Stephen Hawking
Professor Stephen Hawking attends the New Space Exploration Initiative 'Breakthrough Starshot' Announcement at One World Observatory Jemal Countess/ Getty Images

Stephen Hawking and 32 top physicists have penned an angry letter, responding to a recent article published in Scientific American about the origins of the universe. The letter defended one of the world's leading theories on how the universe began and expressed the physicists' "categorical disagreement" with several statements made in the article.

Hawking and his colleagues' letter was in response to the article published in early February, which heavily criticised the inflation theory - that the universe expanded like a balloon just after the Big Bang. In the article originally titled Pop Goes the Universe, physicists Anna Ijjas, Paul J Steinhardt, Abraham Loeb went so far as to deem that the theory "cannot be evaluated using the scientific method".

The physicists said the inflation theory could essentially not be tested in any scientific form. They argued that recent data provided further evidence of the Big Bang and inflation not adequately explaining how the universe began. "The data suggest cosmologists should reassess this favoured paradigm and consider new ideas about how the universe began," the trio summarised in the article.

Hawking and his colleagues fired back in their letter: "We have no idea what scientists they are referring to. We disagree with a number of statements in their article."

Hawking and other leading physicists, including cosmologist Alan Guth, who first proposed the inflation theory back in 1980, wrote that there is "no disputing" that inflation is the "dominant theory" in the field of cosmology.

"By claiming that inflationary cosmology lies outside the scientific method, IS&L [the authors of the earlier article] are dismissing the research of not only all the authors of this letter but also that of a substantial contingent of the scientific community," they wrote. "Moreover, as the work of several major, international collaborations has made clear, inflation is not only testable, but it has been subjected to a significant number of tests and so far has passed every one."

Hawking and his colleagues explained that there are many models of inflation and there is still debate about how accurate they are, adding that the theory is somewhat of a work in progress.

"No one claims that inflation has become certain; scientific theories don't get proved the way mathematical theorems do, but as time passes, the successful ones become better and better established by improved experimental tests and theoretical advances. This has happened with inflation. Progress continues, supported by the enthusiastic efforts of many scientists who have chosen to participate in this vibrant branch of cosmology."

Ijjas, Steinhardt and Loeb responded to the letter with disappointment. They said they have "great respect for the scientists" who wrote the letter but maintained their position on the matter. "We firmly believe that in a healthy scientific community, respectful disagreement is possible and hence reject the suggestion that by pointing out problems, we are discarding the work of all of those who developed the theory of inflation and enabled precise measurements of the universe," the trio wrote.

Although there is still dissension among physicists about the origins of the universe, this latest development appears to have inflamed the debate in the scientific community.