Субтитры (239)
0:00Okay show of hands: how many of you
0:02have felt that surge of satisfaction
after finally getting out of a maze?
0:06Maybe you were forced to go to a corn
maze for a middle school field trip.
0:10Maybe you were an ancient
Greek prince who wanted to stop
0:13a half-bull man from eating a
bunch of your fellow Athenians.
0:17Or maybe you were a mouse in some scientist’s lab,
0:20who knew a snack was at the end.
0:22Whatever your personal
experience, it probably felt like
0:24you had to put some kind of smarts into it.
0:27But the thing is, you don’t need to
have any smarts at all to solve a maze.
0:32You don’t need to have a brain.
0:34Heck, you don’t even need to be alive!
0:36So let’s take a look at five brainless
things that can solve a maze,
0:40and how they manage to do it.
0:46The humble slime mold is probably
the most famous example on our list,
0:50so let’s tackle that one, first.
0:51If you’ve not heard of this kind of
lifeform before, they’re, well, super weird.
0:56For one thing, slime molds aren’t
actually mold, or any kind of fungus.
1:01They’re a unique kind of single-celled
organism that just look like mold
1:05because some of them can
dissolve the membranes separating
1:08their individual cells,
merging their innards together.
1:11The structure this forms, called plasmodium,
1:14is basically a single cell that’s
big enough to see with the naked eye.
1:18And a plasmodium can be shaped into
filaments and tubes called pseudopodia,
1:24which can stretch and reach
out to nearby food sources.
1:27Back in 2000, some researchers
in Japan and Hungary filled
1:31a little maze with a plasmodium of
the species Physarum polycephalum,
1:36and put food sources at two
different ends of the maze.
1:39Within a few hours, almost
all the plasmodium that wasn’t
1:42on the shortest path between the
two food sources had faded away.
1:46The slime mold was essentially
conserving resources.
1:49It chose to only maintain paths through the maze
1:52that were most efficient
at transporting nutrients.
1:55But how did it know which path was
the most efficient to keep using?
1:59Well, it’s tricky to say for sure.
2:00We know it’s using some form of chemotaxis,
2:03which is when a living thing
detects and follows signals
2:06coming from a chemical somewhere.
2:08But the full details of how that slime
mold optimized its path were unclear.
2:13So in 2010, some researchers
in Japan and the UK created
2:17a mathematical model based on that same
2:20slime mold species to gain more insight.
2:22The model focused on a feedback
loop between the thickness
2:25of the plasmodium tubes, and the flow
rate of stuff through those tubes.
2:30If the flow rate got too
low in a given tube meaning
2:33there weren’t enough nutrients passing
through it…the tube would disappear.
2:37That left the tubes
transporting the most nutrients,
2:40and also the most optimum path to transport
those nutrients, through the maze.
2:45But you may already be familiar
with this research paper,
2:47because of what else the team did:
2:49they also used a slime mold to re-create
part of the Japanese transport network.
2:55In this experiment, they placed
food sources on a mini map of Tokyo
2:58and some surrounding cities, with each source
3:01representing the various population centers.
3:04The slime mold was then left to form
plasmodium tubes between all of them.
3:08Sure enough, just by optimizing
its own food transport,
3:12the slime mold managed to create a series of tubes
3:15that was organized as efficiently as the real one.
3:18If you’re feeling envious of
a mindless blob of critter,
3:20you can find comfort in our next example…
3:23Researchers have also coaxed
human cells into solving mazes.
3:26The principle is similar to
before: using chemotaxis to
3:30move as efficiently as possible
towards a chemical source.
3:33And if you think about it, it makes sense
that certain cells are good maze solvers.
3:37Bodies are complex, and not all cells just
sit in one spot for the whole of their lives.
3:43Think white blood cells having to go
somewhere specific to fight off an infection…
3:48or a cancer that starts in one organ
spreading to a completely different one.
3:52So cells like these have some
clever tricks up their sleeve
3:55to help them navigate their surroundings.
3:57For example, they can produce their own
3:59chemical signals for other cells to follow them.
4:02By working together like this,
these cells don’t have to rely
4:05solely on a signal coming
from the end of the maze,
4:08and they can also navigate
even more complex paths.
