Arrochar Frontiers/Project Chrononaut
Can a machine send something back in time?A capability model for travel backwards in time, built so that it can be proven wrong.
Travelling forwards in time is settled physics. The hard problem is coming back. Project Chrononaut treats the return trip as an engineering problem with one master hypothesis, and lists the experiments that would settle it, starting with the four that need no new physics.
- Field
- Backward time travel
- Status
- Hypothesis stated, first experiments scoped
- Started
- August 2026
- Current model
- Capability model version 4.0, 13 September 2026
Mark Macfarlane, principal researcher
Where the problem stands
Travelling forwards in time is settled physics. We do it every day, and we do it faster by moving quickly or by sitting near something heavy. Atomic clocks flown around the world and the relativistic corrections applied to every satellite positioning fix confirm it. The hard problem is the return trip, and everything in this project is about the return trip.
No known law of physics forbids travel backwards in time. General relativity contains exact solutions with closed timelike curves, and they keep appearing from unrelated starting points, which is what a genuine feature of a theory looks like. The strongest argument against them, Stephen Hawking's chronology protection conjecture of 1992, has been proven for one specific family of rotating black holes and not in general. Thirty-four years of serious effort by capable people have not produced a general theorem. That is meaningful evidence, though not proof.
The project reads the field through three bodies of work. Brian Clegg's survey of every serious route anyone has proposed is used to find the gaps. Carlo Rovelli's account of time as emergent and relational supplies the foundation. Stephen Hawking's writing on why the universe should forbid the whole thing is used as the adversary: every one of his objections is logged with a design response, or with an admission that we have none. Where the three disagree, the model does not average them. It records the disagreement as an open experimental question.
The one rule that makes this bearable
A wormhole time machine cannot reach back to a time before it was switched on. This is not a limitation the project invented. It falls out of the physics of every wormhole time machine anyone has proposed, and it is why we are not overrun with visitors from the future. It is also, quietly, the best news in the model. A machine is not competing with history. Switch it on, and every moment from that instant forward becomes a destination.
H0, the master hypothesis
Travel backwards in time is physically permitted. The reason we cannot do it is that we have not yet identified the mechanism, not that the universe forbids it.
It can be falsified
H0 fails if a general chronology protection theorem is proven, one that covers engineered wormhole geometries within a complete theory of quantum gravity. No such theorem exists today. If one arrives, the hypothesis is withdrawn, not defended. A hypothesis that cannot lose is not a hypothesis.
The evidence is lopsided, and the shape matters
Ten independent lines of evidence support H0 and nine argue against it. Almost all of the evidence for is permissive: it establishes that nothing forbids backward travel, not how to achieve it. Almost all of the evidence against is obstructive: it establishes that the job is extraordinarily hard, not that it is impossible. Exactly one objection could kill H0 outright, Hawking's vacuum fluctuation feedback at the moment a machine starts working. It is unproven, unrefuted, and the first thing the programme attacks.
What the hypothesis commits us to
H0 says the mechanism is undiscovered, not unbuilt. If it were merely unbuilt, the right move would be engineering. Because it is undiscovered, the right move is to look in places nobody has looked, and the programme keeps a register of directions that fall between disciplines or were dismissed before anyone looked properly.
The experiments that can start now
The investigation register is ordered so that the cheapest decisive experiment comes first. Four lines can start now. Between them they need a spectroscopy collaboration, time on an existing quantum simulator, a literature review and a mathematician. None needs exotic matter, a wormhole or a new law of physics. Several could return a clean negative that reshapes the model, and it is far better to learn that in 2027 than after a decade of downstream construction.
- 01
Test whether entanglement and geometry are the same thing
The model's whole construction route rests on the ER=EPR conjecture: that an entangled pair and a wormhole connecting them are one object described two ways. A proposed test using hydrogen hyperfine transition shifts is the nearest-term real experiment in the programme and uses existing apparatus.
What settles it. No shift at the predicted sensitivity, and the construction route fails and the model is rebuilt from the geometry up.
