Top Scientist REVEALS: A Kid In The 29th Century Could Have Made This World! | Prof Brian Greene

The question that keeps pulling me back is the true nature of reality. What is the world made of? Is there purpose, or did self-awareness emerge through a remarkable accident? We have learned a great deal, but it feels like gathering sand from a vast shore: the bag gets heavier while the beach remains unimaginably large. The deepest puzzle may be why anything exists at all.

I wanted to begin with the kid who grew up across from the Hayden Planetarium, studied mathematics and physics, and spent decades teaching at Columbia. And I asked for the twelve-year-old version of string theory.

Start with molecules, atoms, electrons, protons, neutrons, then quarks. String theory asks whether quarks and electrons are the final layer. Perhaps beneath them are extraordinarily small vibrating filaments. Like a violin string produces different notes through different vibrations, different patterns would yield different particles: one an electron, another a quark. It is beautiful, but beauty is not proof. We cannot inspect that scale yet. What makes it compelling is that quantum mechanics and general relativity fit together with striking harmony in its mathematics. The math is taking us somewhere our equipment cannot yet reach.

Then I pushed on what makes those hypothetical strings move, and whether this framework tells us why we are sitting here at all.

The universe has energy, and nobody knows why that fundamental currency is present. If string theory is right, energy appears as string vibrations; if not, through particle motion and curved spacetime. The early universe set the conditions. Expansion produced particles; gravity gathered stars and planets; chemistry became elaborate; cells emerged, life evolved, and after billions of years, here we are: two temporary arrangements of matter having this conversation.

AI makes the picture feel less settled. Maybe this table, you, and I are part of an elaborate simulation. If future civilizations make conscious ancestor simulations in enormous numbers, simulated observers could outnumber observers in the original world.

I cannot demonstrate that we are not simulated. But if I let that possibility consume me, I lose grounds for trusting even the reasoning that got me there. So I park it to one side and keep doing science. The decisive unknown is consciousness. Current chatbots can imitate feelings brilliantly; privately, I doubt they possess them today. Still, I see no fundamental obstacle to sentient artificial systems eventually.

Love, grief, jealousy, anxiety, gratitude—all of it is physical activity in a brain connected to a body. That does not make Shakespeare, Beethoven, art, or tenderness less wondrous. Reduction is not dismissal. If an artificial system had the right integrated capacities, perhaps silicon could support experience too. Then pulling its plug would not resemble switching off a lamp. The terrible problem is that consciousness cannot be conclusively verified, even in one another.

I do not expect a simple contest where humans stay in charge or AI replaces us. More likely, biological and artificial intelligence become intertwined. That might produce something no longer neatly called human, and I’m not horrified by that. Evolution did not promise to stop with us. We need openness, care, and a way to make the outcome genuinely good.

I wondered whether that acceleration could bring radical longevity, and whether our finite time horizon quietly shapes our choices.

Aging is increasing disorder and degradation, and science may learn to delay it dramatically—perhaps for centuries. But forever is another claim. On cosmic timescales, I see no route to permanent survival. A longer life would change practical choices, but immortality would be different. I do not think it is coming.

The least satisfying answer to why we exist is brute accident. The more gratifying possibility is one underlying account that yields the laws we know and explains why there is something rather than nothing. Our brains evolved to find food and shelter, yet can calculate an electron’s magnetic properties to around fifteen decimal places and see experiment agree. That is breathtaking.

I’m skeptical of a human-shaped deity beyond the clouds, though religion need not be science’s enemy. It can answer our terror of death and desire for consolation. I was raised culturally Jewish, and on occasion I pray—not because I think someone is listening, but because ritual and directing oneself toward the universe can help.

The Big Bang is not a supernatural stopping point; it invites us to push backward. Distant galaxies are receding, and reversing that film points to a denser early universe. We detect leftover radiation from that hot beginning, with predicted temperature variations matching remarkably well. We have not reached time zero, but each successful step makes me less inclined to insert an explanation before evidence requires one.

Compress cosmic history into a calendar year and civilization occupies the final seconds before midnight. We are one planet around one star, among roughly a hundred billion stars in one galaxy, amid at least hundreds of billions of galaxies. Yet smallness is not insignificance. Our minds can comprehend this predicament. That capacity connects us to the whole.

I have high confidence that free will, as ultimate independent authorship, is not real. We are particle-based systems following lawful patterns. Meaning, choice, morality, and caring emerge from complex brains. They are constructed, yes, but not worthless. My view of consciousness also informs how I live: I stopped eating meat at nine and became vegan after seeing industrial animal treatment firsthand. A cow can suffer. That matters to me.

The far future is dark, but I find it clarifying. The Sun will make Earth uninhabitable; stars will fade; black holes should evaporate. Yet we inhabit an extraordinary brief interval when matter can become alive, look around, and understand something of itself. That is not despair. It is gratitude.

That was the feeling I kept returning to: cosmic scale can make us feel microscopic, but it can also loosen everyday fear. Perhaps we can risk more, love more freely, and pursue what matters.

WorldScienceFestival.com and the World Science Festival YouTube channel are good places to continue. Of my books, I’d point first to Until the End of Time. And what matters most to me? The things that matter most to my wife and children. Because I’m bound up with them, their concerns outrank my own.