# You're reading: Posts Tagged: estimation

### Are there More or Less stars than grains of beach sand?

This week’s episode of More or Less on the BBC World Service answered a question that involved estimating big numbers: Are there more stars than grains of beach sand?

This claim was famously made by Carl Sagan in the seminal programme Cosmos.

The cosmos is rich beyond measure. The number of stars in the universe is larger than all the grains of sand on all the beaches of the planet Earth.

More or Less come to a fairly standard answer, that Sagan was correct. This sort of problem, which involves approximating unknowable numbers based on a series of estimates, is called a Fermi problem. I’ve written about Fermi problems here before. The More or Less approach to answering this raised a question from a reader of this blog.

Alright, actually Paul is one of the writers of this blog, rather than a reader. Even so, are his concerns warranted?

### Rodents of Unusual Size? I don’t think they exist

A man in London claims to have found a rat ‘the size of a small child’, near a children’s play area in Hackney, London. Alongside a photograph of gas engineer Tony Smith proudly displaying the gigantic creature held in the jaws of a litter picking stick, some news outlets have reported the claim that the rat was “about four foot long”.

Photograph: Tony Smith/SWNS

Luckily, mathematicians are here to save the day! Firstly, there’s no way it’s four feet long, as this rigorous analysis shows – estimating the height of the man as 180cm, and using the respective lengths of two of his visible fingers and the width of the litter picker at each end to estimate the effect of perspective:

Furthermore, several other people have successfully managed to recreate the effect of holding something relatively small up in a photo, putting it nearer the camera, and making it look much bigger, including The Guardian’s new formats editor Martin Belam, and in one brilliant case, an employee of Hackney council:

The message to the maths outreach community is that if we try really, really hard, we should eventually be able to get people to understand the thing where closer objects look bigger, although it may take more staring at model cows and pointing at cows out the window than was previously hoped.