Introduction to Fine-Tuning

The Fine-Tuning Argument is commonly used in defense of theism (the belief in God). What does it mean?

Equations That Govern The Universe

To start, we need to talk physics.

Thanks to countless scientists over the years, we have a set of equations that tell us how the universe behaves over time. For example, if you know where an object starts, its velocity, and how much time passes, you can calculate where it will be in the future using the uniform-motion position equation:

Let’s look at a more complicated example: gravity, or the force pulling any 2 objects in space towards one another.

Most of this equation is intuitive: heavier objects and shorter distances mean gravity is stronger. But what is this ?

Free Parameters

is a value known as the gravitational constant: its value is always roughly . That number seems pretty random, so how did we come up with it?

From carefully looking at the universe! In 1797 and 1798, Henry Cavendish performed a famous experiment wherein he prepared some heavy weights and wire, and carefully measured the force between them. He came up with a value of that makes the gravity equation work.

But, why is roughly ?

The short answer is, nobody knows! is just a number that we made up to make the gravity equation work in our universe. This makes , by definition, a free parameter. And quite simply, we don’t know why our universe’s free parameters have the values they do.

A free parameter is a number that can be adjusted to make a model fit the data. When fitting a straight line to some data, we would use the equation , the numbers and are free parameters; is the slope, and is the intercept, and for different values we get different straight lines.

— Geraint Lewis and Luke Barnes, A Fortunate Universe

What is Fine-Tuning?

We say a variable is fine-tuned for a specific outcome if it meets these 3 criteria:

1. It has a wide range of possible values.
2. To reach the specific outcome, its value must fall within a small range.
3. We observe its value to be within that small range.

For example, imagine you want to brew some coffee: you’ve already prepared your machine with 1 cup of water, and you’re about to add coffee grounds. Of course, you have the choice of how much coffee grounds you want to use— a couple granules, or a truckload, or something in between. Most likely, you want a specific outcome— good tasting coffee— so you’ll put in, say, about 2 tablespoons of coffee grounds. Of course, 1.7 or 2.3 tablespoons is probably fine, but move too far outside that small range of coffee grounds, and you won’t make good coffee. To reach a specific outcome (good coffee), you must fine-tune the amount of coffee grounds so that it falls within a small range (about 2 tablespoons).

In cosmological conversations of fine-tuning, we can be a bit more specific about its definition. Specifically, we’re interested in the free parameters like , and whether they’re fine-tuned for life to exist:

1. The free parameters have a wide range of possible values.
2. In order for life to exist, their values must fall within a small range.
3. We observe their values to be within that small range.

Is Fine-Tuned?

To prove whether a free parameter like is fine-tuned for the existence of life, we have to ask: what would happen if it had a different value? Let’s play with the value of and see what would happen in a theoretical universe:

• is much higher: the universe barely expands after the Big Bang before re-collapsing into a singularity (or whatever it was before the Big Bang). There are no stars. Nothing interesting would happen, definitely not life.
• is a little higher: stable stars would be smaller. Smaller stars means their radiation is higher— so high that it’s not usable by any potential life, because it destroys atomic and chemical bonds (which seem to be necessary for life). These high-energy stars also burn quickly, leaving less time for life to form.
• is just right: stable stars are just the right size to spit out radiation with enough energy to be usable, without destroying chemical and atomic bonds. The universe has plenty of time between inflation and eventual heat death for life to occur.
• is a little lower: stable stars would be bigger. Bigger stars mean their radiation is lower— so low, that it’s not usable enough by life. These less energetic stars are also convective and don’t provide the universe with as many useful elements (e.g. silicon, oxygen, neon, carbon)
• is much lower: the universe fails to form “clumps” like galaxies and solar systems. After the Big Bang, everything quickly scatters. Again, no life.

Tweaking the value of by even small amounts leads to sterile universes! At this point, we have proven that meets requirements 2 and 3 for a fine-tuned variable:

1. has a wide range of possible values.
2. For life to form, the value of must fall within a small range.
3. We observe to be within that small range.

