Abstract of a lecture on June 21.6.05, XNUMX) * [Note: The abstract has already been published in "Adafar", in the Open University Town]
Dr. Yoram Kirsh
See explanations for the photo at the end of the article **
In the last hundred years there has been great progress in all fields of science. One of the areas where progress has been particularly impressive is the field of astronomy and astrophysics (the physics of the universe). It is hard to believe how little our astronomical knowledge was less than a century ago. For example, until 1924 astronomers thought that the Milky Way galaxy was the entire universe. This hypothesis was disproved in 1924 by the American astronomer Edwin Hubble, who studied nebula-like celestial bodies at the Mount Wilson Observatory in southern California. Using the observatory's 2.5 meter diameter telescope, Hubble proved that these nebulae are outside our galaxy, and are galaxies in their own right.
In the years 1925 - 1929, Hubble made another discovery: the galaxies in the universe are moving away from each other, and there is a direct relationship between the distance of the galaxy from us and its speed. It can be concluded that about 14 billion years ago all the matter in the universe was concentrated in one small area. According to the accepted theory today, the universe was then created in a kind of tremendous explosion known as the "Big Bang".
The cosmic background radiation
The best proof of the big bang is the "cosmic background radiation" that was discovered in 1965. It was discovered by two physicists from the Bell company, Arno Penzias (Penzias) and Robert Wilson (Wilson), who were testing a new radio antenna for satellite communication. They discovered that the antenna picks up constant "noise" of electromagnetic radiation in the microwave field. This radiation arrived with the same intensity from all directions in the sky and it turned out that it behaves like radiation emitted by a body at a temperature of about three degrees above absolute zero. (Radiation whose characteristics match the radiation emitted by hot bodies is called by physicists "black body radiation"). It was found out that this is radiation that has survived in the universe since the big bang, and gradually cooled due to the expansion of the universe.
According to the theory there should have been small differences between the temperatures of the radiation in different regions of the universe. The reason for this is that the temperature of the background radiation is a kind of "photograph" of the universe when it was about 400 thousand years old. In order for stars and galaxies to form, there had to be slight density differences in the young universe. The denser places attracted the material around them, and thus concentrations of material were formed from which the stars, galaxies and galaxy clusters we see today grew over time. A calculation showed that the temperature differences should be of the order of one in a hundred thousand.
Most researchers believed that there was no chance of discovering such small differences. But there was one "crazy talker" who thought otherwise. It was Dr. George Smoot, (Smoot) from Berkeley, who from 1970 was engaged in measurements of the background radiation with the help of instruments flown in airplanes and balloons. Smoot initiated a study to discover the non-uniformity in the background radiation. The planning began in the mid-seventies and the research was successfully completed in 1992, when a research satellite named COBE (cosmic background explorer), designed by Smoot and his team, did discover differences of the order of one in a hundred thousand in the radiation temperature at different points in the sky. The results provided a renewed and impressive verification of the Big Bang and were widely acclaimed. Smoot wrote a fascinating book about this called Wrinkles in Time (published in Hebrew by Maariv Library).
Following Kobi's findings, astrophysicists began to theoretically test how different parameters, such as the age of the universe and the amount of matter in the universe, affect the fluctuations in the background radiation. The tests showed that it is possible to extract important information from these fluctuations, if they are measured with more accurate devices than Kobe's. The map of the background radiation provided by Kobi allowed the researchers to compare the average temperature between areas with a diameter of seven degrees of arc or more (the complete circle has 360 degrees). This can be compared to a 55 cm passport photo, which consists of 11 mm squares in black, white and shades of gray. We may be able to identify who is photographed in the photo, but it is doubtful whether its quality will be sufficient for a passport or ID card.
NASA, which helped build Kobe and flew it into space, began planning a new research satellite to measure the background radiation. The satellite was called MAP (acronym for Microwave Anisotropy Probe. Later it was called WMAP in memory of David Wilkinson [Wilkinson] who was one of the initiators of MAP). The separation capability in MAP measurements reached a fifth of a degree. MAP was successfully launched in June 2001 and the astrophysicist community eagerly awaited the results.
