Zero - Charles Seife [78]
This was an astounding discovery; the universe was millions of times bigger than previously suspected. As amazing as this observation was, it was not what Hubble is best remembered for. Hubble’s second discovery was what shattered Einstein’s eternal universe.
Hubble measured the distance to galaxy after galaxy with his Cepheid stars, but soon began to notice an alarming pattern: all the galaxies were fleeing with high speed, shooting away from the Milky Way at speeds of hundreds of miles a second or more. The galaxies were so distant that even these great velocities were not directly measurable.
The only way to clock the speed of a galaxy is by using the Doppler effect—the same principle used in state troopers’ radar guns. You might have noticed that when a train zooms by, the pitch of its horn changes. As the train approaches, its horn is high-pitched, but as it passes you, all of a sudden its pitch drops dramatically. This happens because the motion of the train crushes the sound waves in front of it (making a higher-frequency, higher-pitch tone) and stretches out the waves behind it (making a lower-frequency, lower-pitch tone) (Figure 56). This is the Doppler effect, and it works with light, too. If a star is moving toward Earth, the light is crushed and has a higher frequency than normal; it is shifted toward the blue end of the spectrum, blueshifted. If a star is moving away, the opposite happens; the light is stretched out and redshifted.
Police can tell how fast a car is going by testing how light—in the form of radio waves—reflected off the speeding vehicle gets shifted. In the same way, by looking at how a star’s light spectrum gets shifted, astronomers can deduce how fast the star is moving—toward us or away.
Hubble combined the distance data with Doppler speed data, and found something shocking. Not only were galaxies speeding away from us in all directions, the farther away the galaxies were, the faster they were going away.
Figure 56: The Doppler effect
How could this be? Imagine a polka-dotted balloon; the polka dots are like galaxies, while the balloon itself is the fabric of space-time. As the balloon inflates, the dots get farther and farther apart from one another. From any one dot’s perspective, the other dots are all rushing away, and the more distant dots are rushing faster than the close dots (Figure 57). The universe seemed to be expanding, like a balloon. (The balloon analogy has one flaw. Unlike the polka dots, which also get bigger as the balloon expands, the galaxies are staying about the same size, held together by their own gravity.)
Figure 57: The expanding universe
As time runs forward, the universe expands and expands. Looking at it another way, if you had a film of the universe’s history and ran the film backward, the universe would shrink and shrink. At some point the balloon would shrivel and wither, getting smaller and smaller, and then eventually disappear as a point—the singularity at the beginning of time and space. This is the primal zero, the birthplace of the universe: the big bang, a furious explosion that created the cosmos. It is from this singularity that all the matter and energy in the universe spewed forth, creating all the galaxies, stars, and planets that have ever—and will ever—exist. The universe had a beginning, about 15 billion years in the past, and space has been expanding ever since. Einstein’s hope for a steady, eternal universe was all but dead.
One glimmer of hope remained, one alternative to the big bang: steady-state theory. Some astronomers proposed that there were fountains that spat out matter, and the galaxies moved away from these founts, aging and dying. Though the individual galaxies zoomed away and died, the entire universe as a whole never changed. It was always in equilibrium, constantly replenishing itself. Aristotle’s eternal universe still survived.
For a time, big bang theory and steady-state theory lived side by side, alternatives that astronomers chose between depending on their philosophy. In the mid-1960s, that all