Dinesh

Dinesh

Posted on 08/25/2016


Photo taken on August 21, 2016


See also...


Keywords

Summer
Michigan
2016
OUP Blog
Oxford University Press
i phone image


Authorizations, license

Visible by: Everyone
All rights reserved

Photo replaced on August 25, 2016
55 visits

A tree falls in the forest, and there’s nobody around to hear, does it make a sound?

A tree falls in the forest, and there’s nobody around to hear, does it make a sound?

Comments
Dinesh
Dinesh
A tree falls in the forest, and there’s nobody around to hear, does it make a sound?
For centuries philosophers have been teasing our intellects with such questions. Of course, the answer depends on how we choose to interpret the use of the word ‘sound’. If by sound we mean compressions and rarefactions in the air which result from the physical disturbances caused by the falling tree and which propagate through the air with audio frequencies, then we might not hesitate to answer in the affirmative.

Here the word ‘sound’ is used to describe a physical phenomenon – the wave disturbance. But sound is also a human experience, the result of physical signals delivered by human sense organs which are synthesized in the mind as a form of perception.

Now, to a large extent, we can interpret the actions of human sense organs in much the same way we interpret mechanical measuring devices. The human auditory apparatus simply translates one set of physical phenomena into another, leading eventually to stimulation of those parts of the brain cortex responsible for the perception of sound. It is here that the distinction comes. Everything to this point is explicable in terms of physics and chemistry, but the process by which we turn electrical signals in the brain into human perception and experience in the mind remains, at present, unfathomable.

Philosophers have long argued that sound, colour, taste, smell and touch are all secondary qualities which exist only in our minds. We have no basis for our common-sense assumption that these secondary qualities reflect or represent reality as it really is. So, if we interpret the word ‘sound’ to mean a human experience rather than a physical phenomenon, then when there is nobody around there is a sense in which the falling tree makes no sound at all.
2 years ago. Edited 2 years ago.
Dinesh
Dinesh
Albert Einstein once famously declared that God does not play dice. In essence, a quantum particle such as an electron may be described in terms of a delocalized ‘wavefunction’, with probabilities for appearing ‘here’ or ‘there’. When we look to see where the electron actually is, the wavefunction is said to ‘collapse’ instantaneously, and appears ‘here’ with a frequency consistent with the probability predicted by quantum theory. But there is no predicting precisely where an individual electron will be found. Chance is inherent in the collapse of the wavefunction, and it was this feature of quantum theory that got Einstein so upset. To make matters worse, if the collapse is instantaneous then this implies what Einstein called a ‘spooky action-at-a-distance’ which, he argued, appeared to violate a key postulate of his own special theory of relativity.
So what evidence do we have for this mysterious collapse of the wavefunction? Well, none actually. We postulate the collapse in an attempt to explain how a quantum system with many different possible outcomes before measurement transforms into a system with one and only one result after measurement. To Irish physicist John Bell this seemed to be at best a confidence-trick, at worst a fraud. ‘A theory founded in this way on arguments of manifestly approximate character,’ he wrote some years later, ‘however good the approximation, is surely of provisional nature.’
2 years ago.
Dinesh
Dinesh
When Bell devised his famous inequality in 1964 these questions returned with a vengeance. Bell sought a way to discriminate between conventional quantum theory and a whole class of alternative, so-called local hidden variable theories which do not need to assume a collapse of the wavefunction. He deduced a mathematical relationship in which local hidden variable theories predict results that are manifestly contradicted by the predictions of conventional quantum theory, providing a direct laboratory test. Some exquisite experiments performed subsequently proved beyond any doubt that quantum theory, with all its apparent ‘spookiness’, is correct.
In 2003, English physicist Tony Leggett took the debate to another level. Local hidden variable theories are characterized by a couple of key assumptions. In one of these, it is assumed that the outcome of a measurement on a quantum particle can in no way be affected by the setting of the device used to make measurements on a second particle with which it is ‘entangled’ (in other words, both particles are described by a single wavefunction). Leggett chose to drop this assumption to see what would happen.
He went on to deduce a further inequality. For a specific combination of measurement settings, quantum theory predicts results which violate this inequality, implying that the outcomes of measurements on distant particles can be affected by some unspecified non-local influence of the device settings. The result we get depends on how we set up another device, even though this may be halfway across the universe. Spooky, indeed.
The results of experiments to test Leggett’s inequality were reported in 2007. Once again, quantum theory was proved to be correct. This kind of result cannot be reconciled with any theory which ascribes fixed properties to the particles prior to measurement. This means that we can no longer assume that the properties we measure necessarily reflect or represent the properties of the particles as they really are. These properties are like secondary qualities – they exist only in relation to our measuring devices. This does not mean that quantum particles are not real. What it does mean is that we can ascribe to them only an empirical reality, a reality that depends on our method of questioning.

Without a measuring device to record it, there is a sense in which the recognisable properties of quantum particles such as electrons do not exist, just as the falling tree makes no sound at all
2 years ago.
Dinesh
Dinesh
2 years ago.
Dinesh
Dinesh
The Uncertainty Principle { Uncertainty principle, also called Heisenberguncertainty principle or indeterminacy principle, statement, articulated (1927) by the German physicist Werner Heisenberg, that the position and the velocity of an object cannot both be measured exactly, at the same time, even in theory} is inescapable. Its effect may be negligible from heavy objects but it is alwlays there in the background generating tiny amounts of uncertainty. For microscopic particles its effect can never be ignored. But Heisenberg's uncertainty principle is not merely about our inability to measure a system without disturbing it. The uncertainty principle requires a far more profound shift in our view of reality than any recognition of the limitations of measuring devices. I may be uncertain about many things: the size of my next telephone bill, the capital of Azerbaijan, how many pints of milk remain in my fridge. I am confident however tha teach of these properties of the exterior world has an objective reality, whether or not I know them. ~ Page 151

However, the standard interpretation of quantum mechanics states that 'what can't be measured doesn't exist.' In this view, the contents of my fridge would not even exist until I opened the fridge door. In the early days of quantum theory, Niels Bohr was the most ardent proponent of this view point. When quizzed by a fellow physicist on what state a particle must be in, Bohr rqplied in exasperation "Be! Be! But what is this be?" Bohr claimed that 'an independent reality in the ordinary physical sense can neither be ascribed to the phenomena nor to the agencies of observation.' He was so persuasive that this viewpoint became enshrined as the standard interpretation of quantum viewpoint because enshrined as the standard interpretation of quantum mechanics, prevailing for much of this century. It is often known as the Copenhagen interpretation in recognition of the influence of Bohr and his co-workers at Copenhagen's Institute of Physics, where many of the fundamental advances in quantum theory were made.

In the Copenhagen interpretation of quantum mechanics, properties such as position and momentum became real only when measured. This is a revolutionary concept, but in itself amounts to little more than late night metaphysical ramblings concerning whether a tree makes a sound or not when it falls in the forest. I leave such thorny problems to future generations of undergraduates. What is of much more relevance is that, in quantum mechanics, measurement not only makes reality, but that measurement inevitably 'modifies' reality. ~ Page 152 Excerpts from "Quantum Evolution" Author - Johnjoe McCadden
2 months ago.