Monthly Archives: June 2020

Dark Science

by in Boundary Behavior, Hmmm..., Mystery, Numbers, Science | 31 Comments

Warning: Contains some “Science” Content

—

“You can’t lie with math. But it greatly aids obfuscation.”
– Sabine Hossenfelder

“Dark energy” is what scientists call a mysterious force of unknown origin that gives rise to an ever-increasing rate of expansion for the universe on the largest scales. Saul Perlmutter, Brian P. Schmidt, and Adam G. Riess were awarded the 2011 Nobel Prize in Physics for their parts in the discovery of this enigmatic form of energy, which is thought to constitute anywhere from two-thirds to three-quarters of the “stuff” of the universe.

The possibility of an expanding universe was first derived from Einstein’s “General Relativity” equations by Alexander Friedmann in 1922.  Five years later, Georges Lemaître, also came to the same conclusion, and further suggested that the observation of velocities of distant bodies should allow for an estimated value for a constant for a rate of expansion per given distance.

The light from stars is affected in much the same way as the sound-waves of an approaching siren, which will be shifted to a higher pitch, and then to a lower pitch as it passes. Likewise, light from an approaching star will be shifted to a shorter, “bluer” wavelength, while light from a receding star will be shifted to a longer, “redder” wavelength. This change in the apparent frequency of waves from a moving object is called, “Doppler shift”.

In 1929, Edwin Hubble compared both the distances and the Doppler shifts of light from forty-six galaxies, and concluded that the more distant the galaxy, the faster it was traveling away from us.  Hubble calculated that for each additional “Megaparsec” (1-million “parsecs”) of distance (about 3.26-million light-years), the light from a galaxy was red-shifted by an amount that indicated an additional 500-kilometers per second in velocity.  This meant that the universe was indeed expanding.

Although Hubble’s original value was far higher than is currently accepted due to an error in calculating distances, this rate of difference in velocity over distance became known as the “Hubble Constant”, or the “Hubble–Lemaître law”. Today (according to the source of data), its generally accepted value is between 68 and 74 km/s/Mpc. That’s to say that for every additional Megaparsec of distance, objects in the universe are moving apart by an additional 68 to 74 kilometers-per-second.  However, Dark energy, implies this value is not a constant, as it increases over time.

Aside from calculating Doppler shifts (which is itself rather involved), measuring dark energy requires accurate estimates for the distances to faraway galaxies.  The distance to nearby stars can be determined by measuring “parallax”, or the difference in the viewing-angle to a star when it’s observed from the earth while at opposite sides of the sun. 

The “parsec” (parallax arc second) is a unit of distance corresponding to a parallax-angle of one arc-second as viewed against a background of stars too distant to have any measurable movement.  But faraway galaxies are almost unimaginably distant objects, effectively that background of fixed objects against which parallax is measured.  So their distances can’t be calculated in the same way.  

To measure such vast distances, astronomers rely on a technique called the “cosmic distance ladder”.  Imagine measuring the space between two rungs on a ladder, and then noting that there are ten rungs on each ladder.  If ten ladders can be observed to reach the top of a tower where there is a known type of aircraft-warning light, then by measuring the brightness of that light one has a “standard candle”, or a light of known brightness at a known distance.  This can now be used to calculate the approximate height of any tall structures from the apparent brightness of their same types of warning lights.

While this is a greatly simplified analogy, astronomers’ fundamental standard candles are two types of stars known as “Cepheid variables”, and “Type IA supernovae”.  Cepheid variables are stars with a luminosity that varies on a regular cycle.  And in 1908, Henrietta Leavitt determined that the time-interval for the variability of a Cepheid corresponds to its luminosity.  Cepheids are bright enough to be useful for measuring distances out to around 30-Megaparsecs, and these are the kinds of stars that Edwin Hubble used to determine his (albeit incorrect) distances for his calculations.

A “Type-1A supernova” is the explosion of a specific type of massive star.  In this case, a “white dwarf” star in a binary pair steals away gas from a nearby “red dwarf” star.  Eventually, the white dwarf becomes too massive to support itself against gravity, and its core collapses in a runaway nuclear reaction that results in a “supernova” explosion.  Since these collapses and explosions always happen at the same mass, the luminosity of the explosion is also assumed to be the same.  And since supernovae are very bright, sometimes brighter than all the stars in a host galaxy, they can be seen at distances out to 10,000-Megaparsecs.  However, Type-1A supernovae are transient and unpredictable events, so their detection requires a sustained period of observation.

In 1999, Perlmutter, Schmidt, and Riess studied brightness and red-shift data gathered from more than 50 Type-1A supernovae observed by the High-Z Supernova Search Team in 1995, of which Riess was a participant.  They decided that the light from the observations was on average very slightly off from expected values for the observed red-shifts.  And from this, they concluded that a best fit for their data is a universe in which the rate of expansion has been accelerating, at least over some period over time.  Consensus among most astrophysicists is that some form of energy is driving this expansion, though there’s little agreement about its nature or its source… or in some circles, whether it even exists.

