"made of particles called baryons rather than dark matter"
That's clumsily worded, as it makes it sound like it's still something exotic. _We're_ made of baryons: this is just normal matter.
First detection of the missing half of normal matter in our universe
61–70 of 131 posts
Re: First detection of the missing half of normal matter in our universe
#62Oh where would we be without these geniuses!?
Re: First detection of the missing half of normal matter in our universe
#63Can I just check - my understanding is that we can only see 5% of the expected mass in the universe - so we have just found another 5%? meaning dark matter needs to account for 90%? plus, how awesomely beautiful is the idea of tendrils of has connecting the galaxies through space.
Tendrils between galaxies is mind-blowing. Aren't galaxies very very far apart? And there is basically nothing in between? How are subatomic particles - baryons - able to survive the constant expansion? Do the tendrils keep getting thinner? Can they be a medium to transmit intergalactic information someday?
Re: First detection of the missing half of normal matter in our universe
#64> At the largest size, Google image search tells me that it looks exactly like foam rubber. Foam rubber is created by combining a chemical agent that glomps together through the wonder of polymerization with another chemical agent that delivers lots of gas bubbles to make space between the polymers. Universes are created by rapidly expanding a superdense plasma that glomps together through the wonders of gravity, whi…
Why should vacuum expand? Is it due to gravity of the filament molecules pulling those molecules together into larger 'strings' or 'planes' which leave 'holes'? Or some other mechanism?
The universe expands. Things bound by gravity tend not to expand that much. As a result, most of the space that expands is vacuum.
Re: First detection of the missing half of normal matter in our universe
#65Dang I read the first paragraph of the article and immediately went searching for the real papers since I didn't expect any media outlet to include them at the bottom, but here they are for anyone who made the same mistake I did! https://arxiv.org/abs/1709.05024 https://arxiv.org/abs/1709.10378 Not a cosmologist but here's my go at the de Graff paper. (Let's get this out of the way, the title is click-bait and the pa…
> Let's get this out of the way, the title is click-bait and the paper/researchers makes no such claims as to anything near 50%. New Scientist is trolling for hits with the word "half" or the journalist is fundamentally misunderstanding the work. At first I agreed with you, but I've dug into the articles and re-read the New Scientist article too to make sure, and it seems the story is a bit more complicated than it a…
And the combination of your observation and DiabloD3's is an interesting one. The papers on Birkeland currents in the context of a galaxy spanning plasma makes for some fun conjecturing. A coulomb of charge moving in a million light year long filament of plasma is lot of energy.
Re: First detection of the missing half of normal matter in our universe
#66Earlier quoted context omitted.
EDIT: My understanding is incorrect. See the replies to the post for a correction. No. They're saying that 50% of the "dark matter" isn't dark, it's just regular matter that we weren't able to see. The density of this stuff (filaments of gas stretching between galaxies) is so low that it is really, really, really hard to detect. "Dark matter" theories posit that the missing matter isn't just regular matter that's har…
No, this has nothing to do with dark matter. Dark matter has to be in galaxies because the reason we think it exists at all is because galaxies spin 'too fast', so there is more mass in them and therefore more gravity than can be accounted for. This article is talking about gas between galaxies.
Isn't it more probable that the formulars to calculate the spin are wrong?
Re: First detection of the missing half of normal matter in our universe
#67Earlier quoted context omitted.
IIUC, If it interacts with itself through other forces, they can't be through the forces that act on normal matter (which they would interact with if that was the case), including the forces involved in nuclear fusion. They'd have to be dark matter exclusive forces.
Interesting, thanks. So what's preventing "dark matter" from simply being, say, lots of photons traveling through intergalactic space then? That seems like the next obvious candidate after ordinary matter.
If dark matter where a lot of photons, then we could detect it. For example the experiments to detect the cosmic microwave background radiation https://en.wikipedia.org/wiki/Cosmic_microwave_background can detect a very small amount of light that is the leftover of the radiation produced soon after the big bang. We have very good estimations of how many photons are out there.
Re: First detection of the missing half of normal matter in our universe
#68The title is effectively click-bait because of: https://www.reddit.com/r/space/comments/75944s/half_the_univ...
We should assume by default that every headline is clickbait now, unfortunately this is the business model of the internet. It's not good for accuracy and most articles are just a headline and some inane filler up words. I hope we'll smart up and find a better model for news soon. :/
Re: First detection of the missing half of normal matter in our universe
#69Does this mean the universe is more weird or less weird than we thought?
Re: First detection of the missing half of normal matter in our universe
#70"made of particles called baryons rather than dark matter" That's clumsily worded, as it makes it sound like it's still something exotic. _We're_ made of baryons: this is just normal matter.
As a former physics student, I see your point but disagree.
Apologies for the wall of text about just this one choice of wording, but discussing why science communication is a very difficult trade-off takes a bit of space.
One reason to stick to "baryons" is that it is the term used by the researchers in their papers. So it is more true to the research that is being summarised.
The start of the article (unlike its title...) mentions that this research is about normal matter quite clearly, so this should give enough context to avoid confusion:
> This is the first detection of the roughly half of the normal matter in our universe – protons, neutrons and electrons – unaccounted for by previous observations of stars, galaxies and other bright objects in space. You have probably heard about the hunt for dark matter, a mysterious substance thought to permeate the universe, the effects of which we can see through its gravitational pull. But our models of the universe also say there should be about twice as much ordinary matter out there, compared with what we have observed so far.
Baryons are subatomic particles[0][1], not atoms, which is what most people think of when discussing "matter". If we say "normal matter", some people will think we're talking about chunks of dirt floating between galaxies. I'm not joking, have you ever been to a public physics lecture? And mistakes like this are not the audience's fault - it's the expert's fault for assuming non-experts know what they know.
For people with the right background (chemists, physicists, astronomers, etc) it is clear this is "just normal matter". For everyone else - so most people - "normal matter" means matter in earth-typical circumstances of pressure and temperature, in a solid/liquid/vapour phase.
The papers describe intergalactic plasma filaments with a temperature between 10⁴ to 10⁵ K. That is pretty exotic by normal-people standards.
And yes, fire is a plasma, but for most people fire is just very hot gas, and the article even builds on that:
> Because the gas is so tenuous and not quite hot enough for X-ray telescopes to pick up, nobody had been able to see it before.
So the other reason reason to stick to "baryons" is that this is exotic matter from the point of view of non-experts. When describing research you have to start from their model of the physical world, and build your way back to the research.
I think the choice in wording appropriate here. The other paragraphs make it clear this is about normal matter, while this sentence makes it clear it's not normal matter in Earth-circumstances, which is how the average human thinks about it if not corrected.
[0] https://en.wikipedia.org/wiki/Baryon
[1] https://simple.wikipedia.org/wiki/Baryon (the Simple English wiki is probably more useful to us non-cosmologists here)