If we stretch the sheet, the balls move apart. Balls which are close together will only move apart slowly. Balls which are widely separated will seem to move apart very quickly.
There is no limit on how fast space can expand. Space is the geometry of the universe. Changes in the size or shape of space occur because of the movement of matter and energy in the universe or because of changes to the matter and energy content of the universe.
An example of a very small universe containing only 48 stars. A spaceship flying among these stars cannot find the edge of this universe. If it exits on one side of the universe it reemerges on the other side. The people in the spaceship see an infinite number of stars all around them. This universe has no boundary and no centre. Instead, distant light rays move in their original direction, with the fluctuations we have indicating perfect flatness. The magnitudes of the hot and cold spots, as well as their scales, indicate the curvature of the To the best of our capabilities, we measure it to be perfectly flat.
From constraints arising from both the cosmic microwave background and the large-scale structure of the Universe combined, we can conclude that if the Universe is finite and loops back in on itself, it needs to be at least times the extent of the part we observe.
Because we live in three dimensions, times the radius means 3 times the volume, or more than 15 million times as much space. But, big as that is, it still isn't infinite. A lower bound of the Universe being at least 11 trillion light years in all directions is tremendous, but it's still finite. The observable Universe might be 46 billion light years in all directions from our point of view, There's reason to believe our Universe is even bigger than that , though.
The hot Big Bang might mark the beginning of the observable Universe as we know it, but it doesn't mark the birth of space and time itself. Before the Big Bang, the Universe underwent a period of cosmic inflation. Instead of being filled with matter and radiation, and instead of being hot, the Universe was:.
Inflation causes space to expand exponentially, which can very quickly result in any pre-existing It's true that in our region of the Universe, inflation came to an end. But there are three questions we don't know the answer to that have a tremendous influence on how big the Universe truly is, and whether it's infinite or not. Inflation set up the hot Big Bang and gave rise to the observable Universe we have access to, but we How big was the region of the Universe, post-inflation, that created our hot Big Bang?
Looking at our Universe today, at how uniform the Big Bang's leftover glow is, at how flat the Universe is, at the fluctuations stretched across the Universe on all scales, etc. We can learn the upper limit to the energy scale at which inflation occurred; we can learn how much the Universe must have inflated; we can learn a lower limit how long inflation must have gone on for.
But the pocket of the inflating Universe that gave rise to us could be much, much bigger than that lower limit! It could be hundreds, or millions, or googols of times larger than what we can observe But without being able to observe more of the Universe than we can presently access, we don't have enough information to decide. If inflation is a quantum field, then the field value spreads out over time, with different regions In many regions, the field value will wind up in the bottom of the valley, ending inflation, but in many more, inflation will continue, arbitrarily far into the future.
Is the idea of " eternal inflation " correct? If you consider that inflation must be a quantum field, then at any given point during that phase of exponential expansion, there's a probability that inflation will end, resulting in a Big Bang, and a probability that inflation will continue, creating more and more space.
These are calculations we know how to do given certain assumptions , and they lead to an inevitable conclusion: if you want enough inflation to occur to produce the Universe we see, then inflation will always create more space that continues to inflate compared to the regions that end and produce Big Bangs. For all we know some observer 50 billion light years away might be looking up at the night sky wondering why half of it is black.
Or a mirror-image of the other. Or some kind of edge. It is said that in days gone by, people could not conceive of a world that was curved. They could only conceive of a world with an edge. Nowadays I rather fancy that there are some people who cannot conceive of a world that is not curved. They cannot conceive of a world with an edge. See The Foundation of the General Theory of Relativity : "the energy of the gravitational field shall act gravitatively in the same way as any other kind of energy".
Energy is the source of the stress-energy tensor. Matter is only a source because of the energy-content. Also see Inhomogeneous and interacting vacuum energy which refers to spatial energy. An interesting read is the article Universe billion light-years wide featuring Neil Cornish.
