• Question: Is the 'observer effect' applicable to all events in the universe?

    Asked by rajathjackson to Chris, Dave, David, Fiona, Jack on 17 Jun 2013.
    • Photo: David Freeborn

      David Freeborn answered on 17 Jun 2013:

      Hi rajathjackson,

      Interesting question. The short answer is: yes it is.

      Measuring particles changes their properties. Some scientists think that quantum systems only get fixed energy and position when they are observed; before that they have a certain uncertainty. So an atom only gets a “fixed” energy when we actually observe it, before then it has a range of possible energies, which is a very weird effect.

      But everything in the Universe is made from quantum particles, so they should all experience a small “observer effects”.

      Some scientists go even further and say we can only treat the entire Universe as a quantum system. The Universe only took “fixed” properties when people living things first observed it. This is called the “Quantum Anthropic Principle”. That’s pretty weird, and I’m not sure I believe it!

    • Photo: Chris Mansell

      Chris Mansell answered on 18 Jun 2013:

      The way I like to think about it is in terms of measurements rather than observations. I prefer this because the word “observation” leads people to ask who is doing the observing and that is not quite the right question to be asking. Instead, it is slightly better to ask WHAT is doing the observing / measuring and the answer is anything. I’ll explain this a bit more.

      Have you ever heard of the double-slit experiment? If not, it is an experiment in which particles are fired, one at a time, at a wall with two slits (or holes) in it. Let us think about the case where a particl hits the inside edge of one of whichever hole it has gone through. Imagine that this collision heats up the inside edge. If we were to put thermometers next to the holes, we could tell which of the holes the particle has gone through (i.e. the hotter one) and, according to the “observer effect”, nothing quantum-mechanical happens in the experiment.

      Here is the key point: even if we don’t put thermometers next to the holes, nothing quantum-mechanical happens in the experiment. This is because holes themselves, in the process of getting hot or not getting hot, perform the measurement.

      The way to do the experiment so that cool quantum-mechanical phenomena occur is to make sure no trace is left anywhere at all in the surroundings of the experimental appartus as to which hole the particle has gone through. It doesn’t really matter whether or not humans are closely montoring and looking at all the surroundings of the appartus (i.e. whether or not they use thermometers), the “observer effect” still happens (because one part of the surroundings gets hot and not another part). So, to complete my answer to this question, the observer effect does happen everywhere in the universe, even places where there aren’t any humans.

      I hope this has helped your understanding of the observer effect a bit.

      Thanks for the really interesting question.

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