Can anything travel faster than light? Not through space, according to Einstein's relativity. But in March 2021 Erik Lentz, an astrophysicist then at the University of Göttingen in Germany, published a paper arguing that a "warp bubble" which carries a ship along by reshaping space itself could, mathematically, be built from ordinary positive energy instead of the exotic negative energy earlier warp-drive ideas required. The catch is enormous: by his own estimate, the energy needed would be hundreds of times the mass of Jupiter, and other physicists soon challenged the core claim.
Here is what the paper actually showed, what it did not, and where the debate stands.
The light-speed limit and the loophole
Special relativity sets a firm rule: no object can be accelerated through space to the speed of light or beyond. General relativity, however, describes space and time as a flexible fabric that can stretch and bend. The rule applies to motion through that fabric, not to the fabric itself.
That is why distant galaxies can recede from us faster than light as the universe expands without breaking any law of physics. Warp-drive proposals try to use the same idea locally: rather than pushing a ship through space, they reshape the space around it so the ship is carried along inside a bubble while sitting still relative to its immediate surroundings.
From Alcubierre to negative energy
The modern version of the idea comes from the Mexican physicist Miguel Alcubierre, who in 1994 described a solution to Einstein's equations in which space contracts in front of a craft and expands behind it. On paper, the bubble could travel faster than light while the passengers inside feel no acceleration.
The problem is the fuel. Alcubierre's geometry requires regions of negative energy density, something that would need "exotic matter" with properties no one has ever produced in useful amounts. Tiny negative-energy effects do exist in quantum physics, such as the Casimir effect between closely spaced metal plates, but nothing like the quantities a warp drive would demand. Early estimates required more exotic matter than the mass of the observable universe; later refinements reduced the figures dramatically, but the need for negative energy remained.
Wormholes, another favourite of science fiction, run into a similar obstacle: keeping one open is also thought to require negative energy.
What Lentz's paper proposed
Lentz's paper, "Breaking the Warp Barrier: Hyper-Fast Solitons in Einstein–Maxwell–Plasma Theory", appeared in the journal Classical and Quantum Gravity, and Göttingen announced it on 9 March 2021. He explored configurations of space-time curvature that had not been studied before and described a new class of "solitons": compact, self-reinforcing waves that keep their shape as they move.
His central claim was that these warp bubbles could, in principle, be sourced entirely by positive energy, using the physics of electromagnetic fields and plasma rather than exotic matter. He also designed them so that tidal forces inside were minimal and clocks inside ran at the same rate as clocks outside, meaning travellers would not return younger than the people they left behind.
If the energy could be supplied, the press release said, a round trip to Proxima Centauri, the nearest star, might take years rather than the more than 50,000 years a chemical rocket would need for the journey one way.
The energy problem
Lentz was frank about the obstacle. For a bubble 100 metres in radius moving at light speed, he estimated the energy required at hundreds of times the mass of Jupiter, expressed as energy through E = mc². To come within reach of a modern nuclear fission power plant, he said, the requirement would have to fall by about 30 orders of magnitude, a factor of a million trillion trillion.
He pointed out that earlier research had proposed energy-saving tricks for warp geometries that might cut requirements by nearly 60 orders of magnitude, and said he was at an early stage of checking whether they could be adapted to his solitons. In the university's announcement he described the work as moving faster-than-light travel "one step away from theoretical research" and closer to engineering, with prototypes a possible step much further down the road.
Around the same time, Alexey Bobrick and Gianni Martire published "Introducing physical warp drives" in the same journal. They argued that some warp drives moving slower than light could be built from ordinary positive-energy matter, while faster-than-light versions still appeared to need negative energy. Early reports described the two efforts as complementary.
The critics' response
The positive-energy claim did not go unchallenged. In 2021 the physicists Jessica Santiago, Sebastian Schuster and Matt Visser posted an analysis titled "Generic warp drives violate the null energy condition." They argued that earlier positive-energy claims checked the energy only from the viewpoint of one particular family of observers. Looked at from every possible observer's frame, they concluded, all physically reasonable warp drives still require negative energy somewhere.
Lentz himself, in a later summary of the work prepared for a 2021 physics conference, listed problems still to be solved: checking the solutions against a stricter energy condition, dealing with horizons, and finding any mechanism that could actually create such a bubble. Other long-standing objections to warp drives include whether a crew could steer or stop a bubble they cannot send signals through, and whether quantum effects would destabilise it.
What the study did and did not show
- It did present a new family of mathematical solutions to Einstein's equations and argue that they avoid negative energy.
- It did not build or test anything. No experiment has moved any object faster than light.
- It did not overturn relativity. Like all warp ideas, it works within general relativity rather than against it.
- It is disputed. Whether any warp drive can truly avoid negative energy remains an open and contested question among relativity researchers.
The real value of work like this is in mapping what Einstein's theory does and does not allow. Even if warp drives never leave the page, testing their limits sharpens our understanding of gravity, energy and the structure of space-time.
Sources: University of Göttingen press release, 9 March 2021: Breaking the warp barrier for faster-than-light travel; Santiago, Schuster and Visser: Generic warp drives violate the null energy condition (arXiv); Lentz: Hyper-Fast Positive Energy Warp Drives (arXiv); Wikipedia: Alcubierre drive. Story first reported by ScienceAlert.
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