The interference pattern is a supremely strange result because it implies that both of the particle’s possible paths through the barrier have a physical reality.

The path integral assumes this is how particles behave even when there are no barriers or slits around. First, imagine cutting a third slit in the barrier. The interference pattern on the far wall will shift to reflect the new possible route. Now keep cutting slits until the barrier is nothing but slits. Finally, fill in the rest of space with all-slit “barriers.” A particle fired into this space takes, in some sense, all routes through all slits to the far wall — even bizarre routes with looping detours. And somehow, when summed correctly, all those options add up to what you’d expect if there are no barriers: a single bright spot on the far wall.

It’s a radical view of quantum behavior that many physicists take seriously. “I consider it completely real,” said Richard MacKenzie, a physicist at the University of Montreal.

But how can an infinite number of curving paths add up to a single straight line? Feynman’s scheme, roughly speaking, is to take each path, calculate its action (the time and energy required to traverse the path), and from that get a number called an amplitude, which tells you how likely a particle is to travel that path. Then you sum up all the amplitudes to get the total amplitude for a particle going from here to there — an integral of all paths.

Naïvely, swerving paths look just as likely as straight ones, because the amplitude for any individual path has the same size. Crucially, though, amplitudes are complex numbers. While real numbers mark points on a line, complex numbers act like arrows. The arrows point in different directions for different paths. And two arrows pointing away from each other sum to zero.

The upshot is that, for a particle traveling through space, the amplitudes of more or less straight paths all point essentially in the same direction, amplifying each other. But the amplitudes of winding paths point every which way, so these paths work against each other. Only the straight-line path remains, demonstrating how the single classical path of least action emerges from unending quantum options.

Feynman showed that his path integral is equivalent to Schrödinger’s equation. The benefit of Feynman’s method is a more intuitive prescription for how to deal with the quantum world: Sum up all the possibilities. Sum of All Ripples

Physicists soon came to understand particles as excitations in quantum fields — entities that fill space with values at every point. Where a particle might move from place to place along different paths, a field might ripple here and there in different ways.

Fortunately, the path integral works for quantum fields, too. “It’s obvious what to do,” said Gerald Dunne, a particle physicist at the University of Connecticut. “Instead of summing over all paths, you sum over all configurations of your fields.” You identify the field’s initial and final arrangements, then consider every possible history that links them.

Feynman himself leaned on the path integral to develop a quantum theory of the electromagnetic field in 1949. Others would work out how to calculate actions and amplitudes for fields representing other forces and particles. When modern physicists predict the outcome of a collision at the Large Hadron Collider in Europe, the path integral underlies many of their computations. The gift shop there even sells a coffee mug displaying an equation that can be used to calculate the path integral’s key ingredient: the action of the known quantum fields.

“It’s absolutely fundamental to quantum physics,” Dunne said.

Despite its triumph in physics, the path integral makes mathematicians queasy. Even a simple particle moving through space has infinitely many possible paths. Fields are worse, with values that can change in infinitely many ways in infinitely many places. Physicists have clever techniques for coping with the teetering tower of infinities, but mathematicians argue that the integral was never designed to operate in such an infinite environment.

“It’s like black magic,” said Yen Chin Ong, a theoretical physicist at Yangzhou University in China who has a background in mathematics. “Mathematicians are not comfortable working with things where it’s not clear what’s going on.”

Yet it gets results that are beyond dispute. Physicists have even managed to estimate the path integral for the strong force, the extraordinarily complex interaction that holds together particles in atomic nuclei. They used two main hacks to do this. First, they made time an imaginary number, a strange trick that turns amplitudes into real numbers. Then they approximated the infinite space-time continuum as a finite grid. Practitioners of this “lattice” quantum field theory approach can use the path integral to calculate properties of protons and other particles that feel the strong force, overcoming rickety mathematics to get solid answers that match experiments.

“To someone like me in particle physics,” Dunne said, “that’s the proof that the thing works.” Space-Time = The Sum of What?

