## Lecture 21: Geometry of the Universe

Free video lectures for anyone with curiosity and a web browser.
RJN
Baffled Boffin
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Location: Michigan Tech

### Lecture 21: Geometry of the Universe

The lecture video is embedded below but also available here in MP4 format.
Additionally, slides used in the lecture are embedded below but also are available here in Powerpoint format.
Click to play embedded YouTube video.
Wikipedia entries:

Graeme1858
Asternaut
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Joined: Sun Feb 19, 2017 9:38 am

### Re: Lecture 21: Geometry of the Universe

Hello

I have just watched Lecture 21, brilliant!

At about 16 minutes there is a slide on the Bullet Cluster and you use the phrase " the dark matter can be seen" and is shown in blue, separate from the red gas clouds.

Could you clarify please, I understand the requirement for an even spread of mass for the gravitational lens to work smoothly but is the blue a false colour image or does the dark matter cause the gas to appear blue?

Thanks

Regards

Graeme

geckzilla
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Location: Modesto, CA

### Re: Lecture 21: Geometry of the Universe

Graeme1858 wrote:At about 16 minutes there is a slide on the Bullet Cluster and you use the phrase " the dark matter can be seen" and is shown in blue, separate from the red gas clouds.

Could you clarify please, I understand the requirement for an even spread of mass for the gravitational lens to work smoothly but is the blue a false colour image or does the dark matter cause the gas to appear blue?
The blue represents where dark matter is inferred to exist based on how much mass would actually need to be there for the gravitational lens to happen. So yes, it's false-color. In fact the blue part is entirely generated based upon known assumptions.
Just call me "geck" because "zilla" is like a last name.

Graeme1858
Asternaut
Posts: 4
Joined: Sun Feb 19, 2017 9:38 am

### Re: Lecture 21: Geometry of the Universe

Cheers Geck

Thanks for the clarification.

Regards

Graeme