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posted by Fnord666 on Thursday September 19 2019, @09:07AM   Printer-friendly
from the expanding-like-a-waistline-on-Thanksgiving dept.

Arthur T Knackerbracket has found the following story:

Reproduceability is key to science. A one-time “eureka!” could be the first step in a paradigm shift — or it could be a fluke. It’s the second, third, and hundredth measurements that put theories to the test.

That’s why recent measurements of the universe’s expansion have piqued interest. Even though astronomers have applied multiple methods relying on completely different physics, they’re still getting similar results: Today’s universe appears to be expanding faster than what’s expected based on measurements of the early universe. Can systematic errors explain this discrepancy? Or are new physics required?

Now Wendy Freedman (University of Chicago) and colleagues have posted a new, "middle-of-the-road" measurement on the astronomy preprint arXiv, adding a twist to the ongoing debate. The study will appear in the Astrophysical Journal.


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  • (Score: 5, Informative) by Immerman on Thursday September 19 2019, @02:46PM (10 children)

    by Immerman (3985) on Thursday September 19 2019, @02:46PM (#896096)

    I think you're misunderstanding the big bang.

    If there was a superconcentrated ball of material that exploded out into space - then yes, there should be an observable "origin point" to the bang - track all the remnants of a fire-cracker that exploded in a free-fall vacuum, and you can trace their paths back to the point where the firecracker exploded.

    That's not what happened at the big bang.

    Instead you had a bunch of stuff floating motionless, and then space itself exploded - all of it, all at once, and it carried all the still-motionless bits of stuff further away from each other. In that scenario there's no tracing anything back because nothing is moving, and everything is moving away from everything else nearby at the same speed. The classic analogy is draw a bunch of dots (representing "stuff") on a balloon (representing space), and then inflate the balloon.

    It's actually even weirder than that - according to inflationary theory, most of the "stuff" in the universe didn't exist yet - instead there was the inflationary period when the universe was expanding exponentially, much faster than light, under the influence of a spontaneously self-replicating "inflationary energy" in the fabric of space itself. Then at some point some fleck of inflationary energy decayed into a more stable lower energy state, starting a chain reaction that expanded at light speed, creating a bubble of what we consider "normal universe" filled with the decay products of that inflationary energy - a.k.a. most of the normal matter and energy now filling the universe.

    In essence, the matter and energy in the early "normal" universe was created in-place, after the universe had already done most of its expansion.

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  • (Score: 2) by hendrikboom on Thursday September 19 2019, @03:11PM (5 children)

    by hendrikboom (1125) Subscriber Badge on Thursday September 19 2019, @03:11PM (#896103) Homepage Journal

    I moderated you insightful.

    But I dispute that the inflationary period went "faster than light". Even if there had been observers back then, the parts of the universe that you consider to depart from the observer faster then light would have been unobservable, so there would have been no way to know their speed.

    -- hendrik

    • (Score: 4, Interesting) by Immerman on Thursday September 19 2019, @03:28PM

      by Immerman (3985) on Thursday September 19 2019, @03:28PM (#896116)

      Do some reading - for current cosmology to work, the universe had to expand much, much faster than light during the inflationary period.

      Presumably they don't mean every point was expanding away from every other faster than light, but pick a point at the center, and one near the edge, and the distance in between them was expanding far too fast for any causal interaction to take place.

    • (Score: 2) by Common Joe on Friday September 20 2019, @10:08AM (3 children)

      by Common Joe (33) <{common.joe.0101} {at} {gmail.com}> on Friday September 20 2019, @10:08AM (#896446) Journal

      Actually, you can see that yourself. Google the question "How big is the universe?" It will come back with 93 billion light years in diameter... so 46.5 billion light year radius. (That's the known universe we can see.) Then google "How old is the universe?" It will come back 13.8 billion years. If light travels at... well, the speed of light, then how does star light travel 46.5 / 93 billion light years in 13.8 billion years? I think that's what's meant by the inflationary period went faster than light. (I'm not a physicist.)

