5 ms·

Does outer space end – or go on forever?

legrande 5y ago
> If you could keep going out, as far as you wanted, would you just keep passing by galaxies forever? I believe the Universe is self-contained and is not infinite in the true sense, but rather yet another universe among many. If you keep zooming out, eventually you would reach other Universes. I believe the big bang was merely two under-developed universes that simply collided, and now we have this mess we call 'The Universe'.
- Jaruzel 5y ago
  So what is this 'collection' of universes called, and is that infinite? "ooh... is that fairy cake?" [1] ---- [1] https://hitchhikers.fandom.com/wiki/Total_Perspective_Vortex https://hitchhikers.fandom.com/wiki/Total_Perspective_Vortex
  - cercatrova 5y ago
    Playing Space Engine, this is exactly how I felt. I was in the solar system and clicked on another star, and suddenly there was no way to get back to our solar system. It was then that I truly understood the scale of the universe. https://spaceengine.org/ https://spaceengine.org/
  - legrande 5y ago
    > So what is this 'collection' of universes called, and is that infinite? I would imagine so. Humans can't grasp infinity because it tortures them mentally, as per your link you posted. It's called the Multiverse Theory, and I believe there is infinite universes out there that constantly collide with each other in a never ending cycle of creation. Our own universe could already be colliding with a separate universe, it's just that we don't know it yet because we can't travel to the edges to see what's happening and we would have to somehow wait very long to prove that our Universe is not alone.
MadcapJake 5y ago
I've always thought: if the universe was infinite, wouldn't we see light fill all of the sky at night? Curious if my intuition is correct on this or if CMB means that going backward in time is our current bottleneck for observation.
- krapp 5y ago
  https://en.wikipedia.org/wiki/Olbers%27_paradox https://en.wikipedia.org/wiki/Olbers%27_paradox
- Jaruzel 5y ago
  > Shouldn't we see light fill all of the sky at night No, due to the universe expanding, the wavelength of visible light gets longer as it travels massive distances, as such it moves out of the visible spectrum. This is why most of the deep field mapping of the universe is done via radio waves.
- kelseyfrog 5y ago
  If the universe was infinite I would also expect to see the age of stars and by extension galaxies uncorrelated with space and time. Instead we see younger and younger stars and galaxies as we peer farther and father away. It's as if we are standing in the savanna and as we look through our binoculars we see younger and younger giraffes as we look into the distance. At some point there will not be any more giraffes to view as their age intercepts zero as a function of distance(and time).
- John23832 5y ago
  If the universe is larger that the distance a light proton could have traveled since it's creation, then there could be a much larger universe outside of our sphere of visibility.
- pydry 5y ago
  It's also expanding faster than the speed of light. There are right now some galaxies that are so far and moving away so fast that they will effectively stop existing from our perspective. Overhead, without any fuss, the stars are going out.
beeforpork 5y ago
The question is natural, but I think there is a bit more that we already 'know' (well, we concluded with some confidence) to answer this question. (a) Just because you might be able to move in one direction forever, does not mean the space you're in is infinite. You may imagine the universe as the skin, the surface of a balloon that is expanding: the surface is finite, but still you can move in one direction on the surface forever -- you will wrap around at some point (if you're fast enough to overcome the expansion speed). Now imagine this as a 3D surface of space on a higher dimension balloon for the universe. This is quite a plausible way of imagining this intuitively (as long as you don't ask questions about the balloon space), particularly because it also makes futile the question whether we are close to the edge or close to the center, which bugged me for a while -- we are somewhere on the surface of that imagined balloon, and there might not be a center or an edge, despite being finite. (b) The universe is expanding. In fact, it has expanded already so much that it is far larger than its age, so to say: it's 13.7Gy old, but 45Gly (IIRC) across, most likely. The universe is so large, that light that starts at the farthest spots now will never reach the Earth, because the universe expands that light away from us, so even with the best sensors and a very long time to wait, we will never see from Earth light and thus images from what is far away now. We are quite lucky, though: the oldest light that reaches us now is from the beginning of the big bang (photons started their 'normal' way of travel ~400ky after the BB, and that's what we can actually see!), so theoretically, we do see now every part of the universe at some point in the past (well, unless something obscures our view, and obviously in non-optimal resolution). But this view will fade away, and new light from those farthest places will not reach us in the future anymore (a couple of Gy from now) -- it will be getting darker and darker for us. The farthest places are already completely out of reach, we can only see their past and we will never be able to go there -- a bit like the inside of a black hole is out of reach, but, well, with the boundary around us. (c) When moving at the speed of light, you will never ever reach the spot again that you started at, even with a wrap-around in the balloon model, because the expansion is going on, and even speeding up, so the speed of light is just too slow to keep up with the expansion. (d) Practically, it is of course completely impossible to reach speeds close to the speed of light, for various reasons, e.g., energy needed and harmless cosmic rays becoming gamma rays, etc.etc. Different story entirely. It is good that we have stories to imagine this without the practical restrictions. So the whole question is kinda futile. But interesting. The universe is incomprehensibly huge.
niknoble 5y ago
It either goes on forever or wraps around, or the entire question turns out to be nonsense for some weird reason. But there's definitely no edge where the stars just stop.
euroderf 5y ago
How 'bout we go up one more step on the Ladder of Confusing Unknowability. By posing the question: why is there something rather than nothing ?

