Dangerous Wonder

The Scale of Everything

If the Sun were shrunk to the size of a basketball, the Earth would be a tiny peppercorn sitting about 26 metres away. Jupiter, the largest planet, would be a golf ball roughly 130 metres down the road. And the nearest star, Proxima Centauri? It would be another basketball roughly 6,800 kilometres away — across an ocean, on another continent. Space is not mostly empty. Space is almost entirely nothing, and the distances between even the closest things are almost impossible to think about without getting dizzy.

The Andromeda Galaxy, our nearest large galactic neighbour, contains roughly one trillion stars. It is 2.5 million light-years away — meaning the light arriving tonight left before Homo sapiens had even evolved. Photo: Unsplash.

The observable universe stretches about 93 billion light-years across. That is just the part we can see — the light from anything further hasn't had time to reach us yet. Beyond that boundary, the universe almost certainly continues. Whether it goes on forever or eventually curves back on itself is one of the great unanswered questions. In the meantime, we are left staring at a basketball and a peppercorn, separated by 26 metres of absolutely nothing, trying to make sense of the whole arrangement.

Looking Back in Time

Light travels at roughly 300,000 kilometres per second — the fastest anything can move through the universe. But even at that speed, crossing cosmic distances takes a very long time. The light from the Sun takes just over eight minutes to reach your eyes. The light from Proxima Centauri takes more than four years. The light from the Andromeda Galaxy takes 2.5 million years.

"The universe is under no obligation to make sense to you."

What this means is astonishing: every time you look at a star, you are looking into the past. When you see Sirius shining in the winter sky, you are seeing it as it was nearly nine years ago. When you look at the Andromeda Galaxy with binoculars, you are seeing it as it was when early hominids were still figuring out stone tools. The night sky is not a photograph of the present. It is a mosaic of different pasts, arriving all at once, from different eras, all mixed together on the canvas of the dark.

Neutron Stars: The Impossible Objects

A neutron star is the compressed core of a massive star that has exploded. It spins, it beams, it distorts the very fabric of spacetime around it. Photo: Unsplash.

When a star much larger than the Sun runs out of fuel, its core collapses under its own gravity. Electrons are crushed into protons, forming neutrons, and the entire mass of the star — once millions of kilometres across — is squeezed into a sphere about 20 kilometres in diameter. The resulting object is a neutron star.

A teaspoon of neutron star material would weigh about 6 trillion tonnes — roughly equivalent to cramming Mount Everest into a sugar cube. These objects spin at terrifying speeds; some complete hundreds of rotations per second. They possess magnetic fields a trillion times stronger than Earth's. They are, by any reasonable standard, impossible — yet they exist in their hundreds of millions across the Milky Way, quiet and fast-spinning, like cosmic lighthouses beaming radio waves into the void.

The Invisible 95%

Everything you have ever seen, touched, or read about — every star, planet, galaxy, cloud of gas, and speck of dust — makes up roughly 5% of the total universe. The remaining 95% consists of two forces we cannot see, cannot touch, and only barely understand: dark matter and dark energy.

Dark matter, which accounts for about 27% of the universe, reveals itself through gravity. Galaxies rotate too fast; galaxy clusters bend light in ways visible matter cannot explain; the large-scale structure of the universe wouldn't hold together without it. Something is there, exerting gravitational pull, making the math work, and it vastly outweighs everything made of atoms. But it does not emit, absorb, or reflect light. It is invisible in the most literal sense.

Dark energy, comprising roughly 68% of the universe, is even stranger. In 1998, astronomers discovered that the universe is not just expanding — the expansion is accelerating. Something is pushing everything apart, growing stronger as space itself grows larger. We call it dark energy because we have no idea what it actually is. It may be an intrinsic property of space, a new kind of field, or a sign that our understanding of gravity is incomplete. It is, by a wide margin, the dominant force in the cosmos, and nobody can explain it.

The Voyager Golden Record

The Golden Record, mounted on each Voyager spacecraft, is etched with instructions for playback in scientific notation. If found, it would be the first audio ever heard from another civilisation. Photo: Unsplash.

In 1977, NASA launched two Voyager spacecraft on a grand tour of the outer planets. Bolted to the side of each was a 12-inch gold-plated copper disc — the Golden Record — containing a curated portrait of Earth for anyone, or anything, that might find it in the distant future.

