The Spacetime Metric

Profile

Thomas A. Roman

Theoretical physicist researching quantum inequalities and spacetime geometry

Roman’s work with Lawrence Ford and Christopher Fewster examines negative energy and the limits of quantum energy inequalities in specified field models. With Allen Everett, he studied the Krasnikov tube, finding severe negative-energy and wall-thickness requirements in that geometry. Those calculations constrain the model rather than establish a working transport system.

Affiliations

  • Central Connecticut State University, Mathematical Sciences (documented in the publisher biography for his 2011 book; current appointment not established)

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Bibliography

A bibliography listing does not establish authorship. Credits appear under attribution.

Published bibliography entries: 3. Showing 1–3 of 3.

  1. Listed work

    Paper · 1997

    Superluminal subway: The Krasnikov tube

    1. Allen E. Everett(Author)
    2. Thomas A. Roman(Author)

    Everett and Roman extend Krasnikov’s two-dimensional geometry into a four-dimensional spacetime tube that a spacecraft would establish during a subluminal outward journey. Their model has a flat interior, curved walls, and light cones opened to permit rapid travel in one direction relative to outside observers. The first outward trip retains the usual light-speed limit, while the round-trip time measured on Earth can become arbitrarily short. One tube does not create a closed timelike curve, but two separated tubes running in opposite directions can create one. The calculated stress-energy tensor requires negative energy density. Applying quantum inequalities over short sampling times, they find extremely thin walls and enormous negative-energy requirements for useful superluminal travel in their chosen model.

  2. Listed work

    Paper · 1995

    Averaged Energy Conditions and Quantum Inequalities

    1. L. H. Ford(Author)
    2. Thomas A. Roman(Author)

    L. H. Ford and Thomas Roman connect the averaged weak and averaged null energy conditions with quantum inequalities, uncertainty-principle-type limits on negative energy. They study a quantised free massless scalar field in flat spacetime in two and four dimensions. In a two-dimensional universe with a compact spatial direction, they bound the difference between the energy density of any quantum state and that of the Casimir vacuum. That difference obeys averaged energy conditions, which is surprising because the Casimir vacuum alone satisfies neither quantum inequalities nor averaged conditions. Such difference inequalities may limit how far energy conditions can be violated beyond a background such as the Casimir vacuum.

  3. Listed work

    Paper · 2003

    Null energy conditions in quantum field theory

    1. Christopher J. Fewster(Author)
    2. Thomas A. Roman(Author)

    Christopher Fewster and Thomas Roman show, by explicit construction for the massless scalar field in four-dimensional flat spacetime, that weighted null averages of the stress-energy tensor have no lower bound over Hadamard states. So no quantum inequality holds along null geodesics in four dimensions, unlike two-dimensional flat spacetime where one does. The difference arises because in two dimensions any two field modes move either parallel or antiparallel, while the four-dimensional proof uses modes almost parallel to the geodesic. These states still satisfy the averaged null energy condition. In any globally hyperbolic spacetime, null-contracted stress-energy averaged along a timelike worldline does obey a quantum inequality, for massive and massless fields alike.