We know that rotating black holes (Kerr black holes) cause frame-dragging, pulling spacetime along with their spin. If this effect happens at small scales, could it also happen at cosmic scales?

Consider a spinning sphere of water—when the sphere rotates, the water inside begins to rotate as well. If our universe exists within a larger rotating structure, could this explain why:

• Galaxies seem to flow toward the Great Attractor in a spiral motion?

• There are hints of preferred spin directions in large-scale cosmic structures?

• Cosmic expansion might not be due to dark energy but an inherited rotational effect?

Are there any studies exploring large-scale frame-dragging effects in cosmology? Would love to hear thoughts from those familiar with Kerr metrics and cosmic rotation models.

In infinite space, size is relative and only measurable in comparison between particles/objects. Size can´t be limited, so there can´t be "the biggest" as well as there can´t be "the smallest" particle/object.

In other words, there would be far less smaller particles than quarks (in fact particles get smaller endlessly as particles are getting bigger endlessly). This would also mean there is a microcosm inside a microcosm inside a microcosm inside a microcosm...

The only reason we "do not have" smaller particles than quarks, is the fact we are not able to measure/see/sense all the particles being smaller.

I asked this question in multiple physics boards and i mostly get the same stupid answer:

"It is not proven that space is eternal and therefor it is not worth to think about it."

I am not a physicist as well as my native language is not English, so i hope things do not sound more complicated than they are already.

I want to get into Cosmology and I was wanting to read a thorough book on cosmology. And if you also have some books as a good follow-up read for more advanced.

If we live in the aftermath of the Big Bang, what existed before it? I imagine there were civilizations far more advanced than ours, possibly even interplanetary. But why were they unable to prevent or maintain the universe from dying? Could it be that they thrived independently, rather than uniting, and even with their technological prowess, preventing the universe's decay was beyond their reach? Perhaps, at the moment of their decline, they missed the opportunity to come together, advancing further and possibly saving the universe—an achievement that was ultimately out of their grasp?

Isn't it strange that, in this vast and infinite universe, we find ourselves in a time where our technology is not billions or even trillions of years ahead, but still relatively primitive?

It would be amazing if we could begin by putting an end to pointless and unnecessary wars. If we don’t, that could very well be the direction we’re heading.

If there is a multiverse present (or rather, if any multiverse theory states otherwise), are open and/or flat universes still considered infinite? Are there any open or flat universes in a multiverse? I’d like an explanation.

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i thinking about bigbang and i have simple question like "does we know where the bibang start"
so i googled about this but all information said like the bigbang is not look like normal expolde
but it just like a expansion of space itself. so i find more information but i have another question up in my mind "if they said it a expansion of space itself so it must have a point that space start to expand?"
but i cant find more about this question, or we dint know about it now?

First, I am neither a physicist, cosmologist, or astronomer so please correct me for anything I seem to have misstated.

I’ve looked into the Axis of Evil in the CMB and I still don’t completely understand it. I understand it’s a temperature anomaly that aligns with our ecliptic plane (cold above and warm below I think?) I just don’t understand why this is so strange. Isn’t it likely that it’s coincidental?

Cosmological Spacetime Curvature: The Friedmann-Lemaître-Robertson-Walker Metric

This is part of my ongoing Cosmology lectures based on Dr. Barbara Ryden's textbook.

This'll be good for those who don't know the standard model, and what the TC is standing up against.

Hello! I saw the recently published video by PBS Spacetime about timescape and dark energy and some questions were raised in my head, I hope some knowledgeable person can help me out.

So the idea of timescape is that time passes faster in voids and slower closer to galaxies, so that the additional redshift of photons would be due to the greater time they have passed in such voids instead of being due to dark energy. However, our notions that time runs slower closer to a massive object are founded in solutions of the Einstein Equations, which are made in very specific scenarios. The FLRW metric which describes the zeroth order expansion of space and its implications does not attribute a slowing down of time to anything as the time-component of the metric is independent of radius or mass; it is simply g_00 = -1. Even when adding perturbations, let us say the Conformal Newtonian Gauge, the evolution of the perturbations only depends on the overall perturbation of energy density of matter instead of a local perturbation (maybe I'm wrong about this).

