Hawking Radiation - how could it shrink a Black Hole?

Discussion in 'Physics & Math' started by MyBrainHurts, Sep 29, 2008.

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  1. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    You were correct until the end part, which I made red. In the infalling particle's frame it is still being accelerated by the black hole's ever stronger gravity as it rapidly passes inside the event horizon.
     
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  3. Gravage Registered Senior Member

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    Wait a second. If you say nothing exists, not even particles, that would mean there are no particle-antiparticle pairs just outside the event horizon in quantum vacuum of space?
     
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  5. Gravage Registered Senior Member

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    [/QUOTE]


    Firstly, theories are never proven, they can only be disproven. Secondly, every theory that is used in physics today and for the last 300 years or so have been based on equations - One example of a 300 year old one is Newtons gravitational law, \(F = \frac{G m_1 m_2}{r^2}\), which is enough to land people on the moon. In any case, \(E = mc^2\) is only a special case of \(E^2 = (pc)^2 + (mc^2)^2\), it's not really a very important equation, except in the public consciousness.
    [/QUOTE]


    [/QUOTE]

    Hawking radiation is a much stronger result than you are giving it credit for. It seems like you want to say that a hypothesis is when you come up with something off the top of your head like "the sun is made of a conglomeration of farting elves." Hawking radiation has been computed in at least three different ways, and you get the same result each time. Also, there isn't (IMO) an argument to say that you shouldn't be able to combine QFT and GR in the way Hawking did it.
    [/QUOTE]


    [/QUOTE]

    It's true that calling Hawking radiation a theory is not right, because it isn't a theory - it's a prediction of QFT and GR, both of which we have extensively tested and believe to be "right."
    [/QUOTE]

    [/QUOTE]

    There have been plenty of things that have been theoretically predicted before they were experimentally observed. The one that I can think of off the top of my head is the \(\Omega^-\) baryon. I'm not saying that Hawking radiation is scientific fact, but it's far more robust than you're painting it to be.
    [/QUOTE]


    Gravage: Like I said above all of the concepts were created. This is how hypotheses are created, first you take proven theories as a basis, than you only expand it further, but the final result is a hypothesis since it's not proven by empirical facts and data. When it's proven by empirical facts and data, than and only than it hypothesis becomes a theory. Again look at the dictionary to see the difference between hypothesis and theory. It's complex, but the difference between hypothesis and theory is huge.

    You said that Hawking's radiation a prediction of QFT and GR, both of which we have extensively tested and believe to be "right." You said you believe it this is right, but one thing is experiment, and other thing is to use this same thing in every day practice. There is a great leap to be made between experiment and every day practice.
    What I hate about math is that it is represented as totally infallible. and you forget how many times math equations have been proven wrong.

    In math, when there is no enough empirical data, or no empirical data at all, math-experts make their own equations to trying to fill the hole, when there is no empirical data available, that's rubbish, they shouldn't solve the problem where there is no available empirical data, it becomes a philosophy, you're getting lost. And we all know all today's theories would be impossible without empirical data. Math has become equivalent to religion these days, because people who do math think it will solve all of the mysteries, but it never will, actually great majority of them would stay unsolved (approximately 95%).

    Also:
    A hypothesis is a working assumption. Typically, a scientist devises a hypothesis and then sees if it ˝holds water'' by testing it against available data (obtained from previous experiments and observations). If the hypothesis does hold water, the scientist declares it to be a theory.

    In popular usage, a theory is just a vague and fuzzy sort of fact and a hypothesis is often used as a fancy synonym to `guess'. But to a scientist a theory is a conceptual framework that explains existing observations and predicts new ones. For instance, suppose you see the Sun rise. This is an existing observation which is explained by the theory of gravity proposed by Newton. This theory, in addition to explaining why we see the Sun move across the sky, also explains many other phenomena such as the path followed by the Sun as it moves (as seen from Earth) across the sky, the phases of the Moon, the phases of Venus, the tides, just to mention a few. You can today make a calculation and predict the position of the Sun, the phases of the Moon and Venus, the hour of maximal tide, all 200 years from now. The same theory is used to guide spacecraft all over the Solar System.

