The Anthropic Principle: Are the Laws of the Universe Fine-Tuned for Life?

By Korey Haynes | November 12, 2018 1:00 pm
a crescent view of Earth

Our planet teems with life. But are we a fluke, or an inevitability? Credit: ESA

Humans have often looked at the night sky and wondered if there’s anyone else out there. But stare into that darkness long enough, and many wonder instead: how did we get here? What were the odds, in a universe so enormous and chaotic, that humans should have come to exist at all? Is life, let alone intelligent life, such a wildly improbable occurrence that we’re the only ones here? Or are we an inevitable consequence of the laws of physics?

Life exists on Earth (assuming we’re not living in a computer simulation). Therefore, the universe must exist in such a way that we are possible. That’s the essence of the anthropic principle. On the one hand, it sounds tautological. By that, I mean, I’m just saying the same thing twice. But cast another way, it can lead us to important truths about the universe. It means any version of the universe we can fathom has to allow for life to exist at least once. When there are things we don’t understand about the universe — how dark energy works, how the cosmos formed — all our theories have to include the fact that we exist. The universe must allow us.

Are Humans the Universe’s Ultimate Goal?

a blue swirl with an orange central swirl

In addition to measuring the Big Bang’s lingering traces, the Planck spacecraft also measured the universe’s density parameter, omega. (Credit: ESA and the Planck Collaboration)

Some people have taken this anthropic principle theory to extreme ends. It can imply that the universe must favor life, or even life like us, which isn’t exactly the same thing.

And it does seem hard to believe humans exist, given the huge range of paths the universe could have taken. I don’t just mean that the dinosaur-killing asteroid could have hit a few million years later and changed the course of evolution on the planet. A bit more fundamental is the idea that without a moon and its accompanying tides, maybe Earth creatures never would have ventured out of the oceans. But we can dive even deeper. The laws of physics themselves seem perfected just for us.

An old version of this anthropic principle argument involves the Hoyle state, a particular state of a particular type of carbon. If the Hoyle state didn’t exist, stars could not produce the abundance of carbon they do. Carbon is the basic element upon which life is built. If it were scanter in the universe, life wouldn’t exist, down to the simplest microbes. And it wasn’t clear, for a long time, how the Hoyle state worked, just that it must: After all, here we are.

More recently, scientists have pointed out that if one tweaks many of the dimensionless physical constants — numbers like pi that are independent of units and simply exist as fundamental ideas — none of the cosmos we see would exist. One of these numbers is omega, the density parameter, which pits gravity’s pull against the expanding push of dark energy. If gravity were stronger, the universe would have long since ceased expanding, and would have collapsed back down in a reverse Big Bang, often called the “Big Crunch.” If dark energy were stronger, then the universe would race away from itself so that no matter would stick together and stars, planets, and people could never form.

If the cosmos were truly a random and senseless arrangement of particles, it seems eerie or suspicious to many that these two forces balance so delicately.

But we can remember the tautological approach: if the universe were any way other than what it is, we wouldn’t be here to worry about it. Of course the universe seems fine-tuned to us; it’s the only one we know.

Taking the Long View

many earths stretching into space

If our universe is fine-tuned to us, are there universes where we’d be less well-suited? (Credit: NASA/ESA/G. Bacon (STScI))

This argument in itself gives rise to questions about a multiverse. Are there, then, other universes where the laws of physics don’t allow matter to stick together and form stars and planets, dogs and cats? The anthropic principle doesn’t answer this. We’re left to ponder.

The truth is that right now, we’re drastically short on data. We’ve only stepped foot on two bodies in the whole universe. We’ve only sent probes to a handful more. After that, it’s all just long-distance photography skills and a lot of semi-applied math.

We can ask how often the universe provides the things we think are necessary to life — the Drake equation is a good attempt to quantify this. But even that assumes that life must be somewhat as we know it.

What about inorganic life forms? Scientists have posited chemical reasons for and against life forms that vary too much from what we know on Earth. Maybe the Hoyle state is irrelevant, if other forms of life don’t require carbon anyway. You can get pretty trippy heading down this rabbit hole of questioning. How would we even recognize life so different from us? For that matter, how do we know rocks aren’t sentient, and we’ve just never noticed, so caught up in our carbon chauvinism?

