Kavli’s Institutes

When I was at MIT I worked on a cute little planet-finder satellite whose instruments were built and tested on the 5th floor of a certain Building 37. 37 was how it was known around campus, but it had an official name, too, it was the Kavli Center for Astrophysics and Space Research. Anyways, they gave me a key to the front doors for after-hours access and as I had scant few keys I took a little pride in letting it jangle around on my keychain. I ended up doing my senior thesis with this group, come spring I probably spent more nights in that building than in my dorm room, going through tank after tank of liquid nitrogen. Where I really wanted to be back then, though, was one floor up. The theoretical astrophysics at MIT happened on the 6th floor of the Kavli Building. It was much better lit, for some reason, with an open floor plan, wood doors and accents, lounges and common rooms, populated with couches, tables, coffee stations, fresh paint coated every wall. It just exuded this warmth that contrasted the long narrow bleakness of the 5th floor hall. When I took Quantum, General Relativity, I had occasion to venture up there, to drop off homework, to visit a professor, to attend office hours in one of its well-groomed nooks. But I never did work up the nerve to ask to join a theory group. I had this confidence issue that I’ve still not managed to shake completely.

Anyways that was the Kavli Center I knew at MIT. Building 37 where I studied physics and researched engineering. Fast forward a year later I would be so shocked in my sojourns to come across another Kavli Institute. Number two. This time at Stanford– KIPAC, it’s called, its hard-to-pronounce acronym short for Kavli Institute for Particle Astrophysics and Cosmology. Now this was a little different. Stanford is famously home to the longest linear particle accelerator in the world, so naturally, much of what goes on in astrophysics here acquires a particle physics tint– one of the more interesting interdisciplinary fields in my opinion. This Kavli Institute is a bit of a maze. Forget the long, straight halls of Building 37, this one’s filled with round-abouts and dead-ends. It took me 2 months to find the staircase to the second floor. Even so, out of habit I still come in on the elevator and leave through the patio. I’m working with a theory group here. So it resembles more the 6th floor than the 5th. I’ve yet to see a liquid nitrogen tank floating around the halls and that’s just fine with me. They’ve set me up in the visitor’s office and sometimes when most everyone is gone in the evenings I take off my shoes and plod around on the hardwood, marveling at just how clean and smooth the floors are.

Where there’s two, there must be more. Today I was reading an article on a rendition of Copenhagen to take place at UCSB, when I ran into mention of Kavli Institute Number 3:

Gross, director of UCSB’s Kavli Institute for Theoretical Physics, plays Heisenberg — whom he met early in his career. The play is structured around Heisenberg’s famous uncertainty principle: the dizzying notion that observing an event changes it, and so nothing can be known with precision. (…)

Aside from 9 mentions of the Nobel Prize in a 500 word article, it’s actually pretty interesting. I found it particularly curious the bit at the end, where Gross mentions having been able to ascertain the actors’ lack of scientific background from a few telling slips during the performance. Considering a play is scripted I wonder what he could mean.

Where there’s three, there must be many. So finally, today, I looked up the Kavli Institutes. 15 scattered all around the world, seeded by one Fred Kavli, physicist by training, engineer and businessman by trade, one of the world’s most successful private contractors by the age of 40– a self-made man in every way. Some of these institutes he started from scratch, some were existing organizations to which he gave huge sums of money, all in order to further three specific fields which he finds to be most promising: Astrophysics/Theoretical Physics, Nanoscience, and Neuroscience (‘from the biggest, to the smallest, to the most complex‘, he says). The goal? To seed new ideas in their earliest stages, to be the first to offer support, and no doubt to make a name for himself as one of the greatest philanthropists alive.

Right now I’m amused to read about a man like this. At this point, he has made more contribution to science as an entrepreneur than he ever would have as a research scientist or even a professor. Just something to think about.

Decisions, decisions

Spending a day in the sun. Not feeling so bad about anything at the moment.

Ran into the professor who helped me get the job at the UC. As per my usual dilly-dallying I found myself in an empty classroom several hours after the end of my section. He was on his way out and, surprised that I was still hanging around, dropped in to chat a bit.

