Big Think Interview With Edward Sion

Ed Sion: Edward Sion, Professor of Astronomy and Astrophysics at Villanova University.

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Question: What hazards exist in outer space that could pose a grave threat to Earth?

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Ed Sion: Well one of the scenarios is the one regarding what our press release was about, concerning T Pyxidis.  But I think that most scenarios now, for example, trying to account for the mass extinctions that have occurred throughout geological history that the, for example, the gamma ray burst.  A burst of gamma rays from a very massive star that collapses on itself with a prompt formation of a black hole, and then with gamma ray jets that, if they’re oriented just right, the gamma ray burst will be directed at Earth.  These could be potentially devastating, the gamma ray bursts. 

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In addition to that, there is a lot of debris in our solar system that was part of the fundamental building blocks of the solar system.  Primordial matter is what we call it.  Pristine chemical composition.  There’s been no chemical alteration.  The comets are good examples of that.  And some of the asteroids are pretty primitive, that is they have a composition that is very pristine and primordial.  It has been altered by geological evolution.  That is, they haven’t been incorporated in large bodies that undergo geological evolution.  So, these are the basic building blocks.  Well, these building blocks, they’re out there and of course they can potentially collide with the planets, including Earth.  And in fact this is how we think the moon originated. 

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The most widely held theory for the origin of the moon is the giant impacter theory where billions of years ago, after Earth had developed an iron core, after it had what we call it differentiation, where the heavy elements sink to the center of a newly formed planet and the lighter elements float to the surface because of their different density, that Earth once it differentiated early in the history of the solar system when collisions with other bodies was more frequent, earth was struck by a Mars-sized intruder body.  That then liquefied a large portion of the Earth’s mantel at the collision site and ejected this liquid rock out into space.  This liquid rock then cooled and solidified and then reassembled itself by gravity and that’s what we have now, according to this theory as the present day moon.  It eventually then suffered other collisions, the moon suffered other collisions. That gives us the Man in the Moon appearance.  The lunar seas, for example, those blue patches are actually gigantic impact basins that have been flooded with lava, with liquid rock during lunar volcanism, during volcanic activity in lunar history. 

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So, these collisions happened much more frequently in the past, but that doesn’t rule out that they can’t happen now.  So, I think it’s an area that is really deserving of a lot of exploration as is being done now.

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Question: How do you rate the danger of an asteroid or comet impact happening within our lifetimes?

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Ed Sion: Well, within the human lifespan, it’s a very, very low probability.  But on the other hand, one cannot rule it out.  There are three families of asteroids that actually have the potential of colliding with Earth, the Amore Asteroids, the Apollo Asteroids, and the Aten Asteroids. 

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The Apollo Asteroids actually have orbits that are internal to Earth’s orbit and they’re perhaps the most likely, the Apollo Asteroids.  And they are being monitored very carefully by telescopic patrol observatories that have been set up.  And if one of the Apollo Asteroids were to enter into collision course with Earth, hopefully we’d have enough warning, but we do in fact have the technology now and in the future to intercept and possibly deflect such a body.  But during the span of a human lifetime, it’s not likely.  It’s rather improbable that something large enough to do a great deal of devastation of the globe would happen. 

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Now, there was an event in 1908, the Tunguska event, that appears to be a porous primitive asteroid that detonated, that exploded above the ground and this leveled an entire forest in central Siberia near the Tunguska River.  But fortunately the area was very sparsely populated and there were no recorded human fatalities.  But if that event had happened a few hours before, in other words, if it had happened – if the detonation had happened over the ocean, that could have generated tidal waves, tsunamis, and that could have had a devastating effect on the coast lines.  So, it was really a lucky thing that the Tunguska even occurred over central Siberia and not over a populated area.  Like for example in Western Europe.

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Question: What would actually happen if an asteroid or comet threatened us in the near future?

