The Universe's Expansion Could End Surprisingly Soon, Say Cosmologists

The Universe’s Expansion Could End Surprisingly Soon, Say Cosmologists

The universe is not only expanding but accelerating away from us. Now a new theory suggests all this could stop sooner than anyone imagined.

The beginning of the cosmos is obvious to cosmologists. They can see galaxies accelerating away from one another, and when they reverse this motion, the universe contracts to a single event. This implies that it all began 14 billion years ago in an event known as the Big Bang.

Cosmologists, on the other hand, are less certain how it will all end. One hypothesis is that the universe’s expansion will continue to accelerate, driven by a mysterious substance known as dark energy. In that situation, the expansion will be infinite and forever.

Another possibility is that the role of dark energy will decrease over time, causing the fast expansion to stop and gradually transition into a slow contraction. This possibility dovetails neatly with the idea that the cosmos is always expanding and contracting in an ongoing cycle.

This second alternative presents an intriguing question: when will all of this occur?

Sooner Than We Think

Princeton University’s Cosmin Andrei and colleagues have now studied this issue using theoretical models that are consistent with existing observations. And they believe it will happen sooner than we thought, possibly in the millions rather than billions of years.

Andrei and colleagues begin by analyzing how the properties of dark energy might change while remaining consistent with the cosmos as it is now observed by scientists. They then determine the shortest amount of time until these transitions can occur.

The results are fascinating to read. According to Andrei and colleagues, the minimal period before the acceleration ends is “strikingly soon, cosmologically speaking.” “In fact, they can be compared to geologic timescales,” they say.

According to one scenario, the minimal time remaining before the end of expansion is roughly equivalent to the time since life first appeared on Earth. That equates to 3 or 4 billion years.

Dinosaur Timescale

In a different scenario, they calculate that “the time interval remaining before the end of acceleration is less than the time since the Chicxulub asteroid brought an end to the dinosaurs.”  That’s only 65 million years—a cosmological blink of an eye.

However, there is some bad news for astronomers. Even if the expansion did end that quickly, astronomers are unlikely to find evidence of it. “Curiously, we could not detect the oncoming dramatic cosmic events given the best-available observations today,” Andrei and colleagues write.

This is due to the fact that all of the evidence originates from distant things that released light billions of years ago, such as supernovas, and the cosmic microwave background, which is an echo of the Big Bang itself.

These objects will not show evidence of this transformation for a long time, but the scientists believe that there may be alternative ways to look for it.

Andrei and co conclude by debating whether the end of expansion should occur now, when life has developed to observe it. They respond by pointing out that in a cyclic cosmos that alternately expands and contracts, there is only a brief period within each cycle when conditions are ripe for life to emerge. And that’s about now.

All of this points to a stunning conclusion: “the end of expansion could occur surprisingly soon,” they say. However, there is no reason to worry just yet.

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