How Long Would It Take to Walk a Light-Year ?

If you had started just before the first dinosaurs appeared, you’d probably be finishing your hike just about now. Here’s how it breaks down. One light-year —the distance light travels in one year, used as the yardstick for interstellar distances—is about 5.9 trillion miles (9.5 trillion km). If you hoofed it at 20 minutes a mile, it would take 225 million years to complete your journey (not including stops for meals or the restroom). Even if you hitched a ride on NASA’s Mach 9.8 X-43A hypersonic scramjet, it would take more than 90,000 years to cover the distance. You’d need to bring a big backpack, too: Walking such a distance requires substantial supplies. The average adult burns about 80 calories per mile walked, so you’d need about six trillion granola bars to fuel your trip. You’d also produce a heap of worn-out shoes. The typical pair of sneakers will last you 500 miles (800 km), so you’d burn through some 11.8 billion pairs. And all that effort wouldn’t get you anywhere, astronomically speaking: The closest star to the Sun, Proxima Centauri, Is 4.22 light-years away.

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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...

Will Disease Drive Us All to Extinction ?

Virulent infectious diseases and parasites have long been shown to be a significant cause of decline in biological populations. But can disease lead to the actual extinction of the host species—such as humankind? Scientists attempt to determine the extinction-threatening effects of disease by first studying its role in historical extinctions. But proving that infectious disease is responsible for past extinctions is tricky business. After all, the extinct species is not around for scientific investigation. Even if a pathogen or parasite were discovered in a disappearing population, it would not prove that the pathogen itself was responsible for the decline. However, reasonable evidence exists that historical extinctions and extirpations—local extinctions in which a speciesc eases to exist in the specific geographic area of study—are at least partlya ttributable to infectious disease. Avian malaria and bird pox are believe...

Is the Y Chromosome Doomed?

Humans store their genes in 23 pairs of chromosomes, 22 of which are identically matched. The 23rd is a two-sided biological coin—twin Xs mean you’re female; an X and a Y, male. Chromosome pairs often trade bits of DNA in a process called recombination, the purpose of which is to keep genes functioning properly. Talk of men’s path toward extinction began in the late 1990s, when it was discovered that the human Y chromosome, which is stumpy compared with the X, does not share enough genetic material with the X to practice recombination. Left without a way to renew damaged genes, the Y would continue to degrade and would eventually disappear, geneticists announced. They slapped an expiration date on the male half of the species of sometime in the next 5 to 10 million years. To get a perspective on this prediction, scientists looked to our closest genetic relatives—the chimps. Because humans and chimpanzees shared a common ancestor 6 million years ago, genet...

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