The Cosmological Constant

The cosmological constant was originally introduced by Einstein in 1917 as a repulsive force required to keep the Universe in static equilibrium which follows steady-state-theory. In trying to solve the differential equations that describe space-time, his field equations predicted that the universe should be either contracting or expanding. In the year 1922, Russian physicist Friedmann derived solutions to Einstein's equations that corresponded to an expanding universe. Einstein needed to add a constant term to avoid having the universe collapse upon itself. This term balances the attractive force of gravity contributed by all of the matter in the universe.  

Hubble's study of nearby galaxies showed that the universe was in fact expanding and that lead to the Big Bang theory, the concept introduced in 1927 by Georges LeMaitre.Einstein regretted the introduction cosmological constant to keep the universe static and termed it as greatest mistake.

After almost 100 years we realized that the Universe does in fact have a non-zero cosmological constant: that’s what we call dark energy, and use to explain the accelerated expansion of the Universe. Physically, this term represents the vacuum energy, the possibility that empty space possesses density and pressure thus preventing the universe from collapsing.

If indeed the cosmological constant represents the dark energy or vacuum energy then Einstein by mistake proposed the dark energy concept.

Why Diamond The Strongest Element

Graphite and Diamond are allotropes of carbon ,meaning any of two or more physical forms in which an element can exit. Diamond is very strong in fact strongest known where as graphite is very soft. Why ?

Let us look at the electronic configuration of carbon, it has 4 valence electrons and each carbon atom is covalently bonded to four other carbon atoms in case of diamond.The crystal structure of a diamond is a face-centered cubic or FCC lattice. Each carbon atom joins four other carbon atoms in regular tetrahedrons (triangular prisms).

Diamond's strength comes from pyramid-like structure which is the strongest structures known to man, This is a giant covalent structure and it continues on and on in three dimensions. It is not a molecule, because the number of atoms joined up in a real diamond is completely variable depending on the size of the crystal. As all the four electrons form covalent bonds, there are no free electrons or ions in diamond, so it does not conduct electricity. It has very high melting point (almost 4000°C) because very high temperatures are required to break the covalent bonds. Each carbon atom is at the same distance to each of its neighbouring carbon atoms. In this rigid network atoms cannot move. This explains why diamonds are so hard and have such a high melting point.

Graphite has a layer structure, each carbon atom uses three of its electrons to form simple bonds to its three close neighbours. The fourth electron is free and no longer associated directly with any particular atom or pair of atoms meaning delocalized, but are free to wander throughout the whole sheet.The distance between the layers is about 2.5 times the distance between the atoms within each layer. A weak Van der Waals force of attraction acts between the layers and these layers of  carbon slide over each other in graphite, that's why it is very soft and conducts electricity.

Climate Change And Rejuvenating The Rivers

Its very heartening to know that Sadhguruji has raised the issue of reviving and rejuvenating the rivers with 'Rally for Rivers' campaign,but people may want to know what is the plan of action .Basically rivers are nothing but carriers of rain water and hence we can't actually control them, depends more on the climatic conditions. Increasing the forest coverage and planting trees along the riversides as suggested by him may help somewhat. 

We are presently facing serious green house effect through burning of fossil fuels and made the earth more warmer  which could have disastrous consequences like  loss of snow cover, sea level rise, change in weather patterns. Many scientists believe that the damage to the Earth's atmosphere and climate is past the point of no return, meaning almost irreversible.

Atmospheric CO2 levels have increased by more than 40 percent since the beginning of the Industrial Revolution, from about 280 parts per million (ppm) in the year 1800 to 400 ppm today.There was a  landmark Paris agreement on climate change effective from  Nov. 4  2016 to strengthen the global response to the threat of climate change by keeping a global temperature rise this century well below 2 degrees Celsius above pre-industrial levels and to pursue efforts to limit the temperature increase even further to 1.5 degrees Celsius. Controlling and reducing the use of fossil fuels and the urgency to go for renewable energy is the need of the hour.

