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Thread: Absolute Zero

  1. #31
    Senior Member Lateralus's Avatar
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    Quote Originally Posted by forzen View Post
    A black hole would pull everything including light, so i was under the impression that it would be empty space, meaning not even light would be present.
    Just outside the event horizon? Black holes only absorb photons that cross the event horizon. It's possible for a photon to come within a Plank length of the event horizon and still not be sucked into the black hole.
    "We grow up thinking that beliefs are something to be proud of, but they're really nothing but opinions one refuses to reconsider. Beliefs are easy. The stronger your beliefs are, the less open you are to growth and wisdom, because "strength of belief" is only the intensity with which you resist questioning yourself. As soon as you are proud of a belief, as soon as you think it adds something to who you are, then you've made it a part of your ego."

  2. #32
    Senior Member forzen's Avatar
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    Quote Originally Posted by Lateralus View Post
    Just outside the event horizon? Black holes only absorb photons that cross the event horizon. It's possible for a photon to come within a Plank length of the event horizon and still not be sucked into the black hole.
    Ahh, then you will definately have light orbiting there. My knowledge of black holes isn't great, i just know it sucks bit time.
    This post grammatical errors had been intentionally left uncorrected.

  3. #33
    No Cigar Litvyak's Avatar
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    Quote Originally Posted by forzen View Post
    If theres no matter to pull into the black hole, there would not be any motion either, so would mean absolute zero. Unfortunately, Stephen Hawking had said that black holes emit radiation which supprisingly enought is call "hawking radiation."
    It was later proved that it's not emitted by the black hole itself, it's a result of quantum fluctuation based on the uncertainty principle.

  4. #34
    Senior Member Lateralus's Avatar
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    Quote Originally Posted by forzen View Post
    Ahh, then you will definately have light orbiting there. My knowledge of black holes isn't great, i just know it sucks bit time.
    Light wouldn't orbit. Black holes would alter the path the light would take, though.
    "We grow up thinking that beliefs are something to be proud of, but they're really nothing but opinions one refuses to reconsider. Beliefs are easy. The stronger your beliefs are, the less open you are to growth and wisdom, because "strength of belief" is only the intensity with which you resist questioning yourself. As soon as you are proud of a belief, as soon as you think it adds something to who you are, then you've made it a part of your ego."

  5. #35
    Senior Member forzen's Avatar
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    Quote Originally Posted by Lateralus View Post
    Light wouldn't orbit. Black holes would alter the path the light would take, though.
    I'm beat!! I submit lol.
    This post grammatical errors had been intentionally left uncorrected.

  6. #36

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    Quote Originally Posted by Antimony View Post
    Would all motion stop, all over the world, if we reached it here on earth?


    My chemistry teacher was telling us about how some people are worried that if they reached absolute zero that will happen. Of course, someone asked "what if it were in a closed container". His response was that would mean the container would have to be the same temperature, and the surrounding particles would have to be, and it would continue onward.
    Temperature generally flows from hot to cold, but the very notion of temperature really only makes sence when there is a lot of particles all with a fair amount of kinetic energy.

    When we get to really cold temperatures, we get definitions of temperature that are related to quantum mechanics is various ways. For example, in one model, that I learned in my statistical mechanics class, T=0, means that the system is in it's "ground" state. This is different from the classical definition of temperature, since there is still some energy left in the ground state.

    f95toli, on physicsforums, gave what I thought was a rather thorough answer.

    Physics Forums - View Single Post - Absolute Zero

    In reality this is almost a meaningless question since "temperature" is simply not a well defined parameter at low temperatures (and strictly speaking temperature is not defined at all below 0.65K since this is the lowest point that is defined on the international temperature scale ITS-90, but that is another issue).

    I am of course not saying that you can't use the concept of concept of temperature at low temperatures. But one there is no single, well, defined parameter "T" any more.
    A good example is solid state systems where the temperature of the electrons is usually higher than the temperature of the lattice (the phonons); since the interaction times become so long at low T they can differ by several hundred mK.
    (As far as I remember the electon-phonon
    interaction time actually goes to infinity as temperature goes to zero, meaning you will never reach a true thermodynamic equilibrium).

    There are also plenty of room for confusion due to the fact that temperature is also often used as a measure of energy.
    When people talk about laser-cooled gases the temperature they refer to is in reality the "kinetic" temperature, i.e essentially the kinetic energy of the particles divided by Boltzmann's constant. However, the statistics of the gas is not given by a classical distribution so this is not a "true" thermodynamic temperature; it is just a measure of the average velocity of a (small) group of atoms.

