The Sound So Loud That It Circled the Earth Four Times
nautil.us
nautil.us
Reminds me of this recent comment on reddit: http://np.reddit.com/r/space/comments/2h9y9g/the_first_launc...
"the Saturn V rocket produced a SWL (Sound Power Level) of about 220 decibels, which is sufficient to melt concrete nearby and set grass aflame a mile away,"
As an example, its intensity (in W/solid angle) is 14 orders of magnitude (AKA 100 billion times) highter than the 80 dB people usualy use as a safety limit.
Sound that loud wouldn't just kill you, it'd rip you apart.
Saying a burrito is "quite spicy" usually means "surprisingly" but not "excessively" or "extraordinarily".
Those things are already too subtle and hard enough to learn in a second language. People defining the same expression with widely conflicting meanings in different places do literally turn it into a maze :)
"This limit happens to be about 194 decibels for a sound in Earth’s atmosphere."
Therefore, wouldn't 220db be like -280°C?
EDIT: Somewhat of an answer:
194.09(P) = 1 (ONE) AIR ATMOSPHERE = 14.6962 POUNDS PER SQUARE INCH = 14.6962 P.S.I.= 1 ATM SOUND WAVES DISTORT AND ARE NOW DEFINED AS SHOCK WAVES AND THEY BEGIN TO FOLLOW SHOCK WAVE BEHAVIOR. PARTICLE VELOCITY (BLAST WIND) = 590 FEET / SECOND = 180 METERS PER SECOND = 402 MILES PER HOUR. -REF.2.
Source: http://www.makeitlouder.com/Decibel%20Level%20Chart.txt
Once it dissipates a bit it becomes a sound again.
Here's a good example of the sound I'm talking about: https://www.youtube.com/watch?v=OnoNITE-CLc&t=1m44s
I remember also being struck by not only how loud it was, but also how bright. It's something that photos or video just can't capture.
The launch was far and away the loudest phenomenon I've ever heard, or ever hope to hear. Impossible to adequately describe. You don't hear the sound, you are the sound. The universe transforms, and is made of nothing but sound and vibration.
Can you imagine being tucked into the small, cramped Command Module, sitting on top of this magnitude of power at lift-off?
The whole thing, the technology, the sound, the people coming together to make it happen... it's soul-stirring.
"As I hurtled through space, one thought kept crossing my mind - every part of this rocket was supplied by the lowest bidder."
In the interest of completeness, here are the two most powerful launchers even flown in terms of first-stage lift-off thrust
N-1: 4,600 tonnes / 10 million lb
Energia: 3,600 tonnes / 7.9 million lb
Saturn V is currently in third place but will be pushed down if / when Falcon Heavy flies.
Essentially telling us that one volcano could change our lives, if not end a substantial number of them.
This is a reading comprehension error, I think. I guess I'm not 100% sure. That "melting concrete and setting grass aflame" comes from the link, here: http://www.makeitlouder.com/Decibel%20Level%20Chart.txt
That link has many decibel levels, and examples, and factoids about the things producing the sound, unrelated to the sound itself.
I think the chart intends to say that the rocket melts concrete, sets grass on fire 1 mile away, and produces sound that is 220 decibels. Not that the sound itself is melting concrete or setting grass on fire.
The reddit post mentions "At 2 kilometers (140+ db), ..."
2km is a little more than 1 mile. So if the sound alone could set grass aflame a mile away, then that would mean that 140db at distance zero is enough set grass on fire.
If it can set grass on fire, then it can set a lot of other things on fire. Paper, clothing, hair, etc...
Some extremely loud rock concerts hit 150db.
So, while I guess I'm not 100% sure that this is an error, I just doubt that rock concert speakers can/would output enough volume to set things right next to them on fire. There would be huge safety issues, and risk of the speakers destroying themselves and other equipment.
I know nobody is right next to speakers this loud, but still... I doubt the accuracy of this 'melting concrete and setting grass aflame via sound' factoid.
I would love to be shown wrong, because it is really interesting if it's true.
