How strongly can we distinguish between the universe being approximately 13.8 billion years old and our observable region having entered its hot, expanding phase approximately 13.8 billion years ago?
Could what we call the Big Bang have been one event or transition within a much larger, older cosmos perhaps even one with an infinite past? By “local”, I mean a region encompassing our entire observable universe, rather than an explosion at a point within it.
I understand that expansion, the CMB and primordial element abundances strongly support a hot, dense early phase. What I’m less clear about is whether those observations constrain the total age of reality, or mainly the time elapsed since that phase. Are there any viable models along these lines.

Thanks

As the universe expands how does the new space come into being? What is happening?

According to the catalog: "Copernicus’ presentation of heliocentrism radically altered our understanding of Earth’s place within the solar system and universe. Contemporary space exploration would be utterly impossible, let alone inconceivable, without such groundbreaking revelations as set out by Copernicus. Heliocentrism remains a guiding doctrine of all astronomical understanding, marking this book as one of the most revolutionary scientific texts in history."

Link to detailed description, photos and an essay placing this this work in the history of science at https://www.sothebys.com/en/buy/auction/2026/reason-and-revolution-extraordinary-works-from-a-distinguished-private-collection-part-1/copernicus-nicolaus-de-revolutionibus-orbium?locale=en

Disclaimer: OP is not affiliated with Sotheby or any other auction firm. This post is strictly for informational and educational purposes.

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Hi, so I recently discovered about this and I had a question and I can't seem to find anything that explains it, so I just wanted to ask how does the brane cosmology explain the expansion of the universe. idk... It would be really helpful if anyone can recommend me any books or articles where I can read about this and find a conclusion to my question.

https://doi.org/10.5539/apr.v18n2p1

This paper provides an explanation for the apparent excellerating expansion of the visible universe.

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Hi everyone! I’m currently reading Cosmos by Carl Sagan (fantastic book) and came across a passage that has really stayed with me. Sagan suggests that if intelligent beings lived on a planet orbiting a star near the Milky Way’s galactic centre, their night sky might be ablaze with starlight because stars are much more densely concentrated there. Is that accurate? Would their night sky be dramatically brighter than ours, and might it never become truly dark? That also made me wonder re relativity. Because the galactic centre contains a much greater concentration of mass and the supermassive black hole would a clock on such a planet run more slowly relative to a clock here in the Milky Way’s spiral arms? If so, would the difference be meaningful, or far too small to notice unless the planet were extremely close to the black hole? I understand that time would feel completely normal to the beings themselves; I’m asking how their elapsed time would compare with ours. In this sense, could an intelligent civilisation be ahead of us, but then we catch them up and overtake them because we advance more rapidly relativistically.
Cheers!

Hi, everyone, I had a great conversation with Geraint F. Lewis, a Welsh astrophysicist and Professor at the University of Sydney, about some of the biggest questions in cosmology, physics, and our understanding of the world.

We explore what the Big Bang theory tells us about the beginning of the universe, why our current understanding of physics reaches limits when we try to look further back in time, and how neutrinos could reveal secrets about the cosmos — including why matter exists at all. We also mention the 2026 Nobel Prize in Physics, awarded to Francis Halzen for his work on the IceCube Neutrino Observatory.

Professor Lewis also explores what sparked the Scientific Revolution, how modern science transformed our understanding of the world, and why Einstein challenged aspects of quantum mechanics.

Professor Lewis's latest book, The Shortest History of Reality: From Plato’s Cave to the Mind-Bending Discoveries of Modern Physics — The Human Quest to Explain the World, traces humanity’s changing understanding of reality, from everyday intuition and ancient philosophy to the discoveries of modern physics. It explores the ideas that reshaped our view of existence, from Newton’s universe to the strange probabilities of quantum physics and beyond.

If you're interested in these subjects, you can check out our conversation: https://youtu.be/38rUHEeAVHw

I've been working on a small tool called hpvis, a viewer for HEALPix sky maps (CMB maps, dust maps, masks and so on).

I wanted something that opens a big map instantly and lets me look around, without writing a plotting script every time. So the whole thing is rendered on the GPU. You can open maps up to nside 8192, zoom in, rotate the sky and switch between projections (Mollweide, Hammer, Mercator, Gnomonic and a few more) in real time.

A few things I use all the time:
- FITS and .npy files, RING or NESTED
- Masks, histograms and power spectra in docks next to the map
- Select a region and get its statistics on their own

It's built with C++, Qt6 and OpenGL, and it's still early, so feedback and bug reports are very welcome.

Code Repo: https://github.com/dheerajshenoy/hpvis

See also: The publication in ArXiV

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I think I learned about cosmic inflation mainly from people that were very optimistic that it is factual. Sure it has room to be wrong due to the nature of science, but it was practically leading consensus.

I think it’s not quite like that, like it does seem like the leading consensus view but only cautiously and not a lot of people want to get serious about what that means if it is true. I notice “what came before the big bang” is still considered an open question despite cosmic inflation apparently giving an answer to that.

I think the model is right and the conditions it lays out to be roughly accurate to reality. But I’m curious what skeptics feel too or maybe if people think the model is somewhat true?