    In some research fields people also talk about the "temperature" of radiation, this is only a "real" temperature if the radiation is coming from a black body but the word is still used even when this is not true; e.g. for a monochromatic source the "temperature" is just
    h*f/Kb.

    Also, the original meaning of the word "temperature" in statistical mechanics is only meaningful for ensembles; a single particle or small collection of particles can't (according to this definition) have a "temperature" which means that you can't -strictly speaking- talk about the temperature of e.g. ions in an ion trap.
    Quote Originally Posted by Andy View Post
    There can never be no motion - the quantum uncertainty principal doesn't allow for it. It velocity was known to be zero with absolute certainty, then the error in position becomes infinite. Absolute zero is generally considered to be impossible.
    Quote Originally Posted by Andy View Post
    You'd know it was still, but it could anywhere in the entire universe. Arguably, it would have no definable location at all. Have you ever heard of quantum tunneling? Where a particle passes through a potential barrier that is too high for it to breach in conventional mechanics, due to the uncertainty in its location? In this case the absolute zero particle has an equal probibility of being anywhere. If you managed to pin its location down at all, it could no longer have zero motion, and would nolonger be at absolute zero.
    This is applying applying quantum mechanics to a classical notion of temerature. It is an interesting answer, because it shows that there will certainly be weirdness. Again, f95toli, I like f95toli's response, on physics forums.

    Physics Forums - View Single Post - Absolute Zero
    If an a piece of matter had a temperature of absolute zero then that would mean that all of it's atoms had zero velocity. But this is impossible because if we know with 100% that an atom has 0 velocity then according the UP we have no idea what its position is.
    I don't agree. As I wrote above the main problem here is that "temperature" is a very fuzzy concept at low temperatures and is not really well defined. The answer would be "yes" if we defined temperature to simply be a measure of the kinetic energy of the ions in a lattice. However, the "classical" temperature is usually thought of as a measure of statistical properties of an ensemble (i.e. the how the velocities are disitributed. In this case we obviously need the full QM formalism, and the latter does not give results that agree with classical thermodynamics near 0K.

    A good example is quantum browninan motion (see e.g. Gardiner's book "Quantum Noise") which agrees well with classical theory at elevated temperatures. However, a particle will actually slowly move due to zero-point fluctuations even at zero temperature (but the effect would be masked unless the T<< 1e-16 K) but the motion does NOT follow the classical diffusion law and is obviously not caused by a "temperature" as such (since we explicitly have T=0 in the equations). Hence, the fact that particles are moving does not neccesarily mean that you have a non-zero temperature.

    Quote Originally Posted by Antimony View Post
    New question: is time continuous?
    This is a very thorny question. The short answer is that nobody knows as of yet.

    Since energy is often quantized, and since there is in general relativity time is part of the position 4-vector, and Energy part of the momentum 4-vector, the uncertaintly principle seems to indicate that perhaps time should be quantized as well.

    However, also due to relativity, the scales of things (including time) depend on which observer is doing the measurement.

    So there are theoretical problems with quantized time as well.

    Loop Quantum Gravity is a theory that supposedly has resolves the theoretical difficulties of quantized time.

    Here are a few opinions from phsysicists from a decade ago:
    Is time quantized? In other words, is there a fundamental unit of time that could not be divided into a briefer unit? : Scientific American

    Quote Originally Posted by Litvyak View Post
    OK guys, something has stuck in my head (ouch). How cold is it on a black hole's event horizon?
    You can get a swag at the answer for this by looking at the energy of the black body radiation. Basically, the smaller the black-hole the "warmer" it is. Generally though, for block holes the size of the sun and bigger, the answer is really near absolute zero.

    Here is NASA's "ask an astrophysicists" answer (from the late 90s):
    Temperature of a Black Hole

    Quote Originally Posted by ubiquitous1 View Post
    Really? I don't understand why it wouldn't apply,but I guess I'll learn when I take discrete math. Thank you
    The fact that the set of real numbers is dense in itself has little to do with reality.

    Math is only a model of reality. If we chose the wrong math to model reality, then the properties the model predicts will be wrong.

    It is possible that the real numbers model real-life measurements improperly.

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  7. #37
    ⒺⓉⒷ Eric B's Avatar
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    I never did come to quite understand the concept of temperamenture in a vacuum.
    When I was a kid, my father used to tell me that space was basically absolute zero, or infinitely cold, and that if we were up there with no space suit, in addition to suffocating, we would completely freeze. Later on, I learned that hot and cold were not equal poles; cold was the absence of heat, and only matter gets hot. The temperature we feel on earth is largely the air. Direct sunlight would figure as well. So on the moon and other planets with no atmosphere, when they give a "surface temperature" (+200 on the sunlit side and -200 on the dark side), I take it it means the actual surface (ground), and not any kind of ambient temperature above it.
    And space does absorb heat, so IIRC, the Apollo mission, when the heat failed the air was starting to get really cold.

