Gregory Benford

Natural wormholes as gravitational lenses

Once quantum mechanical effects are included, the hypotheses underlying the positive mass theorem of classical general relativity fail. As an example of the peculiarities attendant upon this observation, a wormhole mouth embedded in a region of high mass density might accrete mass, giving the other mouth a net [ital negative] mass of unusual gravitational properties. The lensing of such a gravitationally negative anomalous compact halo object (GNACHO) will enhance background stars with a time profile that is observable and qualitatively different from that recently observed for massive compact halo objects (MACHOs) of positive mass. While the analysis is discussed in terms of wormholes, the observational test proposed is more generally a search for compact negative mass objects of any origin. We recommend that MACHO search data be analyzed for GNACHOs.

Hamilton's forces of natural selection after forty years

Abstract In 1966, William D. Hamilton published a landmark paper in evolutionary biology: “The Moulding of Senescence by Natural Selection.” It is now apparent that this article is as important as his better-known 1964 articles on kin selection. Not only did the 1966 article explain aging, it also supplied the basic scaling forces for natural selection over the entire life history. Like the Lorentz transformations of relativistic physics, Hamiltons Forces of Natural Selection provide an overarching framework for understanding the power of natural selection at early ages, the existence of aging, the timing of aging, the cessation of aging, and the timing of the cessation of aging. His twin Forces show that natural selection shapes survival and fecundity in different ways, so their evolution can be somewhat distinct. Hamiltons Forces also define the context in which genetic variation is shaped. The Forces of Natural Selection are readily manipulable using experimental evolution, allowing the deceleration or acceleration of aging, and the shifting of the transition ages between development, aging, and late life. For these reasons, evolutionary research on the demographic features of life history should be referred to as “Hamiltonian.”

Searching for Cost-Optimized Interstellar Beacons

What would SETI beacon transmitters be like if built by civilizations that had a variety of motives but cared about cost? In a companion paper, we presented how, for fixed power density in the far field, a cost-optimum interstellar beacon system could be built. Here, we consider how we should search for a beacon if it were produced by a civilization similar to ours. High-power transmitters could be built for a wide variety of motives other than the need for two-way communication; this would include beacons built to be seen over thousands of light-years. Extraterrestrial beacon builders would likely have to contend with economic pressures just as their terrestrial counterparts do. Cost, spectral lines near 1 GHz, and interstellar scintillation favor radiating frequencies substantially above the classic water hole. Therefore, the transmission strategy for a distant, cost-conscious beacon would be a rapid scan of the galactic plane with the intent to cover the angular space. Such pulses would be infrequent events for the receiver. Such beacons built by distant, advanced, wealthy societies would have very different characteristics from what SETI researchers seek. Future searches should pay special attention to areas along the galactic disk where SETI searches have seen coherent signals that have not recurred on the limited listening time intervals we have used. We will need to wait for recurring events that may arrive in intermittent bursts. Several new SETI search strategies have emerged from these ideas. We propose a new test for beacons that is based on the Life Plane hypotheses.

Messaging with cost-optimized interstellar beacons.

On Earth, how would we build galactic-scale beacons to attract the attention of extraterrestrials, as some have suggested we should do? From the point of view of expense to a builder on Earth, experience shows an optimum trade-off. This emerges by minimizing the cost of producing a desired power density at long range, which determines the maximum range of detectability of a transmitted signal. We derive general relations for cost-optimal aperture and power. For linear dependence of capital cost on transmitter power and antenna area, minimum capital cost occurs when the cost is equally divided between antenna gain and radiated power. For nonlinear power-law dependence, a similar simple division occurs. This is validated in cost data for many systems; industry uses this cost optimum as a rule of thumb. Costs of pulsed cost-efficient transmitters are estimated from these relations by using current cost parameters (

Sequestering of Atmospheric Carbon through Permanent Disposal of Crop Residue

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Collective emission from rapidly variable quasars

