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While watching a Walking Dead commercial I saw a vast number of zombies walking in a single uniform march in one direction. I wondered why (not knowing the show) and could only presume they heard a sound and therefore were all walking toward said sound. However, this was a large army of zombies, surely the ones in the way back didn't hear the same sound, so perhaps they just heard the moans and footsteps of the zombies in front of them and were following their movements.

This idea got me excited, I wondered if it were possible to create a story where all zombies, given enough time, could come together to the same location by following the loudest sound possible. After a certain number come together surely the sound of (a million?) moaning zombies would be the loudest thing around. Like cosmic debris in orbit fusing together after being pulled toward one another's gravity, I want the zombies to pile up in an ever growing mass, where at the end of the story a single (or close as possible) nuclear strike could wipe them out.

Question:
The only presumptions I want to make about the zombies is that they live forever aside from brain being damaged and that they move toward the loudest sound they hear.

What other presumptions about my zombies would I have to make to get as many of them as possible to the same place? i.e. should they hear a sound and walk forever in that direction or should they stop in the general area they think they heard it. I would think walking forever would be best to get the zombies out of remote locations, but I also want them to clump together which walking forever might impair.

Is it feasible to presume they could all end up in the same location given enough time or is it just too improbable that certain zombies would ever find the "main clump". Obviously they couldn't cross the ocean so is 6 continental clumps the best I could hope for?

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    $\begingroup$ plot device, only writer understands how his/her zombies work. $\endgroup$ – user6760 Sep 20 '17 at 2:51
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    $\begingroup$ Now I'm imagining setting up a large stereo PA system and playing a pure sine wave, and getting a crowd of zombies to show the interference patterns like in physicsclassroom.com/class/sound/Lesson-3/… . $\endgroup$ – Pete Kirkham Sep 20 '17 at 11:23
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    $\begingroup$ Obviously they couldn't cross the ocean - why not? They don't need air to breath, they'll end up looking pretty bloated but while floating they'll drift with the currents (especially if they're wearing life jackets), once they sink they'll shamble across the ocean floor (edit - also explained in Word War Z as @Ash answered). $\endgroup$ – Darren Bartrup-Cook Sep 20 '17 at 13:24
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    $\begingroup$ I think that's the idea. As they don't breath their airways, lungs, stomach - anywhere that water can get in will just fill up and create that equilibrium. $\endgroup$ – Darren Bartrup-Cook Sep 20 '17 at 14:05
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    $\begingroup$ Zombies appear to act like hive/flocking animals. There probably doesn't need to be an explicit motivator. $\endgroup$ – Dave Newton Sep 20 '17 at 14:44

14 Answers 14

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Only if this is a comedic story. Imagine a zombie trapped between Japanese bamboo water fountain and a signboard of a shop moved by wind.

Also in India between tiger and elephant. And walking toward ocean during the tide and away when it's gone.

Also if a zombie hear a louder but shorter sound what does he do? He act like Scooby-Doo or follow quieter sound and only stop when hearing to louder but less frequent one?

How zombie would follow singing bird?

