<Tr> <Td> Vacuum instability </Td> <Td> Collapse of the quantum fields that underpin all forces, particles and structures, to a different form . </Td> <Td> Cosmology traditionally has assumed a stable or at least metastable universe, but the possibility of a false vacuum in quantum field theory implies that the universe at any point in spacetime might spontaneously collapse into a lower energy state (see Bubble nucleation), a more stable or "true vacuum", which would then expand outward from that point with the speed of light . <P> The effect would be that the quantum fields that underpin all forces, particles and structures, would undergo a transition to a more stable form . New forces and particles would replace the present ones we know of, with the side effect that all current particles, forces and structures would be destroyed and subsequently (if able) reform into different particles, forces and structures . </P> </Td> </Tr> <P> The effect would be that the quantum fields that underpin all forces, particles and structures, would undergo a transition to a more stable form . New forces and particles would replace the present ones we know of, with the side effect that all current particles, forces and structures would be destroyed and subsequently (if able) reform into different particles, forces and structures . </P> <P> In this kind of extreme timescale, extremely rare quantum phenomenae may also occur that are extremely unlikely to be seen on a timescale smaller than trillions of years . These may also lead to unpredictable changes to the state of the universe which would not be likely to be significant on any smaller timescale . For example, on a timescale of millions of trillions of years, black holes might appear to evaporate almost instantly, uncommon quantum tunneling phenomenae would appear to be common, and quantum (or other) phenomenae so unlikely that they might occur just once in a trillion years may occur many, many times . </P>

Major epochs in the history of the universe in order