Into The Microscopic

Technology has allowed humanity to extend its vision to scales of reality that our ancestors could have never imagined. Ever more advanced telescopes are allowing us to see the birth pangs of the universe and the formation of the very first large scale objects. In contrast, ever more advanced microscopes are allowing us to see the very structure of all normal matter. It seems like scientists are in a race to see who can see further and deeper faster; and there may not be an “end” or “bottom” in either direction.

few days ago an epic milestone into new realities was reached when a team of physicists captured the first ever image of a hydrogen atom’s orbital structure. This was done using a quantum microscope, which should help physicists better understand the way atoms behave and interact.

Below is a ode to the microscopic. I have assembled images we have taken of objects at ever-decreasing size. The purpose of this exercise is to realize that at every scale of reality there is beauty and new wonder. Every scale of reality seems to be like a world unto itself, just like we imagine our “middle world” to be. Enjoy!

Largest known bacteria (0.001 m) (Image Credit / teachoceanscience.net)

Largest known bacteria (0.001 m) (Image Credit / teachoceanscience.net)

Human egg (0.0001 m) (Image Credit / thetimes.co.uk)

Human egg (0.0001 m) (Image Credit / thetimes.co.uk)

Cell nucleus (0.00001 m) (Image Credit / wikipedia.org)

Cell nucleus (0.00001 m) (Image Credit / wikipedia.org)

X Chromosome (0.000001 m) (Image Credit / scienceclarified.com)

X Chromosome (0.000001 m) (Image Credit / scienceclarified.com)

AIDS Virus (0.0000001 m) (Image Credit / science.nationalgeographic.com)

AIDS Virus (0.0000001 m) (Image Credit / science.nationalgeographic.com)

Hydrogen Atom's Electron Orbital (0.00000000001 m) (Image Credit / i09.com)

Hydrogen Atom’s Electron Orbital (0.00000000001 m) (Image Credit / i09.com)

Also, this is fun.

What do you think of the first picture of an electron orbital?  Let Cadell know on Twitter!

 

 

 

 

 

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Fishing With Gorillas!

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Image Credit / GorillaDoctorsBlog.org

Gorilla culture and tool use is currently shrouded in relative mystery when compared to our understanding of other great apes.  For example, landmark behavioural studies detailing technological variation and distribution have been published for all great apes except gorillas (e.g., bonobos, chimpanzees, orangutans).

In the major gorilla tool use study I am aware of, gorillas were observed engaging in behaviours that can only reasonably be asserted to be technologically complex.  In one situation a gorilla was observed using a stick as a walking stick to aid in balance when crossing a river.  In another situation a gorilla was observed using shrubs to construct a bridge to cross a river.  Both of these observations demonstrate that gorillas have a very complex understanding of how physical systems work.  Furthermore, it is evidence that gorillas have a well-developed understanding of physical systems that extends beyond the acquisition of food.

In most situations throughout the animal kingdom, tool use is stimulated by an inaccessible and valuable nutritional resource.  This is true for New Caledonian crows, bearded capuchin monkeys, bottlenose dolphins, and most other tool using species.  Tool use that is directed towards non-food related goals is theorized to develop later.  So considering that gorillas have already been observed using tools for non-food related goals, it logically follows that they should have a tool kit that involves tools for procuring food.

Gorilla Doctors Blog is reporting that just such an observation has now been made.  The observation was made by Jean Felix, a medical doctor who was making a routine health check on a population of gorillas in Volcanoes National Park in Rwanda.

He reported that a second ranked silverback gorilla was:

eating ants by reaching his left hand into the ant pile before putting it in his mouth. He ran away at one point – it appeared the ants were biting his arm. Afterwards, juvenile female Lisanga joined him and used a piece of wood to retract the ants from their nest.

This is an interesting observation.  It seems as though a high ranking male was unaware that access to an ant food resource required a tool in order to prevent being attacked.  Considering that this was not an official primatological study, no further data is available that I’m aware of, but the observation raises several questions:

  • Was the juvenile female teaching the silverback?
  • Why was a younger individual aware of a tool that the older individual seemed unaware of?
  • Are female gorillas more adept tool users than males?

I don’t think any primatologists have the answers to these questions at present.  But, as I stated a few months ago, I am really excited to see what future research reveals about gorilla culture and tool use.

What do you think of this observation?  Let Cadell know on Twitter!

Infinite Boltzmann Brains

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I have finally encountered an idea that is too mind boggling for me to really comprehend. Unsurprisingly, it is from the world of theoretical physics. In a recent paper published in Physics Review D string theorists Claire Zukowski and Raphael Bousso explore the idea of Boltzmann brains.

