Many reputable scientists agree that, statistically, extraterrestrials must exist within the universe.
Why don’t we have any evidence that extraterrestrials exist within the universe, despite a consensus amongst elite scientists that they should certainly exist? Why don’t alien’s pay us a visit to solve the mystery once and for all?
Additionally, how come all of our search efforts thus far have proved fruitless? These actually happen to be the very questions these scientists also ponder. Let’s take a look at the reasons they conclude as to why we haven’t made contact with any neighbors from outer space.
1. Rare Earth Hypothesis
While many scientists such as Carl Sagan and Frank Drake believe that the universe must indeed teem with complex life other than ourselves, given its enormity, there are a few scientists who disagree.
Scientists Peter Ward and Donald E. Brownlee disagree. They argue that planet earth won some kind of “lottery” that caused it to spawn life. In their book, Rare Earth: Why Complex Life is Uncommon in the Universe, Ward and Brownlee present a hypothesis that it was an almost impossible combination of geological and astrophysical circumstances and events that brought about life on Earth.
According to them, this could mean we are alone within the vast cosmos, and that there are no aliens out there for us to contact, or to visit us.
2. Gaian Bottleneck Hypothesis
Astrobiologists at the Australian National University, Charley Lineweaver and Aditya Chopra suggest that it is likely life has and does emerge on other planets. However, it very quickly becomes extinct before it can evolve into a more complex state.
The fragility of life requires a lottery similar to that suggested in the Rare Earth Hypothesis, and the chances that a planetary environment will remain stable enough to nurture it is extremely challenging and rare.
The examples they give are Venus and Mars, which both appear to have once contained extremely primitive life forms in ancient times.
3. The Great Filter Hypothesis
Economist Robin Hanson first proposed the idea of the Great Filter in 1996, and scientists discussing the Fermi Paradox were quick to recognize it’s relevance.
The Fermi Paradox acknowledges how, on the one hand, we have no evidence of the existence of extraterrestrial life, but on the other hand the statistical probability for its existence is staggeringly high. Hanson argues that the evolutionary path is just too complex and therefore improbable. He suggests a minimum of 9 steps that life must filter through to achieve viability.
Additionally, life on earth survived five mass extinction events, which is extremely rare and almost miraculous. For this to occur somewhere else in the cosmos would mean any extraterrestrial neighbors are exceedingly few and far between.
4. The Great Silence Hypothesis
Even with the scientists doubting that we don’t have many if any, extraterrestrial neighbors in the universe, there are still many more scientists convinced that we shouldn’t be so arrogant. Why should we assume we are so lucky to be the only life that exists? And furthermore, we may even not be so advanced in comparison.
Still, these scientists are concerned by the obvious lack of contact from aliens. Consequently, they hypothesize that we should have been having regular contact with such advanced beings. Which brings them to question “why the silence?”
Consequently, many scientists believe it possible that an advanced civilization from another star may see us as far too primitive to bother with. Just as we would not wish to introduce ourselves to single-cell primitive life forms we could potentially find on a nearby planet; these extraterrestrials are possibly so far advanced, we appear as nothing more than irrelevant amoebas to them.
Furthermore, Stephen Hawking has gone so far as to suggest that it is better that we have made not contact with advanced alien civilizations. He hypothesizes that such extraterrestrials would be dangerous to interact with, and may even wish to annihilate us!
5. The Early Bird Hypothesis
According to a study of comprehensive NASA data, authored by Dr. Peter Behroozi, Earth was one of the earliest to form, giving it more opportunity to evolve lifeforms.
In fact, according to Behroozi, only 8% of the planets that will exist within the lifespan of the universe have been born. Scientists estimate that it will be 120 trillion years until the last star burns out and the universe as we know it disappears.
In other words, there is still plenty of time for other Earth-like planets to form and spawn life.
According to Behroozi, the reason we haven’t made contact with extraterrestrials is that we could be one of the first life forms to have appeared in the universe.
6. Universe is teeming with life, but not as we know it
Some scientists suggest another hypothesis as to why our search for life elsewhere in the universe is proving fruitless. They claim we are judging what life is from a too narrow perspective. In other words, we are only looking for life that mirrors ourselves. However, aliens may have a biology that is nothing like what we are looking for.
Most scientists believe that evidence of life means that an organism breathes oxygen and is carbon-based. In fact, NASA is coming to suspect that Saturn’s largest moon Titan could potentially contain such alternative “life” that may not breathe oxygen and be methane-based.
Hypothetically, according to these scientists, life on other planets may not even be organic. Aliens could even potentially be machine based.
7. We haven’t been looking long enough!
Other scientists believe that there is a simple reason why we have made no contact with extraterrestrials. We haven’t been looking long enough!
For example, the SETI Institute only began seeking evidence of extraterrestrial life in 1984. And altogether, humans have been making technological efforts to make contact for only 80 years. In the scheme of the universe, this is an exceedingly short amount of time! Also, we underestimate the amount of time it takes for messages to arrive after transmission. We have only scanned for alien signals to a distance of 40,000 light-years. Considering the outer perimeter of the milky way is 100,000 light years away, our attempts are quite measly.
Additionally, our technology may be too primitive to send and receive messages to and from alien civilizations. And with the size of the universe, the potential directions in which to send and receive signals is almost endless. We have barely scratched the surface in our attempts to make contact with extraterrestrials.