A note on Emil's post 46:
If the analogue signal has a finite number of Fourier components and you sample at twice the frequency of the highest frequency component (only twice in each cycle of that highest frequency component) your digital sample will EXACTLY reproduce the analog signal! This is for me a hard to believe, but true mathematical fact, which is not hard to prove, but I have forgotten how.
... For example, can you tell that digitally recorded music is not really continous?
No and I just told why if the sampling frequency is high enough.
It is also interesting to note that photographs, even of the old film cameras, are digital. I.e. a 2D array of individual silver halide particles that were hit by at least two photons each.
I also hold a "crackpot" POV about perception. I.e. what we perceive is NOT, as the standard POV states, the "emergent" end product of many stages of neural computational transform of the signals our sensory nerve transducers acquired from environmental stimulation. Instead what we perceive is a
creation of the parietal section of the brain, in what I call the Real Time Simulation, RTS.
To quickly understand the main flaws of the accepted theory of perception read short post at:
http://www.sciforums.com/showpost.php?p=2502342&postcount=12
Read my longer RTS essay at:
http://www.sciforums.com/showpost.php?p=905778&postcount=66 It explains dozens of neurological and psychological facts the accepted POV about perception cannot! (Doing that took about 8 pages if printed.)
As all nerves in the parietal brain either fire or don't*, the RTS is digital.
What you directly perceive has a stronger claim to being "reality" than what you can only infer may exist based on your direct perception. I.e. the "external world" is only INFERRED to exist. It may not exist but I, like almost** all others, do make the assumption that it does exist.
*There are a few optical nerves which don't have this fire or not nature -i.e. appear to be analogue, but not if you look closely at their activity - it is still just the movement of discrete Na+ ions across the axon sheath. I.e. for these nerves, the internal potential does not go quickly from -70mV to slightly positive as the nerve "fires" but can vary slowly up or down within this range.
** Bishop Berkeley did not so assume and has perfect logic in his defense of his position that the real world is only an illusion. (That logic has withstood 300 years of attacks!)
BTW, for John99 only: A piron I think fits between a virus, which must invade and use a cell to reproduce and and a bacteria, which is alive and needs only to eat to reproduce. Like a virus, the piron is not alive, but it can reproduce outside of cells, I think, or at least doesn't need that biological machinery of the cell to reproduce. Some years ago, man had no idea how pirons reproduce. That may not still be true -far out of my field of physics. Pirons cause diseases, including "Mad Cow disease."