This isn't entirely accurate, but the compound interest and the hall of mirrors concepts are of interest. As for the non-sequitur, see this interview with Joseph Silk:. It is flat, and a plane is normally infinite. But you can take a sheet of paper [an 'infinite' sheet of paper] and you can roll it up and make a cylinder, and you can roll the cylinder again and make a torus [like the shape of a doughnut]. The surface of the torus is also spatially flat, but it is finite".
This is akin to the old Asteroids game. But the Planck mission found no evidence of any torus. Reading on further:. I dispute that. There is a third possibility. A flat finite universe with no intrinsic curvature. If anybody can cite some reliable sources that support the assertion that a flat universe must be infinite, I'd like to see them. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Learn more. How can an infinite universe expand? Ask Question. Asked 5 years, 11 months ago. Active 3 years, 4 months ago. Viewed 4k times. Improve this question. Justin Waters. Justin Waters Justin Waters 1 1 silver badge 8 8 bronze badges.
Hubble's law gets things receding faster than light, unobservable, at 40 some billion light years right now. We tend to assume that an observer on that last planet receding at just under c sees a universe that looks just like ours, but with us receding at just under c. That assumption will get you close to an infinite universe. Add a comment.
Active Oldest Votes. Expansion is possible in Universes of both finite and infinite spatial extent. Improve this answer. John Davis John Davis 1, 10 10 silver badges 14 14 bronze badges. Saying it just can does not answer the question. Clearly there is no dependence on the space being finite for distances to increase.
See my answer below for my own thoughts on the matter. This implies the universe to be held within a space. So, space is not part of the universe, but the universe is just one part of space? Seems quite debatable. Walter Walter 5, 1 1 gold badge 14 14 silver badges 28 28 bronze badges. During the twentieth century, scientists learned that space is not "nothingness. In fact, when astronomers talk about the "expansion of the universe," they are referring to the stretching of space between clusters of galaxies - NOT to the motion of galaxies through space.
Later, scientists found other properties of space. For example, matter and anti-matter are routinely created in the laboratory from space itself and an energy source ; the kinds of particles that can exist reflect the structure of space. In fact, there is now evidence that space itself MAY possess some slight amount of energy of its own, of a form previously unknown. If so, space may actually have weight! Discovering the properties of space remains one of the deepest and most important problems in modern science.
Did the Universe expand from a point? The Big Bang was not an explosion IN space. It was a process that involved ALL of space. This misconception causes more confusion than any other in cosmology. Unfortunately, many students, teachers, and scientists! In reality, ALL of space was filled with energy right from the beginning.
There was no center to the expansion, and no magical point from which matter hurtled outward. But that primordial pellet of matter and energy was NOT surrounded by empty space In fact, if the whole universe is infinitely large now, then it was always infinite, including during the Big Bang as well.
Thus the Big Bang took place everywhere in space, not at a particular point in space. For much of the twentieth century, astronomers and physicists believed that space might NOT be infinitely large - that is, space might actually curve around on itself to form a "closed universe. The shape was later favored by Einstein as a possible shape for the universe. Such a closed universe would have a finite volume, yet no boundaries or edges. Although closed universes cannot be visualized from the outside, they CAN be visualized from the inside.
For example, the image at right gives an idea of what a tiny closed universe might look like. In a real closed universe, you cannot see the back of your head, the way you can here.
If you shrink such a space down, then everything in it gets closer together, and the volume of the closed universe gets closer and closer to zero. Current evidence shows that our part of the universe appears not to be curved.
This tells us that either the universe is infinitely large, or else is so large that we cannot detect its curvature from the tiny portion we can observe -- just as we could not tell that the Earth was curved if our measurements were confined to a sandbox!
A large enough clump of matter will collapse to form a black hole, but ONLY if it is surrounded by relatively empty space. During the Big Bang, there WAS NO empty space: ALL of space was filled more or less uniformly with matter and energy; there was no "center of attraction" around which matter could coalesce.
Under these circumstances, a cosmic-scale black hole will not form and lucky for us! Because it takes time for light from distant objects to reach us. We see the sun as it looked about 8 minutes ago Current studies of distant exploding stars have led astronomers to conclude that the universe is not only expanding - the expansion may be accelerating with time. This is not due to an "anti-gravity force" but rather to gravity itself.
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