Its my opinion that there is something about the black hole at the center of these galaxies that's causing discrepancies that we attribute to "dark matter". The fact that this new galaxy is so sparse and distributed and shows no sign of dark matter seems to re-affirm this. I'd be curious to know if it even has a central black hole.
The reality is that we don't know.
What makes you so sure? I think limiting our thinking too much into the confines of regular gravitation is a mistake. Maybe SMB are the source of these theoretical heavy neutrino's we have yet to detect that are the #1 candidate for dark matter/WIMPS. Or maybe the gravitational disturbance of a singularity is far more complex that we imagine?
Take a look at the video on the Galaxy Rotation Curve video in this wiki:
https://en.wikipedia.org/wiki/Galaxy_rotation_curve#Descript...
I stare at it and cant help but wonder is something about that central singularity is unique. We still have no idea what truly happens at the center.
If supermassive black holes do something new and strange with gravity--something big enough to affect an entire surrounding galaxy--it seems likely it should somewhat affect the trajectories of the nearest objects too.
That's not to rule out something strange about black hole gravitation, but the observations do constrain some versions of how strange things can be.
https://en.wikipedia.org/wiki/Galaxy_rotation_curve
I'm simply saying its more likely an unknown effect of the black hole at the center. Possibly some sort of gravitational modification effect that only occures in the presents of singularities. The fact that a sparse galaxy with possible no black hole center (I assume) shows no sign of dark matter is compelling. It may not prove the specific equations/explanations set forth in MOND, but it may hint to some other alternative gravitational theory that has yet to be flushed out, rather than relying on some invisible particles which may not exist.
Black holes are weird objects, they are enormous, have huge mass and density, almost no radiation, have great gravitational effect on surroundings and they are hard to detect etc.
They seem like a perfect candidate for 'dark matter'.
Could anyone explain why it is wrong?
1. https://en.wikipedia.org/wiki/Dark_matter#Baryonic_matter
https://4.bp.blogspot.com/-UN8jPwzj2qI/V9hRVCG1HBI/AAAAAAAAC...
It looks like Occam's razor. To explain an unexpected result, you label the problem so it looks like it must be a new entity.
"Oh no, the existence of dark matter means the universe should be collapsing in on itself, lets invent dark energy to balance out the dark matter"
I always figured that the KISS principle meant maybe we just didn't understand gravity very well, but what the hell do I know. Always found it fascinating though.
Even if you remove dark matter from the picture, there's still the acceleration of expansion (increase of the Hubble term over time), for which there is pretty solid data, namely the discrepancy of brightness and redshift of distant supernovae.
https://en.wikipedia.org/wiki/Accelerating_expansion_of_the_...
By far the "cosmological constant" sort of outweighs all the other terms in the Universe's stress energy tensor.
We see redshift and infer that a pulsar or other know quantity is shifted and assume it has moved because space has expanded. Why don't we ever assume that the length of a second has shrunk in the billions of years that have gone by? Space and time change in relativity, why is only change in space considered in the history of the universe? What's wrong with time?
Not just redshift. We're using two observables: Redshift and brightness of a very specific kind of supernova which always releases close to the same energy, i.e. amount of light. Using the 1/d² law we can relate observed brightness to distance. Redshift OTOH tells us the velocity.
Then we plot "redshift vs. sqrt(1/brightness)" and if the expansion of the universe were constant, i.e. velocity/distance (i.e. the Hubble term being constant) we'd see a linear relation between distance and velocity.
However what we actually observe is that the velocity is accelerating over distance, which means something is putting "something" extra into it. So far we can describe it only as a nonvanishing extra term in the field equations. A term which originally Einstein came up with to stabilize a static universe, but you can use it as well to "push" or "pull" on the whole of spacetime to accelerate/decelerate expansion/contraction.
For all intents and purposes this term behaves like an additional energy term in the equations. We are in the _dark_ about, what's actually causing the effects we see. And when we adjust our models to accomodate for that, an extra _energy_ term shows up. Hence "dark energy". However no astrophysicist worth his salt thinks of it as something concrete.
