Question

Discuss the discoveries that LIGO has made. Why are these discoveries considered to be direct detection of gravitational waves?

Answer 1

LIGO : Laser Interferometer Gravitational-Wave Observatory is a very large experimental setup to observe the variation of space-time fabric.As light speed is universal and does not changes using this principle one can measure the distortion in space-time by just measuring the time taken by light to travel the distance.It started taking data from 2002 . But upto 2012 no gravitational wave data was not detected.Meantime Advanced LIGO project started from 2008 under NSF funding.The First detection of gravitational wave was reported in 2016. In 2017 Nobel Prize was awarded.

Why this is direct detection of Gravitational Wave ?

When gravitational wave travels throught the space it creates a distortion in space-time thus effectively squeezing and expanding space at different places.But speed of light is constant thus using laser one can accurately measure time taken to travel the light from a fixed point A to fixed point B . This distance say "L" , time taken by light to travel is "T=L/c" where "c" is speed of light that is constant even in the presence of gravitational wave.Thus the new spatial distance " L* " gives new time " T* " to travel " T* = L*/c ". Thus observing this change " (T*-T) " on can keep track of the chage in spatial deformation. They plotted this data with time and have seen that this periaodically changing as already predicted by Einstein's General theory of relativity 100 years prior. There was huge noise also so at first they were not sure whether this is noise or pure signal.After detailed investigations when they reached scientific standard accuracy they announced in 2016 the discovery officially.