Assembled by a team led by Carl Sagan, the record holds 116 images, sounds of wind and surf, songs from dozens of cultures, greetings in 55 languages, and music ranging from Bach to Chuck Berry to the Alima Song by the Mbuti people of the Ituri Rainforest. It also includes a recording of a human heartbeat, the sound of a mother's kiss, and a spoken greeting by Sagan's six-year-old son Nick, saying simply: "Hello from the children of planet Earth."

Voyager 1 is now more than 24 billion kilometres from the Sun, travelling outward at about 17 kilometres per second. It will drift through the Milky Way for billions of years. The record is designed to last at least a billion years — longer, by far, than any human monument. Whether anyone will ever play it is an entirely open question, but that is not really the point. The Golden Record is a message in a bottle thrown into the cosmic ocean, a gesture of hope and stubborn friendliness from a small, pale, inquisitive world.

Pale Blue Dot

"That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives."

On February 14, 1990, at Carl Sagan's request, NASA commanded the Voyager 1 spacecraft to turn its camera around and take one last photograph of its home. From a distance of roughly 6 billion kilometres — beyond the orbit of Neptune — the resulting image showed Earth as a tiny point of light, less than a pixel wide, suspended in a beam of scattered sunlight.

Sagan called it the "Pale Blue Dot" and delivered what may be the most beautiful paragraph ever spoken about our planet: a meditation on the absurd smallness of the stage on which all of human history has played out, and an argument, implicit and powerful, for kindness. Every conqueror's army, every emperor's empire, every holy city and every terrible war — all of it took place on that barely visible speck. The photo has no borders on it. It was taken from too far away to show any.

The Great Attractor

Something enormous is pulling our entire galaxy — along with tens of thousands of others — toward it at about 600 kilometres per second. We call it the Great Attractor, and we cannot see it, because it is located in the direction of the plane of the Milky Way, where dust and gas obscure our view.

We know it is there because of the motion it creates. The Milky Way is already moving toward the Great Attractor at considerable speed, along with our local group of galaxies and the much larger Virgo Cluster. The combined gravitational pull required to drag that much mass requires an object — or concentration of mass — of staggering proportions: roughly 3–5 × 10¹⁶ solar masses, a region called the Laniakea Supercluster, of which we are a small suburban outpost. Even larger structures — walls, filaments, and voids that span hundreds of millions of light-years — appear to make up the cosmic web, the large-scale architecture of the universe.

The Great Attractor is not itself an object. It is a gravitational focal point, a knot in the web, a place where an absurd amount of matter has gathered over billions of years. Our galaxy will arrive there — or rather, "there" will be reshaped by the time we get close — in roughly 150 billion years, though dark energy's accelerating expansion may prevent this convergence entirely, assuming nothing tears the universe apart first.

Rogue Planets

Not every planet has a star. Somewhere between the glittering systems, in the vast and frigid spaces where no sun shines, rogue planets drift alone — ejected from their birth systems by gravitational encounters, sent tumbling through the galaxy on paths no orbit governs. Current estimates suggest there may be billions of them in the Milky Way alone, perhaps even more than there are stars.

These worlds can be enormous — some are gas giants, many times the mass of Jupiter — or they can be rocky, Earth-sized, and utterly dark. Without a sun, their surfaces would be frozen solid, but some may retain internal heat, and tidal forces or radioactive decay could sustain subsurface oceans of liquid water. In other words, it is not impossible that some rogue planets harbour life, in the warm dark beneath kilometres of ice, lit only by the faint glow of deep-sea vents, orbiting nothing, warmed by nothing, alive in spite of everything.

The first rogue planets were discovered in 2000, and many more have been identified since, including a gas giant designated CFBDSIR J2149−0403, floating about 130 light-years away. Since then, surveys have identified numerous candidates. The upcoming Nancy Grace Roman Space Telescope is expected to find hundreds more. Each one is a world without a sun, a story without a beginning — or at least, without the beginning we always assumed every planet must have.

If you have read this far, you have just learned that most planets in the universe may be completely alone, drifting between the stars, unseen and uncounted, and that someone, somewhere, thinks that is worth knowing. You are correct.