Here is a list of 10 10 Scariest Theories Known to Man.

1. 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.

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2. 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.

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3. 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.

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4. 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.

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5. 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.

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6. 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.

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7. 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.

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8. 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.

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9. 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

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.