• Question: Quantum Physics tells us that a quanta doesn't exist unless it is being observed. based on that, answer the following question: if a tree falls in a forest and no one is there to hear it, does it make a sound?

    Asked by willemh to Sara, Kimberley, Julia, Drew, Amy on 16 Jun 2011. This question was also asked by rachel1995.
    • Photo: Drew Rae

      Drew Rae answered on 14 Jun 2011:

      Hi Guys. I can see you’ve been thinking about this. Strictly speaking, quantum physics says that the probability waveform doesn’t collapse to a single solution until it is measured. This doesn’t require observation by a conscious being – just interaction with the waveform by something that can measure it.

      The answer to the tree Koan (a Zen Buddhist question) is simpler than this though, because we can collapse the probabilities simply by observing the fallen tree. As soon as we see that the tree has fallen, and we know that the mechanics of a falling tree create sound, we can be sure that it did in fact make a sound.

      If we never observe the fallen tree, then the answer is that the tree both fell and made a sound, and didn’t fall and didn’t make a sound, and as soon as it is observed only one of those will still be true.

    • Photo: Julia Griffen

      Julia Griffen answered on 14 Jun 2011:

      Heisenberg…. and his old uncertainty principle it seems….

      Heisenberg was pulled over by a cop… cop askes Mr H…’Sir Do you have any idea how fast you were driving’ Mr H replies ‘I have no idea how fast but I can tell you exactly where I am!’

      Basically its impossible to measure position and momentum at once… this alll stems from wave particle duality.. These guys were trying to study electrons and found they couldn;t measure position as well as momentum, due to the electron acting as both a wave and a particle. – look up particle in a box experiment for more info!

    • Photo: Amy MacQueen

      Amy MacQueen answered on 14 Jun 2011:

      Science is based on observable things that help us to predict the past and the future…sure no one was there to hear the tree but every time we have seen a tree fall it makes a noise so we could, logically, assume that it had made one.

      But this is based on the natural laws of the universe being consistent – and why should we assume they are? (Well…partly because the alternative would mean we could never be sure of anything and we don’t like that idea).

      Good question!

    • Photo: Sara Imari Walker

      Sara Imari Walker answered on 15 Jun 2011:

      Hey willemh and rachel!! Good question. So quanta do exist even when they are measured – they just don’t exist in any particular state (i.e. don’t have a defined position or velocity). Just as Drew as nicely explained it is the act of observation that makes a system “choose” what state to be in. Before hand it could be 50/50 the tree has fallen or not. But after you observe the fallen tree, the probability collapses to 100% it fell!! Get your head around that 😉

      I love Drew’s addition of a little philosophy here!

    • Photo: Kimberley Bryon

      Kimberley Bryon answered on 16 Jun 2011:

      I saw this question on QI and the argument they made was that in order for sound to be classed as sound you need an ear so that the soundwave can be turned in to a sound. However, all the other components of sound are there. Once you have seen the fallen tree, we know that if we had been there it would have made a sound. I think Sara and Drew have explained the Quantum physics bit nicely.

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