Well it seems my first thread on the Fermi Paradox generated some interest. Not sure if it's because people here on ATS want to talk about it, or
just need a break from all the politics. In any case, it's good to see.
This thread will concentrate on one of the "solutions" to the Fermi Paradox. In this case the Rare Earth Hypothesis.
For those who do not know what the Fermi Paradox is, you can click on this link here to the
intro thread and read the OP for it.
Before we get into this solution, I would like to make sure all understand: The Fermi Paradox is nothing more than a question. The original question
is "Where are they?", which is basically asking: If the universe is so vast with so many planets and stars, where are all the aliens at?"
It's not something that tries to prove that intelligent alien life does not exist. It's really nothing more than a question everyone should ask,
especially if you do believe that intelligent life is out there: Where are they?
Also: all opinions are welcome here. If you disagree with someone, that's fine, just make sure you all keep it civil. I'm sure we can debate things
without the need to get nasty with each other. If you feel the urge to be that way, please go to the Political Mud Pit forum. Keep it out of here. If
you can't convince each other, simply agree to disagree. Considering how speculative much of this can be, there's a good chance of not being able to
prove someone wrong anyways.
So let's dig in!
The Rare Earth Solution, Part 1.
Basically this says that the reason we do not see a bunch of aliens flying around, sending out signals from their home worlds or stopping by Earth for
a pizza, is because "Earth Like" planets are rare.
Now, there's two parts to this: Earth Like planets that can support life as we know it, and Earth Like planets that developed intelligent life.
This thread is going to cover the first part. After all, for a tool using intelligent race, we most likely need a "Earth Like" planet. Having some
strange alien creatures that evolved inside a gas giant or on a world completely covered with oceans where they can't develope fire for smelting
metal, are more than likely going to be disappointing for our tool using advanced civilization that can broadcast signals or fly out into space.
Before we go into "Earth Like" planets, we need to take a look at a couple of things first. That is our galaxy and stars.
Our galaxy, the Milky Way, has somewhere between 100 billion to 400 billion stars in it. However, every galaxy has what we call a habitable zone also,
just like each star has one. For stars the zone is based upon temperatures: too far out you're too cold. Too close in and you're too hot.
For galaxies the way it works is: Too far out, you have much older metal poor stars. Too close to the core and you're having to deal with very large
amounts of radiation and too many stars close together, where stars going nova or super nova will effect many star systems.
Okay, so we don't want to be too close to the core of a galaxy....what's this about "metal poor" stars?
Well, stars have several classifications, most of which deal with their size, temperature, life span, etc. However there is a classification for their
age too. We basically put them in three categories:
"Population 1, 2 and 3" stars.
Population 3 stars are the oldest stars. These are stars that formed closer to the beginning of the universe. When we look at their spectrum, we find
that they have hardly any heavier elements like metal in them. This is hardly surprising since it was the stars themselves that forged our heavier
Population 2 stars are old stars that formed after Population 3 stars, but have a little bit more metal in them...but are still very low in that
Population 3 stars are the newer stars. Our sun is considered one of these, and have a much higher metal content.
So why is this important? It's important because the planets around a star are normally made up of the same thing as the star they orbit. Which means
planets around Population 3 and 2 stars are either not going to be rocky, or if rocky will be very, very low in heavier elements like metal.
The lack of these metals means that even if alien life that becomes intelligent develops on these planets, they will not have the heavier elements
available to them to build technologies, especially anything that can go out into space.
So having a star in "just the right place" is important, and because of this, it lowers the number of stars in a galaxy where intelligent life as we
know it might exist.
Yes, that's right. The stars. You can have a world that's an exact duplicate of our Earth, but if it's around the wrong star, then we have a
Let's look at our star. Obviously it's been a great star for Earth to have since we live on a planet teaming with a large diversity of life.
First, let us look at the classification of stars. Astronomers use letters to classify them. In order they are M, K, G, F, B, and O.
There is a further classification with a number next to that letter. You can have a G type star, but they range from G0 to G9. Those numbers are a bit
less important than the letters for the purpose of our discussion here.
The reason the star is so important is because of how a star behaves, how long it lasts. Those are two very, very important factors.
For example, M type stars are red in color and have low surface temps and long lifespans. O type stars are blue and are very, very hot and tend to
have very short lifespans.
When we look at the population of star types, we find that there are many, many more M, K and G type stars than there are of the others. The most
populus stars that we know of are Red Dwarfs. The reason this is important is because in general, the hotter the star, the shorter it's life span.
Small red dwar stars have life spans measured in hundreds of billions of years. In fact: none of these stars have died yet. The universe itself is too
young for them to of used up all their fuel.
Massive blue super giants have life spans less than 100 million years. From what we know of our sun and Earth, it took several billion years for life
to forum and for tool using humans to come about.
If your star has a life span of less than 100 million years, it means any planets around it have no chance and developing life as we know it long
enough to evolve into a advanced tool using species. From what we know of life here on Earth, that process took billions of years.
The other thing we need is a stable star. Having a star that has a bad temper (throws off massive amounts of itself through flares and CMEs) is not a
good thing to have. The sun is a very stable star for the most part.
So, what we are seeing is:
1) We need a star to be in the right place in the galaxy and staying there.
2) Stars that are high in metals like Population 3 stars.
3) Stars that last long enough and are stable enough for life on planets around it to evolve.
Continued in the next post: