The cosmos didn’t just drip here from another dimension, as the once popular steady-state theory suggested. It started suddenly, then briefly expanded much faster than the speed of light. This is the only way the speed of light and the value of constants such as gravity and the mass of fundamental subatomic particles can be so precisely identical everywhere.
However, any physical truth that applies to our galaxy, such as the strength of the four fundamental forces, is the same everywhere else and through time. And until 1998, an additional universal reality that seemed indisputable was that the expansion of the cosmos was slowing down.
The Big Bang theory, strongly supported by the cosmic microwave background and ubiquitous expansion, says that 13.8 billion years ago, everything first rushed outward, and this cosmic expansion was extremely rapid at first. But the gravitational pull of each group of galaxies on the others continued to pull this expansion like a rubber band, slowing it down. The big question of the 20e last half of the century was: Will everything stop in the distant future? Will the cosmos then go the other way and crumble in a “big crunch”?
No one considered a different, illogical possibility, which took the world by storm in 1998. Two teams of astronomers, examining the bright lights of past supernovae to obtain better-than-ever determinations of galactic distances, independently arrived at an astonishing conclusion:
The universe indeed slowed its expansion during the first half of its life. But about seven billion years ago galaxies everywhere began accelerating their expansion relative to their neighbours. Over the eons since then, this expansion has accelerated until now all the galaxies are moving away from each other in an ever-increasing frenzy that even exceeds the speed of light at some distance from us.
We know that is impossible. Galaxies do not have rocket engines attached to them. What could make them zoom faster and faster? And yet, this is exactly what we observe.
Since no one has a clue what is going on, we postulate 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 the explosion of the cosmos in the first place, during the Big Bang, but then lost its dominance to gravity. When the galaxies moved far enough apart for empty space to become vast enough, this anti-gravity force took over. Now he will push harder and harder and everything will explode forever.
This brings us to the nature of empty space which does all this work of separation. To do the job, this “nothingness” must have such vast power that it comprises three quarters of the substance of the entire universe.
And while we don’t understand its underlying nature, that hasn’t stopped us from giving it a series of different names. You can call it vacuum energy or dark energy or cosmological constant or zero point energy. This last name owes its origin to the fact that it only begins to reveal itself when its temperature is zero degrees Kelvin, or -459.67 degrees below zero Fahrenheit. Hotter than that, and the inherent kinetic energy of moving atoms and molecules dominates the picture and obscures that vacuum energy.
Although it is exploding the universe, which could one day leave us staring into a starless sky, much is unknown about dark energy. Everything, in fact. Although it should be the dominant element of nature, it could – as far as we know – weaken or even reverse over time. Maybe the cosmos could finally come together after all.
And if you find all of this a bit odd, rest assured, you’re not alone.