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0 degrees celsius + 0 degrees celsius -

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Re: 0 degrees celsius + 0 degrees celsius -

#62

Post by shasta »

omaranto wrote: post #53
_delirium wrote: post #7

It looks like it must be using kelvin as its canonical units: 0C + 0C = 273.15 K + 273.15 K = 546.3 K = 273.15 C The weirdness is that conversions like that don't work for units that have different zero points. Perhaps addition of temperatures isn't really well defined? If 273.15 K + 273.15 K does not equal 0 C + 0 C, despite 273.15 K = 0 C, it's not clear what addition "means" in this context. One restricted form of…

You're absolutely right that two different things are measured in degrees: temperatures and temperature differences. And they work as you said: you can add temperatures differences, you can add a temperature difference to a temperature, but you can't add two temperatures. (This is like pointers and ints in C.) Mathematically temperature differences form a group under addition and temperatures (idealized to have no mi…

Well, you can add temperatures. Temperature is defined to be average kinetic energy of particles, and addition of kinetic energies is well defined. The way Google does the addition is in this sense correct - there's a reason it's called absolute zero.

The thing is that you usually don't want to add temperatures, for the same reason that you generally don't want to add other averages: they're usually not particularly interesting quantities. For this reason, you might encapsulate the definition of temperature and not expose the addition operation, but the dimensional analysis is fine the way Google does it.

Re: 0 degrees celsius + 0 degrees celsius -

#63

Post by Groxx »

_delirium wrote: post #7

It looks like it must be using kelvin as its canonical units: 0C + 0C = 273.15 K + 273.15 K = 546.3 K = 273.15 C The weirdness is that conversions like that don't work for units that have different zero points. Perhaps addition of temperatures isn't really well defined? If 273.15 K + 273.15 K does not equal 0 C + 0 C, despite 273.15 K = 0 C, it's not clear what addition "means" in this context. One restricted form of…

>But then addition isn't commutative.

  "30 C warmer than 5 C"
  = 5 C + 30 C
  = 278.15 K + 30 K
  = 308.15 K
  = 35 C
Am I missing something?

Re: 0 degrees celsius + 0 degrees celsius -

#64

Post by JangoSteve »

JangoSteve wrote: post #5

Digging a little deeper... (0 degrees Celsius) + (0 degrees Celsius) - (0 degrees Celsius) = 0 degrees Celsius (0 degrees Celsius) - (0 degrees Celsius) = 0 kelvin (0 degrees Celsius) + (0 kelvin) = 0 degrees Celsius The last 2 of the 3 are wrong, so I'd say this is definitley a bug. EDIT: I think I figured it out. It's converting everything after the first temperature to Kelvin, without converting the first temp to…

Yup you guys are right. This is what I get for trying to overanalyze a problem at 3am.

Re: 0 degrees celsius + 0 degrees celsius -

#66

Post by Marticus »

Moral of the story: Google is a bunch of cheeky bastards.

It took me a while to understand the reasoning behind that as points on a scale versus actual temperature values ("Celsius degrees" versus "degrees Celsius," respectively).

Googling "0 Celsius degrees + 0 Celsius degrees" returns 0 Kelvin, which would be expected given the technicality in wording.

Re: 0 degrees celsius + 0 degrees celsius -

#67

Post by georgecmu »

Groxx wrote: post #63
_delirium wrote: post #7

It looks like it must be using kelvin as its canonical units: 0C + 0C = 273.15 K + 273.15 K = 546.3 K = 273.15 C The weirdness is that conversions like that don't work for units that have different zero points. Perhaps addition of temperatures isn't really well defined? If 273.15 K + 273.15 K does not equal 0 C + 0 C, despite 273.15 K = 0 C, it's not clear what addition "means" in this context. One restricted form of…

> But then addition isn't commutative. "30 C warmer than 5 C" = 5 C + 30 C = 278.15 K + 30 K = 308.15 K = 35 C Am I missing something?

Am I missing something?

Yes

= 5 C + 30 C = 278.15 K + 30 K

30 C != 30 K

Re: 0 degrees celsius + 0 degrees celsius -

#68

Post by georgecmu »

jcdreads wrote: post #51
mhansen wrote: post #9

It's meaningless to add temperatures when the zero level is at +273. It's like adding years relative to 2010 years ago - it would be meaningless to add this year - 2010 - with (say) 1666 - the year of the Great Fire of London. It's meaningful to take differences (the Great Fire happened 344 years ago), but not to add. (Unless we converted to some kind of absolute time units e.g. years since the big bang) I'd say what…

It's meaningless to add temperatures in any circumstance. You can average temperatures, and you can add amounts of heat energy, but it is semantic garbage to try to add temperatures. I'd say what it's doing--converting to an absolute scale then adding--is an interesting bug.

Doesn't averaging temperatures require addiion?
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