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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

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?

ddevault 6y ago
The answer is similar to the one I gave for your other question: https://news.ycombinator.com/item?id=24424912 https://news.ycombinator.com/item?id=24424912 But I'll give you another analogy anyway. Say you put two rocks into a mass of water in an environment without gravity (e.g. the ISS), then freeze the water, causing it to expand. The expanding ice will cause the rocks to become more distant from each other, but they're not "moving" in local terms - the manifold in which they exist is itself expanding. That said, the frozen water and the rocks both exist in space, and the expanding ice moved the rocks through space. But, in this metaphor, there is no second, external "space" - the water itself represents space. And so to for our universe. Space itself isn't a part some other, second "space" that it's expanding into (at least not so far as we're aware). The existence of somewhere for space to expand "into" is not necessary for the expansion to take place. Remember, it's the scale factor which is changing, not a discrete object (i.e. the universe) physically expanding.
javajosh 6y ago
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.)

ddevault 6y ago

The answer is similar to the one I gave for your other question: https://news.ycombinator.com/item?id=24424912 https://news.ycombinator.com/item?id=24424912 But I'll give you another analogy anyway. Say you put two rocks into a mass of water in an environment without gravity (e.g. the ISS), then freeze the water, causing it to expand. The expanding ice will cause the rocks to become more distant from each other, but they're not "moving" in local terms - the manifold in which they exist is itself expanding. That said, the frozen water and the rocks both exist in space, and the expanding ice moved the rocks through space. But, in this metaphor, there is no second, external "space" - the water itself represents space. And so to for our universe. Space itself isn't a part some other, second "space" that it's expanding into (at least not so far as we're aware). The existence of somewhere for space to expand "into" is not necessary for the expansion to take place. Remember, it's the scale factor which is changing, not a discrete object (i.e. the universe) physically expanding.

javajosh 6y ago

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.)