Dark Matter and Cosmic Web Story

by Jaan Einasto

  However, there exist several arguments which make these models unrealistic. The strongest argument in favour of the presence of non-baryonic dark matter comes from the CMB data. In the absence of large amounts of non-baryonic matter during the radiation dominated era of the evolution of the Universe it would be impossible to get for the relative amplitude of density fluctuations a value of the order 10−3, needed to form all observed structures.

  The other strong argument in favour of the presence of some matter in addition to ordinary baryonic matter comes also from CMB data. The wavenumber of the first acoustic peak in the CMB spectrum is a very accurate indicator of the total matter/energy density of the Universe. Experiments show with great accuracy that the total density is equal to the critical cosmological density. On the other hand, both direct determinations as well as the nucleosynthesis constraints show that the density of baryonic matter is only about 4% of the critical density. In other words, there must exist some other forms of matter/energy than ordinary matter. The other forms are dark matter and dark energy. Dark energy causes the acceleration of the Universe, it was detected by comparison of nearby and distant supernovae by Riess et al. (1998) and Perlmutter et al. (1999).

  There exist direct observations of the distribution of mass, visible galaxies and the hot X-ray gas, which cannot be explained in the MOND framework. One of such examples is the “bullet” cluster 1E 0657-558 (Clowe et al., 2006). This is a pair of galaxy clusters, where the smaller cluster (bullet) has passed the primary cluster almost tangentially to the line of sight. Weak gravitational lensing observations show that the distribution of matter is identical with the distribution of galaxies. The hot X-ray gas has been separated by ram pressure-stripping during the passage. This separation is only possible if the mass is in the collisionless component, i.e. in the non-baryonic dark matter halo, not in the baryonic X-ray gas.

  The basic driving force behind the search for new laws of gravity is actually the understanding that something in our physics world view is missing. This is really the case. We still do now know what changes in our physics world view are needed. But when the nature of dark matter, and, more importantly, that of the dark energy is clarified, it is evident that this shall change our understanding of Nature.

  6.4 Tartu Observatory in the late 1980’s

  6.4.1 The singing revolution

  Our friend Mikk Sarv has lectured at theViljandi CultureAcademy of Tartu University in traditional music. As part of the teaching he organised every year in spring with his students walks on village roads singing ancient Estonian folk songs. This is an old tradition, meaning to bring a good harvest. People gathered in weekends and walked singing old songs from village to village, and from farm to farm. So Mikk has revitalised these ancient traditions in his teaching.

  In the 1980’s some other old traditions were revitalised: Hanseatic Days in Tartu, and Old City Days in Tallinn. Mikk with his friends thought about how they can contribute to Old City Days, and decided to walk singing ancient folk songs along Tallinn’s city-walls, stopping at each of the eight main gates of the wall. Eight has an important meaning in Estonian folklore — in Estonian language there are eight cardinal points, each having its own meaning (so, between South and West we have a separate word for South-West, and so on, and each of these directions has its own cultural meaning — this is similar to other Ugro-Finnish languages). Mikk and his ensemble stopped at each gate and explained the meaning of the point as well as the story of the gate, accompanied with appropriate folk songs. Mikk wrote to me that it was very beautiful and sublime to walk during the night, to sing, and to think on our past and future.

  On June 4, 1987 Mikk and his ensemble made the traditional walk through the Old City, and additional people joined them and also started to sing. They were Estonian musicians, singing popular songs. The joint singing continued through Town Hall Square until morning. The next evening they moved through the Old City to the Song Festival Arena, all the time new people accrued and joined the singing. At the Song Festival Arena they continued singing until the morning-light. The night was so emotional and joyful that musicians continued the singing night after night until the end of Old City Days, and decided to do it again in the next year.

  Next year the leaders of various music ensembles prepared the concerts at the Song Festival Arena very carefully. They formed an informal headquarters to coordinate all actions. Soon they were informed that militia and the KGB will try to interfere. To avoid this they informed our radio and TV men, as well as Finnish TV. What Soviet authorities were most afraid of was the truth about the events within the USSR. Also a voluntary ‘bodyguard’ of several hundred young boys and girls was formed to keep order, and to tidy up garbage from the Song Festival place. The motto was ‘everywhere it must be cleaner than before’.

  On the first evening of the Old City Days, June 4, musicians walked through Old Tallinn to the Song Festival place, singing popular and folk songs. Tidings of the event had spread among the community, and much more people accompanied them than in the previous year. Estonian flags were not yet used, but many people had blue-black-white bands on their breast. Each evening there were more people gathering, and radio and TV reporters were there, most importantly from Finland and other countries. Some people had full Estonian flags, more and more every evening. One day the militia made an attempt to rend the flags, but immediately a dozen foreign reporters and cameramen were there, and the militia disappeared.

