As someone who is currently studying dark matter, MOND is currently disfavored in the field of cosmology. It does not as simply or effectively describe galaxies closer to home, or observations of the cosmic microwave background. These galaxies pose a challenge to lambda-CDM, but that does not prove MOND correct.
this post was submitted on 16 Nov 2024
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As someone who watches a lot of PBS Space Time and Dr. Becky, I'm always very suspicious of any news article claiming '"JWST has found evidence for X", especially if it's an alternative to Lambda CDM
Love me some Dr Becky!
However, McGaugh and his colleagues argue that these predictions do not match JWST observations. Instead, the newly observed galaxies appear bright, large, and fully formed, even as scientists peer deeper into the universeβs past. This unexpected brightness directly challenges the conventional understanding of galaxy formation driven by dark matter.
Are you sure these aren't old galaxies? Like, how do we know that we aren't in a relatively small little bubble and there's an infinite universe out there where there isn't a single big bang, but instead small bangs that happen every now and then. Maybe if a black hole gets massive enough then its gravity "overflows" and causes it to vomit everything up; and all those bright, fully-formed galaxies are actually unrelated and proceeded the big bang.
We aren't looking at those old galaxies today. Due to the speed of light and the vast distance involved we are looking at the light from those galaxies when they were very young and early in the life of the universe (that's why we are looking there in the first place). That light is just now reaching us. We have theorized about white holes but never seen one. By looking at closer objects we already know what an old galaxy looks like. And nothing can by definition exist before the big bang. Because before the big bang there wasn't any space for things to exist in. Nothing precedes it.
The last three sentences are not quite accurate. It's not necessarily that nothing existed before the the big bang. It's a singularity event where mathematically we can simply not know what existed at/beforehand that moment. It is somewhat comparable with the event horizon of a black hole.
There is something happening/existing, otherwise a black hole would not be able to occupy space or affect light. We simply do not have the ability currently to understand what that is.
By definition, that is not nothing. It is a that we cannot know/understand it, at that moment. Notably, a lack of evidence is not evidence of nothing.
He means the matter we know as galaxies today.
Our current theory implies that our space we know and love (bound by our time, spacetime) expanded at that moment. We know we shouldn't be seeing older galaxies that look younger than others we know to be young. That's what's implied by these findings at least - they could still be explained by other things we have yet to discover, because we haven't finished processing this data.
The title is just for the clicks.
Not the event horizon of a black hole, but the singularity at the center. The event horizon is only a singularity in certain coordinate systems, but you can select coordinates that are smooth there. The black hole singularity is more comparable to big bang, in the sense that it is an indication of missing physics.
From the formation of the CMB we know that the whole universe was a hot and dense plasma that cooled and became transparent.
Are you proposing that these galaxies existed before and external to the CMB plasma ball "big bang" that we came from?
As in, a bunch of matter appears inside of a pre-existing universe as a local big bang, whose galaxies spread out amongst preexisting galaxies from older big bang events?
Then you propose that matter which has been hoarded by black holes may be the source of the matter in subsequent big bangs, to achieve a steady state.
I like the idea you are proposing.
My biggest question is: why didn't our "bang" blow all of the older generation of galaxies away from it such that we would never see them? My understanding is that spacetime itself is what expands / inflates in Ξ»cdm. It does so faster than the speed of light such that there is material in our universe from which light will never reach us. It's very hard to see things outside of a universe that expands faster than the light we use to observe it. It's spacetime itself that's expanding, not just the objects moving apart.
But, MOND is MOdified Newtonian Dynamics, and currently doesn't work with Einstein/GR... at all! So, if MOND is right maybe we should expect a different mechanism than Einstein expansion.
Most likely we just don't understand what stars and nebula looked like or how they formed back before metals existed and so we don't know how bright these galaxies should be to begin with because we don't know how stars work without metal. The assumption in the paper is irresponsibly invalid, we can't just assume that stars back then followed the same patterns as stars do now. Stars form from nebulae because metals condense out and coalesem creating nucleation sites for mass accretion. Earlier generations of stars would need to rely on different formation mechanisms, and likely had a different size and brightness distribution. We won't understand these early stars and galaxies until we've been looking at them for at least a decade.
The big bang wasn't an explosion in space, but OF spacetime. Anything that might have existed before would have been fundamentally different, and completely destroyed in the event.
I know not enough physics to tell if this is reasonable but...
What if there's not just 4 base forces but 5, or an infinite class of them? Say something that falls off sub-quadratically but with a significantly lower constant than gravity? Or a whole class of forces that fall off less and less slowly, but have smaller and smaller constants as they do?
The forces, to be a useful modelling tool, need a medium to interact with matter. E.g. an equivalent of charge would always be zero, if matter didn't have the ability to have charge. At that point, it effectively doesn't exist.
Interestingly, the strong, weak and electromagnetic forces are also aspects of the same force. They unify at high enough energy levels. They only appear different. The exception is gravity. It doesn't fit the mould. Basically we don't currently have 4 forces, but only 2. Scientists suspect it's actually only 1, but can't yet unify gravity into a theory of everything via a theory of quantum gravity.
But isn't gravity a function of spacetime not matter? Where's the others are all behaviors of matter? Like there isn't a gravity partical or a spacetime partical.
Ultimately, physics follows the maths, everything else is interpretation to comprehend what the maths is telling us.
In relativity, gravity is a smooth, continuous distortion of spacetime. In QM, gravity is just another force, mediated by the graviton. Both theories are consistent with the known maths. The fact that they don't agree shows the large hole we have in the maths.
In short, we don't know what gravity is. Then again, we don't know what most things are, once we did deep enough. We just have maths, with interpretations that let our monkey brains make sense of them.
My favourite example ample of this is the "dark sucker theory". Envision a universe where light producing objects don't produce light, but suck up dark. We can make the model work for our universe. The reason we don't use it is due to it being harder to work with than the light emitter model. Another one is the rabit hole of what relativity says about the existence of light (hint light doesn't exist, from light's point of view).