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Uganda: An ancient circumcision ritual is key to imparting communal knowledge

by Dominic D.B. Makwa, The Conversation

Credit: Pixabay/CC0 Public Domain

Music, dance, drama and poetry are important elements of ritual in African societies. Imbalu, the centuries-old circumcision ritual of Uganda's Bagisu people, is no different. When Bagisu boys between the ages of 16 and 22 undergo this initiation into manhood, they learn the ancient meaning of the practice through music and dance.

Imbalu takes place every even year in August in the remote districts of eastern Uganda close to the border with Kenya. Imbalu ceremonies are not only staged in homes, but also in public spaces. Here, a broader audience witnesses the special dance and music performances.

In previous studies, I have examined these performances. Music and dance are integral from the moment a boy declares he is ready to be initiated until he performs inemba, a final dance marking his return to society.

My most recent study looks at how imbalu music and dance performances act as platforms where boys are tutored about their society's gender ideology, history and ritual practice. The public performance of these rituals at a sacred place called the Namasho Cultural Site is like a communal classroom where community members attending also share what they know of their history, identity and values.

But imbalu, like other cultural performances among the Bagisu, has been affected by fewer and fewer boys undergoing initiation. Hospital circumcision has become more common, and Christianity, Islam and western education have negatively impacted uptake. Many Bagisu who have adopted western religious practices look at imbalu performances as something of a cult and consider these rituals to be "backward" and "primitive."

As a result, there is a risk that the music and dance created, performed and transmitted through cultural sites like Namasho at ceremonies like those staged for imbalu will be lost to future generations. However, they are valuable to the community since they transmit social histories, help form identity and teach social values. They should be documented and archived without delay to preserve traditional knowledge for use by future generations.

Imbalu at Namasho

The initiate and his family and community members all take on different roles during imbalu performances at Namasho.

The site, in Bududa District, stretches from the local school to the confluence of the Manafwa and Uha rivers. It is known as a place where wars were fought, and where fetishes of medicine men and women were dumped during the precolonial period. (Fetishes, in the form of calabashes or gourds, are objects kept by diviners or traditional healers to give them supernatural power. When they didn't have successors, such objects were disposed of.) These histories are part of what is taught in the rituals performed at this sacred site.

Different forms of music are played during imbalu. Khukhubulula is one form. The boy, surrounded by friends and relatives, sings songs praising himself, his family and his clan. These are usually composed by him some months earlier. Some songs will praise his girlfriends, as marriage is the phase that follows imbalu among traditional Bagisu.

Then there are bibiwoyo, coaxing songs usually led by men. They use titles like umwami (chief), umukoosi (the one with respect) or umusani (man) to encourage the boy to go through with the circumcision. The community demonstrates to the boy that he will become a "powerful" person in society if he gets circumcised.

Then there is kadodi music and dance. Accompanied by five drums, kadodi is performed to accompany initiates as they visit cultural sites and relatives. At Namasho, it entertains initiates and visitors besides also enabling some initiates to meet and interact with girls who may be future marriage partners. Kadodi is so popular at Namasho that bands come to play just to advertise themselves. Moreover, although the isonja dance is displayed earlier in the year, it is sometimes brought to this sacred site to give expert singers an opportunity to advertise themselves to future candidates who hire them to learn how to compose and sing songs.

Lastly, groups congregating at Namasho play prerecorded imbalu songs, produced in a studio or recorded live at the event in previous years. This is meant to entertain candidates but also remind circumcised men about the vows about manhood they made during their own ceremonies, including the need to defend and provide for themselves, their families and the broader community.

Communal classroom

Music and dance turn Namasho into a communal classroom for imparting indigenous knowledge and history. Some performances, for example, tell the story of Nabarwa and Masaaba, the woman and man who are believed to have introduced imbalu among the Bagisu. Mythical narrative has it that Masaaba, who met Nabarwa and asked for her hand in marriage, was asked by her to be circumcised before they could marry since she came from a circumcising community. When the Bagisu refer to themselves as Bamasaaba, they explicitly mean that they are children of Masaaba. The relationship between Nabarwa and Masaaba is used as testimony that women and men in this community should play complementary roles.

Another song is about Lutseshe, a famous forefather. In singing this song, the community reminds the initiates about the need to produce children to fill Lutseshe's land. As boys sing, some spectators will advise them to be assertive and objective if they are to manage their households well.

