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Picture a band of happy campers, literal campers, sitting around some fires.

Suddenly they feel their inner-ear "filling up" and after mere instants the ears begin popping, as if they were inside a tunnel, some of them get nosebleeds, some lose balance and fall down if they are standing or back if they are sitting, all feel pain and nausea.

Fairly close by are more of the group, sitting around their own fires, but they feel perfectly normal. They see those suffering and rush to help, and as they approach them they too fall victim to the bizarre circumstances.

What could cause such a sharp, localized event?

The skies are perfectly clear, the conditions are artificially created.

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    $\begingroup$ Reminder to close-voters: The problem cannot be fixed if the OP is not made aware of it. $\endgroup$ – Frostfyre Oct 5 '17 at 14:56
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    $\begingroup$ It's a good idea to wait at least 24 hours before accepting an answer so that people from every time zone get a chance to weigh in. $\endgroup$ – sphennings Oct 5 '17 at 15:40
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    $\begingroup$ If you slowly and sneakily lower a non-reflective glass dome over the campers, you can then mess with the air pressure inside pretty easily. However, I don't think that fits with the specifics of the question, especially how the other campers rush to help and don't run into a glass wall. $\endgroup$ – BrettFromLA Oct 5 '17 at 21:40
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    $\begingroup$ Upvoted because it is a freakishly cool concept. I can see an Xfiles type show starting with this. $\endgroup$ – Willk Oct 5 '17 at 23:54
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    $\begingroup$ Any rapid and severe change in pressure would result in an equally rapid and severe movement of air (which is another term for "sharp, loud, bang". $\endgroup$ – RonJohn Oct 6 '17 at 3:05

13 Answers 13

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None of these are really plausible, may as well list why not.

1 - Rapid weather front. You could have a low pressure system rapidly replaced by a high pressure system, but the high pressure system wouldn't bring a high enough pressure to cause those symptoms and there will be a noticeable boundary between the two fronts with likely high winds and a rapid weather shift. I don't think anything weather wise could cause this.

2 - Weaponry. Put energy in the air above and put pressure on the air below. The weapon would likely need to be massive and hard to miss, and the wave of pressure would be very noticeable. It would not remain static and there would not be a boundary.

3 - Alien tech? I guess you could have a gravity well that puts this pressure and I could speculate all I want there, but all three of these answers suffer from one big problem.

Your key issue here is ultimately equilibrium. Air under high pressure is going to be forced into the low pressure area around it. Even if you get an extreme localized pressure event, the high pressure you just caused is going to push air into the surrounding low pressure area. This means the area surrounding isn't going to be to be perfectly normal, it's going to be windy. If the high pressure is high enough to cause these symptoms and the surrounding area isn't, it's going to be extremely windy and the pressure will rapidly dissipate.

With that in mind, option 4...still in the alien tech range.

Semi permeable dome. An alien force field is erected around the small group and the area is pressurized. Air can't make it through this dome / force field, however solid matter can. Well beyond any technology we can speculate and may as well 'just be magic'.

Edit:

As an alternative...a high frequency sound could be emitted from a single point. If intense enough it could cause some of these effects...and being a such a high frequency it shouldn't have too far of a range dissipating quickly. I'd ask a separate question if you want to pursue that.

A high electric current might do this as well...flowing electricity induces electricity in objects around it, including people to some degree. Admittedly you'd have anything metal basically arcing with electricity (I've had a similar experience under high voltage power lines in rain that managed to cause electric arcs between the metal of my umbrella).

