POPULAR
SCIENCE
100
SCIENCE
MYSTERIES
EXPLAINED
Contents
PHYSICAL MATTER AND FORCES
Is Light a Wave or a Particle?
What Makes a Boomerang Come Back?
Is the Mpemba Effect Real?
What Is the Hottest Temperature Possible?
Is Cold Fusion Possible?
Do Atoms Last Forever?
Can We Travel Through Time?
Will We Ever Be Able to Harness Nuclear Fusion?
Does Spontaneous Human Combustion Ever Happen—and How?
SPACE
What Are Fermi Bubbles?
Why Do Pulsars Pulse?
Does Alien Life Exist?
Why Don’t Moons Have Moons?
What Is the Moon Illusion?
What’s at the Bottom of a Black Hole?
What Does Space Smell Like?
How Long Would It Take to Walk a Light-Year?
What Causes Jupiter’s Red Storm?
Are There Habitable Planets Beyond Our Solar System?
What Is Dark Energy?
How Will the Universe End?
What Is the Shape of the Universe?
Can We Deflect Asteroids?
Why Is the Milky Way a Spiral?
Will We Find Other Universes?
Could We Live on Mars?
What Is Dark Matter Made Of?
What Causes Gamma Ray Bursts?
Is a Space Elevator Possible?
How Does Gravity Work?
How Do Stars Explode?
What Causes the Aurora Borealis?
Is a Holodeck Possible?
How Did Saturn Get Its Rings?
Could a Supernova Wipe Out Life on Earth?
HUMAN BODY
Why Do We Blush?
What Is the Evolutionary Purpose of Tickling?
Why Do We Yawn?
Why Are Peanut Allergies on the Rise?
What Is a Memory?
Why Do We Dream?
Why Do We Laugh?
Do Cells Make Noise?
How Does the Brain Work?
What Is Emotion?
Is It True That You Use Only 10 Percent of Your Brain?
What Causes Déjà Vu?
Is the Y Chromosome Doomed?
Do Men and Women Have Different Brains?
Why Do We Sleep?
Why Do We Hiccup?
Why Aren’t (Most) Humans Furry?
What Is the Science Behind Love?
Why Does Sunlight Make Some People Sneeze?
What Is Consciousness?
Can the Food You Eat Affect Your Descendants’ Genes?
Are Telomeres the Key to Immortality?
Why Do We Have an Appendix?
Why Do We Have Fingerprints?
What Happens When You Die?
Is There an Alternative to DNA?
Why Do We Age?
When Will We Evolve Out of Our Useless Appendages?
How Much of the Human Body Is Replaceable?
Why Do Amputees Sense a “Phantom Limb”?
Can You Upload Your Brain to a Computer?
What Is Intelligence?
EARTH
What Causes Volcanic Lightning?
Just How Old Is Dirt?
How Do Plate Tectonics Work?
How Big Would a Meteorite Have to Beto Wipe Out All Human Life?
Are We Really Drinking Dinosaur Pee?
How Do Fire Tornadoes Form?
When Is the Next Ice Age Due?
Are Earthquake Lights Real or Illusory?
What Is Ball Lightning?
Why Can’t We Predict Earthquakes?
Where Did Earth’s Water Come From?
Why Do Earth’s Magnetic Poles Flip?
How Do Icicles Form Under Water?
OTHER LIFE-FORMS
How Did Life Arise on Earth?
How Do Animals Sense Magnetic Fields?
How Do Animals Migrate?
Why Do Cats Purr?
Why Do Ducks Have Orange Feet?
Will Disease Drive Us All to Extinction?
What Do Whales Sing About?
Can We Clone Extinct Animals?
Could Cockroaches Survive a Nuclear Holocaust?
What Caused the Extinction of the Megafauna?
Why Are Bees Disappearing?
Why Do Geese Fly in a V Formation?
HUMAN TRIUMPHS AND TROUBLES
What Was the Purpose of Stonehenge?
How Were the Easter Island Statues Built?
What Happened to the Neanderthals?
Is the Doomsday Argument for Real?
Why Can’t the Voynich Manuscript Be Deciphered?
Is the Antikythera Mechanism the World’s First Analog Computer?
How Were the Pyramids Built?
What Caused the Decline of the Mayan Civilization?
Index
Credits
CHAPTER 1
Physical Matter and Forces
Is Light a Wave or a Particle?
For centuries, scientists debated the nature of light. Some claimed that light was a wave, behaving like a ripple in a pool. The opposing view was that light was a particle, like the droplets of water that flow from a kitchen faucet. Just when a prevailing view gained momentum, evidence for the other caused confusion. Finally, in the early 20th century, Albert Einstein called a tie: Light is both wave and particle.
Those who believed in the particle theory of light followed Sir Isaac Newton. He described light as a series of particles, using a prism to prove his theory. To Newton, the clarity and sharpness of the prism shadows meant that light traveled as a shower of particles, each following a straight line until disturbed.
