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?

#141

Post by ddevault » Wed, Sep 09, 2020, 8:01 PM UTC

thaumasiotes wrote: post #138

ddevault wrote: post #129

Earlier quoted context omitted.

>The iron rod started out being 1 meter long, and now it's 0.952 meters long. In what sense did it not shrink? In the sense that it did not become 0.952 meters long. It didn't "become" anything - it did not change at all. The universe grew around it, or perhaps "underneath" it. More space appeared for it to exist in. It's like putting an iron rod in a 10 meter square house, then moving the walls out another meter. Ed…

> More space appeared for it to exist in. This is a very different idea from "it's the same amount of space, but bigger", which is what I understand by the claim that a scale factor is increasing.

Well, space isn't a tangible (and finite) thing. It's the manifold in which the universe exists. Increasing the scale factor doesn't "stretch" space, it just makes... more of it.

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

#142

Post by erulabs » Wed, Sep 09, 2020, 8:01 PM UTC

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?

Strictly speaking our observations are not continuous. We pointed a large array at it and then the array probably went on to other work and looked elsewhere - so technically “was” is more correct, since we do not know what it “is” doing, rather only what it appeared to be doing.

Either way it’s a pretty uninteresting difference in tense.

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

#143

Post by Swizec » Wed, Sep 09, 2020, 8:02 PM UTC

dumpsterdiver wrote: post #67

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…

>"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…

My high school physics professor had a great take on this: The universe is defined as “everything”. If we ever find anything outside the universe, we’ll call that the universe too.

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

#144

Post by pas » Wed, Sep 09, 2020, 8:02 PM UTC

iwonderwhy wrote: post #99

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…

Interesting analogy. So in effect to someone “watching” from outside our universe anything moving at the speed of light in our context, is moving either faster or slower than the speed of light in their context. Since the ballon and everything inside is expanding it means that either things are moving at the speed of light + speed of expansion, or speed of light - speed of expansion, when watched from outside. Assumi…

kind of yes, relatively from an "outside observer" that would be the case.

but if the usual laws of physics apply to that outside "observer" then it will not be able to observe photons from those objects.

the usual assumption is that space is basically infinite but we can only observe our own "observable universe" sphere of it. every point in space has its own universe basically.

see also cosmic light horizon: https://www.thedallasgeek.com/single-post/2018/06/11/Our-Cos... (the difference between regions we can communicate with and regions from where a photon coming toward us will eventually reach us)

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

#145

Post by whatshisface » Wed, Sep 09, 2020, 8:07 PM UTC

Swizec wrote: post #143

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…

My high school physics professor had a great take on this: The universe is defined as “everything”. If we ever find anything outside the universe, we’ll call that the universe too.

That doesn't really answer the question, what the parent is really asking about is whether we are living on the surface of a manifold that's due for some kind of a collision with something else.

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

#146

Post by s1artibartfast » Wed, Sep 09, 2020, 8:12 PM UTC

morganvachon wrote: post #66

dumpsterdiver wrote: post #62

Earlier quoted context omitted.

I have a question: Just over 20 years ago when the accepted view was that the expansion of the universe was slowing down, would you have backed that position with as much certainty as you are backing this one? That the universe is a mere 13.7 billion years old? We cannot prove the absence of light in a place that is already so far away that it's light will never reach us. Do you agree? We can prove what we can observ…

> 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

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

#147

Post by peter303 » Wed, Sep 09, 2020, 8:16 PM UTC

iwonderwhy wrote: post #55

All right hackernews. Genuine question, not sure where else to ask. If galaxies and stars at the other “end” formed out of matter resulting from the big bang, just as the matter we are made of, how did we get here at the same time that that matter got there? Is it because speeds faster than light are possible, and around the big bang all matter was spread near instantly at that speed? I don't understand how matter of…

The universe may have alway been infinitely large. Its just that 14.8 billion years it started expanding, first at inflationary rates, then a slower strain of 10E-18 / second.

Its a lot like looking at a number line. That is infinitely long in both directions. And if consider all real numbers, it is infinitely expandable.

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

#148

Post by johncolanduoni » Wed, Sep 09, 2020, 8:29 PM UTC

thaumasiotes wrote: post #135

johncolanduoni wrote: post #130

Earlier quoted context omitted.

The problem with that model is that as was previously said, the electromagnetic, nuclear, and gravitational forces easily countermand the expansion on non-inter-galactic scales, to the point of not being measurable on the scale of a meter. Ultimately the molecular structure of your meter-stick is determined by various structure constants that aren’t changing, so the expansion can’t affect it unless it starts ripping…

> Ultimately the molecular structure of your meter-stick is determined by various structure constants that aren’t changing Really? These structure constants never involve any units of distance? Isn't distance changing at all levels? If I have a meter stick, and then space expands by 10%, you're saying that my meter stick will end up being 0.91 new-meters long, yes? Wouldn't that require the structure constants to cha…

Structure constants are unitless by design. But obviously constants like the speed of light that do involve distance are unchanged too so that’s not a satisfying end to the story.

Let’s come at this from the other direction: if everything including the space between atoms and galaxies expands by 10%, how do you tell the difference between an old-meter and new-meter? For this to be observable, something has to still scale by the old-meter, or you wouldn’t be able to observe a difference at all. That something would be the physical constants with units, like the speed of light. This means the electrical force governing the chemical bonds in your meter stick will still try to restore the distance between them to their original old-meter distance, but in new-meter units.

Then if you define the actual meter by the length of your meter stick, or the physical constants, you end up getting the same meter that everything not macro-scale “snaps back” to.

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

#149

Post by lordnacho » Wed, Sep 09, 2020, 8:31 PM UTC

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?

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

#150

Post by wruza » Wed, Sep 09, 2020, 8:35 PM UTC

ben_w wrote: post #93

mekkkkkk wrote: post #74

Earlier quoted context omitted.

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.

Just to add to your question: The usual response of “it only affects space between galaxies not inside galaxies” is deeply unsatisfying, and feels like it must be an oversimplification. What I think is meant, but I absolutely want someone wiser to confirm or refute , is that the rate of expansion is proportional to distance, and therefore so small inside a single galaxy it can be ignored. What I don’t know is: can an…

it only affects space between galaxies not inside galaxies

It obviously affects all space, inside galaxy or outside of it. Let's just check the rough math, not even bothering about the fact that expansion was not linear. The universe expanded to around 100BLY in about 10BY, i.e. got ten times bigger than its potential light cone. So, for every "initial" 1km, there is additional 9km in 10BY timespan, or 0.0009mm per year, or 0.00003nm per second. The general ratio is around 1e-17 per second per length unit.

Proton size is around 1e-15m, Planck size is around 1e-35m. A thousand Planck units per second is not that much, really. And on sub-milliseconds it just loses its effect completely, due to that Heisenberg guy. (If we take my bullshit math seriously, I mean.)