Nobel Prize in physics awarded to 2 scientists for discoveries that enabled machine learning

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Two pioneers of artificial intelligence—John Hopfield and Geoffrey Hinton—won the Nobel Prize in physics Tuesday for helping create the building blocks of machine learning that is revolutionizing the way we work and live but also creates new threats for humanity.

Hinton, who is known as the godfather of artificial intelligence, is a citizen of Canada and Britain who works at the University of Toronto, and Hopfield is an American working at Princeton.

"These two gentlemen were really the pioneers," said Nobel physics committee member Mark Pearce.

The artificial neural networks—interconnected computer nodes inspired by neurons in the human brain—the researchers pioneered are used throughout science and medicine and "have also become part of our daily lives," said Ellen Moons of the Nobel committee at the Royal Swedish Academy of Sciences.

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Hopfield, whose 1982 work laid the groundwork for Hinton's, told The Associated Press, "I continue to be amazed by the impact it has had."

Hinton predicted that AI will end up having a "huge influence" on civilization, bringing improvements in productivity and health care.

"It would be comparable with the Industrial Revolution," he said in an open call with reporters and officials of the Royal Swedish Academy of Sciences.

"Instead of exceeding people in physical strength, it's going to exceed people in intellectual ability. We have no experience of what it's like to have things smarter than us. And it's going to be wonderful in many respects," Hinton said.

"But we also have to worry about a number of possible bad consequences, particularly the threat of these things getting out of control."

Warning of AI risks

The Nobel committee also mentioned fears about the possible flipside.

Moons said that while it has "enormous benefits, its rapid development has also raised concerns about our future. Collectively, humans carry the responsibility for using this new technology in a safe and ethical way for the greatest benefit of humankind."

Hinton, who quit a role at Google so he could speak more freely about the dangers of the technology he helped create, shares those concerns.

"I am worried that the overall consequence of this might be systems more intelligent than us that eventually take control," Hinton said.

For his part, Hopfield, who signed early petitions by researchers calling for strong control of the technology, compared the risks and benefits to work on viruses and nuclear energy, capable of helping and harming society.

Neither winner was home to get the call

Hopfield, who was staying with his wife at a cottage in Hampshire, England, said that after grabbing coffee and getting his flu shot, he opened his computer to a flurry of activity.

"I've never seen that many emails in my life," he said. A bottle of champagne and bowl of soup were waiting, he added, but he doubted there were any fellow physicists in town to join the celebration.

Hinton said he was shocked at the honor.

"I'm flabbergasted. I had no idea this would happen," he said when reached by the Nobel committee on the phone. He said he was at a cheap hotel with no internet.

Hinton's work considered 'the birth' of AI

Hinton, 76, helped develop a technique in the 1980s known as backpropagation instrumental in training machines how to "learn" by fine-tuning errors until they disappear. It's similar to the way a student learns, with an initial solution graded and flaws identified and returned to be fixed and repaired. This process continues until the answer matches the network's version of reality.

Hinton had an unconventional background as a psychologist who also dabbled in carpentry and was genuinely curious about how the mind works, said protege Nick Frosst, who was Hinton's first hire at Google's AI division in Toronto.

His "playfulness and genuine interest in answering fundamental questions I think is key to his success as a scientist," Frosst said.

Nor did he stop at his pioneering 1980s work.

"He's been consistently trying out crazy things and some of them work very well and some of them don't," Frosst said. "But they all have contributed to the success of the field and galvanized other researchers to try new things as well."

Hinton's team at the University of Toronto wowed peers by using a neural network to win the prestigious ImageNet computer vision competition in 2012. That spawned a flurry of copycats and was "a very, very significant moment in hindsight and in the course of AI history," said Stanford University computer scientist and ImageNet creator Fei-Fei Li.

"Many people consider that the birth of modern AI," she said.

Hinton and fellow AI scientists Yoshua Bengio and Yann LeCun won computer science's top prize, the Turing Award, in 2019.