Those who opposed Newton’s theory followed scientist Christiaan Huygens, who cited light’s diffraction and interference as proof that it is a wave. Diffraction, the bending of light as it passes around an object, and interference, when waves combine to form greater or lesser amplitude, occur in other mediums with wave-like properties, such as sound and water. Astronomers studying moving galaxies proved that light follows the Doppler Effect, the name for the change in sound as waves from the source move closer or farther away from you, elongating as they move away and shortening as they come closer. Visible light, as seen in the colors of the rainbow, exhibits similar properties, with longer wavelengths appearing as a red shift and shorter wavelengths as a blue shift. Until the turn of the century, this overwhelming evidence convinced most scientists that light was a wave, until Albert Einstein settled the score.
One thorn in the argument for light-as-a-wave purists is a phenomenon called the photoelectric effect. When light shines on a metal surface, electrons fly out. But higher intensity of light does not cause more electrons to be released, as you would expect with the wave theory. Albert Einstein studied this effect and came up with a compelling theory that stated light was both wave and particle. Light flows toward a metal surface as a wave of particles, and electrons release from the metal as an interaction with a single photon, or particle of light, rather than the wave as a whole. The energy from that photon transfers to a single electron, knocking it free from the metal. Einstein’s declaration of wave-particle duality earned him the Nobel Prize in physics in 1921.
Since Einstein’s discovery, physicists have embraced this theory. Einstein declared: “We have two contradictory pictures of reality; separately neither of them fully explains the phenomena of light, but together they do.” Understanding light as a wave led to the development of important technology, such as lasers. The discovery of photons made possible the electron microscope.<
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And thanks to Albert Einstein, we can stop the centuries-old debate and declare everyone a winner.
The boomerang is one of humanity’s oldest heavier-than-air flying inventions. King Tutankhamen, who lived during the 14th century, owned an extensive collection, and aboriginal australians used boomerangs in hunting and warfare at least as far back as 10,000 years ago. The world’s oldest boomerang, discovered in Poland’s Carpathian Mountains, is estimated to be more than 20,000 years old.
What Makes a Boomerang Come Back?
Anthropologists theorize that the first boomerangs were heavy projectile objects thrown by hunters to bludgeon a target with speed and accuracy. They were most likely made out of flattened sticks or animal tusks, and they weren’t intended to return to their thrower—that is, until someone unknowingly carved the weapon into just the right shape needed for it to spin. A happy accident, huh?
Proper wing design produces the lift needed for a boomerang’s flight, says John “Ernie” Esser, a boomerang hobbyist who works as a postdoctoral researcher at the University of California at Irvine’s Math Department. “The wings of a boomerang are designed to generate lift as they spin through the air,” Esser says. “This is due to the wings’ airfoil shape, their angle of attack, and the possible addition of beveling on the underside of the wings.”
But a phenomenon known as gyroscopic precession is the key to making a returning boomerang come back to its thrower. “When the boomerang spins, one wing is actually moving through the air faster than the other [relative to the air] as the boomerang is moving forward as a whole,” explains Darren Tan, a PhD student in physics at Oxford University. “As the top wing is spinning forward, the lift force on that wing is greater and results in unbalanced forces that gradually turn the boomerang.” The difference in lift force between the two sides of the boomerang produces a consistent torque that makes the boomerang turn. It soars through the air and gradually loops back around in a circle.
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 was heated first before being put into a freezer. “You were confused,” said his teacher; “that cannot happen.” Mpemba’s assertion also amused his classmates—but their laughter quickly turned to a murmur of assent when a school supervisor ran the experiment and proved the young man correct.
Scientists have offered many explanations to account for the unexpected phenomenon, but to date none has been accepted by the wider scientific community. Here are a few suggestions:
EVAPORATION As the warmer water cools to the temperature of the cooler water, it may lose large amounts of water to evaporation. The reduced mass more easily allows for the water to cool and freeze.
DISSOLVED GASES Hot water can hold less dissolved gas than cold water. This may somehow change the properties of the water, making it easier to develop convection currents, and therefore easier to freeze.
FROST Frost conducts heat poorly. If the containers of hot water are sitting on layers of frost, the water will cause the frost to melt. This would establish better thermal contact with the cold refrigerator shelf or floor.
To date, experiments have not adequately illustrated which, if any, of the proposed processes is the most important one. “It seems likely that there is no one mechanism that explains the Mpemba effect for all circumstances,” explained Monwhea Jeng of the Department of Physics at the University of California, in 1998.
What Is the Hottest Temperature Possible?
It’s easy to understand the theoretical minimum temperature: absolute zero. The absolute maximum, on the other hand, is squirrely. “We just don’t know whether we can take energy all the way up to infinity,” says Stephon Alexander, a physicist at Dartmouth University. “But it’s theoretically plausible.”
