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As soon as Game of Thrones giant ice wall was introduced, I think we all knew
that at some point it had to fall and let the White Walkers through. Now early
on this season, since winter has come, there was a theory that in fact the
Night King and his army of wights would simply walk around the wall on the now
frozen sea... which would have been a bit disappointing. But it turns out (SPOILER ALERT)
it was the zombie ice dragon Viserion
who caused the downfall of The Wall. Many people have shown that melting The Wall
just wouldn't be practical. That's because ice has such a high
latent heat of fusion and specific heat capacity, meaning it would take a
tremendous amount of energy, far more than you could possibly attribute to a
hypothetical fire-breathing creature. But there is a way that we could cause the
wall to fall and its origins are actually in the books. The Horn of Winter
is a legendary horn which the wildlings believe if blown would bring down The
Wall. Now that's not too much of a stretch. If the pitch of the sound produced by
the horn match one of the natural frequencies of the wall, then a resonance
could be set up within it. In resonances all that wave energy gets efficiently
trapped within the structure, meaning it can amplify and amplify more and more
with time. We've witnessed the level of destruction that resonances can cause
for instance with this bridge.
In fact we already employ resonances to break ice, in particular thin sheets of
ice over bodies of water like lakes. Hovercraft traveling over the ice at the
critical speed set up resonances in those thin sheets of ice which amplify
until they break via mechanical fatigue. Now with these thin ice sheets it's
usually shear or surface waves which are set up, but the principle would still
hold for sound or body waves in a giant block of ice. So what should the Horn of
Winter sound like? Well as I established before, the average thickness of The
Wall should be about 90 metres and the speed of sound in ice is 4,000 metres
per second (and don't worry if you like me believe that the wall has to be
actually made of pykrete, it doesn't change the numbers too much. The fundamental
frequency of The Wall then works out to be 22 Hertz, which is barely audible for
most people. But don't forget that harmonics, whole number multiples of that
frequency, will also lead to resonances or standing waves which perfectly fit
within the wall. For instance this sound has a pitch of 66 Hertz, three times the
fundamental, so that means an inception bwah could cause The Wall's destruction.
Mind blown! And it turns out you wouldn't even have
to perfectly tune the Horn of Winter, because the wall would act something
like a waveguide. Now while multiples of 22 Hertz would be just right for any
waves traveling at right angles backwards and forwards through the wall,
any sound waves that were traveling along it as well as through it would
travel a slightly longer distance and therefore would require a higher
resonant frequency. So as long as you're above that critical value, the effect
should be the same. But blowing the Horn of Winter to take
down The Wall might not look quite how you imagine. That's because sound gets
reflected at boundaries between materials which have very different
acoustic impedances, essentially a measure of the resistance to motion
under the pressure of that sound wave. Ice and air have very different acoustic
impedances. 99.95% of all of the sound from the Horn of Winter would end up
being reflected away from the wall, which of course is no good. We do have a way
around this. You know that gel substance using ultrasound scans?
Well that's there to match the acoustic
impedance of your flesh to try
and limit the amount of sound reflected by your skin. So we just need to use
something similar between the Horn of Winter and The Wall to make sure that
that sound gets through and hey presto wall fall down. And that is how this
season of Game of Thrones should have ended, according to physics!
Thanks so much for watching this Game of Thrones video, there's some more on the subject
of the wall over there, do like and subscribe and comment below let me know
what your favorite moments from this season of Game of Thrones was and I will
see you again soon!