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    $\begingroup$ May I humbly but enthusiastically suggest that you narrate a video, using exactly the text of your reply, with an actor depicting the described zombie. I am clicking that up arrow many times, even though it just cycles between 0 and 1. I will stop at 1 when I have had enough. $\endgroup$ – Willk Sep 19 '17 at 15:45
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    $\begingroup$ I don't think zombies understand sign language, so the answer to your last question is no. $\endgroup$ – wizzwizz4 Sep 20 '17 at 7:05
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    $\begingroup$ Don't forget that some zombies will be deaf. $\endgroup$ – G. Ann - SonarSource Team Sep 20 '17 at 8:33
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    $\begingroup$ @G.Ann-SonarSourceTeam Well, the deaf ones should DEFINITELY learn sign language... I guess they'll follow the bird then? $\endgroup$ – Shaamaan Sep 20 '17 at 12:14
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    $\begingroup$ @wizzwizz4 "sign language" LOL. I hope the answer is not edited so your comment's humor does not get lost. $\endgroup$ – user11864 Sep 20 '17 at 14:36
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There is a phenomenon that Max Brooks refers to as a "chain swarm" in World War Z, basically a zombie hears a sound and moans while in pursuit of it, a zombie half a mile away hears the moan and follows the first zombie because the moan is louder than the local ambient sound of wind in the trees or whatever and another hears zombie two and so on until zombies are pouring in from everywhere, not in pursuit of the sound that has attracted them so much as they are in pursuit of each other. In the book armies use loud sounds like rock music to get such swarms started so they can clear out large areas in one sweep. There is a terrible movie that shares a title with the aforementioned, and excellent, book in which they show a siren in a stadium being used for the purpose of concentrating zombies for a missile strike, this is never done in the book but it would work.

The scenario you describe would need a sound so loud that the zombies in the local area wouldn't actually be able to locate it because they'd have burst eardrums, if you want it to be heard at the thousands of miles range of a continental scouring beacon. A viable alternative might be to drop a series of smaller noise stations across the area and by switching them inwards draw zombies towards some central point for extermination. In theory you could eventually dragnet all the zombies on connected landmasses together in two clumps, one including all the zombies in Africa, Asia, and Europe, the other all the zombies in the Americas, islands, including Australia, must be cleared separately as must anywhere above the snow line and in the polar regions because of zombies that have frozen into immobility.

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    $\begingroup$ Don't get me started on that **** film.... everyone could start singing and clapping behind a high wall, because being quiet for months has worked so far but we'll have a big-ol sing'along cos Brad Pitt's turned up. $\endgroup$ – Darren Bartrup-Cook Sep 20 '17 at 13:29
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    $\begingroup$ I liked your answer except for the part that said "islands... must be cleared separately." Such a comment shows no concern for the preservation of the zombie specie. As founder and president of PETZ, I must condemn such nonsense. $\endgroup$ – user11864 Sep 20 '17 at 14:41
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    $\begingroup$ @DarrenBartrup-Cook If you treat the movie as a harebrained scheme from the Panic phase of the war and pretend that it ends with him getting eaten in Cardiff it's not so bad, only terrible as opposed to "oh God, kill me, kill me now". $\endgroup$ – Ash Sep 20 '17 at 18:32
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    $\begingroup$ @AgapwIesu As amusing as that comment may be to my inner sadist you are a terrible person to say anything of the sort. $\endgroup$ – Ash Sep 20 '17 at 18:41
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    $\begingroup$ actually the burst eardrums might not be such a problem (as long as any humans in the vicinity have appropriate hearing protection)... by the time they get close enough to the lure siren that their eardrums burst, the vibrations through the air should be strong enough to transmit sound without aid of an eardrum. This hearing site speaks of a hearing aid that works by acting directly on the mastoid bone, bypassing the eardrum (or lack thereof), which extremely loud sounds may do on their own. $\endgroup$ – Doktor J Sep 21 '17 at 16:27
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Probably not.

There are many loud sounds. When near a loud sound you won't move to a louder sound unless it is sufficiently close. It is rare that there will be a clear gradient of increasing volume. What's more likely to happen is that there will be many local maxima that zombies will congregate towards.

Eventually these congregations will become large enough that the sound of the zombies is louder than any external sound preventing any zombies in the cluster from leaving the cluster.