I see why friendly people are so universally admired. I do pass the occasional resolution to be more sociable, but I can’t ever keep it up. I’ve also considered resolving to be more resolute, but even just thinking about that makes me tired. One day, maybe.

So this incorrigibly friendly and helpful man asked how everything was going, about my plans for break, ideas for life after. I reported the news that I was to get parttime funding for research at Stanford. “Well that’s great!” he said.

“But, I’ve also been offered a full-time possibility here,” I added.

“Ah, but you don’t want to do this,” he laughed. “Take the research. Definitely.”

So I will.

Cows are dipoles

A recent study of Google Earth images revealed a preferential spatial alignment for grazing and resting cattle. In a survey of over 8000 cows in about 300 pastures, the study found conclusive evidence of a significant deviation from random orientation with preference for a magnetic North-South direction. They were able to use global differences in positions to rule out the effects of wind and sun, and show a statistical correlation which favored magnetic north over geographic north as a predictor of cattle pointing direction. In other words, cows are dipoles. But they’re not the only ones. Deer show an even stronger alignment with the magnetic poles. Look at this diagram from the original paper:

A is cattle, B is roe deer, C is red deer.

That’s a great looking distribution in the middle. I wish they’d clean it up and fit to it. I expect to see a follow-up study calculating the effective magnetic dipole moment of the cow.

The theory. If you’ve ever played with two bar magnets you know there is an orientation to the magnetic attraction between them. Indeed, the magnetic field is a vector field and dipoles tend to line up along its field lines. The needle of a compass for example is a magnetic dipole. If allowed to spin freely, it will point toward magnetic north/south. A dipole in a magnetic field feels a torque which is proportional to the strength of the field and the magnetic moment of the dipole.

T is the torque, u is the magnetic moment, B is the external magnetic field (of the earth, in this case).

This torque will tend to spin it in the direction of the magnetic field line. Viewed another way, the energy of a dipole in an external magnetic field is:

The natural inclination of a system is to move from a higher energy state to a lower energy state. The lowest energy in this case is represented by the case where u and B are aligned (theta = 0), therefore their dot product is maximized, and the energy is most negative.

Now, cows are lazy, and they undergo some kind of random motion, so naturally there will be a width to the distribution of the probability that a cow will be pointing in a given direction. Now, if this random motion is associated purely with thermal energy, the pointing probability could be calculated exactly. My guess is that it’s more complicated than that. If I come up with a good way to model it, I’ll probably publish the follow-up paper.

An interesting side note is that many animals have already been well-documented to have internal magnetic sensors. Birds and salmon have been known to use magnetic field lines to navigate their migration. Apparently, even rodents possess some kind of internal magnetic compass. What they need it for is beyond me. Interestingly, some studies suggest humans who sleep oriented East-West experience shorter REM sleep periods than humans who sleep oriented North-South. REM sleep is apparently important for memory, alertness, creativity, and every other good thing our brain does. There’s something, after all, to be said for feng-shuing your room.

From randomness, order.

My life has been evolving slowly to become more and more structured and less and less what I feel like I really ought to be doing. In addition I’ve experienced a noticeable decrease in REM sleep lately as my days and nights have really filled themselves up. This is only adding to my sense of confusion.

Mondays and Fridays I teach at the UC. Mondays are discussion sections and Fridays are labs. I’ve been doing this for 3 weeks now and it hasn’t gotten any easier carrying 50 lab notebooks across Science Hill.

Tuesdays and Thursdays I tutor middle and high school students in Aptos. This last Thursday one of my duties was to help a 7th grader finish his auto-biographical slideshow presentation. His accomplishments included being the last to be cut from the basketball team and almost making the honor roll in the 5th grade. His goals were one day be richer than Bill Gates.

Wednesdays I head up to Stanford to report on the meager progress I’ve made that week in my research. This wednesday I bring up the issue of funding for probably the last time.

Yesterday I helped bartend at a frat party. Someone stole a handle of vodka and a $1.50 jug of safeway brand orange juice. A vinyl record was pilfered from the DJs. Party was eventually broken up by the police around 11:30. Pretty classy stuff. I’ve been thinking about getting a job in sustainable energy and bartending on the side.