/m(2)) as a basis. We show the scaling and give examples of such beacons. Galactic-scale beacons can be built for a few billion dollars with our present technology. Such beacons have narrow searchlight beams and short dwell times when the beacon would be seen by an alien observer in their sky. More-powerful beacons are more efficient and have economies of scale: cost scales only linearly with range R, not as R(2), so number of stars radiated to increases as the square of cost. On a cost basis, they will likely transmit at higher microwave frequencies, approximately 10 GHz. The natural corridor to broadcast is along the galactic radius or along the local spiral galactic arm we are in. A companion paper asks If someone like us were to produce a beacon, how should we look for it?

Fossil AGN jets as ultrahigh-energy particle accelerators

We propose the sequestering of crop residues to capture a significant fraction(12%) of the present U.S. atmosphericcarbon emission through disposal in deep oceans below the thermocline or inriver deltas. In the United States, theannual carbon content in residues from corn, soybeans and wheat crops isapproximately 250 million tonnes. Globally, an additional 1 billion tonnes of carbon in the form of cropresidues may be available. Implementation ofthis sequestering proposal would allow the US to approach the CO2reductions stipulated under the KyotoProtocol.

Microwave beam-driven sail flight experiments

Recently blazars have shown variability in total flux density, polarization, and polarization position angle in both radio and optical bands. This demands brightness temperatures ∼10 6 times the limit set by incoherent synchrotron emission by relativistic electrons. Laboratory experiments displaying just such enhancement when relativistic beam density exceeds 1% of background plasma density are reported. These suggest a model for collective emission from jets explaining variability and spectral features

Electron beam radiation by collective Compton boosting of strong turbulence

Remnants of AGN jets and their surrounding cocoons leave colossal magnetohydrodynamic (MHD) fossil structures storing total energies �10 60 erg. The original active galacic nucleus (AGN) may be dead but the fossil will retain its stable configuration resembling the reversed-field pinch (RFP) encountered in laboratory MHD experiments. In an RFP the longitudinal magnetic field changes direction at a critical distance from the axis, leading to magnetic re-connection there, and to slow decay of the largescale RFP field. We show that this field decay induces large-scale electric fields which can accelerate cosmic rays with an E 2 power-law up to ultra-high energies with a cutoff depending on the fossil parameters. The cut-off is expected to be rigidity dependent, implying the observed composition would change from light to heavy close to the cut-off if one or two nearby AGN fossils dominate. Given that several percent of the universe’s volume may house such slowly decaying structures, these fossils may even reenergize ultra-high energy cosmic rays from distant/old sources, offsetting the “GZKlosses” due to interactions with photons of the cosmic microwave background radiation and giving evidence of otherwise undetectable fossils. In this case the composition would remain light to the highest energies if distant sources or fossils dominated, but otherwise would be mixed. It is hoped the new generation of cosmic ray experiments such as the Pierre Auger Observatory and ultra-high energy neutrino telescopes such as ANITA and lunar Cherenkov experiments will clarify this.

Stability of magnetic equilibria in radio bubbles

We have observed flight of ultralight sails of Carbon-Carbon microtruss material at several gees acceleration. To propel the material we sent a 10 kW, 7 GHz beam into a 10−6u200aTorr vacuum chamber and onto sails of mass density 5–10 g/m2. At microwave power densities of ∼kW/cm2 we saw upward accelerations of several gees and flights of up to 60 cm. Sails so accelerated reached >2000 K from microwave absorption, a capability of carbon which rules out most materials for high acceleration missions. Diagnostics were optical and IR video photography, reflected microwave power and residual gas analysis. Data analysis and comparison with candidate acceleration mechanisms shows that photonic pressure can account for 3 to 30% of the observed acceleration, so another cause must be present. Future research will measure the thrust precisely using a pendulum to try to identify the acceleration mechanism. In the future, microwave-driven acceleration might be used to propel probes to very high speeds for science missions t...