Ethan Siegel write up on this problem: https://www.forbes.com/sites/startswithabang/2018/06/22/why-...
Cosmology Has Some Big Problems
11–20 of 76 posts
Re: Cosmology Has Some Big Problems
#12Interesting view. Near the end, it says: “The crux of today's cosmological paradigm is that in order to maintain a mathematically unified theory valid for the entire universe, we must accept that 95 percent of our cosmos is furnished by completely unknown elements and forces for which we have no empirical evidence whatsoever.” Empiricism is based on sense observations. And a lot of science has been confined to human…
We have no better access to the sense data of the Ampullae of Lorenzini in a shark than we do to the signals recorded by a radio telescope. Arguably, our access is worse for the shark than for the telescope.
Ultimately, no matter what we use to record the data (animal or instrument), we can only access the results through our 5 senses.
Re: Cosmology Has Some Big Problems
#13It is of course entirely plausible that the validity of general relativity breaks down much closer to our own home than at the edge of the hypothetical end of the universe. Is it really? Have people formulated specific break downs, then gone to look for evidence?
A more damning quote seems to be Another recent probe found galaxies inconsistent with the theory of dark matter, which posits this hypothetical substance to be everywhere. There is no reference given, but I have the suspicion that it refers to the discovery of galaxies with almost no dark matter (cf. https://news.ycombinator.com/item?id=16701248 ). That does indeed refute the assumpion that dark matter is everywhere…
Couldn't it just as easily mean that our predictions based on general relativity are wrong?
Either 1) the prediction for a particular galaxy is right, and there's no "dark energy" or "dark matter" or
2) the prediction is wrong, and you add a bunch of dark energy or dark matter to make the equations work out.
It's not testable at all - no matter whether predictions for a particular galaxy are right or wrong, you're still allowing yourself to think that the theory is correct. How is this scientific?
Re: Cosmology Has Some Big Problems
#14It is of course entirely plausible that the validity of general relativity breaks down much closer to our own home than at the edge of the hypothetical end of the universe. Is it really? Have people formulated specific break downs, then gone to look for evidence?
A more damning quote seems to be Another recent probe found galaxies inconsistent with the theory of dark matter, which posits this hypothetical substance to be everywhere. There is no reference given, but I have the suspicion that it refers to the discovery of galaxies with almost no dark matter (cf. https://news.ycombinator.com/item?id=16701248 ). That does indeed refute the assumpion that dark matter is everywhere…
Not necessarily. This great video from PBS Spacetime is a fairly detailed, but good for a 'nearly' layman on the findings in depth. https://www.youtube.com/watch?v=5t0jaE--l0Y
A discussion on how a galaxy could be missing dark matter - or how it could be separated from a galaxy
Re: Cosmology Has Some Big Problems
#15I'm a grad student working on cosmology, and while I agree there is a lot of work still to do (we don't know what 95% of the matter that makes up the universe is!), I disagree with a lot of what the author says.
> Another recent probe found galaxies inconsistent with the theory of dark matter, which posits this hypothetical substance to be everywhere.
We have found evidence of a few galaxies without DM. But most galaxies provide strong evidence for DM - https://en.wikipedia.org/wiki/Galaxy_rotation_curve
> For a crucial function of theories such as dark matter, dark energy and inflation, which each in its own way is tied to the big bang paradigm
Big bang was only the accepted paradigm from the 60s (post CMB observations). We have had DE since Einstein in 1917 and DM since Zwicky in the 30s.
> Historically, Newton's physical laws made up a theoretical framework that worked for our own solar system with remarkable precision. Both Uranus and Neptune, for example, were discovered through predictions based on Newton's model. But as the scales grew larger, its validity proved limited.
Actually some of the earliest evidence for GR came from the orbit of mercury https://en.wikipedia.org/wiki/Tests_of_general_relativity
> It is of course entirely plausible that the validity of general relativity breaks down much closer to our own home than at the edge of the hypothetical end of the universe. And if that were the case, today's multilayered theoretical edifice of the big bang paradigm would turn out to be a confusing mix of fictional beasts invented to uphold the model
This is something that people are working on! This is a hypothesized source of DE. However, disproving GR does nothing to disprove the big bang.
> Today's space telescopes provide no direct view of anything
I have no idea what that means. They literally observe the sky...
There is a ton of work to do: finding what DM is, finding what DE is, finding whether GR is correct. But I'm not sold that the author knows what he is talking about...
