As we look out to the stars, humanity often ponders one of the biggest questions of all: are we the only intelligent life in the Universe? As of October 2025 there are 6,022 confirmed exoplanets in 4,490 star systems. Exoplanets are not rare, there are over 100 billion stars in the Milky Way Galaxy we call home, some estimates put it as high as 400 billion.
However we need to focus in on G class starts like the sun, with a stable long main sequence of 10 billion years+/-, sun-like stars make up about 7% of all starts in the Milky Way. A lot of exoplanets found to date are gas giants, hot Jupiters whose orbit is too close to their parent star for life – as we know it – to evolve. An estimated 300 million potentially habitable rocky worlds may exist in the galaxy, orbiting in the “Goldilocks zone” where liquid water can exist. Kepler-452 b is a potential candidate lying within the habitable zone of a main sequence G class star.
Where is everybody?
In simple terms, the Fermi paradox asks why, given the vast number of stars and potentially habitable planets in our observable universe, there is no clear evidence of extra terrestrial civilizations. The Drake equation allows us to calculate the probability of extra terrestrial civilisations, depending on how you set the values it gives results that strongly suggest we are not alone. The paradox named after physicist Enrico Fermi, who informally posed the question to colleagues over lunch in Los Alamos, essentially his question was “But where is everybody?”
Essentially the Femi Paradox can be surmised as follows, given the fact there are over 100 billion stars in the Milky Way, and taking the probability of habitable planets from the averages discovered to date, the chance of life evolving and both intelligent life and civilisations evolving that would leave some trace of their exitance should be quite high, especially when you factor in that the Sun is a second generation star and some stars and their planets are much older than the Sun. Even with slower than lightspeed travel enough time has elapsed for exploration and colonisation to have taken place. The Fermi paradox is that we should see clear evidence of intelligent life and space faring civilisations in terms of super-structures like Dyson Spheres, visits by extra terrestrial civilizations, or at the very least their probes. However, the paradox is that there is no convincing evidence that visits have happened and to date we have not found any clear evidence of superstructures like Dyson Spheres, Orbital rings, Alderson Disks or Space Elevators. Tabby’s Star is an interesting footnote here, as the variation in light output and its light curve is so far unexplained, although a megastructure is not through to be the most likely candidate.
In short the Fermi paradox seeks to resolve the conflict between the probability that intelligent life is common in the universe, and the total lack of evidence of intelligent life having ever arisen anywhere other than on Earth. And we could argue evidence for intelligence life here on Earth is debateable, listen to the Galaxy Song by Monty Python for an eloquent and succinct outline of that debate
What are the possible explanations for the silence?
One possible explanation to the Fermi paradox is Stellar evolution. We are fortunate enough to live on a planet that is relatively obscure. There are no stars with the potential to go to Supernova within 25–30 light-years of Earth. If that happened it would very likely destroying the ozone layer with high-energy radiation, leading to ecosystem collapse. In more densely populated areas of the Milky Way closer to the galactic core Supernova risk to civilisation could be such that no civilisations which have arisen to date have survived.
Is it a coincidence that we developed he ability to destroy ourselves and the ability to broadcast signals strong enough to get to interstellar space within a few short years of one another? A frequent explanation for the Fermi Paradox is that civilisation go through a type of civilisational adolescence and very few civilisations make it through. Climate change is a huge self inflicted risk to civilisation, one that is being wilfully ignored by a lot of those in power.
The Great Filter
This is the concept used to try and explain the silence and to make sense of where we as a civilisation are. There are lots of potential candidates for the great filter. Self imposed extinction through climate change is a definite possibility. The evolution of intelligence itself could be an evolutionary dead end, if intelligence is defined as the ability to use technology to change our environment, then changing our environment to render it uninhabitable is the ultimate evolutionary dead end, a bacterium never developed a nuclear bomb. A civilisation growing to be powerful enough to shape a planet may inevitably destroy it. Humans have had agriculture for about 15,000 years, throughout human history each generation of tools have been more powerful, we’ve gone from very basic steam engines to the nuclear bomb in less than 250 years. The potential for AI to surpass human intelligence is a very real risk. Have precursor civilisations developed their own versions of AI which over time elect to get rid of wasteful biology from its civilisation? The other evolutionary factor may be individual greed, have other civilisations been eliminated by ecological disasters that follow from self-inflicted catastrophises like runaway climate change driven by personal greed?
Maths is your enemy
The maths is instructive here. Assume a civilisation has 1% chance of destroying itself each century. If you compound this risk the odds of a civilisation surviving a millennium are 90.4%, by 10,000 years with a 1% risk of self-destruction per century you are at around a one third probability of survival, 36.6% to be precise, by 50,000 years the chance of survival is less than 1%. The maths would seem to strongly suggest with reasonable assumptions the probability is loaded against any civilisations long term survival. We have had access to atomic/nuclear weapons for less than 100 years, in that time we have had several close shaves with annihilation, read our blog about Stanislav Petrov if you haven’t already done so. If you compound this 1% chance of self-destruction over a million years the answer tends to zero, this may ultimately be the reason why the universe is silent.
Leave no trace
Very few structures will survive geological time, structure like the pyramids and the great wall of China are starting to decay. If Earth is visited in a million years’ time what would survive and what evidence would there be for our telescopes today if we could look at a planet that had a civilisation a million years ago, what would we see? If civilisation on Earth falters apart from some odd isotopes and nuclear waste we won’t leave many lasting signs of our presence that would be discernible in a million years’ time.
Survival is entirely our own responsibility, engaging with the challenges that face mankind like climate change and over population. We need to tackle these challenges head on, or our civilisation will just flourish very briefly and leave no lasting trace of its existence. We are not aware of any species yet successfully making the transition from intelligent species to interstellar civilisation. We are at an inflection point, it very much looks like the filter lies ahead of us in the very near future.
But, we could be on the cusp of discovery
The James Webb Space telescope has detected potential biosignatures on a number of exoplanets, notably it has detected tentative signatures of dimethyl sulphide a molecule associated with life on Earth, in the atmosphere of exoplanet K2-18b which is located 124 light-years away. The findings suggest a hydrogen-rich atmosphere and liquid ocean, though findings are not yet definitively confirmed. If the JWST ever discovered evidence of industrial pollutants, like CFCs, it would be a definitive answer to the paradox.
Alternately could we be among the first civilisations to break the filter, given that the expected lifespan of the universe is at least one trillion years and the age of the universe is around 14 billion years, it is possible that mankind has emerged at or near the earliest possible opportunity for intelligent life, with the potential to colonise space to evolve. It may be that second-generation stars, like the sun and the planets, formed from gas clouds rich in the heavier elements that are the products of the death of earlier stars are the only potential candidates for complex life. We just don’t know.
The counterpoint to this positivity is that is that the Laws of Physics don’t include a law that intelligent species survive. The universe is indifferent, ultimately the only thing we can be certain of is that in the end entropy will win out.