Mathematicians have used a controversial statistical formula to predict when humanity could go extinct.

The calculation, known as the 'doomsday argument,' starts with an estimate that roughly 117 billion people have lived throughout human history.

Researchers then assume that people alive today occupy a random place in humanity's timeline rather than an unusually early one.

Under that assumption, there is a 95 percent chance that the 117 billion people who have already lived represent at least five percent of all humans who will ever exist.

Because 100 percent is 20 times larger than five percent, mathematicians multiply 117 billion by 20, producing a maximum human population of about 2.34 trillion people.

Based on current birth rates, humanity would reach that number in roughly 17,100 years.

Supporters of the theory argue that the figure represents a statistical upper limit on humanity's future, meaning there is a 95 percent chance our species will disappear within the next 17,100 years, whether the cause is climate change, nuclear war, a pandemic or some other catastrophe.

The theory, however, remains highly controversial and has been rejected by many scientists. 

Critics argue that the assumptions behind the calculation are overly simplistic and ignore countless factors that could dramatically alter humanity's future.

Others point out that if humans colonize other planets, develop new technologies or survive for millions of years, the calculation quickly breaks down.

The argument is based on what scientists call the Copernican Principle, the idea that humans do not occupy a special or privileged position in the universe. 

Scientific American reported on the doomsday argument on Tuesday.

To explain the theory, researchers ask people to imagine every human who will ever live lined up on a giant timeline stretching from the first person ever born to the last.

If around 117 billion people have already lived, then, statistically speaking, it would be unusual for humanity to continue long enough for tens of trillions more people to be born.

Supporters compare it to drawing a numbered ping-pong ball from one of two boxes.

One box contains 10 balls, and the other contains 100,000. If you draw ball number four, you would naturally assume it came from the smaller box because the odds are much higher.

According to the doomsday argument, the same reasoning applies to humanity.

If roughly 117 billion people have already lived, the theory argues it is statistically more likely that humanity's total population will remain relatively limited rather than expanding indefinitely across the galaxy.

The calculation assumes there is a 95 percent chance that the roughly 117 billion people who have already lived do not represent less than five percent of all humans who will ever exist.

If 117 billion people account for five percent of humanity's total population, then the full number works out to about 2.34 trillion people. 

In other words, mathematicians multiply the number of people who have already lived by 20 because 100 percent is 20 times larger than five percent.

Using modern birth rates, researchers calculate that humanity would reach that threshold in about 17,100 years.

While that may sound like a distant future, a study published in May warned that the global population could crash by 2064.

This could be the result of climate collapse, a pandemic, global conflict or resource shortages, scientists warned. 

'The most provocative part of our paper explores hypothetical future scenarios,' the researchers from the University of Milan said.

'We modelled what could happen if major environmental crises abruptly imposed severe carrying–capacity limits on Earth.

'Under a deliberately conservative worst–case assumption that Earth's sustainable carrying capacity suddenly dropped to around two billion people, our model predicts a rapid global population decline, with humanity potentially halving by around the year 2064.'

The researchers maintain that this is not a forecast, but an 'illustrative mathematical scenario' which shows how sensitive population dynamics may be to abrupt changes.