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Measurement, Quantum Wierdness and Single-Effect Events

  1. Jun 11, 2015 #1

    I was reading an article the other day regarding measurement and 'Quantum Wierdness' and it made me think about this whole deal with measuring stuff in QM.

    [EDIT: Article: http://www.anu.edu.au/news/all-news/experiment-confirms-quantum-theory-weirdness ]

    The thing is I regularly work with what's called SEE (Single Effect Events, sometimes also Single Effect Upsets) in my work. This is bit errors, transistor upsets and damage resulting from high energy electrons and protons in outer space (on the ISS).

    Now this can all be dealt with quite classically. Measurements have been made of the particle flux and energy distribution, and then you simply have to design your electronics to be safe, should an SEE occur, or protect your electronics with shielding.

    However, I was thinking about this whole thing from a QM perspective today, since these electrons and protons should be quantum particles, right? I guess the SEE could be seen as a "measurement" of some sort? The thing is the word "measurement" confuses a bit. It leads one toward ideas of experiments and setting up a system to measure some effect, but here it just 'happens' with some statistical probability.

    But how far from the "knowledge" of such an event can we remove ourselves? I mean this in the sense that, what if on the Integrated Circuit, a portion of transistors are running some kind of logic, but with no connections to any interface we are looking at, or perhaps even capable of looking at. Would we still say that, even though we can't 'measure it', these SEE's are happening, meaning that the quantum particle (electron or proton) interacts with the transistor. If this is the case, the 'oberserver effect' is then non-existant.

    This is in the direction of "is there a sound when a tree falls in a forest, but no one is there to observe it".

    Could anyone with some more expertise perhaps shine a little light on my thoughts and tell me if this trail of thought leads to despair down the line.

    Is the cake a lie?

    Thanks in advance :)
    Last edited: Jun 11, 2015
  2. jcsd
  3. Jun 11, 2015 #2
    Oh, and a little funny thought:

    IF it is such that this "isolated" part of the IC (Integrated Circuit) does not experience SEE's before we actually 'look' to see if it has happens. The following is a wierd scenario: The IC is in space, is subjugated to the flux of high energy particles. Is returned to earth. Brought in to a lab. Put under an electron microscope to check this 'isolated' part of the IC, and THEN the wave-function collapses (in the past?) / the world splits in two / the cake is found to be a lie.
  4. Jun 11, 2015 #3
    Right you are having similar thoughts to einstein. This question has ramifications in philosophy as well as physics. The debate raged among founders of quantum mechanics even . Heisenberg stated that two non commuting operators can never both be 100% accurately measured. His uncertainty principle stated particles don't have a definite position and velocity. Others didn't like that pronouncement ( einstein). This is a statement of reality and not of experimental inefficiency. Now that answers part of your question of existence. Now as existing when not looking that is harder. Particles don't have definite values of certain observables at the start. Measurement leads to wave function function collapse and disturbs completely the other variable.

    Now for the question of exsistence when not observed is harder. Schrodinger' s cat being half alive and dead is a particularly fascinating example. Supposition and entanglement serve as tools here. Supposition is the melding together of two quantum states and entanglement is the measurement of one tells info on the other. Entanglement in certain cases proves existence of not measured variables by measuring the other entangled one and gaining info on it. Supposition is the melding together of possible states that in truth is the real state of the particle until measured. As to the existence of those variables as long as time moves forward events will transpire accordingly and those events will still take place according to fundamental laws. I hope this helps. Currently there is no resolution to this debate, but I have presented the view held by the majority of quantum theorists.
  5. Jun 11, 2015 #4


    Staff: Mentor

    You have hit on the good old measurement problem.

    A lot of research has been done on it and what's called decoherence has shed new light on it. It hasn't solved it - but it has transformed our understanding.

    I sense you have the math to understand it so here is a paper that examines the issue:

    Once you have read it we can chat about what it all means - but it hinges on the difference between an improper and proper mixed state.

    If you are really keen THE book to get on it is the following:

  6. Jun 11, 2015 #5
    Thanks both of you!

    And thanks for the article Bill! I'll definitely give it a look! :)
  7. Jun 11, 2015 #6


    Staff: Mentor

    Its never half alive - half dead. The observation occurred at the particle detector - everything is common-sense classical from that point on. At the time it was proposed everyone knew that - the issue was while its obvious you place the observation at the detector the theory doesn't force you to - and that was the issue Schroedinger wanted to highlight.

    In the example of the IC in space the observation occurs in space.

    In modern times however its generally placed just after decoherence which resolves the problem.

  8. Jun 12, 2015 #7
    Bhobba is using the model which puts observations as the primary (only?) reality. Your question used the term "quantum particle". That would imply, I guess, that you have in mind a model in which the system, the cosmic ray plus IC in this case, has a state - the state is not merely a calculating device, it is the actual properties of the system. According to the state picture, the interaction between the cosmic ray and the IC leaves the IC in a superposition - Schrodinger's cat is not, as is repeatedly pointed out, half-dead and half-alive but wholly dead relative to the observer's state when he has seen it as dead and wholly alive relative to the observer's state when he has seen it alive. Decoherence doesn't particularly affect this picture but does account for why the observer tends to see dead cats or alive cats and not wierd quantum state cats.

    So back to the quantum state. The |1> state will be relative to the state of the system when it reads a 1 and the |0> state will be relative to the state of the system when it reads a 0. The state is a simple summation of both "possible" states. Collapse theories assume that the state simplifies by wave function collapse - e.g. immediately after decoherence; this is presumed to be a genuinely random process. In a no-collapse theory there is no real randomness, only the appearenc of randomness to any observer repeating the experiment. Decoherence does not provide an account of collapse in a theory in which the state is real - the awkward quantum cats disappear but the other classical cat does not.

    added: So your choice of interpretation is up to you - you can have the IC registering an error on a truly random basis or you can say that it both does and doesn't misbehave and we only see one outcome because we are entangled with the chip.
  9. Jun 12, 2015 #8


    Staff: Mentor

    The above post has a number of inaccuracies eg
    Every quantum system has a state. The theory is silent on its meaning - it can be just a calculational device or it can be very real - its interpretation dependant.

    I think sorting it out in this thread would be off-topic.

    The OP has been given some material that gives the modern take on the measurement problem and I think other issues are best taken elsewhere.

    As a start if you want to pursue the above then a new thread can be started. But its been done to death in many threads so maybe simply going through them rather than having a rehash would be better.

  10. Jun 12, 2015 #9
    Well either bhobba or I am missing the point of the question as it seems to me that the OP was asking about what happens and when, not about how to do the sums.
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