Re: Cosmology Has Some Big Problems
#16Earlier quoted context omitted.
A more damning quote seems to be Another recent probe found galaxies inconsistent with the theory of dark matter, which posits this hypothetical substance to be everywhere. There is no reference given, but I have the suspicion that it refers to the discovery of galaxies with almost no dark matter (cf. https://news.ycombinator.com/item?id=16701248 ). That does indeed refute the assumpion that dark matter is everywhere…
Couldn't it just as easily mean that our predictions based on general relativity are wrong? Either 1) the prediction for a particular galaxy is right, and there's no "dark energy" or "dark matter" or 2) the prediction is wrong, and you add a bunch of dark energy or dark matter to make the equations work out. It's not testable at all - no matter whether predictions for a particular galaxy are right or wrong, you're st…
It's not that simple. It's not like a) Some galaxies fit predictions, b) Some do not, and we add unknown dark matter.
It's that when they do not fit predictions, there is a single parameter (the mass of dark matter) that does explain its behavior, whose model is that of a weakly interacting gas halo. So dark matter tries to fix things in a very precise way, it's not an arbitrary curve fitting exercise.
Now whether there is really weakly interacting matter out there or some other explanation is valid is still an open question afaik; but the evidence is quite strong so far.
Re: Cosmology Has Some Big Problems
#17Earlier quoted context omitted.
A more damning quote seems to be Another recent probe found galaxies inconsistent with the theory of dark matter, which posits this hypothetical substance to be everywhere. There is no reference given, but I have the suspicion that it refers to the discovery of galaxies with almost no dark matter (cf. https://news.ycombinator.com/item?id=16701248 ). That does indeed refute the assumpion that dark matter is everywhere…
Couldn't it just as easily mean that our predictions based on general relativity are wrong? Either 1) the prediction for a particular galaxy is right, and there's no "dark energy" or "dark matter" or 2) the prediction is wrong, and you add a bunch of dark energy or dark matter to make the equations work out. It's not testable at all - no matter whether predictions for a particular galaxy are right or wrong, you're st…
No, the only consistent explanation for both the overwhelming majority of galaxies as well as the few outliers is general relativity and independent dark mater. All other theories that make testable predictions (modified newtonian dynamics or MOND seems to be the only class that is not completely add odds with almost all observations) cannot explain the behaviour of those galacies that are as big as other galaxies but rotate wih a different speed. But the difference is easily explained with different amounts of dark matter in the galaxies, and the bullet cluster cited elsewhere in this thread give a plausible explanation of how these galaxies might form.
Re: Cosmology Has Some Big Problems
#18Interesting view. Near the end, it says: “The crux of today's cosmological paradigm is that in order to maintain a mathematically unified theory valid for the entire universe, we must accept that 95 percent of our cosmos is furnished by completely unknown elements and forces for which we have no empirical evidence whatsoever.” Empiricism is based on sense observations. And a lot of science has been confined to human…
One way to think of scientific instruments: like telescopes, microscopes, voltmeters is that they are extensions of our senses.
Re: Cosmology Has Some Big Problems
#19Interesting view. Near the end, it says: “The crux of today's cosmological paradigm is that in order to maintain a mathematically unified theory valid for the entire universe, we must accept that 95 percent of our cosmos is furnished by completely unknown elements and forces for which we have no empirical evidence whatsoever.” Empiricism is based on sense observations. And a lot of science has been confined to human…
What aren’t we using from the animal kingdom? We create sensors that are extra human. Infrared etc... Maybe this is an unknown unknown problem. We can’t develop technology for senses we do not know about and so on.
Indeed, I agree with your point, “Maybe this is an unknown unknown problem.”
I’m not sure why my comment is being downvoted, is there something I said that’s in bad taste?
Re: Cosmology Has Some Big Problems
#20It is of course entirely plausible that the validity of general relativity breaks down much closer to our own home than at the edge of the hypothetical end of the universe. Is it really? Have people formulated specific break downs, then gone to look for evidence?
Well... assuming that the local rules are the same as the rules billions of light-years away is an assumption, based on a philosophical presupposition that the rules are uniform. What probability should we assign to that assumption? 100% in the absence of evidence to the contrary? Or should we reserve some skepticism, remembering that it is an assumption?
Your question is reasonable: Have people formulated specific breakdowns, and gone looking? But it's also unreasonable. An assumption shouldn't necessarily be treated beyond plausible doubt until we can prove it wrong.