Here is a list of 20 Scariest Theories Known to Man.

1. False vacuum

False vacuum

This is, in short, a scientific hypothesis that our universe is actually in a false phase state as part of a larger universe, like if it were a temporary thing (think the real universe is a pot of boiling water, and we are just within a bubble forming at the bottom of the pot). Eventually however that false vacuum has to pop, even after billions of years in this false state and we and everything we know in our visible universe will disappear in an instant with no warning whatsoever and there is nothing you can do about it.

2. The Great Filter

The Great Filter

It’s a theory about why the universe seems so filled with potential for life and yet we haven’t found it. It states that somewhere between pre-life and an advanced civilization that is capable of colonizing the stars, there’s a Great Filter that stops them and ends life. This means humans fit into one of these three scenarios:

  • We’re rare, meaning we’ve already passed the Great Filter, unlike other civilizations on other planets.
  • We’re the first, meaning conditions in the universe are only now life friendly and we’re among many on our way to the capability of colonization.
  • We haven’t hit the Filter yet, meaning we are f**ked. If this one is true, it means finding life or proof of life on Mars or Europa would be awful news because it would almost certainly mean the Filter is still ahead of us instead of behind us.

3. Brain in a vat

Brain in a vat

The brain in a vat is an element used in a variety of thought experiments intended to draw out certain features of our ideas of knowledge, reality, truth, mind, and meaning. It assumes the following;

  • The brain is the origin of all consciousness.
  • The brain operates on electrical impulses.
  • External stimuli can affect the way the brain operates.
  • Any external stimuli to the brain can be simulated to a degree that the brain cannot distinguish these simulated stimuli from natural stimuli.

The point is that you could be a brain in a jar, being fed false impulses for your entire life by an external source, or you (still a brain in a jar) could be hallucinating your entire life from lack of stimuli.

4. Higher Dimensional Beings

Higher Dimensional Beings

Imagine if there was a 2D person. If you stare at them a certain way, they can’t see you. All you have to do is look from a top view and they won’t know you are there, and they would never know. Living their life as 2D, they would never be able to comprehend how something could be looking down on them.

Now imagine a 4D person. They could be looking at you from a 4 dimensional angle, an angle that you will never understand. They could be right beside you, but you wouldn’t know, and you would never know. Just as we could interact with the 2D person, the 4D person could interact with us. But as long as they don’t want us to, we could never interact with them or not even know of them.

5. Fermi Paradox

Fermi Paradox

Let’s say we have an ant hill in the middle of the forest. And right next to the ant hill, we are building a ten-lane super-highway. And the question is “Would the ants be able to understand what a ten-lane super-highway is? Would the ants be able to understand the technology and the intentions of the beings building the highway next to them?

So it’s not that we can’t pick up the signals from Planet X using our technology, it’s that we can’t even comprehend what the beings from Planet X are or what they’re trying to do. It’s so beyond us that even if they really wanted to enlighten us, it would be like trying to teach ants about the internet.

When Pizarro made his way into Peru, did he stop for a while at an anthill to try to communicate? Was he magnanimous, trying to help the ants in the anthill? Did he become hostile and slow his original mission down in order to smash the anthill apart? Or was the anthill of complete and utter and eternal irrelevance to Pizarro? That might be our situation here.

6. Roko’s Basilisk

Roko's Basilisk

Roko’s basilisk is a proposition that says an all-powerful artificial intelligence from the future may retroactively punish those who did not assist in bringing about its existence. It resembles a futurist version of Pascal’s wager; an argument suggesting that people should take into account particular singularitarian ideas, or even donate money, by weighing up the prospect of punishment versus reward. Furthermore, the proposition says that merely knowing about it incurs the risk of punishment (Now you know about it. You know who to thank while you will be tortured). It is also mixed with an ontological argument, to suggest this is even a reasonable threat.

7. Terror Management Theory

Terror Management Theory

Everything that humanity has ever accomplished beyond basic survival has been motivated by a fundamental and irreducible fear of non-existence. Our conception of self and self-esteem generally is simply a buffer against the anxiety that comes with recognizing that we will cease to be. Culture is just a massive shared delusion to mitigate our fear of the unknown and ultimately of death. Thus we want to imagine certain works of art as timeless or to place value in family lines and offspring, to project ourselves beyond death. We take comfort in our value systems and the structures that arise from them, whether that’s through conceptions of biological kinship, national/ political identity, religious faith, etc. This includes belief in the inherent value of ensuring the future of humanity through scientific progress. Indeed much of modern western life is devoted to the avoidance of death, the various euphemisms and stock phrases in mourning, the entire funeral home industry that serves to remove death from the ordinary course of life, from the home and onto the embalming table or into the crematorium. We build up the artifice to avoid the brutal reality. In short, everything that we’ve ever done and will ever do is motivated by nothing more than our existential terror in confronting death.

8. Quantum Suicide/Quantum Immortality

Quantum Suicide-Quantum Immortality

A man sits down before a gun, which is pointed at his head. This is no ordinary gun; i­t’s rigged to a machine that measures the spin of a quantum particle. Each time the trigger is pulled, the spin of the quantum particle — or quark — is measured. Depending on the measurement, the gun will either fire, or it won’t. If the quantum particle is measured as spinning in a clockwise motion, the gun will fire. If the quark is spinning counterclockwise, the gun won’t go off. There’ll only be a click.

