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Thread: What expanded the early Universe?

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    What expanded the early Universe?

    As I understand it, dark energy is thought to have only kicked in when the Universe was 10 billion years old and already quite spread out. So what drove expansion prior to that? And assuming there's an answer to that, do we also differentiate between what drove the very-early split-second cosmic inflation versus the subsequent steadier expansion up to 10 billion years? Thanks!

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    The current mainstream answer is "we don't know".

    https://en.wikipedia.org/wiki/Inflation_(cosmology)
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    Goddidit.
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    Quote Originally Posted by Cheap Astronomy View Post
    As I understand it, dark energy is thought to have only kicked in when the Universe was 10 billion years old and already quite spread out. So what drove expansion prior to that? And assuming there's an answer to that, do we also differentiate between what drove the very-early split-second cosmic inflation versus the subsequent steadier expansion up to 10 billion years? Thanks!
    Well,
    Roger Penrose has an idea.

    Big Bang was not the start of our universe rather it was the end of the previous one, Nobel Laureate Roger Penrose told The Telegraph. ... Explaining further he said, “We have a universe that expands and expands, and all mass decays away, and in this crazy theory of mine, that remote future becomes another aeon.”Oct 10, 2020
    www.deccanherald.com › there-was...
    There was a universe before ours, says Nobel laureate Roger Penrose: Report | Deccan Herald”

    He points out that the cosmic background radiation looks like perfect entropy thermally but with clumped gravity. To him, and mathematically speaking, he thinks a solution to that is found before the big bang. If he is right, it is hard to test, but it might also explain what we call inflation.
    sicut vis videre esto
    When we realize that patterns don't exist in the universe, they are a template that we hold to the universe to make sense of it, it all makes a lot more sense.
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    Quote Originally Posted by Cheap Astronomy View Post
    As I understand it, dark energy is thought to have only kicked in when the Universe was 10 billion years old and already quite spread out. So what drove expansion prior to that?
    This might seem like a bit of a weasel answer, but my understanding is that the mainstream cosmology answer is really more that the expansion is in the nature of the universe and does not require an explanation. Itís really more that the universe is built that way. Itís the same for why the speed of light or the Planck length have the values they have. Itís not much that we donít know as that itís a setting that doesnít have an explanation. Of course, some cosmologists will try to come up with ways to explain various numbers.
    As above, so below

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    Jens, to me that sounds like it can be applied to anything. “Why is grass green?” That’s just the way it is. No mention of chlorophyll. We’d get nowhere that way.
    SHARKS (crossed out) MONGEESE (sic) WITH FRICKIN' LASER BEAMS ATTACHED TO THEIR HEADS

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    Just to clarify, the early rapid inflation of the Universe is usually defined differently than the present and ongoing expansion of the Universe in astrophysics. This terminology keeps them exclusive.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by Cheap Astronomy View Post
    As I understand it, dark energy is thought to have only kicked in when the Universe was 10 billion years old and already quite spread out.
    The idea behind dark energy is pretty weird. The theory is that it was there from the beginning. What makes it weird is that as the universe expands, it doesn't become diluted. As expansion causes the distance between objects to double, there's twice as much dark energy, and it stays at the same "strength." When there's enough dark energy between objects, its very weak expansion accelerating effect begins to "kick in," as you say.

    Quote Originally Posted by Cheap Astronomy View Post
    So what drove expansion prior to that?
    Initially it was thought that the expanding universe was just a free-wheeling continuation of the initial burst of expansion, then later, a continuation of the initial inflationary burst. But for the first 7 billion years or so, regardless of what's "driving it," that expansion was slowing, and this is confirmed by observations. But as mentioned, when there was enough space and dark energy between objects, that weak dark energy effect, which had been adding up and adding up, became enough to begin accelerating the expansion -- also confirmed by observations (assuming we are interpreting the observations correctly).

    Quote Originally Posted by Cheap Astronomy View Post
    ...do we also differentiate between what drove the very-early split-second cosmic inflation versus the subsequent steadier expansion up to 10 billion years?
    Yes. Inflation was quite a bit different than the subsequent expansion, at least quantitatively. Whether the dark energy is a residue from inflation, we don't know. Whether the subsequent expansion was just a free-wheeling continuation of the initial inflationary burst, we're not sure. We do know that observations indicate that there is expansion, that it was initially slowing, then it slowly started speeding up. It's a weird universe.
    Everyone is entitled to his own opinion, but not his own facts.

