Sep 30, 2021 04:30 PM
https://bigthink.com/starts-with-a-bang/...-universe/
EXCERPTS: . . . In actuality, however, we know that whatever field drives inflation is overwhelmingly likely to be quantum in nature. That means, as inflation goes on, there’s a certain probability that the field will: “roll” into the valley where inflation ends; a certain probability that it won’t and inflation will continue; and even a certain probability that the field will “roll” in the wrong direction, taking us farther away from inflation’s end. And — here’s the counterintuitive part — because the inflating universe continuously creates new space, all of these possibilities can occur simultaneously in different regions of the inflating universe.
This sets up a fascinating scenario to consider. As long as inflation occurred in the past, which we have copious evidence that it did based on what’s imprinted in our universe, it implies the existence of a multiverse. What’s going on is the following:
Fascinatingly, it’s fairly easy to show that if you want to create a scenario where we get enough inflation to set up the hot Big Bang with the properties we observe, you will always get a multiverse — one where independent, disconnected universes are always being born, forever separated from one another by space that continues to inflate eternally, while new universes and new hot Big Bangs continue to spawn. As long as we’ve got this part of the story correct — and the evidence overwhelmingly indicates that we have — the existence of a multiverse is predicted by today’s best science.
[...] We know that inflation must occur at an energy scale that’s significantly below the Planck energy scale, otherwise we would see signals in our universe that don’t exist. What we don’t know, however, is supremely important. We don’t know how inflation began, or whether it even had a beginning; it’s possible that inflation was the default state of the universe that was happening eternally, until it ended in our region of space and our universe was spawned.
We don’t know whether there are any entangled properties between these different universes within the multiverse. We don’t know whether all of the universes that are spawned have the same physical laws and fundamental constants, or whether there are dynamics that govern these laws and constants that somehow get “set” either during inflation or the final transition to the hot Big Bang. Additionally, we have no idea how to quantify the probabilities of these different outcomes: what cosmologists working on it call the measure problem. These universes are predicted to exist, but we don’t know how many of them there are, whether or how they’re related, and what similarities or differences they have relative to our own universe.
However, the expectation [...] is that the laws and constants should be the same between universes, but the specific initial conditions should be different. What does this mean? It means that the overall properties of each universe should be the same, because they had a common origin: from the end of the same inflationary field...
[...] if you have enough of these universes that spring into existence, there should eventually be one that comes along with the exact same initial properties as our own. Remember that everything that exists in our universe is finite ... These numbers are astronomically large, but they are not infinite.
It may or may not be the same story when it comes to the number of universes that are spawned by inflation. If inflation has proceeded for a finite amount of time, then the number of universes we get increases exponentially with time, but always remains finite. If inflation has gone on for an infinite amount of time, then the number of universes must be infinite, and all allowable possibilities must have occurred in some universe... (MORE - missing details)
EXCERPTS: . . . In actuality, however, we know that whatever field drives inflation is overwhelmingly likely to be quantum in nature. That means, as inflation goes on, there’s a certain probability that the field will: “roll” into the valley where inflation ends; a certain probability that it won’t and inflation will continue; and even a certain probability that the field will “roll” in the wrong direction, taking us farther away from inflation’s end. And — here’s the counterintuitive part — because the inflating universe continuously creates new space, all of these possibilities can occur simultaneously in different regions of the inflating universe.
This sets up a fascinating scenario to consider. As long as inflation occurred in the past, which we have copious evidence that it did based on what’s imprinted in our universe, it implies the existence of a multiverse. What’s going on is the following:
- inflation occurs, stretching the universe and creating new space
- in some places, the field “rolls” into the valley, bringing inflation to an end
- this results in the creation of hot Big Bangs in those regions: what we might call “a universe”
- in between those universes is more inflating space, where inflation doesn’t end but continues on
- new space gets created as the universe expands
- in other places, the field rolls into the valley, bringing inflation to an end there with more hot Big Bangs and more universes
- meanwhile, inflation continues in the regions where it didn’t end, creating more space
Fascinatingly, it’s fairly easy to show that if you want to create a scenario where we get enough inflation to set up the hot Big Bang with the properties we observe, you will always get a multiverse — one where independent, disconnected universes are always being born, forever separated from one another by space that continues to inflate eternally, while new universes and new hot Big Bangs continue to spawn. As long as we’ve got this part of the story correct — and the evidence overwhelmingly indicates that we have — the existence of a multiverse is predicted by today’s best science.
[...] We know that inflation must occur at an energy scale that’s significantly below the Planck energy scale, otherwise we would see signals in our universe that don’t exist. What we don’t know, however, is supremely important. We don’t know how inflation began, or whether it even had a beginning; it’s possible that inflation was the default state of the universe that was happening eternally, until it ended in our region of space and our universe was spawned.
We don’t know whether there are any entangled properties between these different universes within the multiverse. We don’t know whether all of the universes that are spawned have the same physical laws and fundamental constants, or whether there are dynamics that govern these laws and constants that somehow get “set” either during inflation or the final transition to the hot Big Bang. Additionally, we have no idea how to quantify the probabilities of these different outcomes: what cosmologists working on it call the measure problem. These universes are predicted to exist, but we don’t know how many of them there are, whether or how they’re related, and what similarities or differences they have relative to our own universe.
However, the expectation [...] is that the laws and constants should be the same between universes, but the specific initial conditions should be different. What does this mean? It means that the overall properties of each universe should be the same, because they had a common origin: from the end of the same inflationary field...
[...] if you have enough of these universes that spring into existence, there should eventually be one that comes along with the exact same initial properties as our own. Remember that everything that exists in our universe is finite ... These numbers are astronomically large, but they are not infinite.
It may or may not be the same story when it comes to the number of universes that are spawned by inflation. If inflation has proceeded for a finite amount of time, then the number of universes we get increases exponentially with time, but always remains finite. If inflation has gone on for an infinite amount of time, then the number of universes must be infinite, and all allowable possibilities must have occurred in some universe... (MORE - missing details)
