Throughout literature, religion, and myth, some people have always claimed that they can see the future. Even in the modern world, prophecies guide the beliefs and actions of countless groups and people. Objectively analyzing the veracity of prophecy is often difficult because predictions have so many possible interpretations in retrospect. One definitely testable prophecy, which has been given throughout history, concerns the end of the world. People have asserted countless dates for the end of days, but thus far, all have proved false. In Chapter 12, Kaku concluded that time travel may be possible for type 3 civilizations, but current laws of physics deny the possibility of precognition because it would defy the laws of causality, which are fundamental to all known laws of nature. Many people claim that they can predict the future, but these claims have not been convincingly verified under scientific conditions.

Precognition goes against Newton’s laws of physics, but Maxwell’s equations of light (which made use of advanced waves of light from the future) cast some doubt on its impossibility. Richard Feynman (1918-1988) discovered that antimatter is ordinary matter going backward in time, and the electron-antielectron annihilation in Maxwell’s equations corresponds to an electron going forward and then backward in time. An explosion of antimatter is simply one electron traveling backward and forward in time, leading to speculation that the Big Bang actually created just one electron, which travels from the beginning of the universe to its end and back over and over again. This would explain why all electrons in quantum theory are interchangeable. Feynman’s investigations led him to produce a complete quantum theory of the electron called quantum electrodynamics (QED), which experimental data have extensively verified, and which earned him a Nobel Prize. Ultimately, however, Feynman showed that none of this violates the laws of causality because when the electron travels backward in time, it just fulfils what has already occurred.

Tachyons are particles that often appear in science fiction, but despite their existence being purely speculative, physicists study them. They travel faster than light and have an infinite velocity that increases as they lose energy, and an imaginary mass (a mass multiplied by the root of -1). If they did exist, they would violate causality, unless they automatically self-deleted like antimatter-matter reactions. Tachyons may have existed at the moment of the Big Bang, but may not exist anymore. Since their presence in a system destabilizes that system by creating a false vacuum, tachyons may have existed before the Big Bang and led to the creation of the universe when a rip in space-time caused a bubble containing the known universe to form in the false vacuum. This hypothesis is central to the cosmological theory of inflation. Scientists hope that the Large Hadron Collider will validate this speculation by finding evidence of the Higgs-Boson subatomic particle, a remnant of tachyons, and the remaining piece needed to complete the Standard Model. However, even though the existence of tachyons would violate causality, they are no longer a part of the observable universe, meaning that precognition is still impossible according to our current understanding of physics.

Kaku believes that it is always unwise to consider anything as absolutely impossible in the physical sciences. Our understanding of universal laws, which is still incomplete, constrains our estimation of possibility. Countless great scientists throughout history have declared technologies and phenomena impossible, only to be proven incorrect, so perceived impossibilities simply set goalposts for future scientists.

Many prominent scientists believe that discovering anything about the pre-Big Bang era or accurately predicting how the universe will end is impossible, but a new generation of detectors and satellites (which may shed light on the matter) is already in development. Researchers propose to investigate gravitational radiation to determine how waves of gravity affect the fabric of space-time, which could potentially usher in a new era of astronomy. Calculating how the universe is likely to end (prominent theories being the Big Freeze and the Big Splat) would require scientists to calculate the cosmological constant (the force pushing the universe to expand). This is possible only within a theory of quantum gravity, a Theory of Everything encompassing the four fundamental forces of the universe. Since ancient times, great minds have tried their hands at defining the laws of the universe in a single unified theory, but none have yet succeeded. The loftiness of the goal makes it a controversial subject, but while string theory may or may not be the key to success, Kaku considers it the most viable candidate currently under investigation.

Opponents of string theory often dismiss it as a fad, which Kaku finds amusing, given that for many years string theory was an unpopular and oft-derided fringe theory. Like much of modern science, string theory is not directly testable, but like using spectroscopy to determine the composition of distant stars or investigating black holes by examining their effect on other measurable phenomena, string theory can be tested indirectly. String theory proposes testable predictions about the physical properties of dark matter, if laboratories develop the means to detect it, and detectors like Laser Interferometer Space Antenna (LISA) and the Big Bang observer might provide data on the early universe. Scientists are already searching for minuscule deviations in Newton’s inverse square law as proof of higher dimensions, and particle accelerators may prove able to create superparticles. Numerous other experiments hope to find rare phenomena like mini black holes or superstrings.

Some scientists, including Steven Hawking (1942-2018), who himself sought the Theory of Everything, consider it impossible to comprehensively define the laws of the universe. They cite the fact that science is based on math, and Gödel’s incompleteness theorem shows that math cannot prove all true statements. However, mathematicians can work around Gödel’s theorem by simply stating that their work excludes all self-referential statements. Similarly, physicists can avoid paradoxes by producing a comprehensive theorem that provides the same conclusions regardless of where the divide is made in the observer/observed dichotomy. Kaku himself believes that while nature may itself contain inexhaustible possibilities, these possibilities are based on a finite set of principles. The fundamental laws of the universe are knowable, and the coming years may be the most exciting of all as people implement new tools and technologies to explore new horizons.