Travelling into the future is supported by established physics, but journeys into the past may be impossible in a wide range of theoretical universes, according to research by a physicist at the University of Jinan in China.

Hongsheng Zhang’s study examines the conditions required for time travel under Einstein’s theory of relativity. It argues that, in many possible descriptions of the universe, the structure of spacetime prevents objects from returning to an earlier point in their own history.

The argument is based on the relationship between the direction of light and the movement of objects through spacetime. Light defines boundaries that divide spacetime into layers. Objects moving either slower or faster than light must cross these surfaces in the same direction.

Zhang compares this arrangement to climbing a staircase on which every step leads upwards. If movement is restricted to one direction, returning to a previous step is impossible.

The research does not rely on exotic matter, quantum effects or assumptions about the material making up the universe. Zhang told ScienceAlert that the argument is essentially about keeping track of directions in spacetime.

Two possible ways around the restriction

Physicists describe theoretical journeys into the past as closed timelike curves. These are paths through spacetime that return to the same location and moment from which they began.

Although Einstein’s equations permit such paths in certain mathematical scenarios, Zhang’s research identifies two conditions that could allow them to exist.

The first involves the twisting of light rays. Under certain conditions, light can spiral around itself rather than travelling along parallel paths. This prevents the formation of the surfaces that normally enforce the one-way direction of movement through time.

Such behaviour is associated with the intense gravitational effects near the centre of a spinning black hole. Einstein’s theory predicts that rotating masses drag spacetime around them, an effect known as frame-dragging. NASA’s Gravity Probe B mission measured this phenomenon around Earth in 2011.

Near the centre of a rotating black hole, the effect could become strong enough to create paths that loop back towards their starting point. Physicist Brandon Carter demonstrated the mathematical possibility of such curves inside spinning black holes in 1968.

The second possibility concerns the overall shape of the universe. Even if the local structure of spacetime enforces forward movement, its global geometry could allow a path to circle back to its starting point. Some theoretical time machines, including those based on wormholes, rely on this possibility.

Zhang acknowledged that the research does not establish whether either condition occurs in nature. The study is awaiting peer review.

Travelling into the future

Travel into the future is on firmer scientific ground. Relativity shows that clocks run more slowly for objects moving at very high speeds or experiencing stronger gravity.

Astronauts aboard the International Space Station therefore age slightly more slowly than people on Earth, returning a few thousandths of a second younger than they otherwise would have been, according to the European Space Agency.

The findings do not settle whether travelling into the past is possible in our universe, but they identify the theoretical obstacles such a journey would need to overcome.

Some of the world’s largest technology companies are working with environmental organisations to develop national guidelines for data centre construction and operation in the United States, as growing opposition to the facilities raises concerns about their impact on local communities.

The group, known as the Responsible Data Center Collaborative, includes Google, Meta, Microsoft, Oracle, Amazon, Nvidia and Anthropic. Environmental organisations taking part include the Natural Resources Defense Council (NRDC), World Wildlife Fund (WWF) and Sierra Club, according to a document seen by AFP on Thursday.

The members began meeting in September and plan to continue discussions until February 2027. The initiative is supported by the Rockefeller Foundation and its affiliated organisation, Invest in Our Future.

The proposed guidelines will address electricity consumption, infrastructure, water resources, community engagement, economic benefits, transparency and accountability. The group also intends to discuss how the standards should be implemented.

The document setting out the framework for the discussions encourages participants to question assumptions, seek clarification and focus on problems rather than individuals. Meetings will follow Chatham House rules, allowing participants to share lessons from the discussions without attributing comments to specific individuals or organisations.

The initiative comes as resistance to data centre expansion grows in the United States and Europe. More than 100 organisations across 15 European countries are organising protests on 6 and 7 November, calling for a pause on large-scale projects until clearer regulations are introduced.

Rising energy and water demands

Data centres provide the computing infrastructure needed to develop and operate artificial intelligence systems, but their growing electricity and water requirements have raised concerns among residents and environmental groups.

A 2026 report by the International Energy Agency found that global electricity consumption by data centres increased by 17 per cent in 2025. Demand is projected to almost double from 485 terawatt-hours to 950 terawatt-hours by 2030, partly because of the expansion of AI.

The increase is placing additional pressure on electricity grids and raising questions about whether existing infrastructure can meet demand. Critics have also linked new power generation projects to higher electricity bills for households.

Other concerns include noise from data centre equipment and the large quantities of municipal water used by cooling systems. Some cooling towers can also produce mist that may carry harmful bacteria.

In an effort to avoid adding pressure to local power supplies, some newer facilities generate their own electricity, often through gas-fired plants that can create additional noise and pollution.

Public opposition has also entered local politics. During the US midterm elections on Tuesday, voters in dozens of cities reportedly approved measures restricting or banning data centre projects.

The collaborative brings technology companies and environmental groups into discussions over how the industry should expand while addressing concerns about energy use, water consumption and the effects on surrounding communities.

The parents of a 13-year-old girl have filed a lawsuit against Google, alleging that their daughter used the company’s artificial intelligence-powered search features to plan a possible suicide and her funeral.

The case, filed on Monday, 2 November, in a California court, is believed to be the first to accuse Google of negligence over AI features available through its search engine on a school-issued Chromebook. The laptops are widely used in schools, where access to certain online services is often restricted.

The girl, identified in the complaint as Emma, could not access Google’s Gemini app or OpenAI’s ChatGPT because her school had blocked both services. However, she remained able to use Google Search, which offers AI-powered features.

According to the lawsuit, Emma had no previous history of mental illness but experienced what her family described as a serious psychological crisis within months of using the search engine.

On 17 March, school monitoring software alerted staff to a document titled “Funeral”. The school contacted her parents, and her mother later discovered that Emma was writing a farewell letter. Her father intervened after finding out what was happening.

The lawsuit raises questions about whether existing safeguards on AI-powered search tools are sufficient to protect children, particularly when the services are accessed through devices provided by schools.

“Schools should turn search off and keep it off until Google removes AI mode from search or ensures that every single student is always safe when they’re interacting with AI,” Andrew Liddell, one of the family’s lawyers, told AFP on Thursday, 5 November.

Google said it was examining the allegations and took the matter seriously. Company spokesperson Jose Castaneda said its AI Mode included safeguards designed to prevent self-harm and attempts to bypass those protections.

Growing legal scrutiny of technology companies

The lawsuit comes as major technology companies face increasing legal pressure over alleged harm linked to their AI products.

OpenAI is facing several wrongful death lawsuits, including a case brought by the parents of 16-year-old Adam Raine. They allege that ChatGPT provided harmful advice before their son died by suicide.

Google and Character.AI also agreed in January to settle several lawsuits filed by families of teenagers outside court.

Separately, Google, TikTok and Meta filed lawsuits against California on Wednesday, seeking to block a state law aimed at restricting addictive social media features for users under 16.

Signed by Governor Gavin Newsom in September, the legislation is scheduled to take effect on 1 January 2027. The legal challenges add to wider disputes over how technology companies should protect young users from potential harm associated with their platforms.