    In science, a hypothesis is a proposed explanation or model of an event, phenomenon or process. There may or may not be evidence to support it, but it has not been tested and it has not been proven.

    A hypothesis becomes a theory when it has been tested and proven, and is used as a basis for further examination of the subject of the theory. The theory then becomes the model.

    Hypothesis is a scientific assumption quantifying scientific phenomenon. It becomes a theory when theoretically proved to be valid and experimentally found to be valid.
    http://psychology.about.com/od/researchmethods/ss/expdesintro_2.htm

    http://en.wikipedia.org/wiki/Hypothesis
    http://en.wikipedia.org/wiki/Theory#Theories_in_physics
     
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  7. prometheus viva voce! Registered Senior Member

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    Really this is just arguing semantics. Hawking radiation may possibly be a hypothesis as the word is defined in common usage. The word hypothesis is rarely used in theoretical physics because it implies "educated guess," which Hawking radiation certainly is not. It's better to refer to predictions of a theory.

    Lets just stick to Hawking radiation.

    Currently accepted theories of physics are GR and the standard model. By currently accepted I mean that every test that has been devised for them has agreed with the theoretical prediction. If there were one test that disagreed with that prediction then we would have falsified the theory and would have to junk it (or more likely, modify or generalise it so that it got the predictions right while still maintaining the old results). That's the cornerstone of all science - falsifiability.

    As it is, Hawking radiation is a currently untested prediction of GR and field theory like the standard model.

    Hawking radiation certainly is provable (or disprovable). Just because there is currently no known way to test it doesn't make it impossible to test. In actual fact, I recall hearing something about an experiment that looked at Bose Einstein condensates which would test the Unruh effect. That is a particle creation effect that is basically the same problem as particle creation by a black hole, so experimental proof could be closer than you think.

    That's not what Hawking radiation does. It takes GR and QFT, does not make any modifications to either, and derives the expected temperature of a black hole. In that sense it's not a hypothesis.

    Whenever I see this type of argument my will to type a response dies a little bit. Basically what you are saying is mathematics is not physics right?

    That's true, mathematicians work on maths for the sake of doing the maths (some of them do), physicists study physics using maths as a tool. Typically if the maths tells you something that is patently unphysical then it's because you've used the tool wrong. not because maths is wrong.

    Your statement "math-experts make their own equations to trying to fill the hole," is rubbish. The point of maths is to specify a minimal set of rules and see the consequences of those rules. In physics you model the system you're studying using mathematics. I reiterate, mathematicians are interested in the properties of mathematics. Physicists are interested in the properties of the universe.

    Let me put it another way - if we didn't use mathematics in physics then how would you compare data to theory? Let's suppose you're trying to test quantum theory and you're looking at the hydrogen spectrum. Your experimentalist says there are some lines of different colours, but that's in no way precise enough. He could then say something like "the first line is red." which isn't precise enough either. What is really needed is for the theorist to do a calculation predicting the wavelength of the lines, and the experimentalist to go and measure said wavelengths. Clear, precise and impossible without mathematics.

    Mathematics is not a religion and to say so clearly indicates you don't understand it.
     
  8. AlphaNumeric Fully ionized Registered Senior Member

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    6,702
    This shows a fundamental lack of understanding in the relationship between mathematics and physics.

    Mathematics is not physics. It is the language which physics uses to derive the logical implications of physical postulates. 1+1 = 2 is a mathematical statement. The speed of light is independent of the motion of an inertial observer is a physical postulate.

    Mathematic equations are never disproven once they are proven. That is the nature of logic. Likewise, the mathematical equations in a physical model are not disproven by experiment, they are demonstrated not to be the quantitative description of Nature.

    For instance Newtonian physics says Nature is invariant under Galilean transforms of the form \(x \to x-vt\). In special relativity it is \(x \to \frac{1}{\sqrt{1-\frac{v^{2}}{c^{2}}}}(x-vt)\). Both of these are derived, using mathematics, from the physical postulates which underpin their respective theories. Galilean transformations are demonstrably not the behaviour of Nature. This doesn't invalidate the mathematics which was used to derive them from physical postulates, it invalidates the assumption the said physical postulate is valid as a property of Nature.

