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Tuesday, September 2, 2014

The World's Funniest Joke.

You can stop looking.

Many years ago an intrepid group of anthropologists set out to examine the cold weather survival practices of the Inuit people, believing that their traditional ice and snow shelters must surely be inefficient. To determine whether this was true they took the temperature of Inuit who had passed a harsh night either in an igloo, in the body cavity of a traditionally hunted and killed member of the cetacean family known as Phocenidae or Porpoises, or in a stretched-fabric modern temporary shelter held rigid by poles of aluminum.
Two of the scientists met to compare results.
"Observe," the first said. "The Inuit who sheltered in the ice shelters actually showed a lower drop in mean body temperature than those who used the body cavity and residual warmth of recently killed mammalian cetaceans, as well as those in the stretched fabric shelters we provided."
"Sheer bosh!" exclaimed the other. "Do you mean to tell me it is always true that any shelter is worse, in the midst of a harsh Arctic night, than one made of ice and snow?"
The other retorted, "My dear colleague, I do not know if it is true for all, under all circumstances, for our study did not evaluate all options. We can, and indeed should conclude, however, that it IS true . . . for all in tents and porpoises."

What Lies Beneath: Loricifera

So in the course of procrastinating last night (if only I could get paid to do it, although probably some people would think that's exactly what I get paid to do) I ran across something interesting. 

You can basically divide all life on Earth into two groups: the eukaryotes, and everything else (which includes, mostly, bacteria and the archaea.) Eukaryotes include anything --single or multi-celled --with a membrane-bound central nucleus ("eukaryote" is from a Greek root, meaning, roughly, "good kernel.")

Virtually all eukaryotes --humans, animals, plants, fungi, many protozoans, and so on --also contain in their cells, tiny organelles called mitochondria; mitochondria are, essentially, cells-within-a-cell that allow the use of oxygen for the production of energy. (ADP+P-->oxidative phosphorylation-->ATP anybody?) Mitochondria actually existed as free-living organisms at one time; around 2 billion years ago, a bigger cell tried to eat one. The proto-mitochondrion, however, resisted digestion, and became an endosymbiont --its energy producing capabilities traded off to the host cell in exchange for a supply of glucose and, one presumes, some measure of protection from harm.

The other major endosymbiont in eukaryotic organisms is of course the chloroplast, which is found in plants, algae, and even in some unicellular eukaryotes. The chloroplast uses sunlight, water, and carbon dioxide to generate energy and make food (glucose.) An interesting thing about chloroplasts is that there has been an example of the beginnings of an endosymbiotic relationship between chloroplasts and a host cell fairly recently, in evolutionary terms --Paulinella, a photosynthetic amoeba, appears to have, at some point, ingested another photosynthetic microorganism and, apparently knowing a good thing when it saw it, decide to hang on to the chloroplasts.

For the longest time (since high school biology, basically) I was under the impression that was it: the only endosymbionts used in energy production were chloroplasts and mitochondria. As it turns out, however, there is another: the hydrogenosome. Hydrogenosomes, like mitochondria and chloroplasts, appear to be the result of endosymbiosis, and they require no oxygen. Until recently, they were thought to exist only in protozoa (they're the main energy producing organelle in Trichomona vaginalis and Plasmodium falciparum, the latter being the parasite responsible for most deaths due to malaria.)

However, in 2010, scientists investigating the depths of Mediterranean found the first known multicellular organism using hydrogenosomes --which is also the first multicellular animal known that spends its entire life in an oxygen-free environment. The critter in question is Loricifera --there are three species currently known to exist, and they're rather appealing looking, with fronds extending from a protective shell (albeit they're tiny, the biggest run to about a millimeter: giants among their kind.) The ones discovered live in a huge pool of ultra-salty water deep below the surface, at around 3000 meters, in the L'Atalante basin --the boundary between salt and fresh water, or halocline, prohibits mixing of salt and fresh water, so below the halocline the water is totally oxygen free.

Apparently they eluded detection for so long thanks to their rarity, and the extremely firm grip they keep on the bottom gravel.


Delayed Choice Quantum Eraser: Spooky Action At A Distance In Time And Space?

The physicist Richard Feynman once said, approximately, that all of quantum physics could be understood if you understood the double-slit experiment and thought through its consequences carefully.  (This is obviously in spirit, if not in reality, something of a follow-up to the LHC visit article Part III which has yet to be written.)  The double slit experiment is important because it is the experimental evidence of something often talked about but poorly understood: so-called wave-particle duality.

