A Fortunate Universe

Life in a Finely Tuned Cosmos

Geraint F. Lewis, Luke A. Barnes

4/5

"I really liked it"

Review

A Fortunate Universe is a fantastic introduction to the fine-tuning problem, which basically states “Why is the universe just right for the formation of complex, intelligent beings?” It discusses the different parts of nature (e.g. the mass of the electron, the low entropy of the early universe) that seem “fine-tuned” for life to exist.

The first major section discusses some individual fine-tuned parameters, and what would theoretically happen if its value was different. In most scenarios, a small change in a parameter leads to a sterile universe, where life probably cannot form.

Throughout the book, the authors do their best to slowly introduce and explain complex topics like dark energy, the Higgs boson and other fundamental particles, the four fundamental forces, and the arrow of time. Ultimately, I had to consort external resources to really understand what they were talking about. I only fault the authors a little bit for this, because these topics live outside our everyday experience and are just fundamentally difficult for a newcomer (like me) to quickly understand.

Prior to reading A Fortunate Universe, I could have conceptually explained the fine-tuning problem, but I feel that I’ve gained more of a technical understanding of what is fine-tuned, why we consider it fine-tuned, and I’m better equipped to answer the ultimate question: what is the solution? Why is our universe fine-tuned?

In my opinion, the fine-tuning problem is a respectable argument for the belief in God, but it’s not bulletproof. I hope to explore this argument more in the future.

Overview

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 among our Universe’s cousins and distant relatives.

Life?

Life is really hard to define, so the authors tried to avoid it when possible. But to really answer the question “is our Universe fine-tuned for life?” we have to ask: what does life (whatever it actually is) require?

We know what we need for life (e.g. water, oxygen) but we don’t really know what other life might need. Is water really necessary, or are we just biased because all our life on Earth needs it?

There are some safe assumptions we can make, like:

Life may require a lot more than just that (or less!), but using only some simple rules like these, we can rule out a lot of possible universes from ever permitting life.

Energy and Entropy

The 2nd law of thermodynamics states that entropy (or, the spread-out-ness of energy) cannot decrease. In other words, energy will naturally spread out over time.

For example, consider you have two buckets of water: one hot, one cold. If you mix them, you’ll spread out the energy into one tepid bucket. Now, can you reverse the process, and get hot and cold water back? No! Not without introducing some outside system (like a heating element or an ice cube).

Low entropy is necessary for life. If all energy is spread out evenly, no work can be done; we cannot “use” the energy to do anything. Life needs a difference in energy— this is called low entropy.

Thankfully, our early Universe provided plenty of low entropy for life. But, did it have to be this way? And where did that low entropy come from? We can’t answer those questions yet.

Time

Our equations typically use time as a variable: when time moves forward, we can predict what will happen. We can also use the same equations to predict how things will behave if time moved backwards.

If both directions are valid, does that mean they both exist? Or, does time have a “real” direction, known as the arrow of time?

We don’t really know, but using thermodynamics, we can speculate that life will inevitably feel an arrow of time, like we do:

  1. The 2nd law of thermodynamics states that entropy never decreases.
  2. It can be said that the “thermodynamic arrow of time” points towards increasing entropy.
  3. Life, by nature, takes input information and summarizes it, creating patterns and expectations and equations by which it can navigate the world.
  4. This information-processing mechanism will inevitably destroy some of the input information, and generate heat.
  5. Any information-processing life form will experience the thermodynamic arrow of time, always remembering the thermodynamic past (but not the future).

Timeline of the Universe

  1. ???
  2. A singularity (infinite matter, infinite density) probably exists
  3. The Big Bang occurs, and the matter experiences inflation

    • The Big Bang theory [is] simply the notion that in the past the Universe was denser and hotter. That’s it… the theory describes how the Universe was raised; how it was born— even if it was born— is another matter.

  4. The early universe is a dense, hot plasma. It’s mostly homogeneous, with extremely small variances that expand into the large-scale structures we see now (e.g. galaxies, stars, planets)
  5. The universe is slowly gaining entropy (reducing usable energy over time) and inflating (accelerating into infinite space)
  6. You are born on Earth, then you die
  7. Our sun dies
  8. Most energy is stored in black holes, which slowly emit useless low-energy particles
  9. Entropy nears its maximum. Matter is so spread out that nothing ever happens, and there is no usable energy left.