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Ed Sion: Well, I presume that our leadership would meet with NASA officials and plan to intercept such a body with either a kinetic energy device, a missile that would ram into it, but they would have to be very careful because you don’t want to fragment it too much.  You don’t want to fragment it in such a way that the fragments themselves would enhance the devastation.  So, you want to make sure it has to be carefully calculated.  But I think this kind of scenario has been anticipated and I think that both with our space program, with other space programs, the Russian space program, the Chinese, I think there are plans in case of such an event.  And of course you would want to avoid worldwide panic and that kind of thing.  I think the details remain to be seen, but such plans have been in the works in case of, for example, an Apollo Asteroid being perturbed into a collision with us, with Earth.

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Question: What is a Type 1A supernova?

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Ed Sion: A Type 1A Supernova is thought to be a white dwarf that undergoes total thermonuclear detonation.  It explodes and completely obliterates itself leaving no remnant.  For example, we have yet to detect a neutron star or a black hole remnant of a Type 1A supernova explosion.  It appears that the stellar explosion complete destroys the star.  This explosion is extremely energetic.  The amount of energy release is approximately 10 to the 51 – 10 to the 52 ergs of energy.  In other words, a type 1A supernova can outshine the galaxy it’s in.  The entire galaxy for a short time.  And so, they are extremely energetic.

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Question: What properties of the T Pyxidis binary system make it a likely candidate for going supernova?

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Ed Sion: Yes.  T Pyxidis is a recurrent nova, not a supernova, but a classical nova, but it recurs.  Most classical novae we see only once.  T Pyxidis has a classical nova explosion every roughly 20 years.  And this continued from the early 1890s until 1967.  So, there were five nova explosions interspersed every roughly 20 years up until the 1967 explosion. Since 1967, this 20 year cycle has disappeared.  Nothing has happened yet.  In other words, it’s 44 years overdue for the next thermonuclear explosion. 

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What happens in a recurrent nova, and the reason I distinguish it from the supernova is the recurrent nova is a white dwarf.  This is a star about the size of Earth, but it has an extremely high density.  The density is a hundred million grams in a cubic centimeter.  Except for a massive white dwarf, a hundred million grams in a cubic centimeter, which means a thimbleful of this material, would be hundreds of tons if we weighed it here on earth. 

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What happens is, the white dwarf is so dense that the electrons surrounding the nuclei have all been stripped away from the nuclei and the electrons are actually forced to forma separate gas.  We call it a generate electron gas.  What happens is, when you squeeze matter tighter and tighter, there’s a principle in physics called the Pauli Exclusion Principle that states that no more than two electrons with opposite spins can occupy the same energy state.  So, what happens is, when you squeeze matter tighter and tighter to higher density, there are fewer and fewer energy states available for the electrons to occupy because all the lowest lying energy states are filled first.  So the electron is forced to move very, very fast and it can’t slow down.  It can’t de-excite because the Pauli Principle prevents it.  And so what happens is, the electrons move extremely fast and as the density goes up, they move faster and faster and that exerts pressure.  Well, it’s the pressure of these degeneral electrons, the degeneral electron gas, that prevents gravity from pulling this stuff in.  But what happens is that as the white dwarf mass increases, there’s an ultimate mass limit called the Chandrasekhar Limit beyond which a white dwarf cannot exist.  Because at the Chandrasekhar Limit the degenerate electron gas pressure can no longer withstand the pull of gravity.  It can no longer balance gravity and prevent the collapse of the white dwarf. 

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Type 1A supernovae occur very close to the Chandrasekhar Limit.  When the white dwarf mass is very close to the Chandrasekhar Limit, T Pyxidis has a white dwarf which is very close to the Chandrasekhar Limit.  Its presently determined mass, fairly reliably well-determined, is 1.37 solar masses.  The Chandrasekhar Limit for carbon oxygen white dwarf is 1.44 solar masses.  So, it doesn’t have much more material to accumulate until it reaches the Chandrasekhar Limit in which case you would have instantaneous collapse.  But just before that happens, as the white dwarf grows in mass, the compressional heating, the weight of the material from the neighboring star from its companion presses down and raises the temperature high enough to detonate carbon.  That is to cause the carbon nuclei inside the white dwarf to fuse together, releasing energy. 

