Dissolving the Fermi Paradox

[Syne]

https://phys.org/news/2018-06-advanced-c...verse.html

"Many parameters are very uncertain given current knowledge. While we have learned a lot more about the astrophysical ones since Drake and Sagan in the 1960s, we are still very uncertain about the probability of life and intelligence. When people discuss the equation it is not uncommon to hear them say something like: "this parameter is uncertain, but let's make a guess and remember that it is a guess", finally reaching a result that they admit is based on guesses. But this result will be stated as single number, and that anchors us to an apparently exact estimate – when it should have a proper uncertainty range. This often leads to overconfidence, and worse, the Drake equation is very sensitive to bias: if you are hopeful a small nudge upwards in several uncertain estimates will give a hopeful result, and if you are a pessimist you can easily get a low result."

As such, Sanberg, Drexler and Ord looked at the equation's parameters as uncertainty ranges. Instead of focusing on what value they might have, they looked at what the largest and smallest values they could have based on current knowledge. Whereas some values have become well constrained – such as the number of planets in our galaxy based on exoplanet studies and the number that exist within a star's habitable zone – others remain far more uncertain.

When they combined these uncertainties, rather than the guesswork that often go into the Fermi Paradox, the team got a distribution as a result. Naturally, this resulted in a broad spread due to the number of uncertainties involved. But as Dr. Sanberg explained, it did provide them with an estimate of the likelihood that humanity (given what we know) is alone in the galaxy:
...
In the end, the team's conclusions do not mean that humanity is alone in the universe, or that the odds of finding evidence of extra-terrestrial civilizations (both past and present) is unlikely. Instead, it simply means that we can say with greater confidence – based on what we know – that humanity is most likely the only intelligent species in the Milky Way Galaxy at present.

[C C]

https://phys.org/news/2018-06-advanced-c...verse.html

[...] In the end, the team's conclusions do not mean that humanity is alone in the universe, or that the odds of finding evidence of extra-terrestrial civilizations (both past and present) is unlikely. Instead, it simply means that we can say with greater confidence – based on what we know – that humanity is most likely the only intelligent species in the Milky Way Galaxy at present.

Although it was praised by several sources in the beginning, it's remarkable how reviled the Rare Earth Hypothesis became over time online in either a "Sagan-orthodoxy incorrect" or classified as contrarian way. Since 2000, new developments might even be added to its original list of contingent factors.

Isaac Asimov's earlier fiction usually went against the popular grain by featuring a Milky Way dominated by only human intelligence, when a novel was interstellar spanning. A seldom mentioned, much lesser stimulus for Asimov writing the The Gods Themselves, back in 1972, was to demonstrate to mild critics that he actually could write about intelligent aliens (albeit these resided in a parallel universe).

~

[Syne]

I've always liked sci-fi authors like Asimov, Herbert, and Dickson because they wrote only human inhabited universes...which I've always found much more plausible, especially than a proliferation of humanoid life (and why I rarely like reading fantasy).

[Ostronomos]

The probability of finding a human population in other universes is relatively large. This estimation does not take into account Quantum parallelization. Where it is theorized that copies of every individual are manifest. This idea suggests that universes are not isolated but connected in some way by Quantum Mechanics.

[C C]

The probability of finding a human population in other universes is relatively large.

Those in Max Tegmark's camp contend that even if there is only this one cosmos. But there are still no duplicates of ourselves occurring in this galaxy or the Milky Way of this region, though. That's all this stuff is ever skeptical about range-wise, in terms of the general possibility of other intelligent life.

Even if granting in an infinite[*] universe the purely quantitative possibility of observable matter configurations eventually repeating themselves... Duplicates of Earth and ourselves in Tegmark's "Level I" type parallel universe (below) would be too distant to ever observe or come into contact with, and thereby verify.

[*] NOTE: "Endless space" actually can't be a completed condition without contradicting itself, as it would then instead be a finite measurement no matter how bogglingly large the magnitude. Which is to say, in order to make an ascription of "infinite" sound in the non-abstract world, it implies a non-static condition of "more" being continually or intermittently added in terms of extension. The alternative of a set boundary being endlessly divided into yet smaller units would apply to an abstract scenario rather than the "real" world or its description as outputted by physics, since the Planck unit presents a limit to such speculative spatial division (an obstacle of graininess).

