Week 6

Chapter 5 - Why is the Universe Fine-Tuned for Life?

Class Date: September 24, 2025

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Introduction

This chapter will deal with an argument for the existence of God called the fine-tuning of the universe for life. It is one of the arguments that falls under the umbrella term, the teleological argument or the "argument from design," for the existence of God. Another argument from design is the topic of intelligent design in nature. Intelligent design can be defined as, "Intelligent design is the scientific theory that certain features of the universe and of living things are best explained by an intelligent cause rather than by an undirected process such as natural selection." (A whole course on intelligent design and origins could potentially be a Wednesday evening course in the future.)

Let's introduce the chapter with this video:

Introduction

In the beginning of the chapter, Dr. Craig discusses some of the history of mankind observing the heavens and attributing their creation to a divine being.

The Rebirth of Design

In the article, ”The physics of the universe appear to be fine-tuned for life. Why?, John M. Sutter, a cosmologist at Johns Hopkins University, wrote:

The fundamental constants of nature seem perfectly tuned to allow life to exist. If they were even a little bit different, we simply wouldn't be here.
Our laws of physics contain several parameters with values that we cannot predict from theory alone. These are known as the fundamental constants. We can only go out and measure their values and then insert those values into our equations to make physics work. All told, there are about two dozen such numbers. They express such basic facts as the speed of light, the strength of the four fundamental forces, and the masses of elementary particles.
What's especially unnerving about these numbers is how carefully crafted they appear to be. If any were different, even by a tiny amount, our universe would be radically altered. For example, stronger gravity would make stars burn out faster, preventing the rise of solar systems and life-bearing planets like Earth. If the speed of light were faster or the electron were heavier, stars wouldn't even form in the first place. If Planck's constant were different, the cosmos would be totally unrecognizable.
It appears that we live on the knife-edge, where only the narrowest combination of values for the fundamental constants allow life, and especially conscious life, to arise.
This is the heart of the fine-tuning argument: that the universe appears to favor the existence of life. So why are we here?

More succinctly, we seem to live in a “Goldilocks universe.”

Two Kinds of Fine-Tuning

In this section, constants of nature are discussed. Let me provide my own explanation.

Physics "is the science aimed at describing the fundamental aspects of our universe. This includes what things are in it, what properties of those things are noticeable, and what processes those things or their properties undergo. In simpler terms, physics attempts to describe the basic mechanisms that make our universe behave the way it does."[1]

Definition of Fine-Tuning

“The fine-tuned universe is the hypothesis that, because "life as we know it" could not exist if the constants of nature – such as the electron charge, the gravitational constant and others – had been even slightly different, the universe must be tuned specifically for life." Fine-tuned universe - Wikipedia

Examples of Fine-Tuning

This section provides some examples of fine-tuning in order to illustrate the concept of fine-tuning of the universe. To see a list of examples of fine-tuning I have compiled, go to Examples of Fine-Tuned Physical Constants and Their Importance.

A Key Distinction

The point of this section is to simply point out that the term, “fine-tuned” does not mean “designed.” To say that the universe is fine-tuned for life does not describe how the universe’s physical constants originated.

A Possible Objection and Its Answer

Objection: Some may argue that “if the physical constants and quantities had had different values, then maybe different life forms might have evolved.”

Answer: The argument that if the physical constants and quantities were different, maybe different life forms might have evolved is, scientifically, speculative. This claim requires positive evidence, not just possibility, and there is no such evidence exists because we can't observe alternative physics. On the other hand, fine-tuning proponents base their argument on observed physics. The values of the physical constants are known and we can model changes in these constants, and we observe that these changes lead to lifeless universes. This objection often implicitly invokes the multiverse hypothesis. Arguments against the multiverse hypothesis are discussed below, in the section titled, "The Many Worlds Hypothesis - The Multiverse."

Another Objection and Its Answer

Objection: “But maybe in a universe governed by different laws of nature, such disastrous consequences might not result.”

