Would it be loud enough to hear and is there any risk of dangerously loud sound waves being generated if the object being teleported is large enough?
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4$\begingroup$ This sounds very familiar, is this not a duplicate? $\endgroup$– PelinoreCommented Nov 20, 2022 at 12:37
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7$\begingroup$ Also normally best practice to wait at least twenty four hours to choose a best answer rather than choosing one only an hour after posting to allow other answers a chance to appear, this is the internet, there are those in different time zones and the first answer may not be the best answer. $\endgroup$– PelinoreCommented Nov 20, 2022 at 15:57
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9$\begingroup$ If you make teleportation in your world like that, how would you handle the destination of the teleport? Nobody can teleport then to places that are not a vaccuum? Or the molecules of the destination somehow merge with the traveler? Or they move out of the way? The easiest way to handle it is if every teleportation is actually a swap. The air molecules of the destiny then move to the origin to the traveler. Then you also won't have a void. $\endgroup$– IvoCommented Nov 21, 2022 at 7:21
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1$\begingroup$ ...Assume a spherical human with a frictionless vacuum inside... $\endgroup$– leftaroundaboutCommented Nov 22, 2022 at 15:26
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$\begingroup$ Won't the amount of displaced air be the same as that in a human sized balloon, overpressurized to 2 bars? So make a balloon like that, and then make it pop. Loud but not threatening health would be my prediction. $\endgroup$– Jyrki LahtonenCommented Nov 22, 2022 at 15:41
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3 Answers
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A noticeable pop, but not that loud.
I've used vacuum chambers a fair bit at work, and it's not that loud. You definitely notice it when that much air pops back in, but it's not loud enough to hurt your ears or do any notable damage.
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17$\begingroup$ When air enters a vacuum chamber, it only enters from 1 direction (and possibly more slowly, through a valve). When it enters a void, it enters from all directions. Why is this insignificant in terms of sound created? $\endgroup$– RobertCommented Nov 20, 2022 at 13:01
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15$\begingroup$ Yes, but that is not the source of the noise in this scenario. When air goes through a thin valve, sound is coming from the interaction of air with that valve. When there is a void, the energy comes from the shockwave formed by the air collapsing, which is a completely different mechanism. When there is a valve, the void is being filled too slowly for the shockwave to form. $\endgroup$– RobertCommented Nov 20, 2022 at 14:03
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3$\begingroup$ No. When you stab a tire with a knife, air is only being released through a small hole. When you teleport, air is rushing in from all directions. This difference is in the time it takes the effect to take place. Less time means more power means a louder sound. $\endgroup$– RobertCommented Nov 20, 2022 at 15:38
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7$\begingroup$ I dunno; this is more or less how lightning produces thunder; superheated ionized air expands very rapidly, then cools down and shrinks very rapidly. The surrounding air rushes in to fill that void and meets in the middle. Always seemed pretty loud to me. Also, 2 grams of TNT is about 8kJ. 8kJ of energy dissipated in 1s as pure sound energy would be 8000W of sound. That is eardrum-disintegrating-loud. Now the energy won't all be turned into sound, but still, it seems there is plenty of energy to work with. $\endgroup$– marcelmCommented Nov 20, 2022 at 22:52
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5$\begingroup$ @Mazura "Can't compare half a million kJ lightning strike to eight." - Sure you can, that's about 100,000 times less. Sound decays following the inverse square law, so assuming a similar amount of energy is converted to sound, that suggests the teleportation pop would be as loud at 3 meters as lightning thunder at 1km. Still pretty loud. $\endgroup$– marcelmCommented Nov 21, 2022 at 7:59
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Loud
This is not the same as air entering a vacuum chamber. In that case, air only enters from one direction instead of moving in from all sides. Instead, it is more similar to the collapse of a cavitation bubble, where the object being collapsed is surrounded on all sides by fluid. Or maybe, the collapse of a container (like a can) filled with a vacuum. There are plently of youtube videos of that being loud, and some of the energy is being used to deform the container.
A human-sized void in the atmosphere has a volume of about $70l=0.07m^3$. At a pressure of $1atm\approx 100kPa$, the void will have an energy of $7kJ$. Only some proportion $p$ of this energy will go into sound. In liquids, it appears to be about $35\%$, but this is probably different in gases. I will look through 2 scenarios, if compressibility does not make a different ($p=0.1$) and the scenario where compressibility makes a difference ($p=0.01$, I doubt this could be too different from $p$ in liquids and a factor of 30 is a lot). Sound is measured in units of power per meter squared, so the power will be the total sound energy divided by the time it takes for the collapse to take place, which is approximately $\frac{1m}{\text{speed of sound}}\approx 0.003s$. Then, the power released as sound will be about $2\cdot10^6pW$.