"For a long time, people thought what the three of us were doing was nonsense," Hinton told told the AP in 2019. "They thought we were very misguided and what we were doing was a very surprising thing for apparently intelligent people to waste their time on."

"My message to young researchers is, don't be put off if everyone tells you what are doing is silly."

Many of Hinton's former students and collaborators followed him into the tech industry as it began capitalizing on AI innovations, and some started their own AI companies, including Frosst's Cohere and ChatGPT maker OpenAI. Hinton said he uses machine learning tools in his daily life.

"Whenever I want to know the answer to anything, I just go and ask GPT-4," Hinton said at the Nobel announcement. "I don't totally trust it because it can hallucinate, but on almost everything it's a not-very-good expert. And that's very useful."

Hopfield's work was foundation for Hinton's

Hopfield, 91, created an associative memory that can store and reconstruct images and other types of patterns in data, the Nobel committee said.

"What fascinates me most is still this question of how mind comes from machine," Hopfield said in a video posted online by The Franklin Institute after it awarded him a physics prize in 2019.

Hinton used Hopfield's network as the foundation for a new network that uses a different method, known as the Boltzmann machine, that the committee said can learn to recognize characteristic elements in a given type of data.

While there's no Nobel for computer science, Li said that awarding a traditional science prize to AI pioneers is significant and shows how boundaries between disciplines have blurred.

Bengio, who was mentored by Hinton and "profoundly shaped" by Hopfield's thinking, told the AP the winners both "saw something that was not obvious: Connections between physics and learning in neural networks, which has been the basis of modern AI."

Disagreement on AI risks

Not all of Hinton's peers agree with him about the risks of the technology he helped create.

Frosst has had many "spirited debates" with Hinton about AI's risks and disagrees with some of Hinton's warnings but not his willingness to publicly address them.

"Mostly we disagree on timescale and on the particular technology that he's sounding the alarm on," Frosst said. "I don't think that neural nets and language models as they exist today pose an existential risk."

Bengio, who has long sounded alarms about AI risks, said what really alarms him and Hinton is "loss of human control" and whether AI systems will act morally when they're smarter than humans.

"We don't know the answer to these questions," he said. "And we should make sure we do before we build those machines."

Asked whether the Nobel committee might have factored in Hinton's warnings when deciding on the award, Bengio dismissed that, saying "we're talking about very early work when we thought that everything would be rosy."

Six days of Nobel announcements opened Monday with Americans Victor Ambros and Gary Ruvkun winning the medicine prize. They continue with the chemistry prize Wednesday and literature on Thursday. The Nobel Peace Prize will be announced Friday and the economics award on Oct. 14.

The prize carries a cash award of 11 million Swedish kronor ($1 million) from a bequest left by the award's creator, Swedish inventor Alfred Nobel. The laureates are invited to receive their awards at ceremonies on Dec. 10, the anniversary of Nobel's death.

Nobel committee announcement:

The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Physics 2024 to

John J. Hopfield, Princeton University, NJ, U.S.

Geoffrey E. Hinton, University of Toronto, Canada

"for foundational discoveries and inventions that enable machine learning with artificial neural networks"

They trained artificial neural networks using physics

This year's two Nobel Laureates in Physics have used tools from physics to develop methods that are the foundation of today's powerful machine learning. John Hopfield created an associative memory that can store and reconstruct images and other types of patterns in data. Geoffrey Hinton invented a method that can autonomously find properties in data, and so perform tasks such as identifying specific elements in pictures.

When we talk about artificial intelligence, we often mean machine learning using artificial neural networks. This technology was originally inspired by the structure of the brain. In an artificial neural network, the brain's neurons are represented by nodes that have different values. These nodes influence each other through connections that can be likened to synapses and which can be made stronger or weaker. The network is trained, for example by developing stronger connections between nodes with simultaneously high values. This year's laureates have conducted important work with artificial neural networks from the 1980s onward.

