Science a GoGo's Home Page Forums General Discussion Physics Forum What triggers decoherence?

Now if you are as confused by this answer as I am, then my job is done

Specifically, decoherence does not attempt to explain the measurement problem. Rather, decoherence provides an explanation for the transition of the system to a mixture of states that seem to correspond to those states observers perceive. Moreover, our observation tells us that this mixture looks like a proper quantum ensemble in a measurement situation, as we observe that measurements lead to the "realization" of precisely one state in the "ensemble".

Both of these suggest, I think rightly, that the concept of reality is metaphysical, rather than scientific. Ultimately all we can test is whether or not our ideas about reality accord with the answers we obtain when we carry out experiments.

I was taking one thing at a time and trying to sort out if decoherence was linked to thermodynamics in such a way that would let us consider decoherence as a concrete feature in what we perceive as reality;

I personally don't accept that at all, I definitely only experiment and test real things in my reality and my reality rarely changes and most of the time it matches your reality

The truth refers to what is real, while falsity refers to what is not. Fictions are considered not real.

History is full of such folly like classical physics itself as a prime example.

Unfortunately your propensity for launching vitriolic attacks on others, and persistently putting down people with lesser/different qualifications hints at an underlying insecurity.

I have to wonder how arrogant it is to describe classical physics as “folly”. Surely folly would be believing something when you had evidence that it was wrong. Shouldn't classical physics be seen as providing giants on whose shoulders future generations can stand to see greater things.

In the past we have been lazy, classic physics could cover 99.99% of anything in the world and so we never bothered to correct it and hence here we are 100 years down the track. That is no longer true at all, everything in computers and half the new electronic devices are relying on QM. Next year we will have an entangled communication link from a satellite in space to earth. The Higg's discovery will change a whole pile of things over the coming years.

Observing an indeterminate state doesn't lock it in, when we look away it becomes indeterminate again.

“Decoherence occurs when a system interacts with its environment in a thermodynamically irreversible way"

It gets worse extend that thought if you did multiple observations you would sap energy out of the object wouldn't you ... hold that thought we will come back to it.

So the connection is temperature contains information and all objects radiate that information. If that wasn't true you wouldn't and couldn't cool in the situation in space because you are not in contact with anything to transfer heat with by normal convection methods.

I get that convection wouldn't work in space, but why would I not radiate heat?

Reverse the question why do you radiate heat in space and why do you lose energy doing it. I mean you know you radiate heat in space but whats the mechanism that drives it?

Under classic physics there is no mechanism you just have to accept it does it, QM is telling you why it does it think about Haroche’s experiment.

That leaves you in the nasty situation that the thermodynamic laws have no reason to be other than they exist. So what we are what we are trying to do here is fill the WHY in.

I think you are getting a bit ahead of yourself. QM doesn't tell us why any more than classical physics does. It is still just a description of what happens. It may be more detailed than classical physics, but that is just because we know more about how it works.

I started noticing right after you started posting on SAGG that you feel that QM has all the answers, and you don't think much of any other theories, such a GR. You really need to loosen up and accept that QM doesn't have all the answers.

I am not trying to attack Classic Physics here in fact I am trying to tie classic physics and QM together so we have a sort of consistency.

So are we clear I don't remotely think QM has all the answers, hell I don't think it even has a large proportion of them it is a step along the way.

QM we all have had discussions with old people that do it and so I think you are showing your age smile

Bill: We never had QM in my time and we were just fine sonny laugh

Not true it does tell you why it doesn't give you the mechanism.

If QM tells us why then you can explain why:
C is the universal speed limit
Energy comes in quanta associated with Planck's Constant
The Pauli Exclusion Principle works
A lot of other basic laws of physics are the way they are
Bill Gill

you claim thermodynamics has no value other than its existence yet every time I ask what value QM has you run off like a scared dog with his tail between his legs.

Can you answer why GR causes the double slit experiment to work the way it does. Explain how classic physics causes entanglement and why it occurs. Explain how gravity is responsible for what ends up as Quantum electrodynamics?

Those are about the same intelligence as your questions

There is one massive difference between classical physics and QM ... QM hasn't been falsified millions of times

Under classic physics there is no mechanism you just have to accept it does it, QM is telling you why it does it think about Haroche’s experiment.

My feeling is that you aren't really here to help us understand what modern science. You seem to be here more to bolster your own ego, at the expense of us ignorant boobs.

Bill Gill

...you, Orac, are getting arrogant. You appear to feel that we should all bow down and acknowledge you as the master of SAGG.

My feeling is that you aren't really here to help us understand what modern science. You seem to be here more to bolster your own ego...
Bill Gill

What triggers decoherence?

Thread drift!

Well, that's sorted that.

Doh! Just because he thinks everyone is ignorant, don't make it so...

My feeling is that you aren't really here to help us understand what modern science. You seem to be here more to bolster your own ego, at the expense of us ignorant boobs. I suggest you try to be more tolerant of the fact that we really don't know as much about QM as you do. We still do have some intelligence and are capable of figuring things out, with a little guidance.

Nevertheless, RQM is only an approximation to a fully self-consistent relativistic theory of known particle interactions because it does not describe cases where the number of particles changes; for example in matter creation and annihilation

So another belief TT or is that a judgement

So why do you hang out on some back water forum because it stimulates your intelligence TT

As I said at least I get something useful from the forum I get to practice my english, what are you getting from it?

Anyhow as we aren't on topic perhaps lets go back to NQS shall we.

my ego well it got smashed and left the building like Elvis.

TT that is just unkind flogging a guy when he is down where is all your compassion and brotherly love, I confessed to everything you all asked for. I will drag myself up to answer anything you would like me too.

