In 1926 Germanyıs Max Born said that perhaps matter is comprised of waves of probability. If we do an experiment many times with electrons, the electrons won't end up in the same place every time, but are likely to show up about the number of times predicted in each place. This is like tossing a coin. The probability of getting heads is ½, but if you toss a coin only a few times, you may get only tails. The more times you toss the coin, the more likely it is that you will have tossed heads half the time and tails the other half. Where the square of the magnitude of an electron wave is large, you are more likely to find an electron and less likely to find it where the magnitude of the wave squared is small.

A few months after this theory was suggested, a man from Austria, Erwin Schrödinger, created an equation to describe the shape and evolution of probability waves. He wasn't sure how a particle "chooses" between different possible futures, or if it doesn't choose at all and, instead, carries out every possibility, all but one of which take place in parallel universes.

Richard Feynman suggested that an electron travels on every possible path at the same time. He showed that everyday, large objects' possibilities cancel each other out so that only one possible path remains. We could see if this were true by shining light on the electrons while the double-slit experiment was being conducted. The light photons, however, would bounce off and disturb the path of the electrons. If we had just enough light to see the position of the electrons, the experiment would be disturbed just enough to get rid of the interference pattern and the results would be what we would expect if the electrons were just plain particles and not waves at all.