Image: Bruce Rolff
The Science
In 1935 Einstein and Rosen wrote a paper in which the Einstein-Rosen Bridge was introduced. This appeared to be a “bridge” between widely separated regions of the universe. At the middle of the bridge was a singularity.
50 years later the results were used by Throne and Morris to construct traversable wormholes. But there is another interpretation of the bridge, that is at the singularity the arrow of time reverses.
This interpretation solves some other difficult problems in physics like black hole information loss. If one looks at the bridge as between two arrows of time then particles go into the bridge and come out, the difference is that they are traveling in opposite time directions. Information no longer is destroyed or lost but changes its time direction.
Another benefit to this interpretation is that it can lead to a quantum theory of gravity. Since in quantum mechanics there is no asymmetry between forward and backward in time, an antiparticle going forward in time is equivalent to a particle going back in time, this interpretation of the ER bridge brings the same idea into general relativity. An obstacle to the merging of quantum mechanics and GR has been removed.
Now, the singularity of the ER bridge isn't so much a singularity that destroys time and space but is simply a bridge. This interpretation can lead to a form of time travel. Cross the bridge to travel back in time, then recross to continue forward in time but at a point that was originally in the past.
References:
The Particle Problem in the General Theory of Relativity; A. Einstein, N. Rose; Physical Review, Volume 48, July 1, 1935.
A new understanding of Einstein-Rosen bridges; Enrique Gazta˜naga1, K. Sravan Kumar and Jo˜ao Marto; arXiv:2512.20691v2 [physics.gen-ph] 8 Jan 2026.
Physicists Rethink Time… And It Solves Several Big Problems; Sabine Hossenfelder; Youtube, February 2026.
The Extrapolation
So, we have a physical basis for time travel IF we can create a singularity and travel back and forth across its horizon.
Creating the singularity is easy, it already has an extrapolated creation device from my Future Chron Universe, the wormhole generator. I used this device to open wormhole mouths and keep them open for a spaceship to travel through the spacetime shortcut. I also used it to create a wormhole weapon by creating a microscopic singularity and letting it evaporate explosively through Hawking radiation. Soon, I expect to put up my notes for the device and will supply a link to those notes here, Wormhole Generator.
Taking the device as a given, then the next challenge is how to cross the horizon of the ER bridge singularity without being crushed. A clue can be found in the definitions of the event horizon and the apparent (or gravitational) horizon of a black hole. The event horizon is a fixed boundary through which you cross into a black hole, eventually encountering its singularity. The apparent horizon is a variable horizon that coincides with the event horizon after the black hole has existed for a long enough time.
In other words, the apparent horizon is a dynamical property of a black hole that can change over time. Eventually, it will merge into the event horizon, but until it does it can change in size as the black hole changes.
To apply it to the time singularity we can note that this apparent horizon is the beginning and end of the ER bridge. We do not so much cross the bridge as its location shifts with the apparent horizon. We never encounter the time singularity, only the apparent horizon which covers and then uncovers according to the dynamical evolution of the ER bridge.
It's like a curtain that sweeps over us, reversing our arrow of time, then sweeps back, restoring our arrow of time. But before we return to our universe we have traveled in time an interval dependent on the “shifting” of the curtain. This is why, in the story, time travel is called a shifting.
I have always resisted writing a time travel story because I didn't feel that there was any strong speculative science that could be used to support it. But the ideas from the paper A new understanding … above give some hope that when quantum theory and general relativity are combined, and I believe that we will eventually have a quantum gravity, there will be a forward arrow of time and a backward arrow. The rest will be engineering.
The Einstein Nexus will be available in three novellas and eventually a novel. The first novella is available for preorder here.
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