Are We Alone
In the Universe?
Exploring the Possibility of
Extraterrestrial Life
“Eternal silence of these infinite spaces frightens me.”
Blaise Pascal, French philosopher and mathematician.
Overview
A fundamental question that continues to challenge the scientific community and intrigue individuals alike is: are we alone in the universe?
At present, there is no definitive answer. Nevertheless, this ignorance encourages further inquiry, prompting additional questions such as:
- Is intelligent life common in the universe, or is it rare and scattered across distant regions? If life is widespread, why haven’t we observed any aliens yet? What prevents contact or travel to other planets with life?
- Are our detection methods too limited, or is the universe simply too vast for us to find signs of intelligent life? Could more advanced aliens have already visited Earth without our awareness?
Let’s begin by exploring the immense scale of the universe before we try to answer these questions.
Continue reading.
How Big Is the Universe?
It is widely recognized that the universe is incredibly vast beyond comprehension. The sheer magnitude of its dimensions presents an extraordinary challenge to human understanding.
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. It should be pointed out that 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. But 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, astronomers now estimate that there are about two trillion such galaxies. And each galaxy consists of hundreds of billions of stars. No doubt, the universe is incredibly vast.
Andromeda galaxy is the nearest galaxy to our home galaxy. It is 2.5 million light years away from us. Yes, the light from the stars of Andromeda galaxy takes about 2.5 million years to reach us!
Extraterrestrial life may exist within our own galaxy as well as in distant galaxies across the universe. This discussion will first examine whether it is feasible for life forms originating from other galaxies to traverse the immense intergalactic distances required to visit Earth.
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 when 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 that 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 light years 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, that makes us conclude that it is, at present, impossible for us to make a trip to any exoplanet using our current technologies.
How about communicating?
It is clear that interstellar travel remains beyond our current capabilities. Given this limitation, what are the prospects for detecting extraterrestrial life or establishing communication with alien civilizations?
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 light years 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.
The main issue isn’t whether we can travel or communicate; it’s about the likelihood of discovering aliens on a planet orbiting another star within the Milky Way. Let’s try to figure out what those chances might be.
How Common is Life?
We know well that advanced life exists in the universe. Because we are the proof for that. But how common is life 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 the 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