Physicist Luke Barnes writes (from a 2015 essay):
Our “ancient instinct of astonishment,” suggests G.K. Chesterton, is awakened when we consider how the world could have been very different. The possibilities of existence are explored in fairy tales and fuel children’s endless questions about why the universe is the way it is. This kind of curiosity, if left unchecked in youth, can easily develop into a career in physics.
Physicists’ deepest theories of the cosmos have several loose ends. They leave open a set of possibilities — ways that our universe could have been. They describe our universe, but can just as easily describe universes that started differently, or that have different fundamental properties. If we want to know why the universe is as it is, we need to know why, of all the possibilities, ours is the actual universe. Just as science has illuminated our place in the solar system, the galaxy, and the universe at large, we must consider our place in the laws of nature.
Physicists tend to picture the advancement of science in two ways. The experimentalist dreams of new data that overthrows our current theories. For example, in 1905 Henri Poincaré called the element radium “that grand revolutionist of the present time,” a substance that glowed for months on end with no obvious energy source. Perhaps energy is not conserved, or perhaps atoms have an enormous internal reservoir of energy. Either way, something about physics had to change.
The theorist, on the other hand, seeks a creative insight that explains the world in a simpler, more elegant, more unified way. For example, when Apollo astronaut David Scott dropped a hammer and a feather on the Moon, they hit the ground at the same time. This was a dramatic illustration of the long-understood but still counterintuitive truth that weight does not determine how fast an object will fall. But it took the genius of Einstein, reasoning theoretically, to show that gravity is the curvature of space and time, and that this explains why the hammer and the feather fall together — the curvature of space and time caused by the mass of the moon is the same for both, and so both travel in the same locally straight paths along the curvature of spacetime.
Experimentalists are still studying complex phenomena like turbulence and superconductors, still making new observations with supercolliders and space telescopes and other tools, still finding all kinds of unexplained data for theorists to puzzle over. Underlying all of these endeavors, however, is a question that has vexed physicists ever since Thales first postulated that water was the unifying principle of the cosmos: What are the most fundamental laws and principles of nature?
Today, our deepest understanding of the laws of nature is summarized in a set of equations. Using these equations, we can make very precise calculations of the most elementary physical phenomena, calculations that are confirmed by experimental evidence. But to make these predictions, we have to plug in some numbers that cannot themselves be calculated but are derived from measurements of some of the most basic features of the physical universe. These numbers specify such crucial quantities as the masses of fundamental particles and the strengths of their mutual interactions. After extensive experiments under all manner of conditions, physicists have found that these numbers appear not to change in different times and places, so they are called the fundamental constants of nature.
These constants represent the edge of our knowledge. Richard Feynman called one of them — the fine-structure constant, which characterizes the amount of electromagnetic force between charged elementary particles like electrons — “one of the greatest damn mysteries of physics: a magic number that comes to us with no understanding by man.” An innovative, elegant physical theory that actually predicts the values of these constants would be among the greatest achievements of twenty-first-century physics.
Since physicists have not discovered a deep underlying reason for why these constants are what they are, we might well ask the seemingly simple question: What if they were different? What would happen in a hypothetical universe in which the fundamental constants of nature had other values?
There is nothing mathematically wrong with these hypothetical universes. But there is one thing that they almost always lack — life. Or, indeed, anything remotely resembling life. Or even the complexity upon which life relies to store information, gather nutrients, and reproduce. A universe that has just small tweaks in the fundamental constants might not have any of the chemical bonds that give us molecules, so say farewell to DNA, and also to rocks, water, and planets. Other tweaks could make the formation of stars or even atoms impossible. And with some values for the physical constants, the universe would have flickered out of existence in a fraction of a second. That the constants are all arranged in what is, mathematically speaking, the very improbable combination that makes our grand, complex, life-bearing universe possible is what physicists mean when they talk about the “fine-tuning” of the universe for life.The extensive, complete article can be found at The New Atlantis.