1
$\begingroup$

A problem has been presented that goes like this:

Particles normally exist as several mathematical possibilities rather than one actual object. It is said that in the absence of observation, particles exist in a superposition of possibilities rather than one actual thing. But when we look they are not in such an indefinite state.

The problem states that the way to solve finding out why there is something definite when we look is decoherence. But it is said that this doesn't really solve the problem because whatever particles were used to collapse another, what was used to collapse that particle? And so on and on.

And the reason for this is because the wave function of a particle cannot be unentangled from that of whatever is used to measure it. When one photon is measured by another they entangle. If one particle measures another, it inherits part of its wave function, and that particle which is supposed to be measuring, cannot be fully explained without what it is measuring.

So you need another measuring device to collapse that initial measuring particle to a definite state. But then you need something else to collapse that measuring apparatus as well, and so on and so on. This creates a chain of material objects in a superposition of measuring, which is known as a Von Neumann chain.

Since quantum laws are what describe all material objects, some other particles or measuring apparatus is always needed to collapse the next one in line. You keep going back until you get to something nonlocal. Outside the entire material system, which escapes this chain by not being bound by the same physical laws, and is able to cause final collapse of everything in the chain, which is argued to be a conscious observer. Something beyond the material with the ability to collapse the entire physical system.

Is this true? If not, why not.

$\endgroup$
  • 1
    $\begingroup$ I think you are having trouble distinguishing between physical facts and explanation models within theories. In the realm of physical facts, there is no collapse of wave functions. In the model of single particle quantum mechanics (which is not even a particularly valid description of reality), the collapse of the wave function is merely a name for the fact that one does not have to understand the details of the quantum mechanics of the measuring apparatus to extract the relevant information from the observed system. $\endgroup$ – CuriousOne Aug 20 '14 at 3:32
1
$\begingroup$

No, a non-physical conscious observer is not required to explain the collapse of a quantum wavefunction (a perspective called the "Von Neumann-Wigner interpretation"), because wavefunctions don't ever actually collapse. The quantum state of the combination of a quantum system and its environment always evolves purely unitarily, with no true collapse. The quantum state of the system, considered in isolation, only gives the appearance of collapsing, due to an interaction with its environment in a process called quantum decoherence.

$\endgroup$
  • 1
    $\begingroup$ Unfortunately, "quantum decoherence" is basically just a fancy way of saying "collapse of the wave function". By using it we have replaced one thing that doesn't exist (a classical observer) with another (an irreversible thermodynamic process). While both explanations are perfectly valid, ontologically neither is very satisfactory. The better way to handle this would be by using field theory and by counting (outgoing) states. This would, at the very least, explain where the information of the non-diagonal elements is going (outward in a stream of newly generated particles). $\endgroup$ – CuriousOne Aug 20 '14 at 5:27
-1
$\begingroup$

no decoherence can not solve the problem because the environment must also obey the same rules as everything else and and there is nothing to collapse the wave function of the material that makes up the environment. though there is no consensus on the answer of the question

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.