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Cake day: August 9th, 2023

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  • gravitational waves that created “quantum foam”

    That article does not say that these waves created quantum foam. It says that expansion… expanded it. Brilliant writing, I know. This is the what the article says:

    [Inflation] also laid down the seeds of the first structures. It did so by taking the quantum foam, the subatomic fluctuations in spacetime itself, and expanding that along with everything else.

    Quantum foam is what the vacuum of space is theorized to be. Quantum fields that fluctuate constantly at very small scales (Planck scale), hence why we call it a “foam”. It’s not clear to me what the author means by contrasting it with “everything else”, other than to contrast the foam with particles of matter or of light, which are just excitations in their respective quantum fields. It’s all the same thing: quantum fields. If space is quantum foam and space expanded… Obviously the foam expanded. I just find it so weird for the author to say “inflation took what it inflated with it.”

    The article continues:

    Slowly, over time, those fluctuations grew, and hundreds of millions of years later they became the first stars and galaxies…

    That’s also a horrible mischaracterization of what the paper is saying. It doesn’t say the quantum fluctuations increased over time. It says the fluctuations created gravitational waves that themselves altered spacetime to cause the cosmic structures we observe. The paper says there’s no need for the “inflaton field”, a theorized quantum field that inflated the very early universe then basically went away.

    Here’s the abstract from the paper:

    We propose a novel scenario in which scalar perturbations, that seed the large scale structure of the Universe, are generated without relying on a scalar field (the inflaton). In this framework, inflation is driven by a de Sitter space-time (dS), where tensor metric fluctuations (i.e., gravitational waves) naturally arise from quantum vacuum oscillations, and scalar fluctuations are generated via second-order tensor effects. We compute the power spectrum of such scalar fluctuations and show it to be consistent with near scale-invariance. We derive the necessary conditions under which scalar perturbations become significant and much larger than the tensor modes, and we identify a natural mechanism to end inflation via a transition to a radiation-dominated phase. Our proposed mechanism could remove the need for a model-dependent scenario: the choice of a scalar field, as the inflaton, to drive inflation.

    If you want to have a good time, have ChatGPT explain all of that to you. It’s really quite good at it.