- - -

Parallel Universes (PDF)
http://space.mit.edu/home/tegmark/PDF/mu..._sciam.pdf

EXCERPT: Is there a copy of you reading this article? A person who is not you but who lives on a planet called Earth, with misty mountains, fertile fields and sprawling cities, in a solar system with eight other planets? The life of this person has been identical to yours in every respect. But perhaps he or she now decides to put down this article without finishing it, while you read on.

The idea of such an alter ego seems strange and implausible, but it looks as if we will just have to live with it, because it is supported by astronomical observations. The simplest and most popular cosmological model today predicts that you have a twin in a galaxy about 10 to the 10^28 meters from here. This distance is so large that it is beyond astronomical, but that does not make your doppelgänger any less real. The estimate is derived from elementary probability and does not even assume speculative modern physics, merely that space is infinite (or at least sufficiently large) in size and almost uniformly filled with matter, as observations indicate. In infinite space, even the most unlikely events must take place somewhere. There are infinitely many other inhabited planets, including not just one but infinitely many that have people with the same appearance, name and memories as you, who play out every possible permutation of your life choices.

You will probably never see your other selves. The farthest you can observe is the distance that light has been able to travel during the 14 billion years since the big bang expansion began. The most distant visible objects are now about 4 X 10^26 meters away--a distance that defines our observable universe, also called our Hubble volume, our horizon volume or simply our universe. Likewise, the universes of your other selves are spheres of the same size centered on their planets. They are the most straightforward example of parallel universes. Each universe is merely a small part of a larger "multiverse."

[...]

Level I: Beyond Our Cosmic Horizon

The parallel universes of your alter egos constitute the Level I multiverse. It is the least controversial type. We all accept the existence of things that we cannot see but could see if we moved to a different vantage point or merely waited, like people watching for ships to come over the horizon. Objects beyond the cosmic horizon have a similar status. The observable universe grows by a light-year every year as light from farther away has time to reach us. An infinity lies out there, waiting to be seen. You will probably die long before your alter egos come into view, but in principle, and if cosmic expansion cooperates, your descendants could observe them through a sufficiently powerful telescope.

If anything, the Level I multiverse sounds trivially obvious. How could space not be infinite? Is there a sign somewhere saying "Space Ends Here--Mind the Gap"? If so, what lies beyond it? In fact...

MORE: http://space.mit.edu/home/tegmark/PDF/mu..._sciam.pdf

~

[Ostronomos]

The probability of finding a human population in other universes is relatively large.

Those in Max Tegmark's camp contend that even if there is only this one cosmos.  But there are still no duplicates of ourselves occurring in this galaxy or the Milky Way of this region, though. That's all this stuff is ever skeptical about range-wise, in terms of the general possibility of other intelligent life.

Even if granting in an infinite
[*] universe the purely quantitative possibility of observable matter configurations eventually repeating themselves... Duplicates of Earth and ourselves in Tegmark's "Level I" type parallel universe (below) would be too distant to ever observe or come into contact with, and thereby verify.

[*]NOTE: "Endless space" actually can't be a completed condition without contradicting itself, as it would then instead be a finite measurement no matter how bogglingly large the magnitude. Which is to say, in order to make an ascription of "infinite" sound in the non-abstract world, it implies a non-static condition of "more" being continually or intermittently added in terms of extension. The alternative of a set boundary being endlessly divided into yet smaller units would apply to an abstract scenario rather than the "real" world or its description as outputted by physics, since the Planck unit presents a limit to such speculative spatial division (an obstacle of graininess).

- - -

Parallel Universes (PDF)
http://space.mit.edu/home/tegmark/PDF/mu..._sciam.pdf

EXCERPT: Is there a copy of you reading this article? A person who is not you but who lives on a planet called Earth, with misty mountains, fertile fields and sprawling cities, in a solar system with eight other planets? The life of this person has been identical to yours in every respect. But perhaps he or she now decides to put down this article without finishing it, while you read on.

The idea of such an alter ego seems strange and implausible, but it looks as if we will just have to live with it, because it is supported by astronomical observations. The simplest and most popular cosmological model today predicts that you have a twin in a galaxy about 10 to the 10^28 meters from here. This distance is so large that it is beyond astronomical, but that does not make your doppelgänger any less real. The estimate is derived from elementary probability and does not even assume speculative modern physics, merely that space is infinite (or at least sufficiently large) in size and almost uniformly filled with matter, as observations indicate. In infinite space, even the most unlikely events must take place somewhere. There are infinitely many other inhabited planets, including not just one but infinitely many that have people with the same appearance, name and memories as you, who play out every possible permutation of your life choices.

