the anthropic principle takes another hit

A new paper shows that far from requiring precise physics to exist, matter as we know it can form within a relatively wide range of tolerances.





You probably know about the anthropic principle, the idea that the universe has to be fine tuned for life due to the balance between the physical laws that govern it. One important argument in favor of this principle deals with the strong nuclear force which holds together atomic nuclei. It says that if the strong force was just a bit stronger, protons would bind under higher temperatures soon after the Big Bang and leave less hydrogen to form all the stars that would eventually produce the raw materials and habitats for life as we know it.

But according to a paper by University of Delaware physicists, James MacDonald and Dermott Mullan, that’s not necessarily the case. This argument is too simplistic because protons will bind to neutrons easier than to other protons no matter the power of the strong nuclear force. Other protons have a like charge which would generate an electrostatic repulsion barrier that needs to be overcome before the two particles can join. In our present universe, the resulting diprotons will quickly decay into deuterium nuclei due to spin-spin interactions and the Pauli-exclusion principle. Neutrons, on the other hand, have no charge and require a lot less energy for a proton to bind to them, creating stable structures. After the Bing Bang, proton/neutron unions would be a lot more common and more stable than diprotons as free-floating subatomic particles come together.

Boost the strong force and you’ll eventually keep diprotons together but there’s a comfortable range in which they’ll decay as they do today, leaving plenty of hydrogen for star formation, along with a surplus of deuterium. Of course there would be some changes in the synthesis of other atoms but within a certain range, chemistry that makes life possible would go on. The same should apply to a universe with a weaker strong force. There may be less heavier atoms but there could still be the kind of chemistry which allows for stars and ultimately, some sort of life, even if it’s not the kind of life that currently exists. If there’s a range in which chemistry bound to result in organisms like us can happen, it would indicate that the universe is not so much fine tuned for us as we’re really an outcome of a number of possible chemical processes.

And that’s the biggest problem with the anthropic principle. It’s actually a backwards question. Instead of trying to trace back how natural selection got us to where we are today, it asks how the universe accommodated us and how it must have fine tuned everything to create the kind of life we see today. It’s somewhat like looking at the Himalayas, wondering how the Asian and Indian plates knew to collide in order to form a mountain range with these particular shapes and heights. Neither of the tectonic plates had a blueprint. They just collided and the mountain range is the result. The same can be said of the physical laws of our universe. They’re not a fine tuned machine that allows us to exist. Instead, we’re just a product of how things played out when the physical laws of the universe we occupy today took shape.