I've covered a lot of these individually. Dark matter, the deep-space oddities, the things orbiting stars they shouldn't be orbiting. But MSN recently assembled twenty-five of them in one place, and reading them stacked together like that does something to you. It's one thing to fall down a single rabbit hole. It's another to look down and realize the whole field is holes.

The classics are all here. What is dark matter, this invisible something that outweighs everything we can see by a factor of five and refuses to interact with anything except gravitationally, like a neighbor who only communicates by subtly rearranging your lawn furniture. Why did the Big Bang happen at all and weirder, why did it happen with conditions that let matter win its war with antimatter? Because that imbalance is you. It's everything. A universe where matter and antimatter canceled out perfectly is a universe of radiation and no one to wonder about it.

Then you get the ones that keep me up. The Fermi paradox, which I've come to think of less as a question about aliens and more as a question about mirrors: where is everybody, and what does the silence imply? The Wow! signal, seventy-two seconds of narrowband radio in 1977 that never repeated and never got explained, sitting in the archives like a single footprint on a beach.

Some mysteries will probably fall. NASA's own pages on interstellar visitors like Oumuamua read less like X-Files episodes and more like a catalog of frustratingly incomplete observations, objects gone before we could get a good look. Strange, but not inexplicable. I suspect a few entries on lists like this are questions wearing mystery costumes, and in thirty years they'll be textbook chapters with dates attached.

But that's the minority. Most of these will outlive us. We have no idea what 95 percent of the universe is made of. Read that again slowly. All the stars, planets, gas, dust, every human who ever lived, every thought anyone ever had, that's the rounding error. The actual substance of reality is stuff we can name but not describe, and frankly we named it in a hurry, like settlers drawing borders on maps of terrain they'd never walked.

And that's why I keep writing these. The questions are better than the answers because the answers, when they come, tend to close a door. The questions keep it open, and behind the door is everything we don't know, which is most of it. Tonight, if you're up late anyway, go read the full list. Pick one entry and sit with it. My recommendation is the one about why the universe's expansion is speeding up instead of slowing down, because the leading explanation is a force we've labeled "dark energy" and defined almost entirely by the fact that we cannot define it.

Scientists built an entire cosmological model on that. It works. It makes predictions that come true. And its two main ingredients are things nobody has ever detected directly.

Sleep well.