If the Universe Is Fine-Tuned, Why Is It Mostly Inhospitable for Life?

I’m continuing a series on responding to the most common challenges to the fine-tuning of the universe for life. You can read my response to the first challenge here. This week I want to look at a challenge that is summarized beautifully in the comments sections of my last post.

Commenter Angry Grasshopper writes,

Ah the Teleological Argument. Anyone who claims the universe is “finely tuned for the existence of life” has not thought enough about the > 99.9999% of the universe where the existence of life is impossible. It’s kind of silly to call that finely tuned.

This response is confused for three reasons. First, this challenge fails to understand what scientists actually mean when they call a universe finely-tuned for life. When scientists speak of fine-tuned universes, they are referring to universes that are life-permitting. By life-permitting, they do not mean that life can exist wherever. By life-permitting, they do not mean that life can exist whenever. Furthermore, they do not even guarantee that life will exist. It’s a much more modest claim. It only holds that the fine-tuning will permit the existence of life. That’s it.

When scientists consider the landscape of possible universes, they have determined that they would be absolutely dominated by a wasteland of dead, boring, simple, lifeless universes. In my original article, I looked at what would happen if we changed the masses of the fundamental particles that make up everything made of matter: the up quark, the down quark, and the electron. Even minor changes to these values destroy the possibility of chemistry. Life has no chance in a universe with no chemistry, no galaxies, no stars, and no planets.

On the other hand, a fine-tuned universe, like ours, allows for the possibility of life. The fact that there can be life somewhere in a universe is precisely because the fundamental physics is finely tuned. Without this fine-tuning, there would be no life, anywhere, period.

So, to complain about a finely tuned universe not having more locations for life misses the point completely. Ironically, the fact that they can even make their complaint is a testimony to the fact that they are in a fine-tuned universe that allows for their existence. Fine-tuning only tells us that there can be the possibility of life, not that life will be possible everywhere.

Second, this response mistakenly compares particular hospitable locations within our universe (e.g. the Earth) with other inhospitable locations within our universe (e.g. the vacuum of space). However, the fine-tuning of the universe for life—properly understood—compares life-permitting universes, like ours, with other possible universes.

Astrophysicists Luke Barnes and Geraint Lewis give a helpful illustration to expose this mistaken comparison:

Suppose that you are working behind the reception desk of a luxurious mountaintop resort. Bob, a wealthy client, is checking in.

YOU: You’ll be in room 401, sir. The Penthouse. It has wonderful views of the entire mountain range, and on a clear day you can see all the way to the ocean.

BOB: Oh, that’s no good. I don’t want to be able to see the ocean.

YOU: Why not?

BOB: Because I can’t swim.

Now, being well trained and polite, you book Bob into another room. But on a more sarcastic day, you might be tempted to ask why it would be a problem that, from his room, Bob can see somewhere—miles and miles away—that would be rather uncomfortable for him. How does that ruin the room?. . . Even if Bob has a morbid fear of drowning, that’s no reason to give the room a bad review on ratethathotel.com.[1]

Third, many of the regions of the universe that are inhospitable for life are also crucial to a life-permitting universe. True, life cannot exist on the surface of the Sun because it’s nearly 10,000oF. However, the existence of stars is important for why there can be life to begin with. Sure, you don’t want to live next to a supernova—the explosion of a star—but without exploding stars we would have no heavy elements distributed throughout space, which makes life possible.

Or take the vacuum of space. We certainly cannot live in the vacuum of space, but the vacuum of space plays a significant part in making our Universe life-permitting and discoverable. For instance, if we filled our universe with breathable air, then gravity would dominate, and our universe would collapse within 24 hours. If we tried to adjust that expansion rate to keep the universe from collapsing, then the breathable air would become too rarified to breathe within 24 hours.[2] In addition, air resistance would make the Earth spiral into the Sun, and energy from the Sun wouldn’t reach the Earth.[3] Even though the vacuum of space that makes up most of our universe is inhospitable to life, it still plays a significant role in our universe.


[1] Geraint F. Lewis and Luke A. Barnes, A Fortunate Universe: Life in a Finely Tuned Cosmos (Cambridge, UK: Cambridge University Press, 2016), 247-248.

[2] Ibid., 248.

[3] Ibid., 251.

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Tim Barnett