Can Space End, Where Did Time Zones Come From and More Questions from our Readers

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Illustration by Anna Bron

Do astrophysicists believe there is an end to space? If so, what do they think could be on the other side?
Jessica L. Leeper
Frisco, Texas

No, they don’t believe there’s an end to space. However, we can only see a certain volume of all that’s out there. Since the universe is 13.8 billion years old, light from a galaxy more than 13.8 billion light-years away hasn’t had time to reach us yet, so we have no way of knowing such a galaxy exists.
Mark Reid
astrophysicist, Harvard-Smithsonian Center for Astrophysics

Why is Grover Cleveland the only American president who is counted twice? I know he served two nonconsecutive terms, but he was still only one man.
Thomas Hansen
Rolling Meadows, Illinois

No one anticipated nonconsecutive terms, so it had long been the custom to count presidents as individuals rather than by their terms in office. Cleveland is counted as the 22nd and 24th presidents because Benjamin Harrison was the 23rd. It made no sense to revert to 22 when Cleveland regained the White House in 1893. More logically, presidents would be counted by terms—George Washington, for example, would be considered the first and second presidents. Now Barack Obama, the 44th man to hold the office, is occupying the 57th presidential term.
David C. Ward
senior historian, Portrait Gallery

Where did time zones come from?
Romualdo P. Baranuelo
Naga City, the Philippines

The time zones we use today are based on those adopted by North American railroads on November 18, 1883. Those zones recognized the meridian passing through Greenwich, England, as zero degrees longitude, as did an international conference in 1884. The U.S. time zones were recognized in federal law with the Standard Time Act of 1918.
Carlene Stephens
curator of time collections, American History Museum

How does a lightning bolt lasting a second or less produce a thunderclap lasting ten seconds or more?
Richard Pearce
Brattleboro, Vermont

A lightning bolt heats the air so that it expands at tremendous speed—fast enough to create a shock wave that travels outward at the speed of sound. That shock wave is what we hear as a thunderclap. When the shock wave hits the irregular ground surface, some of the energy is reflected to create other waves; these we hear as a low rumbling after the clap.
Andrew Johnston
geographer, Air and Space Museum

How do jellyfish navigate, hunt and otherwise display motor skills when they don’t have a brain?
Martin J. Clemens
Cambridge, Canada

Jellyfish do not have a brain or centralized nervous system, but they do have sensory structures and sensory cells that make up a nervous system. This system, which varies in complexity from species to species, allows jellyfish to react to chemical and physical cues in their environment.
Allen Collins
invertebrate zoologist, Museum of Natural History

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