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What is a physical property?

  1. Feb 23, 2010 #1
    I have so many fundamental questions about physics, i hope they are not considered "speculative" and deleted...

    Physics convolutes things so much, i wonder what does physics define as a physical property. For instance - an electron has a property (quality) of charge. Hopefully - this means that a property is something that an object contains or exhibits. This is where it gets quirky.

    If something appears red - does it exhibit redness because it contains redness causing every other color to be absorbed while red is being reflected? Can something exhibit redness without containing redness? I dont know!!! I can only guess that it must be contained to be considered a property. A cherry flavored drink may not contain any cherries, but it must contain cherry flavor.

    From Thread above: Does Time Exist at c. It seems that Light has a property of frequency meaning that light contains frequency. If light contains frequency, then light must also contain time. Or in other words - Time or Frequency is a property of light.

    According to Debroglie Matter Waves - Mass must also contain time. Is there a substance that exists at Absolute Zero - no molecular motion or zero enthalpy? Furthermore, can there exist a substance that has no Sub-Atomic motion - Zero spin and velocity?

    Why is Light referenced by a frequency, but matter seldom is done as such? Would referencing mass by a frequency according to the Debroglie matter wave be considered "Speculation"....
  2. jcsd
  3. Feb 23, 2010 #2


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    No. Frequency depends on the observer, too.
    No, same thing.
  4. Feb 23, 2010 #3


    Staff: Mentor

    Your use of the word "contain" is very weird. What does it mean to "contain" redness or a frequency? Maybe you could try to rephrase your post in a more understandable way.

    That said, this seems like a non-scientific question.
  5. Feb 23, 2010 #4
    Are you saying that to an observer travelling at the speed of light (barring relativistic impossibilities), light will have no frequency? My question is why does light appear to have a frequency at all? Is it purely a relativistic effect or a property of light - that is relativistically effected???
  6. Feb 23, 2010 #5


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    Light is electromagnetic waves. Waves have frequency, wavelength and phase.
  7. Feb 23, 2010 #6
    Does it? Perhaps i should use the word "Has" instead of "Contains". What's the difference? Doesn't physics say that an electron "Has" a charge. Isn't this the same as saying that an electron "Contains" a charge.

    Furthermore, isn't it said that charge is a "physical" property of an electron - as well as spin because it "Has" a spin. To "Have" something means to "contain" it. SCIENTIFIC??? defining a "PROPERTY" of something is what science is all about...AND defining what a PROPERTY is must be fundamental to science - else science is defining things in terms of ambiguous words. DONT side step the question. WHAT is a PHYSICAL PROPERTY???

    A property is quality that something "HAS". To HAVE something means to CONTAIN it. To CONTAIN it means that it is a part of the thing - This would mean that Light HAS time because frequency (1/s) is a property of light. This is the ULTIMATE scientific question. Does time exist within matter and light or is it merely a disassociated concept of change or perhaps BOTH?
  8. Feb 23, 2010 #7
    Light does not contain frequency, as your use of "contain" goes. It does, however, exist among the range of frequencies - and frequency is defined with time.

    Frequency, and thus Time, is light (at least in the visible spectrum).
  9. Feb 23, 2010 #8


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    No it's not. It means something else.
    Stop SHOUTING.

    No. I have a house but it contains me, not vice versa. You're using terms in your own special way.

    Light has frequency - not 'time'. Time is a difficult thing to define and is not a property of anything. It is not the ultimate scientific question ( why do you think that ?).

    The language of physics is mathematics. It helps to use precise words, but only to explain things to laymen. The formulae speak for themselves.
    Last edited: Feb 23, 2010
  10. Feb 23, 2010 #9
    Your house neither contains you, nor do you contain your house - Though a house is "property" it is not "A" property of you nor you of it. You add a meaning of encompass to "contain" - in your own special way. When something is "contained" it is within its very essence - permeated not encompassed. If you destroy your house, you dont alter the definition of yourself - but if an elec. charge is destroyed, it's physical definition is altered. Same for light and freq. You contain that which defines your existence - i.e. DNA. - that said...

    Light has frequency - not 'time'. Time is a difficult thing to define and is not a property of anything.

    Saying light has frequency (1/s) - not 'time' is the equivalent of saying light has wavelength (m) - not 'length'. Anyway...

    I thought that one of the greatest advances in physics was saying that time was a property of space - uniting space-time. How can it be assumed that "time" is not a property of anything, when ALL known natural phenomena contains time. Time is a property of Everything, Nothing exists outside of Time or without some form of motion. Space Either.

    Time doesn't change - everything changes IN time. At day-light's savings, we don't change time, we all change our clocks. When a second elapses, everone clock changes, but time doesn't. Regardless of the clock you are using, time is "always" causing things to change...It is the Irrresistable Force and Space is an Immovable Object.

    By uniting something - they become properties of each other or one and their existence becomes interdependent. Niether can Space exist without time nor time without space. They can now be said to "contain" each other. Space has time and time has space - They are ONE.
    Last edited: Feb 23, 2010
  11. Feb 23, 2010 #10


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    It never occured to me that my house is a property in the sense of real-estate. Only as a container. An unfortunate pun.

    The unification of space and time in special relativity was a great advance. But time is considered as a fourth dimension in SR - an axis of a graph, or the fourth component in a position vector. Space and time do not 'contain' one another, they have equal status as dimensions.
  12. Feb 23, 2010 #11
    I like the question "what is a physical property". The stuff about the speed of light and time is being covered in another tread so I will ignore it.

    A physical property is any thing you can measure.

    Has versus contains. I would say it does make a difference. Contains implies an electron is like a car trunk full of all sorts of different things like a bucket of charge over here and a pile of spin over there and a box of magnetic moment shoved in the back, etc...
  13. Feb 23, 2010 #12


    Staff: Mentor

    I agree. It makes sense to say that I "have" a height or a weight. I have heard people say "I have a height of 6 feet" but I have never heard anyone say "I contain a height of 6 feet". It is just weird to use the word "contain" in that way.
    Not only is your writing weird, but it is aggressive and rude. However, I will answer the question anyway.

    The word "physical" means "of or pertaining to physics" so that one is easy. The word "property" is a little more complicated; it means either "a quality or trait" or "an effect that an object has on another object". I think that both definitions of "property" are useful in this context. We can think of e.g. length as being some quality or trait that an object has, that would be the first definition. We can also think of length as being the result of a measurement an interaction with a rod, that would be along the lines of the second definition. Both I think are useful, but it probably is best to realize that we cannot know anything about the traits of an object except through its interactions (i.e. what we call properties of an object in science are actually the second definition, even if we can usually get away with treating them as the first).
  14. Feb 23, 2010 #13


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    This is a useful definition of "property": A physical system is said to have property X if an ideal experiment designed to test if the system has property X will find that it does with probability 1.

    "Properties" of this kind are represented mathematically by subsets of the phase space in classical mechanics, and by closed subspaces of the Hilbert space in quantum mechanics.
  15. Feb 24, 2010 #14


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    In relativity, physical quantities are expressed as geometrical objects (scalars, vectors...). Some of these are defined for something without reference to something else, like mass, or four momentum. I'd call these things a property of the object in question alone.
    In that sense, a light wave (or photon) "has" four momentum and position, and that's it. To define its energy or frequency, you have to specify an observer. That's ok, but the difference is crucial for the OP's misconception, at as I understood it: Frequency is not a property of a photon alone,hence you can't conclude that time exists for a photon, or how it "flows".
    If something has an intrinsic frequency, then it follows clearly that time exists for this thing, that it moves on a timelike geodesic, and that it has mass.
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