Nervously, the man takes a breath and pulls the trigger. The gun clicks. He pulls the trigger again. Click. And again: click. The man will continue to pull the trigger again and again with the same result: The gun won’t fire. Although it’s functioning properly and loaded with bullets, no matter how many times he pulls the trigger, the gun will never fire. He’ll continue this process for eternity, becoming immortal.

Go back in time to the beginning of the experiment. The man pulls the trigger for the very first time, and the quark is now measured as spinning clockwise. The gun fires. The man is dead.

But, wait. The man already pulled the trigger the first time — and an infinite amount of times following that — and we already know the gun didn’t fire. How can the man be dead? The man is unaware, but he’s both alive and dead. Each time he pulls the trigger, the universe is split in two. It will continue to split, again and again, each time the trigger is pulled. This thought experiment is called quantum suicide.

9. Transcension Hypothesis

Transcension Hypothesis

The hypothesis proposes that once civilizations saturate their local region of space with their intelligence, reach microscopic technological singularity, create a black hole and leave our visible, macroscopic universe in order to continue exponential growth of complexity and intelligence, and disappear from this universe, thus explaining the Fermi Paradox. Developments in astrobiology make this a testable hypothesis. It proposes space, time, energy and matter compression, as a driver of accelerating change, which must lead cosmic intelligence to a future of highly-miniaturized, accelerated, and local “transcension” to extra-universal domains, rather than to space-faring expansion within our existing universe. You can find a much better explanation in this youtube video.

10. Sixth Mass Extinction

Mass Extinction

We are currently living through what many biologists consider to be the sixth mass extinction that the world has ever seen. This is going to be an interesting puzzle for the species that comes after us. It wasn’t until around the year 1800 that humanity reached a population of 1 billion after thousands and thousands of years. In the 215 years since then, the world population has increased to ~7.2 Billion. That exponential growth has very large and long lasting negative effects on our planet, and will continue to do so until we reach carrying capacity or die off.

11. Kessler Syndrome

Kessler Syndrome

Low Earth Orbit, an area of outer space around Earth that encloses all orbits below 2000 km, is the home of the International Space Station and of other thousands of satellites. It is also becoming a hazardous arena littered with mindless space junk and inoperable spacecraft orbiting at outrageous speeds.

The Kessler Syndrome is a theory proposed by NASA scientist Donald J. Kessler in 1978, used to describe a self-sustaining cascading collision of space debris in Low Earth Orbit. It’s the idea that two colliding objects in space generate more debris that then collides with other objects, creating even more shrapnel and litter until the entirety of LEO is an impassable array of super swift stuff. At that point, any entering satellite would face unprecedented risks of headfirst bombardment. The cloud of debris could last for centuries or more, and the more satellites we launch the more likely it is to happen. . This could effectively make launching satellites (or any manned craft intended for extended stays in space) impossible, sending us into a sort of dark ages again.

12. Heat Death of the Universe

Heat death of the Universe

Thermodynamics dictates that large systems in universe evolve toward equilibrium over time. This is a balanced, calm state where no more reactions are favorable; nothing has energy to gain or lose compared to anything else.

The ‘heat-death’ of the universe is when the universe has reached a state of maximum entropy. This happens when all available energy (such as from a hot source) has moved to places of less energy (such as a colder source). Once this has happened, no more work can be extracted from the universe. Since heat ceases to flow, no more work can be acquired from heat transfer. This same kind of equilibrium state will also happen with all other forms of energy (mechanical, electrical, etc.). Since no more work can be extracted from the universe at that point, it is effectively dead, especially for the purposes of humankind. Eternal stillness.

13. Clathrate Gun Hypothesis

Methane bubbles

Huge quantities of methane are held in ice-like structures in the cold northern bogs and the bottom of the seas. They are called clathrates (or cathrates). They are stable only in the cold or under high pressure. Methane is 24 times more potent a greenhouse gas than CO2. The estimated amount of methane stored in these clathrates is gargantuan. They are the largest concentration of methane found on earth.

The clathrate gun hypothesis suggests that the mass release of methane from methane clathrates on the ocean floor may have triggered catastrophic global warming, in turn causing mass extinction, at least once in the Earth’s ancient past. There is a suggestion that the ocean’s bottom waters couldn’t warm up to 8°C. If so, that would certainly set off massive clathrate destabilization. This is what turns the clathrates into a ticking time bomb.

The “gun” part of the clathrate gun hypothesis refers to both the fact that once it gets going, it can’t be stopped, and its lethal effects. Once the planet starts warming, circulation in the oceans would decrease, causing large areas of ocean to turn anoxic, killing off life in huge numbers.

