Greetings from Palmia Observatory
Well, this week we are watching more activity at SpaceX in Boca Chica, TX.
After the successful test hop of Starship, SN5, the prototype has been transported back to the fabrication area for rework while the next serial number, SN6, has been lifted onto the launch pad structure.
|Starship SN6 lifted into place on the launch pad (Source: @BocaChicaGal)|
Starship SN6 is currently undergoing cryo-testing in preparation for its own live static fire test. It too is expected to perform its own test hop shortly. We are all waiting also for the first of the prototypes to be fitted with an actual nosecone. As you can see a lot of nosecones have been fabricated.
|Lots of Starship nosecones being fabricated (Source: RGV Aerial Photography)|
Then we will know that we are getting serious about getting this thing into orbit when the nosecones get fitted. All this testing and development is supposed to culminate in the final configuration where the Starship is mounted on top of a Supper Heavy booster. This combination will be 120 meters tall and the same 9 meters in diameter. This combination will also have nine Raptor engines in the Starship and something like 31 Raptor engines in the Super Heavy.
|The Starship with SuperHeavy booster is 120 meters in height (Source: SpaceX)|
So how is this big rocket to be manufactured and lifted onto its own launch pad? By chance, this month's issue of IEEE Spectrum had an article in it about the most powerful mobile crane in the world, the Liebherr 11200-9.1. It can lift loads 188 meters and has a lift capacity of 1200 metric tons.. The liftoff weight of the Starship with Super Heavy and both all fueled up exceeds this amount, but the rocket does not have to be lifted full of fuel, which is the heavier portion of the total weight, some similar type crane will be able to mate the two rockets on the launch pad.
|This Liebherr mobile crane can reach 188 meters (Source: Vaclav Smil, Spectrum, Aug 2020)|
So we know that there are mobile cranes that can lift the giant rocket into place. In another photo, from @BocaChicaGal, Mary, we see what to me is a prime example of the rapidity with which development and testing goes on in Boca Chica. Here we see the Raptor engine being transported to the launch pad for SN6, while in the foreground and background all sorts of construction activity is going on. We have some workers in the foreground laying rebar and getting ready to pour concrete for some new structure near the launch pad. We see the ever present Bobcats and rental trucks and activity going on in all sorts of directions. We probably wouldn't recognize much of the place since our visit there back in March.
|The Raptor engine (SN39) moves toward installation with Starship SN6 (Source: @BocaChicaGal)|
Ok, enough SpaceX news, it is now time to sit back and partake in the free, online, two weeks of lectures presented at the SLAC Summer Institute. This 48th season covers 30 lectures on "The Almost Invisibles: Exploring the Weakly Coupled Universe" from August 10-21. Previously, before travel was shutdown, I would have liked to attend this two week event and visit the SLAC facility in Stanford, but not having to travel makes listening to this series of lectures more affordable for all.
|Exploring The Almost Invisibles at 48th SLAC Summer Institute (Source: SLAC)|
I've been able to attend most of the lectures so far, many of which are over my head, but each has been informative. I have selected one lecture on the basics of cosmology and how the measurement of the CMB has enabled us to learn about and mostly understand the history of the universe to summarize here. So for instance, the next slide shows how the interaction of pressure and gravitational attraction can generate patterns or ripples of compression and over and under densities of gas in the early universe. This pattern, called Acoustic Baryonic Oscillation (BAO), shows up in the CMB measurements and the over dense regions are regions where collapse into galaxies and other structures can occur.
You have probably seen the CMB anisotropy map, like that displayed below, many times, but Gruen went over what is hidden in those small fluctuations and how the history of the universe is encoded in the BAO.
|Power spectrum of CMB shows structure variations (Source: Zeeshan Ahmed, SLAC SSI 2020)|
After the latest Planck CMB temperature measurements are processed to remove artifacts like the dipole motion caused by motion of the Milky Way towards Andromeda and other bright radio sources present today, the calculated power spectrum shows the peaks in the BAO as shown in this slide below.
These early pressure and over densities evolve to form the structure and galaxies that we see today. In this slide you see impressions of what the four major eras of evolution were like. Starting from the left we see a brief period of inflation, followed by the formation of stable hydrogen and the release of the CMB, followed by the formation of stars and galaxies and structure that we see today. The size of the universe in each of these eras is traced by the purple line in the figure.