In other news I bought a used 2000 Volkswaggen Passat with a V6 engine and a moon roof. I’m going to use it to learn how to drive stick. Also, I’ll probably use it to get around.

And move.

I don’t know where I’m going to move to come spring but I will move somewhere.

North star is an airplane

Lots of people know a little about science.

During my rather disastrous commute home from Palo Alto today a man looked over, saw the book I was reading, and started talking to me about the atomic bomb. “I’m lousy at math,” he said. “but I understand physical principles well.” This was exciting to me, so I asked him what he meant. “For example, Einstein gets the credit for the atomic bomb, but it was really M—- who did most of the work. He was Einstein’s collaborator, but no one’s heard of him cause Einstein took all the credit.” This was not a physical principle. “Lots of people worked on the atomic bomb,” I said. He ignored me. I named 5 in my head.

“I’m in school, too, you know.” He said.
“I’m not in school.”

“Have you heard of Tesla?”

Did I know that he invented a laser, that it could shoot through the earth and turn ions negative in the atmosphere so that they changed the earth’s gravity because the magnetic field of the earth goes around like this and the ions go around like this… Now environmentalists were worried about the effect so they confiscated his invention because it was capable of making the surface of the water rise into the air did you know this and then you’d have black rain, have you heard of black rain? which is iron, it would levitate things, and fish and frogs would fall out of the sky too, isn’t that wild?

I thought about that for a second. “Like in a tornado?” He continued on. The more he talked, the more excited he got, he began stuttering and saying things that were logically disconnected. Between the noise of the bus pulling itself up highway 17 and this guy’s lack of coherence, I stopped caring and returned to my book. I was just starting a chapter on standard candles and getting excited about the Cepheid variables that had made such a buzz in cosmology. I tried to remember what Feynman had said about them,

Two different populations of stars… Cepheid variables of one type… but there’s another type… universe must be twice, or three times, or even four times older than we thought!

Meanwhile, bus guy does not stop talking. “Have you heard of frictional force?” he asks. I just look at him.

He explains. Bring together 5 people… I did this with my friends. When we all rubbed our hands together we generated enough frictional energy to levitate off the ground… just our hands… He showed me his hands. And rubbed them together to demonstrate what it looked like when you rubbed your hands together. I didn’t like that very much. I wasn’t trying to ignore him, but I was pretty bored. “Cepheid variables are named after the star delta Cephei,” I read from my book. Energy force, man… I swear to god I’m not lying… highly luminous supergiant stars… I swear to god this is the truth… pulsationally unstable… periods between 1.5 and 60 days… 400 pounds, a box… I just lifted it with my bare hands…. relationship between period and flux… would have never happened if I hadn’t rubbed my hands together… you know how it feels warm when you do that?… rare stars… hey… nearest Cepheid is Polaris… difficulty is calibrating luminosity… hey… north star is a variable star. North star is a variable star. I thought there was something profound in that.

… hey! Are you listening??

Can you hear me??

“Ok look,” I hadn’t said anything in about 20 minutes. “You think I can read my book?”

He looked unhappy and I was a little sorry for it. Poor guy didn’t know anything about physical principles. He’d absorbed a couple of keywords here and there, heard about some concepts, and pieced them together into a random narrative that didn’t make a bit of sense. This guy was a little busted but it’s something I’ve been seeing a lot of lately. The assumption is that knowing the names of things is the same as knowing the things. It’s an equivalence of the scientific endeavor which is vast and noble with its by-products, and connected with the idea that the thing science should not be encouraged because of what humans do with the knowledge gained. I glanced at an open book on the dining room table today (The Omnivore’s Dilemma) which accused science of being “reductionist”:

To reduce such a vast biological complexity to NPK represented the scientific method at its reductionist worst. Complex qualities are reduced to simple quantities; biology gives way to chemistry… The problem is that once science has reduced a complex phenomenon to a couple of variables, however important they may be, the natural tendency is to overlook everything else, to assume that what you can measure is all there is, or at least all that really matters.

