Some researchers from India and the US have proposed a novel method to determine the Hubble constant and the Rate of Expansion of the Universe. About 13.8 billion years ago, a really small, really dense, and really hot spot lying beyond spacetime began to expand. Its expansion and cooling – in an event that scientists have called the Big Bang – produced the universe as we know it. The universe continued to expand, at first really rapidly before slowing down to a great degree. Then, about five or six billion years ago, dark energy – an unknown and largely uncharacterised form of energy – accelerated its expansion again.
Hubble Constant
- In 1929, Edwin Hubble formulated Hubble’s law, providing the first mathematical description of the universe’s expansion.
- The precise rate of this expansion, termed the Hubble constant, remains a contentious issue in cosmology.
Two details are required to calculate the value of the Hubble constant
- The distance between the observer and astronomical objects,
- The velocity at which these objects are moving away from the observer as a result of the expansion of the universe.
So far, scientists have used three methods to get these details
- They compare the observed brightness of a stellar explosion, called a supernova, with its expected brightness to figure how far away it could be. Then they measure how much the wavelength of the light from the star has been stretched by the expansion of the universe – i.e. the redshift – to figure how much it’s moving away.
- They use changes to the Cosmic Microwave Background (CMB) – radiation leftover from the Big Bang event – to estimate the Hubble constant.
- The CMB is a faint, nearly uniform glow of microwave radiation that fills the observable universe. It is often referred to as the “afterglow” of the Big Bang.
- They use gravitational waves, ripples in spacetime produced when massive astronomical objects – like neutron stars or black holes – collide with each other. Detectors that observe gravitational waves record the data in the form of curves.
- Using the shape of these curves, astronomers can calculate the amount of energy that the collision released. Comparing this with the amount of energy the waves had when they reached earth allows researchers to estimate the distance between these objects and earth.