npub1c9m22hkc5h6zgrwkz48crhcpw6vch2rf6j97746ugl3neys86jeqyz9xjd (npub1c9m…9xjd) npub1ky223zcc4q69d8t0me4vg5uw8mw0yxeukjgvz6h92laqnenr0ajs5rghvc (npub1ky2…ghvc) -
Second,, I talked to an early-universe cosmologist, John Peacock, about this because I wanted to be sure that the standard theory *does* say that the inhomogeneities in the early Universe arise as quantum fluctuations, rather than being put in "by hand". He said that it does. I pressed him on it, and in the end I felt a bit dumb because it turns out to be textbook stuff. He wrote:
"Many textbooks treat inflationary generation of fluctuations at various levels of detail. You can have an entire (excellent) book dedicated to the subject:
https://www.amazon.co.uk/Primordial-Density-Perturbation-Cosmology-Inflation/dp/052182849X
Or for a briefer tour of the key elements you could look at Section 6.5 of my cosmology notes:
https://www.roe.ac.uk/japwww/teaching/cos5_1213/cos5_full.pdf
The basic idea is to say that the inflaton field must experience quantum fluctuations (since it’s just a harmonic oscillator in the ground state). These fluctuations can be computed on small scales using standard flat-space QFT. Now follow a given field mode in comoving terms, so that the mode becomes stretches beyond the inflationary de Sitter horizon, transforming the inflaton fluctuation into a classical perturbation to the energy density."
Of course this being the standard theory doesn't mean it's true. But I'm greatly relieved that the fluctuations aren't stuck in by hand: the initial conditions are translation and rotation invariant; all inhomogeneities result from spontaneous symmetry breaking, i.e. the total wavefunction retains its symmetry but it's a superposition of inhomogeneous states.
(2/2)
John Carlos Baez /
npub17u…8pd6m
2024-10-16 17:48:40
in reply to nevent1q…s922
Author Public Key
npub17u6xav5rjq4d48fpcyy6j05rz2xelp7clnl8ptvpnval9tvmectqp8pd6mPublished at
2024-10-16 17:48:40Event JSON
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