The universe does seem fine-tuned for our existence. The flip side, of course, is that we are unarguably fine-tuned to the universe we find ourselves in.

MORE ABOUT: cosmology
  • Uncle Al

    Are Humans the Universe’s Ultimate Goal?” The universe exists to create single payer healthcare, guaranteed minimum income, open borders, and irony.

    • 7eggert

      The universe meant for each individual to inhabit one cell. Multi-cellular organisms are an abomination!°

  • Ello

    A constant is just a number that tells you something about the properties of the world around you. Other than that there’s nothing special about it.

    Stating that constants are finetuned to make life possible, is a logical fallacy. One could use the same logic to conclude that pi (π) is finetuned to make it possible for the circle to exist. After all, if π would deviate from it’s value even by a billionth of a fraction, the circumference wouldn’t fit the disc any longer, and that would be the end of the circle.

    So there you have it : there is no such thing as finetuned constants. It is a misconception that arises when humans try to find/give meaning where there is non to be found/given.

    • 7eggert

      For pi, there is a reason why you can tell that it may not be 42. For natural constants, you can’t, it could be any number as far as we know.

      Off cause maybe we know we wouldn’t be there if alpha wasn’t 1/137, but we have NO CLUE why it isn’t 1/128 or 1/144. THAT’s why we’re wondering and guessing.

    • neoritter

      It comes down to definition. Is a circle by definition a circle anymore if that value changes? Is life or the cosmological properties that enable it intrinsic to a universe? This kind of get’s to the point, is the universe still a universe if these “fine-tuned” things aren’t the constant?

      If life or those properties are intrinsic to the definition of a universe, then you’re argument is absolutely true. If a constant is not intrinsic to the definition of a universe then the logic is different. With reference to the article, you can see an example of this in two constants or values presented above. The Hoyle state is arguably not essential to the existence of a universe as we define it. But the density parameter is arguably essential.

    • Chris In PA

      Arguing that constants are fine-tuned is equivalent to arguing that that the underlying properties of the world around you are fine-tuned. That argument can be persuasive or not, but I don’t see how it is a fallacy.

      On the other hand, pi is different than the material constants from this article. Pi is an abstract mathematical constant. Imagining a world in which Pi has a different value is like imagining a world in which 2+2=5. We can predict almost nothing about such a world.

      On the other hand, we can predict quite a bit about a world in which various physical constants are different.

  • Emmette Davidson

    “…it’s all just long-distance photography skills and a lot of semi-applied math.” And the ideas of a few dead giants; let’s not forget those.

  • benboy73

    Just my luck…I got stuck in this variation of the multiverse where I’m unattractive and poor.

    • John C

      I’m stuck in the one with Cablevision as my only provider option.

  • John C

    The problem with the Multi-verse theory is that it is untestable, and therefore outside the realm of science.

    It also seems like intellectual laziness. There is no proof of more than one universe. Instead of trying to figure out why the values are what they are for the one universe, postulate an infinite number of universes with different values of each, ours being the one that just happens to have these.

  • Samuel Fistel

    The anthropic principle is consistent with the god principle: It took a huge series of incredible coincidences for the universe to evolve in such a way that we are having this conversation now. The simplest explanation is intelligent design, which implies the existence of god. But liberal atheists have created “liberal atheist science”, which was originally based on three principles 1) there is no god 2) everything can be explained with no need for god 3) theories with no hope of being proved (such as god) are invalid. Unfortunately for the liberal atheists, modern science has defied them. Since the Big Bang appears to be an act of creation, for which god clearly should be a valid possible explanation, the liberal atheists have been forced to propose different forms of eternal universes (the multiverse, eternal inflation), none of which can ever be proven, just like the existence of god. Accordingly, god is just as “scientific” as the multiverse.

    • Anton P.F.

      Who designed God?

      • Visa Lehtinen

        The answer is fractal.

