Lecture 01: A Grand Tour of the Universe

[RJN]

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.
Questions after the lecture? Please ask them in here.

Click to play embedded YouTube video.

Wikipedia entries:

• Universe
  Electromagnetic spectrum
  Light year

[peter_from_nyc]

Hi:

I just took the 1st lesson, which was nice, and I ran powerpoint in the background to bring up the slides to be the size of my screen (using <F5> to run).

The little video did not get bigger using <ctrl><F2> or <ctrl><F3> as one commenter said, but that may be because the media changed in the intervening years. But that worked out okay, as I put the PowerPoint slides or the APOD pictures referenced on the full screen background, with the tiny lecture screen as an inset.

I did notice a mistake (I believe) where the instructor said:
it is 2.7 degrees Kelvin, which is colder than 2.7 degrees Celsius, which is colder than 2.7 degrees Fahrenheit.

I believe 2.7 degrees Celsius is warmer than 32 degrees Fahrenheit (freezing point of water = 0 degrees Celsius).

Someone may have noticed it before, so perhaps there is a list of corrections somewhere. Can anyone provide that web address?

Thanks for the learning opportunity.

Pete

[geckzilla]

I did notice a mistake (I believe) where the instructor said:
it is 2.7 degrees Kelvin, which is colder than 2.7 degrees Celsius, which is colder than 2.7 degrees Fahrenheit.

I believe 2.7 degrees Celsius is warmer than 32 degrees Fahrenheit (freezing point of water = 0 degrees Celsius).

Someone may have noticed it before, so perhaps there is a list of corrections somewhere. Can anyone provide that web address?

I don't know of any list of corrections, but you are right. He probably flipped C and F on accident. Here are all the numbers converted to Kelvin:

2.7 Kelvin is 2.7 Kelvin
2.7 Celsius is 275.85 Kelvin
2.7 Fahrenheit is 256.87 Kelvin

Also, I just realized there was a mistake on the Lecture Discussions forum that wouldn't allow registered users to start a new topic. That was wrong. You should now be able to start your own topics there.

[Chris Peterson]

I did notice a mistake (I believe) where the instructor said:
it is 2.7 degrees Kelvin, which is colder than 2.7 degrees Celsius, which is colder than 2.7 degrees Fahrenheit.

Yeah, I caught that, too (and a couple of other trivial errors that I'll leave unmentioned).

Have you ever taught a class or given a lecture? Personally, I'd rather not have mine recorded! You have an outline, not a script. You know what you want to say, but there's a component of the actual flow that is off-the-cuff, and there are always little slips. Sometimes you notice them as you speak, but realize that trying to fix what you said will just make things worse. Sometimes you don't notice unless you review a recording. That's just the nature of a live performance.

Of course, if I say something a little wrong in a lecture and somebody catches it, that's good. It means at least one person is paying attention to what I'm saying! Bonus points if it's a student.

[sirnelson]

In Lecture 1, the size of the visible universe is stated as 13.7 billion light years and that is further identified as a "radius" measurement. That prompted a few questions for me which Professor Nemiroff suggested I post in the Asterisk Bulletin Board for all to consider:

1. Is it correct to state the size of the visible universe as 27.4 billion light years using a diameter measurement radiating in all directions from Earth? I ask this because I have never seen size measurement presented that way; I have always read the size of the visible universe as being some figure between 13 to 14 billion light years depending on the latest "most distant object found".

2. Have we been able to spot "most distant objects" at roughly the same distance in all directions? In other words, we have some distant object as a marker that is approximately 13.7 billion light years away. Are there other distant objects at similar distances but in other directions? In raising this question I am not assuming in any way that the Earth is at the center of the universe but I am assuming it should be at the center of the "visible" universe from the perspective of Earth.

3. And finally, do we currently view the visible universe to be symmetrical from the perspective of Earth or do we have evidence that it isn't?

Thanks for your responses.

[bystander]

1. The age of the Universe is about 13.7 billion years, but due to the expansion of space we are now observing objects that are now considerably farther away than a static 13.7 billion light-years distance. The edge of the observable universe is now located about 46.5 billion light-years away (or a diameter of 93 billion light years)
2. We have not looked everywhere. HUDF 2009 is the deepest image we have of the universe, but according to the cosmological principle the universe looks the same where ever we look.
3. As far as I know, the Earth does not occupy any unique position in or enjoy any unique perspective on the universe, see cosmological principle above.

[sirnelson]

Thanks Bystander. I had heard the term "observable universe" before but had assumed it to be the same as "visible universe". I read the Wiki entry on it and now know them to be different terms. An observable ball with a diameter of 93 billion light years is quite a concept. I agree on the non-uniqueness of Earth's position.

As I get deeper into the Astronomy course I hope to see a discussion of the cosmological principle as well as the concepts of the visible and observable universe. If that isn't included in this course then I for one would be interested in hearing such a discussion sometime. Thanks!

[RJN]

When distances become very large, the question of what defines distance becomes strange and diverse. In cosmology, there exists "angular diameter distance", "luminosity distance", "proper motion distance", and even other less well known distance measures. For example, an object will appear half its size when removed to twice its angular diameter distance. An object will appear one quarter as bright when removed to twice its luminosity distance. Due to time slowing, redshifting of photons, and the curvature of space, these distances are NOT usually the same. At distances when the cosmological redshift is well smaller than one, however, they all converge and coincide with our usual single concept of distance.