      • (Score: 2) by hendrikboom on Friday September 20 2019, @02:00PM (2 children)

        by hendrikboom (1125) Subscriber Badge on Friday September 20 2019, @02:00PM (#896491) Homepage Journal

        I have always wondered about that. Clearly that remote matter would not be observable, at least, not for another 46.5 billion years.

        But I wonder how relativistic distance-dilation is taken into account when calculating the 46.5 billion light-years. Is it indeed taken into account? Or is it compensated for?

        I'm often confused when reading a popularization of science, trying to figure out what the original science was before popularization. Translating modern physics into everyday terms is quite misleading, because everyday terminology has assumptions built into it that are quite at odds with the way science has discovered the world really works.

        I do know that relativistic velocities don't add linearly, and I have a sneaky suspicion that these "faster than light" claims rest on linear addition of velocities.

        Take some far-off galaxy, departing from us at the 90% of the speed of light. Now consider another galaxy, even farther out, that's departing from the far-off galaxy, relative to the far-off galaxy, ad 90% of the speed of light. It's commonly considered that addition of velocities should make the farther-off galaxy recede from us at 180% of the speed of light. But that's not how addition of velocities works. Relativistically, it's nonlinear, not naively additive, resulting in a total velocity that's still lower then the speed of light.

        But that's special relativity. But I admit I don't know what measuring velocities at a distance means when using general relativity. For example, the Doppler shift would seem to indicate that photons lose energy when traveling across an expanding cosmos. But I think reality must be more complicated because that would seem to violate conservation of energy.

        -- hendrik

        • (Score: 2) by Common Joe on Friday September 20 2019, @03:58PM (1 child)

          by Common Joe (33) <{common.joe.0101} {at} {gmail.com}> on Friday September 20 2019, @03:58PM (#896534) Journal

          Disclaimer: I'm not a physicist. I only pretend to be one from time to time and I do a horrible job at it.

          But I wonder how relativistic distance-dilation is taken into account when calculating the 46.5 billion light-years. Is it indeed taken into account? Or is it compensated for?

          It is compensated for, but how they do it exactly is beyond my knowledge.

          I do know that relativistic velocities don't add linearly, and I have a sneaky suspicion that these "faster than light" claims rest on linear addition of velocities.

          My understanding is that mass can be accelerated to velocities up to the speed of light. There are no rules against traveling faster than the speed of light. You just can't accelerate beyond the speed of light. If you can make the jump from one speed to another without going in between (something currently beyond our science), then it is (theoretically) possible to travel faster.

          Take some far-off galaxy, departing from us at the 90% of the speed of light. Now consider another galaxy, even farther out, that's departing from the far-off galaxy, relative to the far-off galaxy, ad 90% of the speed of light. It's commonly considered that addition of velocities should make the farther-off galaxy recede from us at 180% of the speed of light. But that's not how addition of velocities works. Relativistically, it's nonlinear, not naively additive, resulting in a total velocity that's still lower then the speed of light.

          A long time ago, I calculated the relativistic equations. I suck at it, but I did it. It does work, but I can't explain it as well as videos on Youtube. I picked a random one, but it's good enough: https://www.youtube.com/watch?v=rVzDP8SMhPo [youtube.com]

          It boils down to this: in your example, time and length are perceived differently by each galaxy. It's that simple (and that complex).

          Another way to look at it: From our perspective: the faster an object goes, the more energy it will absorb to go faster. Let's say we add X energy to get it to accelerate to 10% the speed of light. Now, the more energy it absorbs, the heavier it will become. (E= mc2, right?) If we add X energy again, it will only accelerate 9%. If we add X energy again, it will accelerate only 7%. (My numbers are not accurate, but the idea is.) From the objects perspective, we keep giving it less and less energy. So, the first time, we give it X energy. The next time, we give it only 90% energy. The next time, it's 75% energy. (Again, numbers are not accurate, but the idea is.)

          Hope this helps. It took me a long time before I got it. They have some good videos out there these days that explain relativity decently enough which I didn't have when I was younger. I don't have enough time to track them down right now, though.

