This morning there was the annual remembrance ceremony in Whitehall, London. Two minutes silence begins with a cannon round at precisely 11am, and ends with another round at precisely 11:02.
I was surprised to hear the boom of the first round, since I thought I was too far away. Checking the map, it seems that in fact my current location is only about ten miles north of central London. OK, maybe I was hearing the cannon. To confirm, I listened out for the second boom at 11:02. I was expecting the sound to arrive at about 11:02:50, since sound travels about one mile in five seconds. But I heard the second boom just ten seconds after 11:02.
I checked my clock against internet time servers - it was within two seconds of the correct time. I am sure that the cannons are timed very accurately, let’s say to within two seconds. That means the sound must have reached me in no more than 14 seconds. How is that possible? It’s a quiet and still morning here. I have heard no other booms this morning, and these two sounds two minutes apart were unusual and certainly sounded like a cannon being fired some distance away.
The clue might be here. From the wikipedea page on the Sunday Rembrance Day service:
Thus the two minutes of silence does not start at exactly 11:00:00 but almost certainly not until Big Ben has stuck 11. The first chime of the 11 is exactly on the hour.
Wouldn’t that make the cannon sound late, not early? Anyway, I’m sure that the cannon fires at 11:00:00, roughly simultaneously with Big Ben’s first bong. That is, the eleven bongs sound during the “silence”.
Its possible the boom you hear is from the ground. “Sound” travels much faster in a solid than the air. And as that sound travels in the ground its going to “leak” back into the air as it goes along. So maybe the boom took the faster path to you?
Yes, I think that is the only plausible explanation. It didn’t sound like a nearby gun, and I have not been able to find evidence of a similar cannon salute at about two miles from my location, but I guess it must have been that, and that I did not also hear the gun from Whitehall (Horseguard’s Parade, actually).
Is it possible you heard a closer source? Is there barracks near you? At 10 miles distance I’d be very surprised that you heard the Hyde Park cannon at all.
Either it didn’t start on time, or the laws of physics have been broken and the universe is coming to an end. Watch out for intergalatic constructions crews.
Assuming you are correct about the location and timing of the cannon shot, there are many possible explanations.
Sound travels around 760 mph through a normal atmospheric mix of gases at sea level. However, if the random motion of atmospheric molecules created a channel of pure helium between you and the cannon, the speed would increase by a factor of almost 3, and almost four if the channel were pure hydrogen. That gets the speed up to about 3000 mph, which may be within the limits of error for your human-timed measurement.
The speed could be even higher, depending upon how aware you were of your environment. For example, if you didn’t notice that a sudden flood put both you and the cannon underwater, the speed of sound in pure water is a bit over 3300 mph, and in sea water it’s over 3400 mph, which is so close to your estimated figure that I think sea water is the best working theory.
Or, if you didn’t notice that a thin rod was momentarily extending between your ear and the cannon, the speed could easily exceed your estimated figure. A rod of solid gold would yield a speed of about 7250 mph, and a rod of solid diamond would yield nearly 27000 mph.
I’m closer than 10 miles from central london and i didn’t hear anything. I find it extremely hard to believe you’d hear even such a distinctive sound over that distance, over all the other noise with so much in the way. A closer gun which you just didn’t know about sounds far more probable.