Well, we are finally back home from our Mediterranean odyssey, with stops in Greece, Israel and Italy, and ports of call in several islands, and want to clear up a few loose ends associated with that journey before coming back to future observing plans. First, I should comment about an issue that many cruisers face and that is how much weight gain is acceptable for a a two week cruise. Well, I have no idea of what a norm might be, but can comment on my own personal experience, which resulted in
9 lbs. weight gain over the two week period. I hope that a big part of this gain will just go away over the next couple of weeks as we return to normal eating patterns. Secondly, several previous posts raised the several major physics topics and textbooks that I had hoped to study and make some progress on while on vacation. I couldn't really do any work on the online general relativity course because of limited shipboard internet bandwidth. More about that course below. For the 5 available physics textbooks that I packed up for the cruise (See the November 5 post for the complete list of books), I made quite a bit of progress in "Astrophysics for Physicists" and "3K: The Cosmic Microwave Background (CMB) Radiation". Now as you recall, there were, readers of this blog, smart alecs, we will call them, who claimed that the number of martinis I would order would exceed the number of pages read. Well those smart alecs were completely wrong. I only had three lemon drop martinis and got through maybe 30-40 pages in the textbooks. I should clarify that the small number of martinis consumed was probably mostly due to recognition that the martinis did not come up to my taste expectations and that with wine and beer freely available and included with lunch and dinner, it was just not going to happen with consuming more martinis.
So, I should mention one topic I read about that was of particular interest and more general audiences as well, and that is why is the CMB fits all the characteristics of black body radiation. This means that the early universe must have been in thermal equilibrium, which means that the radiation and matter were matter were interacting and exchanging energy, even as the universe expanded. Then at about redshift z=1100, the universe has expanded and cooled enough that the radiation can freely stream without much more interaction with matter and as the universe expands the wavelength of the radiation increases and appears as microwave radiation today. The text book went in to what types of processes, such as pair creation, were present and how the interaction falls off as the universe expands, until the background is sort of frozen. Going into the details requires an understanding of how the interaction rate changes during universe expansion and is quite involved. Secondly, the textbook went on to discuss other possible interactions that could change the microwave spectrum during the continuing expansion of the universe. These additional interactions would distort the spectrum from a pure black body spectrum and even though these distortions are small, can be used as a probe for how significant these other factors were during the expansion and formation of galaxies. It was interesting and I can see that this topic is quite deep and will require more study to gain a getter understanding. So, even though we didn't get any observing in, it was nice to get indoor study into the formation and development of the universe as outlined by the CMB.
So, yes we were disappointed about missing some observing opportunities at sea and at the OCA Black Star Canyon party, but what is one supposed to do? We didn't have much observing opportunity on the cruise ship, which by the way is very brightly lit up, even though when at sea, the dark skies are very dark, and hoped to get in some observing when we got back to southern California. Well, we arrived at JFK and LAX, it was very cold and wet and raining, so no observing seemed possible. We hoped for good news about the Black Star event, but instead we go the email from OCA President, Steve, that the party had been cancelled and so we really didn't miss out after all. The cancellation email also included OCA Robert Cunningham's photo of the cloudy sky .
 |
| Cloudy weather at Black Star Canyon not good for observing and resulted in party cancellation (Courtesy use of photo forwarded by OCA Steve with photo taken by OCA Robert Cunningham) |
Well, with weather like this, you might want to check out some indoor, free internet courses in physics and in this case, general relativity. The course identified below is offered by www.coursera.org.
 |
| Introductory slide for free online course (Courtesy of www.Coursera.org) The author says he will use the "Russian style" of teaching which includes a lot of hard work and lots of technical details. (Really, just check out the next slide presented below) |
 |
| General Relativity is very mathematical and the first introductory lecture started immediately with the metric and tensor analysis. If you think this screenshot looks difficult, just keep in mind that the instructor, on the opposite side of the transparent blackboard, seems to have written all these equations in real time and backwards. (Courtesy www.coursera.org) |
So, even though a good understanding of GR is essential to working more in cosmology, you can see right away that it will require a certain level of mathematical sophistication. Maybe this is not for you, but for me, as a physicist wannabe, this is just the right kind of stuff. Now, I have had several introductory courses in GR and it keeps getting easier as I pick up more and more of the material from each course, but it is still a difficult subject.
Maybe, if your interests don't quite go in that strict mathematical approach, you still might be interested in a paper forwarded by OCA Secretary and Author, Bob. This paper, although portions of it written in the same mathematical language outline above, it is the big picture questions that the author poses that are the really interesting theme of this paper. The author outlines the case that inflation, as a great cosmological insight that explains many observations, itself does not yet have any firm foundational support. No one knows how inflation started or how it ended. This outline, similar to that outlined by Sir Roger Penrose in his next book (See the blog post of October 2, 2016), describes the same shortcoming. The other issue had to do with the expansion of the universe is described by GR and its ultimate history and future depends on the equation of state for the components that make up the universe, such as matter, both dark and ordinary, radiation and dark energy. The author describes how the equations are unconstrained and there can be many alternate paths and more data is needed to close some of the assumptions and constraints. I never got this understanding from just reading standard cosmological textbooks. This kind of big picture view of how there is still a lot of mystery is really interesting and helps me understand the limitations of certain cosmological interpretations. It is also the kind of education that one gets, not in the classroom, but by hanging out at the bar at astronomy and physics conferences and listen to what the scientists say at that time. Hey, but you already knew that is why I go to the bar anyway, right?
I know my little posse of science squad members will take a look and if anyone else has an interest in the foundations of analysis that go into the science of cosmology then check out the paper at:
https://arxiv.org/pdf/1611.03505.pdf
So, if you like some of the big picture issues raised in the paper and want to delve deeper into that subject, a good place to start is to go back and sign up for the GR course. So much of cosmology depends on GR and equation of state for matter, radiation and dark energy.
Ok, so that sounds like a lot of work. Let's leave it at that until next time,
If you are interested in things astronomical or in astrophysics and cosmology
Check out this blog at www.palmiaobservatory.com
No comments:
Post a Comment