> If you could keep going out, as far as you wanted, would you just keep passing by galaxies forever? I believe the Universe is self-contained and is not infinite in the true sense, but rather yet another universe among many. If you keep zooming out, eventually you would reach other Universes. I believe the big bang was merely two under-developed universes that simply collided, and now we have this mess we call 'The Universe'.

Jaruzel 5y ago
So what is this 'collection' of universes called, and is that infinite? "ooh... is that fairy cake?" [1] ---- [1] https://hitchhikers.fandom.com/wiki/Total_Perspective_Vortex https://hitchhikers.fandom.com/wiki/Total_Perspective_Vortex
- cercatrova 5y ago
  Playing Space Engine, this is exactly how I felt. I was in the solar system and clicked on another star, and suddenly there was no way to get back to our solar system. It was then that I truly understood the scale of the universe. https://spaceengine.org/ https://spaceengine.org/
- legrande 5y ago
  > So what is this 'collection' of universes called, and is that infinite? I would imagine so. Humans can't grasp infinity because it tortures them mentally, as per your link you posted. It's called the Multiverse Theory, and I believe there is infinite universes out there that constantly collide with each other in a never ending cycle of creation. Our own universe could already be colliding with a separate universe, it's just that we don't know it yet because we can't travel to the edges to see what's happening and we would have to somehow wait very long to prove that our Universe is not alone.

MadcapJake 5y ago

I've always thought: if the universe was infinite, wouldn't we see light fill all of the sky at night? Curious if my intuition is correct on this or if CMB means that going backward in time is our current bottleneck for observation.

krapp 5y ago
https://en.wikipedia.org/wiki/Olbers%27_paradox https://en.wikipedia.org/wiki/Olbers%27_paradox
Jaruzel 5y ago
> Shouldn't we see light fill all of the sky at night No, due to the universe expanding, the wavelength of visible light gets longer as it travels massive distances, as such it moves out of the visible spectrum. This is why most of the deep field mapping of the universe is done via radio waves.
kelseyfrog 5y ago
If the universe was infinite I would also expect to see the age of stars and by extension galaxies uncorrelated with space and time. Instead we see younger and younger stars and galaxies as we peer farther and father away. It's as if we are standing in the savanna and as we look through our binoculars we see younger and younger giraffes as we look into the distance. At some point there will not be any more giraffes to view as their age intercepts zero as a function of distance(and time).
John23832 5y ago
If the universe is larger that the distance a light proton could have traveled since it's creation, then there could be a much larger universe outside of our sphere of visibility.
pydry 5y ago
It's also expanding faster than the speed of light. There are right now some galaxies that are so far and moving away so fast that they will effectively stop existing from our perspective. Overhead, without any fuss, the stars are going out.

beeforpork 5y ago

The question is natural, but I think there is a bit more that we already 'know' (well, we concluded with some confidence) to answer this question. (a) Just because you might be able to move in one direction forever, does not mean the space you're in is infinite. You may imagine the universe as the skin, the surface of a balloon that is expanding: the surface is finite, but still you can move in one direction on the surface forever -- you will wrap around at some point (if you're fast enough to overcome the expansion speed). Now imagine this as a 3D surface of space on a higher dimension balloon for the universe. This is quite a plausible way of imagining this intuitively (as long as you don't ask questions about the balloon space), particularly because it also makes futile the question whether we are close to the edge or close to the center, which bugged me for a while -- we are somewhere on the surface of that imagined balloon, and there might not be a center or an edge, despite being finite. (b) The universe is expanding. In fact, it has expanded already so much that it is far larger than its age, so to say: it's 13.7Gy old, but 45Gly (IIRC) across, most likely. The universe is so large, that light that starts at the farthest spots now will never reach the Earth, because the universe expands that light away from us, so even with the best sensors and a very long time to wait, we will never see from Earth light and thus images from what is far away now. We are quite lucky, though: the oldest light that reaches us now is from the beginning of the big bang (photons started their 'normal' way of travel ~400ky after the BB, and that's what we can actually see!), so theoretically, we do see now every part of the universe at some point in the past (well, unless something obscures our view, and obviously in non-optimal resolution). But this view will fade away, and new light from those farthest places will not reach us in the future anymore (a couple of Gy from now) -- it will be getting darker and darker for us. The farthest places are already completely out of reach, we can only see their past and we will never be able to go there -- a bit like the inside of a black hole is out of reach, but, well, with the boundary around us. (c) When moving at the speed of light, you will never ever reach the spot again that you started at, even with a wrap-around in the balloon model, because the expansion is going on, and even speeding up, so the speed of light is just too slow to keep up with the expansion. (d) Practically, it is of course completely impossible to reach speeds close to the speed of light, for various reasons, e.g., energy needed and harmless cosmic rays becoming gamma rays, etc.etc. Different story entirely. It is good that we have stories to imagine this without the practical restrictions. So the whole question is kinda futile. But interesting. The universe is incomprehensibly huge.

niknoble 5y ago

It either goes on forever or wraps around, or the entire question turns out to be nonsense for some weird reason. But there's definitely no edge where the stars just stop.

euroderf 5y ago

How 'bout we go up one more step on the Ladder of Confusing Unknowability. By posing the question: why is there something rather than nothing ?