Tag: EarthSky

Why is intelligent life so rare?

Maybe it is because of a ‘Great Filter‘.

Like so many others I read many items online. One of the websites that I follow is the EarthSky site because for a long time I have been interested in space.

So when I saw an article on why intelligent life is so rare in our Milky Way I read it fully. And hoped it would be of interest to others.

Here it is:

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What is the Great Filter, and can we survive it?

Posted by

Kelly Kizer Whitt and Deborah Byrd

November 17, 2022

This graphic depicts intelligent civilizations as stars. The vertical lines represent Great Filters that civilizations do or don’t survive. This graphic depicts Earth’s human population (the yellow “star”) approaching its own Great Filter. How would we surpass it, and keep going? Image via NASA/ arXiv.

What is the Great Filter?

Is intelligent life common, or rare in our Milky Way galaxy? If it’s common, why haven’t we encountered it? While discussing UFOs on a walk to lunch in the year 1950, the physicist Enrico Fermi is famously said to have asked, “But where is everybody?” Scientists today call that riddle Fermi’s Paradox. Now a new paper by NASA scientists explores one possible answer to the paradox. The answer may be what’s called the Great Filter.

Economist Robin Hanson first proposed the Great Filter, in the late 1990s. It’s the idea of that – even if life forms abundantly in our Milky Way galaxy – each extraterrestrial civilization ultimately faces some barrier to its own survival. The barrier might come from without (for example, an asteroid striking a planet, and wiping out all life forms). Or it might come from within (for example, all-out nuclear war).

Hanson proposed that a Great Filter might be at work within our Milky Way galaxy. He argued – from what we can see here on Earth – life expands to fill every niche. And so, he argued, we should see signs of intelligent life beyond Earth in nearby star systems, perhaps even in our solar system. But we don’t see this.

Is humanity facing a Great Filter?

The authors of the new paper take Hanson’s idea further. They explore the idea that humanity may now be facing a Great Filter. The authors wrote:

We postulate that an existential disaster may lay in wait as our society advances exponentially towards space exploration, acting as the Great Filter: a phenomenon that wipes out civilizations before they can encounter each other … In this article, we propose several possible scenarios, including anthropogenic and natural hazards, both of which can be prevented with reforms in individual, institutional and intrinsic behaviors. We also take into account multiple calamity candidates: nuclear warfare, pathogens and pandemics, artificial intelligence, meteorite impacts, and climate change. 

And they offer solutions, beginning with, as they say:

… a necessary period of introspection, followed by appropriate refinements to properly approach our predicament, and addressing the challenges and methods in which we may be able to mitigate risk to mankind and the nearly 9 million other species on Earth.

In a sense, the authors of the new paper – including lead author Jonathan H. Jiang of NASA’s Jet Propulsion Laboratory in Pasadena, California – are engaging in a “necessary period of introspection” by the act of writing their paper.

And, with their paper, they’re laying out the challenges we’re facing and methods of addressing them.

We’ve already survived some ‘filters’

The scientists point to life’s resilience. Life on Earth has already survived a number of filters in the form of mass extinction events. The Permian-Triassic extinction – aka the Great Dying – occurred 250 million years ago and nearly ended all life on the planet. This extinction event wiped out about 96% of marine life and 70% of land species. The exact cause of the Great Dying is still a matter of study, but some scientists have said it was a combination of warming temperatures and decreasing oxygen.

But these previous filters, or extinction events, have been natural, arising from the evolution of our planet and solar system, including volcanic eruptions and asteroid impacts. 

A Great Filter of our own making

But now, clearly, humanity may be facing a Great Filter of our own making, and one that other intelligent civilizations in the galaxy have faced … and failed to withstand. Perhaps it’s no surprise that the technological advancements humans have achieved might ultimately lead to our undoing. Perhaps that’s nature’s way. As the new paper said:

It seems as though nearly every great discovery or invention, while pushing back the borders of our technological ignorance, is all too quickly and easily turned to destructive ends. Examples such as splitting the atom, biomedical innovations and resource extraction and consumption come to mind with disconcerting swiftness. Still, some have suggested artificial intelligence (AI) as yet another factor, which, pending substantial technical hurdles, may yet have its chance to prove friend or foe.

Here’s a look at some of the issues that might compose Earth’s Great Filter.

