In 1920’s the Universe was thought to be completely static i.e. it’s unchanging. There was no such observational evidence that made humans to think of expanding or contracting Universe. On the other hand, the General Theory of Relativity predicted that the Universe must either expand or collapse. To get rid of this, Einstein worked upon the concept of “Anti-Gravity”. He tried to introduce this anti-gravity in the fabric of cosmos so that the gravitational attraction between stars and planets would cancel and result in a static Universe. Soon this idea was called-off when Edwin Hubble made the discovery of the century. He discovered that the stars and galaxies were actually moving away from us in all directions. This made the scientists to stop worrying about the state of the Universe. The exploration for the cosmos and outer space eventually stopped as Quantum Mechanics rose. It was only in 1990’s when there was something strange to observe.
We all know about how our Universe began. It was the Big Bang. When this explosion of space and time occurred, space expanded. Within a quick time our fabric of cosmos multiplied causing our Universe to expand. But this expansion would not last long. As it was thought the gravity would slow down the expansion causing our Universe to recollapse into a singularity! This idea of expanding Universe fascinated the astronomers so much that they started the exploration to find the rate of expansion. In 1998 two teams of astronomers produced ground-breaking observations that no one would ever imagine. What they found was, the rate of expansion is increasing with increasing time or the rate of expansion was speeding up! Farther is the galaxy, the faster it was going away from us. Let’s take a simple example; throw a ball in the upward direction. The gravity will cause this ball to slow down and it will start to fall downward. On the other hand if we apply this idea of expansion as mentioned above, our ball would never come down. Instead it would dominate gravity and the speed of ball will keep on increasing and we will lose it. Now the question is “what is pushing this ball to go upward?” Similarly what is causing our Universe to expand at such an increasing rate?
Strangely, Albert Einstein was first to introduce this concept of anti-gravity which we call it today as Cosmological Constant. He was desperate to apply this constant in his equation but Hubble’s discovery faded his works.
There is believed to be an unknown form of energy which we haven’t yet detected. It is called as Dark energy. It is present all over our Universe (about 68%). Since this energy is present in large amount, it could rip our Universe apart into pieces. This energy is thought to be a repulsive gravity which causes our Universe to expand. This energy is nothing but the energy of space, as our space-time is expanding it is obvious that this energy is too increasing. And this causes our Universe to expand at even more faster rate. This shows that our cosmos is not just space but much more. Although we have no idea why the constant has a fixed number. This form of energy is difficult to observe. When this energy is present in the fabric of Space-time, it actually pushes everything apart. This corresponds to second model of Friedman. The Cosmological constant is measured in the order of 10-52 m-2.
There are still numerous mysteries to solve about our Universe. We are still aware of only a few ones. This is our Cosmos, Space a place beyond our imagination.