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The Cosmic Concordance

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L'Univers en évolution

4.6 (438 notes) | 48K étudiants inscrits

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This is an introductory astronomy survey class that covers our understanding of the physical universe and its major constituents, including planetary systems, stars, galaxies, black holes, quasars, larger structures, and the universe as a whole.

Avis

4.6 (438 notes)

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JI

Apr 28, 2019

I really enjoyed every lesson. It's an incredible and very complete course. Anyone who loves astronomy should do it. In addition, I was able to improve English, which is my second language.

AH

Oct 19, 2015

Took this professor's course in Galaxies and Cosmology which was for 2nd year physics majors. I think this course is a more general course for non-physics-majors. Excellent course!

À partir de la leçon

Week 10

Matter and Energy Contents of the Universe9:46

Gravitational Lensing: Mapping the Dark Matter5:42

The Dark Energy7:02

The Cosmic Concordance3:50

Enseigné par

S. George Djorgovski
Professor

And so we'll end with so-called cosmic concordance.

These two ladies are called Urania and Calliope.

You guys know who they were?

Urania was the muse of astronomy, which was

regarded as an art in the ancient world, and Calliope was muse of music.

And they have some teaching assistants there with wreaths and what not.

So this is what we mean by cosmic concordance.

That all kinds of different cosmological measurements from different physics,

different tools, different techniques, different ratchets, they're all converging

to the same spot in the parameter space of energy density of matter,

and energy density of dark energy in this cosmological constant.

So each of them has some uncertainty ellipse.

You can trade of areas of one quantity versus the other.

But somehow, you put them all together, and

they always intersect very precisely at this one spot.

And so this is why it's called cosmic concordance.

Any one of these measurements by itself doesn't tell you a lot.

Well, micro-background tells you you're this close to flat.

And supernovae tell you there's gotta be some dark energy.

But only in their combinations you get those precision results.

So the fact is we get same results from all manner of completely different

measurements, supernovae, clusters of galaxy, micro background,

globular clusters, etcetera., etcetera., etcetera., is very reassuring and

makes us think that indeed we know what cosmological parameters are.

We may not know the nature of dark energy.

We're not sure about nature of dark matter either, but

in terms of global descriptors, seems like we nailed it.

And so this is today's best estimate universe largely from Planck satellite.

Those are the best measurements we have,

and handy way to remember this is universe is 13.8 billion years old.

Hubble constant's about 70.

Visible stuff amounts to maybe about 4.5% of everything.

I'm sorry, variance about 4.5% of everything.

But 30% of universe is matter, of including dark matter.

And 70% is this mysterious new thing.

I'm not even going to call it substance, because it's probably not substance.

Just because cosmological constant.

So this is actually pretty remarkable

that we can figure all this out just with sitting here on planet Earth.

And deducing things, observing distant universe, just in past.

This pie chart's a little older.

Percents have changed since then, but pretty much tells what's going on.

And so that completes our cosmic journey Just leave you with

this picture just came out from the Hubble Space Telescope Propaganda Factory.

This is one of their deep fields, which some new images were obtained.

A slightly bigger picture than this with 10,000 faint galaxies.

And you can see some closer ones, we can recognize the spirals or ellipticals.

But every little dot in this picture, except for

two stars that have diffraction spikes, every little dot is a galaxy.

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