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Are We Alone In The Universe? Evidence Seems to Indicate That We Probably Are
There is a large population of people that harbor the idea that we are not alone in the universe. They do not believe we are the only intelligent life in this vast universe since there are evidence of more than 1,500 known extrasolar planets, planets orbiting around a normal star other than our Sun, that may carry the possibility of life living on them, even intelligent life. Of the 1,500 extrasolar planets discovered, we have confirmed the radius, mass and orbital characteristics of only 431 of them so far.
However, of the 431 planets with these known characteristics only a handful of them meet the criteria that planets must satisfy in order for intelligent life to survive such as stability, habitability and water, planetary mass and planetary composition. Also in the referenced paper, Dr. Howard Smith, a senior astrophysicist at Harvard, applies the famous “Drake Equation” to provide estimation of the chances of intelligent life living on other planets. The results of the calculations are remarkably low despite the large number of stars and galaxies out there in the cosmos.
Our Attitudes About Extraterrestrial Life
Some of us have heard about these extrasolar planets and what the significance of these discoveries might mean to us. Last year a symposium held by the Royal Society of London appropriately entitled “The Detection of Extra-terrestrial Life and the Consequences for Science and Society” was held and the primary observation the participants took from it as stated in the article, “Should it turn out that we are not alone in the universe, it will fundamentally affect how humanity understands itself.”
Current polls suggest that most people believe we are not alone and half of this group believed we have been visited by extraterrestrial beings already. Most people hold this attitude because they believe some benevolent alien from a utopian society, a place without war, disease and etc, may save us one day by helping mankind solve its problems and then there are some in general who believe life is ubiquitous.
In other words, they believe life is present everywhere in the universe since it is so vast and because there are probably millions of earth-like planets, planets with liquid water and a suitable atmosphere, out there. Perhaps intelligent beings on these planets are also a product of life and evolution just as we are.
The Evidence That We Are Probably Alone For All Practical Purposes
For starter, we must make two clarifications here before continuing with this discussion. We are talking about intelligent extraterrestrial life capable of conscious, independent thought and has the ability to communicate between the stars otherwise we will still be alone if we discovered life that didn’t have these capabilities. Extraterrestrial life must have some form of radio technology to communicate over vast distances and by the way we have only been using this technology for about 100 years despite the fact the universe is 13.8 billion years old. This implies we must be the youngest intelligent life form in the universe if there are many more intelligent life forms out there.
Secondly, there are two other points we must mention for clarification. The first is relativity, the fastest any electromagnetic signal can travel is the finite speed of light. The other point is the expanding universe. If the universe was full of of every conceivable shape and form of life which we could communicate with it would really be irrelevant to us. The light or communication signal sent from Earth will never reach beyond the cosmic horizon since the universe appear to be infinite in size.
The cosmic horizon is the distance set by how far light can travel in the age of the universe, in this case 13.8 billion light years. The other problem with communication is the universe is expanding and the galaxies are accelerating from us. A Harvard astrophysicist, Avi Loeb, has shown that light sent from Earth today can never catch up to these receding galaxies whose light has taken about 10 billion years to get here. These galaxies are forever beyond our reach. We will never be able to communicate with the aliens out there.
Even communicating with closer stars within our own galaxy would be a problem again due to the light speed limit. As I mentioned in an earlier hub I have written about extraterrestrial life it would still take tens, hundreds or even thousands of years to send a signal and wait for a reply from these nearby stars assuming there are planets orbiting them with intelligent life.
Furthermore, if there were alien civilizations with advanced communication capabilities and they sent these signals millions of years ahead of our time for us to receive them we should be receiving them by now. Remember the universe is 13.8 billion years old. Alien life forms probably took a few billion years to develop intelligence with the criteria I mentioned early. No wonder there are no signals despite decades of looking. As stated in the article, Fermi argued they are not out there, Fermi’s observation implies that intelligent aliens are not only not living in our galaxy, but there are not many living anywhere in the universe.