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And so, that is what we call a detonation and that’s, the T Pyxidis we believe is very close to that point where a little bit more mass accreted onto the white dwarf will lead to so much heating that the temperature will rise to a few billion degrees detonating carbon.  But the carbon, when it ignites, through fusion it ignites, it’s explosive because this weird gas, this degenerate electron gas, unlike an ideal gas like what the sun is made, or the air we breathe where it heat it and it expands, the degenerate electron gas has no sensitivity to temperature, so it doesn’t know it’s being heated.  In other words, the heat builds up, the nuclear reactions occur faster and faster and faster, but there’s no compensating expansion to cool off.  And so it’s like a time bomb.  Energy builds up very rapidly and you get a tremendous thermonuclear explosion.  That’s a type 1A supernova.

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That is, a class – a classical nova takes place when the accreted hydrogen burns.  But it burns in a degenerate region and you get a classical nova explosion.  That’s about 10 to the 45 ergs of energy.  It’s a million times less energetic than a supernova.  The supernova I’m talking about is the carbon nuclei, not the hydrogen, accreted hydrogen, but the carbon nuclei detonate and fuse together and that’s a type 1A supernova.  That will happen to T Pyxidis when it reaches the – close to the Chandrasekhar Limit.

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Question: How soon do you predict that this could happen?

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Ed Sion: At the present rate of accretion that our modeling indicates for T Pyxidis, it will take another 10 million years, roughly 10 millions years to reach 1.4 solar masses.  If the present mass of the white dwarf is 1.37 solar masses and if the accretion rate that we’ve estimated from our accretion disk model fitting, from theoretical models of accretion disk, there’s a pancake of matter surrounding the white dwarf.  A pancake-shaped disk of gas we call an accretion disk.  And that accretion disk is adding material to the white dwarf.  But at the rate at which it is adding material to the white dwarf, it’s going to be another 10 million years, roughly before the Chandrasekhar Limit is reached.

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Question: What would happen to Earth if a nearby star went supernova?

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Ed Sion: Yes.  What will happen is that as the interior – the core of the white dwarf becomes hotter and hotter due to the compression and the temperature gets up into a few billion degrees, the ignition temperature of carbon will be reached.  That is, carbon will be able to undergo carbon on carbon fusion with the release of energy.  This will start out, according to supernova models that have been carried out in the last few years; this will start out as what we call a deathlagration.  A burning front will propagate, will move outward at subsonic speeds, but as this burning front moves out, very soon it will turn into a supersonic burning front.  You’ll have a breakout of the shock wave, or blast wave from this thermonuclear explosion.  That breakout will, should – will produce a burst of gamma rays and hard x-rays – very high energy radiation for a few seconds.  This radiation, if the supernova is close enough.  This radiation could then affect earth.  In other words, you would have input of hard x-rays and gamma rays into our atmosphere.  This could introduce chemical reactions producing nitrous oxides which could then, eventually destroy the ozone layer.  That’s the first thing you think about is if the ozone layer is destroyed, then very high energy radiation is very lethal to DNA, it would destroy the biosphere.  But the supernova has to be close enough. 

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Now, Type 1A supernovae, they’re more common than the Type 2.  The Type 2 supernova, when the ordinary person thinks of a Type 2 supernova, when a public thinks of a normal supernova, they think of a huge massive star that collapses in on itself and produces a black hole or a pulsar at the center and then this high velocity expanding gas.  That type of supernova called a Type 2 Supernova comes from very massive stars that are very luminous before they went supernova.  They can be seen at great, great distances.  What makes a Type 1A supernova really unusual in that regard is that a white dwarf is very dim.  And even white dwarfs in close binaries where mass transfers are going on, they’re really very faint.  You don’t see them out to very long distances, and they are a more common type of star.  And therefore, since they are more common and fainter, they really pose some reason to be concerned because you don’t see them as easily as more massive stars that are much more luminous.  So, I think the main thing that one might be concerned about is the input of high radiation into our atmosphere.  But the supernova – if you go on the basis of Type 2 Supernovae, then the current estimates are that if the Type 2 Supernova is within roughly 30 light-years, 30 or 40 light years, or closer, then you’d really have massive input of high radiation.  But that’s for Type 2 supernovae.

