Stars”, appeared here, the sixth titled: “We Might Understand How the Cosmos Works Before We Understand How Life Works”, appeared here, the seventh titled “Will the Human Survive for Billions of Years”, appeared here, and the eight titled: “The Butterfly Effect of Intelligence in the Cosmos”, appeared here.
***
Before my morning jog at sunrise, I received the following uplifting email:
“Good morning, Avi.
We have spoken over email before.
I read your Medium posts and I recently watched you on Why Files — The Basement, with AJ. It was a great show!
I also own a couple of your books.
I believe you are right about Aliens, Alien probes and life on other planets, other than our own.
The reason I believe that is because every time I consider any single problem that seems absolutely impossible to resolve, I just look up at the stars at night and I think, “it’s impossibe that Avi is wrong, hard data or not, I believe in my heart that he is correct.”
Space goes on forever but on the other hand how can it? Where is the end? Is there a wall? What is on the other side of that wall then? If there’s a wall, then what is containing the wall? If there is no wall, how will you ever reach the end? For this reason alone, I believe that the conclusion is so likely and so undeniable, that people are crazy not to understand that.
I do not think you are wasting your time. I think you are doing immense work for the good of humanity and for our continued existence in the universe. I look forward to reading the results of your future work and people such as myself will always, always, believe in you, no matter what the critics say.
It’s just common sense.
Robin Lindberg”
ABOUT THE AUTHOR
(Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
Professional website:
https://lweb.cfa.harvard.edu/~loeb/
Social media:
https://avi-loeb.medium.com/
https://www.youtube.com/@ProfessorAviLoeb
https://open.spotify.com/show/1zhndXkvSY2b8FdjspFpCd
https://x.com/ProfAviLoeb
View the full article
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By Avi Loeb Medium
(Image credit: Greg Wyatt)The butterfly effect is a concept in the theory of chaos describing how tiny, initial changes in a complex system can result in massive, consequences. The metaphor coined by Edward Lorenz in the 1960s, suggests that a butterfly flapping its wings in Brazil could, through a chain reaction, trigger a tornado in Texas, highlighting extreme sensitivity to initial conditions.
A butterfly is a minor mover drawn from the natural world. But for an intelligent technological civilization with major computational resources, could “flap its wings” in a deliberate fashion so as to accomplish a major goal. The related effect could serve as a technological signature of intelligence in the cosmos, one of many that I discussed in a new podcast interview of the “The Basement/The Why Files”, available at the following link:
https://medium.com/media/0c772e2d60337ed4f21bb7c8b1a8f9ca/href(Image credit: Greg Wyatt)In particular, consider our future in which the Sun will inevitably brighten up and boil off all liquid water on Earth’s surface, turning it into a desert within a billion years through the greenhouse effect, as predicted here.
To avoid this doomsdays scenario and keep the Earth habitable, our descendants might embark on a cosmic engineering project which will aim to grow the orbital distance of the Earth from the Sun at the necessary rate. This task can be accomplished by tugging the Earth gravitationally by another body which orbits the Sun and resonates intermittently with the orbits of the Earth and Jupiter.
Each time the currier body flies past Jupiter, it may “steal” a tiny amount of orbital energy through a gravity assist. As this “butterfly” then returns to the proximity of Earth, it can “donate” that energy during a close flyby, nudging Earth’s orbit slightly outward. This scheme relies on gravity assists and orbital resonances to transfer energy from a massive outer planet, like Jupiter, to Earth. By timing these flybys to be resonant and always transfer energy with the same sign, the effect can be amplified over hundreds of millions of years — much like pushing a child on a swing at just the right moment to increase its height.
This cosmic engineering project to save humanity could involve selecting and equipping suitable Asteroid or Kuiper Belt objects with technological engines so that they will serve as the required “butterflies,” swinging periodically by the Earth and then Jupiter. This could raise the orbit of Earth significantly, but only lower Jupiter’s orbit by a tiny amount, since Jupiter is 318 times more massive than Earth.
(Image credit: Greg Wyatt)The mass of these “butterflies” can be chosen so as to expand the Earth’s orbit by just the right amount over a billion years to maintain a constant solar flux on Earth’s surface over that period. This would mean tailoring the Earth-Sun separation to scale as the square root of the solar luminosity.
