Why isn't temperature a vector quantity?

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Discussion Overview

The discussion revolves around the nature of temperature and whether it can be considered a vector quantity. Participants explore the implications of temperature as a scalar versus a vector, discussing its representation in different contexts such as potential fields and quantum systems.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants question why temperature should be considered a vector quantity, suggesting that it lacks direction.
  • Others propose that temperature could be represented in a vector form to describe variations at different locations, such as in a pipe, to calculate temperature gradients.
  • Some argue that while temperature itself is a scalar, it can be represented as a matrix of values corresponding to different positions, though this does not make it a vector in the traditional sense.
  • A participant introduces the idea that in certain quantum systems, temperature can exhibit directional properties, necessitating separate temperature values for different dimensions.
  • Concerns are raised about the mathematical properties required for something to be classified as a vector, including operations like addition and scalar multiplication.
  • Some participants emphasize that temperatures cannot have negative values in most systems, which challenges their classification as elements of a vector space.
  • There is a discussion about the physical meaning of adding temperatures, with some asserting that the addition of temperatures does not yield a straightforward result as it does with momentum.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the classification of temperature as a vector. There is no consensus on whether temperature can be treated as a vector quantity, with some arguing for its scalar nature while others suggest contexts where it may exhibit vector-like properties.

Contextual Notes

The discussion touches on various definitions and interpretations of vectors and scalars, as well as the implications of temperature in different physical contexts, such as quantum mechanics and thermodynamics. The limitations of these definitions and their applicability to temperature are acknowledged but not resolved.

  • #31


I like Serena said:
The operations are well defined mathematically.
Left on their own they may make no physical sense, but as an intermediate step to a result, they do make sense.

So you add 2 temperature vectors. The result makes no physical sense.
Then you divide it by 2.
There! You have the average of the temperatures, which does make physical sense.

Same thing for calculating a variance, where you would add the additive inverse of the vector to the vector with the mean temperatures.
Next you would multiply the vector with itself to find the vector with squared errors.

DaleSpam said:
More importantly, for every element of a vector space there is an additive inverse which is also an element of the vector space. In most systems a temperature of 300 K makes sense, but a temperature of -300 K does not. So for most systems temperatures wouldn't be elements of a vector space.

I am also not certain that addition of temperature makes sense physically. I mean, if you add a system of 300 K to a system of 400 K you don't usually get a system of 700 K. Contrast this to momentum where if you add a system of 300 kg m/s to a system of 400 kg m/s you do get a system of 700 kg m/s.

the key idea in that temperature does not follow an addition of 300k + 400k=700k is the fact that temperature is seen as averages,when you say 300k ,this is the state of equilibrium,in that context the energy has been distributed uniformly giving it a scalar touch
and that is what @i like serena is trying to highlight
i suppose
 
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  • #32


Hootenanny said:
No it doesn't! You are standing in the same spot. Just because you are looking in a different direction doesn't mean that the temperature will be different.

The temperature only depends on where you are, which is why it is a scalar [field] and not a vector!

Try it: Take a thermometer and stand in your house/school/gym/park facing east (or any other direction you choose). Then, turn by 90 degrees. Does the temperature change?

as i said what you might call as temperature is the equilibrium state,where energy is distributed,do the same experiment as u suggest but with a condition that in that room there is a heater which is just being switched on
 
  • #33


nouveau_riche said:
as i said what you might call as temperature is the equilibrium state,where energy is distributed,do the same experiment as u suggest but with a condition that in that room there is a heater which is just being switched on
That still wouldn't change anything. The temperature only depends on your position, not your orientation. It doesn't matter whether your environment is in equilibrium or not. Provided your thermometer is in the same position, it will register the same temperature regardless of its orientation.
 
  • #34


nouveau_riche said:
depends upon the K.E distribution of particles around
KE is not a vector either.

Please see the above discussion, temperature does not form a vector space.
 
  • #35


Since we are talking about vectors in space, the crucial point is how they convert to a different coordinate system. If your "vector" has temperatures at different locations as components, how do they change if you rotate the coordinate system?
 
  • #36


Hootenanny said:
That still wouldn't change anything. The temperature only depends on your position, not your orientation. It doesn't matter whether your environment is in equilibrium or not. Provided your thermometer is in the same position, it will register the same temperature regardless of its orientation.

why it wouldn't,when i am near the heater the thermometer will give a higher reading than at the other end
that is not my orientation,that is my position
 
  • #37


DaleSpam said:
KE is not a vector either.

Please see the above discussion, temperature does not form a vector space.

why not?
 
  • #38


nouveau_riche said:
why it wouldn't,when i am near the heater the thermometer will give a higher reading than at the other end
that is not my orientation,that is my position
Are you even reading what I have written? This is precisely my point. The temperature doesn't depend on orientation only position. That is why the temperature is a scalar field, rather than a vector field.
 
  • #39


Let me go back to basics and try to pre-empt a few questions and put an end to this thread once and for all.
nouveau_riche said:
why not?
Because it is defined as a scalar.

- Can you define it as a vector?
No.

-Why?
Because it won't make any sense, just as it makes no sense to call temperature a vector.
 
  • #40


HallsofIvy said:
Since we are talking about vectors in space, the crucial point is how they convert to a different coordinate system. If your "vector" has temperatures at different locations as components, how do they change if you rotate the coordinate system?

rotating a coordinate system will change the position vector(of the point,which i am measuring) given by vector laws
 
  • #41


nouveau_riche said:
rotating a coordinate system will change the position vector(of the point,which i am measuring) given by vector laws
Halls was asking about the temperature itself.
 
  • #42


Hootenanny said:
Halls was asking about the temperature itself.

not in temperature
 
  • #43


Hootenanny said:
Are you even reading what I have written? This is precisely my point. The temperature doesn't depend on orientation only position. That is why the temperature is a scalar field, rather than a vector field.

so a vector takes into account the orientation?
 
  • #44


nouveau_riche said:
so a vector takes into account the orientation?
In a manner of speaking, yes. In a vector field, each point is associated with a value and a direction. However, in a scalar field, each point is only associated with a value.
 
  • #45


nouveau_riche said:
why not?
See above. This has all been covered in detail.
 

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