- Coin flips may seem random, but the outcome is governed by predetermined forces like gravity and the strength of your finger flick. So physics formulas could be used to calculate how a coin will land.
- To be truly random, the outcome of a coin flip would need to be determined on a quantum level. That’s the term for the universe of subatomic particles that are constantly and randomly splitting.
- Astrophysicist Sean Carroll recommends an app called Universe Splitter, which cleaves quantum particles in two.
- Visit Business Insider’s homepage for more stories.

Our lives are filled with decisions: Order cheese or pepperoni pizza? Wear a sweater or a jacket? Take the train or the bus?

Sometimes we flip a coin, allowing chance to decide for us.

But the notion that a coin flip is random and gives a 50-50 chance of either heads or tails is, unfortunately, fallacious.

That’s because the mechanics that govern coin flips are predictable.

## Determinism versus randomness

In physics-speak, scientists categorise a coin flip as deterministic, since the outcome is determined by factors that are in place before the coin lands. Those factors include the angle at which the coin starts out on your thumb, the force your hand exerts on the coin, the pull of gravity, friction in the air, and more.

All of those forces governing the coin’s motion could, hypothetically, be calculated based on the laws of physics.

Of course, likely nobody can control all of those factors precisely enough to predict the outcome in real time, so for day-to-day decisions, a coin flip gets the job done.

But even so, the heads or tails you’d see can’t be considered a fully random result.

So according to astrophysicist Sean Carroll, author of the new book “Something Deeply Hidden,” people who want to find true randomness should look to quantum mechanics, which governs the nanoscopic universe of photons, electrons, and other particles smaller than atoms.

These tiny particles don’t follow those orderly cause-and-effect rules that govern the world we can see; instead, subatomic particles are constantly and spontaneously decaying into many other particles. Those decaying events can’t be predicted with certainty; the best we can do (so far at least) is calculate probabilities about the chances certain atoms have of decaying, and when.

## A subatomic world that’s truly random

In his book, Carroll explains that although we can’t predict the behaviour of subatomic particles, once researchers go to measure that behaviour, the act of measuring causes the set of probabilities about whether and when particles will split to collapse down to only one.

Schrödinger’s cat is the thought experiment many physicists use to illustrate this concept. Simplified, it goes like this: A cat is in a box along with some kind of poison, and the animal could be alive or dead. As long as we can’t see inside the box, the cat is simultaneously both alive and dead. Upon opening the box, however, there remains only one possibility, and the cat’s state becomes set.

But according to Carroll, a different theory of quantum mechanics is preferable, one called the “Many Worlds Interpretation (MWI).”

Proponents of this line of thinking argue that all the permutations of decaying atoms (which we can’t accurately predict or measure) get realised, each in a different universe. So every time an atom decays – or the cat-containing box is opened – another universe branches off from this one. Another you exists in it, living out a different life.

“There are infinite versions of us that exist in an infinite number of worlds,” Carroll told Business Insider.

## Many worlds – and versions of you

According to Carroll, the Many Worlds Interpretation can be used to get a truly random result to a binary question.

In his book, he recommends an iPhone app (sorry, Android users) called “The Universe Splitter,” which lets users input two actions, like accepting a job offer or not, into two text boxes. Then you click “Split,” and the app sends a signal to a laboratory in Switzerland, where a single photon gets hurtled toward a splitter.

Put simply, the photon can either go left or right. The copy of the iPhone user in the branch of the universe in which the photon veered left sees their app say: “Take the job.” And in the universe branch in which the photon went right, their screen will say: “Don’t take it.”

Presuming that the version of you in each branch heeds that answer, there will be one world in which you take a new job, and another in which a version of you is still looking for work,Carroll wrote in his blog.

These “many worlds” exist simultaneously, but the beings in them can’t contact each other, Carroll added: “It’s impossible to interact or talk with your alternative selves. You’re separate people with a common past but different futures.”

In that sense, the “Universe Splitter” app gives a fully random result, but it doesn’t choose which of two outcomes gets realised (like a coin toss might). Instead, it reports which of those two universes you are currently living in.

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