The greatest mystery in fundamental physics, however, sits beyond experimental reach. Physicists wish to understand the quantum origin of the force of gravity. In 1915, Albert Einstein recast gravity as the result of curves in the fabric of space and time. His theory revealed that the length of a measuring stick and the tick of a clock change from place to place — that space-time is a malleable field, in other words. Other fields have a quantum nature, so most physicists expect that space-time should too, and that the path integral should capture that behavior.

https://archive.is/dBUUu

Efforts to increase productivity hold lessons for sceptics, too

If Liz Truss can compress a whole premiership into seven weeks, why can’t a standard working week be squashed into something more compact? A six-month pilot scheme, in which around 3,300 workers from 70 companies are testing out a four-day workweek, is due to conclude this month. Proponents say a shorter week delivers a better work-life balance without hurting overall output. Like previous such experiments, it is likely to be hailed a success. A mid-point survey by the trial’s organisers—researchers at the universities of Oxford and Cambridge and Boston College, the 4 Day Week Campaign, a non-profit, and Autonomy, a British think-tank—found that the transition had worked well for 88% of surveyed companies.

Sceptics might observe that the companies involved are self-selecting. Roughly one in five employers who had signed up dropped out before the pilot began, according to the 4 Day Week Campaign. Most of the participants that remain are smaller companies, many of them agencies specialising in management and technology. They also include charities.

But the scheme holds useful lessons about productivity. In particular a four-day week forces firms to think harder about time management. Most businesses in the trial have encouraged employees to leave meetings when they are not contributing, and to be more selective about accepting invitations. Daryl Hine of Stellar, an asset-management company in London, calls this a “diary detox”. This also extends to reducing commutes.

Of the participating organisations, 46% reported maintaining overall output at the same level, and 49% said it had improved. The trial’s largest company, Outcomes First Group, a children’s education and care provider, tracks indicators for its 1,027 participating employees. Its hr department has goals for response time to emails; it staff are given so-called net promoter scores, which track how colleagues rate their services. On both counts, they have made “rare” leaps, says Sharon Platts, the company’s chief people officer. Participants say that their employees feel more motivated. Plenty use the extra day to get errands out of the way before the weekend.

Becoming a four-day operation can be hard in a five-day world, however. Bookishly, an online shop, chose Wednesdays off to avoid having three days in a row when packages are not mailed out; people are warned about the new schedule before they order. But customers are not always prepared to wait, so most firms in the scheme have tried to spread staff more thinly. Platten’s, a fish-and-chip shop in Norfolk, gives its 50-or-so employees two days on and two days off to cover the week. Shifts overlap at busy periods, but organising training and team events has become trickier as a result.

More tests are on the horizon. In January South Cambridgeshire District Council will become the first British local authority to try out a four-day week. The lessons learned are likely to be valuable even if the idea does not spread. Mr Hine says that if performance slips, “gift days” will be rolled back. In busier periods employees may need to come in more. But in one way or another, he says, a slimmer work schedule is “here to stay”. ■7

For more expert analysis of the biggest stories in Britain, sign up to Blighty, our weekly subscriber-only newsletter.

This article appeared in the Britain section of the print edition under the headline "On the fifth day, errands"

A stem cell transplant has cured a man of HIV, researchers have announced.

The Dusseldorf Patient, 53, is only the third person to be cured of the condition using the treatment.

He appears to be the fifth person in total to be cured overall.

He had not taken anti-retroviral medicine, or suppressants, for four years and has not relapsed.

Similar to the other two patients - one in Berlin and another in London), the man, in Dusseldorf, had the transplant to treat a blood disorder, which in his case was leukaemia, that had developed alongside the HIV infection.

More than 10 years after the transplant and four years after ending his HIV therapy, he is in good health.

"I still remember very well the sentence of my family doctor: 'Don't take it so hard. We will experience together that HIV can be cured'," he said.

"At the time, I dismissed the statement as an alibi. Today, I am all the more proud of my worldwide team of doctors who succeeded in curing me of HIV - and at the same time, of course, of leukaemia.

"On Valentine's Day this year, I celebrated the 10th anniversary of my bone marrow transplant in a big way. My bone marrow donor was present as a guest of honour."

Researchers say the virus not returning is the result of thorough scientific and therapeutic preparation and monitoring, adding the study is the longest and most precise diagnostic monitoring of a patient following a stem cell transplantation.

A transplant destroys any unhealthy blood cells and replaces them with healthy ones removed from blood or bone marrow, and due to their high risk, are only carried out within the framework of treating other life-threatening conditions.

The team, which is led by medics at Dusseldorf University Hospital, hope the information they have gained will help more studies into cures for HIV.

Research should now be continued, experts suggest, to help HIV patients overcome infections without the need for this kind of strenuous intervention in the future.

