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?

#91

Post by chowells » Wed, Sep 09, 2020, 6:50 PM 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.

Not in practice. In practice, this provides a very tiny force pulling subatomic particles apart in an atom's nucleus, or pulling atoms away from each other in a molecule, or pulling a celestial body's molecules away from each other. It makes no difference at all, because that force is absolutely dwarfed by the strong nuclear force, electromagnetism, or gravity, respectively. Systems that are coupled together by those forces, up to and including galaxies, are impacted only very minutely by this expansion.

For the expansion to have a significant impact on relative distances, the distances involved have to be so extreme that there's no real other interaction between the objects you're measuring from.

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

#92

Post by DeRock » Wed, Sep 09, 2020, 6:55 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…

If you want to delve further into this idea, check out http://www.flatuniversesociety.com

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

#93

Post by ben_w » Wed, Sep 09, 2020, 6:57 PM 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.

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 any orbits still be stable in an expanding universe?

(In theory I could simulate the orbits question easily; in practice, last time I tried to do astrophysics maths I made an elementary mistake).

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

#94

Post by 205guy » Wed, Sep 09, 2020, 6:57 PM UTC

PopeDotNinja wrote: post #72

s1dev wrote: post #61

Earlier quoted context omitted.

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?

And how would you get them out to, and stop at, 550 AU? Voyager 1 and 2 are nuclear powered with RTGs and they are respectively about 150 AU and 125 AU from the sun, and they are going really fast. The Voyager RTGs are also fairly depleted at this point. I’m guessing these spacecraft would need a faster, more efficient mode of propulsion, like a nuclear thruster or ion drive (or Epstein drive?!). One could also get a…

I was wondering how fast myself and found this:

https://voyager.jpl.nasa.gov/mission/status/

Voyager-1 is the fastest at 38,000 mph (61000 km/h) with respect to the Sun, but currently about 90,000 mph (144000 km/h) relative to earth (I guess this fluctuates annually).

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

#95

Post by onlyrealcuzzo » Wed, Sep 09, 2020, 7:00 PM UTC

z92 wrote: post #78

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…

> 547 AU For comparison Voyager-1 is now at a distance of 40 AU only.

Is Voyager-1 still accelerating?

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

#96

Post by gmadsen » Wed, Sep 09, 2020, 7:00 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…

there is no direction of the big bang. You sitting in your chair is the exact center of the universe for your frame of reference.

all we have is the sphere of light that can reach us. That doesn't imply anything about a global universe frame

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

#97

Post by hashtagmarkup » Wed, Sep 09, 2020, 7:00 PM UTC

z92 wrote: post #78

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…

> 547 AU For comparison Voyager-1 is now at a distance of 40 AU only.

That is not correct... it is 150 AU away from earth.

https://voyager.jpl.nasa.gov/mission/status/

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

#98

Post by cgriswald » Wed, Sep 09, 2020, 7:00 PM UTC

z92 wrote: post #78

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…

> 547 AU For comparison Voyager-1 is now at a distance of 40 AU only.

That is incorrect. It's approximately at 150 AU[0]. For reference, that's about three times the distance of Pluto at aphelion. 547 AU is about 11 times the distance of Pluto at perihelion.

[0] - https://voyager.jpl.nasa.gov/mission/status/

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

#99

Post by iwonderwhy » Wed, Sep 09, 2020, 7:06 PM UTC

zemnmez wrote: post #59

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…

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. Assuming that everything expands along with the balloon. If I understand this correctly, and according to:

“Due to the expansion increasing as distances increase, the distance between two remote galaxies can increase at more than 3×108 m/s, but this does not imply that the galaxies move faster than the speed of light at their present location (which is forbidden by Lorentz covariance).”

But from outside we can move faster than the speed of light? Sorry having trouble getting my head around this.

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

#100

Post by maxekman » Wed, Sep 09, 2020, 7:08 PM UTC

joshspankit wrote: post #82

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…

It would be interesting to hear your answer to mekkkkkk‘s question

It was answered, as far as I can tell:

> However, local forces like gravity and the strong and even the weak nuclear force are more than sufficient to hold everything together despite this, so the expansion cannot be locally observed.