New class of galaxy has been discovered, made almost entirely of dark matter • Hacker News Board

Re: New class of galaxy has been discovered, made almost entirely of dark matter

#101

Post by powertower » Sat, Aug 27, 2016, 1:22 AM UTC

sloppycee wrote: post #60

tomr_stargazer wrote: post #18

Earlier quoted context omitted.

(PhD student in astrophysics answering here.) This is a great question! You're addressing the idea (roughly along the lines of Occam's razor) that if there's any way to explain the "extra mass" without invoking a new form of matter, it should be preferred. Most of these other possibilities have been largely ruled out via careful observations, which are detailed here: https://en.wikipedia.org/wiki/Dark_matter#Composit…

I've always wondered, if gravity is a wave (has it been confirmed?), then there must be areas in space where different waves superimpose. Would the constructive interference between gravity waves be significant enough to account for 'dark matter'? And what would destructive interference look like (dark energy?)

Gravity, in its normal sense (of matter's gravitational attraction), has no frequency or wavelength. Its only property is that of acceleration.

Re: New class of galaxy has been discovered, made almost entirely of dark matter

#102

Post by Retra » Sat, Aug 27, 2016, 1:26 AM UTC

T0T0R0 wrote: post #98

logfromblammo wrote: post #33

Earlier quoted context omitted.

Well... it might. Your closet probably has the same concentration of dark matter in it as everywhere else on the surface of Earth. But that quantity is unmeasurable at our current technology level, because any signal we might get is completely obscured by all the noise from bright matter around here. Dark matter is not matter that does not emit light. A rogue asteroid far from any star is a dark object, but it is not…

Just going to point out that science is filled with garbage theories, and "Dark Matter" certainly feels like one of them. Why not just go back to calling it The Æther? Or mayhap a form of non-luminiferous aether, if I may be so bold? https://en.wikipedia.org/wiki/Aether_theories a space-filling substance or field, thought to be necessary as a transmission medium for the propagation of [...] gravitational forces. You…

Because that would be the kind of 'garbage theory' that would make you look incompetent rather than clever.

Re: New class of galaxy has been discovered, made almost entirely of dark matter

#103

Post by Retra » Sat, Aug 27, 2016, 1:29 AM UTC

jomamaxx wrote: post #64

Florin_Andrei wrote: post #2

This is significant. Now astronomers can study dark matter with less interference from the regular matter background. So you have a more broad range of objects to study, from galaxies with lots of regular matter, to galaxies with almost none of it. Hopefully this will accelerate DM research. It will certainly provide lots more data.

" Now astronomers can study dark matter with less interference from the regular matter background" There is no such thing as 'Dark Matter' yet. Would you people please stop talking about it as though it exists? It is, at this stage, a very crude idea. There is no evidence of its existence. We assume 'Dark Matter' exists because our relativistic equations are broken and it's the easiest thing we can imagine to 'fix' t…

>It is, at this stage, a very crude idea.

It is an idea. Ideas exist. It does exist. There's nothing here for you to argue with.

Re: New class of galaxy has been discovered, made almost entirely of dark matter

#104

Post by Florin_Andrei » Sat, Aug 27, 2016, 1:35 AM UTC

s_q_b wrote: post #65

tomr_stargazer wrote: post #18

Earlier quoted context omitted.

(PhD student in astrophysics answering here.) This is a great question! You're addressing the idea (roughly along the lines of Occam's razor) that if there's any way to explain the "extra mass" without invoking a new form of matter, it should be preferred. Most of these other possibilities have been largely ruled out via careful observations, which are detailed here: https://en.wikipedia.org/wiki/Dark_matter#Composit…

I'm not even close to a physicist, but it has always bothered me that such a huge percentage of the matter in the universe would be nearly unobservable. It's the sort of thing that wouldn't pass my normal sanity check in a scientific computing model. But I trust that these possibilities are being well considered. Is there any significant mainstream buy-in with regard to alternative theories of gravity?

> I'm not even close to a physicist, but it has always bothered me that such a huge percentage of the matter in the universe would be nearly unobservable.

It turns out that in some ways we actually are precious snowflakes. What we are made off (baryonic matter) makes up less than 5% of the whole "stuff" of the Universe. A mere froth on the surface of existence.

Re: New class of galaxy has been discovered, made almost entirely of dark matter

#105

Post by jomamaxx » Sat, Aug 27, 2016, 1:42 AM UTC

Retra wrote: post #103

jomamaxx wrote: post #64

Earlier quoted context omitted.

" Now astronomers can study dark matter with less interference from the regular matter background" There is no such thing as 'Dark Matter' yet. Would you people please stop talking about it as though it exists? It is, at this stage, a very crude idea. There is no evidence of its existence. We assume 'Dark Matter' exists because our relativistic equations are broken and it's the easiest thing we can imagine to 'fix' t…

>It is, at this stage, a very crude idea. It is an idea. Ideas exist. It does exist. There's nothing here for you to argue with.

A) Yeah, uh, in Science, when we refer to 'things that exist', we usually mean 'materially' and not 'in fantasy'. So no, that it is an 'idea' does not mean 'it exists'.