The Dusseldorf Patient was diagnosed with acute myeloid leukaemia (AML), a form of life-threatening blood cancer, six months after starting his HIV therapy, and underwent the stem cell transplant in 2013.

Then, in 2018, after planning and constant monitoring by doctors, the anti-viral HIV therapy - which had ensured any residual HIV was kept under control up to that point - was ended.

On behalf of the international team, Dr Bjorn-Erik Ole Jensen said: "Following our intensive research, we can now confirm that it is fundamentally possible to prevent the replication of HIV on a sustainable basis by combining two key methods.

"On the one hand, we have the extensive depletion of the virus reservoir in long-lived immune cells, and on the other hand, the transfer of HIV resistance from the donor immune system to the recipient, ensuring that the virus has no chance to spread again.

"Further research is now needed into how this can be made possible outside the narrow set of framework conditions we have described."

The Nature Medicine journal has published the study.

In recent years, a man from California has been cured of the condition after his diagnosis in 1988, while Timothy Ray Brown, known as the Berlin Patient, was cured in 2007 - but later died from cancer.

https://en.wikipedia.org/wiki/Optimus_(robot)

I would say it's an expensive publicity stunt, but this is Amazon, $1.5m is nothing to them

The bigger question is why is Amazon investing in seaweed of all things. Wind farm I can understand: cheap electricity to run their datacenters, but seaweed?!

You have 20 seconds to comply.

Treat AI like nuclear weapons, if only one country invests then other countries are at a severe disadvantage. Instead everyone invests in an arms race, which is where we are now

It’s almost as if we are at the knee of an exponential curve just about to go vertical

Eight years ago, a patient lost her power of speech because of ALS, or Lou Gehrig’s disease, which causes progressive paralysis. She can still make sounds, but her words have become unintelligible, leaving her reliant on a writing board or iPad to communicate.

Now, after volunteering to receive a brain implant, the woman has been able to rapidly communicate phrases like “I don’t own my home” and “It’s just tough” at a rate approaching normal speech.

That is the claim in a paper published over the weekend on the website bioRxiv by a team at Stanford University. The study has not been formally reviewed by other researchers. The scientists say their volunteer, identified only as “subject T12,” smashed previous records by using the brain-reading implant to communicate at a rate of 62 words a minute, three times the previous best.

Philip Sabes, a researcher at the University of California, San Francisco, who was not involved in the project, called the results a “big breakthrough” and said that experimental brain-reading technology could be ready to leave the lab and become a useful product soon.

“The performance in this paper is already at a level which many people who cannot speak would want, if the device were ready,” says Sabes. “People are going to want this.”

People without speech deficits typically talk at a rate of about 160 words a minute. Even in an era of keyboards, thumb-typing, emojis, and internet abbreviations, speech remains the fastest form of human-to-human communication.

The new research was carried out at Stanford University. The preprint, published January 21, began drawing extra attention on Twitter and other social media because of the death the same day of its co-lead author, Krishna Shenoy, from pancreatic cancer.

Shenoy had devoted his career to improving the speed of communication through brain interfaces, carefully maintaining a list of records on his laboratory website. In 2019, another volunteer Shenoy worked with managed to use his thoughts to type at a rate of 18 words a minute, a record performance at the time, as we related in MIT Technology Review’s special issue on computing.

The brain-computer interfaces that Shenoy’s team works with involve a small pad of sharp electrodes embedded in a person’s motor cortex, the brain region most involved in movement. This allows researchers to record activity from a few dozen neurons at once and find patterns that reflect what motions someone is thinking of, even if the person is paralyzed.

In previous work, paralyzed volunteers have been asked to imagine making hand movements. By “decoding” their neural signals in real time, implants have let them steer a cursor around a screen, pick out letters on a virtual keyboard, play video games, or even control a robotic arm.

In the new research, the Stanford team wanted to know if neurons in the motor cortex contained useful information about speech movements, too. That is, could they detect how “subject T12” was trying to move her mouth, tongue, and vocal cords as she attempted to talk?

These are small, subtle movements, and according to Sabes, one big discovery is that just a few neurons contained enough information to let a computer program predict, with good accuracy, what words the patient was trying to say. That information was conveyed by Shenoy’s team to a computer screen, where the patient’s words appeared as they were spoken by the computer.

