Great Attractor

We are obviously attracted to the Earth. The second obvious attraction is to the sun. The next attraction is a little bit more obscure because it is located 28,000 light-years away from us. The center of the Milky Way galaxy is a great center of gravitational attraction of most objects visible to the naked eye. The last "Great Attractor" known to us is a little more obscure. It lies 400,000,000 light-years away and seems to attract our entire local group (Andromeda, Milky Way, Triangulum Galaxy, M110, M32 etc…). There are however many things obscuring our view of it. The interstellar medium blocks 20% of our visible sky, and in this case the Great Attractor lies within that 20%. It is a conglomeration of perhaps 100,000 galaxies beyond the local group.

    It appears that the Earth is moving, in the direction of the constellation Leo (RA: 11.2h, dec: -7deg), around 380 km/s. This does however include the revolution of the Sun around the galaxy, and includes the movement of the Milky Way about the center of the local group. This taken into account sum to around 300 km/s in the direction of the constellation Cygnus. After correcting for this one finds the local group is moving at around 600 km/s relative to the cosmic microwave background, measured via Doppler-shift, in the direction of the Hydra-Centaurus supercluster.

The Great Attractor is far bigger than a galaxy. In the terminology of astronomers, there are clusters of galaxies containing maybe hundreds of galaxies, and superclusters containing many clusters. The Great Attractor is a supercluster or something even bigger.

Indian Story of Mathematics

Indian Story of Mathematics.

There was a one number missing in Mathematics, it was Indians who introduced it to the world of mathematics. That number is “Zero”.  Before Indians invented it, there was no number zero to ancient Greeks, and it simply had not existed, for Egyptians, Chinese. Even though zero had been in use but as a place holder, an empty space to show a zero. This brilliant invention revolutionizes mathematics. Using this new number it is now possible to capture astronomically large number in a efficient way. 

There is cultural reason for invention of zero. For ancient Indians the concept of nothing has an eternity . According to Indian believe system the universe was born out of nothingness, and nothingness is the ultimate goal of humanity.

In 7^th century the brilliant Indian mathematician Brahma Gupta  prove some of the essential properties of zero. His rules about calculating with zero is taught in schools  all over the world.

1+0=1.

1-0=1.

1*0=0.

Indians even discovered a new sort of number “Negative number”. This invention gave a new idea of solving quadratic equations that is equations involving power of 2. Brahma Gupta understood the concept of negative number very well. He told that quadratic equations always have two solutions, one of which could be negative. These concepts were not known in west till 1600.

Indians contribution to the world of mathematics was not only new notation for zero. Indian mathematicians were responsible for making fundamental new discovery in the theory of “Trigonometry”.  Indians used their concept of trigonometry in many of their old astronomical observatories called “JANTAR MANTAR”.  

                    

Carl Sagan's Cosmic Calendar

The American astronomer Carl Sagan was the first to suggested a “cosmic calendar”. He put everything starting from Big Bang to till today into a scale of a calendar year. According to Carl Sagan the Big Bang corresponding to the first second of the New Year's Day, and the present time to the last second of December 31st (midnight). Using this scale of time, each month would equal a little over a billion years.

Within the scheme of the Cosmic Calendar, an average human life of 70-80 years is equivalent to approximately 0.16 cosmic seconds. All human history is crowded into last 5 minutes of the last day of the year. Recent time has to be divided into seconds and fraction of seconds. So everything happened over the last 475 years take place in less than the last second of the last minute of the year.

Date/Time	Event
1 Jan(midnight)	Big Bang
15 Mar	First star and galaxies form
1 May	Milky Way galaxy form
8 Sep	Sun forms
9 Sep	Solar System forms.
12 Sep	Earth forms.
13 Sep	Moon forms.
20 Sep	Earth’s atmosphere forms.
1 Oct	Earliest known life on earth.
7 Oct	Earliest Known fossils.
18 Dec	First many celled life forms.
19 Dec	First Fish.
21 Dec	First land plants
23 Dec	First reptiles.
24 Dec	First Dinosaurs.
26 Dec	First mammals.
27 Dec	First birds.
28 Dec	Dinosaurs extinct.
31 Dec	Homo sapiens (modern human) appears.