14. Poincaré Recurrence Theorem

Poincaré recurrence theorem

In mathematics, the Poincaré recurrence theorem states that, after a sufficiently long (unfathomably long) but finite time, all closed systems will sample any accessible state and will return to a state very close to the initial state. The Poincaré recurrence time is the length of time elapsed until the recurrence (this time may vary greatly depending on the exact initial state and required degree of closeness). If you play bridge long enough you will eventually be dealt any grand-slam hand, not once but several times. This means what is happening now will eventually repeat again after a very long period of time in the future and you might have already read this page a long time ago.

15. Grey goo Hypothesis

Grey goo Hypothesis

Grey goo, a term coined by nanotechnology pioneer Eric Drexler, refers to a hypothetical end-of-the-world event involving nanotechnology in which out-of-control self-replicating robots consume all life on Earth while building more of themselves (a scenario known as ecophagy). It is usually used in a science fictional context.

In a worst-case scenario, all of the matter in the universe could be turned into goo (with “goo” meaning a large mass of replicating nanomachines lacking large-scale structure, which may or may not actually appear goo-like), killing the universe’s residents. The disaster could result from an accidental mutation in a self-replicating nanomachine used for other purposes, or possibly from a deliberate doomsday device.

16. Skinnerian Behaviorism

Skinnerian Behaviorism

“Though we feel that we can choose what we do, our understanding of the molecular basis of biology shows that biological processes are governed by the laws of physics and chemistry and are therefore as determined as the orbits of the planets.”

-Stephen Hawking

Basically, free will and consciousness are illusions. It’s all just chemical reactions in your brain and the stronger ones are the ones that make your decisions. That would explain why people can completely change personalities with traumatic brain damage or make stupid decisions when impaired.

17. Solipsism


The philosophical idea of solipsism implies that the only thing that you know truly exists is your own mind. Everything else outside of one’s own mind/conscious is not guaranteed to exist. Your surroundings and the consciousness of others cannot ever be proven to exist. A step further into metaphysical solipsism and one can make the claim that the external world and other minds do not exist, where you are the one true reality, all the stimuli you encounter are a representation of yourself, and everything else has no independent existence. Basically, everyone you know and everything you’ve seen are merely external stimuli created by your own mind.

A depressing idea is that of onism, where because you are limited to only one body at one point in space and time, you miss out on so many experiences, people, and places due to the impossibility of ever encountering everything life has to offer. Life is essentially a series of rooms with varying numbers of doors in each that represent diverging decisions, both small and large, that one must pass through and can never go back through to open and see what might have been. Even if you had the ability to go back through doors you crossed to access other doors in order to experience what may have been (which would basically create billions of permutations as to how your life pans out) , you are still limited to those experiences that you would have encountered because those are just the branching story lines and options granted to you in your own life and time span, due to the impossibility of inhabiting another person at a different point in time and space.

18. Time is Finite

Finite Time

Scientists have come up with the radical suggestion that the universe’s end may come not with a bang but a standstill – that time could be literally running out and could, one day, stop altogether.

The motivation for this radical end to time itself is to provide an alternative explanation for “dark energy” – the mysterious antigravitational force that has been suggested to explain a cosmic phenomenon that has baffled scientists.

A decade ago, astronomers noticed that distant supernovae – exploding stars on the very fringes of the universe – seemed to be moving faster than those nearer to the centre, suggesting that they were accelerating as they shot through space. Dark energy was suggested as a possible means of powering this acceleration of the expansion of the cosmos. The appearance of acceleration is caused by time itself gradually slowing down, like a clock that needs winding.

19. Technological singularity

Technological singularity

Technological singularity was a term coined by Vernor Vinge, the science fiction author, in 1983. “We will soon create intelligences greater than our own,” he wrote. “When this happens, human history will have reached a kind of singularity, an intellectual transition as impenetrable as the knotted space-time at the center of a black hole, and the world will pass far beyond our understanding.”

The idea is that when we become capable of creating beings more intelligent than us, it stands to reason that they or their near-descendants will be able to create intelligences more intelligent than themselves. This exponential growth of intelligences would work much like Moore’s Law but have more profound significance. When there are intelligences capable of creating more intelligent beings in rapid succession, we enter an age where technological advances move at a rate we can’t even dream of right now.

And that’s saying something: thanks to the nature of exponential growth, technological advance is already making headway at the fastest pace we’ve ever seen.

20. Behavioral Sink

Universe 25

Unlimited population growth will hit a mental trigger in animals and create self-destructive behaviors.

The ethologist John B. Calhoun coined the term “behavioral sink” to describe the collapse in behavior which resulted from overcrowding. Over a number of years, Calhoun conducted over-population experiments on rats. He built a mouse paradise with beautiful buildings and limitless food. He introduced eight mice to the population. Two years later, the mice had created their own apocalypse. The colony peaked at 2200 and from there declined to extinction. Once a tipping point was reached, the mice lost instinctual behaviors. Lone females retreated to isolated nesting boxes on penthouse levels. Other males, a group Calhoun termed “the beautiful ones,” never sought sex and never fought—they just ate, slept, and groomed, wrapped in narcissistic introspection. Elsewhere, cannibalism, pansexualism, and violence became endemic. Mouse society had collapsed. Scientists extrapolate this model to humans on earth.

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Last Update: June 10, 2023

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