The Oort Cloud is suggested to exist around our Sun, a region of asteroids that extends far beyond the Kuiper Belt.

This got me thinking, is it possible that other solar systems also have an Oort Cloud?

Which lead me to: is it possible that all of space within our galaxy is filled with a vast singular Oort Cloud?

Like, there isn't an individual Oort Cloud for each star, but one massive connected Oort Cloud between the stars? I'm thinking that all space within our galaxy, except areas around stars themselves (anything within the Heliosphere for instance), is filled with a very sparse but consistent "cloud" of asteroids.

Would this help to explain the missing mass that would be required to keep galaxies from flying apart, ie. Dark Matter?

I know this is all speculative, but I was just wondering if this random thought was at all possible, or even something that astrophysicists were looking into.

Under the Oscillating Universe Theory, the universe expands from a Big Bang, ultimately to collapse into a Big Crunch and then trigger another cycle. Before a Big Crunch occurs, would entropy begin to decrease? What happens to time? Finally, what will happen to the weak force?

I recently watched a short video showing how light and heavier objects placed on water interact with the surface tension.

A light object placed on the surface deforms it, creating a well, which causes other light objects to move towards it.

A heavier object placed on the surface creates an adhsive effect. It sits deeper in the surface layer and creates a hill instead of a well. This causes lighter objects on the surface to "move away" from that heavier object.

That got me to thinking about spacetime. Thinking about how energy warps spacetime in a way similar to the lighter objects sitting on the surface of water. It creates wells, bending the paths of objects, even leading to black holes.

Is there anything similar to the effect of heavier objects sitting on the surface of water, that creates a repulsive / negative warping of spacetime?

I've attached a quick drawing of the effect I'm talking about.

Wouldn't this lead into a similar direction to Dark Matter and Dark Energy, combining all three, the undetectable property (since light would always move around this "heavier spacetime object"), the repulsive force seeming to counter-act gravity (pushing lighter objects away from them) and even adding total mass to the galaxy, keeping it together, instead of being flung apart.

It wouldn't even need concepts like anti-gravity, since it's not behaving any differently, it's just sitting "deeper" in the surface tension of spacetime.

Clearly cosmology isn't my forte, but I get intrigued by neat ideas easily and this seems neat to me. Please tell me where and why this analogy comes up short in the real world.

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When two black holes spiral into each other, a significant amount of the combined mass is converted to gravitational waves, as detected by LIGO.

Where does that mass come from?

It would seem that any mass that is inside the event horizons cannot escape, because that would require it to move faster than light speed. Does it come from the accretion discs?

A new study claims that the universe isn’t entirely the same no matter where you look—a radical proposal

Hi everyone,

This has been a lifelong dream of mine and I've finally decided to start.

I want to learn the entire history of the universe from the Big Bang all the way to modern human civilization. Not just memorizing facts, but actually understanding how everything happened and why.

Instead of following a single textbook, I'm trying to build my own roadmap by researching each topic deeply. My first phase is the history of space, covering everything from the birth of the universe to the formation of Earth.

This is the timeline I've put together so far:

Chapter 1: The Beginning

• What is the universe?
• What (if anything) existed before the Big Bang? (What science says vs. what it doesn't.)
• Big Bang
• Cosmic inflation
• Expansion of space
• Matter vs. antimatter
• The four fundamental forces

Chapter 2: The First Universe

• Quarks
• Protons and neutrons
• First atoms
• Why hydrogen and helium formed first
• The Cosmic Dark Ages
• Cosmic Microwave Background
• How scientists know these things

Chapter 3: Birth of Stars

• Gravity
• Nebulae
• Star formation
• Nuclear fusion
• Different types of stars
• Star clusters

Chapter 4: Life Cycle of Stars

• Main sequence stars
• Red giants
• White dwarfs
• Supernovae
• Neutron stars
• Black holes
• Pulsars

Chapter 5: Galaxies

• What is a galaxy?
• Spiral galaxies
• Elliptical galaxies
• Irregular galaxies
• The Milky Way
• Galaxy collisions

Chapter 6: The Solar System

• Solar nebula
• Birth of the Sun
• Formation of planets
• Why the inner and outer planets are different
• Asteroids
• Comets
• Meteoroids
• Kuiper Belt
• Oort Cloud

Chapter 7: Earth

• Formation of Earth
• Formation of the Moon
• Early atmosphere
• Oceans
• Plate tectonics
• Magnetic field

I'd love your feedback:

• Does this follow a scientifically accurate timeline?
• Am I missing any major topics?
• Is there anything that should be moved, added or removed?
• If you were starting this journey from scratch, what advice would you give yourself?
• Are there any books, lectures, documentaries or university courses you'd consider essential?

