The room that you’re in right now is swirling with invisible air currents caused by heat.

Heat is one of the most influential forces in the universe, but we rarely think about what it actually is.

When we have something that’s really hot, like a Space Shuttle flying through the atmosphere, what is actually happening to it?

The Space Shuttle would face temperatures of about 1,700°C (3,000°F) on reentry into the atmosphere.
The Space Shuttle would face temperatures of about 1,700°C (3,000°F) on reentry into the atmosphere.

It’s actually pretty straightforward. Heat is the vibration of molecules and atoms.

When the Space Shuttle soars through the atmosphere it’s being hit by a barrage of atoms in the air, like a tin roof in a rainstorm. They strike its atoms and make them frantically vibrate.

If you put your hand on something this hot, it’s energetic atoms will give the atoms in your hand a kick and start them vibrating too. The force would break apart the complex molecules in your hand, giving you a burn.

But heat can also come from chemicals and even light.

When a car is under direct sunlight on a hot day, billions of photons of light are crashing into it, making the molecules of the car vibrate.

But the vibration of heat has a ton of other important effects.

The first is that the more molecules vibrate, the more they push against each other, like they’ve all decided they need more personal space. This causes the material as a whole to expand.

The same material at hot (red) and cold (blue) temperatures.

This happens all around us without us noticing. It’s the reason we put gaps in sidewalks to allow for the concrete to expand on hot days.

This expansion is more important than you might think. This is because when material expands, it also gets less dense.

Everything from the twirling waves of smoke rising from a cigarette to the immense clouds of Jupiter are formed by the flow of air from a cold, slightly more dense place to a warmer, less dense place.

This creates a mesmerising movement, called a ‘convection current’.

Every single room swirls with the currents of its own tiny atmosphere caused by the heat from lights, computers, and even our own body heat.

When the Sun’s light hits the Earth, it heats it up unevenly. The equator heats up faster than the poles, and land heats up faster than water. The currents in the atmosphere that it creates are our weather. In the ocean, huge currents push immeasurable tons of water across the planet for the same reasons.

Far under the ground, currents in lava from the Earth’s core shift the continents and raise mountains.

Our planet is alive with the flow of heat.

On a gas planet like Jupiter, the currents create beautiful colours as if from an artist’s brushstrokes – whose paintbrush is larger than the entire Earth.


Convection currents are much more obvious in gasses and liquids than solids.

The only difference between these ‘states’ is how far apart their atoms or molecules have been pushed by heat (and also pressure). But the extra space between atoms in gasses and liquids lets them flow.


What the atoms of a material look like as a gas, liquid, and a solid. Image credit: University of Cambridge, What is an Atom?

When atoms in a material do not vibrate at all, it has a temperature of ‘absolute zero’. It can’t get any colder. But from this starting point, temperature creates a very long spectrum. As far as we know, there may be no limit to how hot something can get in the universe.

  • 273.15° Celcius, (-459.67° Fahrenheit). Absolute zero. The coldest possible temperature. It is when atoms and molecules stop moving altogether (though quantum mechanical particles inside them still keep going).
    • 184°C (-300°F). The temperature on the dark side of the moon.
    • 89.2°C, (-128.6 °F) The coldest temperature ever recorded on Earth, at the Soviet Vostok Station in Antarctica. At this temperature, even petrol has frozen.
    • 0°C (32°F). Melting point of ice.
    • 37°C (98°F). Normal human body temperature.
    • 57°C (134°F). Hottest recorded day in the US. Death Valley, 10 July 1913.
    • 71°C (160°F). Hottest recorded surface temperature on Earth. Lut Desert, Iran.
    • 100°C (212°F). Boiling point of water.
    • 427°C (800°F). Average daytime temperature on the Mercury, the closest planet to the sun.
    • 1,200°C (2,192°F). Temperature of lava.
    • 1,583°C (2,880°F). Melting point of iron.
    • 5,500°C (9,932°F). Surface temperature of the Sun.
    • 6,000°C (10,832°F). Temperature of the Earth’s core.
    • 10,000°C (18,032°F). Fireball of a nuclear explosion.
    • 15,000,000°C (27,000,000°F). Temperature of the Sun’s core.
    • 55,000,000°C (99,000,000°F). A supernova explosion.
    • The theoretical but unproven limit of how hot something can be is called the ‘Planck temperature’. It is about 1,420,000,000,000,000,000,000,000,000,000,000°C.

Say hey to Owlbert Einstein

Curator of the Big Ideas Network

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