Dark Energy

One of a number of seemingly implausible features of dark energy is that its density is assumed to be constant over time. So, even though the universe expands over time, dark energy does not become diluted, unlike the rest of the contents of the universe.

As the universe expands, it seems that more dark energy appears out of nowhere to sustain the constant dark energy density of the universe. So, as times goes by, dark energy will become an increasingly dominant proportion of the observable universe – remembering that it is already estimated as being 73% of it.

An easy solution to this is to say that dark energy is a feature inherent in the fabric of space-time, so that as the universe expands and the expanse of space-time increases, so dark energy increases and its density remains constant. And this is fine, as long as we then acknowledge that it isn’t really energy – since our otherwise highly reliable three laws of thermodynamics don’t obviously permit energy to behave in such ways.

An easy solution to explain the uniform acceleration of the universe’s expansion is to propose that dark energy has the feature of negative pressure – where negative pressure is a feature inherent in expansion.

Applying this arcane logic to observation, the observed apparent flatness of the universe’s geometry suggests that the ratio of dark energy pressure to dark energy density is approximately 1, or more correctly -1, since we are dealing with a negative pressure. This relationship is known as the equation of state for dark energy.

In speculating about what might happen in the universe’s future, an easy solution is to assume that dark energy is just whatever it is – and that this ratio of pressure to density will be sustained at -1 indefinitely, whatever the heck that means.

But cosmologists are rarely happy to just leave things there and have speculated on what might happen if the equation of state does not stay at -1.

If dark energy density decreased over time, the acceleration rate of universal expansion would decline and potentially cease if the pressure/density ratio reached -1/3. On the other hand, if dark energy density increased and the pressure/density ratio dropped below -1 (that is, towards -2, or -3 etc), then you get phantom energy scenarios. Phantom energy is a dark energy which has its density increasing over time.

Anyhow, as the universe expands and we allow phantom energy density to increase, it potentially approaches infinite within a finite period of time, causing a Big Rip, as the universe becomes infinite in scale and all bound structures, all the way down to subatomic particles, are torn apart. At a pressure/density ratio of just -1.5, this scenario could unfold over a mere 22 billion years.

sourse:www.physorg.com

ALTERNATIVES TO DARK MATTER

      Although the evidence for dark matter is wide and deep, it is nevertheless indirect, and is based on the assumption that the laws of motion and gravity as formulated by Newton and expanded by Einstein apply. An alternative possibility is that a modification of gravity can explain the effects attributed to dark matter. The basic idea is that at very low accelerations, corresponding to large distances, the usual law of gravitation is modified.
  The most studied of these modifications is called Modified Newtonian Dynamics, or MOND. According to this hypothesis, the force of gravity falls off more slowly at low accelerations (inversely as the distance rather than inversely as the square of the distance). With this prescription, less mass is required to explain the observed rotation of the outer edges of galaxies or the pressure of the hot gas in clusters of galaxies than in the Newton-Einstein theory. By adjusting the parameters of the theory, the need for dark matter can be eliminated.

  Although MOND has had some success in explaining observations of galaxies, it and other theories that involve modifying the law of gravity have been severely challenged by observations of the galaxy cluster 1E0657-56, a.k.a. the Bullet Cluster.

  The accompanying image shows hot X-ray producing gas (pink), and optical light from stars in the cluster galaxies (orange and white). The X-ray observations show that the Bullet Cluster is composed of two large clusters of galaxies that are colliding at high speeds.

  Using the gravitational lensing technique, astronomers have deduced that the total mass concentration in the clusters (blue) is separate from that of the hot gas. This separation was presumably produced by the high-speed collision in which the gas particles collided with each other, while the stars and dark matter were unaffected. It cannot be explained by an altered law of gravity centered on the hot gas particles, and provided direct evidence that most of the matter in the Bullet Cluster is dark matter. Although such violent collisions between clusters are rare, another one (MACS J0025.4-122) shows the same effect.

 source:www.chandra.harvard.edu