Unchecked population growth

One of the factors Earth faces, according to the paper, is unchecked population growth. Earth just passed a milestone on November 15, 2022, when it reached 8 billion human inhabitants. The paper said with our current population figures, Earth has experienced:

… an exponential rise from about 1.6 billion [people] at the start of the 20th century.

Technological advancements in farming, energy production and distribution have made such a large population possible on Earth. But, as the paper said, these advancements cannot:

… indefinitely offset the multifaceted stresses imposed by an ever-escalating population.

When will Earth’s human population reach its peak size? Some projections report that education in developing nations might allow Earth’s population to peak at 10 billion in the 2060s. But, of course, no one really knows.

Nuclear war

While warfare has long been a factor of life on Earth, only in the past century has humanity had a weapon that could destroy all nations, not just those participating in a nuclear war. The scientists said the greater the number of democracies in the world, the better our chances for avoiding nuclear war. The scientist also saw other encouraging signs, including:

Peace agreements in the historically troubled Middle East, a vast reduction in nuclear warheads since the height of the Cold War and a wide coalition of nations rallying their support for the besieged in Eastern Europe.

Pathogens and pandemics

The threat of illness and pandemics continues to grow simply because our world is so interconnected. Spreading diseases have a much easier time in our global society. But on the positive side, advancements in medicine have also given us an edge. The scientists said that having current and reliable data is crucial:

… in predicting how future pandemics will spread, how deadly they will be and how quickly and effectively we will be able to leverage our knowledge of the life sciences to counter this manifestation of the Great Filter.

Artificial intelligence

While true artificial intelligence as a separate sentient being is not yet reality, the authors of the paper urge a proactive plan to peacefully share Earth. They project that computer sophistication will one day rival that of the human mind. The scientists said:

As for whether AI would be benign or otherwise, self-imposing a Great Filter of our own invention, that will depend on the evolving nature and disposition of Earth’s first high-tech species.

Asteroid and comet impacts

Here’s an extinction event from the past that could still spell our doom in the future. While large impacts are exceedingly rare, there is, as the scientists said:

… a non-zero percentage [of asteroids or comets] which are large enough to survive passage through the atmosphere and, impacting the surface, cause catastrophic destruction to our sensitive biosphere.

The odds of a mass extinction level event in the coming years is vanishingly small. But, over time periods extending into the very distant future, the odds increase toward 100%. Meanwhile, with projects such as the DART mission, and given enough lead time, humanity has a way of defending itself.

Climate change

Climate change has become one of the most studied threats to life on Earth. Because the threats from climate change happen on a slower time scale than, say, the time it takes to launch a nuclear weapon, the efforts to curb these effects have not been as rapid as they could have been. The scientists said:

The major impediment to taking more decisive actions, however, are the challenges imposed by transitioning to non-carbon-based energy sources such as solar, wind, nuclear power. Here again, rapidly advancing technologies in areas such as modularized nuclear power plants and carbon capture and sequestration (CCS) are among the best hopes for avoiding slow-motion ensnarement by this lulling but lethal Great Filter.

Avoiding the Great Filter

So you see there’s not just one possible Great Filter for Earth, but many. Any one of them could be our downfall. These scientists are suggesting something that sounds simple on its face, but is (apparently) hard to do. That is, in order to avoid the Great Filter, humans must work together and recognize the big picture. As the paper said:

History has shown that intraspecies competition and, more importantly, collaboration, has led us toward the highest peaks of invention. And yet, we prolong notions that seem to be the antithesis of long-term sustainable growth. Racism, genocide, inequity, sabotage … the list sprawls.

Meanwhile, we continue to look outward, peering at the dark depths between the stars, hoping for a sign that we aren’t alone in the universe. Ultimately, our quest to find life beyond Earth is part of trying to understand life on our planet and where we fit in. As Carl Sagan said:

In the deepest sense, the search for extraterrestrial intelligence is a search for ourselves.

Bottom line: Scientists say the reason we haven’t found intelligent civilizations in the galaxy is that they may not have survived the Great Filter. And they say we may be facing down our own Great Filter.

Source: https://arxiv.org/ftp/arxiv/papers/2210/2210.10582.pdf

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We are a funny bunch! As was said just a couple of paragraphs ago we humans must work together and recognise the big picture. But we do not!

Why do we not do that?

I wish I knew the answer to that conundrum! Nevertheless, I hope you enjoyed the article.

Simply in awe!