In the cosmology lectures I attended during my studies our professor used to pick some random name, who'd not be a student in the class at the time and instead use that, instead of "Dark Energy" to refer to that term (the "dark name" used when I was there was "Geroge" BTW), just to hammer the fact, that we don't have an effin clue what's going on, only that it's something very observable that's śhows up prominently in all the data collected for the past 20 years and you can't ignore it and have to give it some name.
Gauge fixing.
There is no particular reason to slice up spacetime into spacelike hypersurfaces where each point in the hypersurface has the same time coordinate, other than convenience. Likewise, there is no particular reason to chose one set of time coordinates over another, other than convenience.
You can certainly work in 4 dimensional "block universe" when considering the radar distances between points on the worldlines that the centres-of-momentum of galaxies (or clusters) travel, and choose arbitrary coordinates. You're then using tensors for everything, and considering spacetime 4-volumes.
Slicing or threading into 3+1 resp 1+3 makes the calculations easier, but can introduce fictitious forces and other features that depend on one's choices when doing that sort of gauge fixing.
The standard cosmological frame of reference is a 3+1 slicing wherein the time coordinate is recoverable by an idealized observer locally measuring the spectrum of the CMB photons arriving at a point on the observer's worldline; such an observer will see matter in the bulk as homogeneous and isotropic, and will be far from any of the matter, and will see the CMB spectrum as equal to the emission spectrum of an ideal blackbody with a particular temperature. Add in adiabatic expansion, and the universe gives a quasi-universal time coordinate, which clamps many of the pseudo-forces 3+1 slicing can produce.
Since we are near lots of matter (the Earth, the solar system, our galaxy and the local cluster), we see big anisotropies and thus noise, including a gravitational and peculiar-motion redshift anisotropy in the CMB. As we get a better handle on our local environment, we can better strip out these factors that distinguish us real physical observers from an idealized non-physical "Eulerian" observer of a FLRW universe.
But since an alien astronomer in a far away galaxy could reasonably take the same approach, we could exchange messages like: "at our CMB temperature x K we observed a supernova in your galaxy", which the other side could relate to their measurement of the CMB temperature at time of supernova and at the time of receipt of message, and recover the equilvalent of a radar distance.
This also plays neatly with the Robertson-Walker (RW) spacetime that is fundamental to the cosmological frame: RW spacetimes readily admit a slicing which makes them higher-dimensional equivalents of a set of infinitesmially thin plates stacked one on top of the other, where the metric includes a function which determines the radius of each plate as one goes from the bottommost plate to the topmost. It also makes it easy to set down comoving coordinates such that matter stays at rest at the same spatial coordinates in every spacelike hypersurface: we expand the metric instead of actually moving the galaxies, which is good because there is no distortion of the shape of galaxy clusters implying a real (i.e., gauge-independent) acceleration in any particular direction, and because it makes it easy to take an Eulerian fluid mechanics approach to galaxy clusters in the large.
Additionally, this sort of slicing plays nicely with things like Hamiltonian mechanics and the time-dependent Schrödinger equation, which we are likely to care about when thinking about the microscopic details of events like a supernova inferrable from coarse-grained observables (like the emissions spectrum associated with supernova nucleosynthesis).
However, if something motivated you to do so, you could choose some other expanding-universe metric that is suitable for treating distant galaxies as at a lower gravitational potential, for instance. This would mean fixing a different gauge, and introducing some fictitious (gauge-dependent) forces to deal with some observables of high-redshift objects, and those would tend to complicate hypothetical communications with alien astronomers in distant galaxies. The "real" physics would -- just like the "real" physics in the cosmological frame -- be described correctly using generally covariant tensors. But you could do many calculations using simpler fields, and at least in principle that might highlight features that are obscured in the standard cosmological slicing.
Known in science as Occaam's razor.
> maybe we just didn't understand gravity very well
We definitely don't understand it when it comes to quantum scales. And maybe we don't understand it properly at macro scales.
But know that the universe is in no way obligated to be simple to the layman.
E.g. Speed of light seems to be constant, so we're going to make up all this bizarre stuff about time dilation and space faring twins.
It's been a successful heuristic, but for understanding the things that can be understood simply - we shouldn't believe that nature "wants" to be simple though...
You can come up with a model that perfectly explains the outcome ( P(e|H) = 1 ) but you have to offset the insane improbability of pegging all those free parameters at the value they are at ( P(H) ).