B) Prove to me that dark matter exists. Characterize it. You can't. The only thing we know is that our equations for gravity don't work, and it would be 'nice' if there were this thing called 'dark matter' out there because it would fit nicely with what we previously understand. So - there's plenty for me to argue with.

C) Dark Matter/Energy theory basically states the Universe is made up of 96% of this interesting material we don't know for sure exists, we have no direct evidence of it, and we really can't characterize it very well.

When a principle is '96% wrong' - maybe it would be better to question the very nature of the principle, instead of trying to fit it to observation?

It's highly possible that our understanding of gravity is just plain wrong. That we can make some inferences in our locality, but in the grand scheme it just falls apart. Obviously, it is wrong to the tune of 96%. Which is not good.

There's going to be a lot to 'argue about' with Dark Matter/Energy for the next couple of generations at least.

Re: New class of galaxy has been discovered, made almost entirely of dark matter

#106

Post by wallace_f » Sat, Aug 27, 2016, 1:48 AM UTC

I sometimes enjoy to daydream about the possibilities of dark matter, but probably the simplest explanation, and the least spectacular one, is the answer here: dark matter likely is a product of black holes, and probably just an even distribution of black holes. There is already growing a little bit of evidence that this is the case. I would be thrilled to learn about gravity leaking from other dimensions or alternate forms of matter, but it is probably just normal matter trapped inside black holes.

Re: New class of galaxy has been discovered, made almost entirely of dark matter

#107

Post by evanb » Sat, Aug 27, 2016, 1:50 AM UTC

m_mueller wrote: post #97

biot wrote: post #95

Earlier quoted context omitted.

Given that E=mc^2, how do we know that there isn't simply a form of energy which is overly abundant? If the energy and mass are interchangeable, could it be that a massive amount of energy could be undetectable yet still have the same gravitational effects as what we call dark matter?

as far as I understand, something that invokes gravitational force is by definition 'mass', not energy.

While that's the common understanding, general relativity tells us that the spacetime curvature is dictated by the stress-energy tensor, which is accounts for all different types of mass and energy. For example, if you have a crystal at very low temperature it will gravitate less than the same crystal at a high temperature (though for familiar materials it is a VERY slight effect).

Re: New class of galaxy has been discovered, made almost entirely of dark matter

#108

Post by wallace_f » Sat, Aug 27, 2016, 1:51 AM UTC

tomr_stargazer wrote: post #18

mordocai wrote: post #4

Earlier quoted context omitted.

One thing I don't understand and maybe someone can take the time to explain. Why does it have to be this "Dark Matter" causing the mass differences we've been seeing? How do we know it isn't undetectable-through-normal-means normal matter, or aliens, or mistakes in our calculations/observations, or anything else? Since we haven't been able to detect dark matter, it seems from my layman point of view that any of the a…

(PhD student in astrophysics answering here.) This is a great question! You're addressing the idea (roughly along the lines of Occam's razor) that if there's any way to explain the "extra mass" without invoking a new form of matter, it should be preferred. Most of these other possibilities have been largely ruled out via careful observations, which are detailed here: https://en.wikipedia.org/wiki/Dark_matter#Composit…

Thanks, that was insightful yet down to earth, terse yet well-written, and contained further reading and references.

Re: New class of galaxy has been discovered, made almost entirely of dark matter

#109

Post by andrepd » Sat, Aug 27, 2016, 1:52 AM UTC

wallace_f wrote: post #106

I sometimes enjoy to daydream about the possibilities of dark matter, but probably the simplest explanation, and the least spectacular one, is the answer here: dark matter likely is a product of black holes, and probably just an even distribution of black holes. There is already growing a little bit of evidence that this is the case. I would be thrilled to learn about gravity leaking from other dimensions or alternat…

I don't think anything in your post makes the least bit of sense.

Re: New class of galaxy has been discovered, made almost entirely of dark matter

#110

Post by evanb » Sat, Aug 27, 2016, 1:52 AM UTC

s_q_b wrote: post #65

tomr_stargazer wrote: post #18

Earlier quoted context omitted.

(PhD student in astrophysics answering here.) This is a great question! You're addressing the idea (roughly along the lines of Occam's razor) that if there's any way to explain the "extra mass" without invoking a new form of matter, it should be preferred. Most of these other possibilities have been largely ruled out via careful observations, which are detailed here: https://en.wikipedia.org/wiki/Dark_matter#Composit…

I'm not even close to a physicist, but it has always bothered me that such a huge percentage of the matter in the universe would be nearly unobservable. It's the sort of thing that wouldn't pass my normal sanity check in a scientific computing model. But I trust that these possibilities are being well considered. Is there any significant mainstream buy-in with regard to alternative theories of gravity?

Well, just think about the Dark Scientist who says "OK, we make up 27% of the universe, and there's a missing 5% we don't see because it doesn't interact with us."

And then some dark model builder says, "Guys, guys. I bet it's SU(3)xSU(2)xU(1) with 3 generations and the parameters tuned so that..."