Sean M. Carroll is a theoretical physicist, with a PhD (1993) in astronomy and a B.S. (1988) in astronomy and astrophysics with minors in physics and philosophy. His academic career was exclusively in physics until 2022, and now he is a professor of natural philosophy at Johns Hopkins.
In 2014, Sean Carroll posited five reasons the "Fine-Tuned Universe hypothesis" does not work.
- We don't really know that the universe is tuned specifically for life, since we don't know the conditions under which life is possible.
- Fine-tuning for life would only potentially be relevant if we already accepted naturalism; God could create life under arbitrary physical conditions.
- Apparent fine-tunings may be explained by dynamical mechanisms or improved notions of probability.
- The multiverse is a perfectly viable naturalistic explanation.
- If God had finely-tuned the universe for life, it would look very different indeed.
First, for those unfamiliar, the Fine-Tuned Universe hypothesis proposes the fundamental physical constants, fundamental physical laws, and fundamental forces of the universe are so narrowly defined that a very small change in any of them would result the failure of the universe to exist in a stable form, and therefore, life could not emerge. Notice these are all physics based. Beyond those, there are things like the Galactic Habitable Zone and the Circumstellar Habitable Zone which suggest where life can emerge in a physically fine-tuned universe. But such "Goldilocks zones" are not fine-tuning. The nuclear forces which allow the triple-alpha process to produce carbon-12 in stellar fusion and the 7.656 MeV Hoyle resonance is considered to be evidence of fine-tuning critical for carbon based life.
To be honest, for someone with a minor in philosophy, Carroll does not make good arguments, and it is a little surprising he is holding a position as a professor of philosophy. The above arguments Carroll made were made in a debate with William Lane Craig, who has a masters and PhD in philosophy, and is known for deeply thought out arguments. But more disturbing are Carroll’s arguments above are intentionally deceptive, filled with omissions, misdirection, and fallacies.
We don't really know that the universe is tuned specifically for life, since we don't know the conditions under which life is possible.
This is irrelevant. Because the fine-tuning is not only about life, it is about the very existence of the universe. Fine-tuning is far more about physics than biology. Even if no life emerged in our current universe, the very fact there are stars and galaxies show the fundamental forces and laws of physics are narrowly focused, and if they were slightly different, the universe itself would not exist.
But we also do know the conditions under which life is possible on Earth. We have studied many different types of life to include life in various environmental regions, including very harsh environments like deep under the sea, and in the arctic. We have control planets like Mars and Venus which we have explored and continue to explore. We are planning to explore moons like Titan and Europa which could harbor primitive life. We have meteorites that originated from Mars that some scientists believe contain fossil evidence of primitive life, but we obviously are looking for something that looks like life on Earth, such as bacteria. NASA's Perseverance Mars rover took a sample that contained potential biosignatures. But we are able to observe these potential fossils and biosignatures because the appear similar to the kinds of evidence of life on Earth. Also, for decades scientists have hypothesized about possible life forms that are not based on carbon. But we have not found evidence of non-carbon life. In fact, the very term "organic" when applied to molecules or compounds when scientists look for signatures of life means those compounds contain carbon. Could this be a scientific "blind spot" in that we look for organic molecules, fossils that look like bacteria, and biosignatures similar to what we see on Earth? Possibly. But unlikely because while different biochemistry is possible, chemistry is constant. And scientists have enough speculation on alternative biochemistry to speculate the conditions where such alternative biological processes make sense (such as life on a very cold planet that uses liquid ammonia as its solvent rather than liquid water). We are also at a point where astronomers can accomplish spectral analysis of exoplanet atmospheres. Finally, while the idea of silicon instead of carbon being a building block for life is possible, the Earth's crust has 925 times as much silicon as carbon, but there is no evidence of current or past silicon based life on Earth, even though some carbon based life forms have integrated silicon into their shells. Another thing to consider is not if a life form could exist based on alternative biochemistry, but if the alternative biochemistry would be capable of adaptation and evolution. A less adaptable alternative biochemistry based life form might quickly go extinct.