John Hopfield invented a network that uses a method for saving and recreating patterns. We can imagine the nodes as pixels. The Hopfield network utilises physics that describes a material's characteristics due to its atomic spin—a property that makes each atom a tiny magnet. The network as a whole is described in a manner equivalent to the energy in the spin system found in physics, and is trained by finding values for the connections between the nodes so that the saved images have low energy. When the Hopfield network is fed a distorted or incomplete image, it methodically works through the nodes and updates their values so the network's energy falls. The network thus works stepwise to find the saved image that is most like the imperfect one it was fed with.

Geoffrey Hinton used the Hopfield network as the foundation for a new network that uses a different method: the Boltzmann machine. This can learn to recognise characteristic elements in a given type of data. Hinton used tools from statistical physics, the science of systems built from many similar components. The machine is trained by feeding it examples that are very likely to arise when the machine is run. The Boltzmann machine can be used to classify images or create new examples of the type of pattern on which it was trained. Hinton has built upon this work, helping initiate the current explosive development of machine learning.

"The laureates' work has already been of the greatest benefit. In physics we use artificial neural networks in a vast range of areas, such as developing new materials with specific properties," says Ellen Moons, Chair of the Nobel Committee for Physics.

The Nobel Prize in Physics 2024

This year's laureates used tools from physics to construct methods that helped lay the foundation for today's powerful machine learning. John Hopfield created a structure that can store and reconstruct information. Geoffrey Hinton invented a method that can independently discover properties in data and which has become important for the large artificial neural networks now in use.

They used physics to find patterns in information

Many people have experienced how computers can translate between languages, interpret images and even conduct reasonable conversations. What is perhaps less well known is that this type of technology has long been important for research, including the sorting and analysis of vast amounts of data. The development of machine learning has exploded over the past fifteen to twenty years and utilises a structure called an artificial neural network. Nowadays, when we talk about artificial intelligence, this is often the type of technology we mean.

Although computers cannot think, machines can now mimic functions such as memory and learning. This year's laureates in physics have helped make this possible. Using fundamental concepts and methods from physics, they have developed technologies that use structures in networks to process information.

Machine learning differs from traditional software, which works like a type of recipe. The software receives data, which is processed according to a clear description and produces the results, much like when someone collects ingredients and processes them by following a recipe, producing a cake. Instead of this, in machine learning the computer learns by example, enabling it to tackle problems that are too vague and complicated to be managed by step by step instructions. One example is interpreting a picture to identify the objects in it.

Mimics the brain

An artificial neural network processes information using the entire network structure. The inspiration initially came from the desire to understand how the brain works. In the 1940s, researchers had started to reason around the mathematics that underlies the brain's network of neurons and synapses. Another piece of the puzzle came from psychology, thanks to neuroscientist Donald Hebb's hypothesis about how learning occurs because connections between neurons are reinforced when they work together.

Later, these ideas were followed by attempts to recreate how the brain's network functions by building artificial neural networks as computer simulations. In these, the brain's neurons are mimicked by nodes that are given different values, and the synapses are represented by connections between the nodes that can be made stronger or weaker. Donald Hebb's hypothesis is still used as one of the basic rules for updating artificial networks through a process called training.

At the end of the 1960s, some discouraging theoretical results caused many researchers to suspect that these neural networks would never be of any real use. However, interest in artificial neural networks was reawakened in the 1980s, when several important ideas made an impact, including work by this year's laureates.

Associative memory

Imagine that you are trying to remember a fairly unusual word that you rarely use, such as one for that sloping floor often found in cinemas and lecture halls. You search your memory. It's something like ramp… perhaps rad…ial? No, not that. Rake, that's it!

This process of searching through similar words to find the right one is reminiscent of the associative memory that the physicist John Hopfield discovered in 1982. The Hopfield network can store patterns and has a method for recreating them. When the network is given an incomplete or slightly distorted pattern, the method can find the stored pattern that is most similar.

Hopfield had previously used his background in physics to explore theoretical problems in molecular biology. When he was invited to a meeting about neuroscience he encountered research into the structure of the brain. He was fascinated by what he learned and started to think about the dynamics of simple neural networks. When neurons act together, they can give rise to new and powerful characteristics that are not apparent to someone who only looks at the network's separate components.