So isn't the theory that time passes more quickly in voids an incorrect and mathematically unfounded extension of our comprehension of the behavior of spacetime in some specific models? That is, we can't simply assume that time indeed runs faster in voids because there is no mathematical model that says so, and it would be absurdly difficult to construct one as voids vary in shape, size and symmetry (and so do galaxies).

Is this reasoning correct of am I missing something?

I just finished "The Order of Time" by Carlo Rovelli ; while the book was good for some parts, it presented some interesting ideas, it wasn't an easy read despite being a short book; the difficulty came not from the science, but rather from the lack of it. The analogies and metaphors were sometimes helpful, but often they seemed like a word jumble that don't actually communicate anything useful and only served to confuse me further. The writing and interpretation of time was too philosophical for my taste.

Some things that were insightful came in Chapters 9 and 10 - that time exists only in our perspective because we perceive only a subset of the universe. The main idea - we as a physical system interact with only a few variables in the universe and in relation to our system and the variables we measure, entropy always increases and this increasing entropy creates what we call "time" - was quite useful for me. The book also had a coherent structure - first time is broken down to what it is not, and then reconstructs how our perception of time arises.

I'd like to read more on the subject, but something that's less philosophical and more about what science so far knows about "time", but still written for someone who's not a professional physicist.

dark matter misinterpreted as the flow of time?

Time, when in absence of matter flows relatively faster causing already expanded regions of "empty" space to expand even faster. Which might appear as a force acting on space-time.

Thoughts?

Sorry if this makes no sense, and is mostly questions, some which may already be known and answered.

As far as I understand, and in the most basic of terms, time dilation is affected by gravity and velocity, how fast you are moving through space and the gravity in that space. This is described using relativistic terms, time on a spaceship flying away from Earth would measure slower to an observer on Earth, as time on Earth would measure faster to an observer on the spacecraft. The spaceship should then have a higher rate of time than Earth, moving through spacetime at a higher velocity. Slower relative meaning faster for the spaceship.

My confusion I guess is in how time is measured and/or described, and if it can be measured differently. Is there a sort of base rate of time we can theorize and compare to. Is there a way to calculate how time would pass in a position with no gravitational potential and no velocity, e.g. a theoretical spaceship or person perfectly still far enough away from anything to have no gravity. At what rate would time pass? Could this be used as a theoretical base rate to measure time?

What contributes to our rate of time? Planets orbit stars, which orbit in galaxies, which move through the universe, all at different speeds. How much velocity of each level contributes to time dilation, if at all? How does the gravity of galaxies, systems, and stars each contribute? I have no idea, but it all fascinates me.

I’ll preface this by saying I’m not a scientist by any measure; that said, I’m nonetheless fascinated by this sort of thing.

That said, I read an article about an FRB being detected coming from an extremely large and old galaxy that’s about 11.3 billion years old. It was referenced as being a dying a galaxy, and I’m curious what that means and how that works.

Is a galaxy categorized as “dead” or “dying” when the rate of star production slows?

Hypothetically speaking, what happens to a fully formed galaxy when star production in that galaxy slows to a virtual stop? Does the galaxy maintain its structure and simply continue on as extant, but dormant (akin to a dormant volcano)? Can star production somehow restart?

Apologies, I know that’s a rash of questions that may not even make total sense in context. I’m totally unfamiliar with this, but very curious

Keep in mind I may be misremembering finer details, which is probably why I can't seem to find it anywhere.

When I was much younger, before 2010 for certain, there was a Black Hole documentary my dad would put on for me occasionally. If my memory serves me correctly, it was a History Channel documentary, I don't believe it was part of the Watch The Universe series. The documentary also featured Michio Kaku I believe, among other physicists.

I've exhausted any options I have for finding the documentary; my dad doesn't remember which one, I can only remember so much about it cause I would've been like 6yo or around that then. Any help or pointers to where to look would be greatly appreciated, thanks all.

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As far as I understand it, we assume the universe may be infinite simply because we know it is larger than we can see.

