1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Privatives - Darkness and Cold

  1. Oct 23, 2009 #1
    Hi All

    This is my first post here and I have a question that should be relatively simple to answer.

    I am engaged in a debate with someone at the moment on a scifi forum. My stance is this:

    "Dark" is not a "thing" - it is merely the absence of light. You can measure light intensity, light has a speed etc. Dark cannot be measured in that way. It is not tangible.

    Similarly, "cold" is not a "thing" - it is merely the absence (or lower amount) of heat.

    These words are used in every day language because it's easier than saying "the temperature of the outside medium is less than that inside this building" - instead we say "it's cold". Just as with darkness, we say "it's dark outside" rather than "there is not as much light outside as there is inside".

    I know it's a bit pedantic but I was hoping that someone could confirm this view? I've done some brief research but unfortunately for me, "wikipedia" is not an acceptable source of information and whilst I usually try to follow the sources wiki gives as leads, for the statements of dark and cold being merely descriptive or abstract terms, there are no citations :(

    I apologise if this is the incorrect forum but I couldn't find on that was centered around the EM spectrum.

  2. jcsd
  3. Oct 23, 2009 #2
    I could say bright is the absence of dark just as easily.

    They both convey ideas and that's what words do. Whether or not you would classify darkness as a 'thing' would be up to your idea of 'thing'. Brightness is not a 'thing' in my book, nor is 'darkness'... they are more descriptions of 'things'. Same naturally goes for hot and cold being 'things'.
  4. Oct 23, 2009 #3
    No, bright is a function of the intensity of an electromagnetic wave...

    I can quantify it. Not so sure about darkness, unless you are defining it as the absence of certain degrees of an EM wave, in which case you don't actually need it, you're describing all the physics with one and the other is unnecessary.

    Its really just where you are setting your zero and how you are reading your scale.
    But it really seems like defining darkness as the absence of light, rather than the other way around, makes more "sense" even if it is arbitrary. And since physics has plenty of "because I feel like it" arguments, we'll go with that...
  5. Oct 23, 2009 #4
    Good point, you can quantify brightness... but you can probably also quantify darkness similarly.

    I guess maybe Darkness goes as the inverse of Brightness? So maybe they are both different units for the same quantity and in that sense both 'things'?
  6. Oct 23, 2009 #5


    User Avatar
    Science Advisor
    Gold Member

    I think you are dead on. You can quantify substantive qualities such as brightness and heat and give them units but their privative duals are only relative. I.e. no matter how bright it may be it is always dark relative to some exponentially brighter level. That's sometimes used to argue that "brightness" is meaningless but really it is a failing of "darkness".

    Another such quantity is ignorance. We speak of people being ignorant but it is also a privative quality as compared to knowledge which can be quantified to some extent (e.g. bits of information). This suggests that entropy ought to be replaces with an "orderliness" quantity. I've seen some attempts e.g. "extropy".
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook