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One of the most fascinating and terrifying concepts in astronomy is the expansion of the universe. And a recent study shows that supernovae can tell us a lot about it. If you’ve never thought about it before, it can be difficult to wrap your head around.
Basically, the Big Bang began the universe. And even though it’s called that, it’s better not to think of it as an explosion. Instead, think of it as heat and energy rapidly expanding, then the universe cooling to form matter.
Two things we don’t know yet are:
- What, if anything, was before the Big Bang
- What the universe may be expanding into
But we do know that it is expanding — and that it’s getting faster.
On its face, it’s not hard to accept that objects in space flung out by the Big Bang accelerated. The harder thing to understand is that the rate of acceleration is increasing.
From our perspective, it’s easy to imagine a baseball accelerating when we throw it. What is hard to imagine is the ball not only never eventually hitting the ground, but increasing in speed.
But that’s what our observations tell us about space.
Universe expansion must be understood in the context of space-time.
Most of us understand that we exist in three-dimensional reality. However, one of Einstein’s breakthroughs in his theory of special relativity was space-time. In short, space-time is the idea of three dimensions (height, width, and depth) being fused with a fourth (time) — to create the space-time continuum.
Einstein discovered this through two observations:
- That the speed of light is constant, no matter the speed of the observer
- The laws of physics are the same for all non-accelerating observers.
Knowing this background helps us understand universe expansion as a whole, and the problem physicists are desperate to solve.
What Are Supernovae?
Supernovae are explosions that occur at the end of a star’s life. Sometimes it can even be brighter than an entire galaxy.
Not only that, but a recent study shows that observing supernovae gives us incredible information about universe expansion — namely that it happens evenly in all directions.
The results confirm cosmologists’ understanding of the universe. According to the theory of inflation, the universe expanded extremely rapidly just after the Big Bang (SN: 7/28/12, p.20). That expansion is thought to have proceeded equally in all directions, setting up the universe’s uniform spreading today.
The “uniform spreading” of the universe is good news for us for the time being. There are much less generous theories about the ultimate fate of the universe.
The Big Crunch
One such theory is based on the power of gravity.
The Big Crunch posits that, given the power of gravity to attract objects to one another, it may eventually slow the universe’s expansion. The universe will eventually stop expanding, and then (and this is the scary part) begin contracting.
TBC is thought to be the opposite of the Big Bang. Everything would eventually collapse in on itself into a hot, dense mess and the universe may experience a second Big Bang (we certainly won’t, though!).
Though TBC is far from junk science, newer models of the universe have shown this accelerating rate of expansion, making it less likely.
Remember how we don’t know what the universe is expanding into? It turns out that it might not really … matter (free science joke).
Just as the Big Bang was not an explosion, it’s helpful to think of universe expansion differently, too. Rather than imagining everything in the universe as something inside of the universe, it’s better to imagine space-time itself expanding. It’s tempting to think of an eventual horizon or “edge” that the universe is expanding to, but there’s none that we know of yet.
However, universe expansion still presents big implications to consider.
Even NASA admits that more is unknown than known about dark energy. But it’s important for understanding universe expansion. Before evidence of acceleration, pretty much everyone thought gravity would cause the eventual slow of expansion, and hasten the universe’s collapse.
We now know that 68% of the universe is something called dark energy.
“One version of Einstein’s gravity theory, the version that contains a cosmological constant, makes a second prediction: ’empty space’ can possess its own energy. Because this energy is a property of space itself, it would not be diluted as space expands. As more space comes into existence, more of this energy-of-space would appear.”
For now, it seems we needn’t trouble our heads with thoughts of a collapsing universe. But the infinite expansion of the universe will demand our attention and careful study for years to come.
Feature image provided via NASA/JPL-Caltech