The mechanism of inflation

The theory of inflation (below) offers a very neat explanation for the homogeneity and flatness of our universe, i.e. offers a very neat solution to the horizon and flatness problems of the Big Bang model. But what physical mechanism could have caused inflation? What could cause the infant universe to undergo a psychotic, exponential expansion in the first fractions of an instant?

The basic idea is that the infant universe may have undergone a phase transition. In particle physics, it has long been predicted that the quarks in the quark-gluon plasma must have undergone a phase transition to become trapped in hadrons in the first billionth of a second. Cosmologists now believe that, even earlier in the history of the universe, the fundamental constituents of matter/energy may have undergone a phase transition at even higher energies. Under certain circumstances, such a phase transition would be accompanied by the appearance of energy in empty space (so-called vacuum energy). Calculations show that this vacuum energy could act as an enormous force of repulsion, causing a rapid, exponential expansion of spacetime.

Technically speaking, it is thought that the very early universe cooled into a metastable state of false vacuum - it was then nudged towards genuine equilibrium by a process of quantum tunnelling. However, it was soon shown that the latter process is too violent to result in the universe we observe today. Instead, Linde , Albrecht and Steinhardt calculated that a more realistic model is a universe that moves from false vacuum to equilibrium via a gradual process as shown below.

New inflation vs old inflation

Finally, it was assumed in all the early versions of inflation theory that the vacuum energy liberated by the phase transition disappeared immediately after the hyper-expansion. However, it has recently been discovered that the rate of expansion of the universe is currently accelerating! This observation was a great surprise as it is not predicted by any of the Friedmann models; it is now believed that the cause of the acceleration (known as dark energy) may be a small amount of vacuum energy left over from inflation….more on this next week.

Update: if you can’t wait, there is a very nice summary of dark energy here

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Filed under Cosmology (general), Cosmology 101

8 responses to “The mechanism of inflation

  1. Hasanuddin

    Very good article, therefore I think you’ll be interested in a newly proposed model that appears to define these same phenomena. Perhaps the scenario presented here is compatible with the new model, perhaps not.

    The condensed more scientific version is at
    While the brawl-battle thread is at

  2. cormac

    Thanks for that – will certainly have a look asap

  3. DB

    Maybe a daft question, but what exactly is tunneling, and what sort of barrier is it tunneling through?

  4. cormac

    Quantum tunnelling is the name given to a predicition of quantum physics that subatomic entities are occasionally capable of surmounting an energy barrier far greater than their own energy.
    It explains how particles escape the nucleus in radioactivity, and a great many otherwise inexplicable phenomena in the quantum world
    (“if you fire enough atom-sized shuttlecocks at a wall 10 inches thick, one will eventually penetrate”)

  5. db

    I should have been clearer. I intended to ask what sort of particles were doing the tunneling, and what was containing them in the false vacuum state.

    I should learn to proofread my comments before hitting the “submit” button :)

  6. cormac

    No worries! That, of course, is a much more difficult question. Truth is, no-one knows.
    It was first hoped that the INFLATON (the particle that causes inflation) might be the Higgs boson, but it is now known that it can’t be (apparently).
    Perhaps a supersymmetric particle? I’m not sure there are any definite candidates at the moment, unlike the well-known candidates for Dark Matter for example!

  7. Satviewer2000

    Perhaps the initial energy of the Big Bang was sufficient to “warp” space, much like the warp drive of sci-fi movies, thus propelling the initial matter much farther in a shorter amount of time than would be possible in normal space time?

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