'''Basic Trope''': Humans are the only known intelligent form of life in the universe.
* '''Straight''': In the early 22nd century, humanity has ventured far into the Milky Way and discovered no intelligent life forms, although there are clearly signs of extraterrestrial life, but those extraterrestrials in question are microscopic.
* '''Exaggerated''':
** They can't even find the most primitive single-celled organisms, despite sending orbital probes and scientific rovers to every habitable planet. All of life itself has only evolved on one planet -- Earth.
** In addition to that, there is no other life in all of TheMultiverse.
* '''Downplayed''':
** Alien life has evolved to the level of [[AlienAnimals animals]] at most, but they're non-sapient.
** Every now and then, people allege to have seen [[UnidentifiedFlyingObject UFOs]] or even alien beings, but they have no solid evidence of those claims.
** Aliens exist, but aren't seen and only mentioned in the background and have little to no effect on the plot.
** Aliens are TranshumanAliens.
* '''Justified''':
** Human space travel is in its infancy, and we haven't had time to find them yet.
** The odds of contacting intelligent life forms are so low that, even if they are there, it might take a million years to find one.
** There ''used to be'' [[{{Precursors}} extraterrestrial civilizations]], but [[ApocalypseHow they went extinct somehow]].
** Alien life is so, well, [[StarfishAliens alien]] that it's not even recognized as alien life and exists right under the nose of humanity.
* '''Inverted''': The universe is full of aliens, but humans don't exist.
* '''Subverted''': The people of Earth finally discover a civilization of HumanAliens, and quickly make FirstContact.
* '''Double Subverted''': The so-called "alien civilization" was actually just a [[TranshumanAliens long-lost colony of human descendants]].
* '''Zig Zagged''': The starship ''Lazarus'' searches 1000 Earth-like planets for intelligent life. Some of them offer false leads, but all of them are uninhabited. That is until the [[LastPlaceYouLook last planet they look]] actually does support an alien species, but it is non-sapient. However they find out the intelligent aliens were posing as non-sapient [[SecretTestOfCharacter to see how the humans would treat them]]. Then it turns out that they are actually highly evolved humans, and the starship's crew had experienced 50 million years worth of TimeDilation.
* '''Parodied''':
** Repeated radio signals of "Hello, we come in peace." from a specific point in the sky turn out to be random noise. [[ContrivedCoincidence The cosmic background radiation just happened to make that pattern]].
** The aliens are obviously present and even attempt to communicate with the humans, but the humans [[WeirdnessCensor are too stupid]] or [[ArbitrarySkepticism attached to their preconceptions]] to recognize the aliens' presence.
** Or alternatively, the aliens are [[HumansAreBastards so completely]] [[HumansAreCthulhu disgusted by]] [[HumansAreMorons the humans]], that they [[Literature/TheyreMadeOutofMeat hide and pretend not to be there]].
* '''Averted''': There are plenty of aliens in the universe.
* '''Enforced''': Aliens are avoided to save on a show's budget.
* '''Lampshaded''': "Don't be ridiculous, Bob. There's no way we'll find aliens on this mission."
* '''Invoked''':
** [[FantasticRacism Humans wanted a universe without aliens]], [[HumansAreTheRealMonsters so we killed them all]].
** We know they're there, but avoid making contact with them.
* '''Exploited''': If every planet is uninhabited, then we shouldn't feel too guilty about taking over the universe.
* '''Defied''':
** A scientist, bored of his own species or horrified about the fact that there aren't any other sapients, creates alien life in the lab.
** "Just because we haven't seen alien sapients doesn't mean they don't exist."
* '''Discussed''': "It's strange to think that we really are alone in the universe."
* '''Conversed''': "It's refreshing to see a sci-fi show without those [[RubberForeheadAliens low budget aliens]]."
* '''Deconstructed''': Humans go into a deep state of ennui upon discovering they are alone in the universe.
* '''Reconstructed''': The fact that aliens don't exist just means humans are more important and special, and that they must work at their own civilization.
* '''Played For Laughs''': A {{Cloudcuckoolander}} ConspiracyTheorist desperately tries to find proof of alien life, making very wild (and laughable) claims that [[DeadpanSnarker his skeptical peers mercilessly mock him for it]].
* '''Played For Drama''': The fact that the universe is empty of non-human life is viewed as highly disturbing -- especially when human explorers start finding the ruins of [[{{Precursors}} extinct alien races]], [[FridgeHorror implying that]] [[PrecursorKillers something wiped them out]]...
* '''Played For Horror''': Same as the above, except that all subtlety gets thrown out the window when humans directly encounter the aforementioned PrecursorKillers, and find out the hard way why all other aliens in the known universe have long been dead.
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Go back to AbsentAliens if you like, but you won't find any intelligent life there.
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%%* '''Plotted A Good Waste''': ???
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