A couple of days ago, a question occurred to me:
What’s the furthest I’ve ever been from anyone else?
We all need some space!
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.
But that's less than a factor of 3 difference! For Fermi estimates of numbers of that size, those two answers are essentially the same. It wouldn't take much of an error in either estimate to push sand ahead of stars…
— Paul Taylor (@aPaulTaylor) July 8, 2018
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:
The “giant rat” is two foot rather than the “four foot” claimed in the press. Perspective trick. Here’s my working: pic.twitter.com/DYGE3hPDSz
— Oliver O’Brien (@oobr) March 11, 2016
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:
@standardnews It’s probably not that big. Our pest control team are checking it out though. pic.twitter.com/nqYFYjw4K4
— Hackney Council (@hackneycouncil) March 11, 2016
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.
More Information
Giant rat ‘the size of a small child’ found near Hackney playground, in the London Evening Standard
How to fake a giant rat (and why you shouldn’t trust pictures on the internet), on The Guardian
Hackney council made a wonderful response to that ‘rat as big as a 4-year-old’ story, at The Poke