Rapid bone growth and underwater breathing: Putting the science of Harry Potter’s universe to the test

Natural Sciences students from the University of Leicester have put these arcane medical practices to the test — and have concluded that a little magic might indeed be required in both situations to make them scientifically feasible.

The research is revealed just before Harry Potter and the Cursed Child opens as a West End stage play in London and Fantastic Beasts and Where to Find Them is released in cinemas worldwide.

Gillyweed — Drowning with Gills?

In Harry Potter and the Goblet of Fire, Harry passes the second Triwizard task by consuming Gillyweed, which allows him to breathe underwater by causing gills to grow on his neck.

To check the feasibility of Harry surviving with home-grown gills, in a paper for the Journal for Interdisciplinary Science Topics, students Rowan Reynolds and Chris Ringrose first inspected the gills themselves, estimating them to be approximately 60cm2 in surface area based on their appearance in the film.

Taking into account the oxygen content of the Black Lake and the maximum oxygen use of swimming, they then examined Harry’s weight, suggesting that if he had a normal BMI — providing he hadn’t been binging too much on Every Flavour Beans and Chocolate Frogs — and the average height of a 14 year old boy, he would need to process 443 litres of water at 100% efficiency per minute for every minute he was underwater.

This would mean the water would have to flow at 2.46 metres per second — twice the velocity of normal airflow and therefore far faster than he could inhale and exhale, causing him to suffocate.

Interestingly, Harry is seen swimming with his mouth closed, which is not how gills work — the students suggest that if Harry were to open his mouth to allow water into his throat and out through the gills, it may be plausible he could breathe underwater. By keeping his mouth shut, however, he would not be able to extract sufficient oxygen for survival, and as a result would lose his title as ‘The Boy Who Lived’ quite quickly after suffocating.

Revealing the Magic of Skele-Gro

While Harry’s underwater success may be questionable, the bone-producing panacea Skele-Gro would be equally as farfetched.

In Harry Potter and the Chamber of Secrets, Harry’s tense Quidditch match against Slytherin results in one of his arms being broken by a rogue bludger. After his broken bones are removed, the matron Madam Pomfrey then prescribes Harry a dose of Skele-Gro, used for growing bones that are missing.

In a separate paper, students Leah Ashley, Chris Ringrose and Robbie Roe aimed to find how the rate of normal bone growth compares to this accelerated growth, and how much energy Skele-Gro would need to provide in order to rebuild Harry’s broken arm.

Observing the timings in the chapter in which Harry is struck, the students suggest that the bones in Harry’s arm are removed at 11:13:50am, with Skele-Gro working at roughly 11:50am. As he is healed within the space of 24 hours, Skele-Gro must have accelerated restorative properties.

The students calculated the time taken for Harry to regrow all the bones in his arm with Skele-Gro as being at least 90 times quicker than is possible in real-world bone regeneration.

As Harry’s recovery with Skele-Gro takes approximately 24 hours and there is no mention of him eating during recovery, Skele-Gro has the capacity to supply the additional 133,050 kcal (556.7 MJ) worth of energy required by the body to regenerate bones without causing any negative side effects — a power output of 6443 W.

The students concluded that Skele-Gro must therefore contain unexplained magical properties that allow it to hold such a vast amount of energy — and be able to apply it in a short period of time.

The students presented their findings in a paper for the Journal of Interdisciplinary Science Topics, a peer-reviewed student journal run by the University’s Centre for Interdisciplinary Science. Students from the University of Leicester (UK) and McMaster University (Canada) have contributed to this year’s journal. The student-run journal is designed to give students practical experience of writing, editing, publishing and reviewing scientific papers.

Dr Cheryl Hurkett from the University of Leicester’s Centre for Interdisciplinary Science said: “An important part of being a professional scientist (as well as many other professions) is the ability to make connections between the vast quantity of information students have at their command, and being able to utilise the knowledge and techniques they have previously mastered in a new or novel context. The Interdisciplinary Research Journal module models this process, and gives students an opportunity to practise this way of thinking. The intention of this module is to allow students to experience what it’s like to be at the cutting edge of scientific research.

“The course is engaging to students and the publishing process provides them with an invaluable insight into academic publishing. It also helps students feel more confident when submitting future papers. I find it a very rewarding module to teach and I am always pleased to see my students engaging so enthusiastically with the subject. I encourage them to be as creative as possible with their subject choices as long as they can back it up with hard scientific facts, theories and calculations!”