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I'm new here - Infinite Energy?

  1. Feb 9, 2007 #1
    Hello there.

    This is my post.

    I've recently taken up an interest again in physics, well more reading about it out of interest.

    I was just reading Stephens Hawkings' 'A brief history of time' and there is something which I don't understand about it. I was wondering if someone could help explain to me.

    Ok so, on page 129 "At the big bang itself, the universe is thought to have had zero, size, and so thave been infinitely hot". Am I right in thinking that heat is a form of energy? If so, then there would be an infinite amount of energy in the universe?

  2. jcsd
  3. Feb 9, 2007 #2
    I actually haven't read A Brief History of Time, and know hardly anything about big bang theory, so I can't answer your second question. However, I do know that heat, technically, can only be transferred, not contained (in the same way that something can not contain a force; it can only have a force applied to it). When something is hot, it contains internal energy.
  4. Feb 9, 2007 #3
    I also know nothing...

    But if you had a finite amount of energy, and condensed it into an infinitely small space, it would be infinitely hot. Even if the energy you have is very small... or large.

    Just like if you have some finite amount of matter and condense it into an infinitely small point, then your point would be infinitely dense (even though the matter is finite). Density is mass/volume. Two ways to make that infinity is the limit as mass approaches infinity -or- volume approaches zero.

    Just what I thought upon reading this, I have no clue what Im talking about.
    Last edited: Feb 9, 2007
  5. Feb 9, 2007 #4
    Well this is perhaps not entirely true, since it deals with the universe at the singularity, a point at which as we know general relativity (which is the very theory from which we conclude there is a singularity) breaks down and so does predictability.

    Besides infinity density, temperature and so on make no sense physically and a time scale smaller as the planck time neither makes sense (there is no way to differentiate between 'before' and 'after' at or below this scale).

    I guess this vision of the Big Bang now has been ruled out more or less in favour of more realistic pre-big bang scenario's which make testable predictions.

    I think the Hawking-Hartle-Turok instanton models (with a 'soft' singularity near the begin) have been ruled out because they predict a different universe, and not the universe we actualy see.

    But I'm not completely sure about this. Is a universe starting with a singularity ruled out on theoretical grounds, or on empirical grounds?
    Last edited: Feb 9, 2007
  6. Feb 9, 2007 #5
    I might be going off on a bit of a tangent here, but... how does that work?:confused: Is there an example in logic that can illustrate this (seeming) paradox?

    What kind of universe does it predict?
  7. Feb 9, 2007 #6
    Yes, well or instance, this would also occur in a model of electric field which has point particles. The attracting force between oppositely charged point particles would go to infinity when they would collide.
    But as we know, point particles are just an approximation, and moreover, we need a Quantum theory to describe the interaction.

    Not realy sure, but I guess it was claimed a universe that would have already collapsed or so. But in fact there are several similar models, with different predictions.

    I don't know if they are still regarded as "realistic" models, since inflationary models have more predictive power as these singularity models.
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