Are We Alone
In the Universe?
“Eternal silence of these infinite spaces frightens me.”
Blaise Pascal, French philosopher and mathematician.
Overview
One of the unsettled questions, in the scientific community as well as in the mind of every curious person, is: are we alone in the universe?
The short answer is we have no idea. But that does not stop us from asking more questions such as:
- Is the universe teeming with life everywhere? Or is intelligent life rare but not that rare? Or does extraterrestrial life exist in different corners of the universe separated by vast distances so that communication is just impossible?
- If intelligent life can exist everywhere, why we have not seen any aliens so far (ignoring all those UFO/alien hoaxes like the one reported in The New York Times recently5)? What stops them from visiting us? Can we make a trip to aliens’ planet?
- Why we are not able to detect any sign of intelligent life anywhere else? Is it the lack of technology that is stopping us from detecting intelligent life? Or is it the fact that the cosmos is so vast that we cannot detect or meet them at all? Or is it possible that more advanced intelligent aliens stealthily visited us already, and we could not recognize them?
Before checking if we have answers to these questions, let us first understand how big and vast the universe is.
Keep reading.
How Big Is the Universe?
As you know, our universe is unbelievably big. The scale of its size is simply mind boggling.
We live on the planet Earth which is one of the eight planets revolving around a medium size ordinary star: the Sun. Our Sun is one of the 100 billion or more stars in our Milky Way galaxy. The size of Milky Way is humungous. Light takes about 100 thousand light years to travel from one end of the Milky Way to the other end.
Until the beginning of the last century, astronomers believed that the Milky Way was the entire universe. Edwin Hubble, in 1920s, discovered that the universe was not just the Milky Way alone; instead, it consisted of billions of other galaxies too.
In the observable part of the universe alone, now astronomers estimate that there are about two trillion such galaxies and each galaxy with hundreds of billions of stars in it. No doubt, the universe is incredibly big.
The nearest galaxy to our home galaxy is Andromeda galaxy which is 2.5 million light years away. Yes, the light from the stars of Andromeda galaxy takes about 2.5 million years to reach us!
Aliens may live in our own home galaxy or in other far away galaxies too. First let us investigate if aliens, living in other galaxies, can travel the vast intergalactic distance to visit us.
Intergalactic Travel
In this discussion, we are not going to consider the popular (science-fiction) travel mechanisms such as wormhole or warp-drive which are mere theoretical concepts. Their existence and the feasibility of travelling by making use of them are not yet established.
As mentioned in the previous section, the observable part of our universe alone has about two trillion galaxies. Our next-door galaxy, Andromeda, is 2.5 million light years away. There are many, many other galaxies which are unbelievably distant.
Let us assume that aliens exist in the nearby Andromeda galaxy. Also, let us suppose that they have advanced technologies that help them travel at 25% of the speed of light. Can they make a trip to our Earth? Even at this tremendous speed they need to travel for 10 million years to reach us. Can anyone or anything survive the 10-million-years journey? It should be pointed out that space travel is extremely risky and dangerous, especially while moving at speeds comparable to the speed of light. Any piece of tiny junk can destroy the spaceship.
Hence, the chances of aliens (or their spaceships operated by robots) visiting us, from other galaxies, is very, very slim.
Intragalactic Travel
If intergalactic travel is impossible, what about intragalactic (interstellar) travelling for the aliens?
Our Milky Way is 100,000 light years across. Our solar system is about 28,000 light years from the center of the Milky Way. We live in a sweet spot in our galaxy. In case aliens live in any of the nearby star systems within our Milky Way galaxy, will they be able to travel the interstellar space and visit us? Yes, it is likely provided those aliens have advanced technologies that propel them to speeds comparable to the speed of light.
How about humans travelling to that aliens’ planet? It is impossible for us. Why?