Through the interaction between women and men as they perform these rituals, their mutual roles in society are underscored. For example, as an initiate sings, his sisters and other female relatives are at the center of responding to the songs, symbolizing the need for women and men to work together on daily activities.

Acts like being smeared with clay from the sacred swamp are a reminder of the history of those who came before.

Preserving cultural identity

In the face of the threats to traditions like imbalu from social change, it is crucial that this knowledge be preserved for use by future generations.

Stakeholders like the Uganda Tourism Board, Bududa District local government and academic archives, like Makerere University's Klaus Wachsmann Audio-visual Archive, need to work together to record and preserve these musical and dance materials.

Imbalu will then continue to offer its lessons to the Bagisu and help maintain their rich cultural identity.Music helps patients with dementia connect with loved ones

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Why so many medieval manuscripts feature doodles. And what they reveal

by Madeleine S. Killacky, The Conversation

A drawing of the Italian poet and court writer Christine de Pizan writing. Credit: BNF Archives, CC BY-SA

To "doodle" means to draw or scrawl aimlessly, and the history of the word goes back to the early 20th century. Scribbling haphazard words, squiggly lines and mini-drawings, however, is a much older practice and its presence in books tells us a lot about how people engaged with literature in the past.

Although you wouldn't dare doodle on a medieval manuscript today, squiggly lines (sometimes resembling fish or even elongated people), mini-drawings (a knight fighting a snail, for instance), and random objects appear quite often in medieval books. Usually found in the flyleaves or margins, doodles can often give medievalists (specialists in medieval history and culture) important insights into how people in earlier centuries understood and reacted to the narrative on the page.

It was commonplace to write in margins, underline and annotate, use blank spaces for recipes and handwriting practice, and even color in images. Given the skills and specialization required for writing in the Middle Ages—the training, level of literacy, access to materials, for example—doodles in manuscripts were rarely thoughtless or accidental.

The history of doodling

The origins of doodling in the Middle Ages are hard to pinpoint, but they probably started with pen trials. When we see images of scribes (people who made written copies of documents) writing, they are often depicted with a pen and knife in hand.

The knife was used for a variety of purposes, such as pricking and correcting errors by scraping the parchment. It was also used for gently holding the parchment in place so that the scribe could avoid resting their hand on it, which would risk leaving fingerprints or natural oil from their skin on the surface of the page.

Drawings in the Book of Hours. Credit: Wren Digital Library, CC BY

Importantly, the knife was used to adjust the nib of the writing instrument when it became dull after much use. After trimming the nib, the scribe would usually test the pen on a blank piece of parchment or flyleaf to make sure that his letters were legible. Doodles from pen trials were never meant to be seen by the future reader as the flyleaf would later be glued to wooden covers.

Now, though, with modern technology, medievalists can uncover all sorts of messages that lie behind the pages of these ancient books. These types of doodles—an odd name here and there, modest works of art or even a line of music—are important because they give us a rare glimpse into the real day-to-day life of these medieval scribes and what they really thought about the books they were scribing.

We see this in a manuscript cataloged as Cotton Vespasian D. vi, which is currently held in the British Library in London. The scribe has written the Latin words "Probatio Penn[a]e", which means "pen test."

Sometimes, though, the scribes were a little bit bolder and wrote more emotively about their work. In Aelfric's 11th-century Old English De termporibus anni, a concise handbook of natural science, the scribe finishes with: "Thus, let this composition be ended here. God help my hands."

This scribe was obviously not enjoying their work.

Pen trials such as these show that scribes were not just passive processors of the text, but active participants in making the text.

A copy of Sir Thomas Malory’s Le Morte Darthur, which was composed in Newgate Prison,

 London between March 1469 and March 1470. The copy features many doodles in the

 margin. Credit: The British Library, CC BY

Marginalia

Doodling in medieval books also brings us into the world of play as readers and scribes then, as now, surrendered themselves to the urge to interrupt empty spaces on the page.

Doodles in the margins—properly known as marginalia—offer the reader some respite from the labors associated with concentrated reading, but also tell us something about how readers reacted to and engaged with the literary world on the page.

For example, although Sir Thomas Malory's Le Morte Darthur contains relatively few marginalia compared with other medieval manuscripts (80 throughout the 473 surviving folios, by my count), they often mirror the action happening in the narrative in unique ways and demonstrate that the scribes weren't merely mechanical copiers. Rather, their copying habits are highly sophisticated and provide an example of how, in this case, 15th-century scribes played a role in shaping the reception of literary texts by their contemporary audiences.

