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Inflation and the Planck Era

  1. Sep 28, 2004 #1
    As I understand the inflationary cosmology states that at around 10^-35 seconds to 10^-32 seconds after the Big Bang all matter was created as what Alan Guth called the "ultimate free lunch". However, it is said that at 10^-43, the so-called Planck time, was when gravity became separated from the rest of the forces. As I understand it, gravity is a force mediated by the graviton (in quantum gravity theories) and the other forces are all particles. However how come they were there before inflation if inflation states that all matter (therefore also supposedly the particles that mediated the forces) where created at the moment of inflation? Just a remark.
  2. jcsd
  3. Sep 28, 2004 #2
    "All matter" doesn't mean "all particles". As I understand it, matter has non-zero rest mass. Some particles however have zero mass.
  4. Sep 28, 2004 #3


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    just a technical point about language
    words are used differently in different branches of physics and
    cosmology is mostly under the language conventions of Relativists
    who include light with matter

    so when you read articles (about big bang, inflation, cosmology...) you often see the guy says "matter" and he means to include rest-mass-zero stuff

    Alan Guth does this in things of his I've read

    this may differ from what you are familiar with if you are more used to how particle physicists talk
  5. Sep 28, 2004 #4
    Cool, if that is the case, then I am in the same position as Curious6 as to his question.
  6. Sep 28, 2004 #5


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    The whole issue is far beyond my knowledge but I may give you a hint. In quantum field theory particles are energetic excitations of quantum fields. The quantum fields existed already before inflation, although they existed in a state which was different than now. During inflation the vacuum state of the inflaton (the field exerting the required pressure to inflate space exponentially) accumulated a colossal amount of energy. This energy was transferred to the other quantum fields at the end of inflation in a process called reheating. The quantum fields got enough energy and underwent some transitions (spontaneous symmetry breaking) in which the interactions decoupled and lead to the current state of fields with their respective particles. Reheating produces fermions as well as bosons and (IMHO) strictly speaking the only use of the term "matter" is not correct here.
  7. Sep 28, 2004 #6


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    Gonzolo, I am interested in exploring Curious6 question even tho I cannot speak with authority, and do not know of any single official viewpoint about these things.

    Curious6 says, just to recall his question:
    "How come they were there before inflation if inflation states that all matter ...[was] created at the moment of inflation?"

    I think Curious6 means how come gravitons were there before inflation.

    Relativists distinguish between the gravitational field and matter (which includes light as well as neutrinos, electrons, atoms etc.)

    GR does not involve gravitons. Quantized GR----approaches to Quantum Gravity like LQG---do not involve gravitons.

    Gravitons do not exist in quantum gravity approaches like Loop Gravity, except as rarely used mathematical approximations to the gravitational field in nearly flat situations.

    what exists is the gravitational field---which is the geometry of space.
    I don't know any quantum gravitist who supposes that the gravitational field is made of "gravitons".

    When one quantizes geometry I believe that what one gets quantified into discreet bits are such things as area, volume, length, possibly rotation, possibly speed.

    It is not the neat situation where one can distinguish between the particle and the geometry of what it moves in.

    I have to go, can't finish this post. will try to get back to it later
  8. Sep 29, 2004 #7


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    I misunderstood the question. What I know about this is that to describe this process of particle creation an interaction term between the quantum fields on an expanding background and the inflaton is introduced in the Lagrangian of the quantum fields. The question arises whether one should also consider an interaction between inflaton and the gravitational field. I dont see any reason why this should not be done. I assume that, if this can be done, the gravitational field will be perturbed and gravitons will be created, but the background spacetime will not be modified.
  9. Sep 29, 2004 #8
    Some theories propose the existence of a superpartner of the inflaton called inflatino. According to my notes the inflatino is a Majorana spinor. What's the role played by the inflatino during inflation?
  10. Sep 29, 2004 #9


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    this is a great thumbnail sketch from a QFT, particle theorist perspective.
    I only wish that at the end you wouldnt say calling light "matter" is not correct. It is a time-honored usage among relativists. Sometimes necessary to let different specialties have different viewpoints and cope with some slight divergence in terminology.

    The way (at least some) relativists talk, matter is everything on the righthand side of the einstein equation, which basically says
    "matter tells spacetime how to curve,
    and spacetime tells matter how to move."

    if they were not allowed to include light in with other matter then they would have to say:

    "matter and light tell spacetime how to curve
    and spacetime tells matter and light how to move."

    nevermind the trivial details of language though,
    your concise summary defines its terms and uses them consistently
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