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Why is there a normal galaxy sitting at the edge of the Universe?

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Re: Why is there a normal galaxy sitting at the edge of the Universe?

#181

Post by jecel »

nelsonenzo wrote: post #162
cgriswald wrote: post #105

Earlier quoted context omitted.

> On the traditional balloon model, the surface of the balloon represents space itself... For any still confused, there is also a 'raisin bread' model (which I prefer because it's 3D, unlike the surface of a balloon). The raisins are galaxies, and the bread is the space between them. As it bakes, the raisins get further apart, even though the raisins aren't moving through the dough. (Although galaxies also have movem…

Omg, thank you for this! The balloon model always confused me because I could never understand what was in the middle of the balloon, and why we were on top of it. It's an odd 2d example using an object that is 3d, the balloon. Raisin bread, oh I love thee even more today.

The raisin bread is a 3D expansion in 3D space. So from the viewpoint of a specific raisin the others are moving differently depending on what direction you look and you can use that to determine where the center of the bread is.

The balloon is a 2D expansion in 3D space, which is a better analogy for our 3D universe expanding in 4D space. From the viewpoint of a particular dot you see the exact same thing no matter what 2D direction you look. There is no center.

I agree that the balloon is more confusing, but it is more correct in that it doesn't lead to ideas like "the point where the big bang happened".

Re: Why is there a normal galaxy sitting at the edge of the Universe?

#182

Post by ddevault »

mensetmanusman wrote: post #180
ddevault wrote: post #70

Earlier quoted context omitted.

In case anyone is confused, I prefer to explain the expansion of space without metaphors. Space itself is getting larger, everywhere, all at once. The scale factor of the universe is getting larger. New space is constantly being "made". Every second, every kilometer in the universe grows by 2.2×10^-18 centimeters. If no other forces were in play, it'd carry everything along with it and pull everything a bit further a…

Do particles in this model re-adjust their spacing to the new space being created? e.g. after 10^18 seconds, would the diameter of a hydrogen atom still be the same? or is it scaled to be huge (relative to now) ?

Space is growing, not the matter within it. The diameter of a hydrogen atom is dominated by the fundamental forces, and the expansion of space is insufficient to overcome this force.

Re: Why is there a normal galaxy sitting at the edge of the Universe?

#183

Post by [deleted] »

Aerroon wrote: post #159
meowface wrote: post #137

Earlier quoted context omitted.

From my layman's perspective, I think this is plausible, and many physicists seem to agree it's plausible. Maybe another plausible explanation could be the reverse: maybe before the Big Bang, our/the universe was in the state you describe, and the Big Bang is our perception of it "snapping back" and exploding violently outward (aka a white hole). Carlo Rovelli and others propose that black holes actually only appear…

> So under this hypothesis, a black hole never reaches a true singularity, but as close to a singularity as physically possible, and then it almost instantaneously bounces back like a taut rubber band that's stretched back as far as it'll go. Kind of like a graph of 1/x, where everything behaves predictably, but there's that one point that doesn't fit?

[deleted]

Re: Why is there a normal galaxy sitting at the edge of the Universe?

#184

Post by anigbrowl »

tectonic wrote: post #2

Nice gravitational lens observation! We're hoping to use the same technique with the Sun to observe exoplanets by launching a fleet of small satellites to 547 AU (80 billion km / ~3 light days). The craft would sample the distorted Einstein ring around our Sun from that vantage point, then combine and reconstruct an image of the disk of an Earth-like exoplanet up to 100 light-years beyond, at a resolution of 25 kilom…

That's really cool. If it's good enough to detect geographic features, will it be possible to photograph the same planet from the night side later in its orbit?

Re: Why is there a normal galaxy sitting at the edge of the Universe?

#185

Post by anigbrowl »

jecel wrote: post #181
nelsonenzo wrote: post #162

Earlier quoted context omitted.

Omg, thank you for this! The balloon model always confused me because I could never understand what was in the middle of the balloon, and why we were on top of it. It's an odd 2d example using an object that is 3d, the balloon. Raisin bread, oh I love thee even more today.

The raisin bread is a 3D expansion in 3D space. So from the viewpoint of a specific raisin the others are moving differently depending on what direction you look and you can use that to determine where the center of the bread is. The balloon is a 2D expansion in 3D space, which is a better analogy for our 3D universe expanding in 4D space. From the viewpoint of a particular dot you see the exact same thing no matter…

Is the a term for the 4-dimensional coordinate of the 'inflationary center', like there a 3d coordinate for the center of the balloon (inaccessible from the flat universe on its surface)?

Re: Why is there a normal galaxy sitting at the edge of the Universe?

#186

Post by edjrage »

meowface wrote: post #176
Aerroon wrote: post #159

Earlier quoted context omitted.

