Science is brilliant. It’s cured diseases, sent us to the moon, and let us argue with strangers online from a device in our pocket. But there are still some mysteries that, for all our cleverness, remain frustratingly unsolved. In fact, some of them have been around so long that even scientists seem slightly suspiciously quiet about them. Whether it’s because the data doesn’t add up, or because no one really wants to touch the subject again until we’ve got better tools (or better guesses), these are the big, weird, or just plain stubborn things that science still hasn’t figured out.
1. Why we yawn
Everyone does it. Even babies in the womb. But ask scientists why we yawn, and you’ll get a lot of shrugs. Is it to cool the brain? Increase oxygen? Signal boredom or empathy? Possibly. Or maybe all of the above. Or none. The truth is, we still don’t know for sure. It’s one of those weirdly everyday things that seems too minor to spend huge research money on, so it just keeps lingering in the “unresolved” pile.
2. What consciousness actually is
We all have it—or at least, we think we do. However, defining consciousness—where it begins, what it’s made of, or how it works—remains one of science’s most persistent blank spots. Neuroscientists can track brain activity, but they still can’t explain how those electrical signals become subjective experience.
It’s not just a technical problem, either—it’s a philosophical one. You can observe someone’s brain, but you can’t observe their internal thoughts. Which means that consciousness remains a deeply personal mystery we’re still nowhere near solving.
3. Why cats purr
Yes, they purr when they’re happy, but also when they’re injured, frightened, or even dying. That’s confused scientists for years. There’s also evidence that purring has healing properties, like stimulating bone growth and lowering stress levels, which makes things even murkier. Some researchers think it’s a kind of self-soothing mechanism, or even a way to manipulate humans. But since cats haven’t been especially helpful about revealing their motives, the mystery remains.
4. How gravity actually works
We know what it does—it pulls things together. But how does it work at a quantum level? That’s where things fall apart (ironically). Gravity doesn’t fit neatly into our best theories of physics, especially when you try to combine it with quantum mechanics. Despite decades of research and a lot of maths, no one has managed to come up with a “quantum theory of gravity” that makes all the pieces fit. It’s like we’ve mapped the entire puzzle, except the corner piece is still missing.
5. Why time only moves forward
Time always ticks in one direction: forward. But when you look at the laws of physics, they don’t really demand this. In theory, most equations work just as well in reverse. So why can’t we un-spill milk or watch broken things reassemble? The leading idea is entropy, or the idea that things naturally move from order to disorder. But even that explanation isn’t airtight. It’s like we’re all on a train going one way and no one can find the driver.
6. How placebos actually work
The placebo effect is very real. People can take sugar pills and experience real changes in pain, mood, and even physical symptoms. However, why does belief change the body? And how far can it go? Researchers have found that even knowing something is a placebo doesn’t always cancel the effect. That messes with everything we thought we knew about expectation and biology. The brain-body connection clearly has tricks we still don’t understand.
7. What dark matter is made of
Dark matter makes up about 27% of the universe. That’s more than all the stars and planets we can see. And yet… we have no idea what it actually is. We can’t see it, touch it, or detect it directly. We only know it exists because of how it influences gravity. Every year brings a new theory, from weakly interacting particles to entirely new physics. But so far, it remains invisible, untouchable, and unsolved. Like a cosmic placeholder scientists keep hoping will reveal itself.
8. What causes deja vu
That weird feeling that you’ve lived this moment before? Deja vu happens to most people at some point, but we still don’t really know why. Is it a brain glitch? A memory misfire? A lag in neural processing? Whatever it is, it usually disappears before you can even think about it properly, which makes it really hard to study in a lab. For now, it remains one of those eerie little mysteries that science hasn’t cracked.
9. Why we sleep
We know we need it. Going without sleep messes up everything—mood, memory, health, even sanity. But why does the body insist on shutting down for hours every day? Why is it non-negotiable? There are a lot of theories: that sleep clears waste from the brain, resets emotional regulation, or consolidates memory. That being said, none fully explains why we can’t evolve a workaround. For such a vital function, the “why” is still fuzzy.
10. How life began
We can study evolution all the way back to single-celled organisms, but the moment life first sparked—when molecules became self-replicating cells—that’s still a black box. Did it happen in deep-sea vents? Clay? Space? A lightning bolt in a warm puddle? We’ve recreated pieces of the puzzle in labs, but never the whole thing. It’s one of science’s oldest questions, and it still doesn’t have a solid answer. Just a lot of hopeful experiments and educated guesses.
11. Why some people never get COVID
Through all the waves and variants, some people have been exposed again and again and never tested positive. Are they genetically protected? Is it something about their immune system, or a sheer stroke of luck? Scientists are looking into it, but we’re still in the early stages of figuring out what’s going on. Whatever the answer is, it could hold clues for future vaccines or viral resistance, but for now, it’s one big “huh?”
12. Why we dream
Dreams are one of the most surreal parts of human life. You spend hours each night experiencing wild, emotional stories with no real control, and most of the time, you forget them by breakfast. But why? Some theories say dreaming helps process emotions or solve problems. Others say it’s just the brain entertaining itself while we’re offline. But no one really knows. It’s still one of the strangest recurring things science can’t fully explain.
13. Why the universe exists at all
This one’s kind of the ultimate head-scratcher. Given the way matter and antimatter should’ve cancelled each other out in the Big Bang, there should be… nothing. Just empty space. And yet, here we are. Physicists are still baffled by how matter gained the upper hand. Somewhere in the earliest fractions of a second, something tipped the balance, but we don’t know what or how. Until then, the very fact that anything exists is still on the mystery list.