Answer: Dr. Craig argues that this objection shows a misunderstanding of the argument. "We're not concerned with different universes governed by different laws of nature. We have no idea what such universes might be like! Rather, we're concerned solely with universes governed by the same laws of nature but with different values of the constants and arbitrary quantities."

An Argument for Design

Explanations for Fine-Tuning

Three possible reasons why our universe is fine-tuned for life:

  1. Physical necessity: The constants and quantities must have the values they do.
  2. Chance: The constants and quantities have the values they do simply by accident.
  3. Design: The constants and quantities were designed to have the values they do.

Premise 1

"The fine-tuning of the universe is due to either physical necessity, chance, or design."
This is a valid premise because this seems to be the only possible explanations.

Premise 2

"The fine-tuning is not due to physical necessity or chance."

Physical Necessity?

According to this alternative, the universe has to be life-permitting. More specifically, the constants and quantities "must have the values they do, so that a life-prohibiting universe is physically impossible."

Implausibility of Physical Necessity

But there is no reason to believe that the constants had to have the values they have. The constants found within the laws of nature don't determine what the constants will be.

Chance?

In this section, Dr. Craig discusses the improbability of a life-permitting universe and uses a couple of illustrations to illustrate why chance is not a good explanation regarding how a life-permitting universe came into being.

The Many Worlds Hypothesis - The Multiverse

I asked three different artificial intelligence sites this question: "What is the most common explanation cosmologists give for the fine-tuned universe?" All three of them said the multiverse hypothesis.

According to the multiverse hypothesis, our universe is one of many randomly generated universes. The hypothesis is that there is a very large (infinite) number of universes with varying constants and laws. Our universe appears fine-tuned because we live in one of the rare universes where conditions allow life to occur. The anthropic principle is often invoked here since observers would be present only within those universes that are fine tuned.

First Response to the Many Worlds Hypothesis

One argument against the many worlds hypothesis is that if this hypothesis is true, there must be some plausible mechanism for generating the many worlds. And if that mechanism is to be successful in attributing fine-tuning to chance alone, that mechanism better not be fine-tuned itself. Because if that mechanism is fine-tuned itself, we are right back where we started in attempting to explain how the fine-tuning of that mechanism came about.

Second Response to the Many Worlds Hypothesis

Also, what mechanism generates the multiple universes? We argued before that things can create themselves. Where did this mechanism come from? Also, there is no scientific evidence that there are multiple universes nor is there any any evidence that this mechanism that creates many universes exists.

Other Objections

An objection to the fine-tuning argument that is not discussed in On Guard is one presented by Sean Carroll, the atheistic cosmologist, has argued that we truly don’t know the specific conditions under which life is possible.

Dr. Michael Strauss, the author of The Creator Revealed: A Physicist Examines the Big Bang and the Bible, has this blog post that addresses Sean Carroll’s position - Dr Michael G Strauss: Why The Universe? Critiquing Sean Carroll.

Out of curiosity, I asked the AI site, Perplexity, what counterarguments have been proposed to this claim by Sean Carroll. You can read what Perplexity’s response was here - Counterargument to the claim that we don’t know conditions necessary for life. I also asked Perplexity what are the philosophical counterarguments to Carroll’s claim. You can read those counterarguments here - Philosophical Counterarguments to Sean Carroll’s Objection to the Fine-tuning Argument.

Digging Deeper

Articles

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Intermediate

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Books

Beginner

Intermediate

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Videos

Introductory

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Debates

Footnotes

  1. 1.1 Physics: Definitions and Applications - Physics | OpenStax ↩︎

  2. A Newton (symbol: N) is the International System of Units (SI) unit of force. It is defined as the force required to accelerate a mass of one kilogram at a rate of one meter per second squared in the direction of the applied force. Simple Wikipedia - Newton (unit) - Simple English Wikipedia, the free encyclopedia ↩︎

  3. Coulomb's law - Simple English Wikipedia, the free encyclopedia ↩︎

  4. Strong Nuclear Force: Definition, Properties, and Examples ↩︎

  5. Weak Nuclear Force: Definition, Properties, and Examples ↩︎