Boltzmann brains are hypothesized self-aware (conscious) entities that are produced from random fluctuations in the fabric of spacetime. That just means that stochastic fluctuations in the level of entropy (disorder) in the universe could theoretically produce something complex (i.e., a self-aware entity) if given enough time. Apparently brains can theoretically blink into existence.

Physicist Ludwig Boltzmann first demonstrated that this was mathematically probable in the 19th century.

Fortunately for Boltzmann, dominant cosmological models today allow enough time for his brains. Current models suggest that our universe will produce Boltzmann brains post Black Hole Era, before the universe decays out of existence.

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Image Credit / Wikipedia

Boltzmann brains are a serious paradox for physicists to explain away. If there is enough time remaining in the life of the universe for essentially infinite number of Boltzmann brains to come into existence, our subjective experience of the universe will be highly unusual. We perceive the universe to have a directionality, or an “arrow of time” and all of our understanding of the physical laws derive from this observation. But if the experience of Boltzmann brains is the usual experience then we must question the universality of our physical theories. This is because in a post “Black Hole Era” universe there will be no distinguishable past and future; there will be no arrow of time.

Zukowski and Bousso are working to resolve this insane paradox. Zukowski stated:

It has to be more likely to be an ordinary observer than a Boltzmann brain

They believe that we have to rely on string theory to resolve the paradox. String theorists believe that our universe is just one of an infinite number of universes within a larger multiverse. In this multiverse, universes are constantly budding off of parent universes and inflating over time. Zukowski and Bousso contend that in this framework there are more universes with a discernible arrow of time than universes without (i.e., more universes decay before the appearance of Boltzmann brains than the opposite situation). This would mean experience like our own, with a discernible arrow of time, should be the dominant experience in the multiverse.

Obviously, this is all theoretical. The multiverse itself has not been empirically demonstrated, and is but one of several competing theories to describe the conditions that caused the big bang.

I suppose it is reassuring to know that if the multiverse does exist, it may not be overrun wit Boltzmann brains that have no concept of entropy?

As bizarre as this is to think about, it is too much for me to comprehend for evolutionary reasons. First, I have no idea how the trillions of atoms that create our conscious experience could possibly assemble randomly, even if given infinite time. Second, how strange would it be to have no concept of the arrow of time? To not have a temporal lineage with which to trace your own existence? You just exist, seemingly out of nowhere. You would have no baring on any direction at all. No possible way to understand your origin. A consciousness produced from nothing.

I’ll clarify that I am not saying the math is wrong. I am not qualified to say. Clearly if it is being taken seriously by physicists the math is something to be concerned about. And incredulity is not a good enough reason to doubt the possibility of such entities. If it is theoretically possible, so be it. I’m just saying it is an idea too bizarre for me to really grasp. I don’t think I’ve encountered a stranger idea.

Thanks physics.

What do you think of Boltzmann brains?  Let Cadell know on Twitter.

Cosmic Natural Selection

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If you regularly read this blog, you already know that I believe adaptive evolutionary processes explain system order in the universe. There does appear to be a unity between how systems evolve (whether they be chemical, biological, cultural, technological, etc.). In this sense, selection-like processes generate order in the natural world that many cultural groups assumed was intelligently designed. But can selection be extended to explain the universe itself?

Before humans knew that there were other planets in the universe, many people believed that Earth could only be explained by intelligent design (e.g., God). However, we now know that the Earth’s existence can be explained by probability. There are likely way more than sextillion planets in the observable universe, so it is not necessarily surprising that one suitable for complex life exists. In fact, it would not be surprising if billions of planets suitable for complex life existed just within our own galaxy.

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But people who make the God-of-the-gaps argument never really go away. Now that it is intellectually bankrupt to argue Earth (or life, or our star, or our solar system, or our galaxy) was intelligently designed, many turn to the universe itself. As physicists have pointed out, our universe is well-designed for the emergence of intelligent life (although not that well-designed).