    Physics is about saying "I think that Nature satisfies statements A, B and C" and then working out what A, B and C imply. How do you work out what they imply? You use logics, which mathematics is short hand for (before calculus physicists stated their logic in words).

    The mathematics, if proven by mathematicians, is infallable. That's why if a physical prediction of a model is falsified by experiment we say one of the postulates is falsified, not the mathematics. To think otherwise shows you have never actually done any physics and seen first hand the relationship between the two.

    My previous comments apply to this too. We trust mathematics to take us from the postulates of a physical model to its implications. If you postulate the two assumptions :

    1. The speed of light is independent of the frame of an inertial observer.
    2. Physics is frame independent

    then by using mathematics you get predictions like time dilation, the mass-energy relationship, electrodynamics etc. All of which can be tested. Physical assumptions are made and their physical implications are found. The slew of algebra you see in physics textbooks is all about going from the postulates to the implications, all the implications. It isn't mathematics for mathematics sake, its about finding the precise predictions a set of postulates imply and then testing them.

    Seriously, learn some sodding physics.
     
  9. Gravage Registered Senior Member

    Messages:
    1,241
    For instance Newtonian physics says Nature is invariant under Galilean transforms of the form \(x \to x-vt\). In special relativity it is \(x \to \frac{1}{\sqrt{1-\frac{v^{2}}{c^{2}}}}(x-vt)\). Both of these are derived, using mathematics, from the physical postulates which underpin their respective theories. Galilean transformations are demonstrably not the behaviour of Nature. This doesn't invalidate the mathematics which was used to derive them from physical postulates, it invalidates the assumption the said physical postulate is valid as a property of Nature.

    [/QUOTE]

    Physics is about saying "I think that Nature satisfies statements A, B and C" and then working out what A, B and C imply. How do you work out what they imply? You use logics, which mathematics is short hand for (before calculus physicists stated their logic in words).

    [/QUOTE]

    The mathematics, if proven by mathematicians, is infallable. That's why if a physical prediction of a model is falsified by experiment we say one of the postulates is falsified, not the mathematics. To think otherwise shows you have never actually done any physics and seen first hand the relationship between the two.

    [/QUOTE]

    My previous comments apply to this too. We trust mathematics to take us from the postulates of a physical model to its implications. If you postulate the two assumptions :

    1. The speed of light is independent of the frame of an inertial observer.
    2. Physics is frame independent

    then by using mathematics you get predictions like time dilation, the mass-energy relationship, electrodynamics etc. All of which can be tested. Physical assumptions are made and their physical implications are found. The slew of algebra you see in physics textbooks is all about going from the postulates to the implications, all the implications. It isn't mathematics for mathematics sake, its about finding the precise predictions a set of postulates imply and then testing them.

    Seriously, learn some sodding physics.[/QUOTE]


    You learn to live in the real world, not only in physics and mathematics world.
    No, you learn that physics and mathematics are not omnipotent. That is entire point. You can't prove me that physics will solve the greatest mysteries of the universe. None has ever succeeding in that mission.
    None ever will. It's very arrogant.
    This is why old parts of old hypotheses are either, changed or upgraded, or if there is no data to continue, new equations fill the hole.
    Just how many times equations, or parts of equations were proven wrong, they needed to go from scratch?
    An quantum physicist that it can take months even years just to complete an equation, it's extremely hard job.
    And of course the final equation must be comparable with observable natural phenomenons and experiments.

    Cheers.
     
  10. Gravage Registered Senior Member

    Messages:
    1,241
    Lets just stick to Hawking radiation.

    Currently accepted theories of physics are GR and the standard model. By currently accepted I mean that every test that has been devised for them has agreed with the theoretical prediction. If there were one test that disagreed with that prediction then we would have falsified the theory and would have to junk it (or more likely, modify or generalise it so that it got the predictions right while still maintaining the old results). That's the cornerstone of all science - falsifiability.

