The universe is infinite then how can it expand?
The universe is infinite then how can it expand?
, if it is infinite. The main point here is that, what is referred to as expansion of the universe is a change in the metric used to measure distances. There is absolutely no reason why such a change in metric cannot apply to an infinite space. An oft used analogy to explain expansion is the inflating balloon, or the rising raisin bread. The characteristic of these analogies is that the universe is modelled by a finite structure, the surface of the balloon, or the interior of the raisin bread. But the analogy works just as well with a uniformly stretching infinite rubber sheet or an infinite loaf of raisin bread. Any observer in these models would still bear witness to the fact that distant objects are receding at a greater speed than nearby objects. Infinity and expansion are independent concepts, orthogonal to each other.
what the universe is expanding into. For both the finite and infinite cases, there is no need to imagine the universe expanding into anything. Looking at things that way is called the extrinsic view, because you are trying to be an observer outside of the universe looking back at the universe. But the universe is defined as everything that there is. You cannot look at the universe from the outside, you can only look at it from within, the so-called intrinsic view. The universe is not expanding into anything. It's simply the case that, over time and on a large enough scale, the distance between two fixed points is increasing. On our own scale nothing appears to be happening and distances between objects appear to be fixed.
People are used to visualising concepts such as curvature by imagining something like a circle or a globe, embedded in our three dimensional space. But, mathematically, we can describe curvature by only referring to properties that hold within the space, not even considering any external space in which we might be embedded. Logically, there is no need for an embedding space, which is fortunate because there is no "outside of everything that there is".
, if it is infinite. The main point here is that, what is referred to as expansion of the universe is a change in the metric used to measure distances. There is absolutely no reason why such a change in metric cannot apply to an infinite space. An oft used analogy to explain expansion is the inflating balloon, or the rising raisin bread. The characteristic of these analogies is that the universe is modelled by a finite structure, the surface of the balloon, or the interior of the raisin bread. But the analogy works just as well with a uniformly stretching infinite rubber sheet or an infinite loaf of raisin bread. Any observer in these models would still bear witness to the fact that distant objects are receding at a greater speed than nearby objects. Infinity and expansion are independent concepts, orthogonal to each other.
what the universe is expanding into. For both the finite and infinite cases, there is no need to imagine the universe expanding into anything. Looking at things that way is called the extrinsic view, because you are trying to be an observer outside of the universe looking back at the universe. But the universe is defined as everything that there is. You cannot look at the universe from the outside, you can only look at it from within, the so-called intrinsic view. The universe is not expanding into anything. It's simply the case that, over time and on a large enough scale, the distance between two fixed points is increasing. On our own scale nothing appears to be happening and distances between objects appear to be fixed.
People are used to visualising concepts such as curvature by imagining something like a circle or a globe, embedded in our three dimensional space. But, mathematically, we can describe curvature by only referring to properties that hold within the space, not even considering any external space in which we might be embedded. Logically, there is no need for an embedding space, which is fortunate because there is no "outside of everything that there is".