This criticism of the scientific method, for instance, is no criticism of the scientific method at all. It’s a criticism of human beings with limited capacity for complexity and ambiguity. If a thing can be described by a finite set of parameters, and they each have an effect on the whole, then they, by definition, can be measured (in principle, at least). Science attempts to determine some of these parameters in order to understand better a more fundamental mechanism. If we were to stop at simply describing the properties of the thing itself, then the knowledge gained is narrow and more or less useless (“stamp collecting,” as Rutherford called it), so scientists tend to move on from a particular subject after some time in search of the answers to a more interesting question. They provide documentation of their research so that others may focus on another aspect of the same topic and extend their investigation in perhaps another, also interesting, direction. This gets somehow interpreted as reduction. The actual reduction is not occurring at the level of the science, but at the level of those who are applying some small bit of knowledge gained to public policy, who are careless or pragmatic or what-else. I just can’t justify the defensiveness of the general populace when it comes to scientific principles. I can only imagine it is a reaction to the exclusivity maintained by the scientific community. The average person feels like an absolute outsider, informed by loose threads of dubious journalism which twist the truth this way and that in order to suit a certain personal world view. Then they get scared and think science is trying to take away their individuality. Lately I’ve noticed mainly two kinds of reactions to any general scientific discussion: a complete refusal to participate (“that stuff’s never made any sense to me”) and a thorough and immediate recall of every bit of scientific trivia related to the matter at hand. A general fear of the conversation.

Back on the bus, friction man was disgruntled. Mumbled something about being in the army and a gunshot to the head then stared straight ahead. I didn’t ask him to elaborate.

I did start wishing, though, that I had my pepper spray on me, pepper spray that wasn’t shaped like a toy gun (dad…). Even though that would be a pretty lame thing to do on a bus. I couldn’t read any more for having to watch him out of the side of my eyes. He fidgeted a whole bunch. 5 minutes pass. Finally, he picked up his backpack, and with the dignity worthy of a king, walked up to the only other empty seat on the bus, and sat down, 3 rows up.

I breathed a sigh of relief and read some more about standard candles.

We ended up being on that bus for 3 hours. I realized today (sitting on that bus) that Highway 17 is really the mechanism that preserves this certain “unique”-ness that folks like to attribute to Santa Cruz. In an excruciating way but mindful, discouraging newness like geography and a poorly designed transit systems only could, through its sheer stubbornness and difficulty. When the only artery in and out of a city is a winding, 2 lane “highway” through the mountains for 25 miles with a speed limit of 45, which comes to a frequent and complete halt in the case of any traffic incident or volume (google “highway 17 accidents”), a place can feel pretty isolated. Santa Cruz is less than 30 miles from the heart of the Silicon Valley. Yet it has no living industry besides tourism. It has none of the hustle-bustle intensity of its neighbors, none of the mass-produced mass-consumed mass culture, none of the ambition and restlessness. It’s idyllic– like a beautiful accident. But it’s no accident. Many people are grateful of the state of the place without knowing what they’re grateful toward. It seems to me that Santa Cruz is more a place where people come to settle down. It’s the town of Spectre in the movie Big Fish. This is where young people come to experiment with doing nothing, wind up growing old and living forever.

Jammed up end to a pseudo-science day

We were all thinking the same thing. We had a lot of time. We were 40 people sitting in silence, making private, furious plans to one day move closer to where we work. I made a flow chart.

I didn’t seem to have too many options.

We had waited at the bus stop for the 7:45 until 8:15. And now, finally on the road, the bus hadn’t moved a meter in 45 minutes. When I got sick of reading, I entertained myself by contemplating the nature of traffic jams. How, in a bottleneck-free situation, jams propagate like longitudinal waves through a medium. The cars ahead of the jam dissipate as cars behind pile on, and as long as a constant flow of cars is maintained with a flux which is high enough per unit of time for a car to get from one end of the jam to the other, the jam moves through the cars like a constant amplitude, constant velocity density wave. Much like the spiral arms of the Milky Way Galaxy. Regions of high density, which are the result of small velocity and density fluctuations in the interstellar gas, are not made of the same stars and planets and particles always, instead, stars and gases pass through these regions, like we pass through traffic jams. Eventually.