So to be alone for all practical purposes means to be without any communication or even the knowledge that any signal is coming for a very long time. Just imagine being on island for a long time with no form of communication or the ability to receive communication. You will feel alone. You would think that you are alone. This is why we think we are alone in universe. We have not found or received any evidence that there is any life out there capable of communicating with us yet.
Drake’s Equation, Estimating the Chances of Intelligent Extraterrestrial Life
The famous Drake Equation is an equation used by researchers to estimate the probability of intelligent life elsewhere in universe. The equation was first introduced by Frank Drake in the 1950s. It is a basic equation with a set of multiplicative factors tracking the various natural phenomena thought be to necessary to estimate the number of intelligent civilizations in the universe today.
The answer is based on the product of five terms: the number of suitable stars, the number of suitable planets orbiting a suitable star, the probability of life developing on a suitable planet, the probability that life evolves to be intelligent and the typical lifetime of a civilization compared to the lifetime of its star.
Since the discovery of nearly 1,800 extrasolar planets the second term in this equation have been impacted the most with these numbers. With this new information lets explore this equation. We will estimate the probability of intelligent life in our Sun’s own neighborhood called the Local Bubble. There are about 30 million stars in this region. This is the number for the first factor in the equation.
For the second factor in the equation we must consider the number of Earth-like planets orbiting suitable stars. So far we have confirm the physical characteristics of about 431 extrasolar planets but have not found any of them to be quite Earth-like. The “Rare Earth” hypothesis states that Earth-like planets suitable for intelligent life are few and far between. As mentioned before, an Earth-like planet must have these four characteristics: stability, habitability and water, planetary mass and planetary composition.
Planet must orbit a stable star:
To meet the stability criteria, the star the planet is orbiting must be stable in size and have radiative output for billions of years for intelligence to evolve. Our Sun is one of these stars obviously. Over 90 percent of the stars in our galaxy is smaller than the Sun. These suns are red dwarfs
They simply do not put out enough light, thus putting their habitable zone closer to the star. When a planet is close to a star it does not rotate because one side is gravitationally locked with the star so one side will get extremely hot while the other side will be extremely cold. Life probably will not survive under these extreme conditions.
Bigger stars are probably unsuitable for life because they burn hotter and have a shorter life. Most of these stars die out in few tens of million years which is not enough time for intelligent life to evolve. There are fewer than 10 percent of the stars with acceptable mass suitable for life. In other words, if you are looking at 1 million stars in the night sky only 100,000 stars will be suitable to support life on the orbiting planets. This number will get even smaller if the planets are not suitable for life or if the star does not have any planets orbiting it. Furthermore, some of those stars we are in seeing in night sky are not there any more. We are just seeing the light from them just getting here from where they once were located.
The age of stars also matters. Young stars do not have enough time for life to evolve and the luminosity of older stars increases as the star ages thus changing the habitable zone. This will happen to our Sun and the Earth in another 3.5 billion years.
Furthermore, there are some galaxies where practically all their stars are unstable and therefore would not have any planets revolving around them if the galaxies have an under active or overactive black hole at their centers. The black hole at the center of the Milky Way happens to be at the right activity level, as determined by recent data gathered about black holes published in the August 2012 issue of Scientific American, to form stable stars with planets revolving around them.
So there are millions perhaps billions of galaxies out there that simply cannot support life at all because planets cannot form in them since the stars in them are unstable. Also, there would be no planets formed as we approach the center of the galaxies since that region of the galaxy is too violent for planets and stable stars to exist. Most planets would be in the arms of the galaxy or near the edge of galaxy where the most stable stars are formed. This why the Kepler satellite is aimed to search for exosolar planets in one of the arms of the Milky Way. There is no point in searching for habitable planets near the center of the galaxies.
Planet must be habitable and have water:
The second characteristic of an Earth-like planet for intelligent life to evolve is habitability and water. The planet must be in the habitable zone of it star or have some other way to maintain liquid water. Of the 1,800 exoplanets discovered so far only about 20 of them are in the habitable zone.
