Image 2 Caption: Kelvin old.

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Lord Kelvin was a pioneer of thermodynamics (see Wikipedia: Lord Kelvin: Thermodynamics) and the Kelvin temperature scale was named in honor of his work in that field.
Lord Kelvin also invented the original idea of the heat death of the universe in 1854. He was a cheery Scot.
Lord Kelvin was the first to suggest something like dark matter existed to explain the Milky Way rotation though his evidence may have been insignificant or spurious (see Wikipedia: Dark matter: Early history).
Image 3 Caption: The modern idea of the of the heat death of the universe according to the Λ-CDM model plus other ingredients illustrated cartoonishly.
The idea is that by a cosmic time of order 10**100 years, the black holes may have evaporated and the vastly expanded universe could be only a very dim, dilute gas of electrons, positrons, neutrinos, photons, and dark matter particles.
Some hypothetical dark matter particles decay to baryonic matter with very long half-lives (see Wikipedia: Dark matter: Indirect detection). So maybe the dark matter particles will be gone too by of order 10**100 years ??? in the Λ-CDM-model cosmic future.
The ultimate fate of the universe may be dismal---but it's all wild extrapolation.

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Local file: local link: lord_kelvin.html.
File: Astronomer file: lord_kelvin.html.