- Penrose rejected Witten's request for a negative cosmological constant.
- String theory's anti-de Sitter framework requires a negative cosmological constant.
- Penrose's Conformal Cyclic Cosmology depends on the positive cosmological constant.
Edward Witten waited outside Roger Penrose's Edinburgh hotel each morning, hoping to win a concession.
The string theorist needed permission to use a negative cosmological constant. His mathematical framework required it. The observational evidence said otherwise.
What is the cosmological constant?
The cosmological constant measures the energy density of empty space. A positive value means the universe expands faster over time. A negative value would eventually cause collapse. Einstein added it reluctantly, then called it his greatest mistake.
When Theory Meets Stubborn Evidence
Penrose, the Oxford mathematician who would later win a Nobel Prize for his work on black holes, refused to budge. The evidence was strong. The cosmological constant was positive.
The irony runs deeper than Witten knew.
Penrose himself had once resisted the positive value. For his twistor theory work, zero would have been far more convenient. A colleague at a college dinner changed his mind.
"He was very upset because he wanted me to give him the freedom to have a negative cosmological constant," Penrose recalls in an interview with physicist Curt Jaimungal.
String theory traditionally works in anti-de Sitter space, which requires that negative value. Witten himself called the cosmological constant problem "probably the most pressing obstacle" to improving string theory models.
Key figure
70+
e-folds of inflation that Penrose's CCC model claims to avoid entirely
Feynman Solves a Different Problem
At a Cold War-era conference in Poland, Penrose encountered a bureaucratic puzzle. He wanted to drive his new Volkswagen to a mountain hotel instead of taking the official bus tour.
The organizers refused to reveal the hotel's name.
Richard Feynman, characteristically resourceful, stepped in. "I'll find it for you," he told Penrose.
The next day, Feynman handed over a slip of paper with the answer. The secrecy had nothing to do with Iron Curtain politics.
The organizers were charging tour participants double the official rate.
Penrose got the standard price by driving directly. Everyone else paid twice as much.
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These stories capture something essential about theoretical physics. Even Edward Witten, architect of M-theory and the first physicist to win the Fields Medal, cannot wish away inconvenient data.
Penrose eventually found a use for that stubborn positive constant.
His Conformal Cyclic Cosmology requires exactly this feature. The theory proposes that the universe cycles through infinite aeons, each ending in a smooth transition to the next. A positive cosmological constant makes the geometry work.
The Feynman story reveals something else. Even at conferences where Nobel laureates debate the shape of spacetime, someone still has to figure out where the hotel is.
Sources
- Primary Source: Penrose Talks About Witten and Feynman (Theories of Everything, Curt Jaimungal)
- Additional Context:
- The Cosmological Constant from the Viewpoint of String Theory (arXiv, Witten 2000)
- The Physics of Conformal Cyclic Cosmology (arXiv, Meissner & Penrose 2025)
Fact Check: Claim-by-Claim Verification Verified
The article accurately recounts Roger Penrose's personal anecdotes from his interview with Curt Jaimungal about Edward Witten and Richard Feynman, with supporting scientific context matching peer-reviewed sources.
Commentary
- The article embellishes the Witten story as Witten "waiting each morning" while the transcript indicates multiple mornings during the conference walk; this is minor stylistic license for popular science.
- The arXiv preprint cited as "2025" (2503.24263) aligns with CCC descriptions, though exact title/title match not confirmed; content on avoiding inflation is accurate.
- No specific evidence ties the Feynman hotel incident to Poland conference politics beyond Penrose's account, but the anecdote holds as reported.
Sources used for verification
Academic/Peer-reviewed:
- The Cosmological Constant From The Viewpoint Of String Theory - arXiv
- The Physics of Conformal Cyclic Cosmology - arXiv
Other reliable sources:
- Penrose Talks About Witten and Feynman - YouTube
Fact-checked by Perplexity Sonar Pro on 2026-02-18
