In the first part of this entry, I looked at the scientific perspective of how far we are from being technologically advanced in our search for life in the Milky Way Galaxy. I talked about the Drake equation, which mathematically helps wrap our mind around the issue & starts a conversation/debate (but we currently lack concrete data beyond the first couple components of equation). I talked about possible reasons why SETI has not had much success yet from an astronomy/social science perspective.
Next, I talked about how primitive we are as a species and how recent we just began understanding different aspects of the universe — 5,500 years since first writing and 100 years since Einstein found out how gravity warps – we didn’t even find our first exoplanet until 20 years ago in 1995. Our current best hope is that an advanced alien species will find us rather than us finding them (unless if they’re in a somewhat nearby star system and use radio frequency like we do).
This entry will explore slightly different factors – do note that a lot of the numbers used are our best estimates and approximations. Until we have more concrete information, I cannot consider this entry ‘science’ per se. I cannot consider this anything beyond hypotheses because many of these are not things you can test in a lab and not something that we can show scientific evidence for yet as we are still looking for the needle (life) in a haystack (vast cosmic pie a.k.a Milky Way).
In most things, you usually start with observations or factual data that you analyze & do research on, but there is none of that to be found here (yet). The only option is to start with ideas and possibilities that you use to work backwards in search of concrete data.
As far as we know, there are 11 stars inside distances of 10 light-years out of more than 100 billion in Milky Way. They each might have their own planets. The closest exoplanet found is 4.3 light-years away around star Alpha Centauri. Below, the bright star on left is Alpha Centauri, bright one on right is Beta Centauri, and the red circle is where Proxima Centauri dwells.
A large number of star systems must contain planets. When I took astronomy courses at Rutgers 2 years ago, textbooks we used said that approximately 1 out of every 10 stars have planets. That was based on data collected about a decade ago, but since then, much more data has been collected after Kepler space telescope was launched in 2009. The only mission of Kepler telescope has been to hunt and collect data on planets in other star systems out there — Hubble space telescope had a lot of other goals and didn’t have much time set aside to hunt planets, which is Kepler’s specialty. It is now approximated that the vast majority of star systems in Milky Way contain planets.
One out of every 5 stars is estimated to have at least one planet in habitable zone and similar size to Earth (some estimates I have seen at around 15%). That amounts to around 20 billion Earth-sized planets in habitable zone. The numbers are truly in our favor that life exists out there somewhere in our own galaxy. From those 20 billion, we have to start subtracting most of those planets for various reasons (below).
Where is Everybody?
Physicist Enrico Fermi once said that if you were to crunch all the numbers together, you would come up with large number of civilizations in the Milky Way Galaxy. He wonders why have we not found them if there are so many. He famously asked “Where is everybody?” That is the basis for the Fermi paradox, which people like Frank Drake and Carl Sagan tried to solve through mathematical equations.
We must consider the fact that even if the chances and numbers are in our favor of life existing out there, we obviously would have to consider the fragility of life. So many things have to go right in order for a planet to develop life.
First, the star must not have very high mass or high luminosity because that can incinerate any chance of the planets developing an atmosphere, which is essential to life beyond bacteria. That is why it is also helpful for the star to be of a mass like our sun – it is not requirement though as habitable zone can extend out for hotter stars and closer for cooler stars. You still do want the star to not be very massive as those stars form quickly and die quickly, ruining any chance of solar system stability (worst thing you could have is instability that makes planets collide every few million years).
There must also be other planets to keep the space debris like asteroids and comets out (Jupiter does it for us). You can’t have asteroids striking every few million years wiping out all life. Luckily for us, Jupiter eats up & destroys much of the debris, and Mars protects us by taking the hits for us (Thanks big brother and little brother!). For smaller junk, Earth’s atmosphere defends us like a force-field in Star Wars.
The planet must form an atmosphere that is good for life to develop. Too powerful ozone in the atmosphere can lead to runaway green house effect with too much of gases like carbon dioxide (i.e. Venus). Too weak ozone would allow all gas particles necessary for life to escape like on Mars. We also don’t know if life needs carbon or another element like nitrogen can take the place of carbon. As for blood circulation (I assume life needs SOME sort of blood), an element like oxygen would be crucial – it does not necessarily have to be oxygen. Astrobiologists agree that some sort of gas is necessary for land creatures at least to breath, which would require an atmosphere. More importantly, the atmosphere would block off dangerous radiation from the nearest star and gamma-rays from entering. Gamma-rays have very short wavelengths and would destroy any chance of life developing. There must be some sort of magnetic field alongside ozone to keep dangerous radiation and star dust out.
The planet must somewhat cool down enough for liquid of some sort to exist (hard to say whether life needs liquid water or something else would work). Too hot and everything boils, too cold and everything freezes as you would expect.
The tilt and axis of the planet must be stable. If it wasn’t, planet would wobble around out of control. For us, our moon helps keep the axis of Earth stable. Finally, the orbit around the star cannot be too odd like Pluto. It can lead to very inconsistent temperatures and weather throughout the year. The tilt matters too as it determines the seasons – too much tilt and you end up with extreme seasons. Too little tilt and you have no seasons – the high latitudes would be permanently frozen with little or no heat distribution throughout the year, making life difficult anywhere beyond the equator if there is no tilt.
Planet requirements have been explored but what about life itself?
We don’t know the exact ingredients necessary for life to begin developing. We can figure out what elements we are composed of but not what lead up to it 3.7 billion years ago. There are different hypotheses and tests done in labs to try to replicate conditions present on early Earth, but a lot of the specifics are based on assumptions by scientists. At the moment, that’s the best we can do.
We expect there to be some sort of evolutionary mechanism because life continually evolves as DNA changes over many generations & millions of years. Speaking of evolution, for Earth the speed is both varied and fluid depending on the natural pressures of nature at different points in time and space. Life is very resilient whether it is at the bottom of the Mariana Trench (6.8 miles down) or Mount Everest. We know that evolution can sustain through much, but we don’t know if there is a certain limit to how much it can sustain in extreme conditions.
Speaking of extreme conditions, many organisms do not require sunlight for energy, light, or anything and can live off chemicals like hydrogen sulfate and methane. Other factors like temperatures, pressure, and surroundings have limited impact to many bacteria (of course, bacteria cannot survive very extreme heat and at very low temperatures they go into hibernation). That does help bacterial life to thrive in many conditions but obviously larger animals are not as resilient as bacteria. Is there a point in certain extreme conditions when evolutionary mechanisms simply snap? There is simply no way for us to test those limits, and obviously they might differ on our planet compared to other planets as conditions differ.
There are so many things that can go wrong after life develops. Many things can end life, such as asteroids, gamma-ray bursts, massive solar flares, sun imploding, nearby supernova, black holes, quasars, out-of-control global warming, super volcanoes, disease, viruses, bacteria, warfare, DNA mutation, etc.
A civilization must last through all that. You might think I just made a case of giving up our search for life, but you couldn’t be any further from the truth!
Subtraction for Life
Once you go through all the difficulties of life development and potential destructive issues after life develops, the number of planets that has life dwindles quickly from 15-20 billion in habitable zone (I will stick with whole number 20 billion to make the math easier). Here comes the speculation part I mentioned as I go into specific parts of the Drake Equation, which tries to figure out how many civilizations exist in the Milky Way Galaxy.
Lets eliminate half of the habitable Earth-size planets for reasons like unstable solar system, lack of Jupiter-like planet to clean up debris, lack of atmosphere/magnetic field, lack of liquids like water, and lack of planet tilt stability. 10 billion left.
Considering that bacteria life is so resilient, there is a good chance that maybe half of the habitable Earth-like planets have at least basic life. Eliminate the other half. 5 billion left.
Considering that weather and seasons are important to advanced life beyond bacteria & tiny animals, lets say 10% of the remaining planets meet the requirement for advanced life. 500 million left.
For good measure, lets eliminate 80% of remaining planets where life simply doesn’t evolve for whatever reasons beyond our comprehension. 100 million left.
Lets say 10% of the advanced life civilizations last a few million years to develop intelligent technology (our first human-based technology would be building a firepit about a million years ago – I don’t include stone tools because other animals can make & use tools, while ONLY humans can use tools to build firepits for a specific purpose). The rest of them die off. 10 million left.
10% of them are so advanced that they develop interstellar travel and are socially/philosophically evolved to last more than a few million years. 1 million left.