Deciphering the secrets of creation
The measurements lasted a whole year when MAP orbited the Sun and was constantly 1.5 million km from Earth. Each piece of sky was sampled several thousand times, at five frequencies in the microwave field. The results were published in February 2003 (about two weeks after the Columbia disaster in which seven astronauts perished, including Ilan Ramon). MAP's results exceeded all expectations. Together with the results of ground instruments and instruments launched in balloons, they confirmed the Big Bang theory and yielded very accurate values of various parameters related to the evolution of the universe. For example, it was found that the age of the universe is 13.7 billion years, with an accuracy of one percent (previous estimates spoke of 13-15 billion years).
The results provided confirmation for a modern version of the big bang theory called the expanding universe theory. According to this theory, proposed in 1981 by Ellen Guth from the USA, at a very early stage of the universe's development there was a brief period of very rapid expansion known as "inflation". During this period the universe doubled its size repeatedly, about a hundred times. Then it continued to spread at a much slower rate.
Goth's theory answers the troubling question: Where did the initial energy from which the matter and radiation in the universe came from? According to the bulge model, most of the matter and radiation was created during the bulge, through physical processes that we are able to understand and analyze. (In contrast, according to the standard model of the Big Bang, all the matter and radiation that fills the universe today suddenly appeared out of nowhere). It can be said that the inflation model to some extent removes the veil of mystery over the act of creation.
How much matter is there in the universe?
We can estimate with great precision the mass of the Earth, the mass of each of the planets, the mass of the Sun, and also the mass of more distant stars, but is it possible to estimate the total mass of the universe, or the density of matter in the universe? This question is important because the amount of matter and energy in the universe determines whether it will continue to expand forever, or whether the forces of gravity will cause the expansion to slow down and the universe will begin to contract. The limiting value is called "critical density". If the density of matter and energy in the universe is less than the critical density, the expansion of the universe will continue forever. If it is above the critical density, the expansion will reverse direction at some point, and eventually all the matter in the universe will again be accumulated in a very small area.
MAP's findings solved the puzzle. It follows from them that the density of matter and energy in the universe is equal to the critical density, with a possible error of less than one percent. Only about four percent of this density is made of the material from which the atoms are built. 23 percent is a mysterious substance whose nature still requires clarification, known as dark matter. Another 73 percent is mysterious energy, which is somewhat similar to the energy that drove the expansion of the universe during the inflationary period. This energy was named dark energy. Is dark energy indeed a remnant of that primordial energy, or a new phenomenon that did not exist in the early universe? We still don't know the answer. Let's hope she finds it in the future.
* On the summer solstice: The Open University held a symposium on astronomy and space exploration
The Open University held a symposium on astronomy and space exploration on the occasion of the 100th anniversary of the publication of Albert Einstein's article on the theory of relativity (June, 1905) and as part of the events of the International Year of Physics.
The lectures on the seminar presented the updated and modern astronomical knowledge based on the latest observations from spaceships and telescopes on Earth.
Prof. Yoram Kirsh from the Department of Natural and Life Sciences at the Open University will speak on the day of the seminar about the discoveries of the COBE and WMAP spacecraft and the way in which physics describes the creation of the world. Prof. Elia Leibovitz from the School of Physics and Astronomy at Tel Aviv University, told about the most massive explosion in the universe, of stars known as "gamma radiation bursts"; Yigal Fattal from the Israeli Astronomical Society and the Open University explained what solar and white eclipses are and in particular will present the total solar eclipse that will occur near Israel in March 2006; Finally, Dr. Yoav Yair, from the Department of Natural and Life Sciences at the Open University, presented innovations and discoveries in the study of the planets Mars, Saturn and other bodies in the solar system.
** Explanation for the illustration
The data processing can be described in the following way. The sky is divided into squares with a certain angular width (eg 10) and the difference between the average temperature in each square and the average temperature of the background radiation as a whole is calculated. Then the average of these differences is calculated. When you repeatedly change the size of the squares and repeat the calculation, you get the graph in the figure. The vertical axis in the graph is the average temperature difference (T) in units of 1 divided by 100,000 degrees Kelvin. On the horizontal axis appears the parameter l related to the size of the squares. (1800 divided by l is the angular width of the squares, which appears on the upper scale). The circles in the graph are the results of MAP measurements and some ground experiments. The continuous line shows the theoretical calculation of T, which corresponds to the measurement results.
