Paradox (noun, “PAR-uh-dox”)

A paradox is when a scenario seems — at first — impossible. It goes against what your gut feeling tells you is true. Once resolved, however, a paradox often reveals something crucial about how a system works. It may correct a common misconception. Or it may address incorrect assumptions.

Sometimes, a paradox consists of real facts that seem to defy expectation. Moravec’s paradox is one example. It notes that many abilities that come easily to humans are quite hard to program into a robot. Walking, for instance. On the flip side, many easy-to-program abilities, such as complex math, are hard for humans to learn. Exploring this paradox can help us better understand how the human mind works.

Peto’s paradox is another example. It points out that large, long-lived animals get cancer at about the same rate as small, short-lived ones. For a long time, that fact puzzled scientists. They expected large animals to get cancer more often. Cancer starts when something goes wrong with a single cell’s genetic material. Shouldn’t large animals — which contain many more cells — have this problem much more often than small ones? The data showed this was not the case.

Scientists studied this paradox. They learned that large animals have genes that help reduce cancer risks. Researchers did not know to look for such genes before noticing the paradox. This is one case of a paradox helping us learn things we didn’t know that we didn’t know.

Some paradoxes are thought experiments. That’s an imaginary scenario that allows us to explore an idea that we can’t test in real life. Imagine, for instance, you traveled to the distant past. But then, you accidentally killed a distant ancestor. (Oops!) This might mean that you would no longer be born. But wait. If you no longer exist, that means you wouldn’t be able to travel back in time to kill your ancestor in the first place, right?  

On its own, this sci-fi paradox doesn’t answer questions. But it does help us think about the physics of time. And that can inspire new ideas in scientists who study the nature of our universe.

In a sentence

The “paradox of horror” refers to how people often seek out films that seem — on first glance — to evoke only negative emotions.

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Antimatter (noun, “AN-tee-MAT-ter”)

Antimatter is made of antiparticles. Think of antiparticles like partners of ordinary particles, but with the opposite properties.

You’ve likely heard of protons, neutrons and electrons. These are the tiny particles that make up atoms. But you may not have heard of their anti-twins. These are antiprotons, antineutrons and positrons.

Particles and antiparticles have the same mass. But they generally have opposite electric charges. An electron is negative. So the positron is positive. A proton is positive. So the antiproton is negative. But exceptions to law of opposites exist. Take the neutron, which has no electric charge. It’s neutral. So the antineutron is also neutral.

When matter and antimatter meet, they destroy each other. If an electron meets a positron, for instance, they self-destruct. As physicists say, they “annihilate” each other. This releases energy in the form of gamma rays. That’s a high-energy type of light.

Antiparticles can bind together to form atoms, just as ordinary particles do. Scientists have built antihydrogen in the lab. They do that by pairing a positron and an antiproton. This isn’t an easy feat, though. If either of those antiparticles touch ordinary matter — poof! They cease to exist. That means scientists must “handle” the particles without touching them. They do this through magnetic or electrical fields.

Very, very little antimatter exists today. A tiny amount occurs naturally. For example, cosmic rays constantly smash into Earth’s atmosphere. When they do, they produce tiny bits of antimatter. Some radioactive decay gives off antiparticles, too. But antimatter never lasts very long. Normal matter quickly destroys it.

Scientists believe that the Big Bang produced equal amounts of matter and antimatter. Why does ordinary matter reign supreme today? That’s one of the universe’s biggest mysteries.

In a sentence

Scientists search for mysterious forms of matter such as dark matter and antimatter hoping to reveal secrets of the Big Bang.

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