Published in



The Basis Of The Many Worlds Interpretation Of Quantum Mechanics

Parallel worlds, branching timelines, alternate realities

These notions have been featured in a plethora of science fiction films. In all these films, the one thing in common is the reference to another world(s).

Worlds very much like our own.

Worlds entirely different from our own.

The Terminator franchise

Terminator 2: Judgement Day

The Cloverfield series of films

The Cloverfield Paradox

The Marvel Cinematic Universe

Avengers: Infinity War

How did the Many Worlds Interpretation (MWI) originate?

In order to understand MWI, we first need to grasp some history behind quantum mechanics.

The various interpretations.

The Copenhagen interpretation came about in the aftermath of the 1927 Solvay conference.

Scientists who were in attendance at the 1927 Solvay Conference

Scientists who attended the conference and are featured in the photo were some of the most legendary names in quantum physics.

Albert Einstein, Niels Bohr, Paul Dirac, Paul Ehrenfrest, Werner Heisenberg, Peter Debye, Hendrik Lorentz, Erwin Schrodinger, Max Born and many others.

Following the Solvay Conference, 2 members, Niels Bohr and Werner Heisenberg came together to consolidate their views on the breakthroughs in physics that were presented at the conference.

Similar to the family of axioms that define mathematics, the Copenhagen interpretation provides a basis from which one can understand quantum mechanics.

And this interpretation is the one that is the most widespread till today.

It was first proposed American physicist Hugh Everett in 1957, and is hence also known as the Everett interpretation.

It is noteworthy for it proceeds to provide an explanation that in theory, resolves some shortcomings in the core postulates in the Copenhagen interpretation.

Which postulates in the Copenhagen interpretation?


The Copenhagen interpretations gives the measurement postulate.

What are we measuring? States

Each particle’s state can be described as a linear combination of orthogonal eigenstates.

Upon measurement, the probability of each state existing, P, is given by the square of the probability amplitude:

And the system collapses into one of the definite orthogonal states:


The copenhagen interpretation also postulates that quantum systems are deterministic in nature, governed by the schrodinger equation.

Quantum systems evolve over time, and there are definite values for the quantum state, for each single moment in time.

So we have measurement, and determinism.

In measurement, the system is probabilistic in nature. There are a multitude of different states. And each time a measurement is made, the system jumps into a different state.

Photo by Fleur on Unsplash

In determinism, the system evolves deterministically, in a predictable manner for all time. From now, all the way into the distant future.

Photo by Jeremy Thomas on Unsplash

But, what is the difference, really? (In a quantum sense)

Intuitively, we grasp the two notions. Right?

If we measure something, we actively try to obtain information about it, and it collapses into a fixed state.

If we do not make any attempt to measure it. It evolves deterministically.

However, the Copenhagen interpretation does not provide a rigorous answer as to what constitutes a measurement.

It remain a deeply philosophical debate.

We have formulated a ton of mathematics to model the effects of measurement, which have been empirically tested to be sound.

But we still cannot clearly define what is a measurement.

When a system is slightly perturbed by the tiniest of disturbances, does it evolve deterministically?

Or does it jump into a separate state?

The Everett interpretation

Hugh Everett sought to reconcile these 2 notions by proposing the following:

Each time a “measurement” is made, the system does not “collapse”. Instead it evolves deterministically to a given outcome.

And not just that, it evolves into every possible outcome.

This concept is demonstrated in the Marvel series Loki (2021).

The branching of the timeline that occurs when disturbances are allowed to propagate.

Credits: Loki (2021)

When a disturbance occurs, the timeline diverges into 2.

  1. Where the disturbance did occur.
  2. Where the disturbance did not occur.

In essence:

The Everett interpretation basically says that the entire universe, may be described as one massive and astronomically complex quantum state that evolves with time.

And at each moment, it is being “measured” or perturbed. Correspondingly, the entire universe is at all moments in time branching out into different possible states.

Where said outcome occurred, and did not occur.

And these are what constitute a “multiverse”, where every possible outcome is realized.


Hope you have enjoyed this article! I’ve tried my best to explain this concept in a digestible manner, devoid of most of the gnarly math.

If you have a penchant for such articles, please head over to my profile to view more of them!

Thank you!!



Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store
Daryl Tng

Daryl Tng


Physics major from sunny Singapore! I write about physics, coding and quantitative finance.