For me there is no question about the existence of intelligent life elsewhere. I sometimes do wonder about the existence of intelligent life here on earth. A conversation I had with my father over the weekend did highlight the fact that for others it is very much a question.
I’ve related my experience but, those who haven’t experienced something similar only take that to mean that I’m out of touch with reality. I don’t understand why some people have such a touch time with the possibility of life from elsewhere occasionally visiting earth.
The Royal Observatory in Greenwich provides an estimate of 7 x 1022 stars in the universe. That’s 70,000,000,000,000,000,000,000 stars.
In our galaxy we’ve surveyed a number of stars in the local vicinity looking for planets. Planets are so small and so dim compared to a star that we are unable to detect them directly because they are lost in the glare of the parent star. Since we can’t see them directly, we look for the wobble their gravity creates in the parent star. We can detect this by looking at the spectral lines shift in frequency in a periodic rate (as the planet orbits the star). One other method we can occasionally use is detecting momentary dimming of a stars light by a planetary transit.
The former method only works well if the plane of the orbit of the planet around the star is somewhat in our direction so the star gets pulled towards us and away from us. If it is not close to edge on the star gets pulled back and forth or up and down relative to us and we can’t see that in a Doppler shift.
Additionally, our detection method only works well for massive planets orbiting relatively close to the star. So called “hot Jupiters” that are generally Jupiters mass or heavier orbiting close to the star.
If the orbit of a stars planet is exactly edge on relative to us and transits the star, we can detect somewhat smaller planets that way and planets that orbit more distant from the star but it is extremely rare for such an orbital configuration to line up just right for us to be able to detect a planet transiting a star.
We would not be able to detect any of the planets in our own solar system from another star with our current technology.
Even given these limitations in our ability to detect planets, half of the stars we look at have planetary systems. If our technology were advanced enough see smaller objects, earth sized planets, then there is a high probability we would see a planetary system around virtually every star around which a stable orbit exists.
Many of these stars may have multiple habitable planets. In our own solar system we know of only one planet that has life, but we know of others that may.
In particular, both methane and formaldehyde have been detected in Mars atmosphere. Methane, being the simplest hydrocarbon, is widely found in nature and can be produced by many abiotic processes. Formaldehyde can also be created by abiotic processes but is less common. However, on Mars it is particularly significant because the conditions in the Martian atmosphere gives formaldehyde a half-life measured in hours, so something has to be continuously replenishing it.
The probability that some bacteria or other primitive life forms, possibly lichens, existing on Mars today is fairly high. In addition to the fact that something is producing substantial quantities of methane and formaldehyde on an ongoing basis, the original experiments to look for life in the soil done by Vikings actually had some positive results that were dismissed as chemical reactions.
What we know about the Martian environment now suggests the tests were designed to look for the wrong kind of life and a new life seeking experiment will be launched towards Mars later this year.
We used to believe that life required oxygen. Then we discovered sulfur reducing bacteria that are in fact poisoned by oxygen. Then we discovered whole food chains based upon sulfur reduction around the so called black smokers, volcanic vents at the sea floor rifts.
The life forms we discovered around the black smokers also not only tolerated but actually thrived at temperatures considerably above the surface boiling point of water.
Another potential place where life may exist is on Jupiter’s moon Europa. Europa’s surface is covered with water ice and it is cracked and deformed in a way that suggests a liquid ocean underneath. The density of Europa suggests that an ocean approximately 800 miles deep may exist. Tidal energy resulting from Jupiter’s deformation of Europa’s crust, provides the heat that melts Europa’s ice into an ocean. If liquid water is present, the potential for life forms which obtain their energy chemically as with the life forms surrounding the black smokers on earth, may exist there.
Saturn’s moon Enceladus has water geysers on the south pole which were recently observed by the Cassini space craft. There is speculation that heat is provided by tidal forces and another group speculates by the decay of radioactive elements. Whatever the source, there is liquid water present and organic chemicals present which are necessary for life as we know it.
And then there is Jupiter’s moon Calisto. Long thought to be dead with a surface a billion years old; measurement of Calisto’s magnetic field shows that it changes as Jupiter rotates. The favored explanation is that a current is flowing within Calisto, and the surface ice is too poor of a conductor to allow for such a flow, but a liquid salt-water ocean underneath the ice would do the trick.
So in this Solar system you have one body that definitely has life, might have intelligent life (that’s still open to debate in my book), and four bodies that may have life.
Now multiply that by 7 x 1022 stars or even half that, and you’ve got a lot of potential life harboring planets out there. How many of those will go on to develop tool using intelligent life? That’s a harder question. In this solar system, only one planet has done so and it took it nearly 4.5 billion years. It took several billion just to get around to multi-cellular life.
What if it’s one-in-one-billion? That’s still 7 x 1012 intelligent tool using life forms that will come into existence on various planets throughout the universe or an average of about 70 intelligent tool using species per average galaxy (the Milky Way is larger than average although there are giant ellipticals 1000 times larger).
I suspect the odds are likely to be better than 1-in-1 billion but even with those remote odds this universe is teaming with intelligent life. Then we get down to are they physically able to get here and if so would they come here, after all there are a lot of places they could go, they may be out there but Earth may just not be terribly interesting.
Right now our understanding of science isn’t sufficient to know for sure one way or the other. I know, but my experience isn’t enough to convince many people, so how can it be approached scientifically? Einsteins theory of general relativity makes it appear to be impossible to go faster than light. On the surface this makes it sound impossible because as you accelerate mass towards the speed of light, it’s mass increases towards infinity thus requiring ever increasing amounts of energy. The bottom line is that taking the direct approach it appears that we can not do it.
However, there are several ways know to physicists to cheat, instead of traveling faster than light, compress space in front of you and expand it behind. And scientists know how to do this but it requires something known as exotic matter, and a tremendous supply of energy. Wormholes might be another way to cheat but we neither know how to create on that is stable for get to one that exists, so for us now that method is moot, but perhaps not for other civilizations.
This is one of my areas of interest, given the laws of physics, how might it be possible? The solution to this problem would not only allow us to become a truly space faring race but also solve many domestic problems. But this is a problem that is not solved yet.
And then why would they come here? Many people have speculated on this, the explosions of atomic weapons give off certain signatures such as gamma ray burst, that may have attracted attention. There are reports of UFO like sightings well before the explosion of the first atomic bomb.
Some people speculate that the Earth is a galactic watering hole. I see that is unlikely however because water is not uncommon in interstellar space.
I don’t really know what their motive for coming here might be. I wonder if ants wonder why we do what we do, occasionally coming into their world.