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My collaborator, Dr. Patrick Godon at Villanova, just did a quick back of the envelope calculation and determined that if you had, within a thousand parsecs, a Type 1A supernova go off, and if it was a low tilt such as at the accretion disk and material didn’t block the breakout of the blast, you would have a burst of gamma rays that would essentially be as bright as the sun and the estimate by Peter **** is that 10 to the 48, or 10 to the 50 ergs per second of hard x-rays and gamma rays would be emitted.  And we don’t know exactly how far away – we know that it’s closer than a thousand parsecs, but how much closer.  Our best estimates right now are – the models allow it to be even as close as 500 parsecs.  But that may be too far for it to do real damage to Earth, but we’re still working on this and we’re submitting a paper to the Astrophysical Journal Letters on this topic.

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Question: If nothing destroys Earth from the outside, how will the world end?

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Ed Sion: I think the world would end, leaving out all these other catastrophes and leaving aside all the possibilities that they could completely destroy Earth, which is not clear.  I think that the real end of Earth will take place when the sun, which is now a very average star on what we call the main sequence stage of evolution, when the sun runs out of hydrogen in its core.  It’s building up helium right now.  When this happens, the sun will drastically change its structure.  When it uses up hydrogen it no longer has thermonuclear fusion energy to provide its luminosity.  In other words, it's shining because of its thermonuclear fusion of hydrogen to helium.  When that hydrogen fuel source runs out, the sun will drastically change its structure and evolve into what we call a red giant star.  A red giant star is one like, for example, you may be familiar with Antares, which is the brightest star in the constellation Scorpius.  It’s a very red star.  It’s a red super giant star; another example is Betelgeuse in the constellation Orion, a famous wintertime constellation here in the northern hemisphere.  These stars, these red supergiants, for example Antares, if you placed it where the sun is located our orbit would be inside of that star. 

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So I think the ultimate end of the earth is going to be when the sun expands to a red giant.  Its outer layers swell up to beyond 93 billion miles; Earth will then start to experience viscous drag as it orbits the red giant sun.  This viscous drag will cause the orbit of earth to decay much like an artificial satellite we launch around Earth will eventually burn up in the atmosphere.  Earth will eventually be incinerated inside the sun.  Mercury, Venus, and Earth, and possibly Mars will undergo what we call death spirals.  Their orbits will decay as they loose orbital angle due to the viscous drag they will decay and spiral into the sun where they encounter very high temperatures and essentially Earth will vaporize. 

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Now this won’t happen for at least, well the sun has approximately 5.4 billion more years as a main sequence star.  Then a few hundred million years beyond that.  So, I would say, in roughly six billion years from now, the inter planets should be engulfed by the giant sun.  But by then, presumably advanced life here on earth will have colonized other worlds and so we don’t have to worry about it.  But I think that’s perhaps the best answer to your question is that eventually it’s got to happen.  The sun will become a red giant star and the inner planets will then decay and burn up inside the sun, vaporize.  And then Jupiter will start to accumulate mass and if Jupiter accumulates more hydrogen-rich gas, than its present mass, its present mass is 1/1000 of the sun’s mass.  If Jupiter creates about, I’d say roughly reaches 10 times It’s present mass, and it could do this by sweeping up solar gas as it orbits the sun, or the future giant sun, it could undergo a thermonuclear ignition and become a star and so then you’d have the sun and Jupiter as a binary system.  But this is, of course, something that is billions of years into the future.

Recorded on January 20, 2010
Interviewed by Austin Allen

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A conversation with the astronomer and astrophysicist at Villanova University.

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Why compassion fades

A scientific look into a ubiquitous phenomenon.

