Google has dedicated a doodle to Georges Lemaître, an astronomer and professor of physics who is believed to be the first to have theorised the concept that the universe is expanding. His theory was observationally soon confirmed by Edwin Hubble- it later came to be known as Hubble's Law. Lemaître is also credited with the now popular Big Bang Theory which says that the universe began with an explosion of a single particle. His initial idea was not related to Big Bang specifically, but he later focused his research on the concept of the universe being born from a single atom.
Some of the greatest scientists of the time from around the world gathered to attend a series of lectures in 1933 at the California Institute of Technology. After Lemaître presented his theory, notable theorist Albert Einstein stood up and said: "This is the most beautiful and satisfactory explanation of creation to which I ever listened."
The Big Bang Theory received acceptance and rejection in the following years. In the later 1990s and 2000s, the concept was familiarised by pop culture. American sitcom The Big Bang Theory which began in 2007 (currently in its 11th season) further helped in acquainting youth with the concept.
Here's what the original Big Bang Theory is all about:
According to The Big Bang Theory's leading explanation, the universe began as a single atom and then inflated to the cosmos over the next 13.8 billion years until now, and continues to do so. As today we don't have instruments to look back into the universe's birth, most of the understandings about the Big Bang Theory comes from mathematical formulas and models.
However, astronomers can today see the 'echo' of the expansion through a phenomenon known as the cosmic microwave background (CMB). It is from the time when the universe began and cannot be seen with your naked eye, while it is present everywhere in the universe. CMB is believed to the remnant of the big bang.
It is called early light or the "afterglow" of the Big Bang. CMB was first predicted by Ralph Alpher and other scientists in 1948 but was found accidentally almost 20 years later. The CMB also gave cues that the universe is made up of much more matter and only five per cent of it has planets, stars and galaxies. The universe came into existence 13.7 billion years ago, and the CMB dates back to about 400,000 years after the Big Bang. That's because the universe was just one-hundred-millionth the size it is today and had extreme temperatures.
There is also gravitational waves controversy which states that after the universe was born, our cosmos inflated faster than the speed of light. Current theories state that the universe is not just expanding, but getting faster as it inflates. Due to which we will not be able to see galaxies from Earth or any other vantage point within our galaxy. "We will see distant galaxies moving away from us, but their speed is increasing with time," Harvard University astronomer Avi Loeb told Space.com in a 2014 article. Scientists now say that Big Bang was not the first inflationary period the universe experienced. They also believe that the cosmos goes through regular cycles of inflation and deflation.