10. Scientifically Plausible Time Travel

I have always loved “hard” science fiction. The many considerations of surviving life on Mars in THE MARTIAN, the genetic gymnastics of JURASSIC PARK and the battle droids of the STAR WARS prequels*. Even if not completely scientifically plausible, I love seeing writers manipulate real-world science to create a compelling story.

But at university, as I delved ever deeper into theoretical physics, I wondered what a “hard’ science fiction story about time travel might look like. How would a Time Machine actually work? What would a realistic journey back to the past actually entail?

And so the idea for my novel was born.

My first thoughts were of the mechanics of time travel. Many time travel stories just didn’t sit right with me. The paradoxes were so messy. The more I thought about it, the more I aligned with the multiverse theory of time travel. A time traveler (Chronomad in my books) who grew up in timeline “t” would be sent back to a new universe that travelled in timeline “t*”. Creating a whole universe would require an insane amount of energy so I reasoned that the problem could be waved away** so long as the old universe was destroyed, at least from the Chronomad’s point of view. When the portal shut, the causal link between the universes would disappear. This unfortunately meant that the Chronomad would never be able to return to their timeline – chaos theory meant that the mere act of being back in the past would make their original future impossibly difficult to recreate. But this was great! The Chronomad, and all the matter that made them, would still have experienced timeline “t” and would now experience “t*” so there was no need for paradoxes.

So that was sorted, my Chronomad would need to go on a one-way journey back to the past. There would be no communication with their original timeline. And no going back.

The next thought was how the time travel would actually happen. A physics assignment presented an opportunity to investigate wormholes, theoretical perturbations of spacetime that I had initially heard of through Science Fiction like Stargate. I quickly learned that understanding the differential geometry was well beyond a chronically-distracted undergrad but I grasped enough to progress my plot. The wormhole could be created by stitching two black holes together using exotic “negative mass” matter. Then, the relativistic effects of accelerating one black hole away from the other would result in a time difference. Go through the mouth of the accelerated black hole and you would end up back in the past at the stationary black hole. Our physics classes had also suggested that the Casimir Effect acted as some pseudo negative mass, hinting that such a wacky concept was not completely impossible.

It was around this time that the first tests of the Large Hadron Collider had begun. Start-up of the particle collider had prompted hysteria, with some hypothesising that condensing high energy into such a small space could create micro black holes. We fortunately survived those concerns which also inspired the design of my Time Machine. I initially went into physics hoping to one day work on nuclear fusion – a potential solution to looming energy problems – and I once sought to do vacation work at the National Ignition Facility in the US. This huge experimental device generates nuclear fusion by compressing capsules of fuel using concentrated blasts of high energy lasers. I reasoned that perhaps my novel’s physicists could create their black hole by concentrating huge amounts of energy into a tiny area. If the black hole could be created and steered, then a journey to the past might*** be possible. Steering the black holes to the right location in space and time would be incredibly difficult and would require numerous calibration experiments but, with years of concentrated work, MIGHT be achievable.

Inside the NIF target chamber. Matilda’s Time Machine is a similar size.

The black hole would provide a small spherical volume through which a time traveler could be dropped into the past. A BIG problem was that the amount of energy to create a meaningfully sized black hole would be extremely high. For simplicity I wanted a one meter diameter sphere, big enough that a person or two could crouch inside with a few essential possessions. But looking at the Schwarzchild radius equation, creating a black hole only 1.8cm in diameter would require the entire mass of Earth to be converted into energy. So with some hand waving, an entire nuclear reactor would be used to generate power for the initial black hole creation and then the portal could be widened using more exotic matter. But this all meant that the Time Machine would need to be enormous. It wouldn’t fit on a cute necklace. Not even within a phone booth. This also meant that the Chronomad couldn’t simply recreated the machine when they reached the past. The journey would definitely only be one-way.

So in summary, a nuclear reactor would be used to generate huge amounts of energy that would then be blasted by lasers into a microscopic space to create a black hole. This black hole would somehow be paired with another and sewn together using “negative mass” matter to hold the wormhole stable for long enough that a Chronomad could be sent into the past of a new universe. The portal would be small – limiting the number of people that could be sent – and would only be open for an extremely short amount of time due to the energy requirements. When the portal closed, the time traveler would be unable to communicate with their old timeline and, lacking a reactor and the large infrastructure require to make another Time Machine, would have no way to get home even if reversing the process were possible.

All of this is to say that I unfortunately still have no idea how to make a real life Time Machine. But! There was enough here to somewhat plausibly underpin a journey to the past and, most importantly, define some of the rules that such a journey would entail.

Check out the story to see what such a journey might be like. The book will release on 1 December 2023 and is available for pre-order but I am sharing new chapters each week on Reddit and Royal Road.

I’d love to hear what you think!

* Despite issues in execution, I can even appreciate what they were trying to achieve with midichlorians

** Nevermind the extreme entropy differences between the two time periods…

*** There’s not enough salt in the world to make the grain with which this statement should be taken.