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Sex & Relationships

One victim can break our hearts. Remember the image of the young Syrian boy discovered dead on a beach in Turkey in 2015? Donations to relief agencies soared after that image went viral. However, we feel less compassion as the number of victims grows. Are we incapable of feeling compassion for large groups of people who suffer a tragedy, such as an earthquake or the recent Sri Lanka Easter bombings? Of course not, but the truth is we aren't as compassionate as we'd like to believe, because of a paradox of large numbers. Why is this?

Compassion is a product of our sociality as primates. In his book, The Expanding Circle: Ethics, Evolution, and Moral Progress, Peter Singer states, "Human beings are social animals. We were social before we were human." Mr. Singer goes on to say, "We can be sure that we restrained our behavior toward our fellows before we were rational human beings. Social life requires some degree of restraint. A social grouping cannot stay together if its members make frequent and unrestrained attacks on one another."

Attacks on ingroups can come from forces of nature as well. In this light, compassion is a form of expressed empathy to demonstrate camaraderie.

Yet even after hundreds of centuries of evolution, when tragedy strikes beyond our community, our compassion wanes as the number of displaced, injured, and dead mounts.

The drop-off in commiseration has been termed the collapse of compassion. The term has also been defined in The Oxford Handbook of Compassion Science: ". . . people tend to feel and act less compassionately for multiple suffering victims than for a single suffering victim."

That the drop-off happens has been widely documented, but at what point this phenomenon happens remains unclear. One paper, written by Paul Slovic and Daniel Västfjäll, sets out a simple formula, ". . . where the emotion or affective feeling is greatest at N =1 but begins to fade at N = 2 and collapses at some higher value of N that becomes simply 'a statistic.'"

The ambiguity of "some higher value" is curious. That value may relate to Dunbar's Number, a theory developed by British anthropologist, Robin Dunbar. His research centers on communal groups of primates that evolved to support and care for larger and larger groups as their brains (our brains) expanded in capacity. Dunbar's is the number of people with whom we can maintain a stable relationship — approximately 150.

Some back story

Professor Robin Dunbar of the University of Oxford has published considerable research on anthropology and evolutionary psychology. His work is informed by anthropology, sociology and psychology. Dunbar's Number is a cognitive boundary, one we are likely incapable of breaching. The number is based around two notions; that brain size in primates correlates with the size of the social groups they live among and that these groups in human primates are relative to communal numbers set deep in our evolutionary past. In simpler terms, 150 is about the maximum number of people with whom we can identify with, interact with, care about, and work to protect. Dunbar's Number falls along a logorithmic continuum, beginning with the smallest, most emotionally connected group of five, then expanding outward in multiples of three: 5, 15, 50, 150. The numbers in these concentric circles are affected by multiple variables, including the closeness and size of immediate and extended families, along with the greater cognitive capacity of some individuals to maintain stable relationships with larger than normal group sizes. In other words, folks with more cerebral candlepower can engage with larger groups. Those with lesser cognitive powers, smaller groups.

The number that triggers "compassion collapse" might be different for individuals, but I think it may begin to unravel along the continuum of Dunbar's relatable 150. We can commiserate with 5 to 15 to 150 people because upon those numbers, we can overlay names and faces of people we know: our families, friends and coworkers, the members of our clan. In addition, from an evolutionary perspective, that number is important. We needed to care if bands of our clan were being harmed by raids, disaster, or disease, because our survival depended on the group staying intact. Our brains developed the capacity to care for the entirety of the group but not beyond it. Beyond our ingroup was an outgroup that may have competed with us for food and safety and it served us no practical purpose to feel sad that something awful had happened to them, only to learn the lessons so as to apply them for our own survival, e.g., don't swim with hippos.

Lapses

Imagine losing 10 family members in a house fire. Now instead, lose 10 neighbors, 10 from a nearby town, 10 from Belgium, 10 from Vietnam 10 years ago. One could almost feel the emotion ebbing as the sentence drew to a close.

There are two other important factors which contribute to the softening of our compassion: proximity and time. While enjoying lunch in Santa Fe, we can discuss the death toll in the French revolution with no emotional response but might be nauseated to discuss three children lost in a recent car crash around the corner. Conflict journalists attempt to bridge these geotemporal lapses but have long struggled to ignite compassion in their home audience for far-flung tragedies, Being a witness to carnage is an immense stressor, but the impact diminishes across the airwaves as the kilometers pile up.