Fine-tuning for life would only potentially be relevant if we already accepted naturalism; God could create life under arbitrary physical conditions.
I do not think this is an argument. The first sentence appears to accept fine-tuning as a possible explanation for the natural universe. The second sentence is a logical fallacy (affirming a disjunct). It is true an omnipotent God could create a sentient robot, or a supernatural being that can live in any environment. Then again, many religions believe in created supernatural beings like angels and lesser gods. But that does not in any way disprove that an omnipotent God would not have created the universe we inhabit. It does not change the fact the conditions for known biological life in our universe are very narrow. It does not change the scientific observations of the very narrow path Earth based biological life has followed.
Apparent fine-tunings may be explained by dynamical mechanisms or improved notions of probability.
This may be his best argument. If we get to a point where we can simulate the early universe, we could observe the mechanisms of the formation of the fundamental forces and the laws of physics, and we could find these forces and laws naturally coalesce to the what we observe in our universe. However, then we would have another argument that something tunes the process that causes these forces and laws to form. So we end up with a regression. As for improved notions of probability, I am not sure what that means. Probability is math, which doesn’t change, so perhaps it is the entering arguments of a probability analysis. However, much of the fine-tuning hypothesis is based on a century of probability analysis by some of the smartest physicists in human history.
The multiverse is a perfectly viable naturalistic explanation.
Certainly the Infinite Monkey Theorem suggests random things can align given enough monkeys, but what came first? The monkey or the typewriter? A multiverse created from the Big Bang event still requires narrow parameters in the process of the Big Bang. The most widely accepted Multiverse hypotheses build off of inflationary cosmology. And that means the physical processes from the initial singularity to cosmic inflation would need to be "just right" to produce enough universes for at least one to be like the one we live in. What if cosmic inflation created only ten universes, or one-hundred? But realize the very idea behind a multiverse hypothesis to explain the low probability of a stable universe says we need to have 10100 universes fail to get one that works.
If God had finely-tuned the universe for life, it would look very different indeed.
This is not an argument. It is a logical fallacy (affirming a disjunct). And it is grossly unscientific. It is unobservable and unprovable. One might say this statement is not a scientific statement, but a philosophical one, but philosophy requires logic, and we would need a logical statement on how life would look, or why it would look different.
It is also nonsensical, because life exists, and life has fragility, in addition to adaptability. We would not worry about things like the impact of humanity on the environment and how that impacts other life forms, if life was not fragile, and it is the fragility of life that makes us observe Earth is well-suited for life. In fact, things like extinction suggest fine-tuning, in that minor changes in the environment, combined with an inability to adapt, result in life failing.
But this argument also fails on another point. It assumes an ideal, or good. If there was an omnipotent God, He would make life that didn’t feel pain, was immortal, etc. But that is an opinion. It is like saying an abstract painting is not art because to your eye it is not beautiful. To say true art would look very different indeed. But in addition to an opinion, it points to a universal standard of "good", or "better", or "more moral." Which again is an argument for logic or intelligence that exists beyond the physical world. Carroll doesn't realize it, but he is suggesting there is a morality that exists outside of our universe, which could be used to judge the goodness of various universes.
Finally, physics is a mature and well-understood science, and the physical constants, physical laws, and fundamental forces of the universe are measurable and understood. And physicists know a minor change of a physical constant would result in a very different universe. Such a change can be mathematically modeled. For a physicist such as Carroll to ignore this is really disturbing. It suggests a physicist cannot deny the narrow window in which the physical constants, physical laws, and fundamental forces operate in our universe. Stephen C. Meyer recently stated the multiverse hypothesis only exists and gets any interest because the fine-tuning hypothesis is so strong. In other words, most scientists, including atheist scientists, accept our universe is fine-tuned. They see it as something that needs to be scientifically investigated, not disparaged. One might say: "The science is settled." That would make Sean M. Carroll a science denier.
