The popular story we tell ourselves whenever the subject of alien life comes up is that the universe is nearly infinite, so how could there not be more life in it than just us? Surely, we think, that life exists on Earth proves that it can exist at all, and it’s just a case of finding that right combination of factors that give rise to another form of life.

There’s nothing really wrong with this theory, in a bubble. Our galaxy alone has an approximate 100 billion stars. The universe is estimated to have about 100 billion galaxies. That’s as close to infinite as humans have the capacity to behold, so given the sheer repetition of star making, planet making and life making, we cannot be the only case of life evolving into intelligence.

But time plays a crucial role in deciding these things, and whether or not we ever actually encounter intelligent life at all. Yet we almost never factor time into our popular mythology. Here are five good reasons to suspect that we may never find life in the universe, at all. Sorry.

5. Time, Itself.

Most of us are only thinking in three dimensions when we talk about life in the universe. But time is the critical forth dimension. Yes, the universe is really big. But the universe is also extremely old, and according to our best understanding, due to stay cohesive for billions more years. With this in mind, we’re confronted with the possibility that even if life can exist elsewhere in the universe, it may already have been and gone by now. Or that life may still be “coming soon” to a planet near us. For the moment, it’s out of our reach. Speaking of which…

4. Extinction

Life has only existed on our own Earth for about 3.5 billion years. And in that time, 99.9% of the species that have ever lived here have gone extinct. No more stromatolites, eurypterids, diplodocus. No more sabre tooth tigers. Our time is coming, as well. Will we have extinguished ourselves before we get a chance to find what we’re looking for? Maybe.

How long does it take an intelligent species to become extinct? Here, again, we simply don’t know the answer. If we allow that our species will exist for another 100 million years – a very generous assumption – that is merely a blink of an eye to our vast universe. Which lends itself to another question..

3. Limits on Evolutionary Intelligence

One constant refrain in exobiology is that we may encounter species of vasty more evolved intellect. This is a humble thought, as indeed centuries of space exploration have taught us that our world is rarely the extreme. We are neither the biggest nor the smallest planet in the Solar System. Our Solar System is but one of a sea of star systems. The smallest-known galaxy contains only a few thousand stars, while the IC 1101 mega-galaxy could fit thousands of Milky Way galaxies within it’s expanse without burping.

It makes sense to leave open the possibility that we might not be the smartest, either. But just how smart does life get? We now know a limit must exist for intelligence just as surely as it does for everything else. What are the brackets for most and least-intelligent forms of life? One more answer we do not have.

The idea that we might find life that is vastly more evolved than us may actually be hubristic, from the perspective of intelligent life. How do we know we’re not depressingly close to our own maximum? Or that of intelligent life, itself? What if we really are the very tippy-top of what intelligence can achieve in this universe? We’ve not yet discovered extraterrestrial life. Perhaps all forms of intelligence are doomed to live in isolation?

2. Planetary Orbit Degradation

The vaunted “Goldilocks Zone.” It is the distance a planet must orbit from it’s parent star in order for liquid water to exist. To the best of our knowledge, life requires liquid water, therefore planets that exist within this zone are the ones most likely to harbor life. We’ve even discovered a few candidates.

However, orbits are not fixed things. An orbit is simply the delicate balance of an object falling towards a gravitational field, missing, and sling-shotting around it. Those delicate balances, like all things in the universe, degrade over time.

What this means is that planets can either drift away from or closer to their parent stars. The Earth is getting ever so slightly closer to the Sun every year. Don’t worry: the Earth will not be in any danger for billions of years, by which time, the Sun will have become a white dwarf and we’ll all be cinders in the solar wind anyway. Buck up, explorers!

But it is entirely possible to have a planet that exists within the Goldilocks Zone long enough to get life started, but either drift away from or get pulled into it’s parent star’s gravity well and right out of the Zone altogether. Whatever are the limits on intelligence in the universe may be, this hypothetical form of life will never see them.

1. So many star systems, so very little time.

If this list proves nothing else, it certainly makes clear that time may not be on our side, in this search for extraterrestrial life. And while the fantasy of a near-infinite universe may give hope to those of us hungry to learn about extraterrestrial life, it’s not very comforting to the men and women tasked to find it. Because an infinite number of options means that even if the chances of finding extraterrestrial life are pretty good, the odds are still enormous.

In other words, it’s a bit like hurling someone’s keys into Lake Ontario and then telling them, “well, they gotta be in there, somewhere.” I Want to Believe, indeed.

Truthfully, exploring galaxies other than our own is not practical. We can barely observe stars and planets in our own galaxy with any specificity. We’re only just now able to view Pluto, a planet in our own galaxy. We are able to observe distant star systems and their planets based on tricks of physics and statistics, but we have no idea what they look like, much less what they’re composed of. Much less what may live on them.

Dude. Why ya gotta harsh my buzz?

None of the challenges to finding extraterrestrial life are unknown to science, obviously. They’re not new revelations or road blocks. But colloquially, at least, we don’t discuss them. This is because we all – and especially media outlets – enjoy a bias in favour of speculative science.

Because we all want to believe the next big thing is out there. And it is. But finding that next thing is a non-trivial exercise that’s a lot less sexy. In order for Science to advance, you need the theorist to push our ideas forward. But you also need the practical scientist to spend his or her days grinding away at experiments to prove that the theorist’s ideas match with reality’s sometimes stark truths. And personally, I find that struggle fascinating.