# User:Floaterfluss/My projects/Orders of magnitude (time)

Some radioisotopes have extremely long half-lives:

The following times all assume that the Universe is "open":

• 1014 years – the estimated time until low-mass stars cool off. The smallest red dwarf stars are the longest-lived stars, and are believed to have a lifetime of up to 14 trillion years (1.4 x 1013 years). Star formation is expected to cease in galaxies in about 1013 to 1014 years as galaxies are depleted of the gas clouds they need to form stars. The longest-lived stars formed from the last gas clouds will therefore cool off after about 2 x 1014 years.
• 1015 years – the estimated time until planets detach from stars. Whenever two stars pass close to each other, the orbits of the planets can be disrupted and the planets can be ejected from orbit around their parent star. Planets that orbit closer to their stars take longer to be ejected in this manner on average because a passing star must make a closer pass to the planet's star to eject the planet.
• 1019 years – the estimated time until stars detach from galaxies. When two stars pass close enough to each other, the stars exchange orbital energy with lower-mass stars tending to gain energy. The lower-mass stars can gain enough energy in this manner through repeated encounters to be ejected from the galaxy. This process can cause the galaxy to eject the majority of its stars.
• 1020 years – the estimated time until orbits decay by gravitational radiation
• 1030 years – the estimated time until galaxies disappear due to black holes
• 1036 years – the estimated half-life for proton decay, if GUT is right
• 1040 years – the estimated expiration of all protons in the universe due to proton decay, if GUT is right (probability dictates only less than one proton in the universe will survive its half-life if its true value is close to the theoretical lower bound)
• 1045 years – the estimated half-life of theorized radioactive decay of protons by virtual black holes, if they exist [1]
• 1064 years – the estimated time until black holes decay by the Hawking process
• 1065 years – the estimated timescale at which all matter is liquid at zero temperature due to tunneling effects
• 10100 years (a googol year) – the estimated time until supermassive black holes decay by the Hawking process
• 101500 years – the estimated time until all matter decays to iron (if the proton does not decay)
• ${\displaystyle 10^{10^{26}}}$ years – low estimate for the time until all matter collapses into black holes, assuming no proton decay
• ${\displaystyle 10^{10^{76}}}$ years – high estimate for the time until all matter collapses into neutron stars or black holes, again assuming no proton decay. Dyson, Freeman: Reviews of Modern Physics, Vol. 51, No. 3, July 1979(c) 1979 American Physical Society
This time assumes a statistical model subject to Poincaré recurrence. A much simplified way of thinking about this time is in a model where our universe's history repeats itself arbitrarily many times due to properties of statistical mechanics, this is the time scale when it will first be somewhat similar (for a reasonable choice of "similar") to its current state again.
• ${\displaystyle 10^{10^{10^{10^{10^{1.1}}}}}}$ years – scale of an estimated Poincaré recurrence time for the quantum state of a hypothetical box containing a black hole with the estimated mass of our entire universe.