Why is there a normal galaxy sitting at the edge of the Universe? • Hacker News Board

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

#201

Post by jquery » Thu, Sep 10, 2020, 1:34 AM UTC

meowface wrote: post #170

jquery wrote: post #152

Earlier quoted context omitted.

> Carlo Rovelli and others propose that black holes actually only appear as they do to us due to the extreme time dilation, and similar to how a photon's "perspective" is that it's experiencing all of time at once, a black hole's perspective is that it's basically a massive explosion that occurs at essentially the same moment it forms. So under this hypothesis, a black hole never reaches a true singularity, but as cl…

Don't know why you're being downvoted. It's definitely not too crazy of an idea, given what's been known since general relativity was confirmed and the discovery that black holes do indeed exist. I haven't looked into it, but I wouldn't be surprised if many other people have proposed it in the past. I haven't heard or thought of it before, but when I first read it it definitely made a lot of sense, intuitively. Maybe…

You’re dead-on about humility. I meant it was nothing more than my idle speculation based on my shallow understanding of physics. I was just so excited to see there’s an entire theory around it! Thanks for sharing more resources. Cosmology continues to fascinate me.

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

#202

Post by 0xffff2 » Thu, Sep 10, 2020, 1:37 AM UTC

rosstex wrote: post #165

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…

Why not chocolate chip bread? I suppose raisins more closely represent galaxies.

Is that a real thing? You can buy raisin bread at any grocery store... I've never even heard of chocolate chip bread.

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

#203

Post by moron4hire » Thu, Sep 10, 2020, 1:44 AM UTC

0xffff2 wrote: post #202

rosstex wrote: post #165

Earlier quoted context omitted.

Why not chocolate chip bread? I suppose raisins more closely represent galaxies.

Is that a real thing? You can buy raisin bread at any grocery store... I've never even heard of chocolate chip bread.

It's definitely a thing. And yes, I've bought it in stores, not just made it.

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

#204

Post by sp332 » Thu, Sep 10, 2020, 1:53 AM UTC

lordnacho wrote: post #149

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…

How does the lensing work? Why doesn't the galaxy in the middle between us and the faraway galaxy pollute the image with its own light? It it separated by frequency or some trick?

The light bends around the galaxy. You're right that looking straight at the galaxy wouldn't work, but looking just a tiny bit to the sides does.

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

#205

Post by taotau » Thu, Sep 10, 2020, 2:31 AM UTC

mekkkkkk wrote: post #74

zemnmez wrote: post #59

Earlier quoted context omitted.

this is because things aren’t ‘moving apart’— space itself is expanding (into what? nobody knows). it’s not that the galaxies are being propelled apart from a force in a particular place either; everything is expanding away from everything else . On the traditional balloon model, the surface of the balloon represents space itself. Those dots on the surface of an expanding balloon are not moving relative to space (the…

Sorry for also asking a space 101 question, but since the fabric of space is expanding, does that mean that things are getting bigger as well? Naively, it would seem that way. In your balloon example, the dots would get bigger.

I came up with the analogy of 2 pairs of independent dancers on a large checkerboard floor. Lets say the tiles are 10cm^2 and the two couples start out 10 tiles apart.

Every second, the tiles on the floor push away from all their neighboring tiles by one tile width and new tiles appear in their place. The tiles are small enough that the dancers are easily able to adjust their step/grip on eachother to simply maintain their dance routine.

However, even tho the dancers can stay together, the couples drift apart at an ever increasing rate. They start 10 tiles apart, after one second the couples will be 20 tiles apart from eachother, 40 tiles apart after 2 seconds, 80 tiles apart after 3 seconds (a new tile is being inserted between each pair of existing tiles). My tiling math is probably slightly off, but I think this illustrates the exponential increase in expansion.

The dancers are quarks, atoms, molecules, planets, galaxies, etc. Their grip on eachother is big enough to overcome the relatively small adjustment in the space that was created between them.

A few questions using this analogy arise.

Do the new tiles actually appear between the dancers, or is it more a case of the force of friction the dancers are applying to the floor prevents those tiles between them from moving apart ?

So when 'new space' is being created, is it created around strongly bound things and the things simply slide around through this new space to maintain their current configuration, or do the 'strong' forces prevent new space being formed around them ?

If the new space is not being created, what happens to the energy that would have gone into the creation of the new space ? Does it simply get applied to the nearest point where it can squeeze in more space ?

If the space is being created and the dancers pull themselves together to overcome it, where does this extra energy come from ?

As for the big rip, I always thought it was the equivalent to the dancers finally getting tired and not being able to hold onto eachother hence giving in to the expansion of space. ie. It happens around the heat death of the universe when everything has dissipated its kinetic energy so much that the energy of the expansion is more than is left in the system to keep things together.