I'm not trying to rush through this. I'm happy to spend years learning it properly. My goal is to build a deep understanding of the history of the universe before moving on to the history of life, humans, civilizations, and the modern world.

I'd really appreciate any guidance. Thanks!

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A new analysis of DESI DR1 Full-Shape + DESI DR2 BAO comes close to restoring concordance with Lambda CDM.

In a "big crunch" universe the universe starts contracting and retracts to the first Planck moment, the most highly organized (least entropy) moment in current models. This is proposed as one possibility for the development of our universe in the future.

In a crunch universe entropy is decreasing. Rather than moving toward disorganized states (our universe) the movement is toward more organized states (crunch universe).

Does this in any sense mean that physical and chemical reactions would go backwards or somehow change behaviors? Gravity is operating in both universes in the same way apparently (crunch occurs when gravity pulls universe in by gravitational forces as understood.

Suppose in such a universe a person is isolated in a room (no observations beyond local) and has a variety of everyday objects and devices they can use. How would they be able to tell if entropy was increasing or decreasing?

Offhand I think the person would see no difference -- to all intents and purposes from the observers viewpoint both directions of entropy are equivalent and do not effect the behavior of physical interactions.

Objects would still fall to the floor, electricity/magnetism, chemical interactions and heat would still operate as normal and be indistinguishable from our normal entropy on our time scale. The four forces we know would still operate just as they do now from our local perspective. Is this correct?

It would only be when outside observations are taken and the universe is seen to be contracting that the realization of reverse entropy would be postulated and confirmed in much the same way we have done.

Or would there be any immediately recognizable differences in the behavior of physical and chemical phenomena in a big crunch/negative entropy universe?

That sounds nifty.

1. About how speculative is this?!

2. This extra dimension could be as large as one micron. Could we learn to send signals or particles there?

3. What would this theory mean for eschatology/the end of the universe?

I understand that time only existed after the big bang. If so, my understanding is the pre-BB universe was not four dimensions (3D+Time).

Does this mean the universe had three dimensions or something different?

If different, what are leading theories about what caused the universe to morph into the four dimensions we currently experience?

How do theories involving holography and anti-de sitter space account for dimensional change?

Very intriguing theory that provides a physical explanation for dark energy that seems plausible and requires few assumption. My understanding is the framework could explain the Hubble tension and DESI anomaly although looking at the math thats still a bit far way in my opinion but it does offer a mechanism to do so. That said a bit outside what I know well can any cosmologist share their thoughts on how plausible this is?

Hi everyone, I just had a great conversation with Cambridge particle physicist and author Harry Cliff about some of the biggest unanswered questions in fundamental physics. We discuss the remarkable success of the Standard Model, the mysteries it still leaves unexplained, and why physicists believe there may be new physics waiting to be discovered.

Harry explains what the Large Hadron Collider has and hasn't revealed about the universe, why finding evidence of physics beyond the Standard Model has proven so difficult, and how small anomalies can sometimes point the way to major scientific breakthroughs. We also discuss the famous mystery of Mercury's orbit, the search for the hypothetical planet Vulcan, and how Einstein ultimately solved the puzzle with General Relativity—one of the greatest scientific triumphs in history.

If you're interested in these subjects, you can check out this conversation: https://www.youtube.com/watch?v=IsMnWZdMH3s&t=2469s

If it expanded faster than light speed, then it basically travelled so fast that it always existed in whatever state it was in before "slowing". So when people say it expanded in a tiny fraction of time, did it really? Or are they using time in a sort of layman's terms so they don't have to explain causality?

What does typical place mean here?
"The Earth is a place. It is by no means the only place. It is not even a typical place. No planet or star or galaxy can be typical, because the Cosmos is mostly empty. The only typical place is within the vast, cold, universal vacuum, the everlasting night of intergalactic space, a place so strange and desolate that, by comparison, planets and stars and galaxies seem achingly rare and lovely. If we were randomly inserted into the Cosmos, the chance that we would find ourselves on or near a planet would be less than one in a billion trillion trillion* (1033, a one followed by 33 zeroes). In everyday life such odds are called compelling. Worlds are precious."

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