The Universe is 85% Invisible (And It’s Passing Through You Right Now)

Do you ever catch yourself daydreaming about the "what ifs"?

Like, what if you were born 5,000 years in the future? What if the continents were shaped differently? Or, on a cosmic scale, what if the Sun was just 10 percent larger?

For most of us, these are just fun thought experiments. But for astrophysicist Risa Wechsler, playing with these "what ifs" is literally her day job. She builds entire model universes in a computer, tweaking the ingredients—gravity, mass, time—to see how they evolve.

And in doing so, she and other scientists have stumbled upon one of the strangest, most humbling facts about our existence: The universe is mostly made of stuff we cannot see.

In her recent TED Talk, The Search for Dark Matter and What We've Found So Far, Wechsler breaks down a mystery that is as confusing as it is essential. If you think the universe is just stars, gas, and planets, you’re only seeing the tip of the iceberg.

The 15% Reality

Here is the wildest stat you’ll read today: Everything we can see with telescopes—stars, galaxies, gas clouds—makes up only about 15 percent of the total mass in the universe.

So, what’s the other 85 percent?

It doesn't emit light. It doesn't absorb light. It doesn't reflect radio waves or microwaves. It’s completely invisible to our sensors. But we know it’s there because of how it pushes and pulls on the stuff we can see.

Wechsler uses a great analogy to explain this. Imagine looking at a picture of Earth from space at night. You see lights from cities, which give you clues about where people are. But you can't see the people themselves, or the mountains, or the oceans. You have to infer they exist based on the lights.

That’s exactly what astrophysicists are doing. We call this invisible ocean of mass Dark Matter.

The Stuff Passing Through You Right Now

It’s easy to think of dark matter as some sci-fi concept that’s "out there" in deep space. But Wechsler points out that it’s much closer to home.

Because the Earth is spinning around the Sun, and the Sun is hurtling through the Milky Way, we are constantly moving through a sea of this stuff. Wechsler estimates that dark matter particles are likely passing through your body right now as you read this.

But don’t panic—it doesn’t bump into us. It just ghosts right through normal matter as if we weren’t even there.

No Dark Matter = No Us

So, if we can't see it and it doesn't touch us, why does it matter?

This is where Wechsler’s computer simulations come in. By rewinding the clock to the Big Bang and fast-forwarding 13.8 billion years, scientists can test what the universe would look like without dark matter.

The results are pretty stark.

In the early universe, everything was hot and expanding fast. Gravity needed to work hard to pull dust and gas together into clumps to form stars and galaxies. But normal matter alone wasn't enough; there wasn't enough gravity to hold the clumps together against the expansion of the universe.

Dark matter provided the extra gravitational muscle. It acted as the invisible glue that allowed gas to settle, cool down, and ignite into stars.

Wechsler’s simulations show two side-by-side universes:

1. With Dark Matter: You get clumps, structure, and beautiful galaxies like our Milky Way.

2. Without Dark Matter: The universe remains a thin, soupy mess. No galaxies. No Sun. No Earth. And definitely no us.

   
   

We literally owe our existence to this invisible stuff.

The Hunt is On

Okay, so we know it’s there, and we know we need it. But... what is it?

"We have no idea," Wechsler admits (which is honestly refreshing to hear from a top scientist!).

Physicists have a lot of theories. It could be a subatomic particle. It could be super light or as heavy as 100 Suns. To figure it out, the search is happening on three fronts:

• Underground: Using sensitive detectors in deep mines to catch a dark matter particle crashing into dense material.

• In Labs: Smashing particles together at the Large Hadron Collider to try and create dark matter.

• In the Sky: Looking for "clues" in how galaxies behave.

  
  

One of the biggest clues recently came from the tiniest places. Wechsler mentions that our Milky Way is surrounded by about 60 incredibly small "dwarf galaxies"—some with only a few hundred stars. The fact that these tiny galaxies exist tells us that dark matter is likely "slow-moving." If it were fast, it would have zoomed past these clumps and washed them out before they could form.

Embracing the Mystery

We haven't caught a dark matter particle yet. But that doesn’t mean we’re failing; it just means the mystery is getting deeper.

As we build better maps of the sky and more sensitive detectors, we are inching closer to understanding the invisible scaffolding of our universe. Whether we find the particle tomorrow or in fifty years, the search itself is changing how we understand physics.

For now, just take a second to look around the room. It looks empty, but you now know better. There’s a whole invisible universe passing right through you, holding everything together.

And personally? I think that’s pretty cool.

What do you think dark matter is? Let us know your theories in the comments, and don't forget to check out Risa Wechsler’s full talk here.