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Where are the Aliens? Are We Alone?

Updated on December 26, 2015

Have you ever looked up at the night sky and were amazed by the number of stars that show up. You might have also wondered: ‘Are we alone? Is there no one else like us in this huge place?’ (Huge is a very small word to refer to the universe)

Let’s have a look at the odds of us being alone in the universe by trying to count the total number of stars in the entire universe using the present theories and calculation provided by our scientists.

Stars are not randomly scattered around in the universe rather, they are gathered into vast groups called Galaxies. Our earth is a part of the solar system formed by our star ‘the Sun’. The Sun is an average sized star in the Milky Way galaxy.

This Image known as 'The Hubble Ultra Deep Field' itself contains at least 10,000 galaxies!
This Image known as 'The Hubble Ultra Deep Field' itself contains at least 10,000 galaxies!

It has been said that counting the number of stars in the universe is like counting the number of grains of sand on all the beaches on earth. It can be done by counting the number of grains in a small representative volume of sand and by multiplying one can estimate the total grains of sand on every beach on earth. Similarly, one can estimate the total number of stars by counting the stars in a galaxy and then multiplying that observation to the total number of galaxies.

The Milky Way galaxy consists of stars ranging from 1011 to 1012 in numbers [1]. The total number of galaxies in the universe is also around 1011 and 1012 [2].

Multiplying the number of stars in our galaxy (i.e. 1011 to 1012) with the total number of galaxies (i.e. also 1011 to 1012), we get that there are about 1022 to 1024 stars in the whole universe.

Now that we have counted the stars let’s try to count the number of extraterrestrial civilizations that might be out there waiting to be contacted.

Scientists don’t totally agree on a particular percent of the total stars being sun-like but assumption range from 5% to 20%. Taking the more conservative sides (5% and 1022) into consideration we get that there are at least 500 billion-billion stars that are similar to our sun in size.

A recent PNAS Study [3] shows that about 22% of those Sun-like stars are having a potentially habitable planet like our earth. This gives us about 100 billion-billion planets which are earth-like. Let’s imagine that after many (billions) years of existence 1% of those earth-like potentially habitable planets develop intelligent life form like us (humans). That would mean that there exist 10 million billion planets with intelligent life forms in the whole universe.

Doing the same mathematics for our galaxy, we get that there must be about 100,000 intelligent life forms in the Milky Way itself.

There is a scale which is used to measure the technological advancement of a civilization known as Kardashev Scale (named on the soviet astronomer Nikolai Kardashev) [4]. It groups intelligent civilizations into three broad categories called type I, type II, type III, classified by the amount of energy they can utilize and store.

A Type I Civilization is a civilization which is able to utilize and store the energy available from its neighboring star which reaches their planet.

A Type II Civilization is able to utilize the energy of the entire star. One way of using the energy of the entire star is by forming a dyson sphere-a device which would encompass the entire star and transfer its energy to the planet.

A Type III Civilization would be able to utilize the energy of their whole galaxy and even more. According to Michio Kaku humanity would take 100,000 to a million years to become a type III civilization.

Carl Sagan suggested that humans are at present a type 0.7 civilization and that it would take a few years to become a type I.

Coming back to the calculations and considering that 1% of the 100,000 intelligent life forms present in the Milky Way were born a lot before us and now have become type III civilizations would mean that there should be about 1,000 type III civilizations present here in the Milky Way galaxy itself.

So what prevented them from contacting us? There is an organization known as SETI (Search for Extraterrestrial Intelligence) which is set up to monitor radio signals and electromagnetic waves sent from any intelligent civilization in space. But it has never ever received any single. If there are about 1,000 type III civilizations in our galaxy then why haven’t they sent any kind of message to contact other intelligent civilizations?

That’s what Physicist Enrico Fermi wondered – ‘where is everybody?’ And this came to be called ‘the Fermi Paradox’.

Physicist Enrico Fermi
Physicist Enrico Fermi

There are two types of explanations:

  1. Intelligent life form (like us- humans) is very rare and so there are no other civilizations which are advanced at such a level. The people who believe in this are the ones who cite the existence of the great filter theory. I will cover this explanation in my future article.
  2. The other explanation says that there are other intelligent civilizations in the universe but we have not heard from them yet. There might be certain reasons that didn’t allow communication.

The possible reasons could be:

1. Intelligent Civilizations are two far apart in space.

It could be possible that there exist intelligent civilizations but they are too far apart. The signals would take millions of years to reach the other end and that the civilizations go extinct before any meaningful communication takes place.

2. Human beings have not existed long enough.

Our ability to detect extraterrestrial life has not existed long enough as radio telescopes were invented not even a complete century ago. This might have caused us to miss any signal that might have been sent out to us.

3. We are not listening properly.

It could be possible that other extraterrestrial civilizations are too primitive or too advanced for us to be able to detect the type of signals they might send. There are other limitations of SETI such as it can detect signals sent only from a distance of 0.3 light years which is less than 1/10 of the distance to the nearest star.

4. They are too different from us.

Another possibility is that we might have underestimated how different alien life would be from us. CarlSagan speculated that an alien species might have a thought process orders of magnitude slower (or faster) than humans, which might not allow us to communicate with them.

5. They are non-technological.

It could be possible that there are intelligent civilizations but they are non-technological. Such a civilization would be very hard for us to detect.

6. All of them are listening, no one is transmitting.

Alien civilization might be able to transmit but are only trying to listen instead of transmitting any message just like us. This is called the SETI Paradox [5].

7. There are advanced civilizations which are aware of our existence but are only observing us. (The Zoo Hypothesis)

The Zoo Hypothesis states that advanced extraterrestrial life forms exist but does not contact us and is observing us like we observe animals in a zoo or national park.

8. No wants to transmit first

It is also possible that they might not want to transmit any message before any other civilization due to the Fermi paradox itself. They might also want to receive rather than transmit like we are doing now.


Any of these could be the reason why we haven’t heard from the aliens yet, but I am sure that in the coming years or in the coming centuries one fine day we would know that ‘We are not alone.’

Waiting for that day to come…..

What is your stand on the Fermi Paradox?

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      Divyansh Gupta 19 months ago from Bharatpur, Rajasthan, India

      @jasmeek that is why we aren't sending any signals into the space to invite any predator civilization

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      Jasmeet Kaur 19 months ago from India

      I always wonder if there are aliens??? if 1 day they come on our planet?? and if something wrong happens like happen in movies!!!!