You will probably never see your other selves. The farthest you can observe is the distance that light has been able to travel during the 14 billion years since the big bang expansion began. The most distant visible objects are now about 4 X 10^26 meters away--a distance that defines our observable universe, also called our Hubble volume, our horizon volume or simply our universe. Likewise, the universes of your other selves are spheres of the same size centered on their planets. They are the most straightforward example of parallel universes. Each universe is merely a small part of a larger "multiverse."

[...]  

Level I: Beyond Our Cosmic Horizon

The parallel universes of your alter egos constitute the Level I multiverse. It is the least controversial type. We all accept the existence of things that we cannot see but could see if we moved to a different vantage point or merely waited, like people watching for ships to come over the horizon. Objects beyond the cosmic horizon have a similar status. The observable universe grows by a light-year every year as light from farther away has time to reach us. An infinity lies out there, waiting to be seen. You will probably die long before your alter egos come into view, but in principle, and if cosmic expansion cooperates, your descendants could observe them through a sufficiently powerful telescope.

If anything, the Level I multiverse sounds trivially obvious. How could space not be infinite? Is there a sign somewhere saying "Space Ends Here--Mind the Gap"? If so, what lies beyond it? In fact...

MORE: http://space.mit.edu/home/tegmark/PDF/mu..._sciam.pdf

~

[*]

It may be said that what is possible is inevitable in an infinitely large space (the backdrop upon which things play out and realize themselves). Time plays a factor in bringing possibilities into actualization. The scale of this immense universe allows room for all manner of matter configurations to arise, however the distance makes each possibility seem abysmal in comparison. The calculation of probability above suffices to put things in perspective however.

[Yazata]

The so-called 'Fermi Paradox' is misnamed. It isn't a paradox at all. It's just a question. I think that it gets more attention than it deserves, because Fermi's name is attached to it.

https://en.wikipedia.org/wiki/Fermi_paradox

There are lots of assumptions built in:

1. There are billions of stars in the galaxy. This one seems pretty well established and I don't question it. If we want to be complete, we would need to note that there are billions of galaxies. That's lots of powers of ten.

2. Some of these stars have Earthlike planets. Discoveries of exoplanets suggest that just about every star out there has something orbiting it. Many of these worlds can be expected to occupy orbits where temperatures are suitable for liquid water etc. So I don't question this one either. (Of course, that is interpreting 'Earthlike' in a pretty minimal sense, simply in terms of temperature and presence of water.)

3. Some may have developed life. I have more questions about this one. The simplest known lifeforms on Earth are bacteria and archaea, and these are already hugely complex in a biochemical sense. We have no real information about how they originated.

My own view is that this biochemical complexity makes it exceedingly unlikely that the first prokaryotic cells just popped out of a "primordial soup" ready-made. My guess is that there must have been some long and laborious 'chemical evolution' lead-up to prokaryotic cells' appearance. That's why I'm skeptical about the claims that life appeared on Earth very early during in the hellish Hadean era not long after the Earth's recovery from the formation of the Moon, during the Late Heavy Bombardment when Earth was regularly subject to planet-killer asteroid strikes. If life did appear on earth during that first few hundred million years, then I'd guess that life isn't native to Earth at all.

Another consideration is how we define life. Our problem in that regard is that we only have a sample of one. So we end up imagining all life elsewhere in the universe as being what we see here on Earth.

My own view on that is that we should define 'life' functionally. So life could be derived from any chemical replicator capable of making more of itself and subject to natural selection. There may be many different ways of accomplishing that kind of result. In other words, I don't really expect alien life to have a whole lot of biochemical similarity to us.

Plugging those considerations into estimates of how common life is in the rest of the universe, we find ourselves being pulled in two directions.

On one hand, life seems to be hugely complex and fortuitous, the result of lots of accidents and lucky breaks. So that suggests that life might be exceedingly rare.

On the other hand, if there are many different ways of accomplishing the same kind of thing (self-reproducing and evolving chemical replicators) then life might be a lot more common (and oftentimes stranger) than we think.

