Stars are moving away from Earth, indicating an accelerating universe. Edwin Hubble’s redshift observation showed stars are receding from the solar system at an increasing rate. The universe’s fate is either an oscillating pattern or infinite expansion due to dark energy.
When someone looks at the modern night sky, the starscape they see is different from what it looked like thousands of years ago. This is because every star visible from Earth is actually moving away from the planet. Research has shown that our solar system is part of an accelerating universe, in which each star travels outward from a central point at an ever-increasing speed.
In the 1920s, physicists and astronomers debated the Big Bang theory. This concept establishes that all matter in the universe was originally contained in a single highly condensed form that expanded outward to create the universe in an event called the Big Bang. The question of whether this initial expansion is over or underway did not have a definitive answer at the time. Then, in 1929, astronomer Edwin Hubble addressed this question when he developed a way to measure the motion of a star by analyzing the spectrum of light it emits.
Hubble has observed a redshift — or change in the red-colored light emitted by stars — in its spectral analysis, indicating that stars are receding from the solar system at an increasing rate. Conversely, a blue shift would have meant that the stars are actually approaching Earth. His analysis showed that, not only is each star accelerating away from the Sun, but the further away a star is, the faster it is accelerating. Subsequent research has shown that this is not unique to stars around the Earth, but that every star in the observable universe, including the Sun, is accelerating away from a central point. This behavior of outward accelerating stars has led scientists to describe ours as an accelerating universe.
There are two predominant scientific ideas about the behavior of the accelerating universe. One is that it follows an oscillating pattern. This theory holds that the universe began expanding outward after the Big Bang, but will slow down when the universe’s gravity exceeds the moment of its acceleration. Then the outward motion will stop and all matter in the universe will begin to be pulled back towards the center. In what’s called the Big Crunch, all matter in the universe will eventually condense back into the same highly condensed state it was in before the Big Bang.
The other idea concerning the fate of the accelerating universe is known as infinite expansion, which theorizes that the motion created by the Big Bang never ends. In other words, all matter in the universe will continue to expand outward all the time and will never be pulled back by gravity. Proponents, and some who study the Big Bang model, believe this is due, in part, to something called dark energy. While the nature and mechanics of this mysterious energy are not yet fully understood, it is known to cause stars and other interstellar matter to continually accelerate and escape the inertial pull of gravity.
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