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    $\begingroup$ Thanks, I feel like this is probably the most realistic answer. $\endgroup$ – DasBeasto Sep 19 '17 at 18:57
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    $\begingroup$ So basically you'll get a lot of clusters, but not all the zombies in one place. Imagine a million marbles on a surface with a lot of dents. They'll all roll downhill, but not necessarily all the way to the lowest dent. Most of them will get stuck in some dent that's higher but still a local minimum, so they'd have to travel uphill first to get to the universal minimum. $\endgroup$ – MissMonicaE Sep 19 '17 at 20:06
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    $\begingroup$ If they don't stop moving once they piled up they of course will try to move towards the center but if there's another loud sound in one direction then they might aim a little bit more towards that so on average the pile slowly moves towards another pile. $\endgroup$ – Christoph Sep 20 '17 at 6:54
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    $\begingroup$ Depends a bit on how literal you want to take, "given enough time". Brownian motion or quantum uncertainty can in principle roust a zombie out of its local minimum. On a shorter timescale, geological changes could tend to combine local groups over mere millions of years ;-) $\endgroup$ – Steve Jessop Sep 20 '17 at 13:43
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+1 sphennings. To illustrate with a thought experiment, just consider two factories (A & B) a few blocks apart. Even if A is somewhat louder than B, sound intensity declines with the square of the distance; so not too far from B, B will be the loudest sound. Draw a line from A to B (let us say it goes from left to right), and at some point on that line, everything to the left has A being louder, and everything to the right has B being louder.

Draw another line at right angles to the first, through that point: All zombies to the LEFT of that entire line will be attracted to A, all zombies to the RIGHT of that entire line will be attracted to B. Nothing will change that. The same happens when there are many loud sounds; the lines create borders for a "cellular" diagram with Zombie concentrations in the center.

In fact, it is almost precisely how cell phones work: Each phone is always listening for the loudest cell tower (comparing signal strength). If it gave you a direction and you moved toward the tower, it will always be the loudest tower to your phone. It will never migrate to another.

But phones (or zombies) already closer to some other tower will move toward those towers. The populations cannot meet if they must move to the loudest.

(Phones are forced by their owners travels to move away from one tower, but then that tower eventually stops being the loudest and some other tower that the phone is moving toward becomes the loudest, if that persists then the phone switches to the louder tower.)

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    $\begingroup$ Very nice easy to understand ELI5 answer, makes it pretty clear that it would be impossible to overcome naturally. However it also gives me ideas on how to make it work. @Ash recommended smaller noise stations that you "programmatically" use to draw them in to single location. Cell towers are already dispersed somewhat evenly and have a power supply. May just retrofit them with noise emitters for my story (and hand-waive "dead zones" with no towers) $\endgroup$ – DasBeasto Sep 19 '17 at 19:04
  • $\begingroup$ I don't feel like this answer accounts for the fact that a zombie moving towards a point increases the volume of that point. $\endgroup$ – Reinstate Monica --Brondahl-- Sep 20 '17 at 10:34
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    $\begingroup$ One picky point with this explanation. If the sound does drop off as inverse square, then the line of equal volume (isophon?) will not be straight. Instead it will form an ellipse. One interesting corollary is that, if A is louder than B and these are the only two sources of sound then there are points on the far side of B from A where zombies will still head towards A before getting close enough to B that it dominates. $\endgroup$ – Alchymist Sep 20 '17 at 13:51
  • $\begingroup$ @Alchymist I'll give you a point for that. Wouldn't it have to be a parabola, though? on the line between A & B with A to the left of B, everything to the infinite right of B 'belongs' to B. There is no closure for an ellipse. $\endgroup$ – Amadeus-Reinstate-Monica Sep 20 '17 at 15:40
  • $\begingroup$ Regarding "Nothing will change that": Wind heavily affects the propagation of soundwaves. $\endgroup$ – Nobody Sep 21 '17 at 13:56
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From a mathematical perspective, I would expect them to congregate at the local maxima of sound, rather than the global maxima. For example, if you have all cities with sirens going off, the closest zombies would go there, but zombies in a different region would go to a different city.

Zombies follow a greedy algorithm, which means they won't always find the loudest noises, unless you build your world in a way that makes greedy algorithms optimal.