$p=0.1$. Here, the power will be $2*10^6W$, in the vicinity of the void (less than 1 meter away), it will have a intensity of $170dB$, loud enough to rupture ear drums but not loud enough to be deadly. An intensity of $130 db$, loud enough to cause permanent ear damage will occur up to about $100m$ away.
$p=0.01$ Now, the power will be $2*10^5W$, so near the teleported, the intensity will be about $160dB$. Permanent ear damage will occur up to $30$ meters away
It would require $p<0.00001$ (which seems implausible) to not give permanent hearing damage to those in the vicinity.
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6$\begingroup$ Where are you getting one meter? If a human-shaped void is collapsing inwards, I'd imagine the biggest diameter of void to be somewhere in the torso with a radius of 20cm max depending on how large the person is. $\endgroup$ Commented Nov 20, 2022 at 13:54
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5$\begingroup$ Hmmm. 7 kJ is less than 2 grams of TNT equivalent. I am pretty sure that nobody ever has gone deaf because 2 grams of TNT exploded somewhere in the vicinity, unless maybe they were wearing those 2 grams of TNT as ear rings. (And the 2 grams of TNT would produce a shock wave, tiny but still a shock wave, which air at atmospheric pressure filling a void very obviously cannot do.) $\endgroup$– AlexPCommented Nov 20, 2022 at 16:53
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7$\begingroup$ @alexP I am not sure why this is different. TNT probably produces more heat and gives less energy to the shockwave (the shockwave is a byproduct of the gas created in the reaction, not the reaction directly). But there are animals like the mantis shrimp that uses the shockwaves from voids (admitly underwater, but I tried to account for that in my answer) to deal damage to animals of similar scale. Scaling up to human size makes it seem likely that this could in fact do some serious damage. $\endgroup$– RobertCommented Nov 20, 2022 at 17:17
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8$\begingroup$ @alexP A google search shows that fireworks produce about 150db at 1 meter. They are less than 60 grams. blog.jakesfireworks.com/blog/…. Given that dB are logirithmic and much of firework energy is heat and light, it seems plausible that the void could produce 140-150dB of sound at 1m. $\endgroup$– RobertCommented Nov 20, 2022 at 17:53
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5$\begingroup$ @AlexP Also, I am not sure what you mean by no shockwave. what-if.xkcd.com/6 $\endgroup$– RobertCommented Nov 20, 2022 at 21:36
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This all depends on how fast the teleportation is. Is it truly "instant" or does it take time?
This is important because it is very difficult to create an experiment where we instantly create a void accessible from all directions but I suspect it would be very loud. Forcefully opening a vacuum chamber or similar is not a good approximation, because in such a scenario, the atmospheric movement is restricted and fills the chamber much slower than at maximum velocity.
An approach that could be used to estimate this would be seeing the amount of gas we would need to "instantly" generate using explosives: Assuming (ballpark) that one gram of TNT (Trinitrotoluene explosive) generates about one liter of hot gas at atmospheric pressure when it detonates, and the average human has a volume of 62 liters, one would require 62 grams of TNT detonating right at when the person teleports away to result in a "net zero" pressure change.
I found this somewhat sketchy video which alleges to 100g of TNT being detonated and although it is difficult to convey loudness of something through recording, you can hear the echo and scale of the sound after the explosion.
Without ear protection, people nearby would suffer instantaneous hearing loss and the actual sound would be audible from a long distance away.
answered Nov 20, 2022 at 14:14
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$\begingroup$ (1) Explosions are so very loud because they produce a shock wave. Air at atmospheric pressure filling a vaccum cannot produce a shock wave, because the pressure can never go above one atmosphere. (2) About that "instantaneous hearing loss", you may want to find out how much explosive is in a hand grenade and how many soldiers come back deaf from eac routine training exercise. $\endgroup$– AlexPCommented Nov 20, 2022 at 16:40
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11$\begingroup$ @AlexP Are you sure it can't go above one atmosphere? Remember, air molecules do have inertia. $\endgroup$– HearthCommented Nov 20, 2022 at 22:46
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14$\begingroup$ @AlexP You can absolutely exceed one atmosphere as the air will act as a fluid hammer. $\endgroup$– forestCommented Nov 21, 2022 at 0:59
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5$\begingroup$ @AlexP Modern hand grenades contain around 60 to 100g of explosive, so it is quite comparable, however soldiers are taught to wear hearing protection "ear-pro" with religious zeal... and those close enough to a grenade detonating that they'd be within the "instant hearing loss" range, are also within the painful death range from the actual grenade. $\endgroup$ Commented Nov 21, 2022 at 13:02