What algebraic structure do date, temperature, and similar quantities belongs to?

abstract-algebra

I find that some quantities share serveral characteristics.

For date:

  • "1st July" + "1 day" = "2nd July"
  • "2nd July" - "1st July" = "1 day"
  • But "20th August" + "29th August" is nonsense.

For temperature:

  • An object can be heated up from 25 degree Celsius by 5 degree Celsius to 30 degree Celsius.
  • The temperature of boiling water is 100 degree Celsius. The temperature of the surrounding is 25 degree Celsius. The difference is 75 degree Celsius.
  • But we cannot add the temperature of a cup of tea to the temperature of a cup coffee.

Also, we cannot do multiplication on date or temperature. Depending on context, their relative values are useful, but their absolute value are not relavent. E.g., we don't count date from the Big Bang; weather forecast does not involve absolute temperature.

How does abstract algebra describe these quantities? Is there an algebraic structure captures their characteristics?


Solution 1:

What you are describing is similar to the concept of an affine space.

An affine space over a vector space $V$ is a space filled with points. You can add a vector to a point to get another point, and you can subtract one point from another to get a vector. But you cannot add two points together.

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