A fundamental quantum physics problem has been proved unsolvable

For the first time a major physics problem has been proved unsolvable, meaning that no matter how accurately a material is mathematically described on a microscopic level, there will not be enough information to predict its macroscopic behaviour.

The research, by an international team of scientists from UCL, the Technical University of Music and the Universidad Complutense de Madrid – ICMAT, concerns the spectral gap, a term for the energy required for an electron to transition from a low-energy state to an excited state.

Spectral gaps are a key property in semiconductors, among a multitude of other materials, in particular those with superconducting properties. It was thought that it was possible to determine if a material is superconductive by extrapolating from a complete enough microscopic description of it, however this study has shown that determining whether a material has a spectral gap is what is known as “an undecidable question”.

“Alan Turing is famous for his role in cracking the Enigma, but amongst mathematicians and computer scientists, he is even more famous for proving that certain mathematical questions are `undecidable’ – they are neither true nor false, but are beyond the reach of mathematics code,” said co-author Dr Toby Cubitt, from UCL Computer Science.

“What we’ve shown is that the spectral gap is one of these undecidable problems. This means a general method to determine whether matter described by quantum mechanics has a spectral gap, or not, cannot exist. Which limits the extent to which we can predict the behaviour of quantum materials, and potentially even fundamental particle physics.”

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The research, which was published today in the journal Nature, used complex mathematics to determine the undecidable nature of the spectral gap, which they say they have demonstrated in two ways:

“The spectral gap problem is algorithmically undecidable: there cannot exist any algorithm which, given a description of the local interactions, determines whether the resulting model is gapped or gapless,” wrote the researchers in the journal paper.

“The spectral gap problem is axiomatically independent: given any consistent recursive axiomatisation of mathematics, there exist particular quantum many-body Hamiltonians for which the presence or absence of the spectral gap is not determined by the axioms of mathematics.”

In other words, no algorithm can determine the spectral gap, and no matter how the maths is broken down, information about energy of the system does not confirm its presence.

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The research has profound implications for the field, not least for the Clay Mathematics Institute’s infamous $1m prize to prove whether the standard model of particular physics, which underpins the behaviour of the most basic particulars of matter, has a spectral gap using standard model equations.

“It’s possible for particular cases of a problem to be solvable even when the general problem is undecidable, so someone may yet win the coveted $1m prize. But our results do raise the prospect that some of these big open problems in theoretical physics could be provably unsolvable,” said Cubitt.

“We knew about the possibility of problems that are undecidable in principle since the works of Turing and Gödel in the 1930s,” agreed co-author Professor Michael Wolf, from the Technical University of Munich.

“So far, however, this only concerned the very abstract corners of theoretical computer science and mathematical logic. No one had seriously contemplated this as a possibility right in the heart of theoretical physics before. But our results change this picture. From a more philosophical perspective, they also challenge the reductionists’ point of view, as the insurmountable difficulty lies precisely in the derivation of macroscopic properties from a microscopic description.”

“It’s not all bad news, though,” added Professor David Pérez-García, from the Universidad Complutense de Madrid and ICMAT. “The reason this problem is impossible to solve in general is because models at this level exhibit extremely bizarre behaviour that essentially defeats any attempt to analyse them.

“But this bizarre behaviour also predicts some new and very weird physics that hasn’t been seen before. For example, our results show that adding even a single particle to a lump of matter, however large, could in principle dramatically change its properties. New physics like this is often later exploited in technology.”

Domino's takes the lead in drone delivery

Domino's Pizza has carried out a demonstration of its pizza delivery drones in Auckland, New Zealand. “We’ve always said that it doesn’t make sense to have a 2-tonne machine delivering a 2-kilogram order,” said Domino’s CEO Don Meij in a statement.

Source: Fortune

Israel deploys self-driving military vehicles

The Israeli Defense Forces (IDF) has revealed that it has deployed fully automated self-driving military vehicles to patrol the border of the Gaza Strip. According to reports, the IDF's also plans to place them alongside Israel's borders with Egypt, Jordan, Syria, and Lebanon.

Source: The Mainichi

World's first self-driving taxis available in Singapore

Autonomous vehicle startup nuTonomy has beaten Uber, who plan to introduce autonomous cars in Pittsburgh in the next few weeks, to become the first company to offer a self-driving taxi service. The cars are available to select members of the public in Singapore.

Natural batteries to power ingestible medical devices

A group of researchers have claimed that non-toxic, edible batteries could one day be used to diagnose and treat disease. The team believe batteries made with melanin pigments, naturally found in the skin, hair and eyes would power ingestible devices.

Source: Phys.org

Columbia is using Lego-like architecture to house its urban poor

A company in Colombia is using interlocking LEGO-like bricks to build houses for a few thousand dollars per structure. The houses are made from recycled plastic blocks that are easy to use and require no construction experience to put together.

Source: Web Urbanist

Stem cell therapy may be able to reverse permanent brain damage

The damage suffered by stroke victims may be reversible thanks to a developing therapeutic technique. The new approach combines transplanted human stem cells with a special protein that stimulates neuron growth.

Source: Medical Xpress

Face transplant surgeons herald the dawn of “a new era in transplant surgery”

Surgeons for the firefighter Patrick Hardison, who last year underwent the most extensive face transplant in history, have heralded the dawn of a new era in transplant surgery after reporting extremely successful results from the procedure.

“We have entered a new era in transplant surgery,” said Dr Eduardo D Rodriguez, chair Hansjörg Wyss Department of Plastic Surgery at NYU Langone and lead surgeon of the 100-strong team that performed the transplant.

