The Science of Interstellar

By 1957 it became evident that the relativistic laws and the quantum laws are fundamentally incompatible. They predict different things, incompatible things, in realms where gravity is intense and quantum fluctuations are strong.[5] These realms include the big bang birth of our universe (Chapter 2), the cores of black holes like Gargantua (Chapters 26 and 28), and backward time travel (Chapter 30). In these realms a “fiery marriage”[6] of the incompatible relativistic and quantum laws gives rise to new laws of quantum gravity (Figure 3.2).

We do not yet know the laws of quantum gravity, but we have some compelling insights, including superstring theory (Chapter 21), thanks to enormous effort by the world’s greatest twenty-first-century physicists. Despite those insights, quantum gravity remains terra almost incognita (an almost unknown land). This leaves much elbow room for exciting science fiction, elbow room that Christopher Nolan exploits with great finesse in Interstellar; see Chapters 28–31.

Truth, Educated Guesses, and Speculations

The science of Interstellar lies in all four domains: Newtonian, relativistic, quantum, and quantum gravity. Correspondingly, some of the science is known to be true, some is an educated guess, and some is speculation.

To be true, the science must be based on well-established physical laws (Newtonian, relativistic, or quantum), and it must have enough basis in observation that we are confident of how to apply the well-established laws.

In precisely this sense, neutron stars and their magnetic fields, as described in Chapter 2, are true. Why? First, neutron stars are firmly predicted to exist by the quantum and relativistic laws. Second, astronomers have studied in enormous detail the pulsar radiation from neutron stars (pulses of light, X-rays, and radio waves described in Chapter 2). These pulsar observations are beautifully and accurately explained by the quantum and relativistic laws, if the pulsar is a spinning neutron star; and no other explanation has ever been found. Third, neutron stars are firmly predicted to form in astronomical explosions called supernovae, and pulsars are seen at the centers of big, expanding gas clouds, the remnants of old supernovae. Thus, we astrophysicists have no doubt; neutron stars really do exist and they really do produce the observed pulsar radiation.

Another example of a truth is the black hole Gargantua and the bending of light rays by which it distorts images of stars (Figure 3.3). Physicists call this distortion “gravitational lensing” because it is similar to the distortion of a picture by a curved lens or mirror, as in an amusement park’s fun house, for example.

^{Fig. 3.3. The stars in Gargantua’s galaxy, as seen around Gargantua’s shadow. Gargantua bends the light rays coming from each star, thereby distorting enormously the appearance of its galaxy: “gravitationally lensing” the galaxy. [From a simulation for this book by the Double Negative visual-effects team.]}

Einstein’s relativistic laws predict, unequivocally, all the properties of black holes from their surfaces outward, including their gravitational lensing.[7] Astronomers have firm observational evidence that black holes exist in our universe, including gigantic black holes like Gargantua. Astronomers have seen gravitational lensing by other objects (for example, Figure 24.3), though not yet by black holes, and the observed lensing is in precise accord with the predictions of Einstein’s relativistic laws. This is enough for me. Gargantua’s gravitational lensing, as simulated by Paul Franklin’s Double Negative team using relativity equations I gave to them, is true. This is what it really would look like.

By contrast, the blight that endangers human life on Earth in Interstellar (Figure 3.4 and Chapter 11) is an educated guess in one sense, and a speculation in another. Let me explain.