A Dunbar Correlation

Where is the inflection point at which people become statistics? Can we find that number? In what way might that inflection point be influenced by the Dunbar 150?

"Yes, the Dunbar number seems relevant here," said Gad Saad, PhD., the evolutionary behavioral scientist from the John Molson School of Business at Concordia University, Montreal, in an email correspondence. Saad also recommended Singer's work.

I also went to the wellspring. I asked Professor Dunbar by email if he thought 150 was a reasonable inflection point for moving from compassion into statistics. He graciously responded, lightly edited for space.

Professor Dunbar's response:

"The short answer is that I have no idea, but what you suggest is perfect sense. . . . One-hundred and fifty is the inflection point between the individuals we can empathize with because we have personal relationships with them and those with whom we don't have personalized relationships. There is, however, also another inflection point at 1,500 (the typical size of tribes in hunter-gatherer societies) which defines the limit set by the number of faces we can put names to. After 1,500, they are all completely anonymous."

I asked Dunbar if he knows of or suspects a neurophysiological aspect to the point where we simply lose the capacity to manage our compassion:

"These limits are underpinned by the size of key bits of the brain (mainly the frontal lobes, but not wholly). There are a number of studies showing this, both across primate species and within humans."

In his literature, Professor Dunbar presents two reasons why his number stands at 150, despite the ubiquity of social networking: the first is time — investing our time in a relationship is limited by the number of hours we have available to us in a given week. The second is our brain capacity measured in primates by our brain volume.

Friendship, kinship and limitations

"We devote around 40 percent of our available social time to our 5 most intimate friends and relations," Dunbar has written, "(the subset of individuals on whom we rely the most) and the remaining 60 percent in progressively decreasing amounts to the other 145."

These brain functions are costly, in terms of time, energy and emotion. Dunbar states, "There is extensive evidence, for example, to suggest that network size has significant effects on health and well-being, including morbidity and mortality, recovery from illness, cognitive function, and even willingness to adopt healthy lifestyles." This suggests that we devote so much energy to our own network that caring about a larger number may be too demanding.

"These differences in functionality may well reflect the role of mentalizing competencies. The optimal group size for a task may depend on the extent to which the group members have to be able to empathize with the beliefs and intentions of other members so as to coordinate closely…" This neocortical-to-community model carries over to compassion for others, whether in or out of our social network. Time constrains all human activity, including time to feel.

As Dunbar writes in The Anatomy of Friendship, "Friendship is the single most important factor influencing our health, well-being, and happiness. Creating and maintaining friendships is, however, extremely costly, in terms of both the time that has to be invested and the cognitive mechanisms that underpin them. Nonetheless, personal social networks exhibit many constancies, notably in their size and their hierarchical structuring." Our mental capacity may be the primary reason we feel less empathy and compassion for larger groups; we simply don't have the cerebral apparatus to manage their plights. "Part of friendship is the act of mentalizing, or mentally envisioning the landscape of another's mind. Cognitively, this process is extraordinarily taxing, and as such, intimate conversations seem to be capped at about four people before they break down and form smaller conversational groups. If the conversation involves speculating about an absent person's mental state (e.g., gossiping), then the cap is three — which is also a number that Shakespeare's plays respect."

We cannot mentalize what is going on in the minds of people in our groups much beyond our inner circle, so it stands to reason we cannot do it for large groups separated from us by geotemporal lapses.

Emotional regulation

In a paper, C. Daryl Cameron and Keith B. Payne state, "Some researchers have suggested that [compassion collapse] happens because emotions are not triggered by aggregates. We provide evidence for an alternative account. People expect the needs of large groups to be potentially overwhelming, and, as a result, they engage in emotion regulation to prevent themselves from experiencing overwhelming levels of emotion. Because groups are more likely than individuals to elicit emotion regulation, people feel less for groups than for individuals."

