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It's been a long time since astrophysics class for me (and what I learnt at the time has probably since been proven wrong) but I was under the impression that all the galaxies are moving away from a common central point (some are even colliding), though yes I do realise the big bang wasn't a literal explosion but a rapid expansion of space. Either way and however you phrase it, the galaxies are altering their relative positions from each other, so from what other fixed point would you gage it? Still, leaving that aside if you instead take the galactic centre as the reference point; how far could a solar system travel in 150 years?
Of course if that wormhole/time-vortex crossed space as well as time then it's all rather moot.
quote:Originally posted by Reverend: It's been a long time since astrophysics class for me (and what I learnt at the time has probably since been proven wrong) but I was under the impression that all the galaxies are moving away from a common central point (some are even colliding), though yes I do realise the big bang wasn't a literal explosion but a rapid expansion of space. Either way and however you phrase it, the galaxies are altering their relative positions from each other, so from what other fixed point would you gage it?
There is no fixed point from which you can gage the expansion of the universe. Here in the Milky Way, we see (mostly) every other galaxy moving away from us. The further away the galaxy is, the faster it moves away from us. However, that does not mean that we are at the center of the universe. A galaxy billions of light-years away observes the exact same thing.
quote:Originally posted by Reverend: Still, leaving that aside if you instead take the galactic centre as the reference point; how far could a solar system travel in 150 years?
The sun could travel about .11 light-years in 150 years with respect to the center of the galaxy. The stars in our galactic neck-of-the-woods move at similar rates.
-------------------- "Kirito? I killed a thing and now it says I have XPs! Is that bad? Am I dying?"
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quote:Originally posted by Jason Abbadon: That's crazy, Josh: everyone knows that God made the universe 6000 years ago, and that carbon dating, astrophysics and rational thought are tools of Satan. Also, the universe revolves around Earth and it is flat.
Well, *duh*, but I was talking about the fictional Star Trek universe. You know, the one with FTL travel, energy beings, wormholes, time travel, engrams and katras, red matter... uh, wait...
quote: Phht. I walk .11 light-years to work every day.
Up hill in the snow both ways? I hear ya brother. Kids today... sheesh!
quote:Originally posted by Joshua Bell: Tell me you didn't just ask that...
*sigh*
The Big Bang wasn't an explosion in space, it was an explosion *of* space.
1D analogy: today we live on an expanding rubber ruler; the Milky Way is at the 1cm mark, Andromeda is at the 3cm mark, etc. The ruler is gradually stretching out as time passes; in another billion years they will be 2.5cm apart. Looking back in time, they get closer together. At the Big Bang, the ruler had shrunk to zero length so there was no space between those points. (You have to imagine the ruler has no ends, though. You can pretend the ruler is bent into a loop if that helps.) There is no "middle" of the expansion - it all expands uniformally.
The 2D analogy is usually a balloon, with galaxies being on the surface. It is a 2D world so there is just the surface - east/west and north/south, but no in/out. As the balloon inflates the galaxies on the surface get farther apart since space itself is expanding, but there is no point in the flat universe of the surface that is the center of the expansion.
Derailing the conversation away from Romulus...
A few points and/or questions come to mind after reading this and doing research.
1. I can see how easy it is for people to be confused. You state that the universe is not expanding away from a central point and gave a nice expanding balloon illustration. I also read an illustration using an expanding loaf of raisin bread and how each raisin is expanding away from the other yet, from the POV of an individual raisin everything is expanding away from it. Neither illustration helps clarify this, IMO.
Each illustration shows an expansion. When the larger balloon/raisin bread is contrasted with it's smaller counterpart the expansion is detected. Yet a balloon or raisin bread expand from a common central point. If you look at the two you can measure the growth and backtrack to the central point of expansion.
I see what you're saying about the balloon surface. Just use the 2d balloon surface and ignore the expansion from the center of the balloon. Still, can you see how confusing this can be when everything we ever see expanding expands from a central point?
Is there nothing in real life that is currently doing the same thing (besides the Universe). Nothing you can point to and say "see, just like that!"
It would help.
2. Reverend mentions colliding galaxies. If everything is expanding away from everything else, then how is it they are colliding? Are they not moving/expanding at the same rate?
If an observer were stationed on one of these galaxies that is actually getting closer/colliding with another galaxy, what would it look like? Would his theories about the Big Bang and Expanding Universe differ from ours because, from his frame of reference, things are contracting toward his point of view instead of away from it?
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quote:Originally posted by HerbShrump: Is there nothing in real life that is currently doing the same thing (besides the Universe). Nothing you can point to and say "see, just like that!"
Alas, no. Space-time is a 4D concept, which human beings have a tough time understanding. Hence, the usage of 3D, 2D, and 1D analogies.
quote:Originally posted by HerbShrump: 2. Reverend mentions colliding galaxies. If everything is expanding away from everything else, then how is it they are colliding? Are they not moving/expanding at the same rate?
Galaxies can collide because the gravitational forces between them can locally overcome the expansion of the universe.
From our point of view, the galaxies near us aren't moving away very fast. Gravity can overcome that fairly easily. It's only at much greater distances that galaxies appear to start moving pretty quickly and gravity can't keep up.
quote:Originally posted by HerbShrump: If an observer were stationed on one of these galaxies that is actually getting closer/colliding with another galaxy, what would it look like? Would his theories about the Big Bang and Expanding Universe differ from ours because, from his frame of reference, things are contracting toward his point of view instead of away from it?
Considering how our galaxy and the Andromeda Galaxy are moving towards each other, and will collide in several billion years, no. But again, that's local (cosmically speaking). As you get further from the Milky Way, galaxies overwhelmingly (if not unanimously) move away from us at increasingly faster rates.
-------------------- "Kirito? I killed a thing and now it says I have XPs! Is that bad? Am I dying?"
-Asuna, Episode 2, Sword Art Online Abridged
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