The planet must be in a relatively circular orbit otherwise it will stray out of the habitable zone. The eccentricity of orbit of planet also matters. It is a measure of the closest distant of the planet to star compared to largest distant of the planet to the star. Of the 431 extrasolar planets discovered so far, only 11 of them have orbits with eccentricity similar to Earth. The other 420 extrasolar planets do not meet this criteria for intelligent life to evolve.
The third criteria of an Earth-like planet is planetary mass. The planet must be large enough to hold an atmosphere. Life would be impossible without some form of atmosphere and if the planet is too massive there would be no plate tectonics activities to drive geological processes that might be crucial for life. Plate tectonics are important for volcanic activities to refresh the atmosphere and other processes associated with the carbon cycle. There seems to be plenty of these Earth-like planet with suitable mass based on preliminary data obtained from the Kepler satellite.
The final criteria for Earth-like planet is planetary composition. A suitable planet must contains all the necessary ingredients for complex molecules. At the same time it must contain elements that are not necessarily essential for life but they must be present in the environment to make the planet suitable for life. For example, iron is important in our case for the development of magnetic field around Earth to protect us from lethal charged particles from the Sun via solar winds.
The distribution of elements throughout the universe is not uniform so some of these planets will not have the elements to make them suitable for life and finally, there are planets that do not orbit stars because they were ejected from the system because of gravitational interactions with other bodies. These planets probably will not be suitable for life since they will be extremely cold without a source of radiated energy from a star.
- To Seek Out New Life Forms
We are spending so much time looking for life on other planets when there are countless lifeforms we have yet to see on our own world. Some of the photos here are incredible. You will think we are on another world after seeing these photos.
- Water Is Needed For Life To Exist In The Universe
From a biological and chemical perspective water is a very important ingredient for life to exist on Earth because of its unique properties. Most likely if there are life else where in the universe water is probably the main component that make its p
Intelligent Life Still May Not Be Out There
Even if a planet meet all the criteria to be a suitable place for life to develop it still may be impossible for intelligent life to evolve. For example, Mars meets some of the criteria of suitable planet to harbor life but no civilizations did not develop there.
Furthermore, if life developed as the end product of the chemical processes on all earth-like planet with water, there is no evidence that these processes occurred quickly. It took life a billion years on Earth to form and another few billion years for intelligent life to appear. If these chemical processes had proceeded at a much slower rate it probably would had been too late for us because the Sun would have swollen to the size of Earth’s orbit and destroyed all life by the time it reached the point of being intelligent.
Then there some believers who believed there may be non-carbon based alien life-forms on other worlds but no evidence of this have been found yet, but most agree that intelligence requires some complexity and if the brains of these aliens do not contain DNA it still will take a large amount of time for their complex organs to develop and mature.
The development of intelligent life appears to be random as well even if the planet meet all the criteria for life to develop. Just looking at our evolutionary path appears to indicate that the development of intelligent life was random. Let us follow the path. A collision with Earth created the Moon and tilted the Earth’s axis to its perfect position causing the seasons on Earth to make the environment suitable for life. Later, the dinosaurs appeared and was wiped out by a large asteroid, after ruling the world for 100 million years and then the mammals filled the niche left behind by the death of the dinosaurs. Life on Earth survived five major mass extinctions before humans finally appeared. A statement from the evolutionary biologist Stephen J. Gould argued that our evolution was so random that it could probably never repeat.
Finally, the biggest uncertainty in the Drake’s Equation is the longevity of intelligent civilization because if a civilization typically survives for a short time then there are not many of them around. We have been communicating with radio signals for about 100 years now. According to the equation researchers believe that out of 10 million stars there is probably one with a detectable civilization and if you look around in the our neighborhood, the Local Bubble which comprise of 30 million star, there might be two other civilizations.
If all the conditions in the Drake’s equation were greater than 20 percent it is possible that there might be another intelligent civilization in our neighborhood, but if the probability of some conditions, such as the chances for life to form, evolve or survive is much smaller and the other conditions are 100 percent certain, most likely none of stars near us have intelligent life on them.
American Scientist; JUL/AUG2011, Volume 99, Issue 4, page320-327
© 2011 Melvin Porter