It was thought by Newton that light was "corpuscular" in nature; he thought it must be made up of particles.  Later it was found that if you take a beam of light, and shine it through two tall, narrow, adjacent slits, you get an interference pattern --this can only happen if light is a wave of some sort.  Even later, the photoelectric effect seemed to show the contrary: that light was indeed corpuscular in nature.

The funny thing is this: take a beam of light or some other suitably quantum-sized particle, like an electron.  Fire it through one slit: you will see a simple blurred outline, roughly in the shape of the slit: a diffraction pattern, due to the scattering of the light waves.  Fire it through two slits, and you will see an interference pattern: alternating light and dark bands, which can be interpreted as reinforcing and cancelling wave-fronts.  It would seem the case is closed: light is wave-like in nature --but the case is more complicated.

As it happens, if you are using a beam of light and you have good equipment, you can turn the intensity of the beam down until only one photon is being emitted at a time.  You will see, on your detector, only one "hit" at a time, at a specific location.  Yet, if you let the "hits" build up over time, they will eventually form an interference pattern --as if, somehow, the particle had passed through both slits at once and was somehow interfering with itself.  And this is a very funny thing.  (Here we clearly intend, "funny" to mean "intensely intuitively frustrating; Einstein, and Schrödinger and quite a lot of other physicists, philosophers, and simple well-intentioned layman have found it anything but funny.  It led to one of the best quotes in the history science, which was Schrödinger's remark about the famous equation that bears his name, and describes the wave-function of a quantum system:  "I don't like it, and I'm sorry I ever had anything to do with it.")

Now all this is already trying enough: we are unable to understand intuitively what this means, because at the physical scales our five senses can operate within we are not familiar with any such behavior.  The problem, naturally, has gotten even worse as quantum mechanics has evolved.  Einstein postulated that if you put a detector at each of the two slits, this would reveal which of the slits through which the particle had passed.  If this is the case, then the particle should, so to speak, no longer be able to pass through both slits at once --in technical terms you may say the superposition of states (slot A and slot B) has collapsed into a single discrete value.  It was not technically possible to do such experiments until the 1970s but it indeed proved true.

Now, suppose you were to somehow mark the particle so you could tell after it had passed through the slit, which one it had passed through.

As it turns out, when you do this, what you expect would happen, does.  If you know through which slit the particle passes, then the interference pattern disappears.  But suppose you could somehow erase the mark, so to speak, after the particle passed through the slit?  If we follow through the logic of the experiment, then "erasing" this quantum information should cause the interference pattern to re-appear.

The manner in which the notion has been put to the test experimentally is extremely interesting.

Take a photon source: a laser will do nicely.  Let the photons pass through two slits.  Then let the photons pass through a special prism that splits each photon into two photons.  As each pair came from a single parent they are said to be entangled --as with most common-sensible sounding terms in quantum mechanics this has a precise mathematical formulation which need not concern us here.  It broad terms, it means that the two "child" photons cannot be thought of as completely separate quantum systems: they must be described as parts of a larger quantum system.  In practical terms this means that if you measure some aspect of one "child" you will know the complementary aspect of the other without having to take a measurement of it directly.

Having started with one stream of photons, you passed them through the two slits, yielding two sets of photons.  Having passed each stream subsequently through a producer of entangled pairs, you now have four "children."  One of each set of twins is referred to technically as the "signal" photon, and the other is referred to as the "idler."

Now if you know through which slit the signal photons have passed, you should not see any interference pattern with the signal photons.  If you do not, they should create an interference pattern.  Here is the important part.  You arrange the pathways of the "idler" photons so that they arrive at one of four detectors.

At two of these detectors, you can tell through which slit the parent of the idler photon passed.  If you compare the idler photons from these detectors with the signal photons, then an interference pattern emerges.

Oddly enough, however, if you compare the signal photons with the other two detectors --at which you cannot tell through which slit the parent of the idler photon passed --then the interference pattern disappears.  You have "erased" that information.

The truly peculiar thing about this, is that you can set up your idler photon pathway so that it takes longer for the idler photons to get to the detectors than it does for the signal photons --the usual interval is 8 nanoseconds but in principle it could be as long as you like --billions of years, even.  The results would still be the same --which seems to imply that the idler photons are sending information backwards in time.  This worried a lot of people.

As it turns out, however, there is a catch: you can only observe an interference pattern for the subset of photons which you compare to the idler particles that have arrived at the detectors that erase their origin.  If you look at the whole set of signal photon detections, they do not form an interference pattern taken alone.  This does something very happy: it saves causality.

The information contained in this statement is true to the best of my knowledge and belief.