Laniakea Destroyed by Dark Energy

On the largest cosmic scales, planet Earth appears to be anything but special. Like hundreds of billions of other planets in our galaxy, we orbit our parent star; like hundreds of billions of solar systems, we revolve around the galaxy; like the majority of galaxies in the Universe, we’re bound together in either a group or cluster of galaxies. 

And, like most galactic groups and clusters, we’re a small part of a larger structure containing over 100,000 galaxies: a supercluster. Ours is named Laniakea: the Hawaiian word for “immense heaven.”

Superclusters have been found and charted throughout our observable Universe, where they’re more than 10 times as rich as the largest known clusters of galaxies. Unfortunately, owing to the presence of dark energy in the Universe, these superclusters ⁠— including our own ⁠— are only apparent structures. In reality, they’re mere phantasms, in the process of dissolving before our very eyes.

The Universe as we know it began some 13.8 billion years ago with the Big Bang. It was filled with matter, antimatter, radiation, etc.; all the particles and fields that we know of today, and possibly even more. 

From the earliest instants of the hot Big Bang, however, it wasn’t simply a uniform sea of these energetic quanta. Instead, there were tiny imperfections ⁠— at about the 0.003% level ⁠— on all scales, where some regions had slightly more or slightly less matter and energy than average.

In each one of these regions, a great cosmic race ensued. The race was between two competing phenomena:

1. the expansion of the Universe, which works to drive all the matter and energy apart
2. gravitation, which works to pull all forms of energy together, causing massive material to clump and cluster together

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Expanding Into What?

The universe is everything, so it isn't expanding into anything. It's just expanding. All of the galaxies in the universe are moving away from each other, and every region of space is being stretched, but there's no center they're expanding from and no outer edge to expand into anything else.

But that doesn't mean that the universe is infinite. That brings us to the long answer. To understand how something could be finite but have no edge, think of the fabric of the universe as the surface of a balloon. As the balloon inflates, the surface stretches and every point on that surface moves away from every other point, but a tiny being on the surface of that balloon could walk forever and never run into the edge of its balloon universe. There's no edge, yet that balloon universe has a finite volume.

The Shape of the Universe
But the balloon is just one example. Scientists aren't actually sure whether the universe is finite or infinite, or even what shape the universe is. There are three options: spherical, flat, or hyperbolic (that is, it curves upward). Evidence from the earliest light in the universe suggests that the second option is on the money, and the universe is, in fact, flat.

Even if the universe is flat and not balloon-shaped, however, it's still easy to think about how it could be finite with no edge. Think about a flat piece of paper. You could take two opposing edges and make them touch, creating a cylinder. If a tiny 2-dimensional rocket ship traveled from one of those edges to the other, it would arrive back where it started. You could do the same thing in the perpendicular direction: Connect the two ends of the tube to each other (pretend this is magically stretchy paper, for the sake of argument) and create a donut shape, also known as a torus. Now your 2-dimensional rocket ship could travel anywhere it likes, and it would never encounter an edge — even though your paper torus has finite volume.

But wait, you might be saying. Paper is flat; a torus is curved. Isn't that cheating? No, and that's because scientists have a very specific definition for the word "flat." When they say flat, they mean "Euclidean," which means that parallel lines always run parallel and the sum of the angles of a triangle is always exactly 180 degrees. This doesn't happen on a sphere or a hyperbola, but it does on a cylinder, a torus, and any other shape you can make out of a flat piece of paper.

This suggests something kind of exciting: If we live in a flat universe, you could potentially travel in one direction for long enough (or build a telescope that can see far enough) to end up right back where you started. Even cooler things happen when you think about other weird shapes — shapes that twist back on themselves could make you arrive back at a mirror image of where you started, for example.

But no matter what shape the universe is, it's not expanding into anything. There's nothing outside of the universe because the universe has no edge.  READ MORE