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    $\begingroup$ The winds would almost be instantaneous and the pressure would likely dissipate in one giant wave before ill effects from pressure would even set in (the pressure wave this causes will have more ill effects than being exposed to the high pressure would). Refer to MichaelK's explosive decompression reference for more info...there would only be a second or two where that high pressure bubble would exist. $\endgroup$ – Twelfth Oct 5 '17 at 15:25
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    $\begingroup$ The sound would cause the symptoms, not the pressure. The second you cause a high pressure 'bubble' of any form that has free interaction with low pressure, the system will seek an immediate balance. Pressurize a pop bottle...it has the pressure because the air is held by the plastic bottle. Open the bottle and the pressure releases in seconds...and this second time frame is a longer period as the pressure can only go out the bottle opening, in open atmosphere it goes all directions simultaneously in seconds. $\endgroup$ – Twelfth Oct 5 '17 at 15:30
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    $\begingroup$ Perfect! With a bit of side-fiddling high frequency sound will work. $\endgroup$ – shieldedtulip Oct 5 '17 at 15:34
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    $\begingroup$ @shieldedtulip That looks closer to what you would want here. Pressure in the atmosphere is incredibly difficult to manipulate, sound and frequencies is a much easier realm. Heh, I like it when the answer to a question is an alternative working theory. $\endgroup$ – Twelfth Oct 5 '17 at 16:42
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    $\begingroup$ As it often happens when creating a fantasy world, or at least when I'm doing it, the consequences come before the causes. I knew what was I wanted, just not what could cause it. $\endgroup$ – shieldedtulip Oct 5 '17 at 17:08
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Magic

The answer is: you need magic to make it happen, no matter if you mean Arthur C. Clarke brand of magic, or plain old Fiddling With Reality Through Supernatural Means™ type of magic.

No really, that is what you need. Unless there is a very noticeable whirlwind surrounding the victims, there is no way to make this happen. Just as you cannot have a vacuum bubble spontaneously form in the middle of the ocean without water instantly collapsing on it, nor can you have a low pressure bubble form without the surrounding atmosphere collapsing into it. No matter what caused it... unless there is some kind of physical barrier to separate the low pressure area from the high pressure ditto, there will be a noticeable rush of air as the pressure is normalized within less than a second.

For example: when the aft bulkhead of Japan Airlines Flight 123 collapsed, the passengers reported a bang as the air pressure inside the cabin equalized with the outside ditto. Not a slow hiss or a gentle transition, but an explosive decompression. The transition was so violent that it ripped the vertical stabilizer and rudder right off of the aircraft.

So without magic, this is what would happen to your protagonists.

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  • $\begingroup$ You mean like a failed scientific experiment? Or a weapon of sorts. I don't think magical magic exists in my world. $\endgroup$ – shieldedtulip Oct 5 '17 at 14:23
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    $\begingroup$ No, I meant what I said: magic, something — be it future technology or supernatural means — that is entirely impossible to achieve today. You cannot have a localized low pressure area with such profound effect on the people inside it, not without something very tangible and noticeable that is the cause of it. You cannot achieve this any more than you can ask the sea to spontaneously part for you and leave a void in the middle of it without some supernatural help. $\endgroup$ – MichaelK Oct 5 '17 at 14:31
  • $\begingroup$ @shieldedtulip: I'm with MichaelK. To do this you basically need to change the laws of physics. So, either magic, which I think you don't want, or "advanced aliens" did it. Have the campfire set off some ancient alien artifact buried beneath it, or something along those lines. $\endgroup$ – Binary Worrier Oct 6 '17 at 7:40
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    $\begingroup$ I actually asked a question on how magic could cause changes in air pressure not too long ago; you might find the answers of interest. $\endgroup$ – walrus Oct 6 '17 at 10:20
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    $\begingroup$ @shieldedtulip Yes, or a space time singularity just above the one group that was connected to deep space. It would cause a significant wind towards it but would certainly drop the local air pressure. It would be invisible in the night but show up as a region of night sky after dawn :-) $\endgroup$ – KalleMP Oct 8 '17 at 4:48
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The only known thing I can think of that would create that kind of sharp rapid drop in pressure is the backwash from a very large explosion, after a thermobaric weapon like a fuel-air bomb stops burning it leaves a vacuum which collapses and sucks the air out of the surrounding landscape. The pressure difference between camp sites in this case would be created by some kind of terrain shadow effect, where in the campers on the high ground are exposed to the draw effect but not those lower down behind a ridge. The thing is the campers are not going to be particularly happy before hand, thermobarics are extremely loud and I'm not sure but I think the ground would be on fire from the radiant heat if you were close enough for the vacuum to cause that much damage.

