#488 – Infinity, Paradoxes that Broke Mathematics, Gödel Incompleteness & the Multiverse – Joel David Hamkins
Lex Fridman Podcast
2025/12/31
#488 – Infinity, Paradoxes that Broke Mathematics, Gödel Incompleteness & the Multiverse – Joel David Hamkins
#488 – Infinity, Paradoxes that Broke Mathematics, Gödel Incompleteness & the Multiverse – Joel David Hamkins

Lex Fridman Podcast
2025/12/31
In this deep and wide-ranging conversation, mathematician and philosopher Joel David Hamkins explores the profound foundations of mathematics, from the nature of infinity to the limits of computation and proof. With clarity and insight, he unpacks concepts that have reshaped mathematical thought, guiding listeners through paradoxes, undecidability, and the philosophical implications of modern set theory.
The discussion begins with Cantor's revolutionary discovery that infinities come in different sizes, illustrated by countable sets like the rationals and uncountable ones like the reals, leading to the development of ZFC set theory. Russell’s Paradox is shown to undermine naive set theory, while Gödel’s incompleteness theorems reveal that no formal system can capture all mathematical truths. The halting problem and Rice’s theorem further demonstrate inherent limits in computability. The continuum hypothesis is explored as a pivotal unresolved question, proven independent of ZFC through Cohen’s forcing method, prompting a multiverse view of set theory. Other topics include surreal numbers, Conway’s Game of Life, and infinite chess, where transfinite ordinals appear as game values. Despite theoretical intractability in problems like P vs NP, practical tools often succeed on real-world instances. Hamkins emphasizes community-driven progress in math, exemplified by MathOverflow, and reflects on beauty in mathematics—particularly the distinction between objective truth and formal proof—as a central, humbling insight.
13:23
13:23
Some infinities are bigger than others
40:54
40:54
Some infinities are larger than others, proven by diagonalization.
1:12:50
1:12:50
Russell's Paradox revealed a fatal flaw in Frege's logical foundation of mathematics.
1:26:18
1:26:18
No consistent formal system can prove its own consistency.
1:43:36
1:43:36
The provability problem is undecidable and equivalent to the halting problem.
2:00:21
2:00:21
Infinite trading among countably many people can make everyone infinitely rich.
2:11:10
2:11:10
We understand mathematical existence better than physical existence.
2:18:19
2:18:19
Answering questions on MathOverflow has made me a better mathematician
2:28:09
2:28:09
The Continuum Hypothesis is independent from the ZFC axioms.
2:38:43
2:38:43
Paul Cohen's forcing method proved the Continuum Hypothesis can be false in a consistent set-theoretic model.
2:55:18
2:55:18
Set-theoretic geology allows us to undo forcing, revealing deeper structure in models of set theory.
3:10:59
3:10:59
Determining if a cell will ever be alive in the Game of Life is undecidable, equivalent to the halting problem.
3:19:18
3:19:18
A random Turing machine's head falling off the tape explains most non-halting cases.
3:23:09
3:23:09
P vs NP is a theoretical question about asymptotic behavior
3:45:53
3:45:53
Every countable ordinal can be a game value in infinite chess.
4:02:08
4:02:08
The most beautiful idea in philosophy is the distinction between truth and proof.