4:11In fact, in 2014, one group of researchers created
4:14a competition to push cell
navigation to its limits.
4:18This was the “Dicty World Races”,
named after one of the cells
4:21contestants could use: an
amoeba called Dictyostelium,
4:24which biologists often use as a
model organism in their research.
4:28You’ll note that’s not a human cell,
4:30but other contestants chose to race
a human blood cancer cell, instead.
4:34The actual maze was set up to
imitate the cells’ natural habitats,
4:38and fourteen teams each brought their genetically
4:41engineered cells to clear
it as quickly as possible.
4:44A group from the Netherlands
were declared the “winners”
4:46after their Dicty cells took
48 of the top 100 race times.
4:51It’s a charming story from the world of science,
4:53but this wasn’t just fun and games.
4:55As I mentioned before, some teams
were working with cancer cells.
4:58And understanding how they
move through tissue is critical
5:02if scientists want to develop treatments
to stop cancers from spreading.
5:05So far everything I’ve mentioned
has at least been alive,
5:08with mechanisms to sense their
surroundings and react to them.
5:12But can anything non-living solve mazes?
5:15Well, sure. If you release a gas into a maze,
5:18by simple diffusion and random chance,
5:20some of the particles will
eventually reach the exit
5:23as the gas explores every single path.
5:25That is boring though.
5:27So instead, say hello to the maze-solving liquid
5:30that can traverse a maze without
going down any wrong paths.
5:34In 2018, a research team
filled a small maze with milk,
5:38then put a blob of food dye at the entrance.
5:41When they added a drop of liquid
soap to the blob of food dye,
5:45that blob suddenly spread through the maze,
5:48but only down the path that led to the exit.
5:51This apparent magic trick relies on
a phenomenon from fluid mechanics
5:55called the Marangoni effect, which
is a consequence of a much more
5:59well-known phenomenon called surface tension.
6:02When you’ve got some amount of liquid,
6:03all the molecules in that liquid are
pulling on each other a little bit.
6:08For most of the molecules, they’re
completely surrounded by other molecules.
6:12So the pulling comes from all directions
equally, and basically cancels out.
6:17But at the surface, that pulling is lopsided,
6:20so the molecules are constantly
feeling a slight tension.
6:24Hence, “surface tension”.
6:25As for how this maze experiment worked,
it’s because soap is a surfactant.
6:31That means it lowers the nearby surface
tension when it’s added to another liquid.
6:35Milk also naturally has trace
amounts of its own surfactants,
6:39but no, that does not mean you dairy
lovers are constantly drinking soap.
6:43Imagine you’re a blob of food
dye floating in a milk maze,
6:46and some soap gets plopped next to you.
6:48Suddenly, you have a neighbor
that isn’t pulling on you
6:51quite as hard as you were used to.
6:53So you start moving in the opposite direction,
6:56toward the milk that’s pulling on
you more strongly by comparison.
7:00But what happens whenever you
reach an intersection in the maze?
7:03Well, you’ll be drawn toward the
path with more surface area ahead.
7:07That’s because the scientists designed your maze
7:10so the exit features a large reservoir of milk.
7:13In other words, the correct path to
take…compared with all the dead ends…
7:18has a much bigger surface area.
7:20And since the amount of surfactants
in milk is low compared with the soap,
7:25a path with way more surface area
creates a much lower surfactant density.
7:30And remember, you as a blob of dye are
being pulled away from the surfactants.
7:35So you get pulled toward the exit,
no thoughts needed on your part.
7:39Just the laws of physics.
We’ve got two maze-solvers to go,
7:43but just like all this science, we need funding.
7:47This SciShow video is supported by Brilliant:
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8:37Our non-living maze solvers
only get weirder from here.
8:41Next up is the stuff electricity
and fire is made of: plasma.
8:45In 2002, a UK-US team etched a
thumbnail-scale maze into a glass chip,
8:51filled it with low-pressure helium gas,
8:54and ran an electric current
through the whole thing.
8:56The aim was to observe a well-known
effect called a glow discharge,
9:00where the current turns a gas into a plasma.
9:03The resulting plasma is full of charged
particles called ions that are excited,
9:07energetically speaking, and want to emit some of
9:10that energy to stop being so excited.
