NASA recently announced that they found a planetary system that has seven Earth-like planets. Three out of which are in a habitable zone… this made me excited and worried at the same time.
Why It's Great News?
This kind of discovery was considered impossible. I remember reading about exoplanets in the high-school. Back then we knew one of them:
The consensus was that they’re so far and so dark that we’ll probably never be able to tell anything about them. So the recent discovery is a huge progress by humanity. In such a short time period we made progress from impossible to just a stepping stone.
Why it's grim news?
Because it makes human survival less probable. The discovery doesn’t change our chances for success, it only enables us to reevaluate the probabilities. It's a dark perspective for our years ahead. Here's why.
Enrico Fermi has raised a problem known as Fermi paradox or “Where is everybody”. It says that we should be able to observe intelligent aliens given the vastness of the universe (our galaxy even).
This paradox follows from Drake formula. That formula gives us an estimate of how many civilizations should there be in the universe. The values of coefficients of this formula are constantly updated as the science makes progress.
The thing is that the coefficients are being raised from the original, pessimistic estimates. But even in the beginning the formula suggested that there should be plenty of well developed civilizations out there. Some of which we should be able to observe. So far we cannot see anybody.
The Great Filter
Given how many civilizations should be observable to us and the fact that we see none may mean that there's something stooping those worlds from developing beyond a certain stage. This hypothesis is called a great filter.
Some event or natural phenomena that makes it impossible to expand civilization beyond certain point. This could be a civilization self-destruction. In our case this could be a strong climate change or a global atomic war.
It all may mean the great filter is ahead of us. This means there's something tragic that will happen to humanity in the future. Another explanation is that there is no great filter and we're the first ones to go as far as we did. This would mean that we're the only ones in the universe. Another explanation could be that we're the first ones that got through the great filter, so it's behind us.
Yet another explanation is that at some more advanced stages civilizations change in such a way that they're incomprehensible to us. Say like a human-built highway is beyond understanding to an ant. This is actually more hopeful scenario as it doesn’t assume existence of any filter.
So the more planets we discover the smaller chance we'll survive. That is until we start observing alien civilizations. Either way the biggest hope is in further development of science, our understanding of the world.