It’s both beautiful and yet beyond comprehension.

When we have a clear night there are two occasions for me to gaze upwards and become lost in thought. One is in the evening when the dogs are outside just before going to bed. The other is in the morning because we are usually awake well before sunrise.

We are very lucky in that there is no light pollution locally.

So, in the evening, while I look at the broad expanse of stars, my eyes are drawn to the Big Dipper and to Orion.

In the morning, when we look to the East there is Venus sparkling bright in the night-sky over the hills.

I still vividly remember all those years ago when I was sailing in the Western Mediterranean coming on deck in the middle of the night to find the stars down to the horizon all 360 degrees about me. I am sure it will be one of the last memories of mine just before I die! I hope so!

But I speak of the solar system. Here’s an article that was recently published by EarthSky that goes way beyond the solar system. It is a wonderful essay and almost mystical.

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What is a galaxy?

Posted by in ASTRONOMY ESSENTIALS, September 25, 2020

We live in a galaxy called the Milky Way. But there is so much more to know about these grand and glorious star islands in space! Click in here, and prepare to have your mind expanded.

This is a giant galaxy cluster known as Abell 2744, aka Pandora’s Cluster, located in the direction of the constellation Sculptor. The cluster is about 4 million light-years across and has the mass of 4 trillion suns. It appears to be the result of a simultaneous pile-up of at least 4 separate, smaller galaxy clusters that took place over a span of 350 million years. Read more about this image at HubbleSite. Image via NASA/ ESA/ J. Lotz/ M. Mountain/ A. Koekemoer/ the Hubble Frontier Fields Team.

A galaxy is a vast island of stars in an ocean of space. Galaxies are typically separated from one another by huge distances measured in millions of light-years. Galaxies are sometimes said to be the building blocks of our universe. Their distribution isn’t random, as one might suppose: galaxies are strung out along unimaginably long filaments across the universe, a cosmic web of star cities.

A galaxy can contain hundreds of billions of stars and be many thousands of light-years across. Our own galaxy, the Milky Way, is around 100,000 light-years in diameter. That’s about 587,900 trillion miles, nearly a million trillion kilometers.

Galaxies are of widely varying sizes, too.

There are an estimated two trillion galaxies in the universe.

Illustration showing snapshots from a simulation by astrophysicist Volker Springel of the Max Planck Institute in Germany. It represents the growth of cosmic structure (galaxies and voids) when the universe was 0.9 billion, 3.2 billion and 13.7 billion years old (now). Image via Volker Springel / MPE/ Kavli Foundation.

Galaxies group together in clusters. Our own galaxy is part of what is called the Local Group, for example: a cluster comprising 55 galaxies that we know of so far.

In turn, galaxy clusters themselves group into superclusters. Our Local Group is part of the Virgo Supercluster.

The “glue” that binds stars into galaxies, galaxies into clusters, clusters into superclusters and superclusters into filaments is – of course – gravity, the universe’s construction worker, which sculpts all the structures we see in the cosmos.

Distances from the Local Group for selected groups and clusters within the Local Supercluster, which is called the Virgo Supercluster.

There are several basic types of galaxy, each containing sub-types. Galaxies were first systematically classified, based on their visual appearance, by the famous astronomer Edwin P. Hubble in the late 1920s and 30s, during years of painstaking observations. Hubble’s Classification of Galaxies, as it is known, is still very much in use today, although, since Hubble’s time, like any good classification system it has been updated and amended in the light of new observations.

Before Hubble’s study of galaxies, it was believed that our galaxy was the only one in the universe. Astronomers thought that the smudges of light they saw in their telescopes were in fact nebulae within our own galaxy and not, as Hubble discovered, galaxies in their own right. It was Hubble who demonstrated, by measuring their velocities, that they lie at great distances from us, millions of light-years beyond the Milky Way, distances so huge that they appear tiny in all but the largest telescopes. Moreover, he demonstrated that, wherever he looked, galaxies are receding from us in all directions, and the further away they are, the faster they are receding. Hubble had discovered that the universe is expanding.

A diagrammatic representation of Edwin Hubble’s “tuning fork diagram.” In the late 1920s and 30s, Hubble conducted the laborious observations needed to begin to classify galaxies. His original classification scheme was published in 1936 in a book called “The Realm of the Nebulae.” His original scheme is – like all scientific work – continually being modified. But his idea of a “tuning fork diagram” has continued to be useful. Image via Las Cumbres Observatory.

