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How Will the Universe End?

In 1929, Edwin Hubble discovered that the universe is not in fact static, but expanding. In the years following his discovery, cosmologists took up the implications of the discovery, asking how long the universe had been expanding, what forces caused the expansion, and whether it will ever cease. Cosmologists are pretty confident about the first question: just shy of 14 billion years. A great deal of evidence supports the predominant answer to the second question: The universe rapidly emerged from a singularity in an event that cosmologists call the Big Bang. The third question is a bit more mysterious, and the answer relies on an obscure, confounding phenomenon known as dark energy. The density of dark energy in the universe determines its ultimate fate. In one scenario, the universe does not possess enough dark energy to forever counteract its own gravity and thus ends in a “Big Crunch.” Under this scenario, the universe’s gravity will overcome its expansio...

What Causes Volcanic Lightning?

On March 10, 2010, Eyjafjallajökull volcano, a caldera in Iceland covered by an ice cap, erupted. It sent plumes of clouds across most of Europe and the Atlantic Ocean. Photos of the eruption show lightning originating and ending in the cloud of ash that hovered over the volcanic opening. The largest volcanic storms are similar to supercell thunderstorms that spread across the American Midwest. But while those thunderstorms are fairly well understood, volcanic lightning still remains mysterious. The remote location of volcanoes and infrequent eruptions make volcanic lightning difficult to study. In general, lightning occurs through the separation of positively and negatively charged particles. Differences in the aerodynamics of the particles separate the positive and negative. When the difference in charge is great, electrons flow between the positive and negative regions. A lightning bolt is a natural way of correcting the charge distributi...

Is the Mpemba Effect Real?

For more than 2,000 years, scientists have observed the unique phenomenon that, in some conditions, hot water freezes faster than cold water. In the fourth century B.C.E., Greek scientist Aristotle noted, “The fact that the water has previously been warmed contributes to its freezing quickly: for so it cools Sooner. Seventeenth-century English scientist Francis Bacon noted, "slightly tepid water freezes more easily than that which is utterly cold.” Several years later, French mathematician René Descartes echoed his predecessors' observations, writing, "One can see by experience that water that has been kept on a fire for a long time freezes faster than other." Given the centuries old knowledge that hot water does indeed freeze faster than cold in certain circumstances, it should have come as no surprise when Tanzanian schoolboy Erasto Mpemba claimed in his science class in 1963 that ice cream would freeze faster if it w...

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