“The work being done, not only in face transplantation, but also in areas like hand, uterine, and penile transplantation, is pushing the boundaries of medicine and surgery and opening up new avenues to restore the lives of people like Patrick. It’s a very exciting time.”

Hardison, a former volunteer firefighter from Mississippi, the US, underwent the face transplant in August 2015, having suffered severe burns to his face and neck during a firefighting attempt 14 years previously.

The surgery, which involved the most extensive soft tissue face transplant in history, was somewhat of a new frontier for the field, meaning it was difficult to predict how well Hardison would recover. However, his recovery has been remarkable, far exceeding what his surgeons expected.

“We are amazed at Pat’s recovery, which has surpassed all of our expectations,” said Rodriguez.

Patrick Hardison's recovery over the past year, from immediately post-surgery (top left) to the start of August 2016 (bottom right). Above: Hardison has his eyes examined as part of a checkup

Patrick Hardison’s recovery over the past year, from immediately post-surgery (top left) to the start of August 2016 (bottom right). Above: Hardison has his eyes examined as part of a checkup

Transplant patients often experience some form of rejection, however Hardison not shown any such signs. His transplanted eye lids and blinking mechanisms have also begun to work fully, ensuring his eyesight has been preserved – by no means guaranteed prior to the surgery.

“Most significant is the lack of a rejection episode. We believe this has much to do with the methodical approach we took in the matching process to ensure that Patrick’s donor provided the most favourable match,” said Rodriguez. “Doing so also has allowed us to reduce the levels of certain medications that Pat takes to prevent rejection.”

The recovery has been so quick that the surgeons were able to commence a number of smaller procedures to complete the process considerably ahead of schedule. This included the removal of feeding and breathing tubes Hardison has relied on since his injury, as well as minor adjustments to his forehead, eyes, lips and chin.

Dr Eduardo Rodriguez, who led the 100-strong team to perform the face transplant. Images courtesy of NYU Langone

Dr Eduardo Rodriguez, who led the 100-strong team to perform the face transplant. Images courtesy of NYU Langone

Rodriguez and his colleagues have published extensive details of the case in a series of academic papers, allowing other surgeons to perform similar procedures in the future, and ultimately enabling face transplants to become a commonplace technique, rather than one worthy of international news coverage.

There have also been some efforts to improve access to such surgeries.

“Since last year’s face transplant, other initiatives have progressed,” explained Helen Irving, president and CEO of LiveOnNY, an organ recovery organisation operating in the greater New York Metropolitan area.

“To date, face transplants in the US have been supported, at least in part, by research funding. The US Department of Defense, in concert with transplant centers, is collaborating with insurance carriers to provide coverage for face transplantation. And here in New York, the state government is considering new legislation to strengthen opportunities for organ donation.”

Study finds biofuels are contributing to climate change, not mitigating it

Biofuels such as ethanol and biodiesel are not anywhere near as environmentally friendly as previously thought.

A study by researchers at the University of Michigan, published today in the open-access journal Climactic Change, has found that biofuels actually increase the heat-trapping carbon dioxide emissions responsible for global warming, despite their reputation for being a ‘clean’ fuel source.

It was previously thought that such fuels were carbon-neutral, based on the premise that the CO₂ they produce when burnt was balanced by the CO₂ the plants absorbed as they grew. However, this study has found that the crops’ CO₂ absorption only mitigated a fraction of its emissions.

Using extensive crop production data from the US Department of Agriculture, alongside data on fossil fuel production and vehicle emissions, the researchers found that during a time when biofuel use rapidly increased in the US, the biofuel crops’ CO₂ absorption only offset 37% of their emissions when burnt.

“This is the first study to carefully examine the carbon on farmland when biofuels are grown, instead of just making assumptions about it,” explained research professor and study lead author John DeCicco, from the University of Michigan Energy Institute.

“When you look at what’s actually happening on the land, you find that not enough carbon is being removed from the atmosphere to balance what’s coming out of the tailpipe.”

A vehicle owner tops up his car using the biofuel ethanol in Washington State, the US. The country has promoted biofuels as a green alternative for transport. Image courtesy of Carolina K. Smith MD / Shutterstock.com

A vehicle owner tops up his car using the biofuel ethanol in Washington State, the US. The country has promoted biofuels as a green alternative for transport. Image courtesy of Carolina K. Smith MD / Shutterstock.com

The findings have significant ramifications for climate change mitigation approaches, as biofuels have increasingly been used as a cleaner alternative to petroleum. In many parts of the world they form a vital part of government-backed plans to reduce carbon emissions; a role that may well need to be reconsidered now that such strong doubt has been cast on their effectiveness.

In the US, for example, they are recommended for transportation purposes by the US Renewable Fuel Standard, which has helped to spur growth in production in the country from 4.2 billion gallons in 2005 to 14.6 billion gallons in 2013.

The researchers have even gone so far as to argue biofuels are worse than other traditional fuel sources, due to the false sense of security they provide to policymakers.

“When it comes to the emissions that cause global warming, it turns out that biofuels are worse than gasoline,” said DeCicco.

“So the underpinnings of policies used to promote biofuels for reasons of climate have now been proven to be scientifically incorrect.”

Biofuels are often presented as environmentally friendly, such as in this concept image. This will now have to change as a result of the study's findings

Biofuels are often presented as environmentally friendly, such as in this concept image. This will now have to change as a result of the study’s findings

As a result of the shocking findings, the researchers are now recommending that policymakers reconsider their use of biofuels to mitigate climate change.

“Policymakers should reconsider their support for biofuels,” said DeCicco.

“This issue has been debated for many years. What’s new here is that hard data, straight from America’s croplands, now confirm the worst fears about the harm that biofuels do to the planet.”