  • Tom Aaron

    Write the number one on a page…now add 23 zeros beside it. That’s the number of stars in the Universe. That’s a lot of of real estate that exists regardless of humans.

    Saying that the universe is fined tuned for humans is like saying that the Earth is fined tuned for one particular amoeba that feeds off of one type of bacteria….

    Human centrism is alive and well in the Anthropic principle.

    • dh122

      Does it really matter if the universe is fine-tuned or not? Since we are all just a mass of molecules which will eventually die, what difference does any of this make? Face it, there is no god, no objective Truth, no ultimate basis for morality or meaning and purpose in life and no free will. If thinking that the universe makes you temporarily feel more significant, then fine. But really you should face the facts that you are nothing of any importance and will soon be gone. Be courageous enough to face the implications of our core beliefs. Even your thoughts and feelings are nothing are nothing more than electro-chemical reactions in your brain.

      • Emmette Davidson

        Objective truth: to scientifically resolve the dark mysteries of matter and energy, the world must be deemed indeterminate after all. So, with the gift of free will beyond five sigma, there’ll be no more excuses, and the only judgement will be: who wasn’t courageous enough to seek their purpose.

  • OWilson

    We can only see with human eyes, and on human time scales. Humans demand a beginning and an end to the Universe. A mayfly occupies a different time scale where it is born, mates, lats eggs, and dies in a day.

    On other time scales, rocks deform and flow towards gravity, as does window glass, with the same imperative drive as a plant reaching up to the sun.

    Imperceptable to us on our own time scale.

    A so called “constant” in a Euclidian space, may not be a constant in three dimensional space. Circles and Pythagorian triangles drawn on a sphere have different values, notably in Einstein’s space time. Black holes render all constants irrelevant.

    “The ratio only has the value 3.14159… in a “flat” space, i.e. one in which Pythagoras’ Theorem holds. Since the space of this universe is not “flat”, the ratio for any real circle in this universe is not 3.14159… But it is also not constant.” (Manning, et al)

    That famous standard meter bar archived in France has already seen a number of revisions to it’s actual definition. Now a gravity wave can render even the latest definition moot.

    Science is limited in our definition of the Universe, even the Big Bang defies the first two “Laws” of Thermodynamics! :)

    It is still a mysterious place we find ourselves in.

    Be humble, and wonder!

  • Hirk

    I’d like to pose a question for pondering. What would it mean to all of us if we scientifically proved that “God” (not for lack of a better word, but because that is the word we have given “it”) exists? Would religious people and aethiests all shake hands and say, “I guess we were both right? Or would they simultaneously say, “See! You were wrong!” My bet is on the latter. We are obsessed with battles that need not exist. Rupert Sheldrake has formulated a very strong case for something which has been called, the “Morphogenetic Field.” Others such as Michael Persinger have come to very much the same conclusions as to the existence of such a field through other means of scientific exploration which, in the world of science, makes for a very strong case of the truth to a theory. It’s worth investigating more before we all dismiss the possibility of the existence of a consciousness made of the electromagnetic light flowing through and from each and every one of you as you read this.

  • Ofinfinitejest .

    An extension of this delusion would be a lottery winner who says the entire universe was fine tuned so that he would win the lottery. Stepping back a bit, the universe is 99.9% dark matter and dark energy, so maybe the universe is fine tuned for that stuff.

    Or maybe this “fined tuned” stuff is applying narrow human notions where they don’t actually fit.

  • M1k3G

    There’s no telling how many times the universe was created and destroyed through multiple Big Bangs and eventual Big Crunches before one particular sequence proved ideal to allowing life to emerge. For all we know, there may have been millions of iterations before we appeared. Assuming this as a possibility, there is no need for a god to intervene, and no place for intelligent design.

  • kapnlogos

    The Anthropic Principle means we see ONLY a situation where all the requirements for our existence, life and intelligence are possible. The implication is that every other variation of the universe is possible, and those variations may not allow the natural laws and constants we see. We may find ourselves as a blade of grass growing in the crack on the side of a mountain. One conclusion is that our situation isn’t special, just that it allows us to last long enough to contemplate it.


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