The most straightforward candidate for an upper limit is the Planck temperature, or 142 nonillion (1.42 × 1032) kelvins (K)—the highest temperature allowable under the Standard Model of particle physics. But temperature comes about only when particles interact and achieve thermal equilibrium, Alexander explains. “To have a notion of temperature, you need to have a notion of interaction.”
Many cosmologists believe the hottest actual temperature in the history of the universe was several orders of magnitude cooler than the Planck temperature. In the first moments after the Big Bang, expansion occurred so rapidly that no particles could interact; the universe was essentially temperatureless. In the tiny slivers of a second that followed, Alexander says, ripples of space-time may have begun to vibrate with matter and forced that matter into thermal equilibrium. This would have caused a quick reheating of the universe to something like 1027 K. It has been continually expanding and cooling ever since.
Is Cold Fusion Possible?
Italian inventor Andrea Rossi really wants us to believe in cold fusion. He claims that his Energy Catalyzer, or E-Cat, a liter-sized device he designed, can output three times as much energy as it draws via low-energy nuclear reactions, or LENRs. As hydrogen passes over an electrified nickel-based catalyst, hydrogen nuclei supposedly fuse to the nickel, transmuting the metal into copper and releasing heat in the process. If we could harness that heat, the process could furnish cheap electricity while simultaneously banishing the production of greenhouse gases—all without creating any harmful waste.
There’s only one problem: Cold fusion is almost certainly a myth. Backers aside, Rossi has yet to perform a truly independent test of his E-Cat; in most tests by third parties, Rossi handled the materials or was involved in some way. Critics argue that Rossi’s device doesn’t produce nearly as much energy as he claims and that his suggestion of building factories for large-scale production of electricity is baseless. They also note that his backers refuse to publicly reveal themselves and that the physics behind the project are at best unclear.
Worst of all, every purportedly successful attempt at cold fusion up until now has been the result of experimental error or downright fraud. Martin Fleischmann and Stanley Pons, chemistry professors at the University of Utah, claimed to have discovered cold fusion in 1989. No one has been able to replicate their results since and their ideas were discredited. Rusi Taleyarkhan, a Purdue University professor who claimed to have produced a “bubble fusion” reaction, was found guilty of “research misconduct.” Besides, most physicists say that the findings just don’t make sense: The energy required to bond hydrogen is simply too high for a catalyst to achieve at earthly temperatures.
Except in one case: Muon-catalyzed fusion is the only instance in which a catalyst is known to enable nuclear fusion. Muons are subatomic particles that occur on Earth principally as a result of cosmic rays slamming into the atmosphere. When muons replace the hydrogen atom’s electrons, they can draw those hydrogen atoms close enough to fuse together. Unfortunately, muons require substantial energy to produce, and they don’t last long enough for the chain reaction to produce more energy than goes into the reaction. Until physicists overcome these barriers, cold fusion will remain elusive.
Do Atoms Last Forever?
Despite what you may have heard, diamonds are not forever. Given enough time, your sparkling rock will degrade int
o common graphite. The carbon atoms that constitute that diamond, however, are forever, or close enough. Stable isotopes of carbon are thought to enjoy lifetimes that extend far longer than the estimated age of the universe.
But not every atom of carbon lives forever. Radioisotopes are forms of chemical elements with unstable nuclei and emit radiation during their decaying process to a stable state. Carbon-14, a radioisotope, is unstable, with a half-life of less than 6,000 years; after 5,730 years, there is a 50 percent chance that a carbon-14 atom will lose an electron and become nitrogen-14 (which is itself stable and the most common form of nitrogen on Earth). Carbon-14 is the key element in carbon dating: Since radioactive carbon is only absorbed through respiration by living creatures, the date of their death can be determined by measuring the remaining carbon-14 in the specimen.
In addition to carbon-14, there are scores of other naturally occurring radioisotopes and more than a thousand manmade. Each of these radioisotopes tends to decay into another isotope: some in a matter of days, others in hundreds of millions of years. In this sense, these atoms do in fact die. In another way, however, they are simply reborn as different isotopes.
There is one mechanism by which even stable atoms might “die.” Some exotic models of physics hypothesize that protons (which along with electrons and neutrons constitute atoms) can decay into lighter subatomic particles. Even if protons do decay, they are nevertheless incomprehensibly durable. Experiments put the lower bound of a proton’s half-life at 1033 to 1034 years, or 23 orders of magnitude longer than the current age of the universe. In conclusion, atoms are forever on just about any relevant timescale.
Can We Travel Through Time?
The mystery of time travel as it is portrayed in science fiction is not as simple as building a time machine. In fact, these fictional ideas require overturning Albert Einstein’s special theory of relativity and somehow traveling close to the speed of light.
100 Mysteries of Science Explained Page 1