What is Fine-Tuned?

  1. The existence of the 4 fundamental forces

    • No gravity → everything scatters → no large structures
    • No electromagnetism → electrons fly freely → no chemistry
    • No strong force → no atomic nuclei → no chemistry
    • No weak force → life is possible, but we mostly just have helium to work with, nothing heavier.

  2. The value of gravity to create the right-sized stars

    • Lower gravity → stable stars are bigger
      • → escaping photons have less usable energy
      • → no exploding stars that create higher-energy atoms
    • Increase gravity → stable stars are smaller → escaping photons have too much energy and destroy atomic/chemical bonds

  3. The relationships of the coupling constants of each of the 4 fundamental forces: gravity, electromagnetism, the strong force, and the weak force.

    • Different relationships:
      • → no stable atomic structure
      • → early Universe is way different → unusable collection of atoms (e.g. only hydrogen)
      • → radioactive decay is more likely → no stable atoms or chemical bonds (constant bombardment)
      • → radioactive decay is less likely
        • → Earth isn’t warmed by radiation and cools too quickly for life to form
        • → Earth doesn’t have a protective magnetic field
        • → no plate tectonics
        • → too many stable isotopes → life can’t handle this complexity
      • → electromagnetism is stronger than the strong force → protons repel each other → only hydrogen exists

  4. The masses of the elementary particles

    • Different relationships → no stable atoms
    • Heavier electron → electrons can destroy atomic nuclei → no stable atoms → no chemical bonds
    • Heavier neutrino → universe quickly collapses
    • Smaller Higgs boson → ???

  5. The Universe’s symmetries and antisymmetries

    • Less symmetries → universe is really hard to understand or predict
    • If baryon asymmetry didn’t exist → all particles and their antiparticles annihilate each other, producing useless photons → no particles left for life
    • The weak force barely breaks time-reversal symmetry

  6. The almost completely homogeneous nature of the early Universe ()

    • More homogeneous early universe → gravity cannot act on nonexistent “clumps” → no structures (e.g. galaxies, stars, planets) form
    • Less homogeneous early universe → time exacerbates the differences → too much structure → a bunch of black holes

  7. The ability of stars to produce abundant carbon and oxygen

    • Tweaking the strong force or the sum of the mass of the up/down quarks a very small amount will only allow either oxygen or carbon, but not both
    • Carbon has a “breathing mode” that allows it to handle the high energy of a star without shattering

  8. The low-entropy of the early universe

    • Higher entropy → no usable energy for life

  9. The cosmological constant, or amount of dark energy

    • The (effective) cosmological constant is clearly fine-tuned. It’s just about the best fine-tuning case around. There is no simpler way to make a universe lifeless than to make it devoid of any structure whatsoever.

    • More dark energy → universe expands too quickly for life to form
    • Less dark energy → universe experiences a “big crunch” too fast for life to form

  10. The amount of matter in the Universe

    • More matter → universe experiences a “big crunch” too fast for life to form
    • Less matter → universe expands too quickly for life to form

  11. The quantity of our dimensions (3 spacial, 1 temporal)

    • More time dimensions → world is unpredictable
    • Different quantity of spacial dimensions → laws of nature don’t work

  12. The quantum-classical boundary: the scale at which things stop acting quantum-ish and start acting classically

    • Lower boundary → electrons act classically and collapse into nuclei → no chemical bonds or atoms as we know it
    • Higher boundary → life follows quantum mechanics and is unpredictable

Reactions to Fine-Tuning

The Better (?) Reactions

More Science Will Solve Everything

The “free” parameters only seem free; there is some underlying cause, we just don’t know it yet. Eventually, some “theory of everything” will make sense of it all.

There is no reason to think we’ll find that “theory of everything” anytime soon, but you can hope.

Even if we discover the underlying cause for the free parameters, we’ll still be left with some form of the fine-tuning problem, asking instead “why are the laws of nature (which were deterministic) fine-tuned for a life-permitting universe?”

