Science Made Simple: Everyday Facts That Sound Unbelievable

The best science trivia sounds impossible until you learn the reason behind it. Here is a collection of true facts that are as fun to share as they are useful on quiz night — each with a short explanation, because understanding why is what makes a fact stay in your head.

Biology

Octopuses have three hearts and blue blood

Two hearts pump blood through the gills, and a third pumps it around the body. Their blood uses a copper-based molecule called haemocyanin to carry oxygen, which gives it a blue colour. Ours uses iron-based haemoglobin, which is red.

Sharks are older than trees

Sharks appear in the fossil record more than 400 million years ago. The first true trees appeared later, around 385 million years ago. Sharks have survived several mass extinctions, including the one that wiped out the dinosaurs.

You share about 99.9% of your DNA with every other human

All the visible differences between people come from that tiny 0.1%. You also share a surprising amount of DNA with other living things — a large proportion of human genes have a recognisable counterpart in a banana.

Your body is about 60% water

The figure varies with age and body type — babies are closer to 75%. Your brain and heart are around three-quarters water.

Your stomach gets a new lining every few days

Stomach acid is strong enough to damage the stomach itself, so the cells lining it are constantly replaced, and a layer of mucus protects them.

Chemistry

Honey never spoils

Honey has very little water and is acidic, so bacteria and mould cannot survive in it. Sealed jars found in ancient Egyptian tombs were still edible thousands of years later.

Ice floats because water is strange

Most substances become denser when they freeze. Water does the opposite: as it freezes, its molecules lock into an open, hexagonal structure that takes up more space. That makes ice less dense than liquid water, so it floats — which is why lakes freeze from the top down and fish survive winter.

Hot water can sometimes freeze faster than cold water

This puzzle is called the Mpemba effect, after a Tanzanian student who noticed it in the 1960s. It does not happen every time, and scientists still argue about why it happens at all — possibly evaporation, dissolved gases or how the water circulates as it cools.

Glass is not a slow-moving liquid

Old church windows are often thicker at the bottom, which led to the myth that glass flows over centuries. In fact, old glass-making methods produced uneven panes, and builders usually put the thick edge at the bottom. Glass is an amorphous solid.

Physics

Light travels about 300,000 kilometres per second

That is fast enough to circle the Earth about seven and a half times in one second. Even so, sunlight takes a little over eight minutes to reach us.

Lightning is hotter than the surface of the Sun

A lightning bolt can heat the air to around 30,000°C, roughly five times hotter than the Sun's surface. The heat lasts only a fraction of a second.

Sound cannot travel through space

Sound is a vibration passed from molecule to molecule. Space is very nearly a vacuum, so there is nothing to carry it. Every explosion in a science-fiction film should, in reality, be silent.

You are slightly taller in the morning

During the day, gravity compresses the discs of cartilage in your spine. Overnight, lying down, they recover — so most people are around a centimetre taller when they wake up.

A teaspoon of neutron star would weigh billions of tonnes

Neutron stars are the collapsed cores of giant stars. They pack more mass than the Sun into a ball about 20 kilometres across, making them unimaginably dense.

Why These Facts Stick

Facts are easiest to remember when they surprise you. Each time you learn a "wait, really?" fact, try to remember the one-line reason behind it. "Ice floats because its molecules spread out when they freeze." That context turns a random detail into knowledge you keep — and it means you can often work out the answer to a question you have never seen before.

Feeling sharp? Take a free Science quiz and see how many of these you can turn into points.