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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.
(Score: 4, Insightful) by inertnet on Thursday September 19 2019, @11:52AM (17 children)
Let's assume, like Einstein said, that every observer's measurements must be correct, even if they seem to contradict each other.
The universe is supposed to have started as a Big Bang and we've always been part of it (meaning our observations are from inside this expanding universe). That would imply that we should be able to roughly pinpoint the origin of the Big Bang. But scientists say that, no matter where in the universe you are, your observations will tell you that you are at the center of the universe (based on everything is expanding away from you, with a speed based on distance). This is sometimes explained by assuming everything is on a balloon's surface, but that's 2D, while the universe is clearly at least 3D, meaning the inside of the balloon is also filled with objects.
To me this sounds like a similar problem Einstein had, how can you reconcile all those observations that seem to contradict each other. Not based on science but on a 'feeling', I think that the solution to the Hubble constant inconsistencies has to do with this contradiction. In our mind we see the universe as an expanding sphere (at least I do), but observations don't collaborate that view.
(Score: 5, Informative) by Immerman on Thursday September 19 2019, @02:46PM (10 children)
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.
(Score: 2) by hendrikboom on Thursday September 19 2019, @03:11PM (5 children)
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
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)
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)
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)
Disclaimer: I'm not a physicist. I only pretend to be one from time to time and I do a horrible job at it.
It is compensated for, but how they do it exactly is beyond my knowledge.
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.
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 hendrikboom on Saturday September 21 2019, @08:21PM
Exactly!
(Score: 2) by HiThere on Thursday September 19 2019, @04:29PM (3 children)
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)
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)
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?
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(Score: 2) by Immerman on Thursday September 19 2019, @11:41PM
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
(Score: 2, Insightful) by Anonymous Coward on Thursday September 19 2019, @03:03PM (5 children)
it's not *explained* "by assuming everything is on a balloon's surface".
an *analogy* with a balloon's surface is made.
another analogy would be an explosion in 0 gravity: within the expanding cloud of gas, pressure pushes all gas molecules away from their closest neighbours.
if the explosion is large enough, and you are in a bit far away from the center of the explosion and the edge of the expanding gas, you will see that all of the surrounding molecules are accelerating away from you.
the analogy is not perfect, because space is not at all like a gas, and because in an explosion you are in a non-inertial frame of reference (so in principle you could tell where the center of the explosion is by making experiments). and also because i am saying "pressure pushes molecules", which is very wrong without specifying that I refer to average motion of molecules.
but at least the dimensionality is right (unlike the balloon's surface, which is 2D instead of 3D).
in general relativity, the big bang refers to every volume of space growing in all directions: objects that are at a distance are not accelerating away from us, but more space appears between us spontaneously.
it's a weird non-intuitive concept that you can't understand properly from analogies, you actually need to do the math to get it.
why is this modded insightful?
ignorance of current accepted science is not smart.
if you actually care about understanding, do the right thing and read up what others have done.
the universe doesn't care what you feel.
start with Newton, then learn about Hamiltonians and Lagrangians, then you can move to special relativity.
afterwards you should be able to get better advice than I can give you.
(Score: 3, Insightful) by hendrikboom on Thursday September 19 2019, @03:27PM (4 children)
I moderated you insightful.
The balloon analogy almost works if you consider the 3-dimensional hypersurface of a four-dimensional balloon. (where this fourth dimension is spatial, not temporal). But this is also flawed, because there's no evidence for this fourth spatial dimension that the balloon is expanding into. It is just as flawed as the model where you put a heavy ball on a rubber surface and notice it makes the surface curve. That's not the same kind of curvature (even if you imagine it as a three-dimensional hypersurface and the ball is stretching that.) and the analogy relies on an extrauniversal gravity.
The curvature is more like traveling from the equator to the south pole, carrying a horizontal arrow and making sure you always locally keep it pointing in the same direction, then turn yourself 90 degrees to the right (but not turning the arrow) and then walk back to the equator , and then walk back to the original starting point, and you'll discover that the arrow no longer points in the same direction as when you started. That's the kind of curvature involved, except it's in four dimensions, not two, and one of the dimensions is temporal.
There's no gravity needed to explain gravity.
Or draw a straight line on a cone. You'll find it goes around the apex and intersects itself, though it always follows a geodesic. That's more like the relativistic curvature. (except that in relativity the curvature is everywhere and not concentrated in one point at the apex. These analogies all break down.)
-- hendrik
(Score: 3, Insightful) by Immerman on Thursday September 19 2019, @03:43PM (2 children)
You're trying to take the analogy much too far by involving the whole balloon. The only part of the balloon involved in the analogy is the skin - the 2D (approximately, over a small sample area) skin stretches, and thus the distance between dots increases uniformly, despite the fact that none of them are moving across the skin..
Similarly, 3D space in the universe expanded, and thus all points in the universe got further away, even if nothing were moving. Of course everything was also moving, which complicates things considerably, but if we could paint dots on the fabric of space itself, the distance between them would be growing.
The mechanism behind the stretching of the balloon, and the fact that the balloon exists in 3D space are irrelevant to the analogy - it's just a simple example to illustrate how things can get further away from each other despite not moving. In the case of inflation it probably wasn't anything "stretching" space from the outside, it's that inflationary energy was making space grow all over. Or perhaps making new bits of space everywhere all at once, shoving the old bits further apart. We really have very little understanding of what exactly space *is*, and thus can't do much more than speculate wildly on the mechanisms for its growth.
(Score: 0) by Anonymous Coward on Thursday September 19 2019, @04:12PM (1 child)
The problem with this analogy is that it invokes a 3rd spatial dimension. Thus by anology our 3d space is curved in a 4th spatial dimension.
However experiments and calcuations on the dissipation of energy (I forget the citation, it's gravitational waves) are unambiguous that the energy is lost only in 3 dimensions. Otherwise it would fall off faster. It's a pretty simple argument based on surface area of a spheres in different dimensions. We observe 1/r^2 because the energy dissipates uniformly on the surface of a 3d sphere.
Unless of course your 4d theory also includes a mechanism that prevents forces from extending into that dimension. Good luck with the band aids.
(Score: 2) by Immerman on Thursday September 19 2019, @05:02PM
No, it doesn't. The analogy is constrained to the 2D skin of the balloon expanding the distance between the points without the points moving on the skin. Beyond that, the analogy immediately breaks down.
Remember - all analogies are bad analogies. If they accurately described what you were using them to describe, then they wouldn't be analogies.
(Score: 2) by HiThere on Thursday September 19 2019, @04:37PM
You're trying too hard to may something intelligible which nobody understands, or ever has understood. Even Hawking didn't understand it. If you learn the math, you can follow the math, but that's not the same as understanding it.
For that matter there are lots of unsolved problems with the current theory. Some of them appear to be unresolvable, as they depend on things that can never be observed...e.g. things happening outside our light-cone. If someone invents a way of seeing outside our light cone, of course, the bounds will shift dramatically...but that *appears* to be impossible.
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