  On the last evening Finnish companies had organised special tours, so that more than a thousand Finns participated. In total more than 70 thousand people gathered on Song Festival grounds. Estonian flags were openly carried, as well as flags of free Ukraine, Russia, Latvia and Lithuania. The spirit was high, people sang and cried from happiness. People linked their hands together and sang in chorus, a tradition had begun. This evening was broadcast live to Finnish TV, and suddenly all people started to chant: “Hyvää, Suomi! Hyvää, Suomi!” A bit later a telegram arrived with address “Tallinn Song Festival: Finnish people are with you, Estonian brothers”. The message was read to the microphone, and people again chanted “Hyvää, Suomi!”

  Fig. 6.5 Old Tartu Observatory on a 2011 night with the Estonia flag (author’s photo).

  The festival continued until 7 AM. Then the organisers got a message that the old leaders of the Estonian Communist Party were preparing to suppress the demonstrations. However, Gorbachev understood that this would be a catastrophe for the USSR, since everything that happened was known in the West. Thus he ordered that the previous General Secretary of the Estonian Communist Party be changed with a new one, Vaino Väljas, who understood the needs of the Estonian people. At this time Väljas was the Soviet Ambassador in Nicaragua. He was promptly called back, and on June 16 he arrived in Tallinn to get his new appointment.

  The singing tradition at the Song Festival Arena was taken over by the Popular Front. On June 17, 1988, more than 100 thousand people gathered at the Song Festival Arena, to accompany our delegates to the Soviet Congress of People’s Deputies. On September 11, 1988, a song festival, called “Song of Estonia”, was held. This time nearly 300 thousand people came together, more than a quarter of all Estonians. Our political leaders participated, and were for the first time insisting on the restoration of independence.

  A few words on our flag. Every nation has its symbols, and one of the most important symbols is the national flag. The Estonian national flag is blue-black-white: blue for the blue sky and the devotedness to our ideals; black for our black soul and national coat; white for our hope and aspiration for light and freedom. In the Soviet period the use of these colours in any way was forbidden; many brave boys were imprisoned for years for the use of these colours.

  The very first official building which was decorated with our national flag was the old Tartu University Observatory. This was done on June 23, 1988, on Victory Day. The flag was raised by our astronomers Peeter Traat, Andres Kuperjanov and Kalle Jürgenson on their own ini
tiative. On the same day the daughter of Peeter, Kristina, graduated from high school. This was chosen as an explanation in case the KGB asked questions.

  Recently I met Andres Kuperjanov. He told me that the flag story was more complicated. A few days after the flag was raised it was removed and burned by KGB agents, who had climbed to the dome using the lightning rod. To avoid further removing of the flag, Peeter removed some fixing bolts of the rod and oiled it, so it was impossible to climb up outwards to the dome. Also astronomers formed a voluntary guard to watch the flag at night. The flag has stayed there until now; it is taken down only for replacements with a new flag. This happens 24 times a year. Now the replacement is made by Tartu municipal authorities; earlier astronomers used their own money to buy new flags.

  In the Government Building in Tallinn the Estonian flag was raised on Independence Day on February 24, 1989.

  6.4.2 Academy of Sciences

  In 1981 I was elected to the Estonian Academy of Sciences. A few years later I was appointed to the post of the head of the division on Physics, Mathematics and Technical Sciences, which soon was divided into two divisions — one for Astronomy and Physics, and the other for all technical sciences. In the Soviet Union modern molecular biology and genetics were banned and replaced by Michurin-Lysenko type biology. In our academy also one special institute was formed to apply this form of biology. However, physicists working in nuclear research needed information on how radiation affects organisms, and thus inside physics institutes laboratories on molecular biology and genetics were quietly formed. This happened also in Estonia. Small laboratories of genetic studies were formed in the Institute of Physics and in the Institute of Chemical and Biological Physics. But soon they were too small and the time was ripe to organise a fully independent Institute — the Estonian Biocenter. The driving force for its formation came from Prof. Richard Villems, a good friend of Enn Saar. It was clear that our colleagues in the Academy from the Division of Chemistry, Biology and Geology were against the formation of this Center, so it was formed within our Division ofAstronomy and Physics.Also the first new members of the Academy, specialists in modern biology, were elected to our Division. Presently the Estonian Biocenter is one of the most successful scientific institutions in Estonia. It is working in very close collaboration with Tartu University and with a number of the best centres in other countries.

  In the late 1980’s the time was ripe for another change in the life of theAcademy. So far all Academies of Soviet republics were subordinated to the USSR central Academy of Sciences — we had to coordinate all our activities, including the elections of new members to our Academy. In 1990 we prepared a new bylaw of the Estonian Academy of Sciences where we eliminated all aspects of the subordination to the central Academy. We also wrote in the bylaw that the present Academy is the successor of the Estonian Academy of Sciences formed before the war, and closed by Soviet authorities in 1940. Soon Academies of other Soviet republics followed our example, but we were the first to do this.