Let's look at that purple line showing the history of the size of the universe and get a basic idea of where that came from and how it is calculated based on measurements of the CMB and BAO. In the slide below, Gruen displays the Hubble equation which is used to calculate that curve. The Hubble equation is based on general relativity and how the expansion of the universe is dictated by the amount of radiation, matter, curvature and cosmological constant present. Looking at the equation we see that the effect of radiation on the size of the universe goes down as the inverse fourth power of the size. The effect of matter goes down as the inverse third power of the size of the universe. The effect of curvature, if the universe is found to not be flat as it appears to be, affects the size as the inverse square power of the size of the universe. Finally, the effect of the dark energy term is just to increase the size of the universe as it gets bigger in size. All of this is predicted by general relativity and measurements of the amount of radiation and matter in the universe.
|History of the universe and one equation (Source: Daniel Gruen, SLAC SSI 2020 Presentation)|
This lecture reminded me of the question about entropy and how entropy changes during the evolving universe? The current position is that the universe started off in a very low entropy state at the time of the big bang and has been slowing increasing ever since then. But how do thermodynamic factors change with time as the universe expands? For instance, when it comes to expansion or compression of gases, as in our engineering thermodynamics of vapor compression cycles, we see that compression of a gas or vapor need not increase the entropy, but the transition from a liquid to a vapor will normally result in an increase in entropy. So, the question before us, as we consider the situation outside of the engineering laboratory, and look at the whole universe we must include the effects of special and general relativity.
|Vapor compression Thermodynamic Cycle (Source: Wikipedia)|
So, one good source that ties all of these topics from thermodynamics together with special and general relativity is this great textbook, from 1934, by Richard Tolman. The goal is to get a better understanding of why stars have higher entropy than the initial ball of collapsing gas. It doesn't seem to come from just compressing the gas as seen from our engineering thermodynamics example. Is it because of some feature of gravity that is not being accounted for or is it due to the fusion reaction that ultimately goes on in stars? We hope to find out as we do more of our homework on thermodynamics in stars, black holes and the expanding universe.
|Relativity Thermodynamics and Cosmology by Richard Tolman, 1934 edition|
In the 1934 edition, republished in this Dover edition, Tolman goes over the basic ways in which thermodynamic quantities, such as heat and entropy, transform under the Lorentz transforms of special relativity and further on how general relativity of curved spacetime affects those quantities. Getting into the curved spacetime transforms is beyond my capabilities right now, but let's look at how observers moving at a velocity relative to some observation point affect the value of the measurement. In the following table, abstracted from Tolman, shows how the velocity of the observer affects, respectively, the volume, pressure, energy, work, heat, entropy and temperature. Pretty neat, thanks for that Professor Tolman!
|Summary equations (Source: R. Tolman, "Relativity Thermodynamics and Cosmology, 1934)|
We see that discussions of entropy do not depend on the velocity of the observer, but that temperature measurements appear less than reported by the stationary observer. Why is entropy the only one of the thermodynamics variables that is independent of the observers velocity?
Eventually we need to make the transition to curved spacetime to see how these quantifies are affected. For instance, we want to look at such items as, "Is energy and momentum conserved in an expanding universe?" and recognize that many experts say it is not!
But that time is not now. Next, let us change gears and return to a question asked many blog posts ago about how affects of COVID-19 depend on the age of the infected. We sort of heard that older people are much more likely to suffer more than younger people. Finally, here is some actual statistics. This figure comes from a Facebook post, but seems to represent real CDC data. This data seems to indicate that the death rate for people with and without COVID-19 in the older age brackets is just about the same. It is as if the older people were just going to die anyway and COVID-19 just helped them along or is it that the number of deaths by other causes is just much larger and swamps out any effect? I am interested in following up with some expert who can explain if this is what is going on or not?
|CDC Death Statistics by age (Source: Facebook post of CDC chart, Aug 12, 2020)|
Ok, enough of death and COVID-19 statistics, let's end up with the discovery of new life encroaching on the observatory. I spotted this long tailed lizard trying to sneak into the observatory (the lizard was successful by the way), Anyway, I first thought it was a snake because of the long tail, but turned out to just be a lizard. So, we need to keep our eyes peeled for events on the ground as well as up in the sky!
|Long tailed lizard sneaks into observatory (Source: Palmia Observatory)|
Until next time, here from our burrow, stay safe, as we recover more of our freedom,