Okay show of hands: how many of you have felt that surge of satisfaction  after finally getting out of a maze?

Maybe you were forced to go to a corn  maze for a middle school field trip. Maybe you were an ancient  Greek prince who wanted to stop a half-bull man from eating a  bunch of your fellow Athenians.

Or maybe you were a mouse in some scientist’s lab, who knew a snack was at the end. Whatever your personal  experience, it probably felt like you had to put some kind of smarts into it. But the thing is, you don’t need to  have any smarts at all to solve a maze.

You don’t need to have a brain. Heck, you don’t even need to be alive! So let’s take a look at five brainless  things that can solve a maze, and how they manage to do it. [♪ INTRO] The humble slime mold is probably  the most famous example on our list, so let’s tackle that one, first.

If you’ve not heard of this kind of  lifeform before, they’re, well, super weird. For one thing, slime molds aren’t  actually mold, or any kind of fungus. They’re a unique kind of single-celled  organism that just look like mold because some of them can  dissolve the membranes separating their individual cells,  merging their innards together.

The structure this forms, called plasmodium, is basically a single cell that’s  big enough to see with the naked eye. And a plasmodium can be shaped into  filaments and tubes called pseudopodia, which can stretch and reach  out to nearby food sources. Back in 2000, some researchers  in Japan and Hungary filled a little maze with a plasmodium of  the species Physarum polycephalum, and put food sources at two  different ends of the maze.

Within a few hours, almost  all the plasmodium that wasn’t on the shortest path between the  two food sources had faded away. The slime mold was essentially  conserving resources. It chose to only maintain paths through the maze that were most efficient  at transporting nutrients.

But how did it know which path was  the most efficient to keep using? Well, it’s tricky to say for sure. We know it’s using some form of chemotaxis, which is when a living thing  detects and follows signals coming from a chemical somewhere.

But the full details of how that slime  mold optimized its path were unclear. So in 2010, some researchers  in Japan and the UK created a mathematical model based on that same slime mold species to gain more insight. The model focused on a feedback  loop between the thickness of the plasmodium tubes, and the flow  rate of stuff through those tubes.

If the flow rate got too  low in a given tube meaning there weren’t enough nutrients passing  through it…the tube would disappear. That left the tubes  transporting the most nutrients, and also the most optimum path to transport  those nutrients, through the maze. But you may already be familiar  with this research paper, because of what else the team did: they also used a slime mold to re-create  part of the Japanese transport network.

In this experiment, they placed  food sources on a mini map of Tokyo and some surrounding cities, with each source representing the various population centers. The slime mold was then left to form  plasmodium tubes between all of them. Sure enough, just by optimizing  its own food transport, the slime mold managed to create a series of tubes that was organized as efficiently as the real one.

If you’re feeling envious of  a mindless blob of critter, you can find comfort in our next example… Researchers have also coaxed  human cells into solving mazes. The principle is similar to  before: using chemotaxis to move as efficiently as possible  towards a chemical source. And if you think about it, it makes sense  that certain cells are good maze solvers.

Bodies are complex, and not all cells just  sit in one spot for the whole of their lives. Think white blood cells having to go  somewhere specific to fight off an infection… or a cancer that starts in one organ  spreading to a completely different one. So cells like these have some  clever tricks up their sleeve to help them navigate their surroundings.

For example, they can produce their own chemical signals for other cells to follow them. By working together like this,  these cells don’t have to rely solely on a signal coming  from the end of the maze, and they can also navigate  even more complex paths. In fact, in 2014, one group of researchers created a competition to push cell  navigation to its limits.

This was the “Dicty World Races”,  named after one of the cells contestants could use: an  amoeba called Dictyostelium, which biologists often use as a  model organism in their research. You’ll note that’s not a human cell, but other contestants chose to race  a human blood cancer cell, instead. The actual maze was set up to  imitate the cells’ natural habitats, and fourteen teams each brought their genetically engineered cells to clear  it as quickly as possible.

A group from the Netherlands  were declared the “winners” after their Dicty cells took  48 of the top 100 race times. It’s a charming story from the world of science, but this wasn’t just fun and games. As I mentioned before, some teams  were working with cancer cells.

And understanding how they  move through tissue is critical if scientists want to develop treatments  to stop cancers from spreading. So far everything I’ve mentioned  has at least been alive, with mechanisms to sense their  surroundings and react to them. But can anything non-living solve mazes?

Well, sure. If you release a gas into a maze, by simple diffusion and random chance, some of the particles will  eventually reach the exit as the gas explores every single path. That is boring though.

So instead, say hello to the maze-solving liquid that can traverse a maze without  going down any wrong paths. In 2018, a research team  filled a small maze with milk, then put a blob of food dye at the entrance. When they added a drop of liquid  soap to the blob of food dye, that blob suddenly spread through the maze, but only down the path that led to the exit.

This apparent magic trick relies on  a phenomenon from fluid mechanics called the Marangoni effect, which  is a consequence of a much more well-known phenomenon called surface tension. When you’ve got some amount of liquid, all the molecules in that liquid are  pulling on each other a little bit. For most of the molecules, they’re  completely surrounded by other molecules.

So the pulling comes from all directions  equally, and basically cancels out. But at the surface, that pulling is lopsided, so the molecules are constantly  feeling a slight tension. Hence, “surface tension”.

