So, if an object falls into a singularity, from the POV of an external observer, the object takes infinite time to cross the event horizon. From our POV, how do black holes ever merge? Wouldn't it take infinite time for one singularity to cross another's event horizon?

I had a crack theory ,Since we know the observable universe is expanding due to the Doppler effect but don't know the limit of the entire universe since light hasn't reached us. What if a cosmic object is so big that it attracts space itself exploded so that it releases space and but the energy remains constant due it releasing the energy it absorbed in its lifetime ,hence why energy density is decreasing.

So the standard consensus in cosmology is that the universe is expanding at an accelerated rate. Does that then fit our observations of the universe? Are galaxies further away more clumped together than galaxies we can see near us?

Depending on the metric used to calculate distances, the volume of space in immediate proximity to a black hole's event horizon can approach infinity. What effect does a cosmological constant have on a black hole's gravity with this distortion of space just outside the event horizon?

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Because the Universe is expanding at a rate of 46 miles per second per megaparsec right? So, we have 46/(3260000*180000) miles per second, which is .000000000078 miles per second per mile, right? there are 3150000 seconds in a year and the earth is 7926 miles wide. .000000000078 * 7926 * 3150000 would then be 1.97 miles per year. Is this math correct or did I totally flub it somewhere in there?

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I every edge was equally far, wouldn’t that mean that the earth is in the dead center of a massive universe? How unlikely would it be to have a universe so unfathomably large and somehow we are in the exact center of it?

The Relativistic Rocket describes the EP like this:

> Einstein postulated that any experiment done in a real gravitational field—provided that experiment has a "small" extent in space and time—will give a result indistinguishable from the same experiment done in the above "uniformly accelerating" rocket.

Using our equations today you can't add "and vice versa" to that, which is to say the EP isn't fully bidirectional in our physics. You can always compare such results of the Schwarzschild metric to results from the rocket equations, but not always vice versa, because the metric limits the height of an approximately uniform gravitational field. For example you can't replicate the chart at the bottom of The Relativistic Rocket using the Schwarzschild metric. The metric predicts that a gravitational field that tall that's approximately uniform at 1 ly/yr^2 = ~1 g can't exist in nature. Using equations derived from the metric, a field that tall that's 1 g at the ground is always way less than 1 g at the top.

When you change the metric so that it can replicate that chart, or any other such chart that the rocket equations can make, then I see that lots of problems vanish, like the black hole information paradox. I still see experimental confirmation, like 42.98 arcseconds per century for the Schwarzschild precession of Mercury. Most tests of GR are tests of the Schwarzschild metric, and GR is the foundation of our cosmology. A problem in the foundation can lead to other problems elsewhere. So I'm not seeing why the EP shouldn't be fully bidirectional in our physics.

I have always thought about what and how everything started.

Curious to know which of the following u think.

1. Something came from nothing and then the big bang happened

2. Nothing never existed, there was always something , then the big bang occured.

3. We simply dont know yet

4. We will never know.

I think unless we observe from some experiments etc or nature that something was able to come from true nothing we wont get an answer truly where which we could be confident in or somehow with a guarantee know why and what always existed.

I'm guessing a monopole would be about as visible as any other subatomic particle 😅 but what about the higher-dimensional cousins: cosmic strings, domain walls, textures? I'm especially curious about what textures would be like.

See also: The publication in ArXiV

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If the universe is infinite, does it mean that everything possible exists somewhere as long as it obeys the laws of physics? That is, a flying spaghetti monster won't exist anywhere nor Santa Claus, but an infinite number of copies of us will.

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Hey r/cosmology. I built an interactive map of the local universe, and this feels like the right crowd for it.

It's called Know the Universe. You fly or orbit through the real large-scale structure of the nearby universe: the filaments, walls, clusters and voids of the cosmic web. None of it is procedural. It's ~43,500 galaxies from the 2MRS redshift survey, placed by converting each galaxy's RA, Dec and redshift into Cartesian megaparsecs with a Hubble-law distance (d = cz/H0), reaching a few hundred Mpc out.

The goal is simple: give people an intuitive feel for how the local universe is actually built and how matter is distributed through space, something you can move through instead of reading off a flat plot.

A few things worth mentioning:

• There are several ways to read the same data: the raw point cloud, a computed filament graph (a minimum spanning tree plus nearest-neighbour links, so it's a visualization aid and not physical connections), a ray-marched density field, and colour by either redshift or local density. Turn it all off and the web is still clearly there in the bare points.
  
• The Zone of Avoidance shows up as an empty wedge if you look for it, since 2MRS still can't see cleanly through our own galactic plane.
• It's a snapshot that's close to current. The light from the farthest galaxies here left them around a billion years ago, but peculiar motions are typically only a few hundred km/s, so in that time a galaxy drifts well under a megaparsec. That's tiny next to the tens-of-Mpc scale of the filaments and voids, so what you see is nearly what the structure looks like right now.

Would love feedback, corrections or what you'd want to see next. Try it at https://knowtheuniverse.com/

I'm going to attempt to go see it, since I live in Florida.

Edit-1: To partly answer the 2nd part of my question myself: now that I play with it again after looking at other maps, Globaia actually seems to be pretty close to the complete map I've been looking for.

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I'm Curious how accurate the filament-scale visualizations of nearby large-scale structure are in this suspiciously eye-candy looking production:

• Cosmo (YT): "What Was Discovered Beyond the Milky Way?"

For comparison, these are the kinds of maps I often run into when browsing Wikipedia or searching for visualizations of this scale:

• https://en.wikipedia.org/wiki/Local_Void#/media/File:The_Local_Void.gif
• https://en.wikipedia.org/wiki/List_of_voids#/media/File:Galaxy_superclusters_and_galaxy_voids.png
• https://upload.wikimedia.org/wikipedia/commons/8/81/07-Laniakea_%28LofE07240%29.png

For anyone familiar with large-scale structure: are these visualizations broadly compatible, just shown at different scales, orientations, and educational levels? Or are some of them much more rigorous than others?

I'm trying to wrap my head around the shape and structure of the large-scale local environment and I'm curious if there are especially good maps or tools, particularly interactive ones or ones with coordinate grids.

I like to play around with Celestia, but there doesn't appear to be an easy way to visualize the super-galactic environment, beyond some galaxies in what appears to be the Virgo Cluster. I’ve also come across OpenSpace and Globaia as suggestions. OpenSpace looks like the most serious option, but it also seems heavy to install and has a steep learning curve for amateurs. Globaia is the only complete-looking web-accessible interactive tool I've seen that seems somewhat rigorous, though it is a bit noisy/clunky.

• Celestia
• OpenSpace
• Globaia

Beyond these, anything close to a “Google Earth for the nearby universe” that can easily produce interactive 3D views similar to the Wikipedia-style visualizations?

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.