This argument seems to imply that we have more control over diminishing compassion than not. To say, "people expect the needs of large groups to be potentially overwhelming" suggests we consciously consider what that caring could entail and back away from it, or that we become aware that we are reaching and an endpoint of compassion and begin to purposely shift the framing of the incident from one that is personal to one that is statistical. The authors offer an alternative hypothesis to the notion that emotions are not triggered by aggregates, by attempting to show that we regulate our emotional response as the number of victims becomes perceived to be overwhelming. However, in the real world, for example, large death tolls are not brought to us one victim at a time. We are told, about a devastating event, then react viscerally.

If we don't begin to express our emotions consciously, then the process must be subconscious, and that number could have evolved to where it is now innate.

Gray matter matters

One of Dunbar's most salient points is that brain capacity influences social networks. In his paper, The Social Brain, he writes: "Path analysis suggests that there is a specific causal relationship in which the volume of a key prefrontal cortex subregion (or subregions) determines an individual's mentalizing skills, and these skills in turn determine the size of his or her social network."

It's not only the size of the brain but in fact, mentalizing recruits different regions for ingroup empathy. The Stanford Center for Compassion and Altruism Research and Education published a study of the brain regions activated when showing empathy for strangers in which the authors stated, "Interestingly, in brain imaging studies of mentalizing, participants recruit more dorsal portions of the medial prefrontal cortex (dMPFC; BA 8/9) when mentalizing about strangers, whereas they recruit more ventral regions of the medial prefrontal cortex (BA 10), similar to the MPFC activation reported in the current study, when mentalizing about close others with whom participants experience self-other overlap."⁷

It's possible the region of the brain that activates to help an ingroup member evolved for good reason, survival of the group. Other regions may have begun to expand as those smaller tribal groups expanded into larger societies.

Rabbit holes

There is an eclectic list of reasons why compassion may collapse, irrespective of sheer numbers:

(1) Manner: How the news is presented affects viewer framing. In her book, European Foreign Conflict Reporting: A Comparative Analysis of Public News, Emma Heywood explores how tragedies and war are offered to the viewers, which can elicit greater or lesser compassionate responses. "Techniques, which could raise compassion amongst the viewers, and which prevail on New at Ten, are disregarded, allowing the victims to remain unfamiliar and dissociated from the viewer. This approach does not encourage viewers to engage with the sufferers, rather releases them from any responsibility to participate emotionally. Instead compassion values are sidelined and potential opportunities to dwell on victim coverage are replaced by images of fighting and violence."

(2) Ethnicity. How relatable are the victims? Although it can be argued that people in western countries would feel a lesser degree of compassion for victims of a bombing in Karachi, that doesn't mean people in countries near Pakistan wouldn't feel compassion for the Karachi victims at a level comparable to what westerners might feel about a bombing in Toronto. Distance has a role to play in this dynamic as much as in the sound evolutionary data that demonstrate a need for us to both recognize and empathize with people who look like our communal entity. It's not racism; it's tribalism. We are simply not evolved from massive heterogeneous cultures. As evolving humans, we're still working it all out. It's a survival mechanism that developed over millennia that we now struggle with as we fine tune our trust for others.

In the end

Think of compassion collapse on a grid, with compassion represented in the Y axis and the number of victims running along the X. As the number of victims increases beyond one, our level of compassion is expected to rise. Setting aside other variables that may raise compassion (proximity, familiarity etc.), the level continues to rise until, for some reason, it begins to fall precipitously.

Is it because we've become aware of being overwhelmed or because we have reached max-capacity neuron load? Dunbar's Number seems a reasonable place to look for a tipping point.

Professor Dunbar has referred to the limits of friendship as a "budgeting problem." We simply don't have the time to manage a bigger group of friends. Our compassion for the plight of strangers may drop of at a number equivalent to the number of people with who we can be friends, a number to which we unconsciously relate. Whether or not we solve this intellectual question, it remains a curious fact that the larger a tragedy is, the more likely human faces are to become faceless numbers.