Some have even proposed that the passing of the Solar System through the spiral arms of the Milky Way could be the cause for the temperature and climate fluctuations on Earth. Much like being stuck in a traffic jam could have effects on the temperament and blood pressure of its constituents, the solar system, bathed in the cosmic rays of these more active regions, may experience noticeable changes as well. However, researchers claim to have debunked this theory using more precise mappings of the galaxy. I remember doing this lab in 8.14 (Experimental Physics) using a radio telescope to measure the abundance and redshift of hydrogen gas in the Milky Way. It was not an easy lab. Our errors were pretty huge. This was the best we could do for the location of the spiral arms.

On the other hand, if there is a bottleneck in the road, and vehicles are forced to move bumper-to-bumper, I imagine traffic could be approximated quite well by an incompressible flow with smooth boundary conditions. That’s just a flow with a constant density, or particles per unit volume, everywhere, that runs into no sudden stops or sharp corners. The key concept here in the steady state solution is then conservation of mass. We place the restriction that the rate of mass entering any imaginary volume you draw within the flow must equal the rate of mass leaving (otherwise the density within this volume would change and it would no longer be considered incompressible). If, in particular, you align your volume so that it has an area A perpendicular to the direction of flow and length x that is parallel, you can write

The above holds for all locations in the flow. This implies for any two sites

Applied to our idealized traffic situation, an expression can be found for the average speed of a vehicle stuck in the traffic queue as a function of the speed of traffic currently passing through the bottleneck and the lane reduction.

For instance, an accident causes a 3 to 1 lane reduction. This necessarily results in backed-up traffic moving at about 1/3 the speed of traffic currently passing the site of the accident. Now imagine that this is a really spectacular accident and there is a lot to see. The folks passing by the commotion want to get a good view so they’re driving 15 mph. This limits the speed of the poor blokes in the vehicles farther back to an average of about 5 mph. This is the effect of “rubbernecking”. It’s unlikely that it will end though, who doesn’t want to reap the rewards of hours of boring waiting?

(Of course there are limitations to this highly simplified model. For instance, the assumption of an incompressible flow is unrealistic when vehicle velocities are high, as safe driving practices do not dictate driving bumper-to-bumper at 45 mph. When incompressibility breaks down enter the density waves discussed earlier. In addition, since lane closures do not constitute a smooth transition but rather an abrupt change in boundary conditions, there’s a feedback mechanism which limits the speed of cars in the bottleneck according to how smoothly they can merge and how quickly they can accelerate, which then goes on to affect cars farther back in the queue.)

Anyhow, 2 1/2 hours of crawling later we got our moment. Faces went immediately to the windows.

There were 10 cop cars and 3 tow trucks at the site of the accident and one slow-moving lane of traffic. And though I rubbernecked as hard as I could, I could see no wreck in the darkness. Just 15 or so cops standing on the side of the road with their hands in their pockets. Like they were bored. Like nothing had happened at all.

Uphill both ways — a brief technical study

I have 3 parttime jobs teaching for 3 different tutoring agencies in the bay area. Yet my success with finding odd jobs of any other sort has been decidedly abysmal. My applications have thusfar been unceremoniously rejected by 3 coffee shops, 4 bars, 7 restaurants, 2 book shops, and now 1 party supplies store.

I know it’s not for lack of effort. I put on my best clothes and my best smile. I walked into each venue and introduced myself in the most graceful, cordial way I knew. I laughed when I was supposed to, nodded when the occasion was right, exuded confidence and enthusiasm out of every pore. So then why the bad luck? Recalling the several extremely positive meet-and-greets with no follow up phone calls, I deduced it must have been my resume. Too much research, not enough emphasis on customer service: I probably didn’t seem serious to them, passionate enough about the food industry to be its proper liaison. I tossed it and started over. 4 years of research was condensed into 1 line. GPA and Classes: gone. Fluency in this and the other programming languages: gone. About the only trace of my college education was a mention of my bachelor’s degree in physics. Still, though, no luck. Maybe that’ll have to go, too.

