by Ann » Sun Oct 31, 2021 6:22 am
That's a striking illustration of dark matter and baryonic matter in the Universe. I like it!
A fun thing about the map is that dark matter is very appropriately shown as dark▮, but the parts where there is not a lot of dark matter shown as light gray
▮. But we all know that the Universe is pretty dark, because the night sky is dark. Do you remember why it is dark? What is the correct answer?
1) It's dark because the Universe is young, and the speed of light is slow compared with the size of the Universe, which means that much of the light that the Universe has produced has not had time to reach us.
2) It's dark because the Universe is expanding, and the wavelengths of light are stretched along with it, so that much of the light of the Universe has been stretched far beyond the visible part of the spectrum.
3) It's dark because the Universe is not just expanding but accelerating, so that the ever-growing size of the Universe is
really outrunning the speed of light, which means that much of the light of the Universe will never reach us!
4) It's dark because there is not an infinite number of stars in the Universe. Come on, people. What makes anyone think that there are so many stars in the Universe that there is not a single point along any arbitrary line of sight in the Universe that wouldn't eventually "hit a star"?
Surely there isn't a star along every line of sight in the Hubble Deep Field? Of course there are more stars in the parts of the Universe that are not observable. But, no, we can't see them.
![Small Big Bad Wolf.png](./download/file.php?id=42053&sid=a3969092f82fe5528740f2e8d6af3c4e)
- Small Big Bad Wolf.png (21.06 KiB) Viewed 5728 times
Anyway, take a look at the APOD again and note how the light gray stuff behind the dark filaments of dark matter almost looks like expanding bubbles, huffing and puffing like the Big Bad Wolf. Maybe that's where the dark energy is??
Ann
[float=left][img3="Dark Matter in a Simulated Universe. Illustration Credit & Copyright: Tom Abel & Ralf Kaehler (KIPAC, SLAC), AMNH"]https://apod.nasa.gov/apod/image/2110/DarkMatter_KipacAmnh_960.jpg[/img3][/float]
[clear][/clear]
That's a striking illustration of dark matter and baryonic matter in the Universe. I like it!
A fun thing about the map is that dark matter is very appropriately shown as dark▮, but the parts where there is not a lot of dark matter shown as light gray[color=#D3D3D3]▮[/color]. But we all know that the Universe is pretty dark, because the night sky is dark. Do you remember why it is dark? What is the correct answer?
1) It's dark because the Universe is young, and the speed of light is slow compared with the size of the Universe, which means that much of the light that the Universe has produced has not had time to reach us.
2) It's dark because the Universe is expanding, and the wavelengths of light are stretched along with it, so that much of the light of the Universe has been stretched far beyond the visible part of the spectrum.
3) It's dark because the Universe is not just expanding but accelerating, so that the ever-growing size of the Universe is [b][i]really[/i][/b] outrunning the speed of light, which means that much of the light of the Universe will never reach us!
4) It's dark because there is not an infinite number of stars in the Universe. Come on, people. What makes anyone think that there are so many stars in the Universe that there is not a single point along any arbitrary line of sight in the Universe that wouldn't eventually "hit a star"?
[float=left][img3="Hubble Ultra Deep Field. Credit:
NASA, ESA, and S. Beckwith (STScI) and the HUDF Team"]https://cdn.spacetelescope.org/archives/images/screen/heic0611b.jpg[/img3][/float]
[clear][/clear]
Surely there isn't a star along every line of sight in the Hubble Deep Field? Of course there are more stars in the parts of the Universe that are not observable. But, no, we can't see them.
[float=left][attachment=0]Small Big Bad Wolf.png[/attachment][/float]Anyway, take a look at the APOD again and note how the light gray stuff behind the dark filaments of dark matter almost looks like expanding bubbles, huffing and puffing like the Big Bad Wolf. Maybe that's where the dark energy is??
Ann