For example, in a world where all sound is produced by humans and zombies, the greedy zombie algorithm would cause them all to congregate to one place under these conditions:

  1. All humans stay in cities (causes zombies to congregate)

  2. Zombies stop making noise when there is no food source (prevents zombies from staying in one place).

  3. Cities only make noise when there are humans to run them (consumed cities go silent, preventing zombies from staying in one place).

  4. Zombies make noise when they see people (causes zombies to congregate)

  5. One city is much more defensible than all the others (last city survives long enough for all zombies to arrive)

Of course this doesn't work by itself, since zombies cannot hear across the globe. You will need to get creative with the way the world is built. If you model it as an undirected graph, you could then find 'sound landmarks' of varying scales, and cull the graph in a specific order, so that the zombies converge to a single point.

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Sound is generally very localized and even massive amount of zombies would not make enough sound to be heard a couple miles away. It's conceivable that a very loud sound such as thunder can gather all zombies within a couple miles but just a bit further and other localized sound could overshadow it.

If you imagine a stadium full of people during a football game or something cheering as loud as they can, even though there are tens of thousands of people, if you go down the street a couple blocks from the stadium, the traffic would be louder than the people in the stadium. This means even a ball of hundreds of thousands of zombies would not have that large of a radius to gather more zombies.

What will also happen is that zombies will gather into a very compact area and the effect all the zombies trying to get towards the center eventually reach a point where flesh and bones can no longer sustain the tension and stress and compression of the mob. Even though the zombies are immortal, it would be expected that the middle of a very large gathering will liquify as the zombies are trampled and crushed by other zombies. As such, most mobs will be unlikely to move very much as they reach a sort of equilibrium as the pressure of zombies outside are equalized by the flow of the liquid zombie mass inside.

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    $\begingroup$ "And then the zombies mobbed so densely that they started undergoing fusion..." $\endgroup$ – Mike Caron Sep 19 '17 at 21:07
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One season of Walking Dead had an old quarry that had slopes steep enough that Walkers could not climb out, but not sheer enough to cause damage from falling in (all Walkers appear to be able to walk rather than crawling around on shattered legs).

The roads in and out of the quarry were blocked, so you had a "roach motel" scenario where they can get in but not out. The sounds of the trapped Walkers (possibly echoing from the rock faces) attracted other walkers, who also became trapped.

This was a significant plot point about why a certain area was relatively free of Walkers.

And to be obnoxiously pedantic, you never see any zombies in the Walking Dead TV series. The non-existence of that word (and the zombie genre) is a conceit of the show to explain a lack of knowledge on how to handle them. Each group has come up with their own, generally descriptive, name for them (Walkers, Biters...).

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Without re-iterating what a lot of people have said from a maths and physics perspective, the zombies will conform to local maxima.

That being said, there are loud dynamic moving sounds factors like thunderstorms/earthquakes which behave as catalysts to "joining" two local maxima as a result of expressible/model-able random functions.

Given sufficient time, storms could run all the necessary paths to "herd" all the local maxima together.

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    $\begingroup$ For man-made measures to reduce the sufficient time required, "herd" your zombies repeatedly with low-flying loud planes. $\endgroup$ – Nikola Radevic Sep 20 '17 at 8:49
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Likely not - because sounds get quieter with distance. If they're responding to sound intensity, then it's an inverse square law (if they're responding to sound pressure then it's a straight inverse).

Imagine at two continuous noises -- a medium-loudness sound at A and a very loud sound at B. To a listener halfway between A and B, B is louder, but to one somewhat nearer to A, A is louder. The loud music at the party a block away might be very intrusive to their next door neighbors but the people a block away can't hear it over the sound of a TV.

So an initially scattered set of zombies in a large region of point sources of continuous sound (that they could get close to) would end up concentrated in many locations, each drawing on its local zombies in a patch up to where it was equally as loud as another sources. In a simplified situation with known loudness, one could make a map of the boundaries from which the zombies would be drawn to each source by identifying curves of equal loudness between nearby pairs of sources.