  • (Score: 2) by HiThere on Thursday September 19 2019, @04:29PM (3 children)

    by HiThere (866) Subscriber Badge on Thursday September 19 2019, @04:29PM (#896137) Journal

    Actually, it's even weirder than that. There's no rule saying when the inflation stopped, so probably lots of part of it (outside our light-cone) are still inflating, whereas other parts stopped inflating even sooner than our visible universe did. But since the "edge of the visible universe" is retreating from us faster than light, we'll never be able to seen any evidence that this is happening. (And that "edge of the observable universe" is also why there can't be any justification of saying inflation stopped at some point, unless you come up with a mechanism that isn't based around probability.)

    Theory seems to keep saying that the universe in infinite in lots of different ways. (This is a totally different way than the EGW multi-world "infinity", which isn't actually quite infinite, but is so large that it's hard to tell the difference. This one may actually be an infinite universe, though how one would prove that is a bit beyond me.)

    --
    Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
    • (Score: 3, Insightful) by Immerman on Thursday September 19 2019, @04:58PM (2 children)

      by Immerman (3985) on Thursday September 19 2019, @04:58PM (#896152)

      Quite so. In fact, if the decay of inflationary energy propagates at light speed, while the expansion is much faster than that, then the most reasonable conjecture is that our universe is one tiny bubble of collapsed energy in a nigh-endless sea of still-expanding inflationary energy. Presumably a sea populated by a nigh-infinite number of *other* bubbles of decayed energy that started from a different spontaneous decay, which may or may not closely resemble our own observable universe.

      Of course, without some form of FTL we'll never be able to reach the edge of our observable universe, much less the edge of our "universe bubble". And even with FTL, matter as we know it probably couldn't survive outside that bubble, so unless we come across a wormhole connecting to another bubble with the same decay-state as ours, there's probably no way to confirm that. Ironically this kind of "parallel universe" seems to be both the most credible, and the least accessible, among the several kinds that might exist.

      There's also another implication - there's no guarantee that the decayed vacuum energy in our observable universe is at the lowest-possible energy state - some fleck might spontaneously decay further and trigger a new chain reaction expanding at light speed - and our first warning would be when the bubble of fresh decay swept over our planet, destroying everything in its path at a subatomic level. In fact that might have happened several times already - I don't think there'd be any way to tell for sure.

      As for infinite universe (multiverse?) - I haven't heard any convincing argument for that. Only nigh-infinite. For inflationary energy - even FTL expansion is still not infinitely fast, and thus there's a limit to how much it could expand in any noninfinite amount of time. Though I suppose that there's no guarantee that inflation hasn't been occurring for an infinite amount of time - just because we like beginnings doesn't mean the universe cares. For the several other classes of "parallel universe" that might exists (I think I've heard of at least a half-dozen that are generally considered credible) similar limits seem to exist.

      • (Score: 2) by HiThere on Thursday September 19 2019, @07:33PM (1 child)

        by HiThere (866) Subscriber Badge on Thursday September 19 2019, @07:33PM (#896225) Journal

        The trouble is, the nature of time isn't well understood outside the context of space-time, so how can you assert that there hasn't been an infinite amount of it? So. Maybe it's not infinite. But what are the grounds for making an assumption in either direction?

        --
        Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.
        • (Score: 2) by Immerman on Thursday September 19 2019, @11:41PM

          by Immerman (3985) on Thursday September 19 2019, @11:41PM (#896291)

          Fare enough. However, given the complete lack of evidence that infinity is anything other than a conceptual absurdity, betting against the existence of infinite amounts of anything is generally the more respectable option. At the very least, nobody will ever be able to prove you wrong - there's not enough space in the observable universe to put an infinite amount of anything.

          Even infinitesimals, the one class of things you might reasonably imagine there being an infinite number of, run into problems with spacetime granularity when considering the real world. There are in fact only a finite number of distinct points that exist between two space-time locations, or so the theory goes. Really throws a wrench in Zeno's Paradox, and may help explain why we are in fact capable of motion