  I acted as chairman of the Division of Astronomy and Physics until 1995, after 12 years of service in this post. The work in the Academy was rather timeconsuming, my Academy office was in Tallinn, and I had to drive to Tallinn every week for some days. After 1995 I withdraw from all administrative duties, both in the Academy and in Tartu Observatory. The new head of the Cosmology Department of the Observatory is Enn Saar.

  6.4.3 Towards an independent Estonia

  These years were rather tumultous in both our lives and in the Estonian Academy of Sciences. The scientists of the Academy were actively involved in public life. Here are some episodes from the life of the Academy, and of the Estonian independence movement.

  In May 1987, students and intellectuals initiated a successful protest movement against Moscow’s plans for large-scale, ecologically disastrous mining of phosphorites in north-eastern Estonia. Out of this effort grew the Estonian Greens Movement. Scientific arguments against the Soviet plan were collected by Endel Lippmaa, my colleague in the Estonian Academy of Sciences.

  The next step was the Estonian IME program for economic autonomy, which won widespread acclaim in September 1987 as an attempt to solve national problems by making an Estonian contribution to economic reforms in the Soviet Union. Drawing on examples from China and Hungary, the proposal called for an end to central economic control over Estonia, a separate tax system, and the adoption of a convertible ruble. The idea was popular, not least of all because of the plan’s name, “Isemajandav Eesti”, whose acronym, IME, means “miracle” in Estonian. A committee was formed to prepare the reform plan. One of the leaders of the program, Professor of Tartu University Marju Lauristin, asked me to prepare the science program for IME. This program was later used to prepare the Science law in the Estonian Parliament.

  In the late 1980’s two important developments took place. In April 1988 the Popular Front of Estonia was formed, initially called “Popular Front for the Support of Perestroika”. It was a major force in the Estonian independence movement. Popular Front participated in elections for the new Congresses of People’s Deputies of USSR and the Estonian Supreme Soviet, and formed the last government in the Soviet period, which made actual preparations to achieve independence.

  Radical nationalists formed in 1989 the Estonian Citizens Committee, a nonpartisan political movement, where Estonian emigrants in Western countries played a major role. The purpose was to register Estonian citizens, to carry out the elections of the Estonian Congress, and to convene the Congress as a legislative body. The Committee refused to participate in any Soviet organisation, including Estonian Supreme Soviet and government. The leaders of the movement did not understand that no country will recognise such movement as a legislative body since it had no real power over the country. The conflict between the Popular Front and Citizens Committee was dampened by the fact that a large number of people who wanted to restore Estonian independence participated in both movements.

  In the autumn of 1988 a new constitution was being prepared by Soviet authorities who had the goal of significantly restricting the rights of the Union republics. This alarmed us all and made us rack our brains over what measures to take. One evening Valdur Tiit phoned me and the conversation soon turned to these problems. I cannot exactly recall who initiated the idea, but we decided to find Arnold Rüütel, the Chairman of the Estonian Supreme Soviet (President of the Republic in present terms). His home was close to Tiit’s, and both of us had already known Rüütel for a long time, so there were no diplomatic obstacles to meeting him. We set to it straight away; I drove to Tartu and we knocked on Rüütels door. We told him at once that we had a serious issue to discuss and asked to talk without interference. He considered it for a while and took us to his sauna which he had built himself so he could be sure that no listening devices had been installed in it. We asked for his advice on how we could contribute in order to turn the political situation in our favour. Soon we came to the decision that the most effective way would be to make a declaration or appeal at the general meeting of the Estonian Academy of Sciences.

  The next day I convened all members of the Estonian Academy from the Tartu region to the old University Observatory, and soon a project for the appeal was ready. This was the basis of the general assembly of the Academy taking place a few days later (November 2, 1988). Arnold Rüütel and Vaino Väljas were also present. They did not talk, but observed the ongoings intensely. The appeal we reached was the first step towards the declaration of sovereignty that was accepted at the Estonian Supreme Soviet (Parliament) some weeks later. We translated the appeal to Russian and on the same night I called Andrei Sakharov. I had met him a year before at the Friedmann conference of cosmology. Sakharov asked me to dictate the appeal so he could write it down. I had no doubt that our conversation was being recorded by “the competent authorities”, but there was nothing to lose, since our appeal was going to come to general knowledge in any case.

  The preparations for the declaration of sove
reignty were known to high officials in Moscow, and Rüütel was ordered to Moscow by the prime minister of the USSR for questioning. Later Rüütel told me that he was threatened with ten years’ imprisonment when he would continue preparations for the declaration. In the middle of the meeting the prime minister was called to Gorbachev where the top officials of the USSR discussed what to do. The danger of the dissolution of the USSR was so great that three options were discussed: immediate arrest of Rüütel, the organization of some ‘accident’ (car crash or something similar) to kill him, or let him go. Finally the foreign minister Shevardnadze convinced the rest of the officials that it is best to let him go, since in his opinion there is no hope that the resolution will pass in the Estonian Supreme Soviet. The other argument was that foreign press was already informed of our plans, and every other action would bring complications for the USSR. So after four hours of examination Rüütel was allowed to return home.