In 1980, Hopfield left his position at Princeton University, where his research interests had taken him outside the areas in which his colleagues in physics worked, and moved across the continent. He had accepted the offer of a professorship in chemistry and biology at Caltech (California Institute of Technology) in Pasadena, southern California. There, he had access to computer resources that he could use for free experimentation and to develop his ideas about neural networks.

However, he did not abandon his foundation in physics, where he found inspiration for his understanding of how systems with many small components that work together can give rise to new and interesting phenomena. He particularly benefitted from having learned about magnetic materials that have special characteristics thanks to their atomic spin—a property that makes each atom a tiny magnet. The spins of neighbouring atoms affect each other; this can allow domains to form with spin in the same direction. He was able to make a model network with nodes and connections by using the physics that describes how materials develop when spins influence each other.

The network saves images in a landscape

The network that Hopfield built has nodes that are all joined together via connections of different strengths. Each node can store an individual value—in Hopfield's first work this could either be 0 or 1, like the pixels in a black and white picture.

Hopfield described the overall state of the network with a property that is equivalent to the energy in the spin system found in physics; the energy is calculated using a formula that uses all the values of the nodes and all the strengths of the connections between them. The Hopfield network is programmed by an image being fed to the nodes, which are given the value of black (0) or white (1). The network's connections are then adjusted using the energy formula, so that the saved image gets low energy. When another pattern is fed into the network, there is a rule for going through the nodes one by one and checking whether the network has lower energy if the value of that node is changed. If it turns out that energy is reduced if a black pixel is white instead, it changes colour. This procedure continues until it is impossible to find any further improvements. When this point is reached, the network has often reproduced the original image on which it was trained.

This may not appear so remarkable if you only save one pattern. Perhaps you are wondering why you don't just save the image itself and compare it to another image being tested, but Hopfield's method is special because several pictures can be saved at the same time and the network can usually differentiate between them.

Hopfield likened searching the network for a saved state to rolling a ball through a landscape of peaks and valleys, with friction that slows its movement. If the ball is dropped in a particular location, it will roll into the nearest valley and stop there. If the network is given a pattern that is close to one of the saved patterns it will, in the same way, keep moving forward until it ends up at the bottom of a valley in the energy landscape, thus finding the closest pattern in its memory.

The Hopfield network can be used to recreate data that contains noise or which has been partially erased.

Hopfield and others have continued to develop the details of how the Hopfield network functions, including nodes that can store any value, not just zero or one. If you think about nodes as pixels in a picture, they can have different colours, not just black or white. Improved methods have made it possible to save more pictures and to differentiate between them even when they are quite similar. It is just as possible to identify or reconstruct any information at all, provided it is built from many data points.

Classification using nineteenth-century physics

Remembering an image is one thing, but interpreting what it depicts requires a little more.

Even very young children can point at different animals and confidently say whether it is a dog, a cat, or a squirrel. They might get it wrong occasionally, but fairly soon they are correct almost all the time. A child can learn this even without seeing any diagrams or explanations of concepts such as species or mammal. After encountering a few examples of each type of animal, the different categories fall into place in the child's head. People learn to recognise a cat, or understand a word, or enter a room and notice that something has changed, by experiencing the environment around them.

When Hopfield published his article on associative memory, Geoffrey Hinton was working at Carnegie Mellon University in Pittsburgh, U.S.. He had previously studied experimental psychology and artificial intelligence in England and Scotland and was wondering whether machines could learn to process patterns in a similar way to humans, finding their own categories for sorting and interpreting information. Along with his colleague, Terrence Sejnowski, Hinton started from the Hopfield network and expanded it to build something new, using ideas from statistical physics.

Statistical physics describes systems that are composed of many similar elements, such as molecules in a gas. It is difficult, or impossible, to track all the separate molecules in the gas, but it is possible to consider them collectively to determine the gas' overarching properties like pressure or temperature. There are many potential ways for gas molecules to spread through its volume at individual speeds and still result in the same collective properties.

