At the Edge of Time: Exploring the Mysteries of Our Universe’s First Seconds (Science Essentials Book 32)

by Dan Hooper

If the laws of physics in our universe were even slightly different from what they are, the characteristics of our world could be dramatically altered. For example, if the strength of the electromagnetic force were a mere 4 percent weaker than it is in our world—or if the amount of electric charge carried by protons and electrons were only slightly smaller—protons in stars would be able to bind together, releasing huge amounts of energy and causing the Sun to immediately explode. On the other hand, if the electromagnetic force were much stronger than it is, then carbon atoms would be unstable—making life as we know it impossible. If protons were a mere 0.2 percent heavier than they are, or if neutrons were 0.2 percent lighter, free protons would decay into neutrons, instead of the other way around, leaving the world devoid of stable atoms. In these and many other ways, the characteristics of our universe seem to be remarkably well suited for the emergence of life.

life is very rare indeed—but it is not impossible. Taking into account both the distribution of universes and the likelihood that things like planets and stars will form within a given universe, Weinberg and others have calculated how much dark energy typical observers should find to be present in their universe. Intriguingly, they find that the most common places for life to emerge are those corners of the multiverse in which there is roughly as much dark energy as there actually is in our world. In this sense, the existence of the multiverse resolves the long-standing mystery of dark energy.

The twentieth-century philosopher Karl Popper is most famous for his work on what is known as the demarcation problem, or the problem of how to distinguish truly scientific endeavors from those of pseudoscience. Most people think they can recognize science when they see it, but unless you’ve thought a lot about this issue, it can be pretty difficult to come up with a set of criteria that is satisfied by everything that we think of as science, while excluding things like astrology and moon landing conspiracy theories. Popper’s solution was to insist that in order for a theory to be considered scientific, it had to offer predictions that could—at least in principle—be falsified. A theory that could never be disproven is not a scientific theory.

For example, it’s been argued—and I agree—that what is really essential in order for a theory to be scientific is that some future information, such as observations or measurements, could plausibly cause a reasonable person to become either more or less confident of its validity. This is similar to Popper’s criteria of falsifiability, while being less restrictive and more flexible.

In the history of cosmology, no observations or measurements have borne as much fruit as those of the cosmic microwave background. Providing us with a detailed snapshot of our universe 380,000 years after the Big Bang, this collection of photons represents by far the greatest body of information we have about our universe’s youth. Among other things, if we had never observed the cosmic microwave background, we would know virtually nothing about inflation—in fact we would have had little reason to think that something like inflation took place at all. It was by scrutinizing the cosmic microwave background that we learned that our universe is so geometrically flat and uniform—precisely the features that inflation was originally proposed to explain. Furthermore, modern observations of this radiation have shown that the patterns of its temperature variations closely match what is predicted by most theories of inflation. These observations have convinced most cosmologists that something like inflation likely took place. That said, we still know very little about how this occurred, or how it came to an end.

our universe has only one cosmic microwave background, and it contains a finite amount of information.

There is no place in the inner Solar System that is more radio quiet than the far side of the Moon. It seems likely—and even imperative—that scientists will ultimately turn to the Moon as the site for their most ambitious cosmic investigations. By deploying a few million simple radio antennas across a 100-kilometer region of the lunar surface, astronomers could go a long way toward extracting essentially everything that our universe has to tell us about its history, evolution, and origin. The secrets of cosmic inflation may indeed be waiting for us on the far side of Earth’s only moon.

The strong force, for example, diminishes as temperatures rise, and thus it was considerably less powerful in the early universe than it is today. And although these three forces act with very different strengths in the present universe, our calculations indicate that they were all approximately equally powerful when the temperature of our universe was somewhere around 1028 degrees. Many physicists see this as an indication that these three forces are not as independent as they might seem, but are instead each a manifestation of a single, unified force. In fact, there are many features of the Standard Model that suggest that these three forces and the particles they act upon are all parts of a larger and more complete theory—what we call a Grand Unified Theory.

In theories that describe the curvature of space in terms of a collection of individual gravitons—much as the electromagnetic field is a collection of photons—many of the calculations simply explode to infinity. In technical terms, these theories of quantum gravity are non-renormalizable—a clear indication that they are broken and cannot provide a true or logically self-consistent description of our universe.

“Why is there something, instead of nothing?”