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The world, a little closer

Scale of the universe.

From an atom to a galaxy in one slide. Each stop is a world of its own, and every one of them is built from the one before.

Explore the scene Interactive article

01 / The experiment

From an atom to a galaxy.

Slide from the smallest thing to the largest and read the size at each stop.

Interactive scene

Preparing your experiment…

The explanation below is available while the scene loads.

Each object is drawn at a comfortable size on screen. The slider steps through sizes, not through space.The real jumps are enormous. If the atom were the size shown, the cell would be wider than a city and the galaxy could not be drawn at all.

02 / Three stretches

Small, everyday, vast.

Each stretch is a factor of a trillion or so. Each feels like a different universe.

Atom to cell01

Microscopic

Atoms, molecules, then the cell that packs them. Below the eye’s limit, and where chemistry and life are decided.

From
10⁻¹⁰ m
To
10⁻⁵ m
Factor
×100,000
Cell to planet02

Everyday

From a cell to a person to a planet: the stretch where we live, and the only one our senses were built for.

From
10⁻⁵ m
To
10⁷ m
Factor
×1,000,000,000,000
Star to galaxy03

Astronomical

A star, then its planetary system, then the galaxy it drifts in. Distances measured in the time light takes to cross them.

From
10⁹ m
To
10²¹ m
Factor
×1,000,000,000,000
The big idea

Count powers of ten and the whole universe fits on one ladder of about sixty rungs. Which rung you are on decides which rules apply.

10^60

Powers of ten

Everything in the universe has a size, and the sizes run over a range so vast that ordinary numbers give up. The trick scientists use is to count powers of ten. Each step multiplies by ten: a metre, ten metres, a hundred, a thousand. Written that way, the whole universe fits on one ladder with about sixty rungs, from the smallest distance that means anything to the edge of what we can see.

The slider in the scene stops at six of those rungs. The things it shows are the subjects of other articles here; this one is about how far apart they are.

Down

An atom is about a tenth of a billionth of a metre across, and nearly all of that is the empty space where its electrons roam. DNA is a molecule, so it is only ten times wider than an atom, but it is extraordinarily long: unwound from a single human cell it would stretch about two metres. A cell is a hundredth of a millimetre or so, ten thousand times wider than the DNA packed inside it, and just below the limit of what the eye can make out.

From cell to you is another hundred thousand times. Stand in the middle of the ladder and there are as many rungs below you as above.

Try it: slide from Atom to Cell and count the stops. That is a jump of a hundred thousand times.

Up

The Sun is 1.4 million kilometres wide, a hundred times the width of the Earth. The Solar System, out to Neptune, is nine billion kilometres across, so wide that light takes over four hours to cross it, and the Sun in it is a dot. The Milky Way is a hundred thousand light years across, and the whole Solar System is a dot in that.

Beyond the galaxy the ladder keeps going: clusters of galaxies, then the observable universe, about ninety billion light years across, holding perhaps two trillion galaxies.

Where you stand

A person is about a metre and a half tall. On the ladder of powers of ten, that is roughly ten steps above an atom and twenty-six below the observable universe. We are not at the centre of the universe, but on the scale ladder we sit a little below the middle, small enough to be built from atoms and large enough to think about galaxies.

Why the numbers matter

Size is not just a curiosity. It decides what rules apply. At the size of atoms, particles behave like waves and nothing is quite where it seems. At the size of cells, water is as thick as syrup and gravity hardly matters. At the size of stars, gravity is everything. The same universe, obeying the same laws, looks utterly different at each rung, and the first step in understanding anything is knowing how big it is.