Therefore, it is the job of 21st century science to uncover the mysteries as to why our universe appears to have the physical constants it does. At the moment, the theory is far ahead of the empirical evidence (unlike the situation in evolutionary biology). A dominant theory proposed to explain our universe’s physical constants is Cosmic Natural Selection (CNS). This theory, first explored by physicist Lee Smolin suggests that:

black holes may be mechanisms of universe reproduction within the multiverse, an extended cosmological environment in which universes grow, die, and reproduce. Rather than a “dead” singularity at the centre of blackholes, a point where energy and space go to extremely high densities, what occurs in Smolin’s theory is a “bounce” that produces a new universe with parameters stochastically different from the parent universe. Smolin theorizes that these descendant universes will be likely to have similar fundamental physical parameters to the parent universe (such as the fine structure constant, the proton to electron mass ratio, and others) but that these parameters, and perhaps to some degree the laws that derive from them, will be slightly altered in some stochastic fashion during the replication process. Each universe therefore potentially gives rise to as many new universes as it has black holes.

The analogy with how selection operates in biological systems is impossible to miss. Given that this is how complexity is generated by other natural systems, it seems logical that this could be the case of our universe (within the multiverse). In fact, a study published this month in the journal Complexityposits that Smolin’s CNS theory would mathematically be in concordance with the production of universe’s increasingly likely to produce black holes (and therefore universe’s conducive to complex life).

Let that sink in. If Smolin’s theory is true, our universe exists the way it does because of a cosmic natural selection between universe’s within a multiverse of universes with different physical laws.

But all theories need empirical evidence. There is currently no evidence for the existence of either a multiverse or successive generations of universes that transmit their fundamental constants. And it’s possible we won’t have that evidence in the near future (or ever).

Either way, I’m optimistic. Advances in physics theory are likely to further support the idea of a multiverse and the CNS. And I wouldn’t bet against CNS being lifted from theoretical obscurity. The idea has a certain Copernican principle to it. Just as scientific inquiry revealed that our planet, solar system, and galaxy were not particularly special, it seems increasingly likely that scientific inquiry will do the same for our universe as well.

What do you think of Cosmic Natural Selection?  Let Cadell know on Twitter!

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exc-51882940e4b0cac36db824b3

Should We Send Messages to Space

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Should we purposefully transmit messages to space? That is the question posed by a team of earth and space scientists in the February 2013 edition of Space Policy.

The question has been raised because various independent groups have been sending purposefully directed high-intensity messages intended for extraterrestrial intelligences (ETI), or METI’s.

The authors of this study made two conclusions regarding METI:

1) The benefits of radio communication on Earth today outweigh any benefits or harms that could arise from contact with ETI

2) Current METI efforts are weak, mostly symbolic, and harmless

But are the answers to independent groups sending messages into the cosmos really that simple? I mean I think it is fairly obvious that the potential for ETI in our galaxy should not deter our species from continuing to improve our communication abilities. We have no evidence to support the idea that there are intelligent civilizations in our galactic neighbourhood, much less evidence to support the idea that there is an ETI civilization that poses danger to our existence. However, expanding Earth’s radiosphere and directly sending messages into the cosmos are two very different things. For example, SETI astronomer Seth Shostak has claimed that, due to decreasing signal strength our radiosphere is not detectable beyond five light years. Whereas purposefully directed, high-intensity messages significantly increase Earth’s detectability beyond the radiosphere.

Essentially, this is the reason SETI pioneer Philip Morrison believed that we, “the newest children” in the cosmos, should be passive and just listen for a long time. We should not ‘shout at the cosmos’. We should not explicitly make our presence known before we know the types of intelligence that may exist.

This is a very complex issue. What should we do moving forward? Should we be engaged in an active search for ETI? Or should we be passive?

For me personally, I mostly agree with astrophysicist and science fiction author David Brin. He supports the International Academy of Astronautics Second Protocol for dealing with Transmissions from Planet Earth. This protocol states that:

all of those controlling radio telescopes forebear from significantly increasing Earth’s visibility with deliberate skyward emanations, until their plans were first discussed before open and widely accepted international fora.

To me, this seems like a reasonable position. If we are to purposefully send a METI, that message should be first discussed by an international panel of experts in astronomy, physics, biology, anthropology, history, and politics. And the message should be collectively sent as a message from Earth and by Earth; not from an independent collective. As David Brin stated, no one should feel free to:

broadcast from Earth, whatever, whenever, and however they want.

On the other hand, there are those who would prefer to completely ban METI’s; I disagree with that stance. Don’t get me wrong, I see wisdom in the perspective that we should remain silent, passively listening to the cosmos for thousands of years, before sending messages into a cosmic environment we are just beginning to understand. However, I feel as though we should send controlled and well thought out messages from our species and planet for two main reasons:

1) If there are highly advanced civilizations in the Milky Way, they would know we are here by studying the physical and chemical patterns of our planet, regardless of our radiosphere.