1. Quantum mechanics is valid everywhere, for small and large systems, for intelligent and unintelligent objects; and all quantities that were thought to be "real" classical observables in the ignorant era of classical physics become linear operators on the Hilbert space with their eigenstates, eigenvalues, and their probabilities that can be predicted from the amplitudes (but never deterministically); there is no segregation of contextual and real observables

2. Classical physics is always just an approximation, and can be derived to be a good one under certain circumstances

3. Only probabilities may be predicted by quantum mechanics (i.e. in the real world) and classical determinism only occurs when the probabilities become negligibly small everywhere except for a small vicinity of the "correct" classical history

4. The boundary between the quantum and classical realms occurs when the interference effects get suppressed; this loss of coherence (the loss of information about the relative phases of complex amplitudes) is the only effect that universally occurs to produce a limit that is well described by classical physics in our quantum world

5. The suppression of quantum interference is called decoherence, and is caused by the interactions with the environment (i.e. degrees of freedom that we can't and don't want to keep track of); in this process, the off-diagonal elements of the density matrix plummet and the diagonal entries may be interpreted as classical probabilities; in this regime when the interference is gone, Bell's inequalities (and other manifestations of the classical intuition) become approximately valid

6. Quantum mechanics fully determines where this boundary occurs, and the required inequalities depend on the physical system, its Hamiltonian, the density of the environment, the strength and speed of interactions, and many other things: the emergence of the classical limit is a dynamical question and there is no "universal" answer to the questions e.g. "how many atoms or how long time one needs for classical physics to emerge"; everyone should calculate or review at least five order-of-magnitude estimates of the "critical" quantities where the classical limit becomes valid, in order to see the huge diversity of these scales in different contexts; these calculated boundaries are obviously correct on theoretical grounds and in many cases, the quantum-classical transition can actually be observed (at the predicted place)

7. In a classical regime, the preferred basis vectors of the Hilbert space are those that can imprint themselves into the environment (in Zurek's jargon, these states pass the einselection which makes them immune against decoherence); bizarrely non-local Schrödinger's cat superpositions are not in this category, and one can show, e.g. in the consistent history framework, that they don't allow us to formulate consistent histories (for which the probabilities add as expected from logic); it is fully understood what's wrong with Schrödinger cat superpositions and the derivation of the preferred states depends on the Hamiltonian

8. There is no room for a physical collapse or, on the contrary, for an ad hoc privileged role of conscious observers; the wave functions only predict the probabilities but they can be calculated for any set of consistent histories, regardless of whether the systems look conscious, unconscious, macroscopic, or microscopic; the only "collapse" that occurs is the rapid diagonalization of the density matrix in the preferred basis by the interactions with the environment; however, the "unrealized" diagonal entries of the matrix (probabilities of outcomes that won't come true) are never "physically" set to zero because their interpretation always remains probabilistic, even when the classical approximation becomes acceptably accurate

9. There cannot be any deterministic description that would allow one to know the outcomes non-probabilistically, such as "pilot waves" or "hidden variables", not even in principle, and questions attempting to know "more" than what quantum mechanics predicts are unphysical; the Conway-Kochen Free will theorem is a way to prove that the microscopic outcomes can't be deterministically determined

10. From all practical points of view, Niels Bohr and his friends in the Copenhagen school were right on the money and decoherence may be interpreted as a justification, derivation, or a proof of their assumption that the classical intuition is fine for (mostly) large objects and quantum mechanics is crucial for (mostly) microscopic objects; they didn't know the modern derivation of decoherence but they understood its qualitative implications

11. Decoherence is a process with an inherent arrow of time that makes it analogous to friction, heat dissipation, and other thermodynamic processes with an arrow of time; the effects are related, the arrows inevitably agree with one another, and decoherence is as real as the other processes (that increase the entropy); the time-reversal asymmetry of decoherence is inevitable because the environment can't be assumed to be non-locally entangled with the system in the far past, but it can be shown to be correlated in the future because of the evolution (and one can't ever assume anything about the future or impose "final" boundary conditions by the very definition of the future which is yet to be seen)

12. On the other hand, consistent histories are just a particular convenient framework to formulate physical questions in a certain way; the only completely invariant consequence of this formalism is the Copenhagen school's postulate that physics can only calculate the probabilities, they follow the laws of quantum mechanics, and when decoherence is taken into account, to find both the quantum/classical boundary as well as the embedding of the classical limit within the full quantum theory, some questions about quantum systems follow the laws of classical probability theory (and may be legitimately asked) while others don't (and can't be asked)

1. I think I have the general sense of this, but I guess I would need more maths than I have to be able to get to grips with Hilbert space; not to mention “linear operators on the Hilbert space”. Any simplification on the Wiki article would be appreciated.

4. I would not be able to explain that to someone else, so I guess I don’t understand it.

everyone should calculate or review at least five order-of-magnitude estimates of the "critical" quantities where the classical limit becomes valid

in many cases, the quantum-classical transition can actually be observed (at the predicted place)

5. What are “off-diagonal elements”? I tried to get to grips with off-diagonal long range order, when I was looking at the work of Mazur and Chapline, but got no further than realizing it had something to do with the organization of particles in a quantum state.

6. My understanding of the Hamiltonian is that it quantifies the total energy (kinetic and potential) of the particles in a system, but beyond that it is a mass of mathematical esoterica.

in many cases, the quantum-classical transition can actually be observed (at the predicted place)

Could you give an example of such an observation, please.

7. I’ve no idea what the preferred basis vectors of the Hilbert space are, but this bit seems to be saying that in the classical world what we observe is our reality, and it’s not going to just vanish.

I think I get the bit about consistent histories, but the link between Schrödinger’s cat and the Hamiltonian eludes me.

8. I thought I was doing quite well with this one until I got to the “diagonalization of the density matrix in the preferred basis”.
Lost!

If you are happy with that