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Opposite of light

  1. Jun 24, 2008 #1
    Emission of a specific band of wavelengths results in what we call 'light'.

    If there is such a thing as the 'balance of nature' (ie. 2nd law), then what is the opposite of light?

    It's not darkness (that's the absence of light).

    Use a black hole for example. Light can not escape, therefore we can not 'see' it.
    If these 'negative' photons are traveling 'away from us', shouldn't we call them 'dark' and address them as such?
  2. jcsd
  3. Jun 24, 2008 #2
    2nd Law of what (thermodynamics, newtons laws, us constitution) there are a whole lot of laws out there?

    As for the motion of photons, they are moving everywhere around us, sometimes towards us sometimes away, we just dont see it until it reflects back to us. Say your standing with the sun behind you looking at a tree. The photons must travel past you and hit the tree and come back to you before you can see the tree.

    For the blackhole question, picture the photon as a tennis ball, On the moon, i can throw that tennis ball and itll go off into oblivion, however on earth, the tennis ball is going to come back down. We dont call it a negetive tennisball just because it can escape though.

    Are these serious postulations, or just philisophical conundrums that you are asking?
  4. Jun 24, 2008 #3
    Sorry, I assumed 'the balance' was known as the 2nd law of thermodynamics.

    You are giving examples of reflection or refraction. This is a serious question.
    Why has it not been discussed before?
  5. Jun 24, 2008 #4


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    There isn't. At least, not in physics.

    The 2nd Law talks about entropy. What does it that have to do with 'balance of nature' woo-woo-ism?

    non sequitur. How did you get from 'things we can't see' to 'negative photons'?
    To use a trivial analogy: My dog can't escape from my house, that doesn't make him a negative dog.

    Then you'll need to use correctly-defined physics terms and concepts.
    Last edited: Jun 24, 2008
  6. Jun 24, 2008 #5
    2nd law of thermodynamics:
    "Processes that decrease total entropy of an isolated system do not occur. If a system is at equilibrium, by definition no spontaneous processes occur, and therefore the system is at maximum entropy" - http://en.wikipedia.org/wiki/Second_law_of_thermodynamics

    Well, considering there's no 'correctly-defined physics terms' to properly describe this thought experiment, my words in quotes are a 'rough draft' of something abstract and not easily communicated. And, I agree- the black hole scenario is not a good analogy now that I think about it in greater depth.

    So, let me re-phrase the whole thing...what does one call the 'opposite of light'?

  7. Jun 24, 2008 #6


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    No really. I know that's not the answer you want, but you are the one claiming that there has to be some more substantial opposite. Why do you insist so?

    What's the opposite of hot? Cold. (Wrong: there is no such thing as cold; there is only absence of heat. Cold is an organism-derived relative comparison between two temperatures (both of which are heat)).

    A more generalized and more fundamental version of the same thing: Q: what's the opposite of the universe/existence? A: Nothing/Oblivion. i.e. in any meaningful way, the opposite of something that exists is its absence.
  8. Jun 24, 2008 #7
    I'm not looking for an answer, Dave
    It's just a thought experiment down a road untraveled. What doesn't have an opposite?

    So you think the compliment of light is 'nothing'. If light is traveling in a direction 'X' it can be refracted, reflected or absorbed. But the compliment of light should travel in a direction of 'minus X' ......Right ????
  9. Jun 24, 2008 #8
    but that is the direction it is travelling not what it is
  10. Jun 24, 2008 #9
    Agreeing with Dave

    And thats what the 2nd law is saying, that all systems are trying to move towards no spontaneous reactions, that is the function of light. When particals reach to high of an energy level they drop thier electrons to a lower shell by releasing a photon. That photon travels until it hits a partical that can absorb this extra energy.

    Light doesnt need an opposite to satisfy the rule of increasing entropy, it is the solution to particles not meeting that state of equilibrium.

    2nd law doesnt state that there are opposites, it just says that eventually everything will reach a balance where it wont absorb or let of energy. I think your confusing equilbrium balance with traditional chinese spiritual balance, entropy has nothing to do with ying and yang!
  11. Jun 24, 2008 #10
    a car traveling in reverse is still a car
  12. Jun 24, 2008 #11
    this law applies to temperature as was discussed before... when you put an ice cube into a hot cup of coffee the ice cube is not actually "cooling" the cup of coffee in a literal sense... the hot coffee is distributing its heat to the ice cube melting it and distributing the energy uniformly which is "diluting" it... and then the coffee will distribute the energy uniformly to the room... and the room to the earth and the earth to the universe eventually.
  13. Jun 24, 2008 #12
    Which eventually means that the entire universe will reach the same temperature!
    (hopefully in the upper 80's for comfort :P )

    Hopefully this makes sense to you pinestone. Nothing has to have an opposite but rather a lack thereof, so that it eventually reaches the same temperature!

    Unfortunately, what this also means is that there is no perfect alternative fuel, and no matter what we do, every action we take, we are killing the universe! (in a metaphorical sense, obv the universe is not living, but a state in which nothing can move or happen is as good as dead to me!)
  14. Jun 24, 2008 #13
    Yes, but we call it light because it's an emission away from the source.
    if the travel was 'inward' could we still call it 'light'?

    Great explaination- but what happens if the particles reach a lower energy level?
    Could that result in an in-ward travel ?

    Taking the above statement into consideration, what about the opposite state of decreasing entropy- such as time-invarient conditions?

    I'm not thinking spiritually, just logically. There are theories of parallel universes, multiple strings and the like- what's so difficult in the concept of 'negative' light?

    Yes, you are right. Reference my reply to shamrock5558 (above)
  15. Jun 24, 2008 #14
    this brings up the interesting fact that energy and matter are forms of one and the same thing... but we have matter, anti-matter and energy... is there anti-energy or just lack thereof.
  16. Jun 24, 2008 #15
    I've thought about this before as well.

    Can anything in nature exist without an opposite? You've got matter and antimatter. So, how can the opposite of light be "no light" and cold "no heat" .. Wouldn't this be the same as saying the opposite of matter is "no matter" ... repulsion is to "no repulsion" ... The answer is probably just nobody knows for sure.
  17. Jun 24, 2008 #16


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    There is an opposite to the emission of light, and that is the absorption of light. Astronomical spectroscopy relies on the accurate measurement of both emission and absorption, and the displacement of these lines from those of terrestrial standards is considered to be due to cosmological expansion. Using the displacement of these lines, the apparent distance of the observed object is extrapolated from the Hubble redshift/distance relation.
  18. Jun 24, 2008 #17
    i guess to elaborate on my question before... anti-matter still has mass... can mass be negative? just a thought to ponder.

    pinestone you need to realize that by the car analogy he is just showing that you are not describing negative light you are just talking about light being emitted in the opposite direction. It is still light though.
  19. Jun 24, 2008 #18
    Is is feasible to imagine a 'stand-alone' absorber that 'sucks' light into itself and re-emits it the opposite direction (ie. lower energy state)? There would be no apparent way to observe this phenomenon, but as a logical thought experiment I think it's an interesting concept.
  20. Jun 24, 2008 #19


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    No, that is not why we call it light, and this may be the crux of your confusion.

    Note that we do not see the light emitted from the Sun until it is absorbed by our eyes. i.e. it is light whether being emitted or absorbed.

    Perhaps your question is more accurately 'what is the opposite of the emission of light'. To which the answer is: the absorption of light.
  21. Jun 24, 2008 #20


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    Sure. An ashphalt roadway absorbs sun light in the visible spectrum and emits it in the infrared spectrum.
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