Can you guess the maximum speed any spacecraft, built by us, could attain? According to Guinness World Records, Parker solar probe reached the speed of 163 km/sec which is only 0.0543 percent of the speed of light (FYI, light travels at the speed of 300,000 km/sec). Travelling at 163 km/sec, if we attempt to make a trip to our nearest star system (Proxima Centauri), which is 4.4 lightyears away from Earth, we need to travel for about 8000 years. How is it possible for humans to survive 8000 years of journey? Human life cannot survive that long in interstellar space.
What if we detect life in a star system which is 100 light years away from Earth? To visit those aliens, we need to travel for 184,000 years!
So, we have to conclude that it is, at present, impossible for us to make a trip to any exoplanet using our current technologies.
How about communicating?
Okay we get it. Now, we understand that interstellar travel is not feasible for us. How about detecting aliens or communicating with them?
The fastest tool we have to communicate with any extraterrestrial life is electromagnetic (EM) waves. If we broadcast EM messages in all directions, aliens may never be able to receive them as the strength of EM wave decreases exponentially as it travels through vast cosmos. Remember that the interstellar space is depressingly vast.
Even if we know their exact location in the Milky Way, communicating with aliens is still a big challenge. Assume that they are 1000 lightyears away from us. Our first message, “hello aliens”, will take 1000 years to reach them and their reply, in whatever form, will take another 1000 years. It is not an easy task. We will encounter not only language barriers but also time barrier.
Whether we can travel or communicate is the secondary question. The primary question is: what is the chance of finding aliens on a planet circling another star in the Milky Way? Let us see if we can determine that.
How Common is Life?
We know well that advanced life exists in the universe. Because we are the proof for that. But how common life is in the universe? Is the universe teeming with advanced life everywhere? Or is it extremely rare?
We know that it took several billion years to get the life started on Earth after the formation of sterile planets in the solar system. In addition, it took another billion years to get us on this planet after microorganisms came into existence. Though the exact details of terrestrial life’s origin is still a mystery, it is clear that a big chain of most improbable coincidences occurred. That resulted in intelligent life on Earth.
Can an exoplanet in our galaxy win a similar jackpot? Yes, why not? It can happen.
Drake’s Equation
Now, let us see if it is possible to determine the probability of finding an intelligent life somewhere else in the Milky Way.
The following equation, which is known as Drake equation, should help us estimate the number of intelligent species (N) that may exist in our galaxy.
Though we do have reasonable estimates for the first two factors, as given below, we are unable to estimate the rest of the factors.
nstars : the number of stars in Milky way is about 100 billion.
nplanets :The modern estimate of earths like planets in Milky Way is about 20 billion.
Remember, there is only one data point which is us, the terrestrial life. Besides, we do not fully understand how life might have started on Earth. In this situation, there is no way to estimate the values for the rest of the factors.
Hence, we cannot estimate, N, the number of possible intelligent civilizations in our Milky Way.
Conclusion
Whatever may be going on in the universe, one thing is clear. The life on Earth is a happenstance, and it is shaped by the uncaring laws of nature. It is an end result of a large sequence of random events.
The natural question is can that happen in other star systems too in the Milky Way? Or in other galaxies in the universe? Yes, it can. Given the billions of possible earth-like planets in our galaxy and the trillions of such galaxies in the universe, it is possible. There is no reason nature cannot replicate what it has done on Earth.
Perhaps the universe is teeming with life everywhere, and we are just one of the millions of lives in the universe.
Or perhaps life may be rare, but not that rare. That means that lives could exist in different corners of the universe, and they will never be able to talk to one another because of the incredible vastness of space.
Or perhaps, we are alone in the universe. We have no clue.
References
- We Have No Idea – A guide to the Unknown Universe by Jorge Cham and Daniel Whiteson
- https://www.nytimes.com/2023/08/24/magazine/avi-loeb-alien-hunter.html
- https://www.bbc.com/future/article/20150809-how-fast-could-humans-travel-safely-through-space
- https://www.guinnessworldrecords.com/world-records/66135-fastest-spacecraft-speed
- https://www.nytimes.com/2023/09/13/world/americas/alien-mummy-congress-mexico.html