Parent attempting to get a spoonful of medicine in a toddler: “Mmmmmmn. Yummy. It tastes like candy.”
 
Tight-lipped toddler: “…” (Or a different sounding, lower-pitched “mmmmmmm”)
 
The brain has a way of isolating itself in a defensive mechanism called the blood-brain barrier. The barrier keeps stuff the brain doesn’t want from intruding. But, like all border walls, that barrier always has to deal with newfound mechanisms for penetration. On the macro scale, we see the problem with walls of any kind: The Berlin Wall was breached by individuals at first and then by a massive uprising that tore it apart. A southern USA border wall has for years had holes cut into it. When Nature can’t figure a way to breach a protective barrier except by evolution over long stretches of time, humans invent clever methods to overcome former restrictions of movement.
 
Here’s what I mean:
 
     “We finally demonstrate that the chemotactic behavior of these nanoswimmers, in combination with LRP-1 (low-density lipoprotein receptor–related protein 1) targeting, enables a fourfold increase in penetration to the brain compared to nonchemotactic systems.”*
 
We’re on the verge of developing organic mechanisms that can cross the blood-brain barrier. What’s the good in that? Delivery of therapies. What’s the bad? Unintended physical consequences to someone’s brain, and possibly some brain-altering nanoswimmer that can jump from person to person by contact.
 
So, here we are on the verge of being able to get past a major biological barrier that evolution probably began building as early as Ediacaran time, give-or-take a week, about 635 million years ago. Human ingenuity! Who woulda thunk it?
 
Actually, thinking (or thunking), the very process by which scientists can imagine and produce nanoswimmers presents its own barrier, one that might be more difficult to cross than the blood-brain barrier. I have mixed thoughts (thunks?) here.
 
We have worked for a couple of hundred millennia on devising ways to cross over into another mind. We have tried insidious propaganda, highly reasoned arguments, and even emotional entreaties, all with varying effects. Sometimes they work individually; sometimes, cooperatively. Penetrating the mind seems easy at times and difficult at other times. Mobs and fan frenzy suggest that the penetration of the mind-barrier is easy going. Toddlers who reject medicine and adamant defenders of political, religious, and philosophical views demonstrate the difficulty of breaching the mind-barrier.
 
We seem to be on a path to cross the physical barriers constructed over an eon by the brain, but we might never have an easy or predictable path to cross barriers of the mind that might be as old as 200 millennia or as young as a toddler.
 
*Joseph, Adrian, et al., Chemotactic synthetic vesicles: Design and applications in blood-brain barrier crossing. Science Advances 02 Aug 2017, Vol. 3, no. 8 e1700362
DOI: 10.1126/sciadv.1700362 
Online at http://advances.sciencemag.org/content/3/8/e1700362.full

How is it possible that even for the most significant events in human history many of us aren’t aware of their significance? The short answer: Ensuing generations never experienced the events. So, should we be surprised when two Chinese tourists in 2017 were arrested for making the Nazi salute in front of the Reichstag parliament building in Berlin? Or should we be surprised when we see tourists smiling and taking Selfies in front of the 9-11 Memorial in New York? As a species, we have tried to pass on knowledge, generation to generation, without much success for 200 to 300 millennia.
 
That’s why, also, that on-the-street reporters can encounter numerous people who seem to have little or no knowledge of the names of famous people and events in their country’s history. Are there other reasons for our ignorance? Yes, one lies in our self-absorption and our sense that time itself began when we personally began. Another lies in the abundance of events that might be called significant by various peoples—in a sense all events have some significance. And a third lies in cultural upbringing that is overridden by a desire to strike out on one’s own, to be independent. We’re fortunate that a few of us do what they can to preserve the memories of our ancestors. Unfortunately, some of those memories come with seriously defective baggage, suitcases full of misinformation and misinterpretation. No current or past commentator is devoid of personal perspective.  
 
I don’t know the motive for the actions of the Chinese tourists. Maybe it was all done “in fun” as they perceived fun. Probably, they acted in ignorance of German law that forbids such displays of Nazi symbols. And maybe the people at the 9-11 Memorial also acted out of pure “fun” and ignorance as they stood in front of a huge manmade waterfall and very tall building. We might all want to believe that if the Chinese tourists and the New York tourists had lost someone they knew personally in World War II or on 9-11-01, they would have a different perspective. The magnitude of a loss depends upon its personal meaning. What’s interesting to me is that the Chinese tourists and the NYC tourists don’t realize that without someone in the past there can be no one in the present; they are around to offend because their ancestors survived numerous significant events. Estimates for the number of deaths during WWII run as high as 70 million people, including, because it was also fought on Chinese soil, Chinese victims—but obviously not the progenitors of the offending Chinese tourists making the salute to a dead Hitler. And the 3,000 people who died on 9-11 included people who hypothetically could have been the parents or grandparents of those who visit the site for a Selfie. Obviously, however, not so, since like their Chinese counterparts, they were there to salute and/or photograph.
 