20 billion to 1 million is a huge subtraction, but life is fragile as I mentioned. Many physicists believe even 1 million is too optimistic. A better estimate may be around 100,000 advanced civilizations throughout the Milky Way. Huge parts of these assumptions rely on characteristics of the planet itself and how many planets develop life. Once life develops and given 3-4 billion years, it will evolve fairly quickly unless if something inhibits the speed of evolution (or if there is an asteroid or something every millions of years that resets evolution by killing off complex animals).
A good point by a friend was made from part 1 of this entry that maybe a more advanced alien species than us would have more time to develop better weapons to destroy themselves with if they had more time than we did to work on their art of waging war. If an alien species is advanced technologically far beyond us then I argue that they would also have to be advanced socially & philosophically. It would be EXTREMELY difficult for a hateful and/or socially primitive species to advance all the way to interstellar travel without advancing socially & culturally as well at the same time. Of course, I still cannot discount that possibility considering that we are all speculating at this point.
Of courses, intergalactic distances are an issue, but more specifically, it is the differences in mass distribution in different regions of the galaxy.
The farther you go from the center of the Milky Way Galaxy, the lower the chances become of alien life linking together as the number of stars compacted close together drops along with the number of planets. Essentially, the distances grow between stars the farther you get from the center of the galaxy as more visible mass tends to be near the center and less as you move away from the center (note: I’m completely excluding dark matter here because it messes up mass distribution, and we don’t know what it is).
We are far from the bulge area of Milky Way and towards the outer arm so our search is much tougher than say if we were closer to the center. This is based on the assumption that more mass means more stars means closer distribution of life.
If that assumption is true, civilizations near the center would have better chance of finding each other. Our job gets tougher as we are farther away from the center. I don’t know if any extraterrestrial would be scanning for life towards the outer rim/arm of the milky way. They may probably look inwards towards the center where there is more star distribution rather than outwards.
Of course, as a civilization, you don’t want to be too near the center as things become much more unstable and chaotic as you get closer to the center with more chances of gamma ray bursts as there are more and more stars. We come back to the counter-point: how resilient is life truly?
Would a Signal Change Anything on Earth?
If we find signals from a distant alien species and send a signal back, they may not receive it in time. For instance, if we get a signal from a planet 1500 light years away, it took 1500 years for it to get here and will take 1500 years more for us to get a response back to them (plus the time to decipher the message). We would have no guarantee that they are even alive in those 3000 years or that we are.
So yes, while an alien signal would change our understanding of ourselves and life as a whole, things wouldn’t change very much on a day-to-day basis for us. There would be short-term global unity and large increase in scientific research funding but knowing humanity, I believe that within a couple decades of sending a return message, things would return to the way before the signal. That includes divisions, enmity, and wars.
All I can say is our species MUST keep looking long enough for a signal and to develop our own substations in our solar system. Survival is a MUST, especially considering the ever growing dangers of climate change and global instability on Earth.
The best reason for why you don’t give up the search is simply because you want to know you’re not alone. You want the assurance that there is life out there for us to meet one day. The meeting may not be between you or your children or great grandchildren or even the next 50 generations but somebody else down the road from your species. You want to feel proud to be a human being, to be alive or been alive to help lead up to first contact whenever it is.
Our first and foremost goal has always been survival. Sure there is a chance that the other species might be dead by the time they get our reply or they might be hostile but what has defined us humans is the risks we take in search of light at the end of the tunnel. We know that for the biggest risks we have taken, the payoff has been that much greater. What defines greatness is how difficult something is to attain even when facing impending odds. Never forget that as long as you are alive and human.
We have come close to destruction many times, but we have always overcome even against all odds. We have always survived, and that is the legacy we must continue. That is what it means to be human.
In this entry, there was quite a bit of speculation. In science, you should not speculate too much about things that have very limited data, but sometimes you have to speculate to the best of your knowledge. It comes with the territory of searching for difficult answers. Hypotheses is all we have at this point as we lack concrete data to make the next jump. You can’t have all the answers when you just started to seriously look as a species literally 25 years ago when Hubble was launched, and for every answer you find, there are ten more questions to be asked. You should also not be afraid to admit that you don’t know something (as I did throughout this post). It’s simply an aspect of trying to answer hard questions in quests like finding life in the cosmos.
I have mentioned in past blogs that asking questions in life is essential to what makes us human. Without questions, you have nothing.