Alice laughed: “There’s no use trying,” she said. “One can’t believe impossible things.”

“I daresay you haven’t had much practice,” said the Queen. “When I was younger I always did it for half an hour a day.

“Why, sometimes I’ve believed as many as six impossible things before breakfast.”

- Through the Looking Glass by Lewis Carroll

We’ve uncovered many impossible things over the last 100 years.

We discovered that the world sits on plates that are constantly in motion, reshaping the land and oceans that cover planet Earth. We created materials from nothing, materials that sent us to the moon and captured pictures of the deepest reaches of space. We decoded DNA that altered our very understanding of what makes us human.

Throughout the past year, Science News’ Century of Science invited us on a tour of the impossible, diving deep into the major science breakthroughs that brought us to the world we live in and understand today. The scientists and researchers driving these breakthroughs often believed in the impossible, and now we’re asking you to believe as well.

In our final installment of Science News’ Century of Science, we’re exploring the very nature of reality. Be warned, this is not for the faint of heart. Discussions of what is or what isn’t reality will often stir unpleasant or uncomfortable feelings, and that’s OK. Sometimes, all we need is a little more practice with the impossible – perhaps six impossible things before things before breakfast.

Ready? Buckle your seatbelts and enter the Quantum Reality.

The macroscopic (aka, observable) world we live in is physical. We use our senses to observe things around us and those things happen in an ordered, cause-and-effect fashion. This is because things in our world take on discrete properties. A ball is a round. A pancake is soft (you hope!). A brick is heavy. You get the picture.

But in the quantum world, properties aren’t discrete. Rather, there is only a likelihood of a given property existing and all potential properties exist simultaneously. A ball is round. And oval. And egg-shaped. And maybe not even a ball. You get the picture (again). It’s only once something becomes part of our macroscopic world does it take on a discrete property.

Consider one of the most famous quantum world figures, Schrödinger’s Cat. To illustrate this feature of the quantum world (called “superposition”), physicist Erwin Schrödinger devised a famous thought experiment while in conversation with Albert Einstein in 1935. (The two were actually critiquing superposition and the thought experiment was supposed to illustrate how preposterous it was. Even Einstein missed the impossible from time to time!)

Imagine a cat in box, and in that box is a toxic poison that slowly kills the cat. Until someone observes the cat by opening the box, the cat exists simultaneously in two states: alive and dead. It’s the act of bringing the cat into the observable world that forces it to be one (alive) or the other (dead).

This kind of conundrum makes most scientists’ brains break. Forget about alive and dead cats! The idea that something occurs because it’s been observed basically throws objective science out the window. Yet, Schrödinger’s Cat fits with the math that describes the quantum world, math that Schrödinger himself figured out.

Over the next 20 years, scientists explored this conundrum, developing possible explanations for how superposition and Schrödinger’s Cat could be true while also occurring independently of an observer. In 1957, a graduate student by the name of Hugh Everett offered a titillating idea: The Many Worlds Interpretation.

What Everett suggested was that upon opening the box, reality branches into two new timelines. One marches forward with the observer seeing the cat alive. In the other, the observer sees the cat dead. Both realities are equally valid and real, but the only one that’s observable is the one that the observer is in. The trick is there are now two observers, one for each timeline, and each completely blind to the other’s existence and reality.

The implication for Everett’s Many Worlds Interpretation is that because all possible versions of reality exist simultaneously, there are all possible versions of ourselves spread across those realities … whoa.

Now before we spiral into what it means to have infinite doppelgängers in infinite alternative realities living your – I mean, their – lives, remember that Many Worlds is just one possible explanation that fits with Schrödinger’s Cat and quantum math. There are many other interpretations out there, but all just might require us to believe the impossible.