Books in the Middle Ages were much more valuable than they are today because of the time, skill and expense it took to make them. Besides being regarded as an object of permanence, to be retained, saved and used as a repository for eternity, medieval books were also public spaces owned by groups of people, institutions or generations of owners (up to today).

Doodles, annotations, marks, commentaries and additions become public declarations. Coupled with the book's status as an enduring object, it makes sense that readers felt drawn to write their names or doodle in the margins and flyleaves of these books. Through making their mark, they—as ephemeral beings—were inscribing themselves into the book's eternal living history.

15th-century book owners early 'upcyclers'

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Forest restoration is on the rise, but how we go about it is crucial

by Lander Baeten et al, The Conversation

A staff member from the Pesalat Reforestation Project on the island of Borneo replants trees in a

 peat-swamp forest area that was cleared by fires and logging. The areas are habitat for the

 orangutan, which is highly endangered. Credit: World Resources Institute, CC BY

Politicians have long been fond of tree-planting ceremonies, but today, well-thought-out forest restoration schemes are increasingly important. Indeed, a host of international initiatives aim to substantially increase the world's forest area by bringing back to life millions of hectares of degraded and deforested land.

Launched in 2017, the United Nations' Strategic Plan for Forests is perhaps one of the most emblematic schemes, setting out to boost global forest coverage by 3% by 2030, equivalent to 120 million hectares or an area more than twice the size of France. Encompassing 61 countries, the Bonn Challenge has pledged to restore more than double this, at 350 million hectares by the same year.

These much-needed efforts raise important questions for forest ecologists: How can we ensure that restored forests deliver the range of services we expect of them? How can we make them resilient so that they continue to function well in the future, in particular given ongoing climate change? And how can restoring forests provide an opportunity to help solve other critical global challenges, such as combating the loss of biodiversity and environmental degradation?

Closing the gap in forest restoration

The leap from policymakers' pledges to effective forest restoration by practitioners needs support from science. The first challenge is to identify the areas on earth that have the largest potential to accommodate all these additional trees. This requires advanced landscape planning, reconciling different perspectives, such as:

• Securing rising demands for food production.
• Avoiding biodiversity-rich areas such as extensively managed grasslands, which should not be converted to forests even though they are potentially suitable for tree growth.
• Acknowledging the economic and cultural values linked to land uses other than forest.

Scientists are developing detailed maps showing this global restoration potential outside of existing forests, agricultural land, and urban areas. Still, there is a debate about how much of this land should be turned over to forests.

Once we determine where to prioritize forest restoration, the next challenge is to decide what these forests should look like. Forest plantations will have an important share in the restoration efforts. Forests now cover about 30% of global land surfaces, and according to the Global Forest Resources Assessment (FAO 2020), planted forests already represent 290 million ha. This is about 7% of the global forest area and it provides nearly 50% of harvested timber.

A crucial question for forest managers is which tree species should be planted, as the trees will form the future forest for decades to come. They should thus provide the largest benefits in terms of the services we want them to deliver, such as strong growth potential, high carbon sequestration, and optimal support of biodiversity. At the same time, they need to be able to withstand the 21st century's rising environmental challenges—including climate change. The trees will need, for instance, to be able to take on unprecedented droughts, such as the ones seen in spring and summer 2022 in many regions of Europe.

The catch is that there are no single tree species that combines all of these features, so that it ultimately comes down to trade-offs between criteria when choosing between different types of trees for reforestation.

Science guides toward diverse plantations

Until now, most large-scale tree-planting schemes reproduced monocultural systems, almost exclusively relying upon a handful of commercial tree species—typically pines, spruce, or eucalypts. However, the existing monocultures give us little information about how we can design, plant and manage other types of forests that will be resilient to environmental stresses. Fortunately, scientists worldwide have established experimental tree plantations that can be particularly informative.

An X-ray scan of a core sample from a lime tree (Tilia cordata) growing in the Belgian experiment 

FORBIO. The left is the centre of the tree, the right shows the bark. Annual growth is visible as 

individual bands, with broader bands corresponding to years of higher growth.

