According to reports, 21 people had to be treated for burns from walking over hot coals at a Tony Robbins inspirational event.

Robbins is a successful self-help guru with a schtick that depends upon the scientific illiteracy of his audience. After a session of telling people how to “unleash the power within” he demonstrates their new-found power by inviting them to walk barefoot over hot burning coals while thinking about cool moss. This is meant to demonstrate the power of mind over matter. This is, of course, nonsense.

The Hot Coal Deception

Many physicists have used the hot coal demonstration to teach a bit of elementary physics, as there is a very simple explanation for how people can walk over hot coals in their bare feet. I have, in fact, heard three (non-exclusive) explanations. The first, and the one that I think is probably the biggest factor, is that wood coals have a very low thermal capacity and conductivity. This means that they do not hold on to a lot of heat energy, and they conduct that energy very slowly. Therefore little heat is transferred to the soles of the feet – if you walk briskly across them and give little time for heat transfer.

Compare this to other substances with very different thermal properties. Aluminum is interesting because it has a very high thermal conductance (250 W/(m.^oC)), but it has a very low thermal capacity. Iron has a thermal conductance of 80, but with a much higher capacity than aluminum. This is why aluminum cookware will cool down very quickly – even moments after you take it out of a hot oven it will be cool enough to touch. An iron pan, however, will take a long time to cool down once it has heated up.

Compare this to the thermal conductance of wood (specifically oak) – 0.07 W/(m.^oC). This is tiny. So even though the coals are about 1,500 degrees F, not much of that heat gets transferred to the feet. You would not, of course, want to walk across a slab of iron heated to the same temperature, or even much less. I would rather walk across wood at 1,500 degrees than iron at 200 degrees.

That is enough to explain how a brisk walk across burning wood coals can be safe, but there are two other contributing factors. One is the ash that builds up on top of the burning coals. Ash is a good insulator, and a thin layer of it is enough to slow down heat transfer even further. This could explain why some people at the event were burned and others were not – how disturbed the layer of ash was before an individual walker went across.

A third factor that I’ve heard used to explain the phenomenon (I am not sure how much of a contribution this is) is perspiration on the bottom of the feet, which evaporates and causes a bit of an insulating barrier as well. This seems like the least consistent and important factor of the three.

None of this, of course, has anything to do with the power of the mind. You can think of hot burning lava while walking over the coals, rather than cool moss, and it won’t make a bit of difference. It is the laws of physics that protect your feet, not the ramblings of a self-help guru.

Ramblings of a self-help guru

Speaking of which, what is it, exactly, that Robbins is selling? I think Lisa Simpson summed it up best when she said of a similar character:

“This is madness. He’s just peddling a bunch of easy answers.”

Robbins promises:

Your success coaching plan is your “Pathway to Power.” It is not based on hope. It is not based on theory. It is modeled after those who have already achieved the real results you desire through life success coaching, at the highest and deepest levels.

Life coaching and self-help programs like this are generally not evidence-based in any meaningful way. They are usually just based upon a few simple ideas or catch phrases. They all have a common element, however – spending time thinking about your life, your goals, and how you deal with the people in your life. For anyone who is mostly coasting through life without much introspection, spending a weekend thinking about how to get motivated, achieve one’s goals, and make real changes is one’s life can be a profound experience. That’s the real hook. The details don’t matter.

Wrap that up with some common sense, that “motivational speaker” personality, and a good gimmick and you will probably do well as a self-styled life coach.

Richard Wiseman has done an excellent job of debunking the self-help industry in his book 59 seconds. Most of the advice and “easy answers” that are being peddled is not only improvised, it’s largely wrong. We have decades of psychological studies that actually provide evidence for which strategies are likely to be more successful, and often the real answers are counter-intuitive.

For example, you should not praise a child when they accomplish something. This sounds crazy at first – how can it be wrong to praise a child when they do something good? The problem is praising the result, rather than the effort. This can make children anxious, because they think they will only get praise and acceptance when they do well, something they cannot always control. What they can control is the amount of effort they put into something, so that is what you should praise (even if the result was less then stellar).

What is frustrating is that there is actually a great deal of published evidence that can inform the very questions raised by the self-help industry, but the big sellers in the self-help industry seem to be completely disconnected from that evidence. What they are selling are made-up easy answers, personality, and gimmicks.

It’s all the more annoying when the gimmick is based upon a misunderstanding of basic physics.