Why does Celsius temperature in degrees have +/- signs, since it's scalar?

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Why does Celsius degrees have +/- signs, since it's scalar?

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phinds
Gold Member
2019 Award
Why does Celsius degrees have +/- signs, since it's scalar?
How would you recommend temperatures below zero Celsius be indicated?

davenn
Dale
Mentor
Scalars can be negative. You are thinking of a magnitude which is strictly non-negative. Temperature is not a magnitude.

Scalars can be negative. You are thinking of a magnitude which is strictly non-negative. Temperature is not a magnitude.
Thank you so much for the distinction. That makes perfect sense.

sophiecentaur
Gold Member
Why does Celsius degrees have +/- signs, since it's scalar?
The Celcius scale (also the Fahrenheit scale) uses values that relate to arbitrary points on an absolute temperature scale. That scale starts at Zero K so all temperature values are actually 'in the same direction'.

Scalars can be negative. You are thinking of a magnitude which is strictly non-negative. Temperature is not a magnitude.
The Celcius scale (also the Fahrenheit scale) uses values that relate to arbitrary points on an absolute temperature scale. That scale starts at Zero K so all temperature values are actually 'in the same direction'.
Yea, the Kelvin scale makes more intuitive sense to me, but yea the arbitrary nature of that zero point makes sense too, as representing another temperature scale. Thank you!

Gold Member
Yea, the Kelvin scale makes more intuitive sense to me, but yea the arbitrary nature of that zero point makes sense too, as representing another temperature scale. Thank you!
It's not really arbitrary, though. The scale for Celsius was chosen so that 0 was the freezing point and 100 the boiling point of water, two commonly-occurring phenomena in everyday life. Similarly, Fahrenheit's scale was chosen to relate to a human's every day experience. Absolute scales like Kelvin or Rankine are non-negative, which is nice, but they are much harder to intuitively relate to what you experience in life. It's a lot less convenient to talk about freezing occurring at 273.14 K and boiling at 373.14 K.

ELLE_AW
Staff Emeritus
2019 Award
The scale for Celsius was chosen so that 0 was the freezing point and 100 the boiling point of water
Originally, the reverse. It was changed by Linnaeus (yes, that Linnaeus) after Celsius' death.

It's not really arbitrary, though. The scale for Celsius was chosen so that 0 was the freezing point and 100 the boiling point of water, two commonly-occurring phenomena in everyday life. ...
Yes, but in the big picture it is arbitrary -- we could be doing our labs on the planet Zork, where atmospheric pressure is different.

Where I live, water boils at 204F. Oops, I mean 95.6 Celsius.

Gold Member
Yes, but in the big picture it is arbitrary -- we could be doing our labs on the planet Zork, where atmospheric pressure is different.

Where I live, water boils at 204F. Oops, I mean 95.6 Celsius.
Still not arbitrary. It has a specific and logical reason.

It has a specific and logical reason, but it is arbitrary.
Lots of other values could have been used for equally
specific and logical reasons.

-- Jeff, in Minneapolis

ELLE_AW
LURCH
Originally, the reverse. It was changed by Linnaeus (yes, that Linnaeus) after Celsius' death.
You mean 0° used to be the boiling point of water, and 100° was the freezing point? Well then I’m glad it got changed; that’s just confusing.

A.T.
It's not really arbitrary, though. The scale for Celsius was chosen so that 0 was the freezing point and 100 the boiling point of water, two commonly-occurring phenomena in everyday life.
If the Celsius scale is "arbitrary", then so is the Kelvin scale. The difference of 1K is still based on boiling and freezing of water.

Gold Member
It has a specific and logical reason, but it is arbitrary.
Lots of other values could have been used for equally
specific and logical reasons.

-- Jeff, in Minneapolis
ar·bi·trar·y
/ˈärbəˌtrerē/
1. based on random choice or personal whim, rather than any reason or system.

So... not arbitrary.

A.T.