Wondering the reason for the weird title? You're not alone. Well, watch this video first:


Clip from DM4 showing Gru during a Heist.

Now, you might have understood the reason for the title, at least I hope so: Gru's amidst a heist, he reveals a laser, and wait, science?
Yup, Science.

You couldn't have not noticed in the clip, what happens after Gru blows baby powder. He blows the powder, and the laser reveals itself. Fiction/Magic? Nah; Science 💪.

Okay, so this phenomenon is ubiquitous. You might have noticed the same in rave parties, or during a night in a dusty location with headlights of cars on - the path of light is visible, like this:

Image showing visible path of light

But this isn't always so; there are many occassions where the path of light isn't visible, for example, in the solar system, from the ISS, you wouldn't see rays of the sun going through the vacuum of space like you would on a misty morning!
The reason for this is that all organisms with the sense of vision see things only when light enters their eyes, either directly from a source or after being reflected from objects. So, you see a tree because sunlight falls on the tree, and the tree reflects some of that light into your eyes. Similarly, you see a bulb glowing because light from the bulb enters your eyes directly. You couldn’t perceive the tree if it hadn’t reflected light into your eyes, and you wouldn’t see the bulb if its light didn’t reach your eyes directly.

Going by this logic, you would (hopefully) ponder over this: was there something which made the light from laser reflect INTO the eyes (from the viewer's POV)? Well, (drumroll), you are right! That is exactly what the baby powder did when Gru blew it; It created a heterogenous mixture (a mixture in which the particles aren't evenly distributed among the medium) with the air around the laser, and the powder particles scattered (reflected in many directions, simplified) the light from the laser, essentially making the path of the laser visible.

This is a fascinating concept in science, called The Tyndall Effect, named after its discoverer John Tyndall.

“The Tyndall Effect is the scattering of light by the particles of a colloid or a fine suspension, making the path of the light beam visible.”

Now, a colloid is a type of mixture in which very small particles of one substance are evenly dispersed throughout another substance, but these particles do not settle out on standing. More simply, a colloid is a mixture where tiny particles of one thing are spread out in another, and they don’t settle down.

What's more interesting, is that not all mixtures scatter light. For the path of light to be visible, the size of particles has to be greater than 1nm, but less than 100nm. Such mixtures with particles of these sizes are called colloids, or colloidal solutions. The reasons for these are:

  • If the size of particles is less than 1nm, then this would be a pure solution. And the thing about a pure solution is that, due to the extremely small size of the particles, the scattered light would be too little in amount to be perceived by the eyes.
  • If the size of particles is more than 100nm, then this would turn into a suspension. A suspension is a heterogenous mixture in which particles are so large that they settle down when left undisturbed for a while. Due to this, the path of light would be visible strongly for some time until there are a few particles throughout the container to scatter light, but after some time, when all the particles settle down, the solvent would be devoid of any particles to scatter light. Therefore, the Tyndall Effect observed, would be very weak, due to lack of particles throughout the solution, i.e, where light enters the container.
An image summarizing conditions for paths of light



So, pretty cool, huh? So, the next time you notice this phenomenon, I hope you'll remember this post 💙. I hope you enjoyed reading this and uncovering the reason why Gru blew baby powder to reveal the lasers which would have comprmoised the heist. At this point, I think the G in Gru stands for Genius. Respect+ to the villain 😎.