> So under this hypothesis, a black hole never reaches a true singularity, but as close to a singularity as physically possible, and then it almost instantaneously bounces back like a taut rubber band that's stretched back as far as it'll go. Kind of like a graph of 1/x, where everything behaves predictably, but there's that one point that doesn't fit?

I'm absolutely terrible and uneducated when it comes to math, so I'm not sure exactly what you mean. But if you mean 1/x where x = infinity, then yes, the classical idea of a singularity (such as what's been theorized to exist within a black hole, curving to an infinitely small point) is basically like 1/infinity or dividing by zero. Rovelli hypothesizes this never actually happens and is not physically possible, and…

I'm not terribly educated either, but if you don't mind a minor possible correction, I suppose GP would have meant x = 0, which is the only point where the function would be typically undefined, and the closer x gets to 0, the more f(x) approaches infinity. Conversely, the more x approaches infinity, the more f(x) approaches 0. Also, because of the way these things are usually defined, it doesn't make sense to say x = infinity, it only makes sense to say x approaches infinity (but it might make sense in nonstandard calculus, where infinitesimals are defined - here my ignorance already shows).

I really appreciate your comments! If you're interested in hypothesizing about physics, I think it would do you a lot of good to learn at least a bit of math to go with it.

Re: Why is there a normal galaxy sitting at the edge of the Universe?

#187

Post by svachalek »

anigbrowl wrote: post #185
jecel wrote: post #181

Earlier quoted context omitted.

The raisin bread is a 3D expansion in 3D space. So from the viewpoint of a specific raisin the others are moving differently depending on what direction you look and you can use that to determine where the center of the bread is. The balloon is a 2D expansion in 3D space, which is a better analogy for our 3D universe expanding in 4D space. From the viewpoint of a particular dot you see the exact same thing no matter…

Is the a term for the 4-dimensional coordinate of the 'inflationary center', like there a 3d coordinate for the center of the balloon (inaccessible from the flat universe on its surface)?

Imagine that the balloon is actually completely flat and (to all intents and purposes) stretches infinitely in X and Y directions without wrapping around. As I understand it, we currently believe we're in a 3D version of that:

https://en.wikipedia.org/wiki/Shape_of_the_universe

Re: Why is there a normal galaxy sitting at the edge of the Universe?

#188

Post by svachalek »

natch wrote: post #21

I never understand why articles like this use present tense to talk about past events. It was churning out a lot of new stars.. not is. I guess the “as seen from our current vantage point” is understood, but to me the needless emphasis of that perspective just muddies things, no? Anyone of you downvoters care to enlighten me?

Our language tenses weren't really designed for distant space phenomena. Should we say Betelgeuse is a red supergiant or was a red supergiant? When we look at the sky it exists "now" for us and there's no way to know if it's exploded since the light that we're seeing now left its surface. And even if we talk about the light that's leaving it in our "now" that's kind of vague since there's no real universal common clock.

Re: Why is there a normal galaxy sitting at the edge of the Universe?

#189

Post by morganvachon »

s1artibartfast wrote: post #146
morganvachon wrote: post #66

Earlier quoted context omitted.

> Perhaps the Big Bang was merely a "localized" event and there are Big Bangs occuring in distant places whose light will never reach us. Perhaps we have gone through many Big Bang / Big Crunch cycles. This was always my view of the state of the universe from childhood onward. The Void of space is infinite, and within that Void our universe could be one of an infinite number of other universes that we will never know…

I don't think your childhood view holds up with contemporary views. My understanding is that 3 dimensional space, as well as time are properties of our local universe. There is no space outside the big bang and between universes if multiple exist

That's exactly what I have such a hard time wrapping my head around: The concept that there is not even a Void outside of the borders of our own universe, that existence itself doesn't, well, exist. The fact that "space" (as we define it) is finite just feels so wrong, so impossible.

Re: Why is there a normal galaxy sitting at the edge of the Universe?

#190

Post by [deleted] »

meowface wrote: post #137
dumpsterdiver wrote: post #67

Earlier quoted context omitted.

>"space itself is expanding (into what? nobody knows)" I have a terrifying theory on this (granted, the Earth will be long gone). What if the universe is not actually expanding in the sense that it is being propelled by an initial explosion, but instead falling towards a much greater mass - the end of time so to speak, where all mass ends. Considering that gravity is a "weak force", the scale of such a mass makes me…

From my layman's perspective, I think this is plausible, and many physicists seem to agree it's plausible. Maybe another plausible explanation could be the reverse: maybe before the Big Bang, our/the universe was in the state you describe, and the Big Bang is our perception of it "snapping back" and exploding violently outward (aka a white hole). Carlo Rovelli and others propose that black holes actually only appear…

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