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Scientists have uncovered a remarkable parallel between the way humans build cities on Earth and how galaxies form in space.

They say how galaxies evolve is mathematically equivalent to the way settlements grow.

American linguist George Kingsley Zipf noticed that if cities are listed according to size, then the rank of a city is inversely proportional to the number of people who live in it.

Scientists have uncovered a remarkable parallel between the way humans build cities on Earth and how galaxies form in space. Pictured on the left is Antwerp, and on the right galaxy NGC 3310

For instance, if the largest city in a country has a population of 10 million, the second-biggest will have a population of five million (10 divided by 2), and the third a population of 2.5 million.

'Zipft's law' is a scaling law. 

It can also be found in the strange fact that whether one person will be friends with another, is inversely proportional to the number of people who live closer to the first person than the second.

But while scientists know the law to be true, they have no idea why it works.

Now researchers claim they have the source of these scaling laws in space, according to Quartz.

Henry Lin and Abraham Loeb at the Harvard-Smithsonian Centre for Astrophysics in Cambridge have used models for showing how galaxies evolve to create a theory for scaling laws on Earth.

American linguist George Kingsley Zipf noticed that if cities are listed according to size, then the rank of a city is inversely proportional to the number of people who live in it (shown by the black dots). The blue dashed line shows how the population is predicted to behave according to Zipf's law

'We treat the population density as the fundamental quantity, thinking of cities as objects that form when the population density exceeds a critical threshold,' Lin and Loeb wrote in their research paper.

'The situation is therefore conceptually and mathematically analogous to the formation of galaxies in the universe.'

According to a report by MIT Technology Review, the team used models governing the spread of galaxies, to show that this approach works for urban growth.

They then analysed any variations in the density, and used equations to predict how this density can grow over time.

'The results are in good agreement with the theoretical prediction across a broad range of spatial scales, from a few km to ∼ 10^3 km.'

Their research suggests human behaviour on a massive scale follows the same patterns as galaxy growth. 

They believe this unifying theory for scaling law, can also be used to predict other phenomenon, such as the spread of disease. 

WHAT IS ZIPF'S LAW AND HOW DOES IT WORK? 

Linguist George Kingsley Zipf noticed that if cities are listed in size, then the rank of a city is inversely proportional to the number of people who live in it

American linguist George Kingsley Zipf noticed that if cities are listed according to size, then the rank of a city is inversely proportional to the number of people who live in it.

For instance, if the largest city in a country has a population of 10 million, the second-biggest will have a population of five million (10 divided by 2), and the third a population of 2.5 million.

This relationship is known as the scaling law, and can also be found in the strange fact that whether one person will be friends with another, is inversely proportional to the number of people who live closer to the first person than the second.

Another example of Zipf's law is in language. 

It states that the frequency of any word is inversely proportional to its rank in the frequency table. 

This means the most frequent word will occur twice as often as the second most frequent word, three times as often as the third most frequent word.