The most common type of galaxy is the one most people are familiar with: the spiral galaxy. The Milky Way is of this family. Spiral galaxies have majestic, sweeping arms, thousands of light years long, made up of millions upon millions of stars. Our solar system is situated about 2/3 of the way out from the galactic center towards the periphery of the galaxy, embedded in one of these spiral arms.

Spiral galaxies are also characterised by having a bright center, made up of a dense concentration of stars, so tightly packed that from a distance the galaxy’s center looks like a solid ball. This ball of stars is known as the galactic bulge. At the center of the Milky Way – within the galactic bulge – the density of stars has been calculated at 1 million per 34 cubic light-years, for example.

Meanwhile, in the vicinity of our sun, the stellar density has been estimated as 0.004 stars per cubic light-year. Big difference!

A stunning view of the center of our Milky Way galaxy as seen by the Murchison Widefield Array (MWA) telescope in Australia in 2019. Image via Natasha Hurley-Walker (ICRAR/ Curtin)/ GLEAM Team/ Phys.org.

The Milky Way is, in fact, in one of Hubble’s spiral galaxy sub-types: it’s a barred spiral, which means it has a bar of stars protruding out from either side of the center. The ends of the bar form the anchors of the spiral arms, the place from where they sweep out in their graceful and enormous arcs. This is a fairly recent discovery: how the bar forms in a galaxy is not yet understood.

Also established recently is the fact that the disk of the Milky Way is not, as most diagrams depict, flat: it is warped, like a long-playing vinyl record left too long in the sun. Exactly why is not known, but it is thought to be the result of a gravitational encounter with another galaxy early in the Milky Way’s history.

Artist’s illustration of our warped Milky Way. Image via Ogle/ Warsaw University/ BBC.

Elliptical galaxies are the universe’s largest galaxies. They are huge and football-shaped.

They come to be because – although most galaxies are flying apart from each other – those astronomically close to each other will be mutually gravitationally attracted. Caught in an inexorable gravitational dance, eventually they merge, passing through each other over millions of years, eventually forming a single, amorphous elliptical galaxy. Such mergers may result in the birth of new generations of stars as gravity’s shock-wave compresses huge clouds of interstellar gas and dust.

The Milky Way is caught in such a gravitational embrace with M31, aka the Andromeda galaxy, which is 2 1/2 million light-years distant. Both galaxies are moving toward each other because of gravitational attraction: they will merge in about 6 billion years from now. However, both galaxies are surrounded by huge halos of gas which may extend for millions of light-years, and it was recently discovered that the halos of the Milky Way and M31 have started to touch.

The two galaxies have had their first kiss.

Galaxy mergers are not uncommon: the universe is filled with examples of galaxies in various stages of merging together, their structures disrupted and distorted by gravity, forming bizarre and beautiful shapes.

Galaxies may take billions of years to fully merge into a single galaxy. As astronomers look outward in space, they can see only “snapshots” of this long merger process. Located 300 million light-years away in the constellation Coma Berenices, these 2 colliding galaxies have been nicknamed The Mice because of the long tails of stars and gas emanating from each galaxy. Otherwise known as NGC 4676, the pair will eventually merge into a single giant galaxy. Image via Wikimedia Commons.

At the lower end of the galactic size scale, there are the so-called dwarf galaxies, consisting of a few hundred to up to several billion stars. Their origin is not clear. Usually they have no clearly defined structure. Astronomers believe they were born in the same way as larger galaxies like the Milky Way, but for whatever reason they stopped growing. Ensnared by the gravity of a larger galaxy, they orbit its periphery. The Milky Way has around 20 dwarf galaxies orbiting it that we know of, although some models predict there should be many more.

The two most famous dwarf galaxies for us earthlings are, of course, the Small and Large Magellanic Clouds, visible to the unaided eye in Earth’s Southern Hemisphere sky.

Eventually, these and other dwarf galaxies will be ripped apart by the titanic maw of the Milky Way’s gravity, leaving behind a barely noticeable stream of stars across the sky, slowly dissipating over eons.

Lynton Brown captured this beautiful image of the Milky Way over Taylor’s Lake near Horsham, Australia, on April 22, 2019. The 2 objects on the right are the Magellanic Clouds. Thank you, Lynton!