In the decades since Perlmutter’s, Schmidt’s, and Riess’ work, many more Type-1A supernovae have been observed, and there’s emerged some question regarding their application as a standard candle.  Some researchers have suggested that more recent (high “metalicity“) generations of Type-1A supernovae may have a slightly different brightness than that of their earlier counterparts.  And since very distant observations also imply that we are looking farther back into time, astronomers would also be looking at the explosions of earlier generations of stars.  This could have an effect on measurements taken from increasingly distant Type-1A supernova that might also mimic an increasing rate of expansion. 

In January of 2020, a team including the Oxford physicist, Subir Sarkar, published results from its own analysis of data gathered from hundreds of supernova observations.  Sarkar and his co-researchers concluded that the supernovae studied by Perlmutter and his team appeared as they did only because observations were concentrated in a direction that was affected by the relative motion of our local galactic region.  Accounting for this while using both the 1995, High-Z Supernova Search Team data as well as data from hundreds of other observations from various parts of the sky, Sarkar’s team found a best fit to a model that didn’t include dark energy at all. 

Since the publication of Sarkar’s and his team’s research, there have been numerous strong criticisms of its conclusion, as well as rebuttals by Sarker and others.  And despite most media dropping the topic after the first criticisms, the subject remains far from settled within academic circles.  Though it should be noted that there are other lines of research that support the idea of an accelerating rate-of-expansion for the universe, as well as other lines of research that don’t.  Regardless, the works of several high profile scientists with Nobel Prizes to their names along with anyone who has followed on their coattails are heavily invested in the existence of dark energy, so it shouldn’t be any surprise that the scientific furniture they’ve built isn’t going to be so easily tossed out. 

And after all, it’s the fate of the universe that hangs in the balance!

Post Script:  If you didn’t detect the undercurrent in my writing here, I suggest reading (or viewing) Sabine Hossenfelder’s post, “How Scientists Can Avoid Cognitive Bias“.  Just this morning, she also posted a (somewhat amusing) article and accompanying YouTube clip titled, “How to tell science from pseudoscience“, which is also worth a look.

Hungry Ghosts

by in Cambodia, Culture, Environment, Hmmm..., Humanity, Japan | 39 Comments

My family roots are essentially founded in farming. As owners of two fairly extensive tracts of arable land in Japan, two of the family’s elder males are the beneficiaries, as well as the obligated administrators of an occupation that has been officially declared a national “cultural heritage”. Agriculture is an area of particular concern to the Japanese, as the country has a long history of famine and presently cannot produce enough food for its own population.

The region near the family farmlands in the northern part of Japan’s main island of Honshu is the source of my family name. My cousin who now looks over the lands there grows various seasonal vegetables, and also inherited the workings of a not yet productive orchard started by his father. My family in Kyushu raises cattle, though about two-thirds of the animals were being kept on land owned by others at the time of my last visit. Both operations, however, include large, terraced tracts that can be seasonally flooded for the production of rice.

Rice is the staple food for half of the world’s human population, accounting for at least 20% of yearly food-calorie intake for almost 4-billion people. It’s by far the most important crop throughout Asia. China alone has irrigated more than 80-million hectares for its production, an area the size of Vietnam, Laos and Cambodia combined, and now produces three-quarters of the world’s rice. In nearby Cambodia, ninety-percent of the country’s agricultural land is used for rice production.

Relatively easy to store, transport and process into an edible form, rice has also been used as a primary form of famine relief in locations around he world. In this regard, its grains have been compared to “pearls”. But rice is also a labor-intensive crop, requiring careful land preparation and arduous handwork. And rice production alone accounts for the use of almost a third of Earth’s fresh water while creating an environment that promotes mosquito-borne diseases.  So it shouldn’t come as a surprise that the Japanese consider it an inconsiderate and unmannered act to leave even a single uneaten grain of rice from a meal.

—

Evenings in Phnom Penh, some of the shop-keepers would lay out a small cloth and carefully place a bowl of rice, or rice wrapped in banana leaves on the sidewalks outside their businesses. Often, there would be a lit candle next the rice, and perhaps a sweet banana or some other fruit. It was explained to me that these were usually left by ethnic Vietnamese as offerings to “hungry ghosts”, spirits who wandered the darkness in perpetual want.

Likewise in Japanese tradition, offerings of rice, or sake, may be left, though usually for ancestors. Such offerings of rice can usually be discerned by a pair of “hashi”, or chopsticks left standing in the rice. This is why it’s considered rude in Japan to leave hashi stuck into a bowl of rice.

Such offerings of rice will usually be left at an altar or grave, or some other place where it’s felt that the spirits can easily find them.  And after some time, the rice is simply thrown away, its essence as food having been consumed by the attending spirit. But I saw something entirely different in Cambodia.

Those nightly offerings on the streets of Phnom Penh would actually disappear. Someone would inevitably emerge from the darkness and eat them while the shop-keeper turned a blind eye.  It all seemed terribly wrong to all of my cultural perspectives.  To my Japanese mind it was disrespectful.  To my American mind, it was merely theft.

“Why do they keep leaving the offerings if people just eat them?” I asked.

My far more enlightened guide responded, “They are the hungry ghosts in this place.”