Highlights of Science Issues
(Please send your comment/suggestions to This email address is being protected from spambots. You need JavaScript enabled to view it.)
1.The Fastest Speed in The Universe
The speed of electromagnetic radiation, c = 2.997925 x 105km/sec, is called simply the speed of light. Similarly, the speed of gravitational (attraction) wavevgis called simply the speed of gravity.What speed is the fastest one in the whole universe?Is the speed of light or gravity the fastest one? Or perhaps there is something which is much faster than both of them.
According to Einstein's special relativity (SR), nothing could propagate in forward time at a speed greater than that of light in a vacuum. However, from celestial mechanics by Sir Isaac Newton, all gravitational interactions between bodies in all dynamical systems had to be taken as instantaneous. If the speed of gravity is the same as or just a few times larger than the speed of light, then the actions of two bodies in one celestial orbits would introduce a delay into gravitational interactions. These orbits are unstable if forces propagate with finite speed because of increased angular momentum of the system in the two bodies' orbital motions.
Based on the "Motion of attracting bodies" chapter in Celestial Mechanics published by Marquis De Laplace, 1966, p. 645, Laplace finds that the velocity of the fluid producing gravitation will be about7 millions of timesgreater than that of light(7 x 106c); and as it is certain that the moon's secular equation depends almost wholly upon the cause Laplace has assigned in their sixth books, Laplace must suppose that the gravitating fluid has a velocity which is at leasta hundred millions of timesgreater than that of light (1 x 108c); or at least Laplace must suppose, in its action on the moon, that it has at least that velocity to counteract her gravity towards the earth. Therefore mathematicians may suppose, as they have heretofore done, that the velocity of the gravitating fluid is infinite.
Laboratory, solar system, and astrophysical experiments for the "speed of gravity" yield a lower limit of 2 x 1010c (T. Van Flandern, 1998, Physics Letters A 250, 1-11). Van Flandern found that forces from electromagnetic radiation pressure and from gravity do not have the same propagation speed. These two forces come from the same source and propagate along straight, radial lines from the Sun to the Earth, yet their respective effects are non-parallel, implying different aberration and therefore different propagation speeds.
In ideal cases, as proposed by Van Flandern, the difference between the propagation speeds of gravity and light can be seen in the case of solar eclipses.The Moon's orbital speed around the Earth is 1 km/s and its synoptic period is 29.5 days. The Earth orbital speed around the Sun is 30 km/s. Compared the Earth's orbital speed to the light speed, the Sun has an aberration of just over 20 arc seconds. It takes the Moon about 40 seconds of time to move 20 arc seconds on its orbit relative to the Sun.With the exact timing, the Sun, the Moon and the Earth would line up in a straight line. Because the observed times of eclipses of the Sun by the Moon agree with predicted times to within a couple of seconds, we can use the orbits of the Sun and the Moon near times of maximum solar eclipse tocomparethe time of predicted gravitational maximum(measured on the Earth's surface, due to shieldingof the gravitational attraction of the Sun)or minimum(due to penetrating of the gravitational attraction)withthe time of visible maximum eclipse. In Jul. 22, 2009, we may have a very good case of solar eclipse event. Specifically, in ChengDu, China, starting 01:10 - 01:50UT, the solar eclipse may pass by ChengDu, WuHan, SuZhou, ShangHai, and the open sea near ShangHai areas. We may be able to view the longest total eclipse of the century at sea (6 minutes 39 secondsvisible at sea).
Light behaves either as waves or as localized particles (photons), depending on how it is observed, e.g., interference, diffraction or scattering phenomenon. In either cases, light carries radiant and outward energy. Compared to light, gravity behaves also either as waves or as particles (gravitons), carrying attractive and inward force.Einstein assumed that radiant energy is quantized into concentrated bundles, or bundles of energy. Each bundle of energy is initially localized in a small volume of space and it remains localized as it moves away from the source with velocity c. The energy content E of the bundle or photon is related to its frequency only.
We find that Van Flandern proposed solar eclipse observations may not be suitable for determining the speed of gravity. First, we find that the gravitational attraction has no (or relatively insignificant) obstacles. When a person stands on a 3000 m tall mountain or on a 3000 m height (altitude) above the ocean surface, this person would feel no difference in gravity. Of course there is a subtle difference. This subtle difference makes scientists to locate, e.g., the gold mines or oil fields. The mountain does not block the gravitational attraction. The farther we stay away the center mass of the Earth, the smaller gravity we would feel. Neither should the Moon block the gravitational attraction of the Sun. Whether we are in the solar eclipse event or not, the gravitational attraction measured on the Earth surface should depend on two factors: the distance variation between the Sun and the Earth and vector sum of the gravitational attractions of the Sun and the Moon. We find these variations should be relatively small in the projected lunar subtending angle of 0.5 degree on the Earth surface. Moreover the diffraction of the Sun light would make it hard to determine the exact timing that we have an optical totality.
... Work in Progress ........