As for how this maze experiment worked,  it’s because soap is a surfactant. That means it lowers the nearby surface  tension when it’s added to another liquid. Milk also naturally has trace  amounts of its own surfactants, but no, that does not mean you dairy  lovers are constantly drinking soap.

Imagine you’re a blob of food  dye floating in a milk maze, and some soap gets plopped next to you. Suddenly, you have a neighbor  that isn’t pulling on you quite as hard as you were used to. So you start moving in the opposite direction, toward the milk that’s pulling on  you more strongly by comparison.

But what happens whenever you  reach an intersection in the maze? Well, you’ll be drawn toward the  path with more surface area ahead. That’s because the scientists designed your maze so the exit features a large reservoir of milk.

In other words, the correct path to  take…compared with all the dead ends… has a much bigger surface area. And since the amount of surfactants  in milk is low compared with the soap, a path with way more surface area  creates a much lower surfactant density. And remember, you as a blob of dye are  being pulled away from the surfactants.

So you get pulled toward the exit,  no thoughts needed on your part. Just the laws of physics. We’ve got two maze-solvers to go,   but just like all this science, we need funding.

So here’s an ad. This SciShow video is supported by Brilliant: the online learning platform designed to  help you reach serious learning goals. Instead of passively watching lectures, this year you can be more active about learning with Brilliant’s interactive  problems and challenges.

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They’re also giving you unlimited daily access to everything on Brilliant with 20%  off an annual Premium subscription. Our non-living maze solvers  only get weirder from here. Next up is the stuff electricity  and fire is made of: plasma.

In 2002, a UK-US team etched a  thumbnail-scale maze into a glass chip, filled it with low-pressure helium gas, and ran an electric current  through the whole thing. The aim was to observe a well-known  effect called a glow discharge, where the current turns a gas into a plasma. The resulting plasma is full of charged  particles called ions that are excited, energetically speaking, and want to emit some of that energy to stop being so excited.

When they do, they let off a distinctive glow. If you’re wondering, “Is this how some  neon lights work.?”, the answer is “Yes”. But here’s the thing, you may remember  from school that an electric current will always try to follow  the path of least resistance, which almost always means the shortest distance.

So if you put your two electrodes  at the entrance and exit of a maze, the current will only form glowing plasma along the shortest path through that maze. Like with the food dye, the laws  of physics force it down one path. But unsurprisingly, the specific laws of  physics that apply here are different.

When you switch on the current in a circuit, an electric field spreads  over it at the speed of light. Any charged particles in the circuit will  react to this new field and move around. But since they’re charged particles,  they’re also emitting their own tiny fields, so their movement winds up  changing the larger field, too.

And on paths with more resistance, the charges rearrange themselves to cancel  out the flow of current. This feedback loop happens at near light-speed, so the current is able to  explore every path in the maze almost instantly when it’s switched on. And this exploration and  re-arranging of charges always leaves only one path for the current to  follow: the path of least resistance.

Of course, the scientists behind  this plasma maze didn’t stop with a mere explanation of the  science, and a simple maze design. To one-up themselves, the team etched  a road map of London onto glass. By putting electrodes at  different points on the map, they could make the plasma show the  shortest route between any two locations.

So, if you want to know the  fastest route from Victoria Station to Imperial College London, and your  friendly neighborhood slime mold is on vacation, just ask your friendly  neighborhood glow discharge plasma, instead! And finally, let’s talk about how one group of Italian researchers got a  beam of light to solve a maze. Here, the centimeter-scale maze was  made out of a special optical material, with branching pathways etched  into it for the light to follow.

The light could then bounce  between different pathways in ways that looked a lot like  choosing paths to take in a maze. But because the light is doing all that bouncing, it winds up traveling slower than  your standard “speed of light” speed you wind up memorizing if you go to  college for astrophysics or whatever. That meant the team could test to see how fast the light could find its way out of  the maze under different circumstances.

Because just like letting  a bunch of gas into a maze, light would eventually make  it to the end simply by bouncing around randomly  between the different paths. But could the light be coaxed into  traversing the maze more efficiently? It turned out, yes!

By exploiting special quantum  properties of the light, like its ability to take  multiple paths at the same time, the researchers could shorten the time  it took their light to reach the exit. But interestingly, they  found that they could improve the light’s maze-solving abilities thousands  of times over if they also introduced just a little bit of “noise”  to the circuit…in other words, effects that destroy the quantumness of the light. To be more specific, they made sure  their etching process wasn’t perfect, meaning the light waves couldn’t  bounce as cleanly through the material.

In the end, the fastest solves were made by light that had about a ten percent  chance of losing its quantumness. The team speculated that,  when there was no added noise and the light was fully free to be  in multiple paths at the same time, the light might wind up getting  stuck in certain places. By adding a small amount of  quantum-destroying noise, it might serve as a sort of ‘kick’ to  push the light down a certain path, so it could continue its journey to the exit.

Once again, this wasn’t all just fun and games. The researchers speculated that this could explain how photosynthesis works so  efficiently, since that also involves light bouncing down a complicated  network of cellular stuff. So the next time you find  yourself needing to solve a maze, just remember that you have a lot more  options than your standard tricks, like “put your hand on the wall  and don’t let go until you’re out” or “use this ball of string from a  princess who fell in love with you”.

Ok, now somebody needs to  do a retelling where Ariadne gifts Theseus a pet slime mold. I would read the heck out of that. [♪ OUTRO]