Other Variables

Scientists see evidence that there are many variables besides that govern our universe and also meet requirements 2 and 3.¹ Here’s a short list:

• The existence and coupling constant ratios between the 4 fundamental forces (gravity, electromagnetism, strong force, weak force)
• The masses of the elementary particles (e.g. electron, Higgs boson, etc.)
• The almost completely homogeneous temperature of the early universe
• The entropy of the early universe

In A Fortunate Universe: Life in a Finely Tuned Cosmos, Geraint Lewis and Luke Barnes put it like this:

The message: messing with the make-up of the Universe can have a disastrous effect on the emergence of complex life like you and me, and especially the physical conditions that underlie life such as the usable energy and organic chemistry. Our conclusion is that the fundamental properties of the Universe appear to be fine-tuned for life. We need a cosmos that expands not too fast and not too slow, that forms structure, with a mix of stable elements that can form stars, planets and cells, with the right mix of forces for stars to burn for billions of years, with plenty of carbon and oxygen, with a low-entropy past and free energy into the future, with a life-supporting number of dimensions, and even with mathematically elegant and discoverable laws. Such a cosmos is a rarity…

— Geraint Lewis and Luke Barnes, A Fortunate Universe

The Fine-Tuning Problem is this: why do all these free parameters seem to be fine-tuned for life to form?

Fine-Tuning Denial

One response to fine-tuning is to deny that it exists, most commonly by denying requirement 2:

2. For life to form, the value of must fall within a small range.

We don’t really know what life requires to form. The only life forms we’re familiar with are those on Earth, and even if life looks diverse across Earth, it’s all really quite similar. So of course, it’s possible that we’re being too restrictive in our predictions; perhaps life can thrive even in universes with extremely different circumstances than ours.

But in my opinion, this argument is not compelling. You only have to make a few, very basic assumptions about life before the fine-tuning problem appears, like:

• Low entropy/usable energy
• The existence and stability of atoms
• The existence and stability of certain atoms (e.g. carbon)
• The existence and stability of chemical bonds
• The predictability of the universe

Life also seems hard to form— we don’t really know how the first organisms on Earth started, and we’ve never seen anything like that happen since then, nor has it been replicated in a lab. We’re also yet to detect life outside of Earth; if it does exist in the universe elsewhere, it seems to be incredibly rare.

You can always say “well, we just don’t know what life needs, so we can’t really say” in a hand-wavey motion,² and while that’s true to some extent, I just don’t find it compelling.

What Could Have Been?

Recall requirement 1:

1. The free parameters have a wide range of possible values.

Is requirement 1 also met? Are and the other the free parameters “restricted” to a single value, or do they have a wide range of possible values?

We don’t yet know the answer, but we can hypothesize about these possibilities and what they mean for us.

Restriction

For some reason that we don’t know, the values of free parameters are restricted to 1 possible value. It follows that the values we observe in our universe are the only possible values they can have.

If this is the case, then fine-tuning doesn’t exist! Our universe has the illusion of being fine-tuned, but it couldn’t have been any other way. But why are the free parameters restricted?

As a hypothetical example, let’s say scientists discover that the value of is based on the mass of some new, undiscovered particle called the johnitron. Well, what determines the mass of a johnitron? And what determines that thing?

You see where this is going: if we keep asking these “why” questions, there are basically 2 options:

1. Brute Fact(s): We eventually bottom-out on one or more “brute facts” of the universe, which have no reason or cause. Theoretically, we can eventually know all the brute facts, but never be able to explain them (because they have no reason or cause).
   • Examples of brute facts: ” has a specific value”, or “God exists”
2. Infinite Regression of Causes: you can continue asking “why” forever; everything has a cause, yet there is no “first cause”.

No Restriction/Random

The values of the free parameters are random across some probability distribution space.

In this is the case, then our universe really is fine-tuned! But, how did we get so lucky to land in the right universe? It would seem that either:

1. Only 1 Universe: and we got extremely lucky!
   • This seems unfathomably unlikely.
2. Multiverse/Infinite Universes: If there are infinite universes, then some of them will be life-permitting.
   • The Weak Anthropic Principle (WAP) helps explain why we see a life-permitting universe: obviously, any life will look around and see that it’s in a life-permitting universe.

Conclusion

We’ve now identified at least 5 potential “answers” or “solutions” to the problem of fine-tuning:

1. Fine-Tuning Denial
2. Brute Fact(s)
3. Infinite Regression of Causes
4. Only 1 Universe/Extreme Luck
5. Multiverse/Infinite Universes

In some future posts, I’ll explore these explanations in further detail.