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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: 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.