Earlier quoted context omitted.
Very interesting. So the I wonder if everything expands along with the universe, does it mean that from outside, things moving at the speed of light in our universe, are potentially moving at speeds greater than the speed of light within our universe? If i was watching from outside, a rectangle moving at the speed of light in our universe, would one of its edges be moving away from me at the speed of light + the spee…
That question is too abstract for me to reason about. A "rectangle" couldn't move at the speed of light; light is point-like (oh dear, saying that could get me in trouble). Anything with mass cannot move at the speed of light, and anything without mass must move at the speed of light, and all known objects without mass are point-like. And then there's the question of observation in the first place - observation itsel…
Why is there a normal galaxy sitting at the edge of the Universe?
131–140 of 252 posts
Re: Why is there a normal galaxy sitting at the edge of the Universe?
#132Nice 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 do you propose to power a fleet of spacecraft at 550AU? Would you be able to acquire enough RTGs? What about DSN time for the downlink?
https://arxiv.org/ftp/arxiv/papers/2002/2002.11871.pdf
for downlink can't they launch a few extra sats that just sit around the Sun and form a big virtual dish (via baseline interferometry or what's that occult DSP magic called these days)?
Re: Why is there a normal galaxy sitting at the edge of the Universe?
#133Earlier quoted context omitted.
>And if so, why do all particles pack at exactly the same new density? Shouldn't it differ from molecule to molecule? The dominant factor on this scale is the strong nuclear force, which governs interactions at the scale of quarks - much smaller than molecules.
But the scale of quarks increases just as much as every other scale, doesn't it? Why did the iron rod shrink while space grew? Why are the iron atoms closer together now than they were before? Why are the protons in each iron atom closer together now than they were before?
No, there is no scaling of matter or light. It just has a bigger space to play in.
Re: Why is there a normal galaxy sitting at the edge of the Universe?
#134All 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…
Re: Why is there a normal galaxy sitting at the edge of the Universe?
#135Earlier quoted context omitted.
> 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. I am not that person. But I feel like this can't work -- if all space is expanding equally, in proportion to its own extent, then we would perceive no expansion at all. If two points start out 1 light year apart,…
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…
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 change, to allow for the same molecules to take up less space?
Re: Why is there a normal galaxy sitting at the edge of the Universe?
#136All 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…
Re: Why is there a normal galaxy sitting at the edge of the Universe?
#137Earlier 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…
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 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. From our perspective on the outside, it's an intense explosion occurring in very slow motion, and from the perspective on the inside, it's an intense explosion happening all at once.
Rovelli posits a Planck star, not a singularity, exists past the black hole's event horizon, and the Planck star is the state of maximal compression between the black hole and white hole phases. And somewhat related to this, if I understand the theories correctly, our universe might be a supermassive white hole, and we might hold the perspective of being inside of a super(super)massive black hole that's turned into a white hole and is exploding and jettisoning everything inside of it. Or some stage after that. The ultra-compressed energy before the Big Bang would be an (extremely massive and dense) Planck star.
I have no idea how likely the Planck star theory or white hole universe theory might be, but my blind speculation is that if it's true, maybe dark energy is whatever's fundamentally responsible for gravity/curvature causing our white hole explosion to bend some outer medium - the hypothetical potential medium which our black hole/universe originally formed in - and interact with other extreme contractions and explosions also happening in that medium, in complex and multivariate ways. Maybe a white hole being pushed into or prodded or yanked by many other black holes and white holes from different directions and angles could be perceived from the inside as accelerating expansion of space at certain scales.
Maybe this is happening recursively, even; maybe that outer medium is itself within another even greater medium, which also is within another greater medium, etc. Maybe the nesting depth is small, or near-infinite, or infinite. Or maybe there is no outer medium to our universe, in which case that whole idea's shot.
And I'm not sure if this could be related, but Rovelli suggests the hypothetical Planck star cycle of black hole to white hole applied to primordial black holes that formed in our early universe could explain dark matter, so even without the outer medium idea there could be something here that helps us understand our large-scale observations. Maybe there could be some relation to the "dark fluid" and negative energy idea, too: https://en.m.wikipedia.org/wiki/Dark_fluid
I have absolutely no clue if your or my speculation is reasonable or not (there's currently zero evidence of any sort of outer medium, as far as I know), but the general concept of our universe being the result of a black and/or white hole does definitely seem to interest a lot of physicists.
Re: Why is there a normal galaxy sitting at the edge of the Universe?
#138Earlier 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?
>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…
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.
Re: Why is there a normal galaxy sitting at the edge of the Universe?
#139Earlier 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…
I think you're getting tripped up on a variation of this idea, e.g. moving a laser pointer across the moon's surface faster than light. https://www.universetoday.com/109147/how-a-laser-appears-to-...