Fundamental Physics and Chemistry Space Science in the Twenty-First Century -- Imperatives for the Decades 1995 to 2015 (1988) / Chapter Skim
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2. Basic Issues in Gravitation
2. Basic Issues in Gravitation
Pages 8-20
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From page 8... ...
This implies that gravity does not differentiate between the strong and the electromagnetic interactions. Using laser ranging to the corner reflectors left on the Moon by the Apollo program, precision measurements of the motion of the Moon and Earth as they orbit the Sun have determined that the contribution to the mass of the gravitational binding energy of the Earth shares in this equivalence of the masses.
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From page 9... ...
The way that the principle of equivalence is incorporated in the general theory of relativity goes further than merely the equivalence of inertial and gravitational mass. The indistinguishability of gravity and acceleration implies that all physics in a local region experiencing free fall is the same whether free fall occurs near a massive object such as a black hole or far from other matter; in other words the gravitational potential does not enter local physics in any measurable way.
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From page 10... ...
The perihelion advances of Mars and the asteroid Icarus have also been measured and are in agreement with general relativity to an error of 20 percent. The gravitational red shift is now confirmed to 0.01 percent uncertainty in the field of the Earth using atomic clock comparisons between a ground-based and a suborbital space platform.
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From page 11... ...
These regions include sufficient mass, m, in a spatial dimension, r, that GM/Rc2 approaches 1 On a surface called the horizon that separates the outside and the inside worlds. Observers viewing the formation of a horizon from the outside would see the interior vanish in a finite time (an observer at the horizon of a region containing a solar mass would see the interior vanish in about 10 ps)
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From page 12... ...
Current wisdom holds that compact objects with masses greater than a few solar masses are black holes. Black holes are the most efficient converters of rest mass to energy posited in nature.
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From page 13... ...
A l~solar-mass black hole wait produce a pulse with strong 1-kHz components and is detectable using terrestrial instruments. The search for signals from holes with mass larger than 104 solar masses is best carried out by space-borne gravitational wave detectors.
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From page 14... ...
In 191S, Einstein established that time-dependent free field solutions to the gravitational field equations should exist. These are gravitational waves traveling at the speed of light that distort space-time transverse to their propagation direction.
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From page 15... ...
The direct experunental confirmation of the wave solutions by laboratory experiments using a terrestrial source and receiver, in analogy to the Hertz experiment for electromagnetic waves, appears to be impossible with present technology or that of the forseeable future. As a consequence, the direct detection of gravitational waves has become an astrophysical problem, for it is in this realm that we expect to observe phenomena in which the coherent motions of large masses at high velocity will make measurable gravitational wave strains at the Earth.
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From page 16... ...
The observational problem is to estate fish the cosmic distance scale by coupling red shift measurements with reliable absolute sizes or luminosities of astronomical objects. Advances in detector technology and the planned large-aperture, ground-based and space-borne observatories are expected to make significant progress in this program by observing larger and fainter parts of the universe.
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From page 17... ...
The nature of the dark matter ~ the universe is a major puzzle. Dark matter candidates must be consistent with other cosmological observables, in particular the measurements of the 3K cosrn~c background and the measured isotopic abundances of light elements.
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From page 18... ...
The new particles, if long-lived, could be candidates for the invisible mass, but must be tailored to have properties that would not upset the isotopic abundances determined in the earlier epoch of primeval nucleosynthesis . The space program offers important opportunities for the oh servation of the 3K background.
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From page 19... ...
The primordial abundance ratios of the light elements was established at this time. The relative abundances are calculated by nuclear reaction theory with the cosmic temperature, the baryon density, and the expansion time as input variables.
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From page 20... ...
The inflationary universe mode! provides an explanation of the large-ecale isotropy of the 3K background by having the entire universe expand rapidly from a single causally connected region of the vacuum.
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