 Credit: Lander Baeten/Ghent University, Fourni par l'auteur

Our team's experiments, part of the global Tree Diversity Network TreeDivNet, were all rigorously designed to study how well individual tree species and, especially, mixtures of different tree species grow. Still relatively young, these experiments currently cover only trees up to 20 years old and are thus most relevant for the initial stages of forest development. Still, these stages are the most critical regarding successful establishment and growth after planting.

The current focus of our work is on tree growth. For example, do trees grow faster if they share growth space with other species that use resources differently? We also look at the resistance of many species of trees to climate variability and other threats. Teams associated with TreeDivNet have sites in most major climatic regions of the world, including the boreal and temperate zones, the Mediterranean, and the tropics. Together, they cover more than 850 hectares—the equivalent to 1,200 soccer fields—and represent one of the most extensive ecological research facilities in the world. Nearly 30 experiments are testing the performance of around 250 species. All are gathering crucial data that will help inform us about what mixes of species can best achieve multiple objectives and have the highest resilience to threats.

Decision trees

To help us adapt to a warming planet, TreeDivNet Scientists are teaming up to investigate the optimal combinations of tree species that will allow tree plantations to thrive in a changing and uncertain climate. Their potential for climate mitigation and adaptation will depend on how young trees can survive climate extremes, particularly drought, fire and threats such as bark beetles.

Our work has provided survival assessments for hundreds of thousands of trees in their first years, and early results reveal that mixed plantings are less at risk of complete failure. In contrast, monocultures that may be more productive are often less resilient, and may not withstand periods of extreme stress. The diffusion of tree mortality risk in mixtures, known as the "portfolio" or "insurance effect," may offer an adaptation pathway to forest managers striving to secure forest persistence under uncertain future conditions. As the term indicates, it's akin to how we diversify our economic portfolio to ensure more stable long-term revenues.

Trees being studied are subjected to thorough check-ups using advanced techniques. X-ray scans of wood cores identify trees that have experienced delayed growth because of drought or other threats. Looking at carbon isotopes in wood can reveal whether trees have experienced stress from drought, which reduces photosynthesis during that time. The ambition is to summarize these measurements in ecological profiles of tree species, supporting forest managers' decisions between different tree species combinations that can cope with the challenges ahead.

Making the science practical

Academics perform much of the research work, but a key ambition is to make the science practical so that it can serve as a science-based guide for forest managers in the field. In the months ahead, we will be looking to reach out and build on scientific advances to help develop workable afforestation practices that landowners and land users can widely adopt.

Also crucial is forming enduring alliances with land users, research groups, and forestry organizations worldwide. These partnerships can provide the combined impetus for accelerating a nature-based transition from monocultures of few commercial species to rich, biodiverse plantations that are well adapted to many stressors, particularly climate change, for decades to come.Tree species diversity enhances forest drought resistance

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'Astonishing': Global demand for exotic pets is driving a massive trade in unprotected wildlife

by Freyja Watters and Phill Cassey, The Conversation

Otter sold via Instagram in Indonesia. Credit: Instagram

Global demand for exotic pets is increasing, a trend partly caused by social media and a shift from physical pet stores to online marketplaces.

The United States is one of the biggest markets for the wildlife trade. And our new research has identified an astonishing number of unregulated wild-caught animals being brought into the U.S.—at a rate 11 times greater than animals regulated and protected under the relevant global convention.

Wildlife trade can have major negative consequences. It can threaten the wild populations from which animals and plants are harvested, and introduce novel invasive species to new environments. It can also lead to diseases transmitted from wildlife to humans and threaten the welfare of trafficked animals.

Tackling this problem requires an international effort—particularly by rich nations where the demand for exotic pets is greatest.

Shining a light on the pet market

Most live animals transported through the wildlife trade are destined for the global, multi-billion dollar exotic pet market. Captive breeding supplies a portion of this market, but many species are collected from the wild—often illegally.

Animals such as otters, slow lorises and galagos or "bushbabies" are frequently depicted on social media as cute, and with human-like feelings and behaviors. This helps create demand for such species as pets which drives both the illegal and legal wildlife trades.

Non-native animals frequently smuggled into Australia in the past, include the corn snake, leopard gecko and red-eared slider turtle. Reptiles and birds are among the most commonly trafficked species because they can be easily transported.

Species deemed at risk from international trade are regulated through the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). It aims to ensure sustainable and traceable legal international trade.

