PrepTest 83, Section 4, Question 6

In a typical Hollywood action movie, the hero skirts death to complete a mission. Bad guys shoot, cars explode, objects fall from the sky, but all just miss. If any one of those things happened just a little differently, the hero would be dead. Yet the hero survives.

In some respects, the story of our universe resembles an action movie. A slight change to any one of the laws of physics would likely have caused some disaster that would have disrupted the normal evolution of the universe and made life impossible. For example, if the strong nuclear force had been slightly stronger or weaker, stars would have forged very little of the carbon that seems necessary to form planets and living things. Indeed, it seems that in order for a universe to support life, the laws of physics must be so finely tuned that the very existence of such a universe becomes improbable.

Some cosmologists have tried to reconcile the existence of our universe with the seeming improbability of its existence by hypothesizing that our universe is but one of many universes within a wider array called the multiverse. In almost all of those universes, the laws of physics might not allow the formation of matter as we know it and therefore of life. But given the sheer number of possibilities, nature would have had a good chance to get the "right" set of laws at least once.

But just how exceptional is the set of physical laws governing our universe? The view that the laws of physics are finely tuned arises largely from the difficulty scientists have had in identifying alternative sets of laws that would be compatible with life.

The conventional way scientists explore whether a particular constant of physics is finely tuned is to tweak it while leaving all other constants unaltered. The scientists then "play the movie" of that universe—they do calculations, what-if scenarios, or computer simulations—to see what disasters occur. But there is no reason to tweak just one parameter at a time. By manipulating multiple constants at once, my colleague and I have identified numerous scenarios—hypothetical universes—where the physical laws would be very different from our own and yet compatible with the formation of complex structures and perhaps even some forms of intelligent life.

Fine tuning has been invoked by some cosmologists as indirect evidence for the multiverse. Do our findings therefore call the concept of the multiverse into question? I do not think this is necessarily the case for two reasons. First, certain models of the birth of the universe would lead us to expect the existence of something like the multiverse. Secondly, the multiverse concept may well prove to be the source of solutions to certain other long-standing puzzles in cosmology.

In a typical Hollywood action movie, the hero skirts death to complete a mission. Bad guys shoot, cars explode, objects fall from the sky, but all just miss. If any one of those things happened just a little differently, the hero would be dead. Yet the hero survives.

In some respects, the story of our universe resembles an action movie. A slight change to any one of the laws of physics would likely have caused some disaster that would have disrupted the normal evolution of the universe and made life impossible. For example, if the strong nuclear force had been slightly stronger or weaker, stars would have forged very little of the carbon that seems necessary to form planets and living things. Indeed, it seems that in order for a universe to support life, the laws of physics must be so finely tuned that the very existence of such a universe becomes improbable.

Some cosmologists have tried to reconcile the existence of our universe with the seeming improbability of its existence by hypothesizing that our universe is but one of many universes within a wider array called the multiverse. In almost all of those universes, the laws of physics might not allow the formation of matter as we know it and therefore of life. But given the sheer number of possibilities, nature would have had a good chance to get the "right" set of laws at least once.

But just how exceptional is the set of physical laws governing our universe? The view that the laws of physics are finely tuned arises largely from the difficulty scientists have had in identifying alternative sets of laws that would be compatible with life.

The conventional way scientists explore whether a particular constant of physics is finely tuned is to tweak it while leaving all other constants unaltered. The scientists then "play the movie" of that universe—they do calculations, what-if scenarios, or computer simulations—to see what disasters occur. But there is no reason to tweak just one parameter at a time. By manipulating multiple constants at once, my colleague and I have identified numerous scenarios—hypothetical universes—where the physical laws would be very different from our own and yet compatible with the formation of complex structures and perhaps even some forms of intelligent life.

Fine tuning has been invoked by some cosmologists as indirect evidence for the multiverse. Do our findings therefore call the concept of the multiverse into question? I do not think this is necessarily the case for two reasons. First, certain models of the birth of the universe would lead us to expect the existence of something like the multiverse. Secondly, the multiverse concept may well prove to be the source of solutions to certain other long-standing puzzles in cosmology.