Official files, each with a short plain-language summary.
Peer-reviewed letter: for a universe that does not recollapse, the only anthropic limit on the cosmological constant is that it must not prevent gravitationally bound structures from forming. Weinberg finds the bound fairly loose.
“It turns out that the bound is quite large.” source
Weight ‘official’ here means a peer-reviewed research record, not a government finding.
Library record for the book: first published in London in 1999 (Weidenfeld & Nicolson, Science Masters); the record shown is the 2000 Phoenix paperback.
A catalogue entry, used only for the book's publication details.
Internet Archive record of the book (New York: Basic Books edition, 2000; first published 1999).
“Just six numbers : the deep forces that shape the universe” source
Lending copy; the book text itself was not read.
Newspaper and magazine coverage, then and now. Linked, never copied.
Review of Martin Rees's book listing his six numbers: N (the relative strength of gravity and electromagnetism), epsilon, Omega, lambda (the cosmological constant), Q, and the three dimensions of space.
“It would seem that in order for you and me to exist, so must the rest of the universe as it is today.” source
The page does not name the reviewer.
Our own reading of the file, written from the sources on the other sheets. Opinion is marked as such.
Two claims are often run together. The first is physical: if certain parameters were different, the universe would contain no galaxies, stars or complex chemistry. Much of this is ordinary physics and widely accepted for specific cases, such as the cosmological constant, which on theoretical grounds is expected to be larger than its measured value by somewhere between 10^50 and 10^123. The second claim is about explanation: that this sensitivity is improbable and therefore points to something, whether a designer or a multiverse.
The disagreement lives mostly in the second claim and in how wide the life-permitting ranges are. Barnes argues the cases in the literature are real and that Stenger's dismissals do not hold. Stenger and, more recently, the physicist Fred Adams argue the ranges are wider than often claimed. Philosophers add a further problem: with no natural way to assign probabilities to constants that could in principle take any value, it is unclear what ‘improbable’ means here. Weinberg's 1987 paper shows how an anthropic bound can be calculated; it does not show which explanation is right.
Our label is Unexplained: the physics is investigated and partly agreed, the inference from it is not. It would move only if physics derived the constants from deeper principles, or if a multiverse theory made a confirmed prediction.
The case against calling this a mystery: observers can only ever find themselves in conditions that allow observers, so finding such conditions is not surprising. Several authors add that the life-permitting ranges are much wider than often claimed (Fred Adams), that life depends on so many factors that sensitivity to some parameter is to be expected (Juhl), and that probabilities over constants which could take any real value are ill-defined, so ‘improbable’ has no clear meaning (McGrew and colleagues). On these views there is no fine-tuning problem to explain.
| For | Against | |
|---|---|---|
| The numbers | Theory expects the cosmological constant to be 10^50 to 10^123 times larger than it is; only values a few orders of magnitude above the actual one allow galaxies. [sep-fine-tuning] | Stenger: our exact form of life needs these values, but some form of life could arise over a range that is ‘not infinitesimal’. [stenger-2012] |
| The literature | Barnes' review of the scientific literature finds many of Stenger's dismissals ‘highly problematic’. [barnes-2012] | Stenger: Barnes ‘misunderstands and misrepresents’ the book and does not invalidate its conclusions. [stenger-2012] |
| Life | Rees: the universe can be characterised by six numbers; the review notes that what happens if any had a different value ‘make[s] surprising reading’. [plus-rees-review] | Carroll: we do not know which conditions life actually requires, so it is unclear the universe is tuned for life at all. [carroll-2014] |
| Design | A designer who intended life would make life-friendly conditions likely; Bayesian versions treat fine-tuning as evidence for design. [sep-fine-tuning] | Carroll: ‘If God had finely-tuned the universe for life, it would look very different indeed.’ [carroll-2014] |
Peer-reviewed reference entry on the physics of fine-tuning (cosmological constant, strong force, initial conditions) and the responses: design, multiverse, observation selection and ‘no fine-tuning’. Substantive revision 26 February 2026.
“The term fine-tuning refers to situations where certain phenomena of interest depend sensitively on parameter values falling within extremely narrow ranges.” source
A 77-page review of the scientific fine-tuning literature (Carter, Carr and Rees, Barrow and Tipler and later work), framed as a critique of Stenger's book. Barnes says he does not defend any conclusion drawn from fine-tuning.
“The claim is that in the space of possible physical laws, parameters and initial conditions, the set that permits the evolution of intelligent life is very small.” source
Revised 7 June 2012 to match the published version (DOI 10.1071/AS12015).
Stenger defends his 2011 book against Barnes: our exact form of life needs these values, but some form of life could evolve over a range that is not infinitesimal.
“I concluded that while the precise form of life we find on Earth would not exist with slight changes in these parameters, some form of life could have evolved over a parameter range that is not infinitesimal, as often claimed.” source
Carroll's five objections to the fine-tuning argument for God: we do not know what life needs; it only matters under naturalism; physics may explain it; a multiverse would; and a universe designed for life would look different.
“If God had finely-tuned the universe for life, it would look very different indeed.” source
Review of how sensitive the existence of observers is to the constants of physics; argues that the parameter ranges permitting habitable universes are wider than often claimed.
Peer-reviewed (Physics Reports, DOI 10.1016/j.physrep.2019.02.001); arXiv copy linked, dated 11 February 2019.
Weinberg presents the 1998 supernova discovery of accelerating expansion as following his anthropic bound on the vacuum energy.
“Soon after this work, observations of type Ia supernovae revealed that the expansion of the universe is accelerating” source
Talk at Trinity College, Cambridge, 2 September 2005. This is Weinberg’s own account, not an independent assessment.
Counter-argument: the anthropic ‘prediction’ depends on how universes are weighted and can give very different answers.
“We conclude that anthropic reasoning within the framework of probability as frequency is ill-defined” source
Found, but not linked to a source we trust. Not on the sheets until they are.
Level 2. The Archivist's notes are now pinned to the files, redactions open as you read, and your clearance card is ready.
Majestic Archive