But the convention lists less than 10% of all described plants and terrestrial vertebrates, and less than 1% of all fish and invertebrate species. No international regulatory framework exists to monitor the trade of the many unlisted species.

Australia has rigorous regulations for exotic pet ownership and trade. Broadly, our native wildlife cannot be commercially exported.

However, Australia's fauna is poached from the wild and illegally exported for the international pet market. Once the animal is smuggled out of Australia, its trade in recipient countries is often not monitored or restricted.

For example, research last year showed four subspecies of Australia's shingleback lizard—one of which is endangered—were being illegally extracted from the wild and smuggled out of the country, to be sold across Asia, Europe and North America.

This lack of overseas regulation prompted the former Morrison government to push for 127 native reptile species targeted by international wildlife smugglers to be listed under CITES. They include blue tongue skinks and numerous gecko species.

But in the meantime, the global illegal wildlife trade continues. Our new research analyzed the extent of this, by focusing on the movement of unlisted species to and from the U.S.

Unregulated global trade threatens the wild populations of the Asian water dragon. Credit: Wikimedia

What we found

The U.S. is one of the few countries that maintains detailed records of all declared wildlife trade, including species not listed under CITES.

We examined a decade of data on wild-harvested, live vertebrate animals entering the U.S. Most would have been headed for the pet trade. We found 3.6 times the number of unlisted species in U.S. imports compared with CITES-listed species—1,356 versus 378 species.

Overall, 8.84 million animals from unlisted species were imported—about 11 times more than animals from CITES-listed species. More than a quarter of unlisted species faced conservation threats—including those with declining populations and those threatened with extinction.

For example, we found a substantial trade of the unlisted Asian water dragon. These bright green lizards are native to Thailand, Vietnam, Cambodia, Laos, Burma and southern China, and are considered vulnerable.

In the decade to 2018, more than 575,000 Asian water dragons were imported to the U.S. from Vietnam. The species has been proposed for inclusion in CITES. But decades of unregulated global trade poses a major threat to the survival of native populations.

How do we fix this?

Our study highlights the urgent need to monitor all traded wildlife species, not just those listed under CITES.

The biodiversity of life on Earth is under enormous pressure. Given this, and the other harms caused by the wildlife trade, this lack of regulation and monitoring is unacceptable.

For a species to be considered for listing under CITES, a national government must demonstrate that regulation is needed to prevent trade-related declines. But if trade in the species has never been monitored, how can that need be proven?

Sadly, the trade of many species is not formally regulated until it's too late for their wild populations. Clearly, tighter regulation is needed to prevent this decline.

Traded wildlife predominantly flows from lower-income to higher-income countries. Many source countries do not possess the frameworks needed to monitor the harvest and export of unlisted species.

So what should be done? First, all nations should follow the lead of the U.S. and record species-level data for all wildlife imported and exported. This information should be gathered as part of a standardized data management system.

Such a system would increase compliance with the rules and make the origin of wildlife easier to trace It would allow trade data to be shared and integrated between countries and allow timely assessment of species which may need further protection.

And second, affluent countries—where demand for exotic pets is largest—must take the lead on sustainable trade practices. This should include supporting supply countries and pushing for better data collection.

Such measures are vital to protecting both wildlife and human well-being.Stopping the illegal trade of Australian lizards

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How philosophy turned into physics and reality turned into information

by Peter Evans, The Conversation

John Bell in his office at CERN in Switzerland. Credit: CERN

The Nobel Prize in physics this year has been awarded "for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science."

To understand what this means, and why this work is important, we need to understand how these experiments settled a long-running debate among physicists. And a key player in that debate was an Irish physicist named John Bell.

In the 1960s, Bell figured out how to translate a philosophical question about the nature of reality into a physical question that could be answered by science—and along the way broke down the distinction between what we know about the world and how the world really is.

Quantum entanglement

We know that quantum objects have properties we don't usually ascribe to the objects of our ordinary lives. Sometimes light is a wave, sometimes it's a particle. Our fridge never does this.

When attempting to explain this sort of unusual behavior, there are two broad types of explanation we can imagine. One possibility is that we perceive the quantum world clearly, just as it is, and it just so happens to be unusual. Another possibility is that the quantum world is just like the ordinary world we know and love, but our view of it is distorted, so we can't see quantum reality clearly, as it is.