The states in which the individual components can jointly exist can be analysed using statistical physics, and the probability of them occurring calculated. Some states are more probable than others; this depends on the amount of available energy, which is described in an equation by the nineteenth-century physicist Ludwig Boltzmann. Hinton's network utilised that equation, and the method was published in 1985 under the striking name of the Boltzmann machine.

Recognising new examples of the same type

The Boltzmann machine is commonly used with two different types of nodes. Information is fed to one group, which are called visible nodes. The other nodes form a hidden layer. The hidden nodes' values and connections also contribute to the energy of the network as a whole.

The machine is run by applying a rule for updating the values of the nodes one at a time. Eventually the machine will enter a state in which the nodes' pattern can change, but the properties of the network as a whole remain the same. Each possible pattern will then have a specific probability that is determined by the network's energy according to Boltzmann's equation. When the machine stops it has created a new pattern, which makes the Boltzmann machine an early example of a generative model.

The Boltzmann machine can learn—not from instructions, but from being given examples. It is trained by updating the values in the network's connections so that the example patterns, which were fed to the visible nodes when it was trained, have the highest possible probability of occurring when the machine is run. If the same pattern is repeated several times during this training, the probability for this pattern is even higher. Training also affects the probability of outputting new patterns that resemble the examples on which the machine was trained.

A trained Boltzmann machine can recognise familiar traits in information it has not previously seen. Imagine meeting a friend's sibling, and you can immediately see that they must be related. In a similar way, the Boltzmann machine can recognise an entirely new example if it belongs to a category found in the training material, and differentiate it from material that is dissimilar.

In its original form, the Boltzmann machine is fairly inefficient and takes a long time to find solutions. Things become more interesting when it is developed in various ways, which Hinton has continued to explore. Later versions have been thinned out, as the connections between some of the units have been removed. It turns out that this may make the machine more efficient.

During the 1990s, many researchers lost interest in artificial neural networks, but Hinton was one of those who continued to work in the field. He also helped start the new explosion of exciting results; in 2006 he and his colleagues Simon Osindero, Yee Whye Teh and Ruslan Salakhutdinov developed a method for pretraining a network with a series of Boltzmann machines in layers, one on top of the other. This pretraining gave the connections in the network a better starting point, which optimised its training to recognise elements in pictures.

The Boltzmann machine is often used as part of a larger network. For example, it can be used to recommend films or television series based on the viewer's preferences.

Machine learning—today and tomorrow

Thanks to their work from the 1980s and onward, John Hopfield and Geoffrey Hinton have helped lay the foundation for the machine learning revolution that started around 2010.

The development we are now witnessing has been made possible through access to the vast amounts of data that can be used to train networks, and through the enormous increase in computing power. Today's artificial neural networks are often enormous and constructed from many layers. These are called deep neural networks and the way they are trained is called deep learning.

A quick glance at Hopfield's article on associative memory, from 1982, provides some perspective on this development. In it, he used a network with 30 nodes. If all the nodes are connected to each other, there are 435 connections. The nodes have their values, the connections have different strengths and, in total, there are fewer than 500 parameters to keep track of. He also tried a network with 100 nodes, but this was too complicated, given the computer he was using at the time. We can compare this to the large language models of today, which are built as networks that can contain more than one trillion parameters (one million millions).

Many researchers are now developing machine learning's areas of application. Which will be the most viable remains to be seen, while there is also wide-ranging discussion on the ethical issues that surround the development and use of this technology.

Because physics has contributed tools for the development of machine learning, it is interesting to see how physics, as a research field, is also benefitting from artificial neural networks. Machine learning has long been used in areas we may be familiar with from previous Nobel Prizes in Physics. These include the use of machine learning to sift through and process the vast amounts of data necessary to discover the Higgs particle. Other applications include reducing noise in measurements of the gravitational waves from colliding black holes, or the search for exoplanets.

In recent years, this technology has also begun to be used when calculating and predicting the properties of molecules and materials—such as calculating protein molecules' structure, which determines their function, or working out which new versions of a material may have the best properties for use in more efficient solar cells.

More information: www.nobelprize.org/prizes/phys … dvanced-information/

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