Additionally, even if the laws of nature are deterministic, they still act on an initial condition that would (likely still) seem fine-tuned.

The Multiverse

During inflation, some parts of the Universe kept expanding. They’re so far away from us now, that for this discussion, they may as well be different “universes”. Each universe could have slightly different free parameters, so some of them will inevitably contain life.

The many-world interpretation of quantum mechanics is correct, are there are basically infinite worlds out there, each with different laws of physics, so some of them will inevitably contain life.

If there are infinite universes (however they’re generated), it would make sense that some of them (randomly) are fine-tuned for life. But, this view introduces some problems, like Boltzmann brains.

Boltzmann Brains

Technically, the 2nd law of thermodynamics states that entropy almost never decreases. In reality, it can happen. The greater the entropy decrease, the less likely it is to happen. In other words, small entropy decreases are more likely than big ones.

If we imagine an infinite universe, these entropy decreases are happening all the time, everywhere. What would that look like?

  1. All universes are experiencing small fluctuations in entropy. Occasionally, entropy decreases (this breaks the 2nd law of thermodynamics, but it’s very unlikely).
  2. A small entropy change is much more likely than a big one.
  3. Generating a human brain with memories and thoughts is much “easier” (requires much less entropy change) than say, generating an entire universe with real brains and observers.
  4. Unless you can somehow say how ordinary observers are more common, the set of all observers would seem to be mostly Boltzmann brains.

This is the Boltzmann Brain Problem: either you are (probably) a Boltzmann brain, or you must generate a cosmological model that makes ordinary observers more common than Boltzmann brains. If you assume you are not a Boltzmann brain, then you are just left with the second option: you must explain how ordinary observers are more common than Boltzmann brains.

There are valid cosmological models that solve this problem (e.g. by saying that each universe won’t expand into eternity, or by saying that real universes are actually easier than Boltzmann brains), but none are established as fact.

Bottoming Out

If you keep asking the Universe “why?”, you will eventually hit a roadblock. At some point, our best science can’t answer “why”. Even if we eventually answer our current “why”, we will reach a deeper one, and so on until we “bottom out”. At the deepest level, the universe is not capable of providing an answer to our question.

(While it’s possible that the chain of “why?“s continues forever, known as infinite regression, most scientists reject this option for reasons I can’t really explain at this point.)

In a podcast discussing fine-tuning with Sean Carroll and Luke Barnes, Sean puts it like this:

I’m more or less completely convinced that we are always going to bottom out our series of explanations, that they will end somewhere… the language of causes and explanations is inappropriate when we’re talking about the fundamental nature of reality.

— Sean Carroll

Our Last Resorts

At this point, we have (at least) two options:

  1. Naturalism: the natural world is all there is.

    • There is no reason why the fundamental constants are what they are.
    • There is no reason why the laws of the universe are what they are.
    • There is no reason why our multiverse provided some universes with life at all.

  2. Theism: God, for whatever purpose(s), caused the universe to be.

    • God, unlike us, is a necessary being: a thing which must be.
    • God has no cause; he is Aristotle’s “unmoved mover”.

So, how do we decide?

I think that you’re faced with these two competing ontologies, theism and naturalism, and your burden, if you want to decide which one is true, is to be very, very honest with yourself about what you would expect the universe to look like under each theory. And that’s very hard to do because we know what the universe looks like to some extent, right? And if you favor one theory over the other, then inevitably you’re going to say yep, that’s exactly what the universe should look like under my theory. So personally, and at some level, there’s a problem… predicting what the universe should be like is not at all straightforward.

— Sean Carroll

In other words, we should follow a process like this:

  1. Pick two strictly defined, competing models (naturalism and theism).
    • Strictly defining naturalism or theism is not an easy task, but it can be done.
  2. For each model, determine what the universe would look like if it were true.
    • E.g., if naturalism is real, we would expect the multiverse to exist to explain the fine-tuning of our universe, etc…
    • E.g., if God is real, then we would expect him to show up on Earth, etc…
  3. Compare: which model more accurately describes our universe?

In reality, as Sean says, this is extremely difficult to do. Both ontologies have their own issues. I’d like to tackle these at a later point.