In the early decades of the 20th century, physicists were divided about which explanation was right. Among those who thought the quantum world just is unusual were figures such as Werner Heisenberg and Niels Bohr. Among those who thought the quantum world must be just like the ordinary world, and our view of it is simply foggy, were Albert Einstein and Erwin Schrödinger.

At the heart of this division is an unusual prediction of quantum theory. According to the theory, the properties of certain quantum systems that interact remain dependent on each other—even when the systems have been moved a great distance apart.

In 1935, the same year he devised his famous thought experiment involving a cat trapped in a box, Schrödinger coined the term "entanglement" for this phenomenon. He argued it is absurd to believe the world works this way.

The problem with entanglement

If entangled quantum systems really remain connected even when they are separated by large distances, it would seem they are somehow communicating with each other instantaneously. But this sort of connection is not allowed, according to Einstein's theory of relativity. Einstein called this idea "spooky action at a distance."

Again in 1935, Einstein, along with two colleagues, devised a thought experiment that showed quantum mechanics can't be giving us the whole story on entanglement. They thought there must be something more to the world that we can't yet see.

But as time passed, the question of how to interpret quantum theory became an academic footnote. The question seemed too philosophical, and in the 1940s many of the brightest minds in quantum physics were busy using the theory for a very practical project: building the atomic bomb.

It wasn't until the 1960s, when Irish physicist John Bell turned his mind to the problem of entanglement, that the scientific community realized this seemingly philosophical question could have a tangible answer.

Bell's theorem

Using a simple entangled system, Bell extended Einstein's 1935 thought experiment. He showed there was no way the quantum description could be incomplete while prohibiting "spooky action at a distance" and still matching the predictions of quantum theory.

Not great news for Einstein, it seems. But this was not an instant win for his opponents.

This is because it was not evident in the 1960s whether the predictions of quantum theory were indeed correct. To really prove Bell's point, someone had to put this philosophical argument about reality, transformed into a real physical system, to an experimental test.

And this, of course, is where two of this year's Nobel laureates enter the story. First John Clauser, and then Alain Aspect, performed the experiments on Bell's proposed system that ultimately showed the predictions of quantum mechanics to be accurate. As a result, unless we accept "spooky action at a distance," there is no further account of entangled quantum systems that can describe the observed quantum world.

So, Einstein was wrong?

It is perhaps a surprise, but these advances in quantum theory appear to have shown Einstein to be wrong on this point. That is, it seems we do not have a foggy view of a quantum world that is just like our ordinary world.

But the idea that we perceive clearly an inherently unusual quantum world is likewise too simplistic. And this provides one of the key philosophical lessons of this episode in quantum physics.

It is no longer clear we can reasonably talk about the quantum world beyond our scientific description of it—that is, beyond the information we have about it.

As this year's third Nobel laureate, Anton Zeilinger, put it: "The distinction between reality and our knowledge of reality, between reality and information, cannot be made. There is no way to refer to reality without using the information we have about it."

This distinction, which we commonly assume to underpin our ordinary picture of the world, is now irretrievably blurry. And we have John Bell to thank.

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What is quantum entanglement? A physicist explains the science of Einstein's 'spooky action at a distance'

by Andreas Muller, The Conversation

According to quantum mechanics, particles are simultaneously in two or more states until

 observed – an effect vividly captured by Schrödinger’s famous thought experiment of a

 cat that is both dead and alive simultaneously. 

Credit: Michael Holloway/Wikimedia Commons, CC BY-SA

The 2022 Nobel Prize in physics recognized three scientists who made groundbreaking contributions in understanding one of the most mysterious of all natural phenomena: quantum entanglement.

In the simplest terms, quantum entanglement means that aspects of one particle of an entangled pair depend on aspects of the other particle, no matter how far apart they are or what lies between them. These particles could be, for example, electrons or photons, and an aspect could be the state it is in, such as whether it is "spinning" in one direction or another.

The strange part of quantum entanglement is that when you measure something about one particle in an entangled pair, you immediately know something about the other particle, even if they are millions of light years apart. This odd connection between the two particles is instantaneous, seemingly breaking a fundamental law of the universe. Albert Einstein famously called the phenomenon "spooky action at a distance."

Having spent the better part of two decades conducting experiments rooted in quantum mechanics, I have come to accept its strangeness. Thanks to ever more precise and reliable instruments and the work of this year's Nobel winners, Alain Aspect, John Clauser and Anton Zeilinger, physicists now integrate quantum phenomena into their knowledge of the world with an exceptional degree of certainty.

