Well I am back after years as I was busy with my research
After a short talk about Dark Matter, this blog will talk about Dark Energy.
Lets begin, I hope all of us agree with the law of inertia. The law states that a body preserves its velocity and direction as long as no force acts on it (In fact a form of Newton’s first law of motion). This means that once a body entered a state of motion (being at rest is a special case of motion with velocity equal to zero) because of an external force an instant acceleration boosts it to a certain velocity. Now this imparted velocity will not change (increase or decrease) until an unless another external force acts on it. While driving a car when we apply accelerator the velocity increases otherwise it remains uniform (ok I know about friction but lets assume an utopic case at the moment). This basic understanding will be instrumental in understanding the concept of Dark Energy.
Now we go back in time, really back, some 13.8 billion years ago (way too long, I know). Time when the so called Big-Bang happened (I am not talking about Lorre and Pardy sitcom). The Big-Bang is a the most accepted theory rather say model for the origin of universe. The models depicts the origin universe we know as an outcome of a sudden expansion extremely dense state (of what?) . This sudden expansion is called the Big-Bang. The Big-Bang: mostly described as an explosion provided a force that set the mortars of the explosion into motion. These mortars of the explosion later formed galaxies stars and probably everything that we see (matter) and don’t see (dark matter) around. This motion is explained by the phenomenon of red shift in galaxies (many other proofs available).
Now since the Big-Bang is the only known cause of setting motion in the known universe, this motion should have a uniform velocity. But we have gravity, coming from Newton’s apple. The gravitational energy is an attractive force. If we consider gravity in our case it should pull the above mentioned mortars of Big-Bang towards the centre of the explosion thus causing a deceleration (slow-down). So the galaxies should nevertheless move either with a uniform velocity (if gravitational force is negligible) or slow down their motion. Illustrating again with our car example the initial boost of acceleration (engines power, counterpart of Big-Bang) is impeded by the friction (a counterpart of gravity here)
But the real picture is somewhat different. The motion is neither uniform nor slowing down. This is actually accelerating. This mean the speed at which galaxies are moving away from each other with increasing velocities. Isn’t that intriguing? What is causing this acceleration? There has to be a force to provide this acceleration (the accelerator in car) and for a force there has to be some form of energy. Scientists call this energy the Dark Energy. Dark because we do not know about it.
With this basic idea of Dark Energy, I close the session. In my next blog I will bring about the computational approach to study this form of Energy; the Dark Energy. It could be the energy of Darth Vader ;)