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Quantum tunnelling matters in two very different space contexts: it helps explain how some nuclear reactions can occur inside stars, and it is a subject of proposed experiments with ultracold atoms in orbit. NASA’s Cold Atom Lab has demonstrated space-based atom-interferometry research, but its work is not a direct reproduction of tunnelling inside a star.
What quantum tunnelling means
In classical mechanics, a particle without enough energy to cross a barrier cannot get to the other side. Quantum mechanics describes particles with a wave function, which can extend into and beyond that barrier. As a result, there is a finite probability of finding the particle on the far side: it has tunnelled through a region that classical physics treats as forbidden.
NASA illustrates the idea with alpha decay, a nuclear process in which tunnelling helps an alpha particle escape a nucleus. The same basic quantum effect is relevant to some nuclear reactions in stars. NASA’s educational explanation emphasizes that the universe’s large-scale structures and behavior still depend, in part, on quantum processes at microscopic scales (NASA Goddard Space Flight Center’s explanation of quantum tunnelling).
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Stars produce energy largely through reactions between atomic nuclei. Those nuclei are positively charged and repel one another, so a classical account would require them to overcome an energy barrier to get close enough to react. Tunnelling gives some nuclei a probability of crossing that barrier even when a purely classical picture would rule out the reaction under those conditions.
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That makes tunnelling a contributing quantum mechanism in stellar nuclear physics, not a complete explanation of how stars work or their only source of energy. A NASA-hosted white paper lists nuclear fusion and the formation of low-mass stars among phenomena connected with tunnelling (Bondar and coauthors’ white paper on tunnelling physics in microgravity).
What “tunnelling in space” means in orbital research
“In space” can also mean experiments conducted in a laboratory in orbit, rather than physical processes occurring in stars. NASA’s Cold Atom Lab (CAL), aboard the International Space Station, prepares ultracold gases for quantum research. Laser cooling and magnetic trapping allow scientists to study gases such as rubidium and potassium. In microgravity, the gases can be observed for longer and cooled to lower temperatures than in comparable quantum-gas studies on Earth, according to NASA’s June 2026 update.
CAL launched to the ISS in 2018, NASA reports. In a study published in November 2023, researchers carried out simultaneous atom-interferometry experiments with rubidium and potassium gases in space. NASA describes this as a laboratory capability—not as a measurement of tunnelling inside a star (NASA Science’s overview of matter-wave interferometry aboard the ISS; NASA JPL’s 2023 report on the Cold Atom Lab).
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What has flown and what remains proposed
NASA’s Cold Atom Lab has conducted ultracold-atom and atom-interferometry research in orbit. A NASA white paper, by contrast, outlines a broader program of possible experiments with interacting quantum gases in microgravity, including spaceborne tunnelling accelerometers. Describing those proposals does not establish that every proposed experiment has flown or produced a result.
The distinction matters: CAL provides a controlled setting for studying quantum gases, while tunnelling in stars is an astrophysical process inferred and explained through nuclear physics. The reviewed NASA accounts do not establish that CAL directly reproduces or observes tunnelling inside stars. The white-paper authors summarize the classical-versus-quantum difference this way: “While in classical physics particles reflect from barriers, quantum theory allows them to tunnel through such classically forbidden regions.”
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NASA identifies possible future uses for space-based quantum sensors, including more precise gravity measurements and tests of fundamental physics. Matter-wave interferometers may also have applications in positioning, navigation, and timing. These are prospective uses, not demonstrated operational services. NASA JPL’s June 2026 update describes the upgraded CAL science module as part of work toward such capabilities. Jason Williams, CAL project scientist at JPL, said: “What we’re doing with cold atom science in general is looking for and learning about new tools that nature gives us.” Ethan Elliott, CAL deputy project scientist at JPL, said: “As the first project to create Bose-Einstein condensates in orbit, we’re demonstrating that we can make quantum technology work reliably in space.” (NASA JPL’s June 2026 Cold Atom Lab update.)
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What the evidence does not establish
- There is no quantified rate or percentage for “quantum tunnelling in space as a whole” in the NASA sources covered here.
- The Cold Atom Lab’s orbital experiments are not evidence that it has measured tunnelling inside stars.
- NASA’s discussion of organic molecules in star-forming regions does not establish that tunnelling formed any particular interstellar molecule (NASA Astrobiology’s research overview).
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