2) I believe it to be probable that any civilization with the capability of traveling to another solar system would not do so with the intention of eradicating life and high intelligence.

The first point is simple, not controversial, and easily explained: a sufficiently advanced civilization could easily detect the presence of our civilization by analyzing the spectrum of reflected ultraviolet, optical, and near-infrared sunlight for our planet’s surface. They could also, perhaps more easily, become cognizant of our existence from artificial nighttime lighting and the unusual chemical composition of our planet due to the excessive burning of fossil fuels.

The second point is far more complex, certainly controversial, and not easily explained. Biologists have often warned that contact between species that evolved in different ecosystems often leads to one species going extinct. Likewise, historians have argued that “first contact” between more advanced and less advanced civilizations have often led to disastrous inter-human relations (e.g., slavery, colonialism, civilization collapse, etc.). From this reasoning, they often conclude that if we make our presence known to a vastly more advanced civilization than our own, we are placing own existence in extreme peril.

However, consider the following: as our species has become more knowledgable and technologically advanced, we have also moved strongly in the direction of compassion, altruism, and the inclusion of all within the protection of law. I believe that this is directly tied to satiation. As we create a world of abundance; a world with drastically reduced levels of hunger and poverty, we elevate our cultural ideals. David Brin referred to this as:

an abstract sympathy, unleashed by full bellies and brains that are capable of seeing enlightened self interest in the long term survival of the world.

Natural selection is the driving force for the creation of our biosphere. It may be that natural selection is the driving force for all biological evolutionary processes in the universe. Natural selection permits populations to evolve via differential survival rates. And although we are a very young species, we are already close to releasing our species from this process. In essence, natural selection is permitted to operate because of resource scarcity. But as we continue to raise the standard of living for our speciesas a whole, we accelerate ourselves into a world where we all live long enough to reproduce. Differential survival rates will no longer drive our evolution. As a result, we also accelerate ourselves towards a world free of the byproducts of resource scarcity (i.e., extinction, war, slavery, etc).

When we create science fiction work depicting human-alien conflict, we are projecting biological system conflict produced from a world governed by natural selection. But the interaction between two highly advanced technologically-based systems will not likely be governed by that type of system conflict. A new, more intelligently directed form of evolutionary change should take the place of natural selection. Surely, any species with the capability of visiting our planet would have long ago released themselves from the biological tyranny of the process that created them.

As many scientists have pointed out, including theoretical physicist Paul Davies, biological intelligence is likely to be a fleeting phase in the evolution of the universe. If this is the case, it stands to reason that any civilization able to receive our messages and visit our planet would undoubtedly be post-biological. This essentially means they would be post-singularity. And a post-singularity species has not only lifted itself from a world governed by differential survival, but has also lifted itself from finite sentience and death. Therefore, I would not expect conflicts produced by the mechanism of natural selection to dominate an encounter between us and an advanced space faring civilization.

At least, that is my reasoning, and it is why I fully support a controlled, globally agreed upon form of METI. I think the benefits of discovering extraterrestrial intelligence and making “first contact” would outweigh the risks.

That being said, I am sure many would disagree with me. Perhaps it is foolish of me to assume that all advanced intelligent species would have lifted themselves from natural selection and tend towards extraterrestrial altruism. But that is why we must have open dialogue about METI. We can’t tolerate random independent groups to send messages without first consulting the global community. If we send messages we must be prudent. And, from my perspective, prudence would be making sure that any message is sent from Earth and by Earth. No one should be allowed to send whatever messages they want, whenever and however they want.

What do you think?  Let Cadell know on Twitter!

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The Ratchet Svbtle

The Largest Living Systems

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For anyone who studies evolution, it is important to realize that there are characteristic evolutionary patterns. For example, evolution tends towards greater complexity (although not always). Evolution also has a variable speed (which is often contingent on the environment). And a study recently published in PNAS indicates that evolutionary processes generally select for species-level living systems with universal size distribution. Science Daily summarized the importance of this universal size distribution well:

Flocks of birds, schools of fish, and groups of any other living organisms might have a mathematical function in common [… researchers] showed that for each species studied, body sizes were distributed according to the same mathematical expression, where the only unknown is the average size of the species in an ecosystem.

For the researchers of this study, these apparent universal size distribution may be useful for understanding how systems of living matter operate. However, this study made me think of the role of size in evolutionary processes. Specifically, what causes different living systems to evolve different sizes? And what living system has evolved the largest overall size?