Searching for such a scaling among habitable planets around other stars can be used to detect the signature of advanced technological civilizations which chose to engage in similar cosmic engineering projects. If this idea was popular among our siblings in the family of intelligent civilizations within the Milky-Way galaxy, then it would result an overabundance of Earth-mass planets in the habitable zone around old Sun-like stars as these stars evolve along the red giant branch of the Hertzsprung-Russel diagram — an inevitable consequence of the natural evolution of these nuclear fusion furnaces.
(Image credit: Greg Wyatt)***
Cosmic engineering projects might not be restricted to planetary systems. Given the accelerated expansion of the Universe, intelligent civilizations which were used to communicating with each other across cosmological distances might have decided to propel themselves closer together so that they would not be pulled apart and lose contact with each other in the distant future due to the accelerated expansion. Could we identify the related motions or artificial clustering of sources in cosmological data sets? I showed As in a paper here that the power required to move a star at a constant speed across cosmological distances can be supplied by the nuclear energy production in the star. Assuming that a significant fraction of this power is emitted in the infrared, the Webb Telescope will be able to detect a single stellar-mass object propelled at a constant speed out to a distance of about 30 million light years times the speed in units of 10,000 kilometers per second. Discovering the non-gravitational clustering and dynamics of many such sources would provide evidence for a new phenomenon of cosmic engineering on large scales.
***
This paper was inspired by an email exchange that I had with Freeman Dyson (as documented here). Back then, I published a paper here which calculated that in a trillion years from now, all extragalactic light sources will cease to be visible due to the accelerating expansion of the universe. Future astronomers would therefore be stuck looking only within their own galaxy. Not only would the absence of extragalactic sources make for a lonely universe, but it would deprive future astronomers of the tools that we have used to arrive at our current understanding of cosmology, such as extragalactic supernovae and the cosmic microwave background (CMB) radiation. Despite this, I suggested an observational signature by which these astronomers could still derive the standard cosmological model: hypervelocity stars.
In our correspondence, Freeman as the “ultimate optimist” suggested a means by which future civilizations could avoid this fate. He proposed that a civilization could harness the gravitational energy of a group of galaxies in some way as to pull together colossal collections of galaxies before they were thrown apart from each other by cosmological expansion.
Two years before I was born — in 1960, Freeman conceived here of civilization-scale engineering project, currently labeled as a Dyson Sphere, a megastructure which intends to harvest much of the energy output of a star by its resident civilization.
In our correspondence, Freeman suggested searching for anomalous clustering of galaxies to detect such “cosmic engineering.” In response, I mentioned two possible observational signatures of cosmic engineering: redshift surveys and the Sachs-Wolfe effect. Redshift surveys use galaxies to trace the distribution of matter on large scales throughout the Universe. By the Sachs-Wolfe effect, if some advanced civilization pulled together an cluster of galaxies far bigger than “normal” superclusters, then we could detect it from the energy lost by CMB photons as they climb out of the cluster’s enormous gravitational potential well. Signatures of anomalous clustering are not actually observed in either type of surveys, but Freeman noted that given the trillion-year timescale of the problem, “we have plenty of time to start doing it ourselves.”
Below is the full scope of our email correspondence in 2011.
Avi Loeb:
Dear Freeman,
In 2002 I wrote a paper about the long-term future of our Universe (Phys.
Rev. D65, 047301, 2002). Back then, you asked me in an e-mail to let you
know if I have any interesting follow-up thoughts on the subject.
Attached is a short paper that I had just submitted for publication on the
same subject. I would love to hear any comments you might have about it.
With best wishes,
Avi
Freeman Dyson:
Dear Avi,
Thank you for sending the paper. I found nothing wrong with it.
It presents a dismal picture of the future awaiting our descendants.
Since I am an incurable optimist, I raise the question, how much this
future could be changed by a large-scale intervention of intelligent life.