I was listening to a podcast by Joscha Bach, where he says that he truly doesn’t believe in infinity as having any relevance to the real world. Sure, it is a useful and essential construct for mathematics. But the universe isn’t built on mathematics, it’s built on computation. The infinite surface area of a fractal, the infinitesimals of calculus, or the infinite expanse of the Real Numbers is in no way representative of something in real life. Infinitely small? Asking about a size of something below Planck scale is meaningless. Infinitely hot? We max out at the Planck energy. Infinitely still? ZPE means we will never have less than half an h-bar of ‘motion’.

And infinitely large? Where does this come from? If we have no reason to believe that any infinities exist outside of idealism and thought, why would we even suggest such a thing for the size of our universe?

Are there any more concrete reasons that we would have to suspect the existence of an infinite universe?

This might be more of a techy question so feel free to direct me to the right people. I am trying to setup the GUI interface for CMB Easy provided by NASA (lambda.gsfc.nasa.gov/toolbox/) with source code in this repository https://github.com/EdoardoCarlesi/cmbeasy.git. I am running Ubuntu 20.04 LTS on WSL 2 ON Windows 11 but everytine I try to make the C++ code it gives me an error for some outdated syntax. I've tried solving this issue with chatGPT but we all know how bad that is, failing with even small migrations or changes in code. Don't ask it to write code for openai's API. I think the only solution is for me to downgrade Ubuntu to 10.x or something.

So The term "observable" only includes the regions of the universe from which light (or other signals) has had time to reach us since the bing bang 13.8 billion years old. The actual universe are much larger. The observable universe is centered around the observer, wherever they happen to be(for us it is earth). Every point in the universe sees itself as the center of its own observable universe. The radius of the observable universe is approximately 46.5 billion light-years. This is larger than the universe's age (about 13.8 billion years) because the universe has been expanding during that time.

We couldn't see beyond this because the light outside the Observable Universe will never reach us due to the explansion of the universe, But if we somehow Travel at the edge of the Obervable Universe through Worm Hole we could see another 46.5 billion light-years in all direction if we again do this we would get another 46.5 billion light-years and so on, If it’s finite but unbounded (like the surface of a sphere in three dimensions), traveling far enough in one direction will it just you back to your starting point?

Im an undergrad planning to pursue a career in this field. I wanna know what steps I should take to land a permanent position at an observatory or a research lab that does research on cosmology.

This question probably gets asked all the time, but still I want to know if there's any hope. Could there be a way life could continue after he death? Could entropy be reversed, or could a new universe again out of this one, or could this universe repeat?

Did time have a start? Or it has always been flowing/ passing or will keep passing forever?

If this is the wrong sub, lemme know...

It is a conceptually simple question that i can not find a simple way to ask.

The best analogy would be if the Apollo mission went to Europa(or Andromeda) rather than the moon and maintained a similar level of synchronicity with ground control in Houston. AKA a Zoom call with Europa.

Time dilation says that is impossible, right?

Without throwing the baby out with the bathwater and falsifying all of physics and cosmology, are there any competing theories that would allow synchronized passage of time between two far-flung observers if we discover a smallish defect in our current understanding?

Put another way, astronautical engineering could put a human on Europa in closer to a century than a millennium.

Assuming quantum computing, AI, or the Wizard of Oz make similar progress possible for synchronicity, at least in telecommunications, what inventions or 'work arounds' are we missing today that would allow that?

[Hoping for an ELI30 explanation for how a quantum entangled iPhone or whatever could theoretically (almost) work :) ]

The idea is that inflation never happened and the expansion was was caused by gravitaitonal waves... https://interestingengineering.com/space/space-possibly-created-galaxies

Remember that post I made about my hypothesis about re-imagining the big bang as wave that was met with pretty strong resistance because I said, as an engineer, it doesn't make sense? Yeah. That one. I self-published that and sent it everywhere. Apparently I wasn't the only one thinking the same way.

It's a bit of dubious I told you so, but still. This is good.

Simplest question, if universe is finite... It means it has edges right ? Anything beyond those edges is still universe because "nothingness" cannot exist? If after all the stars, galaxies and systems end, there's black silent vaccum.. it's still part of universe right? I'm going crazy.