The role of size in evolutionary processes has always been a contentious issue for evolutionary theorists. Central to the issue of size has been the idea that natural selection tends to drive the evolution of larger and larger overall size, regardless of whether the living system is a bacterium, a hydra, or a chimp. This observed trend has been labeled Cope’s rule after Edward Cope, a 19th century paleontologist who first proposed the trend. The late evolutionary theorist Stephen J. Gould disregarded Cope’s rule as a “psychological artifact”, however recent studies have provided empirical evidence to support the general pattern.

Paleontologist Joel Kingsolver supports the idea that evolution tends to favour large body size, stating that:

In 80 percent of the studies, there’s consistent selection favouring larger size.

Disappointingly, the theory to explain this pattern is still underdeveloped. In fact, Kingsolver contends that there may not be any universal driver of larger body size:

My guess is that it’s a mix of particular reasons for particular speices. You may be able to make through lean times better than someone who’s smaller. Females that are larger are able to produce more eggs. If males are competing for females, larger size is often favoured.

Paleontologist and science blogger Brian Switek echoed a similar perspective recently in an article about large dinosaur body size:

The evolutionary driving forces behind the evolution of truly huge body size are not clear, and likely differed from one group to the next.

Although evolutionary theory explaining the drive behind selection for larger body is underdeveloped, we do have a better idea of proximate determinants of body size. For example, many theorists have demonstrated that mode of locomotion and reproduction are both important factors either constraining or enabling large body size.

As Brian Switek discussed at length recently, the monstrous sauropod infraorder was able to “sidestep” the costs and risks that constrain mammalian size by “externalizing birth and development.” The size distribution of sauropods dwarfed the size distribution of all other known terrestrial organisms to ever exist.

So of these supermassive sauropods, what species holds the title of largest? The answer to this question was far more difficult to find than I originally thought. Michael Stevens from VSauce recently claimed that Giraffatitan was the largest known “with certainty of a complete skeleton”. Estimates of Giraffatitan come from one skeletal sample, and was thought to be 72-74 feet in length and weigh ~30-40 tons. Compare that to the largest known African elephant which weighed ~12 tons.

However, there is general consensus in the paleontological community that there were larger sauropods than Giraffatitan. Thankfully, I had some help from Brian Switek to better understand the contemporary debate:

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According to Switek Argentinosaurus and Supersaurus
are the leading contenders for heavyweights in the dinosaur world. The longest known of these giants was a Supersaurus that is estimated to be 108-111 feet long. The heaviest was a Argentinosaurus estimated to have weighed 73 tons. They were the giants of the gigantic sauropoda order.

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But we can’t forget about a living clade of animals that has experienced an explosive increase in size distribution: cetaceans. The largest (by far) of our mammalian cousins is the blue whale. And the blue whale is not just a contender for largest living animal, they are also contenders for largest animal of all time. In fact, in terms of absolute weight, it doesn’t appear to be close at all. Whereas Argentinosaurus weighed 73 tons, the largest known blue whale weighed over 200 tons! More than double the weight of the largest known dinosaur! But to be fair, blue whales don’t have to worry as much about the crushing weight of Earth’s gravity. The battle is much closer when we compare length: Supersaurus was between 108-111 feet and the largest known blue whale was ~110 feet.

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Blue whale Balaenoptera musculus = heaviest of all time?

The SV-POW paleontology blogger team made a brilliant point that we should suspect that Supersaurus was on average longer than blue whales because we are comparing with biased sample sizes:

A huge sample of blue whales included none longer than 110 feet, while our comparatively pathetic sample of sauropods has already turned in one animal (Supersaurus) that may have just edged that out, and another (A. fragillimus) that – assuming it was really as big as we think – blows it out of the water.

In case you were wondering, A. fragillimus is estimated to have been between 130-200 feet long! It completely blows my mind that a terrestrial organism can reach those sizes on our planet (just imagine how big they would have been if they had evolved on a planet the size of Mars!).

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The red image represents A. fragillimus, potentially the longest organism ever

In case you were wondering, no primate species has ever been a contender for largest living system. The primate order is comparatively small, with the largest contemporary species (gorillas) weighing between 300-400 lbs (or about 0.15-0.2 tons!). Even if we consider extinct species, no primate has ever even been a contender for largest land mammal. The largest, Gigantopithecus, weighed approximately 1,200 lbs (or about 0.6 tons). Of course, I think Gigantopithecus is aptly named (and I think sympatric populations of Homo erectus would agree); but they are only aptly named in comparison to our relatively puny order. Primate size has probably always been constrained by underdeveloped quadrupedalism and selection for long-term infant dependence.