Somebody once warned me about being “branded”. I had noticed a strange phenomenon. It’s partly a sensation and partly an observation. It was that as I learned more, as I became more educated, instead of finding a world full of increasing possibility, I found my options narrowing. When I first began studying physics, it was out of curiosity. When I discovered I actually wasn’t bad at it, I continued out of satisfaction. It was only when I began thinking of graduate school out of obligation that I launched my somewhat catastrophic rebellion against the forces of inertia. The idea was to rid my head of it. To get clear enough out of the orbit of academia to take a good, hard look back… at it, and at everything else. But most of all, to prove that there was time in the world for such silly things.

The idea wasn’t to get back into academia on account of having failed at everything else.

But alas, after handing over my first and last month’s rent, there’s not much left in my bank account. And it’s back to Stanford again tomorrow. These trips are getting real expensive for me. I just wish everything didn’t have to take so damn long.

 

Lately, my life has revolved around two things: physics, and biking everywhere. As is often the case when you spend a lot of time doing two things one after another, you start looking for ways to connect the two, to integrate them into one giant hobby that just sucks up all of your time. Clearly, the end result is that I’ve been thinking a lot lately about the Newtonian physics of bicycles. Of particular interest to me was my personal ineptitude at climbing hills. It surprised even me. I decided that there must be a reason– something was standing in my way of personal achievement, and that something was probably physics.

Before attacking any problem, I first consider the answers to two questions. 1) Is it doable? That is, within bounds and reason. And 2) Is it profitable? By which I mean, will it yield a result of actual interest and relevance? Oftentimes, particularly complex problems require so many approximations that ultimately, the answer you get is an unrecognizable idealization devoid of all possible usefulness.

After I assured myself of the doability and profitability of this endeavor, I posed the question in this way. Given the dimensions and mass of my primary bicycle (and my person), what is the steepest slope I can reasonably hope to surmount assuming the maximum pedaling force I can apply is equal to my body weight? This latter assumption, as many would love to point out to me, is not necessarily true. One can theoretically apply a downward force greater than one’s weight by pulling up on the handle bars. But, since that’s not something I’m hoping to have to do in order to get up a hill, I’m sticking with my original criteria.

The constants:

• mass of bike (m): 12kg (I don’t actually know if it’s this heavy)
• mass of person (M): 48 kg (I do know that I am this heavy)
• gravitational acceleration (g): 9.8 m/s^2
• angle between normal and vector from the contact pt on the front tires to the center of mass of M+m (phi): 60 deg (assumption: geometry is symmetric wrt front and back wheels) (not necessary)
• crank length on pedal (Rc): 0.16 m
• chain ring to rear wheel gear ratio (R2/R1): 1 (I have 3 speeds on my bike, this is close to the setting on the middle lowest gear
• wheel radius (Rw): 0.34 m

This statics problem took me a lot longer to solve than I’d really be comfortable admitting. There were several computational dead ends; hair-raising crises about fundamental principles of Newtonian physics.

The most round-a-bout way of doing this problem, ever.

Ultimately, I had this to show for it. The point at which the torque exerted by my weight through the bike chain on the rear wheel of the bike can no longer be expected to propel me forward against the counter-influence of gravity: a lowly 33.2 degrees an even lowlier 22.2 degrees.

This exercise was very gratifying to me. I don’t feel nearly as bad anymore about starting a backwards roll down some of those hills.

As just a point of interest, I wondered how strong was the dependence of this angle on the weight of the rider, assuming all other parameters held constant. I hear a lot about the advantage smaller riders have on heavier riders when climbing, but at least when propulsive power comes from weight alone, I found that more massive riders have an advantage over less massive riders. Unfortunately, this advantage becomes less and less significant as weight goes up, and of course, gets all kinds of scrambled up when you throw brute force into the mix (this is why cyclists talk about power-to-mass ratios, I suppose). But for now, I find an asymptotic relation, as, I think, to be expected.

Max climbable slope (degrees) vs. cyclist mass.