9:12When they do, they let off a distinctive glow.
9:15If you’re wondering, “Is this how some
neon lights work.?”, the answer is “Yes”.
9:19But here’s the thing, you may remember
from school that an electric current
9:22will always try to follow
the path of least resistance,
9:26which almost always means the shortest distance.
9:29So if you put your two electrodes
at the entrance and exit of a maze,
9:33the current will only form glowing plasma
9:35along the shortest path through that maze.
9:38Like with the food dye, the laws
of physics force it down one path.
9:42But unsurprisingly, the specific laws of
physics that apply here are different.
9:46When you switch on the current in a circuit,
9:48an electric field spreads
over it at the speed of light.
9:52Any charged particles in the circuit will
react to this new field and move around.
9:57But since they’re charged particles,
they’re also emitting their own tiny fields,
10:02so their movement winds up
changing the larger field, too.
10:05And on paths with more resistance, the charges
10:08rearrange themselves to cancel
out the flow of current.
10:11This feedback loop happens at near light-speed,
10:13so the current is able to
explore every path in the maze
10:17almost instantly when it’s switched on.
10:19And this exploration and
re-arranging of charges always leaves
10:23only one path for the current to
follow: the path of least resistance.
10:27Of course, the scientists behind
this plasma maze didn’t stop with
10:30a mere explanation of the
science, and a simple maze design.
10:33To one-up themselves, the team etched
a road map of London onto glass.
10:37By putting electrodes at
different points on the map,
10:40they could make the plasma show the
shortest route between any two locations.
10:44So, if you want to know the
fastest route from Victoria Station
10:47to Imperial College London, and your
friendly neighborhood slime mold
10:51is on vacation, just ask your friendly
neighborhood glow discharge plasma, instead!
10:56And finally, let’s talk about how one group of
10:58Italian researchers got a
beam of light to solve a maze.
11:02Here, the centimeter-scale maze was
made out of a special optical material,
11:06with branching pathways etched
into it for the light to follow.
11:10The light could then bounce
between different pathways
11:12in ways that looked a lot like
choosing paths to take in a maze.
11:16But because the light is doing all that bouncing,
11:18it winds up traveling slower than
your standard “speed of light” speed
11:23you wind up memorizing if you go to
college for astrophysics or whatever.
11:26That meant the team could test to see how fast
11:29the light could find its way out of
the maze under different circumstances.
11:33Because just like letting
a bunch of gas into a maze,
11:35light would eventually make
it to the end simply by
11:38bouncing around randomly
between the different paths.
11:41But could the light be coaxed into
traversing the maze more efficiently?
11:47By exploiting special quantum
properties of the light,
11:50like its ability to take
multiple paths at the same time,
11:53the researchers could shorten the time
it took their light to reach the exit.
11:57But interestingly, they
found that they could improve
11:59the light’s maze-solving abilities thousands
of times over if they also introduced
12:04just a little bit of “noise”
to the circuit…in other words,
12:07effects that destroy the quantumness of the light.
12:10To be more specific, they made sure
their etching process wasn’t perfect,
12:14meaning the light waves couldn’t
bounce as cleanly through the material.
12:18In the end, the fastest solves were made by light
12:21that had about a ten percent
chance of losing its quantumness.
12:25The team speculated that,
when there was no added noise
12:28and the light was fully free to be
in multiple paths at the same time,
12:32the light might wind up getting
stuck in certain places.
12:36By adding a small amount of
quantum-destroying noise,
12:39it might serve as a sort of ‘kick’ to
push the light down a certain path,
12:43so it could continue its journey to the exit.
12:45Once again, this wasn’t all just fun and games.
12:48The researchers speculated that this could explain
12:50how photosynthesis works so
efficiently, since that also involves
12:54light bouncing down a complicated
network of cellular stuff.
12:58So the next time you find
yourself needing to solve a maze,
13:00just remember that you have a lot more
options than your standard tricks,
13:04like “put your hand on the wall
and don’t let go until you’re out”
13:08or “use this ball of string from a
princess who fell in love with you”.
13:11Ok, now somebody needs to
do a retelling where Ariadne
13:14gifts Theseus a pet slime mold.
13:16I would read the heck out of that.
