Universe smaller than wavelengths?

AI Thread Summary
The discussion centers on the existence of particles in the very early universe when its diameter was smaller than their wavelengths. Participants question whether wave descriptions are adequate for understanding this phase of the universe. It is noted that current theories struggle to explain conditions in the early universe, highlighting the lack of a comprehensive quantum gravity theory. The conversation emphasizes the importance of developing new theories to accurately describe these phenomena. Overall, the quest for a better understanding of the early universe remains a significant challenge in physics.
kashiark
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How did particles exist in the very, very early universe when its diameter was smaller than their wavelengths? Are we just supposed to be content with the supposition that wave descriptions are impractical in this situation?
 
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I believe you are talking about the observable universe.

I discussed it here:
https://www.physicsforums.com/showthread.php?t=371333

so correct, it early Universe only short wavelengths were allowed, hence particles were very hot. I looked at it from E and t as non-commuting variables, you - from p and maximum size.
 
kashiark said:
How did particles exist in the very, very early universe when its diameter was smaller than their wavelengths? Are we just supposed to be content with the supposition that wave descriptions are impractical in this situation?

As of now we have no theory that describes the very early universe. All our current theories run into big problems there. Are we supposed to be content with it? No. That's what physics is all about: figuring it out, coming up with a theory that accurately describes these things.
 
We don't have quantum gravity theory yet,
so the semi-classical approach is the best we can do
 

Thread 'Matter density right after the decoupling'

https://en.wikipedia.org/wiki/Recombination_(cosmology) Was a matter density right after the decoupling low enough to consider the vacuum as the actual vacuum, and not the medium through which the light propagates with the speed lower than ##({\epsilon_0\mu_0})^{-1/2}##? I'm asking this in context of the calculation of the observable universe radius, where the time integral of the inverse of the scale factor is multiplied by the constant speed of light ##c##.
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Thread 'Hubble Constant, Dark Energy and the Expanding Universe'

Why was the Hubble constant assumed to be decreasing and slowing down (decelerating) the expansion rate of the Universe, while at the same time Dark Energy is presumably accelerating the expansion? And to thicken the plot. recent news from NASA indicates that the Hubble constant is now increasing. Can you clarify this enigma? Also., if the Hubble constant eventually decreases, why is there a lower limit to its value?
View full post »

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