This Halloween—like every Halloween—we like to indulge in superstition.

And yes, while paranormal creepypasta stories are unsettling, it doesn’t compare to the real world—a world in a chaotic, violent, and unforgiving universe.

What science can teach us about the world may be more disturbing than any horror movie you’ll ever watch, because at the end of the day, we know those film stories are not real (well, at least some of us know…).

This week, Reddit user SwankyCrunch asked the Ask Reddit community, “What scientific theory scares the shit out of you?”

Here’s what terrifies the scientific community:

The death of the sun

Someday, humanity, and all memories of humanity, will disappear from existence. In one billion years (a wink in cosmic time), the sun will shine brighter and hotter. The water on our planet, the key to life, will vaporize, according to the Scientific American. Earth will quite literally turn into a fiery hell, and, eventually, the sun will devour it. Sleep tight—this is our future.

Being alone in the universe

Terror Management Theory

Humans are a peculiar species—we’re actually keenly aware of own mortality. We know that all of our worries, our heartbreaks, our thoughts, will one day fade away when our life ends. To shield ourselves from the terror of morality, we attempt to create meaning (think religion) out of nothing. This is called Terror Management, a psychology theory proposed in the 1980s.

The death beam

When a star collapses into a black hole it emits a beam of light—a gamma ray burst—which releases more energy than the sun. According to scientists, roughly every five million years a gamma ray burst comes close enough to affect life on Earth. When a beam directly collides with our planet, Earth will be blasted with dangerous levels of radiation. The ozone layer will then disappear. Life, as we know it, will go extinct.

Our universe collapsing at any moment

This is a theory proposed by some scientists that our universe exists in a false vacuum. According to the theory, at any moment, our universe can collapse into a true vacuum. When this random collapse happens, everything will be destroyed within an instant. We won’t even see it coming.

Heat death of the universe

Eventually, everything in the universe will die. Every star will burn out. Matter will decay. What’s left? Nothing. Even heat will die, causing what’s called “the big freeze.” The universe will quite literally turn into an empty, dark abyss. Perhaps, a worse fate than a fiery inferno.

The first and second law of thermodynamics?