    As it is, Hawking radiation is a currently untested prediction of GR and field theory like the standard model.

    [/QUOTE]


    Hawking radiation certainly is provable (or disprovable). Just because there is currently no known way to test it doesn't make it impossible to test. In actual fact, I recall hearing something about an experiment that looked at Bose Einstein condensates which would test the Unruh effect. That is a particle creation effect that is basically the same problem as particle creation by a black hole, so experimental proof could be closer than you think.

    [/QUOTE]

    That's not what Hawking radiation does. It takes GR and QFT, does not make any modifications to either, and derives the expected temperature of a black hole. In that sense it's not a hypothesis.

    [/QUOTE]

    Whenever I see this type of argument my will to type a response dies a little bit. Basically what you are saying is mathematics is not physics right?

    That's true, mathematicians work on maths for the sake of doing the maths (some of them do), physicists study physics using maths as a tool. Typically if the maths tells you something that is patently unphysical then it's because you've used the tool wrong. not because maths is wrong.

    [/QUOTE]

    Your statement "math-experts make their own equations to trying to fill the hole," is rubbish. The point of maths is to specify a minimal set of rules and see the consequences of those rules. In physics you model the system you're studying using mathematics. I reiterate, mathematicians are interested in the properties of mathematics. Physicists are interested in the properties of the universe.

    [/QUOTE]

    Let me put it another way - if we didn't use mathematics in physics then how would you compare data to theory? Let's suppose you're trying to test quantum theory and you're looking at the hydrogen spectrum. Your experimentalist says there are some lines of different colours, but that's in no way precise enough. He could then say something like "the first line is red." which isn't precise enough either. What is really needed is for the theorist to do a calculation predicting the wavelength of the lines, and the experimentalist to go and measure said wavelengths. Clear, precise and impossible without mathematics.

    [/QUOTE]

    Mathematics is not a religion and to say so clearly indicates you don't understand it.[/QUOTE]


    I understand mathematics and physics are extremely useful when it comes to down-to-earth sciences like engineering projects, seismology, geo-science Earth science, meteorology and etc... The problem becomes when they tell me physics and mathematics will resolve Hawking's radiation or anything that is inside the black hole, or dark matter, big bang and etc... I'm sorry equations can help, but only as speculation. This is where matematics and physics are becoming religious because it is always thought that both mathematics and physics will answer all of the mysteries of the universe and everything else. Everyone can have their own opinions, because there is absolutely no way of knowing these things. It isn't possible to make any experiments with this, because of the energies that are required to actually to do these experiments, not to mention if we know all empirical data, which we don't and never will.
    LHC's highest energy level is way too low to actually find something about the black hole, or Hawking's radiation or dark energy, or dark matter. It can be anything, because we don't know enough and never will.


    Cheers.
     
  11. BenTheMan Dr. of Physics, Prof. of Love Valued Senior Member

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    Would you say that Newton's laws were invalidated by the fact that they cannot adequately explain the orbit of Mercury around the sun?
     
  12. Gravage Registered Senior Member

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    I'm not familiar with the fact they cannot explain the orbit of Mercury around the sun.
    But since Newton's laws are the best so far to explain these phenomenons, I must take them.
    If it's true they cannot explain the orbit of Mercury around the sun, than the theory needs an upgrade in better and more accurate understanding of Mercury's orbit around the sun, and to find out why is this a case, at least for this part you mentioned.
    This is how I see it.
     
  13. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    You need to study physic some. Newton's laws have already been refined by General Relativity to now explain the orbit of Mercury.

    You need to study the history of science too. Your idea that many experiments can confirm that a theory is correct is false. As others have told you already, one can only falsify a theory, never prove it. For example, during at least a 100 years, perhaps 100,000 thermal experiments all confirmed the Phlogiston theory of heat.

    Once you are better informed, then you will cease to be so silly.
     
  14. BenTheMan Dr. of Physics, Prof. of Love Valued Senior Member

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    In light of this response, I am obliged to close the thread. I will leave you with BillyT's advice, repeated for effect:

     
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