The doomsday clock is now 85 seconds to midnight, the closest it has ever been, with the concept of "mirror life" one of the reasons for scientists' deep concern.
The clock was introduced in 1947 by the Bulletin of the Atomic Scientists to indicate threats to humanity and the planet. On Wednesday (AEDT), the bulletin's Science and Security Board said it was now so close to midnight because of the risk of nuclear war, continued climate change, artificial intelligence (AI) and four developments that increase the risk of biological catastrophe.
Those biological developments are: AI tools that can help design biological threats, state-sponsored biological weapons programs, the dismantling of US public health efforts, and research into self-replicating "mirror life".
So what exactly is this potential threat? Where did the idea come from? And why are scientists worried now?
What is 'mirror life'?
If you’re not a chemist, it can be difficult to understand what mirror life is.
The concept builds on a discovery from more than 170 years ago, when French scientist Louis Pasteur showed that some molecules come in mirror-image forms.
In an explainer published after a conference on the risks of "mirror life" hosted by Institut Pasteur, a biomedical research centre in Paris in June last year, and jointly organised with the Mirror Biology Dialogues Fund (MBDF), an international group supporting discussions on the topic, it is described as hypothetical life built from mirror-image versions of the molecules used by all known organisms on Earth.
It explains that all organisms have "left-handed" amino acids to build proteins, and "right-handed" sugars as part of DNA and RNA.
But a mirror organism would flip that and instead use right-handed amino acids and left-handed sugars — a chemical "handedness" known as "chirality".
Currently, no such organism is known to exist in nature. But scientists say it could theoretically be created in a laboratory one day.
What could mirror life mean for humans and the environment?
Some scientists say mirror life could present a threat to not only the environment, but also human life.
Because their chemistry would be reversed, mirror bacteria might evade parts of the immune system, potentially making infections harder to control.
Institut Pasteur's explainer warns that if laboratory-created mirror organisms were released into the environment, ecosystems could be severely disrupted, because existing life may be unable to effectively compete with or regulate them.
In their statement announcing the Doomsday Clock's latest time, the Board of Atomic Scientists referenced a warning from a group of scientists in 2024, which it said had described the synthetic organisms as a "potentially existential threat to all life on Earth".
At the time, the group wrote in the journal Science: "Unless compelling evidence emerges that mirror life would not pose extraordinary dangers, we believe that mirror bacteria and other mirror organisms, even those with engineered biocontainment measures, should not be created."
Some, however, argue there are benefits to researching mirror life.
In meeting notes summarising the views of participants of a round table facilitated by the United Kingdom's Government Office for Science, experts said it's important to distinguish between individual mirror-image molecules and living mirror organisms capable of reproducing.
Benefits are likely to come from the molecules rather than from creating whole mirror organisms. The notes say these molecules may be useful in medicine because they could be less visible to the immune system and harder for the body to break down, meaning treatments could last longer.
The participants also acknowledged risks, though noted that many would not be understood unless mirror life came into being.
They said mirror organism or cells were likely decades away from reality, but could not rule out "fundamental breakthroughs" which could accelerate progress.
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