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    Is dark energy a fifth force?
    SHARKS (crossed out) MONGEESE (sic) WITH FRICKIN' LASER BEAMS ATTACHED TO THEIR HEADS

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    Quote Originally Posted by Tom Mazanec View Post
    Is dark energy a fifth force?
    There are ideas about what it could be that make it a fifth force, there are ideas about what it is that don't. Jury is out because none of the ideas have really led to rigorous predictions that would allow them to be selected from.

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    Quote Originally Posted by Cheap Astronomy View Post
    What expanded the early Universe?
    You did! Seriously though, by the end of inflation the energy of the inflaton field got turned into the particles that make up you and everything else we have in the universe right now. ETA: though as Noclevername said, these processes are not very well understood at this time.

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    Quote Originally Posted by Tom Mazanec View Post
    Jens, to me that sounds like it can be applied to anything. “Why is grass green?” That’s just the way it is. No mention of chlorophyll. We’d get nowhere that way.
    But we might see fewer physicists making ontologically unsupportable claims. Which I, for one, would welcome.
    Your example reduces to, "Grass is green because it has green stuff in it," which isn't a great step forward. Knowing what chlorophyll does with the red light it absorbs is useful in understanding how plants grow, but it doesn't really explain the greenness of grass.

    Grant Hutchison

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    Science can tell you how grass is green, but not why. Why is for philosophers, First Causes and all that.

    We are still working on the how of Universal expansion (and acceleration of that expansion). That's the only mainstream answer so far: we don't know yet. When could we know? After we get fusion power.

    Dark Energy is just a placeholder, as has been pointed out in the Forum by many posters. We have a Mad Libs of wild hypotheses proposed by various authors to fill that conceptual void, because human beings don't like voids in our understanding. But none of them have advanced to the point of scientific theory yet.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by grant hutchison View Post
    But we might see fewer physicists making ontologically unsupportable claims. Which I, for one, would welcome.
    Your example reduces to, "Grass is green because it has green stuff in it," which isn't a great step forward. Knowing what chlorophyll does with the red light it absorbs is useful in understanding how plants grow, but it doesn't really explain the greenness of grass.

    Grant Hutchison
    In what way doesn't it explain the greenness of grass? The reason why grass is green is because light interacts with the chemical compounds in grass in such a way that the spectrum of the reflected light is what we call "green."

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    Quote Originally Posted by Noclevername View Post
    Science can tell you how grass is green, but not why. Why is for philosophers, First Causes and all that.

    We are still working on the how of Universal expansion (and acceleration of that expansion). That's the only mainstream answer so far: we don't know yet. When could we know? After we get fusion power.

    Dark Energy is just a placeholder, as has been pointed out in the Forum by many posters. We have a Mad Libs of wild hypotheses proposed by various authors to fill that conceptual void, because human beings don't like voids in our understanding. But none of them have advanced to the point of scientific theory yet.
    In what way would the accelerated metric expansion of space (described by the de Sitter metric) be any less known than, say, basic gravitational orbits (described by the Schwarzschild metric)? Both are exact solutions to the Einstein Field Equations.

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    Quote Originally Posted by caveman1917 View Post
    In what way would the accelerated metric expansion of space (described by the de Sitter metric) be any less known than, say, basic gravitational orbits (described by the Schwarzschild metric)? Both are exact solutions to the Einstein Field Equations.
    Do we know the mechanism of gravity? We do not. Do we know the mechanism of expansion? We do not. We can describe the process, we can't explain it.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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    Quote Originally Posted by Noclevername View Post
    Do we know the mechanism of gravity? We do not. Do we know the mechanism of expansion? We do not. We can describe the process, we can't explain it.
    That doesn't mean that General Relativity (which describes both) isn't a scientific theory though. It seems that by your logic we can't explain anything. Scientific theories aren't about providing "mechanisms" (whatever that even means), they are mathematical models that predict observations.

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    Quote Originally Posted by caveman1917 View Post
    That doesn't mean that General Relativity (which describes both) isn't a scientific theory though. It seems that by your logic we can't explain anything. Scientific theories aren't about providing "mechanisms" (whatever that even means), they are mathematical models that predict observations.
    Well then, I withdraw that statement. I used the term incorrectly and I apologize.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

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