APOD: Planck Maps the Microwave Background (2018 Jul 22)

[APOD Robot]

Planck Maps the Microwave Background

Explanation: What is our universe made of? To help find out, ESA launched the Planck satellite from 2009 to 2013 to map, in unprecedented detail, slight temperature differences on the oldest optical surface known -- the background sky when our universe first became transparent to light. Visible in all directions, this cosmic microwave background is a complex tapestry that could only show the hot and cold patterns observed were the universe to be composed of specific types of energy that evolved in specific ways. The final results, reported last week, confirm again that most of our universe is mostly composed of mysterious and unfamiliar dark energy, and that even most of the remaining matter energy is strangely dark. Additionally, the "final" 2018 Planck data impressively peg the age of the universe at about 13.8 billion years and the local expansion rate -- called the Hubble constant -- at 67.4 (+/- 0.5) km/sec/Mpc. Oddly, this early-universe determined Hubble constant is slightly lower than that determined by other methods in the late-universe, creating a tension that is causing much discussion and speculation.

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[bystander]

viewtopic.php?t=38526

[Roberto]

Just a minor fastidious remark: why the Hubble constant is not expressed in proper SI units i.e. 1/s, rather than using those bizarre Megaparsecs?

[De58te]

Interesting, but which part of the reds and blue color is the dark matter and which is the baryonic matter that we can see? They say that 80% of this is dark matter, but it doesn't look separated into 80 /20. Also I heard that the big bang created an equal part matter and anti-matter. So of the 20% of this picture that is our visible universe, only 10% is made out of the matter we know.

[Devil Particle]

They are starting to talk about it.

[heehaw]

Interesting, but which part of the reds and blue color is the dark matter and which is the baryonic matter that we can see? They say that 80% of this is dark matter, but it doesn't look separated into 80 /20. Also I heard that the big bang created an equal part matter and anti-matter. So of the 20% of this picture that is our visible universe, only 10% is made out of the matter we know.

It is not showing EITHER the dark matter OR the baryonic matter, it is showing nothing but electromagnetic radiation. That radiation is almost completely uniform over the sky, but not quite. It has extremely weak ripples, and the coloring (red, blue) is just to let us see the ripples. The ripples are slight density variations, that over the last 13 billion years have gravitationally collapsed to form all the galaxies.

[heehaw]

Just a minor fastidious remark: why the Hubble constant is not expressed in proper SI units i.e. 1/s, rather than using those bizarre Megaparsecs?

Oh, I could not agree with you more! The parsec is a bizarre unit based solely on the size of planet Earth's orbit! Parsecs should never be used ever; light years (although based on Earth's year, yes) are FAR superior. As far as physics itself is concerned it is even MORE important: the limiting velocity set by the four-dimensional geometry of spacetime is the velocity at which all massless particles (e.g. light photons) move; the velocity is 1 light-year per year. That is, the velocity of light is exactly 1. So Einstein's famous E=mc^2 really should be written (since c = 1), " E = m "

[neufer]

Just a minor fastidious remark: why the Hubble constant is not expressed in proper SI units i.e. 1/s, rather than using those bizarre Megaparsecs?

The Planck Hubble constant [~1/(14,500,000,000 years)] is pretty darn small in terms of 1/s.

I never Megaparsec I didn't like.

[Chris Peterson]

Just a minor fastidious remark: why the Hubble constant is not expressed in proper SI units i.e. 1/s, rather than using those bizarre Megaparsecs? :?

Oh, I could not agree with you more! The parsec is a bizarre unit based solely on the size of planet Earth's orbit! Parsecs should never be used ever; light years (although based on Earth's year, yes) are FAR superior.

To be slightly clearer, it is based on a Julian year, which is a derived SI unit (365.25 days x 86 400 seconds/day). So the IAU defined light-year itself is a derived SI unit. As you note, far superior to a parsec.

(Technically, we could consider a parsec as an SI derived unit, as well, since the AU is standardized to a fixed number of meters, and the radian is a derived SI unit. But the conversion path is more twisted, and the underlying logic is even more geocentric.)