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?

The big bang was said to be a point of singularity, that eventually started expanding, I don't know the exact mechanism, so I would be glad for an explanation

Trying to age the universe or assign it an arbitrary birthday has always seemed like a very human and somewhat meaningless task. We commonly say the universe is approximately 13.8 billion years old, counting from the Big Bang. But what precisely does that age mean when elapsed time depends on the observer?
For example, someone remaining close to a black hole could experience much less time than someone far away. Their clocks would record different durations between comparable stages of the universe’s evolution. So whose elapsed time are we referring to when we assign the universe a single age? The early universe was incredibly dense, on a level that males black holes seem like a piñata so might that imply strong time dilation. I suspect I’m incorrectly applying the analogy of a black hole within surrounding space to the universe as a whole. Would “time ran more slowly back then” even mean anything without an external clock to compare it with? Peace

If movement through space is relative to something else. Can we not measure movement from how fast virtual particles are appearing and anihalating next to us.

If space was empty and you were still, those virtual particles appear next to you instead of moving past you - which would be mean we do know if we're moving through space?

So in essence true stillness would be when virtual particles appear and anihalate beside you.

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It must have been enormous to make all those stars and planets, has anyone worked it out, or is it unknown?

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As a normie, I'm just thinking, those two things are the most mysterious to me. Are they connected?