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

#206

Post by ineedasername » Thu, Sep 10, 2020, 3:00 AM UTC

withinboredom wrote: post #172

skissane wrote: post #161

Earlier quoted context omitted.

The problem with dates like that is they are pure best wishes. They might have funding for a demo in 2024 – although it isn't even clear they've got that yet, it sounds like they may just have funding to develop their proposal further. Even assuming the tech demo is successful, it sounds like they don't even yet have a detailed costed proposal for a 2034 launch, and no idea how likely that it will actually get funded…

> Politicians and bureaucrats want immediate results This makes me sad. The entire point of Government is to be an enterprise spanning multiple generations.

Even without politicians, the effective limit to most enormous projects is a human life span. Even if you look at projects that spanned 100-200 years like some cathedrals, they tended to be built in chunks: the main hall might be the first and largest, but things like trancepts, side chapels etc. would come later

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

#207

Post by javajosh » Thu, Sep 10, 2020, 3:28 AM UTC

iwonderwhy wrote: post #122

ddevault wrote: post #102

Earlier quoted context omitted.

I don't fully understand your question to give a direct answer, but I think that's mostly due to a number of misconceptions you hold about the universe. So I'll just try to clear those up instead. First of all, the big bang didn't happen somewhere , it happened everywhere . There's no "center" of the universe that everything is moving away from. The universe did not start from a point, it started from a small scale f…

Ok, thanks for clarifying - indeed i seem to have had quite a few misconceptions. But from outside the universe, are things inside of our universe moving faster than the speed of light due to our universe expanding, and as such, things traveling at the speed of light when seen from the outside are traveling at the speed of light + speed of expansion?

There is nothing outside the universe. The cosmic background radiation is, in a sense, the furthest thing we can observe, which is the remnant of the big bang. And yet it is the same everywhere. So the surface of the bubble actually represents a single historical point! That implies some strange geometry! The universe may seem static on a small scale (like Earth) or an expanding sphere at a larger scale (inter-galactic), but at the universal scale something even weirder is happening. It may be more useful to think of the "expansion of the universe" as an illusion created by zooming into that singularity, which is itself fixed, even unchanging, but your inexorable motion "into" it makes it look like things are flying apart. (In this case, "you" is an astronomer looking at distant galaxies; you can't really notice this effect at human-scale, and apparently you can't even measure it at lower-than-human scale, which is why quantum gravity is ...difficult shall we say.)

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

#208

Post by skissane » Thu, Sep 10, 2020, 3:29 AM UTC

ineedasername wrote: post #206

withinboredom wrote: post #172

Earlier quoted context omitted.

> Politicians and bureaucrats want immediate results This makes me sad. The entire point of Government is to be an enterprise spanning multiple generations.

Even without politicians, the effective limit to most enormous projects is a human life span. Even if you look at projects that spanned 100-200 years like some cathedrals, they tended to be built in chunks: the main hall might be the first and largest, but things like trancepts, side chapels etc. would come later

In a hereditary absolute monarchy, the son (or more rarely daughter) may feel motivated to continue to the projects of his father (or more rarely mother), out of a sense of filial duty. In principle, it seems like hereditary absolute monarchy may avoid the problem you describe.

In practice, hereditary absolute monarchy suffers from the problem of the dud heir: Marcus Aurelius is remembered as one of the greatest Roman Emperors, his son and successor Commodus is remembered as one of the worst.

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

#209

Post by dumpsterdiver » Thu, Sep 10, 2020, 3:32 AM UTC

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…

I don't know why you were downvoted, the theories you referenced sound as plausible as any other to me (but then again I tend to assume everything comes with a touch of bullshit).

The situation you described would result in a game of universal pong, in which matter is passed from one side of the universe to the other before reaching a critical point where it bounces back. Obviously I have no means of validating the "Plank star beyond the horizon" theory, but nor can anyone else can prove differently at this point.

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

#210

Post by noizejoy » Thu, Sep 10, 2020, 3:35 AM UTC

ddevault wrote: post #116

noizejoy wrote: post #111

Earlier quoted context omitted.

So will expansion accelerate enough to eventually be a stronger “force” than local gravity?

We don't understand why expansion is occuring, so we can't say for certain. It would be a very long time in the future if that were to come to pass, and that's a whole lot of time for poorly-understood physics to happen in. But yes, it is accellerating, and if it continues to do so, eventually it will overcome gravity. But like I said, this depends on an incomplete understanding of physics, and the current evidence s…

Sometimes a simple upvote just doesn’t seem enough. So here’s a heartfelt Thank You for this and your other explanations - I really appreciate your knowledgeable and thoughtful responses!