Quick Answer: Odds are very much stacked against earth being the only planet with life in the universe.
Now that being said, until we have found definitive evidence proving that there is life elsewhere in the universe, we can’t actually prove that there is life anywhere aside from our lovely blue planet. But, what we can do is start making some assumptions and look at the probability of whether or not there is life out there in the heavens. And when you do this, the statistical probability that we are the only life in the universe becomes very low. The reason for this is because the universe is really, really, really, really big (click here to see our article on the size of the universe) and all the numbers associated with it are mind-bogglingly really, really, really, really big.
So how do we figure out what the probability is that there is life on other planets in the universe other than Earth? Well, it’s time to put our math hats on! Thankfully, we don’t have to start from scratch because someone named Frank Drake already came up with a conceptual equation for determining the probability of intelligent life back in the 1960’s. Francis Drake worked at the National Radio Astronomy Observatory and was listening for radio signals that could be from intelligent life coming from space within our own Galaxy. He came up with an equation that would take into account all the different variables to calculate the number of planets where there would be intelligent life. I would encourage you to go look up more on Francis Drake and the Drake Equation (here is a good place to start). This is a breakdown of the Drake Equation:
If you want to look at this equation in more depth, I would recommend going here which is a great website by Astrodigital where you can play with all the different variables and it spits out an answer to the equation.
In this article we’re going to be modifying this equation and updating it a bit. We’ve made a lot of advancements in understanding our universe since the 1960’s, so we have a much better grasp on how many stars are out there, how many planets, and where planets can exist and have liquid water.
Because of this, and since we’re only looking for planets with life, and not necessarily intelligent, broadcasting life, we are going to make our own version of this equation. We also want to broaden our scope and look outside our own galaxy and look at the entire universe.
We’ll call this the Drake-Sagan equation (in respect to both Frank Drake and Carl Sagan):
Now let’s see how this equation actually works. First, let’s make some assumptions:
- Factor Su: We have estimates that there are 1×10^24 (1 with 24 zeroes after it) stars in our observable universe
- Factor Pp: Let’s say that the probability of a star having planets is 1% (probably obscenely low but let’s be conservative for argument’s sake)
- Factor Np: Let’s say the average number of planets if a star does have planets is 2 (again probably low but we scientists like to be consistent).
- Factor Ph: Let’s say that the probability that a planet will be in a habitable zone is 0.0001% (this is the equivalent of 1 in a million sticking with our consistent conservative pattern).
- Factor Pl: Let’s say that the probability that a planet in the habitable zone has developed life is 0.0000001 (the equivalent of one in a billion (rinse and repeat conservative pattern!!!)).
What happens when we plug those values in?
20 million planets with life. Even if you make the assumptions on the probabilities absurdly low; even lower than we assumed, there is still going to be a high probability of life elsewhere in the universe.
And because we know we have a hard time visualizing big numbers like this, lets look at it this way: If you looked at each one of those 20 million planets for only one second each, it would take you 231 days, 11 hours, and 33 minutes to go through all of them if you were working 24 hours a day, 7 days a week.
So, what is the point of this exercise if we still don’t have actual proof of life? I think the biggest point in doing this exercise, is that it gives us a reason to explore space and push our boundaries and technologies as far as we can. If there are 20 million or more potential planets out there with high statistical potentials for life, we need to start figuring out how to get out there and explore them.
Now the next question that comes out of this is, what form is that life most likely in? Are we going to find more human-like forms or alien animals? We will tackle that fascinating question in a future article coming soon!
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