A very rough estimate indicates that large-scale “cosmic engineering”
could be feasible. Using available gravitational energy as the motive
power, roughly ten percent of the mass from one percent of the observable
universe could be collected within a volume small enough to remain
permanently bound together gravitationally. The collection could be done
in a single Hubble time and could then be maintained with small active
adjustments. So, our descendants would stay in communication with a
hundred million galaxies instead of only one. It is also possible that
some of our more advanced colleagues elsewhere in the universe already
began this process. We should look out for evidence of large-scale
coordination of gamma-ray bursts or other phenomena indicating high
velocity movement of large masses. It would be interesting to examine
such possibilities in detail. Thank you for the suggestion. Yours ever,
Freeman Dyson.
Avi Loeb:
Freeman,
Your underlying assumption is that intelligent beings prefer as much
company as possible. I can only say that as I get older, I prefer to stay
away from other people as much as possible, since I have the feeling that
I heard it all. Extrapolating to the distant future, I am entirely
complacent with us being surrounded by vacuum and protected by an event
horizon. Aside from the benefit of not having any distractions, this
will reduce the risk of a hostile invasion by another civilization.
Yours,
Avi
Freeman Dyson:
Each to his own taste. History without hostile invasions would be very
boring. FD.
Avi Loeb:
Putting prejudice aside, we already have relevant data for testing your
proposition about “cosmic engineering” on very large scales. SDSS provided
us with a map of the distribution of galaxies out to a redshift of z=0.3
(and SDSS III is now reaching farther out). The biggest bound systems in
the survey are clusters of galaxies, containing at most ~10^{15} solar
masses or ~1000 galaxies each. The existence of clusters is fully
consistent with the initial conditions we detect in the microwave
background at redshift z=1000. Since the initial conditions are Gaussian,
it should be easy to identify “cosmic engineering” in the form of a rare
over-dense region (supercluster) containing many more than ~1000 galaxies.
A region compact enough to bind a million galaxies against cosmic
acceleration would have imprinted an anomalously large Sachs-Wolfe effect
on the microwave background or would have induced unusually high peculiar
velocities. We do not see anomalies of this magnitude. The biggest
supercluster in our vicinity is the Shapley supercluster, but it is
expected to be dissolved in the future by the cosmic acceleration according
to the calculation in
Munoz, J, & Loeb, A. “The Density Contrast of the Shapley Supercluster”,
MNRAS, 391, 1341
Of course, it is possible that the Shapley supercluster is still “under
construction”, or that “cosmic engineering” operates on much smaller
scales.
Avi
Freeman Dyson:
That is disappointing. On the other hand, if our colleagues have been
too lazy to do the job, we have plenty of time to start doing it
ourselves. FD.
*******
In this essay, I featured four amazing watercolors from a series created by the celebrated artist, Greg Wyatt. These watercolors incorporate inspiring statements by Giordano Bruno and Marsilio Ficino. This is the eighth in a sequence of essays, where Greg and I collaborate on the interface between art and science. The first essay in this series, titled “Music of the Cosmic Spheres,” appeared here; the second essay, titled: “Cosmic Waterfalls in Spacetime Cliffs,” appeared here; the third titled “Missing Elements in the Cosmic Jigsaw Puzzle,” appeared here; the fourth essay, titled: “Why Do We Exist?”, appeared here, and the fifth titled “Inspiration from the Stars”, appeared here, the sixth titled: “We Might Understand How the Cosmos Works Before We Understand How Life Works”, appeared here, and the seventh titled “Will the Human Survive for Billions of Years”, appeared here.
ABOUT THE AUTHOR
(Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
Professional website:
https://lweb.cfa.harvard.edu/~loeb/
Social media:
https://avi-loeb.medium.com/
https://www.youtube.com/@ProfessorAviLoeb
https://open.spotify.com/show/1zhndXkvSY2b8FdjspFpCd
https://x.com/ProfAviLoeb
View the full article
-
By Avi Loeb Medium
The Rubin Observatory Could Discover Corner Reflectors or Artificial Lights in the Outer Solar System
(Image credit: YIC-electronics)A week ago, the Rubin Observatory initiated the release of its much-anticipated flood of data from its 3.2 gigapixel camera (as announced here).
Solar-system astronomers are accustomed to discovering asteroids by detecting the reflection of sunlight from their surface. However, a class of objects with the same surface area are potentially detectable to much greater distances in the outer solar system. They could be discovered, for the first time, by the Rubin Observatory.
