Self-driving cars are just around the corner. Such vehicles will make getting from one place to another safer and less stressful. They also could cut down on traffic, reduce pollution and limit accidents. But how should driverless cars handle emergencies (突发情况)? People disagree on the answer. And that might put the brakes on this technology, a new study concludes.

To understand the challenge, imagine a car that suddenly meets some pedestrians in the road. Even with braking, it’s too late to avoid a crash. So the car’s artificial intelligence must decide whether to swerve (急转弯). To save the pedestrians, should the car swerve off the road or swerve into oncoming traffic? What if such options would likely kill the car’s passengers?

Researchers used online surveys to study people’s attitudes about such situations with driverless cars. Survey participants mostly agreed that driverless cars should be designed to protect the most people. That included swerving into walls (or otherwise sacrificing their passengers) to save a larger number of pedestrians. But there is a hitch (困境). Those same surveyed people want to ride in cars that protect passengers at all costs — even if the pedestrians would now end up dying. Jean Bonnefon is a psychologist at the Toulouse School of Economics in France. He and his colleagues reported their findings in Science.

“Autonomous cars can completely change transportation”, says study coauthor Iyad Rahwan. But, he adds, this new technology creates a moral dilemma (道德两难) that could slow its acceptance.

Makers of driverless cars are in a tough spot, Bonnefon’s group warns. Most buyers would want their car to be programmed to protect them in preference to other people. However, regulations might one day instruct that cars must act for the greater good. That would mean saving the most people. But the scientists think rules like this could drive away buyers. If so, all the potential benefits of driverless cars would be lost.

Compromises might be possible, Kurt Gray says. He is a psychologist at the University of North Carolina. He thinks that even if all driverless cars are programmed to protect their passengers in emergencies, traffic accidents will decrease. Those vehicles might be dangerous to pedestrians on rare occasions. But they “won’t speed, won’t drive drunk and won’t text while driving, which would be a win for society.”

Chinese scientists have created the world’s first light-based quantum (量子) computer named Jiuzhang. It is a milestone in which a quantum machine can solve a problem no classical supercomputer can tackle within a reasonable amount of time.

Experts recognized the Chinese machine as a “state-of-the-art experiment”. Fabio Sciarrino, a quantum physicist at Sapienza University of Rome, told Science News that his first impression of the Chinese quantum computer was, simply, “wow”. Anton Zeilinger, another famous quantum physicist, said that, following this experiment, he predicts there is a very good chance that quantum computers may be used very broadly someday.

Quantum computers stand out at running simulations (模拟) that are impossible for conventional computers. Quantum machines can take computational shortcuts when simulating extremely complex situations, while conventional computers have to force their way to a solution, taking significantly more time in the process. Moreover, it can perform an extreme calculation, called Gaussian boson sampling (玻色子取样), in 200 seconds. The same task would take the world’s fastest classical supercomputer, Fugaku, around 600 million years.

Pan Jianwei, who is recognized as China’s top quantum scientist and one of the key researchers behind Jiuzhang, said the calculations they carried out can not only showcase the machine’s computing power but also demonstrate potential practical applications in machine learning and quantum chemistry.

“Quantum computing has already become a fierce competition area among the United States, Europe and other developed regions,” Pan said, adding that China’s quantum computational advantage took about 7 to 10 years to achieve, since the team first decided to tackle the problem around 2013.

However, Pan stressed that the quantum computer is a highly specialized machine, and is currently only programmed to do boson sampling. “It is not a general-purpose quantum computer, ” he said. In the near future, scientists may increase Jiuzhang’s possible output states — a key indicator of computing power — from 10 to the 30th power to 10 to the 40th power.

In the not-too-distant future, fully autonomous vehicles will drive our streets. These cars will need to make quick decisions to avoid endangering human lives—both inside and outside of the vehicles.

To determine attitudes toward these decisions, a group of researchers created a variation on the classic philosophical exercise known as “the Trolley problem”. They posed a series of moral dilemmas involving a self-driving car with brakes (刹车) that suddenly give out: Should the car change direction to avoid a group of passers-by, killing the driver? Or should it kill the people on foot, but spare the driver? Does it matter if the passers-by are men or women? Children or older people? Doctors or murderers?

To pose these questions to a large range of people, the researchers built a website called Moral Machine, where anyone could click through the situations and say what the car should do. “Help us learn how to make machines moral,” a video asks on the site.

What the researchers found was a series of near-universal preferences, regardless of where someone was from. People everywhere believed the moral thing for the car to do was to spare the young over the old, spare humans over animals, and spare the lives of many over the few. Their findings were published Wednesday in the journal Nature.

Researchers found that the 130 countries with more than 100 respondents could be grouped into three groups that showed similar moral preferences. And these preferences seemed to correlate with social differences. Respondents from collectivistic cultures, which “emphasize the respect that is due to older members of the community,” showed a weaker preference for sparing younger people.

The researchers emphasized that the study’s results should be used with extreme caution (谨慎), and they shouldn’t be considered the final word on societal preferences—especially since respondents were not a representative sample.