Negative feedback vs. Time and Classical and Quantum Mechanics.

[Circlotron]

http://cdsweb.cern.ch/search.py?recid=622019

Abstract: It is postulated there is not a precise static instant in time underlying a dynamical physical process at which the relative position of a body in relative motion or a specific physical magnitude would theoretically be precisely determined. It is concluded it is exactly because of this that time (relative interval as indicated by a clock) and the continuity of a physical process is possible, with there being a necessary trade off of all precisely determined physical values at a time, for their continuity through time. This explanation is also shown to be the correct solution to the motion and infinity paradoxes, excluding the Stadium, originally conceived by the ancient Greek mathematician Zeno of Elea. Quantum Cosmology, Imaginary Time and Chronons are also then discussed, with the latter two appearing to be superseded on a theoretical basis.
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Whew! Now I'm no world renowned expert on this sort of stuff, but upon thinking about it, it seems to me that there might be some kind of flaw in the application of negative feedback to a signal that changes with time. It means you cannot say that "now" the output voltage is X so feed back X/10 volts to the input and subtract it... blah blah, because if there is in reality no such thing as "now" then the whole NFB thing looks a bit wobbly. Is this maybe the reason that some people don't like the sound of amplifiers with large amounts of NFB?

/Circlotron - long on intuition, short on highbrow mathematics.

[SY]

Completely irrelevant. Sorry. The signals we deal with are soooooo far beyond the quantum limit in magnitude and time that you might as well worry about the gravitational influence of the Andromeda galaxy.

I'm no world-renowned expert on quantum mechanics, either, but at least I've had my papers on the subject published in reputable refereed journals.

[Bricolo]

Quantum mechanics and relativity is something you deal with when the particles you consider are moving at a speed of at least 1/10th of the light's speed.

Calculate the speed of a flux of electrons, say 1A in a 1mm² cable.
You'll get a few meters per second. Far from 30 000 000 m/s

[sam9]

Setting aside the theoretical discussions, consider tis empirical datum: NFB circuits function.

Ca. 1900 (+/- a decade) a physist whose name escapes me "prooved" that a bumble bee couuld not fly. Fortunately for flowering plants, bumble bees don't study physics so they fly along in merry ignorance.

[pinkmouse]

Hmm, I read the abstract as stating that you can't measure exact physical values at any point in time, not that time itself is uncertain.

There are also some physicists that theorise that it is our comprehension of quantum uncertainty that is wrong, and if we had the right way of describing the phenomena, uncertainty would no longer be an issue.

[Steve Eddy]

Originally posted by Bricolo
Quantum mechanics and relativity is something you deal with when the particles you consider are moving at a speed of at least 1/10th of the light's speed.

Calculate the speed of a flux of electrons, say 1A in a 1mm² cable.
You'll get a few meters per second. Far from 30 000 000 m/s

That's a number you'd get using the classical Drude model which assumes that all free electrons are participating in conduction. However QM says that that's not the case.

The Pauli exclusion principle says that no two electrons can be at the same energy level and that the electrons fill all the available energy levels from the bottom up. The highest energy level occupied at 0 degrees K is the Fermi level which for copper is an energy level of about 7 electron volts (eV).

Since an electron can only occupy an energy level which isn't already occupied, the electrons at the lower levels can't go anywhere because the energy levels above them are occupied.

So, as you add energy to the system, thermal and/or electrical, the only electrons available are those at or near the Fermi level so working in reverse, it's a top down rather than a bottom up function because the only available energy states are those levels above the Fermi level.

Because the energy levels involved in the typical thermal and electrical processes in audio equipment add energies of just fractions of an eV, only those electrons within a tiny fraction of an eV of the Fermi level participate in conduction.

The end result being that the number of electrons participating in conduction are far fewer than that assumed by the Drude model which means that the electron velocities will also be far higher.

For copper, that velocity (called the Fermi velocity) is about 1.5 x 10⁶ meters per second.

Still rather shy of 300,000,000 meters per second, but far greater than a few meters per second.

But at the macroscopic level it doesn't really matter. All the same laws apply. 1 A of current still involves moving 1 C of charge per second.

se

[Steve Eddy]

Originally posted by SY
I'm no world-renowned expert on quantum mechanics, either, but at least I've had my papers on the subject published in reputable refereed journals.

But what SY isn't telling you is that his papers were published in QMTV's Physicist Deathmatch and were referreed by Judge Mills Lane.

se

[SY]

Hey! "Weekly Reader" and "Highlights for Children" are reputable!

[Pjotr]

Originally posted by Steve Eddy

That's a number you'd get using the classical Drude model which assumes that all free electrons are participating in conduction. However QM says that that's not the case.

The Pauli exclusion principle says that no two electrons can be at the same energy level and that the electrons fill all the available energy levels from the bottom up. The highest energy level occupied at 0 degrees K is the Fermi level which for copper is an energy level of about 7 electron volts (eV).

Since an electron can only occupy an energy level which isn't already occupied, the electrons at the lower levels can't go anywhere because the energy levels above them are occupied.

So, as you add energy to the system, thermal and/or electrical, the only electrons available are those at or near the Fermi level so working in reverse, it's a top down rather than a bottom up function because the only available energy states are those levels above the Fermi level.

Because the energy levels involved in the typical thermal and electrical processes in audio equipment add energies of just fractions of an eV, only those electrons within a tiny fraction of an eV of the Fermi level participate in conduction.

The end result being that the number of electrons participating in conduction are far fewer than that assumed by the Drude model which means that the electron velocities will also be far higher.

For copper, that velocity (called the Fermi velocity) is about 1.5 x 10⁶ meters per second.

Still rather shy of 300,000,000 meters per second, but far greater than a few meters per second.

But at the macroscopic level it doesn't really matter. All the same laws apply. 1 A of current still involves moving 1 C of charge per second.

se

Ehm SE,

If you could mark a single electron that is going into a cable with "a red blob of paint", that "red" electron will come out at the other end of the cable after a relative long time. So its average speed is very low. That is all what Bricolo was telling IMHO.

However what counts is the speed of total charge indeed. And for normal cables that is about 0.6 to 0.9 the speed of light. Or in other words a delay of app. 5 ns/m.

Cheers

[Petter]

I think that the reason why many people don't like (global) feedback power amplifiers is that the loads are so reactive that they interfere with the feedback circuitry.

This is IMHO also the reason why we see such an active (and mostly bogus, again IMHO no flames, please) cable market.

Petter