- its ignition was the most powerful artificial explosion in human history
- The seismic shock created by the detonation was measurable even on its third passage around the Earth
I'd love to hear the pilot's thoughts on this. From what I can guess, he couldn't have traveled very far away by the time the explosion occurred. At the very least, he must have felt tremendous turbulence.
I wonder if the scientists knew how close the explosion would be to the aircraft.
I once saw a talk about this at a scientific meeting, so the papers are out there. All I can remember from it is that they estimated the ejecta at "about the mass of the Sierra Nevada". This was quite a while ago so I'm sure they've got a better estimate by now.
This article was about a wideband sound that was so loud that it defies comparison. Loudness is related to the amplitude, or "height" of the wave, not frequency.
Do you have a cite for this? A "directional" outdoor infrasound weapon would be huge (10s of feet) and quick web search seems to indicate these types of weapon are at best "not mature" and at worst fiction.
But this [infrasound weapon] has seemed to be not a very practical weapon, since large banks of speakers were required to provide directionality, and power demands were deemed excessive.
The article goes on to describe LRAD which does exist and has been deployed, but is a high-frequency weapon, not an infrasound weapon (and can be defended against with a good pair of earplugs).
In both cases there is a total of something (sound energy or electric field lines) and that total must be split over all possible directions. The total electric field must be split over the surface area of increasingly larger and larger spheres hence the 1/r² behaviour (1/4πr² to be precise). The sound energy is spread uniformly over a circle with circumference C=2πr, hence giving a 1/r decay, over short distances.
For longer distances, the curvature of the earth will play a role. Come to think of it, it must have been really loud somewhere diametrically opposite to Krakatoa, 17 hours after the eruption...
The divergence is probably even less that 1/r because the Earth is roughly sperical, and the sound will focus at the antipode of its source. There might even be a region, approaching the focus, where as the sound propagates its sound level is actually increasing, not decreasing!
It would be interesting to know what history has to say about Medellin, in Colombia, in 1883. Being at coordinates 6N 75E, it is roughly at the antipode of Krakatoa and could well have had an awful lot of energy dumped in it general direction a few hours after the eruption.
If I had to completely guess, I would think that gravity might have something to do with its behavior in this case, because if sound decayed at 1/r^2, it seems highly unlikely that the sound could survive four trips around the Earth. Yet we also have to explain how the sound was able to preserve itself even though sound travels "sort of spherically" (if you're up in the sky and someone shoots at you, you can hear it, so sound must be going up-down as well as left-right and every other direction) but if it was simply spherical in this case then it would decay into the upper atmosphere. If you imagine a sphere that grows from any point on the surface of the Earth, most of it will wind up in space, but since it circled the Earth, it must not have traveled exactly as sphere, which implies it didn't fall off as 1/r^2.
The most likely explanation seems to be that sound of huge intensity somehow follows the curvature of the Earth, which is very interesting. I wonder if gravity is influencing the soundwaves directly (which might actually be nonsense, since waves aren't matter, but something that travels through matter) or if gravity somehow sets up the propagation medium in a way that lets the sound curve around the earth without losing intensity as 1/r^2.
I don't think that's much of a nonsense. These are waves propagating through a medium - in this case mostly air. And particles of air are affected by gravity, therefore I would very much expect them to follow Earth's curvature.
Gravity isn't the reason sound waves curve around the earth. One reason is that the curved surface is the only avenue open to them. There are a number of other, less influential reasons like different temperatures at different altitudes, but gravity isn't on the list.
The radius of the Earth is roughly 6000 km, while the thickness of the atmosphere is about 120km. Thus, the ratio of the two heights is about 1/60. Because the ratio of atmosphere thickness to terrestrial thickness is so small, for the purposes of modeling wave propagation through the atmosphere we can approximate the atmosphere as a thin spherical shell around the Earth.
Furthermore, the Earth's surface forms a hard boundary below the shell, further confining the sound to the atmosphere, while the force of gravity also prevents the sound wave from escaping into space via the atmosphere.
As other posters have stated, this forms a 2-dimensional propagation layer which results in a linear falloff rather than an inverse square falloff.
http://hyperphysics.phy-astr.gsu.edu/hbase/acoustic/invsqs.h...