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  • $\begingroup$ Hmmm... need to come up with a thermobaric explosion without the thermo part of it I guess. $\endgroup$ – shieldedtulip Oct 5 '17 at 14:37
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    $\begingroup$ Maybe, maybe not, like I said I'm not sure about the radiant burn range, but you would definitely need a reason that they didn't notice the very loud bang. Actually it's more of a roaring noise but it is extremely loud. $\endgroup$ – Ash Oct 5 '17 at 14:43
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    $\begingroup$ @shieldedtulip The explosion comes before the vacuum so it has to have run it's course before the pressure shifts, even just the pressure shift itself is going to be really quite loud because sound is the change in pressure of the air around us as interpreted by the ear. $\endgroup$ – Ash Oct 5 '17 at 14:52
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    $\begingroup$ @shieldedtulip You'd need to do more reading than I've ever committed myself to on the subject to get some specificity on the topic in terms of fine-tuning explosion size versus post blast vacuum versus audible range etc... $\endgroup$ – Ash Oct 5 '17 at 14:56
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    $\begingroup$ @N2ition They would have difficulty breathing if the effect was sustained and severe enough. Not sure about that, that may or may not be possible, per my comment to shieldedtulip I don't know enough about the practical limits of thermobaric weapons to make a fine-tuned model answer. $\endgroup$ – Ash Oct 8 '17 at 9:31
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Based on your question it sounds like you read, or will enjoy reading, the following discussion that more or less talks about this issue: https://hackaday.com/2017/09/25/cuban-embassy-attacks-and-the-microwave-auditory-effect/

Possible causes mentioned are:

  • The Microwave auditory effect: "popping" sounds inside the ear/head from rapid heating

  • Being hit by a proton beam

  • Sharp sound waves with high peak energy (relevant for the "popping" sounds, probably not so much the nausea part)

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When you say "localized," it sounds like you mean within feet or tens of feet. I'm going with that idea.

It's easy to create a drop in barometric pressure within a small enclosed space. Say, for instance, an empty water bottle. Suck the air out, put the cap on, the pressure inside is lower than the outside.

Option #1: Create a Container

Create a "container" and suck the air out. The "container" must be something people can pass through. A force field or a strong enough magnetic bubble would do the trick. Getting the air out without a local tube hooked to a vacuum pump might be interesting, but simply adding heat inside the bubble would also work if the heated air can be forced outside the bubble after which it can't get back in.

Option #2: Make the molecules all the same charge

If creating a container isn't your cup of tea, try turning the air molecules into magnets of all the same charge. The stronger the charge, the more they will repel from one another and the lower the resulting pressure. Bear in mind that nature abhores a vacuum, meaning the higher pressure air wants the get back in. So long as the tool you're using to charge the particles remains in operation, this won't happen. You'll likely need two "projectors" such that crossing the streams results in the effect of charging the molecules.

The downside to this particular idea is that the air molecules inside the body charge, too, but offhand the consequence is no different than standing in the field: lower air pressure. So, everybody's happy. Loopy... but happy.

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  • $\begingroup$ Maybe some weaponized form of a plasma speaker would work, but I am not sure if you can avoid the visible light and if being in the plasma would not be felt otherwise. $\endgroup$ – Nobody Oct 6 '17 at 9:09
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It is just barely possible, but it is a natural phenomenon.

Quantum fluctuations allow anything possible to occur. So, if the random motion of molecules just so happen to sort themselves into different pressure zones, then the campers could experience the suggested event. Once this happens, in accordance with normal probability (and the statistical laws we call thermodynamics) normal pressure distributions will be restored.

So, how improbable. Without exact details, and a fair bit of math, can't answer this. But in reality, I don't care -- Take the entire visible universe, with its expected lifetime, and there is essentially zero chance this would ever happen. Take 10^100 visible universes and expected lifetimes, still very close to zero that it ever happens once.

Supply an infinite universe though, and it happens literally all the time. Infinite is not just a big number. Comparing the energy of a supernova to a mosquito flapping its wings once, you get a really big number. Compared to infinity, really big numbers, including Grahams Number, etc. are essentially zero -- just like the probability of the proposed event.

