How long is TIME and how do you measure it?

Our current best estimate is that the universe is about 13.799 billion years old. We don't have a good sense of when, or even how, the universe will end. But we expect that in 3.5 billion years, the Sun will heat up to the point that life will be unable to survive on the surface of the Earth. In 6 billion years, the Sun will expand into a red giant, and will consume the Earth. The base unit for time is the second, which is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.