[FoRK] FoRK Digest, Vol 89, Issue 10

Dave Long dave.long at bluewin.ch
Sun Feb 13 10:17:41 PST 2011

> At 10 GBit, a bit is roughly 3 cm in vacuum, slightly shorter in  
> glass.

Olympic fencing is a twitch game.  For instance, in order to count a  
clean hit in épée, the scoring touch has to land at least 40 ms  
before the opponent's point.

Given that human choice reaction times are far longer, on the order  
of 150-200 ms[0], one might think that double hits would only occur  
in the rare cases where the opponents coincidentally decided to  
attack at the same time.

However, double hits are not that uncommon, and my current  
explanation for this apparent paradox is that closing the distance to  
make an attack, even without the defender's conscious reaction,  
symmetrically lessens the distance that the defender's point must  
travel before touching the attacker; therefore we should expect just  
about any attack launched from a neutral position to result in a  
double hit.  (hence the relative importance of preparing an attack by  
first gaining the positional advantage)

The worst case occurs when the putative defender takes advantage of  
the collapse of distance to launch a counterattack, thereby  
collapsing it even faster.  If we model the point motion in a simple  
attack as closing from 0 to 4 m/s to 0 over about 600 ms, and the  
defender's counterattack starts when they first react, at 150 ms past  
the initial attack, there will be a significant plateau where both  
points are moving towards target at 6 m/s [1].

Now, Google tells me that:

((6 (m / s)) * 40 ms) / (3 (cm / bit)) = 1 octet

Therefore (albeit entirely coincidentally) the advantage in position  
an épéiste should maintain to get a clean hit is (at 10GB) about a byte.


[0] it is no coincidence that the notion of a "fencing time" within a  
phrase is on the order of 140-180 ms.
[1] this explains the difference between cavalry sabers and fencing  
swords; two cavaliers at full tilt close on each other much faster,  
with roughly 24 m/s.  For such an engagement the "fencing time" is  
about 3,6m, well over a horse length.

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