Despite all the advancements made in technology and science over the last 1,000 years, the intricacies of outer space remain a mystery to us, although the scientific community is always making new discoveries about what lies beyond our planet. During the past century, we discovered that the universe was not only expanding but that it was expanding at an ever-increasing rate.
While this new discovery was agreed upon by the scientific community as a whole, there was no definitive explanation for the accelerating expansion. Still, in many ways, the ever-expanding nature of the universe does make sense, simply because it accounts for the universe not collapsing in on itself. To boil it down to its basics, since there are many planets, stars, comets (which we will refer to under the blanket term masses), one would expect all of these masses to collapse into a single point, as a result of the gravitational force acting upon all of them. Since the universe has not yet collapsed in on itself, it stands to reason that there is something that is counteracting gravity, or that the Universe is expanding. More importantly, the expansion of the universe is accelerating and is not slowing down as a result of any gravitational forces.
Of course, there are still many questions that remain, but it looks like scientists might now have an answer to why the expansion process doesn’t slow down. As reported by Forbes, astrophysicist and author Ethan Siegel explains that dark matter plays a key role. You see, one would expect the universe’s expansion to slow down over time because as it expands, its energy density would also drop. However, dark matter acts very differently from other forms of matter in the universe, and it isn’t subjected to the same changes in energy density.
“Dark energy doesn’t make the Universe accelerate because of an outward-pushing pressure or an anti-gravitational force; it makes the Universe accelerate because of how its energy density changes (or, more accurately, doesn’t change) as the Universe continues to expand.
As the Universe expands, more space gets created. Since dark energy is a form of energy that’s inherent to space, then as we make more space, the energy density doesn’t drop. This is fundamentally different from normal matter, dark matter, neutrinos, radiation, and anything else we know of. And therefore, it impacts the expansion rate in a different fashion than all these other types of matter-and-energy.”
To summarize, although the amount of matter and radiation will become less dense as the universe continues to expand, space itself will continue to have the same energy density. Needless to say, astrophysicists still have a lot of mysteries to solve, with dark energy being the biggest one.