Here's a toy example:

Dots indicating zombies with 5 point sources of noise; image 2 shows which zombies hear which source as loudest

The left side of the picture shows 1000 zombies initially scattered over a square region. The five coloured spots show continuing point sources of noise of varying loudness (green is loudest, then blue, red, brown and purple is the quietest). On the right side, the zombies are coloured by which point source has the higher sound intensity at their location. If they all move directly toward that source however, three of the zombies marked in green (the three pointed to by the yellow triangle near the very top) will pass close enough to the purple source - the quietest one - that it will sound louder than the green one, and presumably be "captured" by the purple source instead.

That situation will be somewhat altered by the separation of loud noises in time -- not all noises occur together. That may lead to some clumping on a larger scale as occasional briefer but quite loud noises occur. However the decreasing effect of sound with distance still enforces local clumping. I might hear a factory explosion over a couple of kilometers but probably not much more than that -- and then other, subsequent sounds may distract zombies before they even get to that distant loud noise that finished before they got there.

As long as sound was the main cause of them gathering (we're not concerned about a keen sense of vision or smell, say), in the end you'd get zombies collecting in groups, for sure, but there would be many such groups rather than one.

[If you added that the groups eventually wandered away from "unproductive" noises, but tended to stick together in a herd as they moved, then such wandering bands might lead to some substantially larger-scale clumping - armies on the march, as it were as they followed whatever instinct led them when there wasn't a new noise to head toward.]

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Most answers seem to ignore, that sources of sound are not necessarily constant in loudness or even constantly existing. An automated factory can make some constant noise until it breaks down. Thunder may be louder than all other sources in an area but is only heard very shortly. A Train passing by my draw zombies into a certain direction.

Assuming zombie behaviour is such, that they don't get crushed when gathering in very large groups, we still have a problem. Thunder, trains and other temporary or moving sources of sound may draw them together, but when the sound of the zombies adds up, it will at some point be loud enough, to drown out every other sound. When you have several hundreds of thousands of zombies (still much less than a large city) moaning and groaning and rattling things, you will reach a point, where even a thunderstorm close by will be drowned out by the sound of the horde itself.

You would have to have very loud things to move that horde.

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  • $\begingroup$ That depends on how loud you believe your horde of moaning zombies can become A loud rock concert is estimated to be 120db - ref A clap of thunder typically registers at about 120 dB in close proximity to the ground stroke - ref $\endgroup$ – Nikola Radevic Sep 20 '17 at 8:56
  • $\begingroup$ At bigger rock concerts, the crowd can grow so loud, that you can't hear the music anymore. That means, the humans (and zombies are like humans in that matter) can be as loud as thunder, when a lot of them gather in point. A big concert has still a lot less people than a big city. So I think it's unlikely that there is much noise that can be heard against a few million zombies, even if they don't cry at the top of their voices. $\endgroup$ – Till Sep 20 '17 at 9:55
  • $\begingroup$ Actually, I think a horde that is the main source of sound in the area can easily be moved, because it sits at an non-stable equilibrium. Set off a firecracker at one edge of it: a few nearby zombies move towards the firecraker, and drag the centre of mass of the horde slightly over, and it regroups around the new centre. A thunderstorm, which lasts longer than a firecracker, isn't completely drowned out by the horde, it actually adds a little noise to one side of the horde. Those in the middle, previously with no reason to move, now hear more noise on one side than the other, and move. $\endgroup$ – Steve Jessop Sep 20 '17 at 13:47
  • $\begingroup$ That said, if a horde manages to find its way into some kind of acoustics that make its equilibrium more stable, then it'd be much harder to move even a tiny amount. A horde filling a cave, perhaps: to entice even one zombie out, the one standing on the edge, you'd have to make a noise outside the cave mouth that's loader than the noise emerging from the cave. $\endgroup$ – Steve Jessop Sep 20 '17 at 13:50
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Well, I don’t claim to be the great specialist about sound or zombies either, but here is my answer to your question part which is based on the logics of mine. It might have some holes, but I’ll try to concentrate on main points of the way I see this situation. This said, I have to say that I do not think those zombies have a chance of being concentrated at one same point unless being lead there manually or affected by some sort of magic/spell or collective consciousness. Here is why:

Firstly, if they get attracted by the sound, that means that any possible sound – i.e. wind playing with trees or plastic bag, rotten building falling apart, ocean waves or waterfalls, etc. – will catch their “attention”.