Given that the universe is known to be about 13.7 billion years old, I assumed that there must be SOME cosmological distance scale, perhaps "comoving proper distance" or some such, that would match it, so that using that distance measure, the visible universe would be, correspondingly, about 13.7 billion light years in radius. For more background, please see also Lectures 21 and 22. - RJN

[sirnelson]

So is there a quantum difference between what we term "visible" universe vs. "observable" universe or are they essentially the same?

I don't mean to belabor the point but this term "observable" is new to me and I'm trying to understand its relationship to "visible". Underlying all this is my own crazy fascination with the size of the universe as we can perceive it. To imagine a never-ending universe is impossible, for me anyway, and to imagine one that ends begs the question of what lies beyond that ending point. In the latter, I try to imagine what the night sky on a planet orbiting a star at that end point would look like. I assume it would be devoid of any objects whatsoever. If I place myself an enormous distance (10 billion light years for example) beyond that end point would I look back and just see a collection of light sources in a portion of an otherwise empty dark void? I realize this may be beyond the traditional field of Astronomy but I find it fascinating in any event. Sorry for the digression.

[bystander]

Observable and visible universe are essentially synonymous. The observable universe assumes that light from the most distant objects has had time to reach us, that is, the age of the universe. The visible universe might be somewhat smaller because BBT assumes first light occurred at some later time (reionization), but for the most part the two terms are interchangeable. If you search Wikipedia for visible universe, you will end up on the same page as observable universe.

[rstevenson]

... To imagine a never-ending universe is impossible, for me anyway, and to imagine one that ends begs the question of what lies beyond that ending point. In the latter, I try to imagine what the night sky on a planet orbiting a star at that end point would look like. I assume it would be devoid of any objects whatsoever. If I place myself an enormous distance (10 billion light years for example) beyond that end point would I look back and just see a collection of light sources in a portion of an otherwise empty dark void? ...

Being a fool, I will rush in where angels fear to tread.

The concept of "outside the universe" is essentially meaningless, according to our most well-supported theories. There is no place at the "end" of the universe from which you could turn and look "out". Odd as it sounds, the universe should look more or less the same no matter where you are within it. (Even saying "within it" is wrong -- there is no outside from which you could be thought of as "within", if you see what I mean.)

The real source of this seeming paradox lies in trying to express mathematical results in a spoken language like English. To "get it" you have to speak Math, dialect Physics, a tongue insufficiently well taught in our schools.

Rob

[bystander]

What do you mean there is no End of the Universe. If that's the case, how can you have:

The Restaurant at the End of the Universe

• There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable.
  
  There is another theory which states that this has already happened.

Chapter 1

• The story so far:
  
  In the beginning the Universe was created.
  
  This has made a lot of people very angry and been widely regarded as a bad move.

Douglas Adams

[sirnelson]

Believe it or not, I do have a slight understanding of the point you are making. I have an undergrad degree in math although I have forgotton most of it by now. I do remember some odd concepts dealing with curved spaces and I assume that is along the lines of what you are saying. I will however not make any claim that I truly understand that. For me this has been a very interesting discussion and I am sure there are a few related tangents it could take to become even more interesting. Thank you all for the dialogue!

[rstevenson]

The Restaurant at the End of the Universe

One of my favourites. Try the deep-fried moose nose.

Rob

[Skooter]

This may be a silly question, but slide 9 says "Universe Age: 13.7 Billion light years"

I thought that "light year" was a measure of distance.
Should it say "13.7 Billion years?"

I just discovered this series of lectures because of a link on APOD. So far I really like what I see! Thanks for putting this together.

[geckzilla]

This is a belated reply but yes, Skooter, I think you are correct.

[starship]

There are even kilolight- megalight- and gigalight-years!! (http://en.wikipedia.org/wiki/Light-year)
Imagine a distance like a billion light-years... or give up, its just cannot be grasped by the human mind...

[TMAVRK]

The Very Large Array is NOT in Arizona. It is located in New Mexico.

[mst66186]

I've just watched Lecture 1 (and read some of the Wikipedia pages referenced in the lecture).

I don't know if this makes sense to you but it would be nice to have a mini-test to take after watching lecture one, just to make sure I'm following up to the 'correct extent'. Then, based on the results of the lecture one mini-test, I can be confident I'm studying the material at the level to get the grade I want at the end of the series (grade 'A' - obviously).

Alternatively - if there is such a test, can you tell me where to find it?

[eleanormars]

i just watched the first lecture as well. as a newbie, i find it absolutely fascinating, and also at times too abstract to wrap my mind around it. but it sure is fun trying to do it

[aghatech]

Interesting. Power point slides are also helpful.

[projecte1]

RJN! Thanks for this useful post.
I really appreciate you input the video. I am new to the world of astrology and I am slowly learning more.

With Google Sky Map this forum and perhaps I will learn something

[bystander]

Well, you're certainly not going to learn anything about astrology here.

[princessjulia]

This is my most interesting subject and i am happy to be here to view all lessions on it .. thanks for share great resource without any cost..

[Jenpicks]

hi,i´m really fascinated with this subject,thanks for shared it with us.