Earlier quoted context omitted.
https://en.m.wikipedia.org/wiki/Russell's_teapot
Not at all relevant, as we can see the effects of dark matter in many places, very clearly.
So you can detect it after all?
Battle of the bulges: Have astronomers been wrong about spiral galaxies? (2019)
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Re: Battle of the bulges: Have astronomers been wrong about spiral galaxies? (2019)
#22Earlier quoted context omitted.
> Just because you cannot detect something does not make you wrong nor does it mean it doesn't exist. What a ridiculous statement. If you cannot detect something, it's can be equally ridiculous to say it exists.
Many discoveries in physics have quite large timespans between being theorised to exist, and being actually detected. Was it ridiculous to say those might exist?
Well, most of the other theories back then would seem ridiculous and obviously wrong nowadays. That's the nature of theorizing when you have little information.
Obviously we mostly remember those theories that turned out to be right.
Re: Battle of the bulges: Have astronomers been wrong about spiral galaxies? (2019)
#23Given that most cosmology relies on a huge percentage of dark matter, which cannot be detected, and a huge amount of dark energy, with enormous conflicting calculations, I think it's fair to say that astronomers are wrong about a lot of things.
You seem to be having a weird definition of 'detect'. The only reason the concepts dark matter and dark energy are on the table in the first place is that we seem to be detecting a lot of both. You might not like that scientists can't really explain what it is that's being detected, but for sure it's being detected. There's pretty good summaries of how dark energy and dark matter are being detected on Wikipedia [1][2…
Ok, but at the risk of being pedantic...
They are "placeholders" because our models are wrong. Which is fine: all models are wrong, but some models are useful.
And astronomy is particularly vulnerable to this - its models are being applied to make predications at extremes of both time and scale.
But I PROMISE you, we're wrong. We know we're wrong, and we don't know why (and recently there's even been some fair criticism of our models that we use to gauge distance, so no, I'd argue we have not reasonably "detected" anything other than that our models are wrong - STILL USEFUL but wrong)
Re: Battle of the bulges: Have astronomers been wrong about spiral galaxies? (2019)
#24Earlier quoted context omitted.
Not at all relevant, as we can see the effects of dark matter in many places, very clearly.
So you can detect it after all?
We're not sure it's matter, but let's just say 'dark matter' is a useful abstract label (like 'teapot'). We know that SOMETHING is perturbing our models that are useful (to simplify the analogy, let's just posit that newtonian orbits are casually affected, for example) by measurement. As much as an orbiting 'teapot' is ridiculous, it's also provable that something is unaccounted for, 'teapot' or 'dark matter', whatever the label.
This does not mean that it's matter specifically (just a label), but is a phenomena.
Re: Battle of the bulges: Have astronomers been wrong about spiral galaxies? (2019)
#25Huh. I thought that there was a solid theoretical basis for the density wave hypothesis. But TFA implies that the main constraint was consistency with the Hubble tuning fork diagram. That would be funny, because I've never really understood the density wave hypothesis.
I don't claim to understand it either, but the animations on the Wiki page at least give a feel for it - https://en.wikipedia.org/wiki/Density_wave_theory
Thanks :)
I get the idea of standing waves.
But TFA at least implies that galaxy structure might not be stable. So there's perhaps a cycle of waves forming, wrapping up, and then reforming. So at any given time, we'd see whatever mix we see.
I mean, I doubt that we've observed any particular galaxy long enough to see whether its structure is stable or not. At least, if the cycle is longer than some hundreds of years, which seems likely.
But then, we do see what galaxies looked like in the past, at increasing distance. And I vaguely recall something about more distant ones not so much being spiral. Even so, that doesn't necessarily constrain ongoing structural stability.
There's also gravitational lensing, which sometimes lets us see events through different paths, and so at different times. However, I recall that the path/time differences were on the order of years at most. But even so, maybe we wouldn't have noticed cases where path/time differences were great enough to see galaxy structure changing. Or maybe such path/time differences are just implausible.
It really is hard when all you can do is look at stuff.
Re: Battle of the bulges: Have astronomers been wrong about spiral galaxies? (2019)
#26The Hubble fork isn't "wrong". It's just a classification scheme. The fork has nothing to do with how spiral structures form or how long they last, it's just a way to quickly describe them.
According to the article, it's a classification scheme that doesn't work. It describes categories that real galaxies don't fit in.
"It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." - (Somebody)
Re: Battle of the bulges: Have astronomers been wrong about spiral galaxies? (2019)
#27Earlier quoted context omitted.
Many discoveries in physics have quite large timespans between being theorised to exist, and being actually detected. Was it ridiculous to say those might exist?
Well, most of the other theories back then would seem ridiculous and obviously wrong nowadays. That's the nature of theorizing when you have little information. Obviously we mostly remember those theories that turned out to be right.
And how do you find out if they turn out to be right, if you dismiss them immediately as "ridiculous"?
That is not how science works. There are other ways of judging if a theory is worth exploring than just a "it must be testable right now".
Re: Battle of the bulges: Have astronomers been wrong about spiral galaxies? (2019)
#28Re: Battle of the bulges: Have astronomers been wrong about spiral galaxies? (2019)
#29Re: Battle of the bulges: Have astronomers been wrong about spiral galaxies? (2019)
#30Earlier quoted context omitted.
Indirectly, yes. Directly, not yet.
Define "directly". The definition of dark matter is that it's electromagnetically non-interacting, therefore observing it's gravitational effect is as direct as it gets.
Since we do not know what exactly it is, defining "directly" is not really something you can do.
But, for instance, electroweak interaction is being looked at, I gather?