Can you hear the shot before it kills you?
April 12, 2011 9:24 AM   Subscribe

Hypothetical game of Russian Roulette. Real bullets. Will you hear the shot before it kills you?

Assume the bullet kills you as quickly as it can. Assume the gun is pressed right up against the most optimal killing location on your head. I realize this question is much easier if the gun/victim are far apart.

In general, bullets travel faster than the speed of sound. But are there other variables?

1) Is there a delay in the bullet being propelled down the chamber?
2) I'm assuming the bullet slows down as it enters your head... How quickly can the bullet actually kill you/kill your awareness to sound?
3) Does it take time for your brain to actually register the sound?

I think you would hear the sound...
posted by shew to Sports, Hobbies, & Recreation (13 answers total) 2 users marked this as a favorite
Not all bullets travel faster than the speed of sound, and even those that do have to be accelerated to their muzzle velocity, so they are subsonic for a portion of their flight down the barrel. Also, given that the gun is placed against your head, the sound would travel primarily through metal and bone (your skull) to get to your ears. If you look up the speed of sound in various solids it is generally much faster than through air, so I think it is safe to say the sound would reach your ears before the bullet exits the muzzle. As far as your brain registering the sound, I am not so sure and don't have the time to look it up right now, but look up latency of auditory evoked potentials to get an idea of how long it takes the brain to process sounds.
posted by TedW at 9:33 AM on April 12, 2011 [2 favorites]

If the sound wave is created when the propellant gases escape the barrel from behind the bullet then I would have to assume no.

If the sound exits the barrel at the same moment as the bullet then even with the bullet travelling subsonically it's going to reach the medulla oblongata ("the most optimal killing location") before the sound wave reaches the inner ear, and certainly before the brain can process the stimulus.

Startle response to a sound is around 100ms during which a just-subsonic bullet would travel more than thirty metres.
posted by alby at 9:54 AM on April 12, 2011 [3 favorites]

There is no spot on the brain that will surely kill you 100% of the time, and it's pretty impossible to measure the time it takes for awareness of the world to cease, short of assuming it ceases instantly in the case of complete obliteration of the brain. People tend not to be interviewed while being shot in the head; there is little data. You might be able to answer the question "will the bullet enter the brain before the sound is percieved" with simple mathematics but not "will you be unaware of the sound of the bullet being fired due to being dead".
posted by tehloki at 9:55 AM on April 12, 2011

I probably should have said "surely cut off the awareness of the world 100% of the time" instead of "surely kill you 100% of the time". There are a few places that are effectively 100% kill shots.
posted by tehloki at 10:45 AM on April 12, 2011

First off, its not going to kill me, its going to kill you. I am going to win this game dammit.

I surmise that you will hear the bang prior to expiring. Is death faster than sound? How fast is death even with the optimal bullet placement? The bullet will probably not even enter your brain before the sound wave hits your closest eardrum. The bullet achieves a high velocity but it must accelerate from zero. Given that the muzzle velocity of a pistol is about the speed of sound or a little faster, and it must accelerate from zero to that speed down the barrel, that the average velocity of the bullet through the barrel is less than the speed of sound. Of course the distance from the sound source to your ear drum is not necessarily the same as the distance to your brain. You then need to consider how long it takes your brain to register the sound from the vibrations in your ear drum and also how long it takes you to die. By the way, define die. Its all very complicated and we have only begun to scratch the surface of possible variables and definitions. Why do you need to know this by the way?
posted by caddis at 11:18 AM on April 12, 2011

Don't worry, caddis... no one actually interested in finding out the answer to this question. My brother and I were debating it and in the end, I think it's a math problem. Isolating all the right variables seems to require some medical knowledge as well as some firearms expertise that I don't have.
posted by shew at 12:03 PM on April 12, 2011

As far as I understand from neuroscience your body (your ears) may hear the sound but it takes an additional fraction of a second for that pulse to reach your brain and be processed and therefore you wouldn't hear it as such. This is for Russian roulette, I'm fairly confident that at a longer distance you would in fact hear the sound if as others have responded the bullet is traveling slower than the speed of sound.
posted by boobjob at 12:18 PM on April 12, 2011

It's something of a consciousness problem. If our roulette player shoots himself as lethally as possible, he'll still take a short amount of time to expire, but cellular activity is still going to go on. The relevant nerves in the ears will fire away, and the neurons not directly destroyed by the bullet's path, or ripped apart by hydrostatic shock around the wound channel, those are going to be firing away as well, until they stop getting oxygen due to blood no longer flowing.

