It's not an explosion from a specific place, with galaxies hurtling out like cosmic jetsam. It's an expansion of space. There's no center, and the universe isn't expanding into anything. I'd suggested that this is a terribly oversimplified model for our universe expanding. Unfortunately, it's also terribly convenient.
I can steal it from my children whenever I want. Imagine you're this node here, and as the toy expands, you see all these other nodes moving away from you.
And if you were to move to any other node, you'd see all the other nodes moving away from you. Here's the interesting part, these nodes over here, twice as far away as the closer ones, appear to move more quickly away from you. The further out the node is, the faster it appears to be moving away from you. This is our freaky friend, the Hubble Constant, the idea that for every megaparsec of distance between us and a distant galaxy, the speed separating them increases by about 71 kilometers per second.
Galaxies separated by 2 parsecs will increase their speed by kilometers every second. If you run the mathatron, once you get out to 4, megaparsecs away, two galaxies will see each other traveling away faster than the speed of light.
How big Is that, is it larger than the universe? The first light ever, the cosmic microwave background radiation, is 46 billion light-years away from us in all directions.
I did the math and 4, megaparsecs is a little over There's mountains of room for objects to be more than 4, megaparsecs away from each other. Thanks universe?!? Most of the universe we can see is already racing away at faster than the speed of light. So how it's possible to see the light from any galaxies moving faster than the speed of light.
How can we even see the Cosmic Microwave Background Radiation? Thanks universe. Light emitted by the galaxies is moving towards us, while the galaxy itself is traveling away from us, so the photons emitted by all the stars can still reach us.
The dynamics of the universe are governed by competing forces whose influence varies with scale, so local forces can override universal forces in discrete regions. On scales larger than galaxy clusters, all galaxies are indeed moving apart at an ever increasing rate. The mutual gravitational attraction between two galaxies at that distance is too small to have a significant effect, so the galaxies more or less follow the general flow of the expansion.
But it is a different story in a galaxy's local neighborhood. There the gravitational attraction can be very significant and the interactions much more exciting. Dark energy, believed to be causing the acceleration of the expansion of the universe, provides a constant outward force that does not dilute as the universe expands.
Pitted against this relentless push is the gravitational pull from the rest of the matter and energy in the universe. Early on, the universe was much denser than it is today, and the attractive force of gravity was winning the battle, on scales both large and small. Clouds of gas condensed to form stars and galaxies, and galaxies drew together to form clusters. Watch the video, noticing that the cake represents a part of the universe, and the raisins represent galaxies.
As the video shows, an observer living on any particular raisin inside the expanding cake would see all the other raisins moving away, with more distant raisins moving faster. This is exactly what Hubble observed for galaxies in the universe, and today scientists have made many more observations confirming the same ideas. The obvious conclusion is that, much like the cake, our universe is expanding with time. Credit: The Cosmic Perspective.
Back Next. Figure 1. How do we know? When it moves away from you, there's more space between each wave crest, and so it sounds lower-pitched, analogous to a redshift. But the expansion of space plays a more important role, particularly on larger scales. If you envision the fabric of space as a ball of dough, with raisins throughout it representing gravitationally bound structures like galaxies , then any raisin will view the nearby raisins as receding slowly in an omnidirectional fashion.
But the farther away a raisin is, the faster it appears to recede, even though the raisins aren't moving with respect to the dough. The dough is expanding just like the fabric of space is expanding, and all we can do is view the total redshift. The 'raisin bread' model of the expanding Universe, where relative distances increase as the space The farther away any two raisin are from one another, the greater the observed redshift will be by time the light is received.
The redshift-distance relation predicted by the expanding Universe is borne out in observations, and has been consistent with what's been known all the way back since the s. If you measure the value of the expansion rate, you'll find that it can be expressed in terms of a speed-per-unit-distance.
Where an Mpc is about 3. Either way, there's a critical distance where the apparent recession speed of a galaxy will exceed the speed of light: around a distance of to billion light-years. Beyond that, galaxies appear to recede faster than light, but this isn't due to an actual superluminal motion, but rather to the fact that space itself is expanding, which causes the light from distant objects to redshift. When we examine the sophisticated details of this relationship, we can unequivocally conclude that the "motion" explanation fails to match the data.
Definitively, only General Relativity's predictions match what we observe. The Universe really is expanding, and the reason we see the light from distant objects as so severely redshift is due to the expanding fabric of space, not due to the motion of galaxies through space.
In truth, individual galaxies typically move through space at relatively slow speeds: between 0. But you don't have to look to very great distances — million light-years is totally sufficient — before the effects of the expanding Universe become undeniable.
The most distant galaxies visible to us are already located more than 30 billion light-years away, as the Universe just keeps on expanding and stretching that ultra-distant light before it arrives at our eyes.
As we move from the era of Hubble to the era of James Webb, we hope to push that frontier back even farther. However, no matter how far we become capable of seeing, most of the Universe's galaxies will forever be beyond our reach. The observable yellow and reachable magenta portions of the Universe, which are what they are All the galaxies in the Universe beyond a certain distance appear to recede from us at speeds faster than light.
Even if we emitted a photon today, at the speed of light, it will never reach any galaxies beyond that specific distance.
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