Mark Changizi is an evolutionary neurobiologist and director of human cognition at 2AI Labs. He is the author of The Brain from 25000 Feet, The Vision Revolution, and his newest book, Harnessed: How Language and Music Mimicked Nature and Transformed Ape to Man.”
The silent purr of an electric car is a selling point over the vroom of a gasoline engine, but it comes with an undesirable side effect: An electric car can pounce on unsuspecting passerbys like a puma on prey. In fact, the NHTSA found that hybrid electric cars are disproportionately dangerous to pedestrians. To deal with this problem, it has been proposed that sound be added to hybrid and electric vehicles, whether it be bird-songs or recordings of someone making “vroom vroom” sounds.
In this light, I wondered whether it might be possible to add “smart sound” to these dangerously quiet cars destined to rule the road in the near future. The solution, I realized, might come from faster-than-light-speed objects on the moon. I’ll get to this crazy-sounding part in a bit.
The Melody of Movement
In setting out to solve this problem, I reasoned that when electric cars are moving very fast they make enough sound to be heard due to the rumblings of the car parts. It’s when they’re moving at lower speeds that they’re most perilous, because at these speeds they’re most silent. Therefore, if electric cars are to be fitted with some sound, it should be designed to work even at lower speeds—or, especially at lower speeds.
Next question was, What sort of sound do we want on slowish, stealthy electric cars? To answer this, it helps to grasp the sorts of cues your auditory system uses for detecting the movement of objects in your midst.
The most obvious auditory cue is that nearer objects are louder, and so when you hear a moving object rising in loudness, you know it’s getting closer.
But that’s not the most important auditory cue. To illustrate why, imagine walking along a curb with traffic approaching and passing you from behind. The important observation here is that when this happens you aren’t in the least worried. Even without seeing the car, you know it’s merely passing you despite the massive crescendo in its sound. Why?
The Doppler shift changes the observed pitch of the siren as the car moves.
You know the car isn’t going to hit you because of its pitch. Due to the Doppler shift, this car has a falling pitch, and this falling pitch contour tells your brain unambiguously that, although the car is going to get arm-reachably close, it is going to pass you rather than collide with you. If it were going to collide with you, its pitch would be high and constant—that’s the signature of a looming collision.
Fermilab’s Tevatron, the largest particle accelerator in the United States, was shut down on September 30 after a celebrated career of 28 years that has provided us with some of the greatest discoveries in particle physics. This leaves the European lab CERN (see photo on left) to lead the way into future discoveries with its Large Hadron Collider.This landmark in experimental physics is an opportunity to reexamine the theoretical model physicists have constructed and relied on in their search to understand the workings of the universe: the standard model of particle physics. The standard model is a comprehensive theory about nature’s elementary particles and the forces that control their behavior, and it has been constructed over a half-century of intensive work by many theoretical physicists as well as experimentalists. The model has worked amazingly well, harmoniously combining theory and experiments and producing extremely accurate predictions about the behavior of particles and forces. But could the model now be beginning to show some cracks?
It all started on a wintry evening in 1928. While staring at the flames in the fireplace at St. John’s College, Cambridge, Paul Dirac made one of the most important discoveries in the history of science when he saw how to combine the Schrödinger equation of quantum mechanics with Einstein’s special (but not general) theory of relativity. This achievement launched relativistic quantum field theory—which forms the theoretical basis for the standard model—and produced two immediate consequences: an explanation of the spin of the electron, and Dirac’s stunning prediction of the existence of antimatter (confirmed a few years later with the discovery of the positron).
In the late 1940s, Richard Feynman, Julian Schwinger, and Sin-Itiro Tomonaga, all working independently, presented the first quantum field theory, called quantum electrodynamics, which explained the electromagnetic interactions of electrons and photons. It forms the first part of the standard model by handling interactions that are controlled by the electromagnetic field. The theory’s success inspired other theoretical physicists to construct similar quantum field theories for addressing the actions of the weak and strong nuclear forces—thus together accounting for everything in particle physics except for the action of gravity, the subject of Einstein’s general theory of relativity. By the 1970s, the result, the standard model, was ready: a quantum field theory of all elementary particles—leptons and quarks and their interactions through the actions of particles (such as the photon) called bosons.
In 1917, a year after his general theory of relativity was published, Einstein tried to extend his field equation of gravitation to the universe as a whole. The universe as known at the time was simply our galaxy—the neighboring Andromeda, visible to the naked eye from very dark locations, was thought to be a nebula within our own Milky Way home. Einstein’s equation told him that the universe was expanding, but astronomers assured him otherwise (even today, no expansion is evident within the 2-million-light-year range to Andromeda; in fact, that galaxy is moving toward us). So Einstein inserted into his equation a constant now known as “lambda,” for the Greek letter that denoted it. Lambda, also called “the cosmological constant,” supplied a kind of force to hold the universe from expanding and keep it stable within its range. Then in 1929, Hubble, Humason, and Slipher made their monumental discovery using the 100-inch Mount Wilson telescope in California of very distant galaxies and the fact that they were receding from us—implying that the universe was indeed expanding, just as Einstein’s original equation had indicated! When Einstein visited California some time later, Hubble showed him his findings and Einstein famously exclaimed “Then away with the cosmological constant!” and never mentioned it again, considering lambda his greatest “blunder”—it had, after all, prevented him from theoretically predicting the expansion of the universe.
Fast forward six decades to the 1990s. Saul Perlmutter, a young astrophysicist at the Lawrence Berkeley Laboratory in California had a brilliant idea. He knew that Hubble’s results were derived using the Doppler shift in light. Light from a galaxy that is receding from us is shifted to the red end of the visible spectrum, while a galaxy that is approaching us has its light shifted to the blue end of the spectrum, from our vantage point. The degree of the shift is measured by a quantity astronomers call Z, which is then used to determines a galaxy’s speed of recession away from us (when Z is positive and shift is to the red).