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Reconstruction of Homo erectus and Gigantopithecus in Southeast Asia

However, it is interesting to know that all species body sizes (from prokaryotes to sauropods) are distributed according to a potentially universal power law. This universal describes how ecology influences average species size, while genetics contains variability around that average. In the future, I’ll be interested to see whether evolutionary theorists can better describe the adaptive pressures selecting for larger size. It is useful to have a grasp on the proximate causes of body size, but the ultimate causes will be necessary to better describe how living systems develop over time.

What do you think about the evolution of large size?  Let Cadell know on Twitter!

Also posted via Svbtle:

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“Earth-like”

Earth-Like Planets

The search for an Earth analogue is heating up. And although we may have to wait for the James Webb Space Telescope to see another Earth, indirect methods are bringing us closer and closer to finding an Earth-like exoplanet every month. These findings are also bringing us closer to estimating the number of Earth-like planets in the Milky Way (e.g., study 12).

The latest research, and for some the most exciting, was the discovery of Kepler-62e. Kepler-62e is a planet located approximately 1,200 light years away from Earth in the Kepler-62 star system. This system is composed of a smaller and cooler star than our Sun, and is accompanied by five known planets, two of which are rocky worlds in the stars habitable zone.

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From the limited data available to astronomers at this point in the detection process, Kepler-62e has been touted as the “most Earth-like” planet known to date. In fact, by utilizing the Earth Similarity Index (ESI) equation Kepler-62e scores a 0.82 (scale: 0-1.0). That score matches the unconfirmed exoplanet candidate Gliese 581 g (Figure 1).

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Figure 1 – Current Potential Habitable Exoplanets

ESI is calculated using data on the mean radius, bulk density, escape velocity, and surface temperature of an exoplanet. In the popular science media a high ESI (~0.80-1.00) is code for “Earth-sized planet within the habitable zone.” In essence that is what everyone means when they say “Earth-like.” But a growing number of scientists, myself included, are beginning to realize that we are getting way ahead of ourselves. At the moment we have no way of understanding an exoplanet’s geophysical history, present state, or the dynamics of the entire star system. Astronomer Phil Plait recently tempered enthusiasm re: Kepler-62e by stating there are too many unknowns to call it Earth-like yet:

Kepler-62e could have a thick CO2-laden blanket of air, making its surface temperature completely uninhabitable, like Venus. Or it might not. We just don’t know yet, and won’t for quite some time.

In short, more data on Kepler-62e could radically alter its ESI number from 0.82 to 0.44! And that is not even factoring in data on how a radically different solar system would affect Kepler-62e’s development and present state.

This frequent, and perhaps cavalier, use of the term “Earth-like” has caused some astronomers concern. Astrobiologist Caleb Scharf recently forced us to consider what is meant by “Earth-like” when used in the context of exoplanet discovery:

Utterance of [Earth-like] can evoke all sorts of images. It may make us think of oceans, beaches, mountains, deserts, forests, fluffy clouds, fluffy bunnies, warm summers, snowy winters, the local pub, or the fabulous hubbub of the local souk. But this is typically far from the meaning attached by scientists. It can simply indicate a planet with a rocky surface, rather than a world with a thick gaseous envelope. It can mean a world that is roughly the same mass and density as Earth. It can mean a planet orbiting a star like the Sun. Or it can just mean that we got bored of saying things like ‘a two-Earth mass object in a close to a circular orbit around a roughly 4 billion year old main-sequence star that is similar in mass to the Sun’.

For me, Scharf adequately articulates the complexity in this galactic search. He also reminds me that we still must be humbled by what we can’t know at this point in time. Our estimates on the number of Earth-like worlds are going to be in constant flux this century because our data will be imperfect. All we need to do is remind ourselves of Earth’s history to know our current data are insufficient to label an exoplanet “Earth-like”. Despite the fact that our planet’s orbit and size have been relatively static, it has gone through phases (and will go through future phases) that we would consider inhospitable.

On a final note, we must also remember that our planet has the current temperature, chemical composition, and general climate it does because of the biosphere. Life, as far as we know, creates an “Earth-like” world. So perhaps, moving forward, the term “Earth-like” should be reserved for planets that we can tell are operating in a Gaia-like way. By that I mean that we should only call a planet Earth-like if the light elements (e.g., carbon, nitrogen, sulphur, and nitrogen) are being dominated and controlled by biology.

What do you think about our search for another Earth?  Let Cadell know on Twitter!

Also posted via Svbtle:

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