JosephKK said:
A little excessive snipping? 140+ dB vision, upwards of 240 dB sense
of smell?
I don't buy it. But then, are we talking humans specifically, or any animal
at all? For sure, a simple sanity check will show that a whopping 240dB is
impossible (1 mole = 6 x 10^_23_ molecules).
I don't think humans can detect single molecules. Finding information on
this is amazingly difficult, but one reference:
http://makingscents.typepad.co.uk/making_scents/2007/04/the_worlds_smel.html
states 0.1 ppt, or -130dB concentration. Mind, this is one blog reference,
on one molecule, in humans. This is not a good start. It is true that most
mercaptans are sensible on the ppt level by humans.
On the top end of the scale, many molecules have no smell, so naievely one
might assume the range is at least -130 to 0dB, roughly speaking. But I
suspect the sense of smell saturates much sooner than "0dB". Some odors are
weaker, perhaps in the parts per thousand range (I know matter-of-factly
that pure propane gas has a very mild odor), putting the ceiling at
perhaps -20 or -30dB, but that's measuring a completely different
molecule -- comparing odor thresholds is NOT comparing threshold to
saturation! For sure, the sense of smell fatigues after being exposed to an
odor, giving some limit to dynamic range over time at least. Unfortunately,
I doubt I could find any data on how strong a smell can be sensed.
Elsewhere, bloodhounds are mentioned as up to 100 million times (70dB) more
sensitive than humans (again, on completely unspecified terms!), putting
their sense down around perhaps -200dB. Now, one [human] breath of air
contains a couple liters volume, which is about 0.1 mole of air, or 6 x
10^22 molecules. That means humans can smell, per breath, about 6 billion
molecules of that grapefruit stuff. That also means bloodhounds can smell
on the order of hundreds or tens of molecules, which is quite impressive.
The most sensitive insects supposedly can detect single molecules, which is
even more impressive (all in the name of sex, of course).
Vision has a wide range, but I wouldn't put that much confidence in human
vision. After adjusting, our eyes can maybe see some details on a moonless
night, which Wikipedia gives as 1mlx. Our eyes really evolved to cope with
direct sunlight, which pretty well maxes them out at 100k lux. That's a
range of 80dB. Very little detail can be seen in that darkness, not even
color, and it takes a half hour to adapt to those conditions, so it's not a
very useful range for the first 20 or 30dB.
Tim