A lot of our notions about space are based on the concept of gravity, or more accurately our current understanding of it. Our understanding of gravity until the late 1990s was that gravity attracts things, holds things together, and in a way, stabilizes the universe as a whole. It was in 1998 that scientists stumbled upon the fact that the expansion of the universe was happening at a rate faster than we had concluded it would, and that there were more forces at play.
The other side of gravity
The community of astronomers has been closely observing the phenomenon of supernovae for centuries now. A supernova, or the atomic level disintegration of a star, is a super explosive event that can be clearly observed thousands of light-years away. This is because a supernova releases light energy that is equal to around 10 billion suns. However, astronomers and scientists observed that the light was fainter than expected.
At first, they just thought that the light was getting dimmer due to interstellar dust. In the last few decades, however, scientists have been able to gather conclusive proof that the reason for this dimming supernova phenomenon was the fact that the universe was expanding at a rate far greater than we had projected based on our understanding of gravity.
It’s important to understand that our universe is constantly expanding at a speed that is constantly increasing. All the galaxies in our universe are drifting away from each other over time. For this to happen, scientists conjectured that there needs to be a counterforce that is stronger than gravity. In recent years, scientists have been attributing this to an invisible force loosely termed as “dark energy.”
According to Forbes: “Over the past two decades, it’s become abundantly clear that a new form of energy — dark energy — is not only driving this accelerated expansion, but is the dominant form of energy in our Universe.”
There is no clear definition of what dark energy is. As of now, there are two main hypotheses for what dark energy might be. One is that dark energy emanates from empty space and its strength value can be assumed to be constant. Another hypothesis is much more complex wherein this dark energy is responding to changes in the universe within a variable energy field, and hence its strength can also change accordingly.
Though we have come to the undisputed point that the universe is constantly drifting away from us, we have yet to ascertain whether the speeding up of this drifting is recent or whether it has always been this way.
Dark energy vs gravity
The duel between the two great forces, gravitation’s pull and dark energy’s push, is determined by density. It can be assumed that there is a gradual deterioration in the density of matter as the universe expands owing to the increase in space volume. In the current spectrum of observation, dark energy has a higher density than matter; however, in the past, matter must have had a higher density, which leads to the hypothesis that universal expansion was actually slowing down at that point in time.
To further study this phenomenon, scientists are required to find a specific type of supernova known as type Ia. These supernovae are so bright that telescopes can view them. Over the last 10 years, scientists have been successful in determining the intrinsic luminosity of such supernovae, and so, the distance to such a supernova can be accurately calculated from its perceived brightness.
Understanding dark energy
To understand the future of our universe, it is crucial to have a better understanding of dark energy. Currently, we have different versions of the future, ranging from “eventless” to “intergalactic catastrophe” based on whether dark energy density decreases or increases. Either way, it is dark energy that will determine the future of our cosmos.