# Wavefunction collaps past/future effect

• batmanmg
In summary, the conversation discusses the concept of wavefunction collapse and its implications in quantum mechanics. It is mentioned that the collapse is a controversial topic and interpretations differ on whether it is a real phenomenon or just an approximation. Some interpretations suggest the use of hidden variables to explain the collapse, while others do not incorporate it in their formalism. There is currently no experimental evidence that favors any of the interpretations.

#### batmanmg

Wavefunction "collaps" past/future effect

A newb writes,

Do wavefunctions really "collapse?" It seems like this implies that they are destroyed and then recreated. Would it be more accurate to consider them like a guitar string and that observing it is like hitting the harmonic?

I guess another way to put this question would be to ask, Does a wavefunction's past effect its future once a certain observation has made it "collapse" and "reform"?

Wave Function

_______wave's past_________observation___Future
.-------------^------------------. V .--------^-------.
|~~~~~~~~~~~~~~~~~~~~~~-~~~~~~~~~~~~|
^_____________________________.^.
Neck_______________________The harmonic
Guitar String

My poiny of view:
1. QM equations give us the probabilities about something. And are the best ones that we have to describe that ultra-micro world.
2. "observations" give us measures about what happen.
3. Between two measures we simple doesn't know how the ultra-micro world is or behave.
To now more, you can see the following thread:
Can future events affect the past?

In the standard interpretation, wave function "really" do collapse, but we don't know whether the wave function is real, so we don't know whether the wave function really collapses.

It is often said that the collapse is just analogous to the transition from uncertainty to certainty when one throws a die and gets a result. However, this is difficult to make precise in the standard interpretation, because quantum uncertainty without hidden variables is not uncertainty about reality, since the wave function is not necessarily real.

However, in some cases, eg. non-relativistic quantum mechanics, we can imagine that there are hidden variables. In this case, quantum mechanics is very much like a classical theory, just a bit unusual in its nonlocality. In this case, one can derive the wave function collapse as an effective approximation to a reality in which there is no wave function collapse. Bohmian Mechanics is an example of this sort of hidden variable theory. At present we don't know if it can be extended to cover all relativistic quantum phenomena.

Another sort of hidden variable theory postulates that the collapse is real. Example of this sort of hidden variable theory are the GRW and continuous spontaneous localization (CSL) theories.

At present, we have no experimental evidence favouring any of the hidden variable theories.

Last edited:
afcsimoes
batmanmg said:
Do wavefunctions really "collapse?"

In interpretations that have collapse - yes. But not all interpretations do. The formalism that all interpretations use doesn't have it.

Thanks
Bill