In this case, the soundwave was able to follow the curvature of the Earth, which implies that it wouldn't decay as a sphere but rather a plane, which would be a 1/r falloff. I wonder why sound of massive intensity will follow Earth's curvature?
I'm having trouble understanding how diffraction would cause that end result of "waves go where the atmosphere is." If waves could bounce off of the thin atmosphere near space, that would make total sense. But they can't bounce due to thin atmosphere, only disperse, so it seems like there's some other phenomenon in play.
I'm having trouble seeing how that explanation would explain the case at hand. Your explanation is likely correct, and I'm probably just thinking about it incorrectly. Would you mind pointing out the flaw in my logic?
In this scenario, a volcano's boom was so loud that it traveled through the atmosphere, all the way around the Earth. Your explanation is perfectly reasonable for thick atmosphere. In thick atmosphere, a soundwave is a pressure differential, and since molecules are densely packed together (since the atmosphere is thick), there's no choice but for the molecules to "slosh around." The high pressure areas will spread to the low pressure areas within the thick atmosphere and create a moving wavefront, exactly like you said.
But as the soundwave travels closer to space, the atmosphere becomes thinner. There are fewer molecules for the soundwave to travel through. That means a pressure differential will have less medium through which to traverse. Since there are fewer molecules, there's more room between them to absorb a pressure differential, right? For example, the reason sound travels so well underwater is because water is extremely dense in comparison to the atmosphere, so less energy is needed to travel an equal distance underwater. Correspondingly, near space where the atmosphere is thin, more energy would be needed to traverse an equal distance. That must mean that as the wavefront approaches space, the wavefront should dissipate. Since more energy is required to travel through less atmosphere, then as the atmosphere approaches zero, the energy required for a wavefront to travel one meter should approach infinity, and that's why it seems like the wavefront should dissipate near the edge of the exosphere.
But in this case, the wavefront didn't dissipate. The volcano's boom kept on going all the way around the Earth, and it was somehow able to maintain its energy. If the soundwave travels as a sphere from its point of origin, then that sphere should have a hard time traveling all the way around Earth, shouldn't it? So it must not be travelling as a sphere, but something else.
You're saying that "something else" is diffraction. I'd like to understand that. How is it that a wavefront of such intensity can approach the exosphere where it should dissipate, yet not dissipate and instead keep traveling all the way around the Earth due to diffraction?
[As a physics prof, I probably ought to be doing some sort of calculation to justify that, but I don't have the time. I'm sure it's been analyzed formally somewhere already. Just off the cuff, though, the speed of sound is lower at low temperature, so refraction of a sound wave in the upper atmosphere will tend to bend it outward, away from the Earth. I'm thus imagining that loud sounds may tend to locally push the atmosphere out from the planet a little bit, and I expect that coming back to equilibrium will be a lossy process that doesn't preserve the shape of the wave.]
Dang, this was your chance to say the word "antipode" in everyday conversation!
Notably Bogota sits in a huge valley, so they are also less likely to have been affected by the surface sound wave as well.
Any Colombians reading this...?
When you think about it, we're living on a extremely thin crust that's formed on the surface of a molten, roiling ball of rock and metal. People are strangely obsessed with the threat of asteroid impacts when what's beneath our feet presents a perhaps even greater danger, one which we know next to nothing about!
I'd wager we're much closer, technologically, to do something about asteroids, though. Not quite so much about eruptions.
Disclaimer: I am a software engineer, not any kind of geologist.
Also interesting are how quickly the volcano has risen out of the sea again after being totally obliterated, and how much life now thrives on it.
[1] http://en.wikipedia.org/wiki/Caloris_Basin#Antipodal_chaotic... ("It is thought by some to have been created as seismic waves from the impact converged on the opposite side of the planet.")
At the antipode you would feel an identical pressure wave from both side. This would manifest as compression which you would feel since you are compressible.
A flag would not move in either direction (i.e. the wave is canceled out), but there would still be a compression wave in it.
Like imagine hitting a piece of wood with two hammers simultaneously.
I wonder if anyone was there at the time to notice a pressure wave coming from all directions.