Lawrence H. Ford

Affiliations

• Tufts University, Department of Physics and Astronomy (emeritus)

Channels

• institution
• orcid · 0000-0002-8359-120X

Bibliography

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

Published bibliography entries: 4. Showing 1–4 of 4.

1. 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.

2. Listed work

   Paper · 1997

   Restrictions on Negative Energy Density in Flat Spacetime

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

   L. H. Ford and Thomas Roman start from the fact that quantum fields can have negative energy density at a point, as in the Casimir effect and squeezed light. Their earlier bound for the massless scalar field limits how large negative energy density can be, and for how long, as seen by any inertial observer, in the style of an uncertainty principle. This paper gives a much simpler derivation using plane wave modes instead of spherical waves. They derive similar quantum inequality bounds for the electromagnetic field and for the massive scalar field in two- and four-dimensional flat spacetime. The energy-time uncertainty principle itself is not an input to these bounds.

3. Listed work

   Paper · 1999

   The Quantum Interest Conjecture

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

   L. H. Ford and Thomas Roman study the limits quantum field theory places on negative energy, which it allows locally but restricts in size and extent. Quantum inequalities require a negative energy pulse to be followed by a compensating positive pulse, with a separation inversely proportional to their amplitude. Their quantum interest conjecture adds that the positive pulse must overcompensate by an amount that grows with the separation. They prove it for massless scalar fields in two- and four-dimensional flat spacetime and show it follows from the quantum inequalities. In short, a negative energy loan must be repaid with interest that grows with its size or duration, illustrated by pulses from a moving mirror.

4. Listed work

   Paper · 1997

   The unphysical nature of 'Warp Drive'

   1. Michael J. Pfenning(Author)
   2. L. H. Ford(Author)

   Pfenning and Ford examine the negative energy required by the Alcubierre warp metric using quantum inequalities for a free, massless scalar field. They apply a flat-spacetime bound over sampling times much shorter than the local curvature scale, rather than solving the field theory exactly in the curved geometry. For their representative sampling choice, the resulting wall-thickness limit is roughly one hundred Planck lengths multiplied by the bubble speed in light-speed units. Their hundred-metre-radius example requires a negative energy magnitude far beyond the visible universe’s mass equivalent. Increasing the speed permits thicker walls but also increases the estimated total energy requirement. They conclude that macroscopic human-transport bubbles in this model demand unattainable negative energy, including at subluminal speeds.