The significance of the past is irrelevant if one isn’t around in the present. Imagine, as the 1946 Jimmy Stewart movie It’s a Wonderful Life and the Stephen J. Gould book Wonderful Life ask us to imagine, what the world would be had our ancestors—human or animal—encountered a significant tragic event like WWII, 9-11, or even, for Gould, a pre-human catastrophe that ended their existence before they left a human legacy called “you.”
 
 
If you travel to Moundsville, West Virginia, you will see a “mound.” You can climb it. Mound builders made it centuries ago. We have some sense, thanks to archaeologists, of what the mound represented. We cannot know exactly its meaning for the people who constructed it, nor can we know any significant event with which it might have been associated, though we do know that it was a burial mound. But how did those ancient mound builders perceive it: Was it a sacred cemetery on which only anointed ones could stand? In climbing to its top, do we desecrate it?
 
For a species as ubiquitous as we are, places can even be redundant sites of significant events, as, for example, Manassas in Virginia is because of two Civil War battles. During those two battles, someone died before leaving a human legacy. Tourists to the battlefield are not people in direct line of progeny from someone who died there before having children. Tourists, even the most ignorant of them, have a “wonderful life” because the significant events did not affect them personally.
 
A common problem lies in how we can convey the significance of our generation to the next one. Grandparents and parents have tried to teach the lessons of their generations with varying levels of success since humans originated. Think you have any method that might succeed where they failed? Falling short of having such a method, you will see more Nazi salutes, 9-11 Memorial Selfies, and desecrated cemeteries. 

​We’re all good at detection. We detect our bodies’ needs: “I’m hungry.” We detect children’s needs: “She needs a nap.” We detect our own and others’ financial, medical, and educational needs. There are many general conditions that we detect. Detection is necessary for survival. Some place feels dangerous? Some creature appears ready to attack? Someone appears ready for an angry outburst? From experience, we detect.
 
What we detect isn’t always very specific. I know, for example, that a small child might be hungry. I don’t necessarily know what the small child wants to eat. We offer food, sometimes futilely; the child accepts or rejects. The level of my detection is only general. Maybe the important condition lies in my ability to know “in general” that the child is hungry. That detection then sets up my sundry offerings: Crackers? Milk and cookies? PB & J sandwich? Ice cream? In our daily lives detection is often very general.
 
Think neutrinos. They are really tiny and very numerous. They are hard to detect regardless of their abundance. Consider that trillions of neutrinos produced by the Sun pass every second through an area the size of an office desk surface —and when I say “through,” I mean THROUGH. Neutrinos pass through you as though you are a mere ghost. They pass through Earth as though it isn’t there. Because neutrinos are capable of passing through solids without interacting with matter except on rare occasions, physicists use giant “detectors” that weigh many tons, detectors that they place in deep mines and the newest of which weighs 70,000 tons. They need very sophisticated and large detectors if they want to identify any one of the three kinds of neutrinos: Electron neutrino, muon neutrino, and tau neutrino. The process of neutrino detection is also complicated because neutrinos can change character just as a child might say “I want peanut butter and jelly” followed by “I don’t want this; I want milk and cookies” (Observe this especially unpredictable and frustrating ability in children to change character at restaurants).
 
Now a group under the name COHERENT* has devised a detector that fulfills the 1974 prediction of Daniel Freedman that experimental neutrino detection doesn’t necessarily require an expensive, 70,000-ton buried detector like the Deep Underground Neutrino Experiment (DUNE). Instead, the group has a 32.2-pound device that “sees” neutrinos surprisingly frequently. But it has a limitation. It cannot distinguish among neutrino types. The little neutrinos are like little children—they allow us to detect their general hunger, but we have to go into something more complex to know their specific and often changing desire.
 
In physics as in life, we can detect generally. That’s easy, especially with a portable 32.2-pound neutrino detector and some commonly shared emotional experiences. Both general and specific detection are useful in both physics and life; however, we need very specific devices and methods to truly know and understand. For most of us the analysis of neutrino types is of little interest, but most of us need to analyze the nature of particular humans. Often, we assume that our general detection is sufficient as we deal with larger entities—adults. But the reality is that we’re all tiny "neutrino people" in a very big universe and that we pass through the lives of one another without detection in many circumstances all over the planet. Often, we don’t interact. We just pass through the lives of others the way neutrinos pass through us. Occasionally, however, we do interact; we bump into and make a change—either great or small. Is it strange that we don’t always know when we make such changes in others through our interaction?  It takes some sophisticated detection to determine the exact nature of “neutrino people” and the products of their interactions. It also takes a very powerful detector to determine the exact nature of the changes that interactions cause. Not everyone who is hungry will be satisfied with PB & J sandwiches. Sometimes we have to keep trying to detect that which eludes us.
 
