Do we actually live in a multiverse? | Dr. Ethan Siegel

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Jun 23, 2025

Join Dr. Ethan Siegel, an astrophysicist and author of 'Starts with a Bang!', as he dives into the tantalizing concept of the multiverse. Explore the mind-bending implication that every choice we make spawns countless alternate realities. Siegel discusses how cosmic inflation might create 'bubble universes' with varying laws of physics, and unpacks the fascinating world of quantum mechanics—a realm where every possibility could exist simultaneously. Buckle up as you contemplate the mysteries of infinity and the nature of reality!

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INSIGHT

Quantum Mechanics and Multiverse

Quantum mechanics suggests a multitude of possible outcomes exist simultaneously, but only one outcome manifests upon measurement.
This forms the basis of the multiverse idea, where every possible outcome occurs in some universe.

INSIGHT

Many Worlds Interpretation

The many worlds interpretation posits all possible quantum outcomes physically exist as separate branches.
Each branch represents a different universe within a vast multiverse structure.

INSIGHT

Types of Infinity Explained

Infinity comes in different types, including linear, exponential, and combinatoric infinities.
Combinatoric infinity is the largest and surpasses simple counting or exponential infinities.

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"Welcome to the multiverse. Or should I say our one universe within a multiverse of possibilities?"

Do we have proof of a multiverse?

Our idea of the multiverse stems from the notion of quantum mechanics: The idea that every time we enter a situation there are potentially infinite possibilities to arise as the outcome. But when we make a decision, we only get one of these outcomes.

Science fiction as well as our media and films are bewitched by the concept of the multiverse. But what can science tell us about its legitimacy? Dr. Ethan Siegel explores.

Chapters for easier navigation:-

0:00 Is there a multiverse?

3:32 The “many worlds” interpretation

4:43 The notion of infinity

8:45 Types of infinity

10:16 Degrees of freedom

17:01 Quantum mechanical spreading

19:22 The universe beyond our universe

21:46 How fast do universes get created?

27:15 The hope of the multiverse

The idea of the Multiverse suggests that every quantum possibility—every outcome that could happen—does happen, in a different universe. From choices we make to random atomic events, reality may split endlessly.

Cosmic inflation—a rapid expansion after the Big Bang—might have created countless "bubble universes." Each one with different physical laws or histories. These bubbles never touch, separated by ever-expanding space.

But here's the twist: Quantum mechanics produces a combinatoric explosion of outcomes—far more than the exponential growth from cosmic inflation. So, can the inflationary Multiverse actually contain all quantum possibilities?

Only if inflation has been going on forever, into the infinite past and future.

Otherwise, the full-blown sci-fi-style Multiverse? It's just in our minds.

About Ethan Siegel:

Ethan Siegel is a Ph.D. Astrophysicist and author of "Starts with a Bang!" He is a science communicator, who professes physics and astronomy at various colleges. He has won numerous awards for science writing since 2008 for his blog, including the award for best science blog by the Institute of Physics. His two books "Treknology: The Science of Star Trek from Tricorders to Warp Drive" and "Beyond the Galaxy: How humanity looked beyond our Milky Way and discovered the entire Universe" are available for purchase at Amazon.

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