When I first got to Santa Cruz, I got myself a $20 clunker from the used bike yard. It weighed about 45 lbs and sent me into crippling fits of exhaustion trying to navigate this hilly terrain. This next plot is in honor of the old bike. It’s official: while more massive people can potentially use their gumption to their advantage, more massive bikes are nothing but a pain in the ass.

Max climbable slope (degrees) vs. bike mass for a 50 kg rider.

After I finished making those graphs, I went and ate pizza and played Settlers of Catan with my housemates for 2-3 hours. And that was pretty much the highlight of my day.

The sky is full of holes

Ancient Egyptians lived inside of a great celestial sphere. To them, the sun, the stars, the moon, were all points of light plastered on the under-surface of this sphere, born each night out of the horizon as the sphere rotated east to west. All these things: stars, sun, moon, horizon, held deep wonder and spiritual meaning for the civilization. And life revolved delicately around these beliefs.

But no, the truth is more beautiful. We are points of light floating in deep space; we are one of many. I’d like to think they’d be amazed to hear it.

I remember from cosmology class the Night Sky Problem. It’s a great illustration of the many things we take for granted. In 1826 Olber asked a simple question, why is the night sky dark?, and astonished everyone. You see, back then, we believed the Universe was infinitely large and infinitely old, filled with an infinite number of stars at some finite density and luminosity. This means, intuitively (also rigorously, but that won’t be necessary here), every line of sight should end on a star. The sky should be, on average, everywhere as bright as our sun.

It was Edgar Allen Poe who preempted all the scientists by providing the first hint at a solution to the problem. Finite time. He wrote, in the rather controversial “Eureka”:

“Were the succession of stars endless, then the background of the sky would present us an uniform density… since there could be absolutely no point, in all that background, at which would not exist a star. The only mode, therefore, in which, under such a state of affairs, we could comprehend the voids which our telescopes find in innumerable directions, would be by supposing the distance of the invisible background so immense that no ray from it has yet been able to reach us at all.”

No one would be sure whether or not he was joking, (“because nothing was, therefore all things are.”), but on this topic, he would be right. The universe (that we know and live in) has a finite age. Current estimates place it at approximately 13.5 billion years. Light also travels at a finite speed. As we look deeper into space, we look further back in time. In fact, the whole history and evolution of the universe is painted right into the sky, it’s there for us to read if we know how, and where, to look. Imagine being able to look at a person, or an object, and see its whole history. This is one of the most profound things about cosmology.

The horizon distance is the distance to the edge of the current, observable universe. The distance from which light emitted immediately after the Big Bang is just now reaching the earth. This distance is very large. But it is not infinite. This is the main reason why the sky is full of holes.

But not the only. Light from the most distant sources are also redshifted dramatically as it travels to earth, by the continuing expansion of the universe. For example, the sky is nearly isotropically covered in a faint glow of microwaves from the last scattering of photons by the plasma which pervaded the early universe (at redshift 1100). Since our eyes cannot see in radio, or microwaves, or infrared, the sky appears dark to our eyes where it doesn’t, say, to a powerful radio telescope.

On the other hand, if you were to climb to Glacier Point in Yosemite and look up into the night sky there, you might not think it dark at all…

 

(This all goes back to the importance of asking questions. Easy questions. Obvious questions. Those are usually the ones most difficult to answer.)

 

Meanwhile, back on earth, my to-do list hasn’t changed in 2 weeks:

• finish cosmology problem sets
• read papers
• order b&w film

The last time I worked with film was high school. But then we had to develop our own negatives and enlarge our own prints in the dark room. For a small(?) fee of $7 here, Fuji will do all the work for you. I got my first 2 rolls of slide film back, shot with a borrowed Nikon FE film camera with a 35 mm lens and UV filter. The film is Velvia ISO 50 slide film, which is famous for its warm tones and almost offensively vivid colors.

Slides are such dainty little things.

A few I’ve scanned into the computer using AJ’s scanner. All shot during the last 2 weeks in Santa Cruz, CA.

My brain’s telling me there’s some really satisfying quality about these pictures that I can’t achieve with digital. But maybe it’s just the placebo effect. In any case, I really need to go back to Wilder Ranch.