Are We Alone?

We’ve all wondered if there’s other intelligent life out there, and we’ve wondered if we’ll ever make contact with them. But if there are hundreds of billions of stars in our galaxy, and each of these stars likely has a planetary system, and many of these planetary systems have Earth-like planets hospitable to life, then how come we haven’t heard from any of these aliens?

The Fermi Paradox

How come there’s been no solid evidence at all of intelligent, extraterrestrial life capable of interstellar travel or communication up to this point?

In 1950, physicist Enrico Fermi was discussing this with some fellow physicists and famously asked, “Where is everybody?” This has come to be known as the Fermi paradox.

With the sheer number of Earth-like planets out there, it seems impossible for there NOT to be other intelligent life. Bill Nye comments on this:

Jodie Foster’s character in Contact, Dr. Ellie Arroway, says pretty much the same thing but with sentimental music and sexual tension:

The Drake Equation

One analytical exploration of the question is the Drake equation, a systematic formula by astrophysicist Frank Drake to propose an answer to this question. Check out Carl Sagan’s explanation of the Drake equation in his dated but nonetheless brilliant Cosmos (1980) documentary:

In a beautifully understandable way, Sagan walks us through the equation and gives us a way to make an estimate. He also suggests that life began quite quickly on Earth.

It’s been 40 years since that video was made, so where do we stand now? I’ve spent many hours watching more recent videos of lectures and arguments on this subject. Here are two of the more interesting ones I found recently.

The Emergence of Life on Earth

In the first, professor David Kipping agrees that simple life appeared on Earth relatively quickly (within 900 million years at the latest, or about 20% into Earth’s existence), and that life appearing quickly is the most likely scenario on other Earth-like planets hospitable to life.

After doing a bit more research to collect more data points, here’s how things transpired on Earth (Incremental Time shows how much time has transpired from one step to the next):

If we use the end of Late Heavy Bombardment as a starting point, then life certainly appeared quickly on a habitable Earth. At most, it took 0.3 billion years for simple life to appear on a habitable Earth, but there is some evidence to suggest that simple life appeared almost immediately after the Earth became habitable.

But then it took another 2-ish billion years for simple life to evolve intelligence. If these numbers are the typical case on new planets, Kipping implies, then a majority of Earth-like planets out there might have life, but more likely simple life and not intelligent life.

Here, astrophysicist Brian Cox (one of the few public science figures today who approaches Sagan’s level of philosophical wonder and eloquence) makes similar points and suggests that there may be a few, intelligent, technologically advanced, spacefaring civilizations out there right now. Cox goes further and argues that we should consider the possibility that we ARE alone, because that will encourage us to more prudently safeguard our existence and care for our home and species.

The Great Filter

Many hypotheses about the apparent rarity of intelligent life in the universe revolve around the concept of the Great Filter, which suggests there is some nearly insurmountable barrier to the development of sustained, advanced civilizations. According to the Great Filter, the following steps are required for such civilizations to emerge, with at least one being so improbable that it prevents most from advancing further:

1. Formation of a Habitable Planet
   A planet must form in a star’s habitable zone, where conditions allow for liquid water and organic chemistry essential for life.
2. Emergence of Reproductive Molecules
   Molecules capable of reproduction and self-replication, like RNA or DNA, must form to support the development of life.
3. Simple (Prokaryotic) Single-Cell Life
   The initial forms of life should be simple, single-celled organisms, such as bacteria or archaea.
4. Complex (Eukaryotic) Single-Cell Life
   Evolution of more complex cells with a nucleus and organelles (eukaryotes) must occur, allowing for greater cellular complexity.
5. Multicellular Organisms
   Life must progress from single cells to multicellular organisms, enabling specialized functions and larger structures.
6. Sexual Reproduction
   Sexual reproduction must develop to increase genetic diversity and evolutionary potential.
7. Development of Animal-Level Intelligence
   Intelligent life forms capable of complex behaviors and problem-solving must evolve.
8. Technological Civilization
   Tool-using intelligent species must reach a stage of technological development that allows for advanced technology, communication, and potential for space exploration.
9. Avoiding Existential Threats
   The civilization must avoid self-destruction or collapse due to existential threats like nuclear war, pandemics, asteroid impacts, artificial intelligence risks, or climate change.
10. Sustained Space Colonization
    The final step is achieving sustainable space colonization, spreading life and civilization to other planets and star systems to ensure long-term survival.
    

The Great Filter implies that at least one of these steps presents a barrier so high that further progress becomes impossible, preventing the universe from being filled with intelligent civilizations. Which step, or combination of steps, is the true filter? What is holding the universe back from teeming with advanced life?

Final Thoughts

In the end, I’m on board with the assumption that, if there is life out there, most of it is probably simple, microbial, and not intelligent. But what about intelligent life? We still don’t fully understand intelligence and consciousness, and until we do, it’s hard for scientists to form any real opinion on how common it might be.

The way I see it, here are all the possible scenarios for intelligent life in the universe:

1. We are the only intelligent civilization in the universe…
   1. …and always have been and always will be (“rare Earth” hypothesis)…
      1. …because we are special
      2. …because some Great Filter barrier generally prevents life from developing intelligence [Brian Cox’s position]
   2. …but there may be others in the past or future that we will never have the opportunity to make contact with…
      1. …because intelligent, technological civilizations inevitably destroy themselves relatively quickly
      2. …because some Great Filter barrier prevents them from developing the technology
2. We are one of many intelligent civilizations in the universe right now… [Carl Sagan’s position]
   1. …but they can’t explore or communicate with other civilizations…
      1. …because their intelligence is social and cultural (like dolphins and whales), not technological, and therefore they are unlikely to ever develop the technology
      2. …because they destroy themselves before they are able to make the technology
      3. …because they are hibernating until the universe cools off enough for them to fire up their megacomputers (“aestivation” hypothesis)
      4. …because some Great Filter barrier prevents them from developing the technology
   2. …and they can explore and communicate with other civilizations…
      1. …but don’t want to… [Michio Kaku’s position]
         1. …out of disinterest (they are so advanced that they have nothing to gain)
         2. …out of fear (“dark forest” hypothesis)
      2. …and do want to…
         1. …but they are too far away to have heard from us yet (radio signals from Earth have only had enough time to reach about 75 stars, many of which do indeed have Earth-like planets)
         2. …but we are not listening properly because our current methods of detecting extraterrestrial signals (e.g., radio telescopes) are inadequate for identifying advanced civilizations that use different communication technologies [Bill Nye’s position]
         3. …and we will detect their signals soon [SETI researcher Seth Shostak’s position]
         4. …and they have heard from us and they are coming…
            1. …and they will be nice
            2. …and they will destroy us
               1. …and they won’t bother engaging because it’s easier to destroy us with autonomous and self-replicating von Neumann probes (“berserker” hypothesis)
         5. …and they already found us…
            1. …and they left…
               1. …because they weren’t interested
               2. …but gave us the gift of technology and Egyptian pyramids
            2. …and they’re here…
               1. …and are silently watching us (“zoo” hypothesis)
               2. …and are hiding the presence of intelligent life from us (“planetarium” hypothesis)
               3. …and are doing a sloppy job of hiding themselves (UFOs)
               4. …and have made contact and are being covered up by governments
3. We are not intelligent, it is only an illusion as we exist in a simulation created by other intelligent beings (“simulation” hypothesis) [Elon Musk’s position]

Honestly, I don’t know where I stand. With a complete absence of concrete evidence for any intelligent life other than our own and so many unknowns, any one of these positions would be a wild guess. But it sure is fun to think about.