First detection of the missing half of normal matter in our universe • Hacker News Board

Re: First detection of the missing half of normal matter in our universe

#11

Post by mirimir » Tue, Oct 10, 2017, 5:32 AM UTC

> 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, while lots of expanding vacuum makes space between the galaxy clusters.

https://palmstroem.blogspot.de/2016/01/no-universe-is-not-br...

Edit: This explains, in a light-hearted way, why there are filaments between galaxies and galaxy clusters.

Re: First detection of the missing half of normal matter in our universe

#12

Post by brianyu8 » Tue, Oct 10, 2017, 5:33 AM UTC

nielsbot wrote: post #10

I am not an astrophysicist... but does this mean dark matter has finally been "seen"? That's a big deal, right?

I was also confused about this. However the article states that half of the normal matter (not dark matter) thought to exist has been detected. Basically we just found the missing normal matter and have not yet found dark matter.

Re: First detection of the missing half of normal matter in our universe

#13

Post by mcbutterbunz » Tue, Oct 10, 2017, 5:33 AM UTC

nielsbot wrote: post #10

I am not an astrophysicist... but does this mean dark matter has finally been "seen"? That's a big deal, right?

No, this is just the half of the 5% of regular matter that was "missing".

Re: First detection of the missing half of normal matter in our universe

#14

Post by warent » Tue, Oct 10, 2017, 5:33 AM UTC

nielsbot wrote: post #10

I am not an astrophysicist... but does this mean dark matter has finally been "seen"? That's a big deal, right?

I think it's actually saying that we discovered missing matter that isn't dark matter. So now all that's remaining unaccounted-for is dark matter (and dark energy)

Disclaimer: also not an astrophysicist

Re: First detection of the missing half of normal matter in our universe

#15

Post by JohnBooty » Tue, Oct 10, 2017, 5:33 AM UTC

nielsbot wrote: post #10

I am not an astrophysicist... but does this mean dark matter has finally been "seen"? That's a big deal, right?

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 hard to see; they posit that this dark matter is a fundamentally different... something.

I don't believe this announcement addresses some of the other oddities (possibly) explained by dark matter, such as the rotation of galaxies: https://en.wikipedia.org/wiki/Galaxy_rotation_curve

Re: First detection of the missing half of normal matter in our universe

#16

Post by Meegul » Tue, Oct 10, 2017, 5:34 AM UTC

lifeisstillgood wrote: post #9

Can 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.

Like many of us, I'm no astrophysicist, but one of the linked papers [1] references that we've thus far been able to locate 10% of baryon content, with this discovery bringing this number up to 30%.

Assuming I'm interpreting this correctly, this means that there's still around 70% of expected baryonic matter unaccounted for.

1: https://arxiv.org/abs/1709.10378v1

Re: First detection of the missing half of normal matter in our universe

#17

Post by wheresmyusern » Tue, Oct 10, 2017, 5:35 AM UTC

im confused about baryons. they say that it is a particle (presumably like an electron or photon or other particle) but then they go on to say that its a gas, not a particle. very confusing.

Re: First detection of the missing half of normal matter in our universe

#18

Post by sanxiyn » Tue, Oct 10, 2017, 5:36 AM UTC

nielsbot wrote: post #10

I am not an astrophysicist... but does this mean dark matter has finally been "seen"? That's a big deal, right?

It's not a dark matter.

Re: First detection of the missing half of normal matter in our universe

#19

Post by nitrogen » Tue, Oct 10, 2017, 5:37 AM UTC

wheresmyusern wrote: post #17

im confused about baryons. they say that it is a particle (presumably like an electron or photon or other particle) but then they go on to say that its a gas, not a particle. very confusing.

Isn't a gas just a swarm of particles?

Re: First detection of the missing half of normal matter in our universe

#20

Post by mrpopo » Tue, Oct 10, 2017, 5:38 AM UTC

lifeisstillgood wrote: post #9

Can 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.

> 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.

My understanding is that, up until now, we could only observe half of the 5% expected mass, e.g. 2.5%, and we can now see the rest of it. The rest of the universe is still made up of 25% dark matter and 70% dark energy.