Far from expert in the field, but assuming that gravity is acts in a 3+ND and we observe it in our 3D world, shouldn't we observe weird peculiarities with it rather that just its amplitude?
Think that you live on a line, and you see projections of a 2d object doing circles on top of you. You would see the shade moving and changing sizes in a non-explainable manner to you.
We do observe really weird gravitational effects. Dark matter, for instance. Under Newtonian and Einsteinian physics, galaxies shouldn't be able to form in the way we observe. The way galaxies and their contents move makes no sense with our present understanding of gravity-- unless we assume there's a lot more mass. So we invented dark matter as a sort of placeholder variable to make the math make sense.
More anomalies: simply being near a large gravitational field alters the flow of time. Frame dragging around black holes (spacetime itself twists into a rotating spiral). The final parsec problem (co-orbiting black holes bleeding energy as gravitational waves). And don't forget the gravitational singularity of a black hole.
But perhaps the most important thing to know is that we've only just gained the ability to examine gravitational waves. Once we build more detectors (especially LISA), we'll probably discover a lot more is wrong with our understanding of gravity.
> More anomalies: simply being near a large gravitational field alters the flow of time. Frame dragging around black holes (spacetime itself twists into a rotating spiral). The final parsec problem (co-orbiting black holes bleeding energy as gravitational waves). And don't forget the gravitational singularity of a black hole.
These are not really anomalies per se - they are predicted by the relatively well tested theory of GR and (except for the singularity part) also experimentally observable. They are weird from our point of view, but not weird to contemporary physics.
From recent discussion though it seems as though the time dilation effects or that time itself moves differently in different patches of spacetime- that could remove the need altogether for dark energy/dark matter:
Yes, but none of that is anomalous. The primary novelty of the timescape model is just a more careful application of boring old General Relativity to cosmological models, which are highly idealized in order to make them tractable. It is still very misleading to characterize effects like frame dragging or time dilation as unresolved mysteries. They are very straightforward, experimentally confirmed, elements of classical General Relativity.
Movement doesn't make sense when we can't predict or explain it. Based on our understanding of gravity as confirmed by observations of our solar system we expect to see galaxies do X but instead they do Y, and then we collectively fail to identify a simple explanation like bad math or a bad assumption.
In one sense this is a vindication of our application of the scientific method and the way we make theories: a bad theory wouldn't be able to be checked, whereas a good theory can make precise enough claims that when a limitation is found (such as when our predictions about reality do not match our observations) that the results of the check are clear.
Being able to precisely calculate movement of planets in Solar system and also calculate their mass was a huge triumph of physics. The problem is the same math doesn't work with visible stars orbiting in galaxies nor galaxy clusters. Simplest explanation is there's much invisible mass - dark matter. Or the laws are different at these scales.
They greatly simplify models, otherwise they’re too complicated to calculate.
So they simplify the data points, assume point particles, assume no interactions due to electromagnetism, no tidal locks, and Newtonian gravity instead of relativity.
And then it turns out galaxies sometimes rotate too quickly.
Yeah, no shit. If your data is known to be wrong and your model uses the wrong theory of gravity and makes known false simplifications it would be quite strange if it somehow did predict without some discrepancies
I thought the final parsec problem is that co orbiting black holes can't have accretion discs which makes GW the only way for them to inspiral, and that's way too slow for us to have seen any.
The more distance along your 4th dimension you allow, the more strange geometric effects you will observe. If you let a 4th dimension be very, very, very small (imagine a 2d universe that actually has a third dimension, it's just subatomic in scale) the geometric effects are negligible.A 3d volume can exist in that 2d + 1 tiny dimension, in the technical sense, but not in any macroscopic sense. Your 3rd dimension curls around to where it started nearly immediately.
Think that you live on a line, and you see projections of a 2d object doing circles on top of you. You would see the shade moving and changing sizes in a non-explainable manner to you.