What Scripture says
Scripture presents the world as deliberately made and ordered:
- God “formed the earth and made it… he did not create it empty, he formed it to be inhabited” (Isaiah 45:18, ESV).
- “The heavens declare the glory of God” (Psalm 19:1).
- God “determined the measurements” of the earth and “stretched the line upon it” (Job 38:5).
- He “made the earth by his power… established the world by his wisdom” (Jeremiah 10:12).
The Bible doesn’t mention physical constants, of course. But it leads us to expect a universe set up for life on purpose.
What the evidence says
Science
Physics describes the universe with laws containing a handful of numbers, called constants, whose values aren’t fixed by any deeper theory we know of. We have to measure them. When physicists ask what would happen if these values were different, the answer, again and again, is a universe with no stars, no chemistry and no life.
Some examples
- The strength of the strong nuclear force, which binds protons and neutrons. If it were a few percent weaker, many elements couldn’t form; a little stronger, and stars would burn their hydrogen too quickly. Estimates of the allowed range vary between studies.
- The cosmological constant, which drives the expansion of space. Simple theoretical estimates suggest it should be enormously larger than it is, by many orders of magnitude. Even a modestly larger value would have blown matter apart before galaxies could form. Physicists regard this as one of the most striking fine-tuning problems.
- The ratio of electromagnetism to gravity. If gravity were much stronger relative to electromagnetism, stars would be smaller and burn out quickly; much weaker, and stars might never ignite.
- The masses of the electron, proton and neutron. The neutron is only slightly heavier than the proton. Small changes would make hydrogen unstable or prevent stable atoms from forming.
- Carbon production. In 1953, Fred Hoyle predicted that the carbon nucleus must have a specific energy level (a resonance) for stars to produce carbon in large amounts, and experiments confirmed it. Hoyle, an atheist at the time, later wrote that it looked as if a “superintellect” had monkeyed with physics.
- The initial order of the universe. The universe began in a state of extremely low entropy. Roger Penrose estimated the odds of this by chance as unimaginably small.
Some popular figures are exaggerated, and not every claimed example is equally strong. Luke Barnes, a cosmologist, reviewed the technical literature in 2012 and concluded that fine-tuning is real and robust, while noting which claims are weaker.
Who accepts it
Fine-tuning isn’t only a religious claim. Physicists across worldviews accept the basic fact:
- Martin Rees, Astronomer Royal and not religious, wrote Just Six Numbers about it.
- Paul Davies, who isn’t a traditional theist, has written extensively about it.
- Leonard Susskind, a leading string theorist, takes it seriously enough to argue for a vast multiverse to explain it.
Philosophy
The debate is about the explanation. Philosophers usually list three options:
| Explanation | The idea | Main difficulty |
|---|---|---|
| Physical necessity | A future theory will show the constants had to be this way | No sign of such a theory; it would push the question back to why that theory |
| Chance plus a multiverse | Countless universes with different constants; we find ourselves in a rare life-permitting one | No direct evidence; the universe-generator may itself need fine-tuning |
| Design | A mind chose the constants for life | Requires belief in a designer, which some see as less simple |
There is also the anthropic principle: we shouldn’t be surprised to find ourselves in a life-permitting universe, since we couldn’t observe any other. Critics reply with an analogy from philosopher John Leslie: if a firing squad of fifty marksmen all miss you, you shouldn’t shrug and say “Of course they missed, or I wouldn’t be here to notice.” The fact that you survived still calls for an explanation.
Where they meet
Fine-tuning is just what you would expect if a Creator made the universe for life. It is surprising if the constants are a brute accident. That’s why many see it as one of the strongest pieces of evidence for design (see 1.1).
What’s still open
The fact of fine-tuning is rated Settled. The explanation is not.
- Whether a multiverse exists, and whether it could explain fine-tuning without needing fine-tuning itself.
- Whether deeper physics might reduce the number of free constants.
- How to assign probabilities to constants that could, in principle, take any value. Some philosophers argue this makes fine-tuning arguments hard to state precisely.
Bottom line
Physicists broadly agree the constants sit in very narrow life-permitting ranges, so the fine-tuning itself is rated Settled. Whether design or a multiverse best explains it is the part still argued, and that belongs to 1.1 and 2.13.