Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

ElectroWeak symmetry breaking.

  1. Jan 13, 2012 #1
    Hello, new member here. I've been fascinated reading some of the threads and decided I had to register to ask a question that's always been a bit confusing to me.

    From what I've learned The Big Bang theory seems the most likely explanation of the start of the universe but there's one thing in particular I don't understand about it.

    Until after about a billionth of a second after the Big Bang when ElectroWeak symmetry breaking (the Higgs mechanism) occurred particles had no mass, yet the start of The Big Bang was supposed to be a singularity. Singularities are points of infinite density, how could it be a singularity if no particles had mass?
  2. jcsd
  3. Jan 13, 2012 #2
    In our current models with the Penrose–Hawking singularity theorems require the existence of a singularity at the beginning of cosmic time.

    The problem with these theorems is that they assume GR is correct, however GR will probably have broken down before the Planck Temperature. If we manage to repeat the models using a good theory of quantum gravity we may avoid the singularity.

    However the fact that we have calculated it to become a singularity means we most likely don't have the full theory and the singularity is basically a way of saying "this is what our current model says will happen" but if we improve our theories we may discover that something different might occur.
  4. Jan 13, 2012 #3


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    Good point. There are currently several approaches to quantum gravity being explored (according to which the geometry of the universe has a quantum fuzziness and the bigbang singularity is eliminated.)
    So there are several models of Quantum Cosmology (QC) being worked on. People are already thinking about how to test them by looking for traces in the cosmic microwave background (ancient light) connected with whatever the models say happened instead of a singularity.
    It should be possible to constrain or even rule out one or more of the QC versions being studied.

    But ShoX's question still stands! Even if the classical breakdown "singularity" is avoided the QC models still predict a VERY HIGH energy density at the start of expansion. Just not infinite (which would be nonsense) but still very high.

    ShoX asks how can there be very high energy density if the particles, e.g. like photons, have no rest mass?

    So we should point out that just because, say, the Higgs mechanism is not giving rest mass to quarks does not mean you can't have a high energy density. Indeed over 95% of the mass (inertia) of your body is not due to the Higgs mechanism. The inertia of the proton is mostly due to the energy of stuff moving around inside the proton and binding it together.
    Last edited: Jan 13, 2012
  5. Jan 13, 2012 #4
    Thanks for your replies, I think I get it now.

    Basically me thinking the Big Bang singularity and black hole singularities are the same is wrong. The Big Bang 'singularity' is used instead of 'we don't know what it was'?
  6. Jan 13, 2012 #5


    User Avatar
    Science Advisor

    Actually, all singularities signal a point of breakdown of the theory, including those at the center of black holes. Although geometrically distinct, both big bang and black hole singularities correspond to points of infinite density in general relativity, which is a physical impossibility cautioning us that a more complete theory of gravity -- applicable at high energy densities -- is needed.
  7. Jan 13, 2012 #6

    Theory of Everything (TOE) symmetry breaking would have been the first symmetry breaking event between the strong nuclear force and quantum gravity, which would have resulted in the generation of a boson, however there is a theoretical disagreement on what kind of boson is generated, quantum gravity predicts a massless graviton and General Relativity predicts a massive Planck mass boson, both are considered to be in the hypothetical class of particles.

    TOE scale Planck boson mass energy:
    [tex]\Lambda_{TOE} = E_p = \sqrt{\frac{\hbar c^5}{G}} \approx 1.22 \cdot 10^{19} \; \text{GeV}[/tex]

    Grand Unification (GUT) symmetry breaking would have been the second symmetry breaking event between the strong nuclear force and the electroweak force, which would have resulted in the generation of an X boson:

    GUT scale X boson mass energy:
    [tex]\Lambda_{GUT} = E_X = \left(\frac{10^9 e \tau_p m_p^5 \alpha_s^2 (m_Z)}{\hbar} \right)^{\frac{1}{4}} = 4.320 \cdot 10^{16} \; \text{GeV}[/tex]

    X bosons definitely have a theoretical mass and are considered to be in the hypothetical class of particles.

    Electroweak (EW) symmetry breaking would have been the third symmetry breaking event, in absentia of any Higgs mechanism, between the electromagnetic and weak nuclear force, which would have resulted in the generation of a W boson.

    Electroweak scale W boson mass energy:
    [tex]\Lambda_{EW} = E_W = 91.1876 \; \text{GeV}[/tex]

    The mass of a Higgs boson could occur anywhere between:
    [tex]\Lambda_{EW} - \Lambda_{GUT}[/tex]

    [tex]91.1876 \; \text{GeV} - 4.320 \cdot 10^{16} \; \text{GeV}[/tex]

    Infinities are artifacts of mathematics and do not actually occur in nature. There is no such thing as an infinite anything. The magnitudes of physical quantities can be extremely large or small, but never infinite.

    For example, according to Loop Quantum Gravity (LQG) for which Quantum Cosmology (QC) is a subset, all matter inside a black hole oscillates on the order of a Planck radius and does not collapse into an infinite point. The primary reason for this is because space-time itself becomes quantized.

    According to Quantum Cosmology, the same is also true for a Universe collapsing into a singularity, the matter 'bounces' off the Planck singularity without ever actually achieving an infinite quantity.

    Big Bang Expansion and the Fundamental Forces - Hyperphysics
    Theory of everything - Wikipedia
    Planck energy - Wikipedia
    X and Y bosons - Wikipedia
    Orion1 #68 - doublet-triplet problem
    Grand Unified Theory - Wikipedia
    Loop quantum gravity - Wikipedia
    Last edited: Jan 14, 2012
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook