The Advance of Science in the Last Half-Century
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The advance of science in the last half-century
Published by BiblioLife New Paperback Quantity Available: New Hardcover Quantity Available: 1. I had been looking for the right term for months, ruminating in bed, in the bathtub, in my car, whenever I had a free moment. Suddenly, that name seemed totally correct to me. The name was catchy, and it stuck, but the explanation was mistaken as I pointed out above, a pulsar is driven by a neutron star.
The Advance of Science in the Last Half-Century : Thomas Henry Huxley :
While the history of black holes began with the physics work of Oppenheimer and his collaborators, mentioned above, for some years, the field was dominated by purely mathematical studies like the previously mentioned ones by Penrose and Hawking. The underlying physical idea was that they must be very different than any other type of star, even though their origins were linked to them.
They would occur when, after exhausting its nuclear fuel, a very massive star began to contract irreversibly, due to gravitational force. The center of a black hole is its point of collapse. However, there is a possible way out of such a paradoxical situation: the general theory of relativity is not compatible with quantum requirements, but clearly, when matter is compressed into a very reduced area, its behaviour will follow quantum rules. Thus, a true understanding of the physics of black holes calls for a quantum theory of gravitation either by quantizing general relativity, or by constructing a new theory of gravitational interaction that can be quantized.
At the present time, this has yet to be done, although some steps have been made in that direction, including one by Hawking himself, the grand guru of black holes. As a result, we do not really know what those mysterious and attractive objects are. Do they, in fact, exist at all? The answer is yes.
There are ever-greater indications that they do. On 12 December , the United States launched a satellite from Kenya to celebrate its independence. Among the identified sources is Cygnus X-1, one of the most brilliant in the Milky Way, located in the region of the Swan. This source was later linked to a visible super-giant blue star with a mass 30 times that of the Sun and an invisible companion.
The movement of the blue star indicated that its companion had a mass 7 times that of the Sun, a magnitude too great to be a white dwarf or a neutron star. It must be, therefore, a black hole.
The Advance of Science in the Last Half-Century
However, some argue that its mass is 3 solar masses, in which case it could be a neutron star. In over two hundred cases, it has been possible to indirectly determine the masses of those super black holes, but a direct determination has only been possible in a few cases. One of the latter is in our own Milky Way. The study of the Universe is enormously puzzling. Obviously, measuring such basic data as distances, masses and velocities is extremely complex there.
With the data then available, there was a time when the model that offered the Robertson-Walker-Friedmann solution to general relativity was sufficient. It represents a Universe that expands with an acceleration that depends on its mass-energy content.
But there were increasingly clear problems with the cosmology of the Big Bang. One of these was the question of whether mass-energy is such that the Universe will continue to expand forever, or if it is large enough that gravitational attraction will eventually overcome the force of the initial explosion, reaching the point where it begins to contract and finally arrives at a Big Crunch. Another problem lay in the considerable uniformity with which mass appears to be distributed throughout the Universe.
This is observable using units of measurement of some million light-years or more of course, on a small scale, the Universe, with its stars, galaxies, cumuli of galaxies and enormous interstellar voids, is not homogeneous. Background microwave radiation is good proof of this macro-homogeneity. To resolve this problem the idea of an inflationary Universe was proposed.
In other words, the mini-universe must have experienced a growth so rapid that there was not enough time to develop physical processes that would have led to non-homogeneous distributions. Once that inflationary stage ended, the Universe must have continued evolving according to the classic Big Bang model. Among the scientists responsible for this inflationary theory, we should mention the American, Alan Guth b.
But, more than specific names, what I want to point out is that it is impossible to understand this theory without recourse to high-energy physics—what used to be called elementary-particle physics, which I will discuss further on—especially the Grand Unified Theories GUT , which predict that there would have to be a phase shift at temperatures around degrees Kelvin So, inflation lies at the origin of a uniform Universe.
But then, what caused the miniscule primordial non-homogeneities that, with the passage of time and the effect of gravitational force, gave birth to cosmic structures such as galaxies? One possible answer is that inflation may have enormously amplified the ultramicroscopic quantum fluctuations that occurred as a result of the uncertainty principle applied to energies and time? If that were the case, what better place to look for non-homogeneities than the microwave radiation background?
The answer to this question appeared in the work of a team of US scientists led by John C. Mather b.
In , NASA approved funding for the construction of a satellite—the Cosmic Background Explorer COBE , which was put into orbit kilometers above the Earth in the fall of —to study the cosmic microwave background. The entire project was coordinated by Mather, including the experiment in which he used a spectrophotometer cooled to 1.
Meanwhile, Smoot measured the miniscule irregularities predicted by inflation theory. Ten years later, following the work of over a thousand people and a cost of million dollars, it was announced Mather et al. Just how thrilled those researchers were when they confirmed their results is clear in a book for lay readers published by Smoot soon thereafter.
Wrinkles in Time Smoot and Davidson, , :. I was looking at the primordial form of the wrinkles, I could feel it in my bones.
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Some of the structures were so huge that they could only have been generated when the Universe was born, no later. What was before my eyes was the mark of creation, the seeds of the present Universe. COBE was a magnificent instrument, but it was by no means the only one.
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There are many examples of astrophysics and technology working hand in hand, not only with Earth-based instruments, but also spacecraft. At this point, scientists have been exploring our Solar System for quite some time using satellites with refined instruments that send us all sorts of data and images: space probes such as Mariner 10, which observed Venus from a distance of 10, kilometers in ; Pioneer 10 and Voyager 1 and 2, which approached Jupiter, Saturn, Uranus and Pluto between and , and Galileo, aimed at Jupiter and its moons. Since it was launched, and especially since its defects were corrected, Hubble has sent, and continues to send, spectacular images of the Universe.
Thanks to it, we have the first photos of regions such as the Orion nebulous where it appears that stars are being born.