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  • $\begingroup$ Flip a coin 1 Decillion times an infinite number of times and receive an infinite number of all head results ;) $\endgroup$ – Twelfth Oct 6 '17 at 16:20
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Targeted powerful low frequency waves (a bass canon)

If you aim very loud soundwaves, below ~10Herts, at a high volume at a group of people, this might result in those results.

Humans can't hear below 20Hertz, but essensially those are powerfull bass waves. When you play a regular song at a loud enough volume, you can feel the bass pressure go through you. If you increase this effect, your body will get messed up.

Sound works by creating a sort of air pressure wave, messing up your ears because the air pressure goes up and down. If it is extreme and properly timed it could, with a little handwavium physics, create a too big pressure inside your body, causing your eyes, nose and ears to bleed (the only way to relieve the pressure for your body).

The combination of not hearing it (which makes it confusing), your ears getting messed up (and thus your balance organs) and the physical power the basspulse can have you could get disorentied, making you fall over and nausius.

Not to promote a specific brand, but this page explains the basics.

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A Portal

A scientist is experimenting with a new portal technology that he has invented.

The portal is exactly the kind of thing you might think of when you hear that word: it is a wormhole-type object that connects two locations in space and allows for instantaneous travel between the two.

The scientist has opened one end of the portal in his lab, and the other end in the open countryside some distance away from the lab, in a location that happens to be close to where your camping group is hanging out.

The portal is effectively an open door between the two locations; any and all matter can flow freely between the two ends of the portal for the duration that it is open.

Unfortunately, the scientist hasn't factored for differences in air pressure between the two ends of the portal. The air pressure at his lab is different to that at the camp site.

This could be due to altitude or even just different local weather conditions. Whatever the cause, as soon as the portal is opened, the pressure difference immediately causes a rush of air moving from one end of the portal to the other as the pressure tries to equalise.

The scientist manages to his emergency cut-off button and close the portal pretty quickly, but there is significant damage to his lab as a result of sudden hurricane-force winds in an enclosed space. At the other end, the effects are less obvious, as it is an open space and the effect was short-lived, but people in the vicinity would experience a sudden pressure change, which may result in feelings similar to vertigo, ear popping, and even nosebleeds. They may also experience a sudden rush of wind which may be strong enough to knock them off their feet, depending on how close they were to the portal.

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ARK: Aberration, if you're unfortunate enough to be there, then it would be a common occurrence... Granted, the ARK is in worse shape as of the use date so I would guess it would be the ARK in the earlier days before it completely broke. Regardless, it's a terrifying place.

I tend to follow the game master code. If you want it in your story and it doesn't make sense, don't explain it. If you want to explain it, then use techno babble. If you want your explanation to make sense, remember that science in it's current state is incomplete with many theories being (currently) impossible to prove or disprove. Do the explanations from the point of view of someone who doesn't fully comprehend the science behind it. The bulk of your readers won't know what an ohm is or that a particle is a wave until observed. I prefer string theory since the reader will have an easier time understanding it.

It's scientifically possible, but unlikely to have an event just like you want. It will probably be fatal if it's cosmic related. For instance, if a distant neutron star has a fist sized rock slam into it at exactly the wrong angle, it will create a burst of energy in the form of light and radiation. If it's concentrated just right, that beam could hit an area no bigger than a penny from a thousand light years away with the full force of the remaining radiation. I believe it was pulsar that caused one of the mass extinctions. A good reason to work underground.

Ultimately it's what you decide it is. If this is a horror story, then I suggest not explaining it since nothing is scarier. If it's mystery, then you'll have to explain it. One thing I will point out is, someone will always try to process your story as fact. Don't let it bother you. People are still working out the calculations on how fast the Millennium Falcon travels. Because Falcon's apparently exist but the speed is in question.

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To answer your question, I think it would be helpful to first address what air pressure is and how you can have relatively localized changes in pressure.

In a nutshell, gas pressure is the force exerted on the environment or objects in the environment by the random collisions of gas particles as they float around. The speed and direction at which those particles move is related to the temperature of the gas and its flow; for example, air that's moving at high speed (like a gust of wind) exerts more pressure on a surface in the flow than still air would exert under the same conditions.