But, that immediate trauma will probably knock him unconscious, due to wrecking the very biology that produces consciousness. So there's no "him" left to hear the bang in that case, because consciousness has died before the rest of the brain can follow; the sense of hearing is reporting to an empty office.
posted by Drastic at 12:39 PM on April 12, 2011 [2 favorites]

Let's use some round numbers:
  • Speed of sound = 1000 ft/sec (real number is ~1120 ft/sec)
  • Length of gun's muzzle = 6 in.
  • Speed of bullet at muzzle = 2000 ft/sec (~2x speed of sound), not particularly fast compared to what is available, from my quick googling
  • Distance from gun's firing point to ear = 9 in. (suppose the gun is at the temple, it makes a little triangle)
Assumption: Bullet kills once it's travelled 2 in. after exiting the muzzle, and it doesn't slow down during that time.

Quick math (stuff like s=1/2 at2) says: Bullet will take 0.00058 sec to kill. Sound will take 0.00075 sec to reach the ear. Chances are, the victim will never hear it coming; in fact, the sound won't even reach the ear by the time the person is (probably) dead.

Thanks for brightening up my evening!
posted by Simon Barclay at 6:21 PM on April 12, 2011 [2 favorites]

As TedW said, the sound wave will probably travel through the skull bone, rather than through air. I mean, it will travel through air too, but the sound wave will reach first. I don't have time to do the math, but this link suggests that the speed of sound in pig jawbones is faster in mature animals (denser bones) and ranges between around 2000 m/s (piglets) and about 4000 m/s (adult pigs). If we substitute 4000 m/s into Simon Barclay's analysis above and continue assuming 9 inches of travel, it will take 57 microseconds for the sound wave to reach the eardrum before the bullet reaches the tip of the muzzle (250 microseconds by my calculation, but I didn't assume any acceleration, just an instantaneously 2000 ft/s bullet) . But, also as TedW said, just reaching the eardrum isn't enough for the brain to register sound. Neurons will need to fire and the signal will need to travel down axons into the brain, which will probably add some small but nonzero amount of time to the calculation.

So, by my back of the envelope calculation, you will indeed hear the bullet first, but this is pretty quick and dirty math, and I know nothing about neuronal response times. If they are more than about 200 microseconds, then you probably won't hear it.
posted by wondercow at 7:47 PM on April 12, 2011

The question isn't the speed of sound, because the distances are so close. The question is the brain, and I think the answer is that even an "instant" death isn't really so instant. The brain cells will be doing their things until they die.

Answer: the player would hear it, but probably wouldn't know they heard it.
posted by gjc at 7:38 AM on April 13, 2011

I just had to toss all my maths out after realising at the end of doing it all that I'd used a cartridge you wouldn't find in a revolver (barring some sort of custom nightmare). Don't ever play Russian roulette with me as apparently I think it's acceptable to play it with a semiautomatic...
posted by longbaugh at 6:32 AM on April 14, 2011

If they are more than about 200 microseconds, then you probably won't hear it.

I did some looking around and according to this reference the major cortical response (the cortex being the part of the brain that does your thinking and so where you"hear" the sounds your ears detect) is 50-300 milliseconds after the stimulus with other responses occurring up to 1000 msec out. So based on the other calculations upthread it is likely that you would just be beginning to hear it when the bullet enters your brain.
posted by TedW at 7:25 AM on April 14, 2011

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