It is believed that all galaxies rotate: the Milky Way takes 226 million years to spin around once, for example. Since its birth, therefore, the Earth has travelled 20 times around the galaxy.

At the center of most galaxies lurks a supermassive black hole, of millions or even billions of solar masses. The record holder, TON 618, has a mass 66 billion times that of our sun.

The origin and evolution of supermassive black holes are not well understood. A few years ago, astronomers uncovered a surprising fact: in spiral galaxies, the mass of the supermassive black hole has a direct linear relationship with the mass of the galactic bulge. The more mass the black hole has, the more stars there are in the bulge. No one knows exactly what the significance of this relationship is, but its existence seems to indicate that the growth of a galaxy’s stellar population and that of its supermassive black hole are inextricably linked.

This discovery comes at a time when astronomers are beginning to realize that a supermassive black hole may control the fate of its host galaxy: the copious amounts of electromagnetic radiation emitted from the maelstrom of material orbiting the central black hole, known as the accretion disk, may push away and dissipate the clouds of interstellar hydrogen from which new stars form. This acts as a throttle on the galaxy’s ability to give birth to new stars. Ultimately, the emergence of life itself may be tied to the activity of supermassive black holes. This is an area of much ongoing research.

While astronomers still know very little about exactly how galaxies formed in the first place – we see them in their nascent forms existing only a few hundred million years after the Big Bang – the study of galaxies is an endless voyage of discovery.

Less than a hundred years after it was realized that other galaxies beside our own exist, we have learned so much about these grand, majestic star cities. And there is still much to learn.

Bottom line: What is a galaxy? Learn about these starry islands in space.

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There are an estimated two trillion galaxies out there. It is beyond comprehension. Well it is to this mind sitting in front of his Mac in a rural part of Oregon. Two trillion! I can’t even get my mind around the fact that our local galaxy, our Milky Way, is 100,000 light years across. Although some would say that it is even larger; about 150,000 light years across. And what is a light year?

Here’s NASA to answer that:

A light-year is a unit of distance. It is the distance that light can travel in one year. Light moves at a velocity of about 300,000 kilometers (km) each second. So in one year, it can travel about 10 trillion km. More precisely, one light-year is equal to 9,500,000,000,000 kilometers.

Why would you want such a big unit of distance? Well, on Earth, a kilometer may be just fine. It is a few hundred kilometers from New York City to Washington, DC; it is a few thousand kilometers from California to Maine. In the universe, the kilometer is just too small to be useful. For example, the distance to the next nearest big galaxy, the Andromeda Galaxy, is 21 quintillion km. That’s 21,000,000,000,000,000,000 km. This is a number so large that it becomes hard to write and hard to interpret. So astronomers use other units of distance.

In our solar system, we tend to describe distances in terms of the Astronomical Unit (AU). The AU is defined as the average distance between the Earth and the Sun. It is approximately 150 million km (93 million miles). Mercury can be said to be about 1/3 of an AU from the Sun and Pluto averages about 40 AU from the Sun. The AU, however, is not big enough of a unit when we start talking about distances to objects outside our solar system.

For distances to other parts of the Milky Way Galaxy (or even further), astronomers use units of the light-year or the parsec . The light-year we have already defined. The parsec is equal to 3.3 light-years. Using the light-year, we can say that :

  • The Crab supernova remnant is about 4,000 light-years away.
  • The Milky Way Galaxy is about 150,000 light-years across.
  • The Andromeda Galaxy is 2.3 million light-years away.

So here we are. In a remote part of our galaxy, the Milky Way, far, far from everywhere, on a pale blue dot. As Carl Sagan put it in his talk from The Age of Exploration given in 1994:

On it, everyone you ever heard of… The aggregate of all our joys and sufferings, thousands of confident religions, ideologies and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilizations, every king and peasant, every young couple in love, every hopeful child, every mother and father, every inventor and explorer, every teacher of morals, every corrupt politician, every superstar, every supreme leader, every saint and sinner in the history of our species, lived there on a mote of dust, suspended in a sunbeam. …
Think of the rivers of blood spilled by all those generals and emperors so that in glory and triumph they could become the momentary masters of a fraction of a dot.

Carl Sagan, Cornell lecture in 1994

It all seems impossible for us mortals to understand.

But it won’t stop me from peering up into the night sky and wondering about the universe with total awe.

And thank goodness for dogs!