Threshold moments are magical moments where something utterly new appears almost out of nowhere in the universe, and at each threshold, the going gets tougher because complex things become more fragile and vulnerable, and Goldilocks conditions become more stringent.

In New York City alone, there are approximately 10 billion SKUs (distinct commodities) being traded, which is hundreds of times as many species as exist on Earth.

Nearly seven billion individuals are linked by trade, travel, and the Internet into a global system of stupendous complexity.

What makes humans different is human language—a system of communication so powerful and precise that we can share what we've learned with such precision it can accumulate in collective memory, outlast individuals, and accumulate from generation to generation, making humans creative and powerful with a history.

The second law of thermodynamics states that the general tendency of the universe is to move from order and structure to lack of order, lack of structure—toward mush.

Simple atoms of hydrogen and helium appeared 380,000 years after the Big Bang, forming huge clouds with no structure that represented a cosmic mush, despite tiny temperature variations detected by satellites such as WMAP that were sufficient for the universe to move to the next stage of building complexity.

Stars create Goldilocks conditions for crossing new thresholds by creating the temperatures necessary for proton fusion in exotic combinations to form all elements of the periodic table, enriching the universe chemically.

The Cuban Missile Crisis demonstrated that the entire biosphere seemed to be on the verge of destruction from nuclear weapons, and while that specific crisis passed, the same weapons remain armed and present an ongoing existential threat.

Big history can show humans the nature of our complexity and fragility and the dangers we face, but it can also show us our power through collective learning, providing both warning and hope.

Life introduces an entirely new trick: instead of stabilizing individual complex molecules, it stabilizes the template (the thing that carries information) and allows the template to copy itself, with DNA being the beautiful molecule that contains this information in its double helix structure.

Humans appear to be the only species in four billion years to possess the gift of collective learning, which is the ability to accumulate knowledge across generations through language and cultural transmission.

The universe can create complexity, but with great difficulty, and complexity appears in pockets where 'Goldilocks conditions' exist—conditions that are not too hot, not too cold, but just right for the creation of complexity.

Slightly more complex things enable the creation of slightly more complex things, allowing complexity to build stage by stage through threshold moments.

As extremely complex creatures, humans desperately need to understand how the universe creates complexity despite the second law of thermodynamics and why complexity means vulnerability and fragility.

The Big Bang occurred approximately 13.7 billion years ago, creating an entire universe that was initially smaller than an atom, incredibly hot, and expanding at incredible speed, with distinct forces and matter emerging within the first second.

Gravity is more powerful where there's more stuff, so slightly denser areas cause gravity to compact clouds of hydrogen and helium atoms, breaking the early universe into about a billion clouds where density increases, temperature rises at the center, and when temperature crosses 10 million degrees, protons fuse to create stars.

Stars began to appear throughout the universe approximately 200 million years after the Big Bang, making the universe significantly more interesting and complex.

A gold ring was forged in a supernova explosion, illustrating that the heavy elements comprising objects in our world originate from stellar nucleosynthesis.

Rocky planets like Earth are significantly more complex than stars because they contain a much greater diversity of materials, representing the fourth threshold of complexity.

Living organisms are created by chemistry, and chemistry is dominated by the electromagnetic force, which operates over smaller scales than gravity, explaining why living organisms are smaller than stars or planets.