- 02
Settle which paradox regime the universe uses
Three candidate resolutions of the grandfather paradox are live: Novikov self-consistency, Deutsch's many-worlds circuits, and a relational reading in which differently coupled observers hold divergent but individually consistent records. A quantum-simulator campaign on existing hardware, with Polchinski's billiard-ball problem as the concrete case, can tell them apart without building anything physical.
What settles it. Which regime governs closed timelike curves, and therefore what the first demonstrator must be built to measure.
- 03
Size the stasis problem
The only track in the model that needs no new physics: how long a biological payload could be held in reversible stasis on the far side of a trip. A literature review across cryobiology and induced hibernation, with collaborators identified, on conventional funding.
What settles it. The maximum credible reversible stasis duration, which sizes the whole far-side requirement whether or not the rest succeeds.
- 04
Find a throat that does not shake itself apart
A mathematics and simulation survey of candidate wormhole throat geometries, computing their quasinormal-mode spectra and looking for a family with no purely growing modes and round-trip feedback gain below unity. It is the cheapest high-value work in the model.
What settles it. Whether a stable throat family exists. If none does, the strongest objection hardens from an objection into a blocker.
The objective
Send a message before a person
The programme's near-term objective is an information-only demonstrator we call the Light Loop: pass information backwards through an engineered throat and prove it arrived before it was sent. Its resource requirement is smaller than a passenger-carrying machine's by many orders of magnitude, and it answers the same central question. Nothing with a heartbeat goes until it works. Human transit remains beyond the horizon of the current roadmap, and the model does not pretend otherwise.
Three gates decide everything
- 1Is ER=EPR real? If not, there is no known construction route and the model is rebuilt from the geometry up.
- 2Can a throat be stable against growing modes? If Hawking's divergence proves general, H0 is false and the programme stops.
- 3Does negative energy scale and shape? If not, the Light Loop cannot be built from the sources the model assumes.
Where the project stands
A capability model (version 4.0, 13 September 2026) and a draft solution blueprint exist. Nothing has been built. No backward transit has ever been observed, by anyone. The model's deepest unknown is whether entanglement can be converted into traversable geometry at any scale; nobody has demonstrated it. Its strongest unresolved objection may not be resolvable without a theory of quantum gravity we do not have. Neither is a reason to stop. Both are reasons to run the cheapest experiments first, because they tell us which world we are in.
What we publish and what we keep
We publish the premise, the master hypothesis and the next experiments. The full model, its layered architecture, the constraint and blocker registers and the solution blueprint stay internal. If H0 falls, this page will say so.
The reading behind the project
Every claim on this page traces to one of the sources below. The published books and papers are public. The two Arrochar documents are internal and are not published.
- 1Public
Ten Short Lessons in Time Travel
Brian Clegg, Michael O'Mara Books, 2021
- 2Public
The Order of Time; Reality Is Not What It Seems; Helgoland; White Holes
Carlo Rovelli, 2014 to 2023
- 3Public
A Brief History of Time; Brief Answers to the Big Questions
Stephen Hawking, 1988, 2018
- 4Public
Chronology protection conjecture, Physical Review D 46, 603
S. W. Hawking, 1992
- 5Public
Wormholes in spacetime and their use for interstellar travel, American Journal of Physics 56, 395
M. S. Morris and K. S. Thorne, 1988
- 6Public
Quantum mechanics near closed timelike lines, Physical Review D 44, 3197
D. Deutsch, 1991
- 7Public
Chronology protection for Dyonic Kerr-Sen black holes, arXiv:2408.06023
arXiv preprint, published in European Physical Journal C, 2024, 2025
- 8Public
Proposed ER=EPR test via hydrogen hyperfine transition shifts, arXiv:2512.02156
arXiv preprint, December 2025
- 9Arrochar-owned
Time Travel Capability Model Hypothesis, version 4.0
Arrochar Labs, Mark Macfarlane, 13 September 2026. Internal. Not published.
- 10Arrochar-owned
Time Travel Machine Solution Blueprint, draft v1.1
Arrochar Labs, Mark Macfarlane, 3 October 2026. Internal draft. Not published.
Working on any of this?
The next experiments need a spectroscopy group, quantum-simulator time, a cryobiology collaborator and a mathematician. If that is you, or you think the hypothesis is wrong and can show why, we want to hear it.