I don't really have a clue how to assign numbers to that so as to fit it into Drake's equation.

4. Some of this life may have evolved into intelligent life. Again it depends on how we define 'intelligent'. Life seems to have had some kind of intelligence since Cambrian times some 500 million years ago. We see the appearance of crude jawless fish, trilobite-like arthropods and squid-like cephalopods (probably the smartest of the bunch back in those days), even before life left the oceans for dry land. But nothing like a human being's intelligence. Keep in mind that the first cells are thought to have appeared very early, some 3.5 - 4 billion years ago, and the Cambrian explosion was only a little more than 500 million years ago. So the Earth for most of its history had bacterial life, or single-celled protozoa after eukaryotes appeared, but no advanced nervous systems or sentience.  

We only see advanced hominins in the last million years or so, with anatomically modern humans only about 150,000 years old.

The point being that there might be many exoplanets with bacteria-like life (little self-reproducing chemical factories), quite a few with simple animal-like things with some rudimentary awareness of their surroundings, but only a few with life approaching (or surpassing) ourselves. Our chances of discovering the simpler forms will be much higher than our chances of discovering intelligent aliens.

5. Some of these may have developed technological civilizations capable of spaceflight. The Scientific Revolution was only about 400 years ago and the Industrial Revolution less than 300 years ago. The pyramids were constructed some 4600 years ago. The Neolithic revolution (when humans domesticated animals, adopted agriculture and settled village life) was about 10,000 years ago.

The point being that even if there are intelligent aliens out there, we will have to catch them at just the right point in their development for them to be space travelers.

6. So the earth should have already been visited by extraterrestrial aliens.

Star-traveling space aliens might be few and far between, probably scattered very thinly around the galaxy. Assuming that the speed of light restrains them as our current physics suggests it should, their range might be comparatively small, compared to galactic and intergalactic scales.

7. But there isn't any convincing evidence that the Earth has been visited by aliens. (Hence the supposed 'paradox'.)

But... maybe the Earth has been visited by aliens. Maybe that's how life first arrived here, tracked in by an alien with dirty boots.

Maybe aliens visited the Earth when cyanobacteria were just starting to oxygenate the Earth's atmosphere several billion years go, or when dinosaurs ruled the planet several hundred million years ago.

It seems to me that two independent forms of life encountering each other at just the proper moment in their respective evolutions that both can recognize each other as intelligent might be an exceedingly rare event.

[Magical Realist]

The simplest and most popular cosmological model today predicts that you have a twin in a galaxy about 10 to the 10^28 meters from here. This distance is so large that it is beyond astronomical, but that does not make your doppelgänger any less real. The estimate is derived from elementary probability and does not even assume speculative modern physics, merely that space is infinite (or at least sufficiently large) in size and almost uniformly filled with matter, as observations indicate. In infinite space, even the most unlikely events must take place somewhere. There are infinitely many other inhabited planets, including not just one but infinitely many that have people with the same appearance, name and memories as you, who play out every possible permutation of your life choices.

In an infinite universe, all the events that have ever occurred in our galaxy, down to the positions of every atom of all the matter therein, will not only be repeated in another galaxy, but will also be repeated an infinite number times in an infinite number of galaxies, by mere chance.

[Zinjanthropos]

Some great info Yaz. I would think that the lifespan of a star might come into play should life require some time before getting truly established. Then there's always the possibility that the Earth itself was once part of another galaxy where life had formed.....

http://viewzone.com/milkyway22.html

Edit: I forgot about luck

[C C]

I've always liked sci-fi authors like Asimov, Herbert, and Dickson because they wrote only human inhabited universes...which I've always found much more plausible, especially than a proliferation of humanoid life (and why I rarely like reading fantasy).

Might be part of the reason why I like *The Expanse*. Something different than all the non-artificial, heterogeneous humanoid aliens running around in the other space opera universes of Star Trek, The Orville, Babylon 5, Star Wars, etc. Winding everything back to just intrigue, action, warfare, and politics taking place in the Solar System is a different and almost faded-away tradition of SF, too.

The Martian cowboy pilot with the drawl has to be an obvious strategy to lure Firefly fans, along with the Roscinante mirroring a gunship version of the Serenity. Ah, I keep forgetting this is based on a series of novels, though. But the theory is still ever tempting.

~