Does heat always rise in a gravitational field?
I recently read that heat could be traveling down to the deep part of the ocean. Is there some new or old physics that makes heat sink?
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Heat does not rise or sink because it isn't actually a substance, it's energy being transferred. It is hot air which rises. The reason for this is that hotter air is more dilute than colder air. Or equivalently: colder air is denser than hotter air. The temperature of the air only plays a secondary role in determining which layer will be higher. The real decisive parameter is density.
In the sea, warmer water can sink because the density of water behaves peculiarly as a function of temperature. Water is densest at around 4 degrees Celsius. So if the rest of the water is cold enough, say at e.g. 1 degree Celsius, it will be less dense than the 4 degree water: the warmer water will be below the colder. This is related to the reason why ice floats on water: the ice is less dense than the warmer water below.
Read also this excellent answer by Lagerbaer on a related question.