Firewalking is possible in physics

Science in dialogue

Why can one walk over glowing coals, as is customary with fakirs?

Like so many things, it has to do with physics. More precisely: with good and bad heat conductors. Metal and water, for example, are good conductors of heat. Wood and coal are bad.

You would quickly find out what good and bad heat conduction means if you put your hand first in a 90 degree hot sauna (i.e. in air) and then in 90 degree hot water. You wouldn't do the latter a second time, because water is a very good conductor of heat and the pain would be unbearable immediately. Air, on the other hand, is a poor conductor of heat. Most people can easily stand a quarter of an hour in a 90 degree sauna. Nevertheless: the air in the sauna and the water in the saucepan have the same temperature. Only: It feels different - depending on whether the person touches a good or bad heat conductor.

Coals are poor conductors of heat: you have to stand on them for a while before they are perceived as hot. But that's not what a fakir does when running over glowing coals. He walks over the coals so quickly that the total time your feet are actually on the coals in a typical fire walk is perhaps a second. That is not enough for heat transfer.

In addition, the coals are often covered with a thin layer of ash, which provides additional insulation and makes them even worse conductors of heat. Conclusion: What firewalkers do is not incredibly tricky or even superhuman. But of course you can always marvel and admire them.

The question was answered by Dorothee Menhart, science journalist and editor at Wissenschaft im Dialog.