The new result builds on previous work by Edward Chang at the University of California, San Francisco, who has written that speech involves the most complicated movements people make. We push out air, add vibrations that make it audible, and form it into words with our mouth, lips, and tongue. To make the sound “f,” you put your top teeth on your lower lip and push air out—just one of dozens of mouth movements needed to speak.
A path forward

Chang previously used electrodes placed on top of the brain to permit a volunteer to speak through a computer, but in their preprint, the Stanford researchers say their system is more accurate and three to four times faster.

“Our results show a feasible path forward to restore communication to people with paralysis at conversational speeds,” wrote the researchers, who included Shenoy and neurosurgeon Jaimie Henderson.

David Moses, who works with Chang’s team at UCSF, says the current work reaches “impressive new performance benchmarks.” Yet even as records continue to be broken, he says, “it will become increasingly important to demonstrate stable and reliable performance over multi-year time scales.” Any commercial brain implant could have a difficult time getting past regulators, especially if it degrades over time or if the accuracy of the recording falls off. A 67-year-old ALS patients broke speed records using a brain implant to communicate. The implanted device uses neural signals to detect the words she is trying to say, conveying them to a computer screen.

WILLETT, KUNZ ET AL

The path forward is likely to include both more sophisticated implants and closer integration with artificial intelligence.

The current system already uses a couple of types of machine learning programs. To improve its accuracy, the Stanford team employed software that predicts what word typically comes next in a sentence. “I” is more often followed by “am” than “ham,” even though these words sound similar and could produce similar patterns in someone’s brain.

Adding the word prediction system increased how quickly the subject could speak without mistakes.
Language models

But newer “large” language models, like GPT-3, are capable of writing entire essays and answering questions. Connecting these to brain interfaces could enable people using the system to speak even faster, just because the system will be better at guessing what they are trying to say on the basis of partial information. “The success of large language models over the last few years makes me think that a speech prosthesis is close at hand, because maybe you don’t need such an impressive input to get speech out,” says Sabes.

Shenoy’s group is part of a consortium called BrainGate that has placed electrodes into the brains of more than a dozen volunteers. They use an implant called the Utah Array, a rigid metal square with about 100 needle-like electrodes.

Some companies, including Elon Musk’s brain interface company, Neuralink, and a startup called Paradromics, say they have developed more modern interfaces that can record from thousands—even tens of thousands—of neurons at once.

While some skeptics have asked whether measuring from more neurons at one time will make any difference, the new report suggests it will, especially if the job is to brain-read complex movements such as speech.

The Stanford scientists found that the more neurons they read from at once, the fewer errors they made in understanding what “T12” was trying to say.

“This is a big deal, because it suggests efforts by companies like Neuralink to put 1,000 electrodes into the brain will make a difference, if the task is sufficiently rich,” says Sabes, who previously worked as a senior scientist at Neuralink.

For these large machines hydrogen makes more sense then lithium ion as these machines work 24 hours a day and there is simply no time to charge the batteries, especially given just how many batteries would be needed for these beasts.

I was trying to be funny

https://i.imgur.com/XVW1Zss.png

It is possible that the increased use of AI in various industries could lead to job loss in certain fields, as machines and algorithms become capable of performing tasks that were previously done by humans. However, it is also possible that the development and implementation of AI could lead to the creation of new jobs, particularly in fields related to technology and data analysis. Additionally, some experts believe that AI could lead to a more efficient division of labor, where humans and machines collaborate to perform tasks more effectively.

> I can't take AI seriously right now, it feels like each post is written by an AI and each comment agreeing is written by an AI. And there 30 posts per day about AI with no substance.

It is true that there is a lot of hype around AI, and not all of it is grounded in reality. However, it's important to remember that AI is a rapidly-evolving field with many exciting developments happening all the time. While it's true that not every article or post about AI is going to be informative or valuable, it's still a worthwhile area of study and research. It's also important to keep in mind that AI can be useful in many different fields, from healthcare to finance to transportation, and that its potential for improving people's lives is significant.

https://i.imgur.com/XVW1Zss.png

More like 20:30 (half past eight the same day)

I remember the scene in Kim Stanley Robinsons Red Mars where the space elevator was destroyed and wrapped around the planet a few times causing death and destruction. Was a fun read, recommended!

Monkeys first. Then you. Then me.

The global rate includes the water, which is 70% of the planet. Strangely the land is the bit that gets reported on most and is the bit that warms fastest.

Once the oceans get to 2 degrees warmer it’s game over because the land will be 5 degrees warmer

Maybe it's 14.4 inches