Pressure is related to volume, temperature, and gas species by the Ideal Gas Law: Pressure = (Amount of Gas * Temperature) / Volume. Basically, increase the temperature and hold volume and amount of gas constant, and the pressure will rise. Shrink the volume and hold temperature constant, and the pressure will rise.

But gasses are not uniform in composition, and their constituent particles can't move instantly. If you take a room full of air, the air on one side might be a bit cooler than the air on the other side. Air near the air conditioner might be moving, while air on the other side of the room might not. But the whole room is still filled with air and the particles are free to move around and interact with one another. So say you increase the temperature of a small pocket of air in the room. This would cause the particles in that pocket to move faster, and collide more often with their surroundings, thus increasing the pressure. But their neighbor particles will be moving at their original speed until something hits them, so the pressure outside of that suddenly warmer pocket would stay the same for a short time. This is the principle that gives rise to regions of varying pressure. But as the particles collide, they'll transfer their energy to their neighbors, and the little pocket of higher temperature, higher pressure air will dissipate across the room in a very short time.

This dissipation is the problem with your particular scenario. Within the realm of physics, it's doable if you raise the temperature very rapidly, but the pressure change won't stay local. As the warmer, higher-pressure air particles collide with their neighbors, the pressure increase will move outward in a wave, diminishing the further it spread, so your other camping group would feel a shockwave. And the amount of temperature change necessary to cause physical trauma to your campers would be immense: although you only need to increase the local pressure by around 10 pounds per square inch (almost double normal atmospheric pressure), your volume is on the order of 1,200 cubic feet! You'd have to raise the temperature by more than a factor of 10, instantaneously to get the desired effect.

So, as mentioned in other answers, magic is probably the only way to do what you're trying to accomplish without nasty side effects like shockwaves and plasmas.

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For nosebleed, pain and dizziness you need a pressure differential of around 30 kPa (absolute minimum).

You might get it using an acoustic standing wave of sufficient intensity, and sufficiently low frequency. Given the sound speed at STP of ~340 m/s, we're in the ELF range.

As you see in the animation, pressure (estimating by the distance between the two red points) can about double between minimum and maximum, and you might go from 60 to 120 kPa.

enter image description here

The problem lies in generating such a wave. For the most effect, you'd need a whole ring of super-subwoofers capable of displacing tremendous quantities of air in a synchronised manner, all around the campers with the victims in the center.

But you'd notice a sort of strong breeze all around.

Another possibility is a (relatively) stable pressure vortex being "fired" from straight above. Like this. Now you'd have a small storm all around you, even if nosebleed and eardrums bursting are a virtual certainty, and the storm would propagate to hit the neighbours.

More contrived possibilities, they might be camping over a camouflaged grille suddenly expelling prodigious quantities of air from a subterranean base. The flow would go straight upwards and, apart from a lot of dust being blown from the ground and the appearance of a dust geyser, next to nothing would be felt at more than a few meters. I was standing three feet from a giant vertical airblower some cirque guys were using to "fly" using wing suits; it was enough to make them rise twenty feet in the air, and except for the noise I just felt a small breeze. If instead of a steady flow there had been "explosions" of air, I believe I still would have felt nothing, while the poor souls on the flow's path would have been seriously injured.

It would also possible to build a localized tornado, but the pressure differential would be too low to have appreciable effects, you'd need enormous blowers, and the artificial "wind" would be something incredible.

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Based on the edit on @twelfth's answer, I've got just the device for you: an ultrasonic standing wave generator. Look at this video from Smarter Everyday where he helps the Ford team with the acoustic levitation machine and see what happens with the droplets when they crank up the amps around 4:10.

Obviously to do this with people you need some handwaving and big devices, or you can perhaps have smaller low power devices hidden in the trees with their phases and frequencies tuned to hit the specific camping spot.

I hope this would give some insight and inspiration.

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Opening a portal nearby could cause a massive change in barometric pressure. For instance, let's say a portal opened 10 feet above their head and they were at 5,000 feet above sea level. Put the other end of the portal at 35,000 feet and the vacuum created would change the pressure where they are extremely quickly, causing accelerated versions of the symptoms of altitude sickness.

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  • $\begingroup$ The question has the [physics] tag, though. How would you open a portal? $\endgroup$ – Renan Jun 11 at 2:54

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