Comment by Zamicol | Hacker News Reader

Comment by Zamicol | Hacker News Reader

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My money is still on additions/modifications to relativity in the next 100 years. (Sorry for the sources, just using Google to pull up something.)

- Hubble's constant has not been calculated, and when it is, there are problems. https://www.space.com/38496-hunt-for-hubble-constant-standar...

- Like the fallacious search for Vulcan, there are modern problems with the orbits of some of the outer planets. https://solarsystem.nasa.gov/planets/hypothetical-planet-x/i...

- A galaxy with 99 percent dark matter and one almost without any. https://www.quantamagazine.org/a-victory-for-dark-matter-in-... https://www.theverge.com/2016/8/25/12647540/dragonfly-galaxy...

- The bullet cluster, the speed of rotation in galactic arms, etc.

- The apparent changing rate of expansion in the universe.

- We have no idea of the physics behind red shift "caused by the metric expansion of space".

- We still don't know what gravity actually is.

The 1998 discovery of the accelerating expansion of the universe was beautifully simple and clean. It proved a huge swath of experts dead wrong. https://en.wikipedia.org/wiki/2011_Nobel_Prize_in_Physics

Dark matter/energy could be apart of the mix, but in light of the problems I would not bet it's the end of the story.

Your second point - I don't think the potential Planet Nine has anything to do with "problem with the orbits of some of the outer planets". It has been proposed as a solution to the orbits of some distant smaller Kuiper Belt objects. This in return doesn't really have anything to do with relativity, just basic orbital mechanics.

I could have sworn there were problems with Pluto's orbit where it was faster/slower than it should have been, but it looks like I'm wrong.

>Specifically, this paper shows that, contrary to recent assertions in the literature, the current ephemeris for Pluto does not preclude the existence of the Pioneer effect. We show that the orbit of Pluto is currently not well enough characterized to make such an assertion.

https://arxiv.org/pdf/0905.0030.pdf

The Pioneer Effect has been explained as "anisotropic radiation pressure caused by the spacecraft's heat loss".

https://en.wikipedia.org/wiki/Pioneer_anomaly

That's an interesting case because they "solved" the problem by basically increasing the estimated uncertainty. See the dual sets of error bars in Fig 3: https://arxiv.org/abs/1204.2507

> "A galaxy with 99 percent dark matter and one almost without any. https://www.quantamagazine.org/a-victory-for-dark-matter-in-.... https://www.theverge.com/2016/8/25/12647540/dragonfly-galaxy...

Interesting that both of these surprising (in the dark matter framework) observations are consistent with MOND:

https://arxiv.org/abs/1804.04167

https://arxiv.org/abs/1610.06189

> We have no idea of the physics behind red shift "caused by the metric expansion of space".

What do you mean we have no idea? Redshift is one of the few simple concepts in Astrophysics, whether it's doppler, cosmological or gravitational.

I could have better said, "We don't understand the physical causes for the metric expansion of space". It's the physical reasons for the expansion we don't understand.

> It's the physical reasons for the expansion we don't understand.

Sure we do; it's the Einstein Field Equation and the initial conditions at the Big Bang.

What we don't fully understand is how the initial conditions at the Big Bang came about. The current front-runner hypothesis is some form of inflationary model (in which the Big Bang is really the end of inflation), but the question is still open.

The bullet cluster is famously an object which is very hard or impossible without having some dark matter like substance. We observe the mass and gas are offset from each other in a collision.

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