universe could come from nothing without breaking this law of the conservation of energy. He theorized that all the positive energy from mass and all the negative energy from gravity cancel, giving a universe with zero energy. Tryon gives credit for learning this idea from the general relativist Peter Bergmann. The person who first proposed the idea that we might live in a universe with zero net energy because positive energy from mass cancels the negative energy from gravity was the physicist Richard C. Tolman. Because Tryon believed our universe has zero net energy, in his paper Tryon wrote: "If this be the case, then our Universe could have appeared from nowhere without violating any conservation laws." Tryon then went on to describe how our universe could have come from a quantum fluctuation of the vacuum. He did this by simply applying the currently known scientific laws, including quantum mechanics and quantum field theory, to the era before our currently-known universe was present. Like many physicists he believed that a vacuum, or empty space, existed before our universe existed. According to quantum mechanics and quantum field theory, an apparent vacuum with no matter can support vacuum fluctuations. At the quantum level, because of the uncertainty principle, the law of the conservation of energy can be broken for just a brief moment, causing virtual particles to pop in and out of existence. Tryon says virtual particles also existed in the vacuum that was here before our universe existed, and these quantum fluctuations from nothing (the vacuum) eventually led to one of these particles popping into existence and becoming our universe. Tryon was not able to explain how one of these virtual particles grows to become a universe like ours, but he does say in his paper "that the laws of physics place no limit on the scale of vacuum fluctuations". He also mentions in his paper how "vacuum fluctuations of our Universe are probably quite rare". Although Tryon was the first person to suggest that our universe developed from a quantum fluctuation of the vacuum, the German physicist Pascual Jordan was the first person to talk about how a star might be created from the vacuum by a quantum transition. In the 1930s a number of physicists were looking at how to explain how matter arose if we lived in a continual, eternal, universe. Jordan knew how a sun's mass positive