physical paradigms, stretching the limits of our imagination. Some of the suggestions include introducing an altogether novel type of energy field called quintessence or even modifying the law of gravity itself.

Recent results from probes of the cosmic microwave background have pinned down the relative abundance of dark matter and dark energy on the one hand, compared to luminous materials on the other. According to the WMAP survey, considered the most precise scan of cosmic background radiation ever conducted, about 23 percent of the mass of the observable universe is composed of dark matter, about 73 percent is dark energy, and only 4 percent is ordinary visible material.

Presented with such startling evidence of our minority status in a vast and dark cosmos, scientists can no longer assert that their celestial charts reflect the true picture of reality. These findings have presented cosmology with one of its greatest challenges in history: shedding light on the shadowy substances that dominate the physical world.

CALLING ON EINSTEIN

Intuition took us far in pondering solutions for Olbers’ paradox and the Fermi paradox. By pressing forth the ramifications of several basic principles—the finiteness of the speed of light, the limited age of the universe, and the Hubble expansion of space—we found ways to explain nocturnal darkness and the lack of alien communication in the face of a possibly infinite universe. Keeping these successes in mind, let’s apply scientific reasoning to cosmology’s greatest enigmas—including the puzzles of dark matter and dark energy.

One of the great champions of thought experiments, Albert Einstein, developed a remarkable equation that will aid us in our pursuit. It is not his most famous equation, linking energy and mass, but rather a relationship between the matter and geometry of any



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