India has another big problem on hand, severe river pollution , Majority of Indian rivers are polluted because of industrial and human waste,particularly the Ganges . Our immediate concern must be to stop polluting the rivers and start cleaning them which requires massive effort from the government ,industries as well the people. Reducing consumption or usage of a polluting products,treatment of wastes, discharges and disposals of a pollutants. Govt. need to shutdown all the industries causing the river pollution or have strict guidelines for the industries to treat the pollutants and have proper waste management.

It is time for concerted action by world leaders on climate change . The climate change certainly made Harvey and Irma worse though they are not caused by climate change. Hurricanes thrive over warm water and strengthen in intensity, oceans have warmed on an average 1 to 3 degrees Fahrenheit. Climate change is a harbinger of doom.Time to act or face the consequences.

science and Technology blog: Doppler Effect

science and Technology blog: Doppler Effect: The change in the observed frequency of an acoustic or electromagnetic wave due to relative motion of source,observer or both is called Do...

Doppler Effect

The change in the observed frequency of an acoustic or electromagnetic wave due to relative motion of source,observer or both is called Doppler effect. As the source moves towards the observer the frequency increases or wavelength decrease and if the source is moving away then the frequency decrease or wavelength increase.

The movement of the source alters the wavelength and the received frequency of the waves ,even though the source frequency and wave velocity are unchanged. The Doppler effect can be observed for any type of waves like water waves, sound waves, light waves, etc.

There are many practical applications of Doppler effect ,let us look at few specific examples.

Astronomy

Astronomers have found that Universe is expanding by Doppler effect . When a star or a galaxy moves away from us the frequency decreases or wavelength increases.This change to longer wavelengths towards the red end of the visible spectrum for visible wavelengths is called a redshift. Conversely, if the source is moving towards the observer, there is a change to shorter wavelengths, i.e. a blueshift. Most of the galaxies appeared red shifted and hence moving away from us .This is the basis for the conclusion that the Universe is expanding and was one of the greatest intellectual revolutions of the twentieth century.

Radar Gun

Police use Radar gun to measure the speed of moving vehicles ,the radar gun function on the principle of Doppler effect .The radar gun includes a radio wave transmitter integrated with a radio wave receiver. The gun emits radio waves at a particular frequency so that the radio waves travel via the air and bounce off the moving vehicles. Some of these reflected waves will return back to the radar gun, and the waves that are reflected from the vehicles undergo a Doppler Shift.This Doppler shift in turn causes a change in the frequency of the radio waves. The radar gun makes use of this frequency change to measure the speed of the vehicle.

Ocean Depth 

The depth of a ocean can be determined by using Doppler effect ,the sound waves are transmitted from the ship towards the ocean floor using a sonar(sound navigation ranging) and they are reflected from the ocean floor back to the ship.The depth can be 

calulated using the formula

        v X t

   d= --------

            2

where v is the velocity of sound and t is time taken from the ship towards the ocean floor and back to the ship.

Future Trains

Future trains may travel in the air with no tracks hence no surface as well as air friction.Japan is using maglev(magnetic levitation) technology for fast speed trains, levitation means to rise or cause to rise into the air and float in apparent defiance of gravity. Maglev uses magnets to travel above the ground and hence can travel at high speeds.The magnetic field created by the electrified coils in the guideway walls and the track combine to propel the train. Maglev transport systems are in operation in just three countries Japan, South Korea and China.

 

A Japan Railway maglev train hit 603 kilometers per hour on an experimental track in Yamanashi setting a decisive new world record. The train is planned to begin service in 2027. Right now China operates the world's fastest commercial maglev, which has hit 431 kilometers per hour on a route through Shanghai.

Elon Musk new concept of Hyperloop transporation technolgy where a train can travel upto 700 mph .Hyperloop would work by propelling pods at high speeds through a vacuum tube with almost all air removed, capsules carrying passengers or cargo would be pushed along by a series of electromagnets. The almost complete lack of friction due to low air pressure means the train could travel at speeds of over 800mph, and 760mph with passengers on board.

China to take on Elon Musk hyperloop with supersonic flying train .China working on flying train which can travel at around 2500Mils/hour according to China Aerospace Science and Technology Corporation in short called CASC. Although the technology is still in its teething stages,the flying train is in essence a passenger pod that uses magnetic levitation and travels through a near-vacuum tube according to CASC  manager Liu Shiquan. The concept is similar to that of the Hyperloop.