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Thread: Question on Higgs field & Big Bang

  1. #1 Question on Higgs field & Big Bang 
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    The Big Bang is seen by Alan Guth as having been produced by a relatively short burst of negative pressure, as a result of a high energy state that is temporarily trapped on some sort of non-zero plateau in the vacuum. I have a quote here from a popular science book by Green to clarify things:

    "The Higgs field will stay on the plateau, in the high-energy, negative-pressure state, only for the briefest of instants, and while it is on the plateau, the repulsive outward push it generates is enormous."

    I have two basic questions:

    1) how does this "plateau" of potential energy emerge in the vacuum, enabling energy to be temporarily trapped at a non-zero value?
    2) why is it that this trapped energy necessarily possesses negative pressure?

    Kind regards.


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  3. #2  
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    The big bang was not produced by the negative pressure, inflation was.

    1) I believe Guth used an analogy to supercooling, where water is cooled very quickly to temps below freezing yet water remains liquid in an unstable equilibrium state. The smallest deviation will cause the equilibrium to collapse to the lower energy ( crystalline ice ) state, and freeze. This is akin to the universe reaching a false bottom (non- zero) of the energy curve, but it is highly unstable. The slightest deviation causes the energy to drop to its actual zero (maybe ) state. This is explaned in terms of scalar fields and the spontaneous symmetry breaking of said fields ( see Higg's mechanism, fields and bosons ).

    2) Pressure is a form of energy. The negative is assigned by convention to indicate direction.


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  4. #3  
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    Thank you for your reply. I have two slight remarks, though.

    Firstly, why do you distinguish so rigidly between the Big Bang and inflation? Aren't they roughly the same phenomenon, the Big Bang being a short and enormous burst of expanding spacetime?

    And secondly: I have also found this analogy in the book, but I don't really see how it would contribute to a fundamental explanation of the false bottom. I see that false bottoms are possible in supercooled environments, but how exactly is that possible in the vacuum that a Higgs field essentially is? How on earth can a quantum fluctuation get stuck on a false bottom in a vacuum, the energy being as low as it is?
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  5. #4  
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    Well, inflation, the exponential increase in universal size lasted only moments, while the big bang is still happening.

    Imagine a minimum energy curve, or bowl, if dealing with three dimensions. The bottom of this bowl is the zero energy condition. Now imagine a field, which has a strength but no direction and which permeates all of space. This imparts an energy to space such that there is a raised symmetrical part ( remember no direction ) to this energy bowl.giving it the shape of a Mexican sombrero.
    We note that when the universe falls to this false vacuum energy, it is balanced on the top of the hat part of the sombrero, and this is extremely unstable as any small deviation will send the universe tumbling down into the real zero point energy in the brim of the sombrero shape.
    Again we note that the false vacuum energy is unstable but completely symmetrical. Symmetry breaking involves falling to the real zero energy condition which is completely stable, but, since the universe is in the brim of the sombrero shape, it has lost one aspect of its symmetry.

    Symmetry breaking in the early stages of universal expansion have been shown to account for the separation of the electroweak force into the electromagnetic and weak nuclear force. Similar symmetry breaking is postulated to account for the further separation of the strong nuclear and gravitational forces at even earlier, more enrgetic times.

    Sorry but I cannot think of a book to recommend which would explain this theory better than the messy, and maybe incomprehensible way that I've used.
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    I see your point and understand what you're getting at, but you visualise this process in a three-dimensional space. Spacetime, however, was only created during the initial inflationary period after the big bang moment (before this point we cannot speak of "time" or "space" as we know it). I would agree with your explanation (with a symmetrically raised plateau) were it not for the fact that it uses dimensions that are not there until after the actual process of inflation has started.

    How, then, is it possible for such false bottoms to occur in a non-dimensional vacuum, would you say, as Guth's theory suggests?
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  7. #6  
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    No, you're stll confusing the big bang with inflation.

    Space/time was created at the moment of the big bang, ie t=0. We are unsure of the dimensionality of space that was created, but at t=10^-43 ( planck time ) the dimensions we are familiar with started expanding while all others, if any, remained at the planck scale. At this point the size of the universe is such that light and so information can easily traverse it. All points in the universe are causally connected and we have an even, isotropic distribution of energy ( with only small variances ). At some point after this, inflation occurrs and the size of the universe grows exponentially for a brief time. This is enough to causally disconnect the universe so that the observable universe of today, even though vastly smaller than the actual universe, shows aisotropy at large scales. And that is one of the resons Guth came up with his inflationary big bang theory. At least as I understand it

    The energy diagram that I had you visualise was in 3d because I could then use a sombrero shape to further describe it, but if you understand what I was trying to explain, it could have been a familiar 2d energy well. The dimensionality makes no difference, its an anlogy.
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    OK, I now fully understand the distinction between inflation and the big bang. Many thanks for that!

    I have only one small question left: if this false bottom theory explains only inflation but not the big bang itself, what cosmological model is there for the latter? I had always heard that the inflationary model was in contention with for example the ekpyrotic universe, where the big bang is seen as a consequence of the collision of 3-branes. Is this ekpyrotic the only hypothetical model we have as to what caused the big bang itself?
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  9. #8  
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    Quote Originally Posted by Maximise24
    OK, I now fully understand the distinction between inflation and the big bang. Many thanks for that!

    I have only one small question left: if this false bottom theory explains only inflation but not the big bang itself, what cosmological model is there for the latter? I had always heard that the inflationary model was in contention with for example the ekpyrotic universe, where the big bang is seen as a consequence of the collision of 3-branes. Is this ekpyrotic the only hypothetical model we have as to what caused the big bang itself?
    The basic big bang model is based on general relativity. General relativity is the best currently available theory of gravitation. It is well-defined, mathematically consistent and is supported by a mountain of empirical data. It is known to be incompatible with quantum mechanics, and appears to break down in circumstances where quantum phenomena become important, as with events prior to about 10^-33 sec after the big bang.

    Ekpyrotic theory is based om M theory. Mtheory is in turn based on string theories. Neither string theories nor M theory have ever been rigorously defined, and the major open problem in M theory is "What is M theory ?". Neither any of the string theories, nor M theory have ever made a new physical prediction, and none of them have even a shread of empirical supporting data. So before ekpyrotic theory is in contention for anything someone will have to actually define what M theory really is, show that it is mathematically consistent, make quantatitive predictions using it, and privide experimental data showing that those predictions are correct.
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  10. #9  
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    I see. Maybe a last question (though maybe a speculative one): were the energy and mass of the universe created at the moment of big bang or only during inflation (1 Planck time later)? Should we view the big bang only as the emergence of a Higgs field with primitive dimensions (a very local spacetime expansion in the original vacuum due to quantum fluctuations), while it was the energy of the negative pressure of early inflation that filled it up (while, of course, expanding it enormously)?
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