    So I guess absolute zero is not the temperature of a particular region of space. It would only be matter, with all of the heat removed, and heat is the motion of molecules. (And again, any matter near a black hole will be superheated from all the friction of surrounding matter). Scientists often speak of absolute zero, but they probably are referring to close to absolute zero.
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  8. #38

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    No its not the event horizon, its that other one i forget its name

    thus once and for all proving what a gullible lot we are

    Is hawking radiation ejected before it crosses that event horizon, or the other one I forget its name off (perhaps someone will post its name)

    Further more which planck lenght does one speaketh of, I hopes it the theoretically unprovable minimum one..though I like the ideal if

    To what ever gibbering frothy at the mouth type of tomfoolery fool said that
    Whoever said it was theoretically impossible is talking my language.if this is the absolute zero post thingie?

    look i read a few replies do i need to read em all,,,cos its about midnite

    is a photon sucked it, well if its not ejected into it them on would hypothesised it flows in

    would the world stop to OP

    well most likely on account of us albeing deed and not caring a jot, less or we all have to fill hot water bottles

    does matter/energy need temperature for movement...no idea what is what i think if i was thinking in a thinky kind of way was your original point

    exits stage left
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  9. #39
    Artisan Conquerer Halla74's Avatar
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    Quote Originally Posted by Eric B View Post
    I never did come to quite understand the concept of temperamenture in a vacuum.
    Alot of this conversation is beyond me, but I do have the following real world example to illustrate the gist of the phenomena mentioned by you earlier.

    TEMPERATURE IN A VACUUM:
    There is a thermos bottle that is sold, it is metal, and the walls of it are hollow, and the air space inbetween the walls are evacuated and sealed upon manufacture to be a vacuum.

    A friend of mine bought one of these thermos bottles, and made some tea to take with him and his wife on a day trek up and down a mountain while on on holiday.

    They made the tea at 5 AM that morning. They consumed it at 6 PM that evening, and he reported that the tea was damn near close to the temperature that it was upon being poured into the thermos bottle.

    Apparently, the complete absence of particles (ala the vacuum) that can bounce to and fro between the outer and inner walls of the thermos bottle creates a situation where the tea inside the thermos has very little opportunity to transfer its heat to anything in the outside world.

    I thought this interesting when I heard it.

    Quote Originally Posted by Eric B View Post
    When I was a kid, my father used to tell me that space was basically absolute zero, or infinitely cold, and that if we were up there with no space suit, in addition to suffocating, we would completely freeze.
    My Dad told me the same thing, and when I saw the space suttle Challenger blow up I relinquished any and all aspirations I ever had of becoming an astronaut, and let loose of any curiousities I had about what it might be like up there. I'm the ultimate realist. If I'm not going to experience from it, or have a high probability of benefitting from knowledge of a given phenomena, I quickly lose interest in it.

    Don't get me wrong, I respect astronauts immensely, and I am really glad I had a chance to eat NASA ice cream as a kid, and read of how tomoato plants grew in zero gravity up on the international space station, but in the big picture of things, that's as far as my interest goes, and I'm real comfy down here in my thermal underwear.



    Later on, I learned that hot and cold were not equal poles; cold was the absence of heat, and only matter gets hot. The temperature we feel on earth is largely the air. Direct sunlight would figure as well. So on the moon and other planets with no atmosphere, when they give a "surface temperature" (+200 on the sunlit side and -200 on the dark side), I take it it means the actual surface (ground), and not any kind of ambient temperature above it.
    And space does absorb heat, so IIRC, the Apollo mission, when the heat failed the air was starting to get really cold.

    So I guess absolute zero is not the temperature of a particular region of space. It would only be matter, with all of the heat removed, and heat is the motion of molecules. (And again, any matter near a black hole will be superheated from all the friction of surrounding matter). Scientists often speak of absolute zero, but they probably are referring to close to absolute zero.[/QUOTE]
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  10. #40
    Ruler of the Stars Asterion's Avatar
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    Does space have energy? It doesn't have mass at all, so it has no Kinetic Energy, and hence reaches absolute zero right? Are people saying that you can only apply temperature when/where there is mass?

    *is yet to read most of ygolo's refered post which probably contains the answer*
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