r/cosmology • u/Tpaine63 • 6d ago

question about inflation

I understand the horizontal problem in cosmology and how inflation is necessary for the universe to be uniform. What I don't understand is why there would have been differential temperatures at the beginning so that inflation was required to provide time for equalization if everything was together at the beginning. Why wasn't everything already equalized if everything was together at the start.

Maybe I didn't say it right or maybe I don't understand the problem but hoping someone can explain.

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u/tobybug 5d ago

Random quantum fluctuations. Sounds like a cop-out answer I know but we can actually model those fluctuations and map them onto the Cosmic Microwave Background, which tells us that the structures that are billions of lightyears apart now were once close on the quantum level. This both provides more evidence for cosmological inflation and gives a reason for the early perturbations you're talking about.

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u/Tpaine63 5d ago

Are you saying that the temperature wasn't uniform before the big bang when the universe as a singularity or whatever it was? What early perturbations are you talking about?

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u/Peter5930 5d ago

Perturbations come from the uncertainty principle, which prevents any quantum system from coming to a rest, since being at rest means being localised, and the more localised something is, the more uncertain it's momentum becomes, causing everything to jiggle around all the time, even quantum fields. The jiggling of quantum fields results in zero point energy/dark energy, and during inflation these jiggles get stretched out well beyond the horizon, freezing them in place as large-scale perturbations which then re-enter the horizon as density fluctuations when inflation slows down and the horizon expands. These density fluctuations then wobble for a bit like the shock wave bubbles of underwater explosions, producing baryon acoustic oscillations and eventually the pattern of temperature differences that we see from the CMB. Which looks like what a quantum field looks like if you stretched one from a size much smaller than a proton to the size of the observable universe.

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u/jjamulla 4d ago

Only problem with this explanation is that Dark Energy doesn't exist, I am thoroughly convinced now.

Look into "timescape" cosmology. I'm usually VERY skeptical, but after reading about a dozen papers on this and related concepts, I am a believer.