Secondly, you say: “Obviously they couldn't cross the ocean so is 6 continental clumps the best I could hope for?” – why not? Well, technically they will be carried away by the streams instead of “walking the ocean bottom” or swimming, but this will make all of them go to certain points where those streams pull stuff they carry. Unless sea life will eat them out before they reach the place, the streams carry everything to.

Also as far as I remember zombies do not make sounds themselves unless we talk about the sound of footsteps or bumping into something.

Finally, you said: “The only presumptions I want to make about the zombies is that they live forever aside from brain being damaged…”. In your intro part you mentioned WD. In case it is the universe like WD then zombies do not live forever (unless magic, but that’s a different world). As the tissues of their bodies getting more and more rotten they will start falling apart and as their brain (or what’s left of it) is rotting as well – they will “die” eventually after a while (unless again – magic, which will turn them into ghosts, wraths and so on).

Plus the statement of “… they move toward the loudest sound they hear” also has some holes. Ok, they move. But simply moving towards something making a sound wouldn’t make zmbs any kind of a problem (unless traffic jams). What I mean is that they need some sort of a pointer to mark a target to attack. If the sound is the only marker, they are capable of recognizing (which makes it attack marker as well), those zmbs will eventually tear each other to pieces without any need for humans to interfere.

Thank you for reading and pardon for possible mistakes. All the best.

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If zombies simply migrate toward the loudest sound around, they will indeed clump. The problem is that they will only clump into pairs, or small groups at most - since sound diminishes based on the square of the distance, when two zombies are next to each other and moaning the loudest thing around for either of them will be each other. They won't end up going anywhere.

It is far more sensible if, rather than simply progressing toward the loudest sound, zombies tend to position themselves at the average point between sources of noise. This will enable zombies to travel as a group, but will also allow them to "gravitate" toward other noise sources.

Most actual animals that behave in this way also have "quorum sensing" behaviors that prevent them from clumping up in oversized groups, as this would cause them to run out of food. If zombies don't have this, they will likely end up clustering together, at least up until the distance that the ambient noise overwhelms the sound of the zombie herds.

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You could do it with programable noise makers.

In effect you have rings of noise makers. You sound the outer ring first. Then turn it off, and sound the next ring in. Once the sound has moved in about 4 rings, you can start he outer one again. The effect is to create a "zombie sink" where any zombie who wanders into hearing range of the outer ring gets pulled into the centre.

The inner ring could have it's own phasing with sound going around the ring. This results in zombies that endlessly shuffle on a circular track.

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The answer is not. It is impossible in the real word due to its high variance.

There is an easy way to think of it as about a 3-dimensional plot, where 2 dimensions are zombies coordinates and third dimension is the loudness level. So zombie will always go to a louder point every distinct moment of time. But the problem is, when a zombie reaches a local maximum sound, they need to go to a slightly smaller noise level to find a louder point. But the problem is zombie won't go to a quieter point on the plot. So zombies will always be stuck in local maximum points. You can also expand loudness level to zombie attraction level(sound, movement, light and maybe smell together) and add time dimension, but due to real world variance, it's still impossible to have a strictly monotone(correct me if there is a wrong word in English) function in real world.

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  • $\begingroup$ This answer is based on the premise that loudness is stationary. However, it is certainly possible for loudness to change. Also, loudness of an event depends on the distance to the listener. $\endgroup$ – M.Herzkamp Sep 20 '17 at 10:33

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