We don’t number in the trillions per second like neutrinos passing through an office desk. There are only seven billion of us. What we should realize is that lives are always moving through other lives. And the principle of passing through applies not only to the present, but also to the past and future. You encounter the remnants of lives of people you never personally knew, and you will affect the lives of future people. You did not acquire your culture and your knowledge in a vacuum. Plato, Buddha, Confucius, Christ, and a host of other people now long gone still pass through you as do a myriad of unknowns who have shaped the world into which you were born. They pass through just as surely as neutrinos from a distant supernova have passed through you, me, and the entire planet.      
 
*ww.sciencemag.org/cgi/content/full/science.aao0990/DC1
Akimov, D., et al. Observation of coherent elastic neutrino-nucleus scattering, Science, 03 Aug 2017, DOI: 10.1126/science.aao0990 

Democritus was ahead of his time. He gave us the idea that there was on some unseen level a fundamental composition of indivisible things called atoms. Couldn’t see them, but even if you could, you couldn’t cut them up. Of course, today we know that we can “cut them up” and that they are divisible into smaller units called protons, neutrons, and electrons, and they, the first two, can be “cut up” into quarks. Someday, even those little bits of whatever might be cut into “strings.” Democritus was, regardless of his lack of knowledge derived from huge cyclotrons, accelerators, and CERN, ahead of his time.
 
Being ahead of one’s time was a bit ironic for Democritus, at least in the critical eyes of Aristotle. Here’s the story as retold by Frank N. Magill.* Some famous guy of ancient times died when an eagle dropped a turtle on his head. His contemporaries remembered that the oracle predicted he would be killed by Zeus’ lightning bolt. Okay, a turtle falling from the sky isn’t exactly a zigzag bolt of static electricity, but what are the chances of being hit by a falling turtle? Maybe Zeus forgot to recharge his lightning bolt battery that day, so he used a turtle. Democritus, as the story goes, knew about the guy’s death and the oracle’s prediction. Then one day as he was walking along the beach, he saw an eagle pick up a turtle and drop it on a rock to crack open its shell. Nifty trick, and birds using gravity to get at food is documented in our own times. Democritus recalled that the guy the turtle killed was bald. From above, he reasoned, his head might have appeared to be a rock.
 
And this is where Aristotle's criticism comes in: Aristotle faulted Democritus for seeing the past in the present when he looked at Nature.  

Democritus began a way of thinking that can be found in modern science, particularly in geology. Sir James Hutton’s Principle of Uniformitarianism (term coined by William Whewell), though modified by modern geologists, stands as a modern version of Democritus’ thinking. Hutton realized that if, as an example, streams erode their banks today, they probably eroded their banks in the past. The processes of the present are probably not much different from the processes of the past. Applied to Democritus, the idea can be reduced to saying that what has happened can re-happen. Aristotle didn’t like that. He complained that Democritus pared down his explanations of Nature to the statement, “Thus it happened formerly, also.” If eagles pick up and drop turtles today, it’s a pattern they have had. The ancient bald guy just happened to be in the wrong place at the wrong time and just happened to look from the perspective of an eagle like a rock. Democritus made a reasonable assumption based on an observation.
 
“Thus it happened formerly also” might not have been Aristotle’s way of thinking. In his criticism of Democritus, however, he missed what Democritus and the eighteenth-century “Father of Geology” Hutton had not missed. There’s a consistency to the world that we rely on if we want to achieve a scientific explanation. Anomalies are tough to deal with. So, we look for some consistency when we construct theories from hypotheses. And we do so when we deal with one another. In explaining behavior and thought in others, we are very much students in the school of Democritus and Hutton. We believe “thus it happened formerly also.” If a person was "a certain way" before, well, that’s the way the person has to be now.
 
Recognizing that people can effect change in their lives is difficult for all of us. Oh! Not in general, but specifically. That is, those whom we have known and who have “dropped turtles on rocks” still, in our way of thinking “drop turtles on rocks.” It’s in their nature, we think. If we see the past recaptured in the present in our physical surroundings, why shouldn’t we think we see the past recaptured in the present behavior and thought of those with whom we associate or with strangers we want to “explain”? We are behavioral uniformitarians, particularly in regard to "bad" behavior. For us, the past often presages the present.
 
“Formerly, also” works in physical Nature. “Formerly, also” is not necessarily applicable to human nature.

*Magill, Frank N., Ed. Masterpieces of World Philosophy, HarperCollins Publishers, 1990, p 19.