The key ideas

Until the End of Time: Mind, Matter, and Our Search for Meaning in an Evolving Universe

Brian Greene, 2020

Everything in the universe slides toward disorder, and yet stars, life and you appeared in it. Brian Greene walks through the whole history of the cosmos, from the Big Bang to a distant future where, according to current models, thought becomes impossible. Along the way he shows how entropy and evolution assembled consciousness, language, religion and art. And he asks where meaning comes from in a universe that has no need of it.

Who it is for

For anyone who has ever wondered whether anything matters if it all ends one day, and wants to hear a physicist's answer.

We mourn our brief lives and take comfort that something of us will remain. But in a universe that will hold neither life nor mind, even that legacy, a whisper to distant descendants, will vanish into the void.

What this book is about

Imagine your life will end in thirty days. Much of what seemed important might suddenly lose its weight. Brian Greene asks the next question: what if everything ends? Not one life, not humanity, but the very possibility of thinking anywhere in the universe. Physics, he says, suggests that this is likely. So why should a deadline unimaginably many years away be more comforting than thirty days?

Greene answers as a theoretical physicist. He walks through the whole history of the universe, from the Big Bang to its distant future, and follows two engines. The first is entropy, the pull of everything toward disorder. The second is evolution, the selection of whatever is good at lasting. The first makes stars and life possible, the second grows consciousness, language, religion and art out of life. And according to current models, these same engines will one day make thought impossible.

The path runs along the timeline: the cosmos, then humans, then the cosmos again. By the end it will be clear what Greene proposes to do about meaning in a universe that has no need of it.

Idea 1. Why time flows forward

A broken cup never puts itself back together, even though the laws of particle motion barely tell the past from the future. So where does time get its direction?

Greene starts with the steam engines of the 19th century. Engineers wanted to know why some energy always escapes as heat, and that is how the idea of entropy was born. Later Ludwig Boltzmann gave it a simple meaning: entropy counts how many ways particles can be rearranged so that, from the outside, everything looks the same. Disordered arrangements vastly outnumber ordered ones. That is why systems left to themselves almost always drift toward disorder. This is the second law of thermodynamics.

Status: a law confirmed by every observation. But it is statistical: running in reverse is not forbidden, just wildly improbable.

Livria analogy: toss a hundred coins. There is exactly one way to get all heads, and an astronomical number of ways to get roughly half and half. So you almost always get roughly half and half.

For Greene, the direction of time may come not from a special law but from counting arrangements. The past differs from the future because there was more order back then.

Read in Livria

About the author

Brian Greene is an American theoretical physicist, a professor at Columbia University and one of the best-known researchers in string theory. He wrote the popular science books The Elegant Universe and The Fabric of the Cosmos, and co-founded the World Science Festival in New York.

All books by this author: Brian Greene

Terms from the book

  • Jackson
  • Hawking
  • Nabokov
  • Dyson
  • Entropy
  • natural selection
  • Dark energy
  • Neuron
  • Thought experiment
  • Boltzmann: Ludwig Boltzmann, an Austrian physicist of the 19th century. He explained entropy by counting the ways particles can be arranged; his entropy formula is carved on his gravestone in Vienna.
  • Second law of thermodynamics: The law that the total entropy of a closed system almost always grows over time. It is statistical: the reverse is not forbidden, only extremely unlikely.
  • Entropic two-step: Greene's term: a system lowers its own entropy by releasing even more entropy into its surroundings, usually as heat. It is the author's image, not a standard scientific term.
  • Schrödinger: Erwin Schrödinger, an Austrian physicist, one of the founders of quantum mechanics and a Nobel laureate of 1933. His book What Is Life? (1944) influenced future biologists.
  • Cosmic inflation: The hypothesis that in the first tiny fraction of a second the universe expanded unbelievably fast. Many cosmologists support it, but there is no direct confirmation yet.
  • Chalmers: David Chalmers, an Australian philosopher who studies consciousness. In the 1990s he formulated the hard problem of consciousness.
  • Hard problem of consciousness: David Chalmers's name for the question of why physical processes in the brain come with experience. There is no accepted answer yet.
  • Mary: The heroine of the Mary's room thought experiment devised by Frank Jackson. Philosophers use it to argue about whether experience can be reduced to physical facts.
  • Rank: Otto Rank, an Austrian psychoanalyst and a student of Sigmund Freud. He wrote about how the fear of death drives human creativity.
  • Becker: Ernest Becker, an American cultural anthropologist, author of The Denial of Death (1973), which won the Pulitzer Prize.
  • Immortality projects: Ernest Becker's phrase for the things through which people hope to outlive themselves: children, creative work, buildings, faith, being remembered.
  • Red giant: A stage at the end of the life of a star like the Sun: it swells to hundreds of times its size, cools on the outside and turns red.
  • DESI: A large instrument on a telescope in Arizona that builds a three-dimensional map of millions of galaxies to study dark energy. Its results from 2024 and 2025 hint that dark energy may be weakening over time.
  • Horizon: Here, the cosmic horizon: a boundary from beyond which light will never reach the observer, because space is expanding too fast. By calculation, such a horizon glows with a very faint heat.

All terms

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