The branch of science called cosmology — which is not about hairdressing and permanent waves, but the study of the universe as a whole — regards the cosmos as a single entity. Meaning, everything was born together and shares universal properties. The cosmos didn’t just leak in here drop by drop from another dimension, as the Steady State theory suggested. Instead, the nature of space, the speed of light and the value of such constants as gravity are identical everywhere. In short, we truly live in a UNI-verse where E Pluribus Unum rules, a oneness out of which the many stars and planets are free to experiment and frolic.
If this is so, then any physical truth that applies to our galaxy, such as the strength of the four fundamental forces, is identical everywhere else and throughout all of time. Such a view dominates astronomical thought, even if a few physicists have periodically questioned it. Until 22 years ago, one universal addendum that seemed inarguable was that the cosmos’ expansion has to be slowing down.
The Big Bang theory, strongly supported by the cosmic microwave background and the omnipresent expansion, says that starting 13.8 billion years ago, everything initially raced outward from everything else like an inflating balloon. (Don’t ask what the universe expands into. There is no “outside” to the cosmos, and such a perspective is nonexistent. Instead, picture each galaxy cluster increasing its distance from all others.)
The cosmic expansion was explosively rapid at first. But the gravitational attraction of every galaxy group on every other kept tugging at this expansion like a rubber band, slowing it down. The big question of the 20th century’s last half was: Will the outrush come to a stop in the far future? Will the cosmos then go the other way, and collapse into a “big crunch?”
Nobody entertained a different and illogical possibility, which took the world by storm in 1998. Two teams of astronomers, examining the brilliant lights of past supernovae to obtain better-than-ever determinations of galactic distances, independently came to an astonishing conclusion:
The universe indeed slowed its expansion for the first half of its life. But then six or seven billion years ago, galaxies everywhere started speeding up their expansion from their neighbors. As the eons passed since then, this expansion has accelerated until now all galaxies are flying away from each other in an ever-increasing frenzy that even exceeds light speed at a particular distance from us.
We know this is impossible. Galaxies don’t have rocket engines attached to them. What could possibly make them zoom faster and faster? And yet this is exactly what we seem to be observing.
Since nobody has a clue to what’s going on, we posit that space itself must have an anti-gravity repulsive property and we call this ‘dark energy.’ We assume that this dark energy was responsible for blasting out the cosmos in the first place, in the Big Bang, but it then lost its dominance to gravity. When galaxies grew far enough apart so that empty space got vast enough, this anti-gravity force gained the upper hand. Now it will push harder and harder, and everything will explosively fly apart forever.
Lest the concept of a darker and ever-lonelier cosmos drive you to antidepressants, be aware that much is unknown about dark energy. Everything, actually. Although it must be nature’s dominant item, it might — for all we know — weaken or even reverse itself over time. Perhaps the cosmos could eventually come back together after all.
And if you find all this just a tad peculiar, rest assured you’re not alone. It all seems like we’re performing the same type of exercise we did back in college when we had to write an essay about something about which we were clueless.
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