Einstein’s theories of special and general relativity, presented around the turn of the last century, were said to be confirmed in two main ways, firstly in providing an explanation, where the application of classical Newtonian mechanics could not, for the slight precessive aberration in the orbit of Mercury, and secondly, and more importantly, by the results of the observations of stars close to the suns surface during the eclipse of the sun in 1919 that confirmed that the observed position deviated fractionally (1-2 seconds of arc) from the true position.
It was the general belief of scientists at this time that the Michelson and Morley experiments on the velocity of light in the 1880’s were a confirmation of the, then long-held assumption of many scientists, that the atmospheric matter of the earth extended to a certain (undefined) altitude whereupon the pure vacuum of space began.
In the last century however, as a result of balloon experiments, high altitude flights and latterly space exploration, our knowledge of the composition, the characteristics and extent of the earth’s atmosphere has improved considerably and it is now known that there is no definitive point or border that divides the atmosphere of earth from the matter that exists in the space between the earth and the sun. Aside from a difference in composition, there is a progressive reduction in density between the gases at the earth’s surface and those in space thousands of kilometres from the surface, and the atmosphere of the earth extends well out into space and merges with the atmosphere of the sun.
‘The NASA Space Shuttle at 250- 300 Km altitudes ‘in space’ was found to be in air, with the same proportions of oxygen and nitrogen as at sea level, at a concentration of 1 billion atoms per cc compared to 3 x 1019 per cc at sea level. – Thus in no sense could it be called a vacuum’.
‘The sun too has an atmosphere, and because the sun accounts for more than nine tenths of the total mass of the solar system, its atmosphere is much larger than that of any planet. – The solar atmosphere extends far beyond the orbit of the earth, and at 80,000 Km our atmosphere merges imperceptibly with that of the sun’. (1)
The resurrection in the early 1900’s of Newton’s concept of light as particulate (the photon), led to the assumption and the prediction by Einstein that light, in passing through a strong gravitational field, would be deflected by it.
The Royal Society of London sent out two expeditions to observe the 1919 eclipse of the sun. One to Sobral in Brazil and one to the island of Principe, off West Africa, and the latter was led by Sir Arthur Eddington, who was an enthusiastic supporter of the new relativity theories.
Photographic plates were exposed at the time of the eclipse in both places and later analysis showed that the position of a star that was near to the suns surface was shown to deviate from its true position by about 1.6” (seconds of arc) in Principe and 2” in Sobral. Eddington interpreted these results as confirming Einstein’s prediction of a deflection of 1.74”.
The refractive effect of the passage of light through different layers of density in the earth’s atmosphere was well known then to both navigators and astronomers.
The figure below is a representation of that in the Admiralty Manual Of Navigation, 1954 and shows a ray of light from body X being refracted(2) by layers of air of increasing density so that its position is viewed as being at X’.
Eddington considered the possibility of gases surrounding the sun having a similar effect and accordingly worked out what would be the necessary density to produce the required refractive index, but concluded: – ‘It seems obvious that there can be no material of this order of density at such a distance (an altitude of 400,000 miles) from the sun’ (3).
In other words he made an assumption, based upon the beliefs current at this time, that at this altitude above the sun no atmosphere or gaseous matter existed that would have any refractive effect on the passage of light and accordingly made no allowance whatever for such an effect.
I would suggest that it is now obvious that the density of the suns atmosphere, like the earth’s, is inversely proportional to altitude, and that accordingly in these circumstances there is no question that light, emitted from an object whose physical direction is in the near vicinity of the sun when viewed from the earth, will be refracted in passing through the differing layers of density of its atmosphere, and that the degree of refraction will be proportional to the altitude of the rays passage above the suns surface.
The figure below shows how the transit of light emitted by a distant object, through the different layers of the solar atmosphere, will result in an angular variation between the true position and the observed position on the opposite side of the sun.
If we consider a ray of light passing through the sun’s atmosphere from point A it will be deflected towards the surface as it encounters progressively denser gases up to point B where the ray is tangential to the suns surface and the variation in density is neutral, from this point the ray encounters gases that are progressively reducing in density and the refractive effect is then in the opposite direction away from the sun up to the altitude (corresponding to that of point A) at point C.
Clearly the distance travelled and the total refractive effect from A to B is greater that that from B to C, which will result in an angular distortion of the body’s true position as seen by an observer at C.
In summary it is indisputable that, contrary to the belief of scientists at the turn of the last century, the sun has an atmosphere and that its gravitational forces would result in this atmosphere varying in density with altitude.
That this would result in a refractive distortion of light at the observers position from any object viewed tangentially through this atmosphere is again indisputable, and therefore Eddington’s complete rejection of any refractive effect was wrong, and the so called ‘proof of relativity’ invalid.
In 1900 had been known for some time that there was an anomaly in the orbit of Mercury that could not be explained by Newton’s laws. Its elliptical orbit is precessional, or in other words is of itself rotating around the sun and the anomaly was a minute excess in this precession, in that it was proceeding at a greater rate than predicted. General relativity gave an explanation for this (mass dilation) and this, together with the 1919 eclipse observations, sealed the reputation of Einstein in the scientific world.
The argument for the advance of Mercury’s perihelion however does not appear to view the orbit of Mercury from the perspective of the focus of its orbit, which is the centre of the sun. If this were applied and taken to its logical conclusion, by starting from the basis of the average velocity/mass and applying mass dilation in the hemisphere of the aphelion, a lower than average mass would result and thus a reduced velocity at the aphelion and an undershooting of its predicted position. And as the time Mercury spends in the hemisphere of the aphelion is far greater than that in the opposite, the result would be to more than cancel out the suggested perihelion advance, which in turn would have the overall effect of reversing the observed precession.
The elliptical orbit of Mercury is, of all the planets (apart from that of Pluto which orbits over 4,000 million km from the sun) the most accentuated, in that the nearest point in its orbit, the perihelion, is 46 million km from the sun, while the aphelion, the furthest point, is nearly 70 million km, as represented in the figure below, and there will be a significant difference in the densities of the solar atmosphere at the minimum and the maximum orbital altitudes.
Therefore these variations in the density of the solar atmosphere, depicted by the dashed circles in the figure above, would result in a greater frictional retardation of the orbital motion of Mercury in the region of the perihelion compared to that at the aphelion, which would have the effect of accelerating the rate of precession. Which effect in these circumstances can easily be explained by the application of classical mechanics.
(1) ‘Air – The Nature of Atmosphere and Climate’ Michael Allaby
(2) The degree of refraction in this figure is of course exaggerated for clarity; the degree varies from zero at the observer’s zenith to the maximum refraction of about 33 minutes of arc at the horizon.
(3) ‘Space, Time and Gravitation’, Arthur Eddington