• Question: Consider me tossing a coin and I got tail as a result on observing it. Then, what would be the result of the 'parallel me' in another universe? If the 'parallel me' gets head as a result then, considering all the parallel universes the probability of occurrence of any event would be 1!!! In that case the whole concept of probability(considering all the parallel universes) goes wrong. What's your opinion about this or am I thinking in the wrong way???

    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,

      This is a really interesting question. You are thinking about it in the right way.

      If we have an infinite number of parallel universes, all with slight differences, then yes, the probability of you getting heads in somewhere in some Universe is 1.
      But the probability of it happening in any particular Universe where you happen to toss the coin is still 1/2.
      So, yes, it depends on whether we are considering the probability in a particular Universe, or in any of the possible Universes.

      A lot of probability theory depends on how we use it. If there are an infinite number of parallel Universes, then yes, I am probably a supermodel and not a physicist in one of them. But the probability of me being a physicist in any particular Universe is extremely low.

      In practice, it’s most useful to consider the probabilities in a restricted zone, say to one Universe, or a handful of possible Universes with very restricted properties. For example, I sometimes consider the probability of an event occurring in any Universe which obeys a certain very restricted set of laws of physics.

      A lot also depends on what sort of parallel Universes we are considering. String theory allows a set of Universes with very different laws of physics, but “Many Worlds” Quantum Mechanics would leave every parallel Universe with the same laws as our own. So not every event would happen- a lot of events would still be impossible and not happen in any of the infinite Universes.

    • Photo: Jack Miller

      Jack Miller answered on 18 Jun 2013:

      I think it’s also important to say that when people talk about many different universes, what they’re really discussing is, to a greater or lesser extent, a theoretical tool towards getting a greater understanding of this universe. Theoretical physicists can spend a lot of time considering what seem like really crazy ideas, but they usually turn out to be very important in their own right, and worthy of exploration in a lot of odd circumstances.

Comments