However, even until the 1970s, researchers were still divided over whether quantum entanglement was a real phenomenon. And for good reasons—who would dare contradict the great Einstein, who himself doubted it? It took the development of new experimental technology and bold researchers to finally put this mystery to rest.

Existing in multiple states at once

To truly understand the spookiness of quantum entanglement, it is important to first understand quantum superposition. Quantum superposition is the idea that particles exist in multiple states at once. When a measurement is performed, it is as if the particle selects one of the states in the superposition.

For example, many particles have an attribute called spin that is measured either as "up" or "down" for a given orientation of the analyzer. But until you measure the spin of a particle, it simultaneously exists in a superposition of spin up and spin down.

There is a probability attached to each state, and it is possible to predict the average outcome from many measurements. The likelihood of a single measurement being up or down depends on these probabilities, but is itself unpredictable.

Though very weird, the mathematics and a vast number of experiments have shown that quantum mechanics correctly describes physical reality.

Two entangled particles

The spookiness of quantum entanglement emerges from the reality of quantum superposition, and was clear to the founding fathers of quantum mechanics who developed the theory in the 1920s and 1930s.

To create entangled particles you essentially break a system into two, where the sum of the parts is known. For example, you can split a particle with spin of zero into two particles that necessarily will have opposite spins so that their sum is zero.

In 1935, Albert Einstein, Boris Podolsky and Nathan Rosen published a paper that describes a thought experiment designed to illustrate a seeming absurdity of quantum entanglement that challenged a foundational law of the universe.

A simplified version of this thought experiment, attributed to David Bohm, considers the decay of a particle called the pi meson. When this particle decays, it produces an electron and a positron that have opposite spin and are moving away from each other. Therefore, if the electron spin is measured to be up, then the measured spin of the positron could only be down, and vice versa. This is true even if the particles are billions of miles apart.

This would be fine if the measurement of the electron spin were always up and the measured spin of the positron were always down. But because of quantum mechanics, the spin of each particle is both part up and part down until it is measured. Only when the measurement occurs does the quantum state of the spin "collapse" into either up or down—instantaneously collapsing the other particle into the opposite spin. This seems to suggest that the particles communicate with each other through some means that moves faster than the speed of light. But according to the laws of physics, nothing can travel faster than the speed of light. Surely the measured state of one particle cannot instantaneously determine the state of another particle at the far end of the universe?

Physicists, including Einstein, proposed a number of alternative interpretations of quantum entanglement in the 1930s. They theorized there was some unknown property—dubbed hidden variables—that determined the state of a particle before measurement. But at the time, physicists did not have the technology nor a definition of a clear measurement that could test whether quantum theory needed to be modified to include hidden variables.

Disproving a theory

It took until the 1960s before there were any clues to an answer. John Bell, a brilliant Irish physicist who did not live to receive the Nobel Prize, devised a scheme to test whether the notion of hidden variables made sense.

Bell produced an equation now known as Bell's inequality that is always correct—and only correct—for hidden variable theories, and not always for quantum mechanics. Thus, if Bell's equation was found not to be satisfied in a real-world experiment, local hidden variable theories can be ruled out as an explanation for quantum entanglement.

The experiments of the 2022 Nobel laureates, particularly those of Alain Aspect, were the first tests of the Bell inequality. The experiments used entangled photons, rather than pairs of an electron and a positron, as in many thought experiments. The results conclusively ruled out the existence of hidden variables, a mysterious attribute that would predetermine the states of entangled particles. Collectively, these and many follow-up experiments have vindicated quantum mechanics. Objects can be correlated over large distances in ways that physics before quantum mechanics can not explain.

Importantly, there is also no conflict with special relativity, which forbids faster-than-light communication. The fact that measurements over vast distances are correlated does not imply that information is transmitted between the particles. Two parties far apart performing measurements on entangled particles cannot use the phenomenon to pass along information faster than the speed of light.

Today, physicists continue to research quantum entanglement and investigate potential practical applications. Although quantum mechanics can predict the probability of a measurement with incredible accuracy, many researchers remain skeptical that it provides a complete description of reality. One thing is certain, though. Much remains to be said about the mysterious world of quantum mechanics.Quantum entanglement: the 'spooky' science behind physics Nobel

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