Is there anyone out there?

In it’s simplest terms, the Fermi Paradox asks:

“Given that the chances for life to arise seem abundant, why have we never detected it apart from our own planet?”

Asked another way: “Is there anyone out there?”

Scientists plug their best guesses into the Drake Equation—and most come to the conclusion: Yes! It seems very likely that the universe is abundant with life.

If this is the case, then, why have we not detected evidence of radio waves, space probes, industrial constituents in the atmosphere of other planets—or even byproducts of plant life or bacteria, etc?

𝐈𝐧 𝐨𝐮𝐭𝐥𝐢𝐧𝐞, 𝐭𝐡𝐞 𝐚𝐫𝐠𝐮𝐦𝐞𝐧𝐭 𝐫𝐮𝐧𝐬 𝐥𝐢𝐤𝐞 𝐭𝐡𝐢𝐬:

1) The Milky Way contains hundreds of billions of stars, and billions of them are similar to the sun.

2) It is highly likely that some of these stars will have planets that are similar to Earth.

3) If we assume – via the Copernican principle – that Earth is not particularly special, then intelligent life should also exist on some fraction of these Earth-like planets.

4) Some of these intelligent life-forms might develop advanced technology, and even interstellar travel.

5) Interstellar travel would take a long time, but as there are many sun-like stars that are billions of years older, there has been plenty of time for such travel to have occurred.

6) Given all this, why haven’t we met or seen any trace of aliens? Where is everybody?

𝐓𝐡𝐞𝐫𝐞 𝐚𝐫𝐞 𝐬𝐞𝐯𝐞𝐫𝐚𝐥 𝐠𝐨𝐨𝐝 𝐫𝐞𝐚𝐬𝐨𝐧𝐬 𝐚𝐬 𝐭𝐨 𝐰𝐡𝐲 𝐰𝐞 𝐡𝐚𝐯𝐞 𝐧𝐨𝐭 𝐲𝐞𝐭 𝐝𝐞𝐭𝐞𝐜𝐭𝐞𝐝 𝐥𝐢𝐟𝐞, 𝐞𝐯𝐞𝐧 𝐢𝐟 𝐢𝐭 𝐢𝐬 𝐯𝐞𝐫𝐲 𝐚𝐛𝐮𝐧𝐝𝐚𝐧𝐭. 𝐇𝐞𝐫𝐞 𝐚𝐫𝐞 𝐣𝐮𝐬𝐭 𝐚 𝐟𝐞𝐰:

1) The galaxy and the universe is vast. It covers far greater distances than we can grasp. Even if there are trillions of populated planets, it would amount to a tiny fraction of star systems. The chances are slim that we would have encountered or identify one of them yet, given our nascent stage of sky searching and space exploration.

2) It is possible that intelligent species exist, but have not invented radio or radio telescopes. This removes our key means of detecting them.

3) It is possible that intelligent species exist, but have no desire to ponder their place in the universe or communicate with anyone far from home.

4) It is possible that intelligent species have existed in the past, but their timeline did not overlap with ours observation distance. That is, even after accounting for the distance and time involved, they may have extinguished themselves with pollution, war, global warming (as we are doing)—or they may have been killed off by a celestial event such as a large asteroid or solar discharge.

5) It is possible that intelligent species exist and have already reached out to us (or we have already detected the evidence), but that we simply didn’t understand what we were observing. That is, we may not have any way to communicate with nor even recognize life that is very different than our own. They may use things other than speech, radio, sign language, etc. They may not even have eyes and ears.

6) We are rare. (For life to achieve intelligence and develop technology is very rare; natural catastrophes or just ordinary predation can easily eliminate any branch of evolution that goes the “big brain” route, so it’s entirely possible that there are millions of planets where the *dinosaurs* are the dominant species and *intelligent creatures* cannot overcome them.)

7) 𝐓𝐡𝐞 𝐆𝐫𝐞𝐚𝐭 𝐅𝐢𝐥𝐭𝐞𝐫 : This one is one of the most scariest and worth dwelling into, with no evidence of intelligent life other than ourselves, it appears that the process of starting with a star and ending with "advanced explosive lasting life" must be unlikely. This implies that at least one step in this process must be improbable. Hanson's list, while incomplete, describes the following nine steps in an "evolutionary path" that results in the colonization of the observable universe:

1) The right star system (including organics and potentially habitable planets)

2)Reproductive molecules (e.g. RNA)

3) Simple (prokaryotic) single-cell life

4) Complex (eukaryotic) single-cell life

5) Sexual reproduction

6) Multi-cell life

7) Tool-using animals with intelligence

8)A civilization advancing toward the potential for a colonization explosion (where we are now)

9) Colonization explosion

According to the Great Filter hypothesis, at least one of these steps—if the list were complete—must be improbable. If it is not an early step (i.e., in our past), then the implication is that the improbable step lies in our future and our prospects of reaching step 9 (interstellar colonization) are still bleak. If the past steps are likely, then many civilizations would have developed to the current level of the human species. However, none appear to have made it to step 9, or the Milky Way would be full of colonies. So perhaps step 9 is the unlikely one, and the only things that appear likely to keep us from step 9 are some sort of catastrophe, an underestimation of the impact of procrastination as technology increasingly unburdens existence or resource exhaustion leading to the impossibility of making the step due to consumption of the available resources (for example highly constrained energy resources). So by this argument, finding multicellular life on Mars (provided it evolved independently) would be bad news, since it would imply steps 2–6 are easy, and hence only 1, 7, 8 or 9 (or some unknown step) could be the big problem.

Although steps 1–8 have occurred on Earth, any one of these may be unlikely. If the first seven steps are necessary preconditions to calculating the likelihood (using the local environment) then an anthropically biased observer can infer nothing about the general probabilities from its (pre-determined) surroundings.

In a 2020 paper, Jacob Haqq-Misra, Ravi Kumar Kopparapu, and Edward Schwieterman argued that current and future telescopes searching for biosignatures in the ultraviolet to near-infrared wavelengths could place upper bounds on the fraction of planets in the galaxy that host life. Meanwhile, the evolution of telescopes that can detect technosignatures at mid-infrared wavelengths could provide insights into the Great Filter. They say that if planets with technosignatures are abundant, then we can increase our confidence that the Great Filter is in the past. On the other hand, if we find that life is commonplace while technosignatures are absent, then this would increase the likelihood that the Great Filter lies in the future.

Though the Fermi Paradox is the accepted name for the argument, some argue that it more properly belongs to Hart.

Whoever is responsible for it, there are any number of proposed answers to the question.

The most obvious is that we are alone: Earth is unique, or close to it, in having life. Alternatively, large-scale interstellar travel may be impossible. Or perhaps intelligent life will inevitably destroy itself via nuclear weapons, or runaway artificial intelligence, or global warming, or something else.

Other ideas include the suggestion that we are not looking for the right kind of signs, or that aliens are so alien we cannot even recognise them as living things. Or perhaps other civilisations are deliberately keeping us in the dark until we are ready to join the galactic community.

Or perhaps other life is abundant, but living in subsurface oceans – such as that thought to be on Enceladus – unaware that anywhere, or anything, else exists.

The possibilities are endless, and speculation will no doubt continue forever, or until we find extraterrestrials.

Fermi’s lunchtime conversation petered out, according to Edward Teller, another physicist who was present, with the conclusion that “as far as our galaxy is concerned, we are living somewhere in the sticks, far removed from the metropolitan area of the galactic centre”.

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