Natural objects which reflect sunlight get dimmer inversely with distance to the 4th power at distances that are much larger than the Earth-Sun separation. The reason is simple. The flux of sunlight impinging on their surface declines inversely with distance squared and the observed flux as a result of reflection off their surface declines by another factor of inverse distance squared. Combining these factors implies that asteroids or the nuclei of interstellar objects get dimmer inversely with heliocentric distance to the 4th power.
On the other hand, a source that generates its own light, like a spacecraft or a city, would brighten inversely with distance squared as it approaches us from the outer solar system. This resembles the way that a lamppost brightens as we approach it from a dark street.
The difference between scaling with distance to the 4th and 2nd powers can distinguish between a natural and a technological object. In 2012, I published a paper here with Ed Turner from Princeton University, which showed that existing optical telescopes and surveys can detect artificially-illuminated objects comparable in total brightness to a major terrestrial city out to the outskirts of the Solar System. Since orbital parameters of Kuiper belt objects are routinely measured to exquisite precisions, we proposed to measure the variation of the observed flux from such objects as a function of their changing orbital distances. This idea is particularly feasible now with the Rubin Observatory. If objects with an inverse-square brightening law are found, follow-up observations can measure their spectra to determine whether they are illuminated by artificial lighting. The search can also be extended beyond the Solar System with future telescopes, which would be capable of detecting phase modulation due to very strong artificial illumination on the night-side of planets as they orbit their parent stars.
Another interesting class of objects which would follow the inverse-square brightening law are corner reflectors along the Sun-Earth axis. A corner reflector is a passive retroreflector consisting of three mutually perpendicular, intersecting flat surfaces that reflect waves directly back toward their source, regardless of the incidence angle. They are essential for enhancing radar visibility, satellite tracking, and laser ranging.
Corner reflectors were particularly helpful in measuring the distance between the surfaces of the Earth and the Moon using lasers. The distance is calculated from the round-trip time of laser pulses propagating at the speed of light, which are reflected back to Earth by the Moon’s surface or by reflectors on the Moon. Three reflectors were installed by the United States’ Apollo program, two by the Soviet Lunokhod 1 and 2 missions, and one by India’s Chandrayaan-3 mission. The precise distance measurements so far imply that Newton’s constant does not change by more than a part in ten trillion per year (as reported here and here).
Now, consider a corner reflector created by another technological civilization. If that corner reflector happens to be aligned with the Sun-Earth axis, it will follow the inverse-square brightening law because it will reflect rays of sunlight back to where they came from, allowing an observer on Earth to detect them. The shadow of the Earth has a negligible effect at large distances, because the surface area of Earth is 12,000 times smaller than that of the Sun. Our situation resembles a fly hovering over a lamppost and observing the reflection of light from a corner reflector in a dark street.
As long as the Earth is observed to transit the Sun from the vantage point of the corner reflector, we would observe the corner reflector to follow the inverse-square brightening law. This favorable geometry selects a swath that covers 0.47% of the sky, the ratio between the radius of the Sun and the Earth-Sun separation. In other words, only one out of 214 corner-reflectors that are randomly distributed around the Sun will follow the inverse-square brightening law from the Earth’s vantage point. Gladly, these corner reflectors will all be detectable at nighttime when the body of the Earth blocks the sunlight and allows a ground-based telescope to search for them. They would all appear in opposition to the Sun within a cone of 0.25 degrees, corresponding to the angular radius of the Sun from Earth. The Rubin observatory or other survey telescopes resemble the eyes of the fly havering near the lamppost and looking away for reflected light from objects in the dark street.
A corner reflector can be distinguished from a source of light by its spectrum matching that of sunlight and by its position in the sky being in opposition to the Sun. Here’s hoping that the Rubin Observatory will show evidence for either sources of artificial light or a corner reflector. Any such detection will surely make our life on Earth far more exciting.
ABOUT THE AUTHOR
(Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
Professional website:
https://lweb.cfa.harvard.edu/~loeb/
Social media:
https://avi-loeb.medium.com/
https://www.youtube.com/@ProfessorAviLoeb
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