Monthly Archives: June 2002

BETELGEUSE

 

  “Twinkle Twinkle little star

   How I wonder what you are “

 This line from the most popular nursery rhyme has a profound “meaning”.

The child looks at a star and is filled with wonderment. As a child whenever I used go to my ancestral village I used to spend hours looking at the starry heavens at night. In places far away from big cities you can see tens of thousands of stars on a clear night. In cities there is too much light and you cannot see much. A few days back I looked up at the sky and I could not see more than 5-10 stars. When was the last time you saw a night sky filled with countless stars?? As technology grows would we have so much light at night that would not be able to see the stars. Would our children not wonder about stars? It is wonder that is the foundation of Science. Or would our children confuse Science with Technology and say uneducated statements like ” Science makes our lives easier” : :-O !! 

   Today in VERITAS we shall wonder about a little star. The name of this star is Betelgeuse and it is not a little star. It is the biggest star known to us. It is about 700 times wider than the sun ie if Betelgeuse were placed where the sun is now its surface would extend beyond the orbits of Mars and even Jupiter… it is that big. The surface temprature of this star is about 6000F which is a lot cooler than our Sun’s 10,000 F. Its low temperature makes it appear red in color.

   We have all seen Betelgeuse. It lies at the shoulder of the Orion constellation(“the hunter”). For an idea of its position see the attached gif file. The name Betelgeuse comes from an Arabian phrase: “Armpit of the giant”. We can see the Orion constellation only in winters(in the northern hemisphere). The distance of this star from earth is about 600 light years.

  Betelgeuse belongs to a category of stars which called  supergiants. Red supergiants are those stars which are approaching their death. A middle age star like our sun has two forces which balance each other: the gravity which pulls the surface inside and the pressure of the nuclear fusion which pushes it outside. When a star is about to die( its hydrogen has nearly finished in the core) then there is no force to counter gravity in the core: . So the core contracts. This causes a lot of heat and starts off bigger nuclear reactions and the star begins finishing up its hydrogen rapidly and starts expanding at a very fast speed. It then becomes a red super giant. Betelguese is a star going through this expansion. Such a star has a very small dense core surrounded by a gassy exterior. Some very violent reactions are going on in the core: the core is fusing not only hydrogen into helium but also bigger elements together(nitrogen , Silicon… all the way to iron!). One day the core will blow up in a huge explosion leaving the exterior of the star in space as a huge huge cloud. This cloud would later form new stars. The death shall be a new beginning. All that would be left of such a huge giant is a small neutron star : about the size of a town.This is the remnant of the dense core. A single spoonful of this neutron stars would weigh a million kgs.

  Betelgeuse was the first star to be pictured as a disc ie the first star whose “surface” was photographed. Is this the largest star? Maybe not… Some Astronomers believe that Mira in the constellation Cetus is probably larger. The Story of Mira we shall take up in some later VERITAS.

“Up above the sky so high… like a diamond in the sky”

 

kanwar

 

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  Go, wondrous creature! mount where Science guides:                 

  Go, measure earth, weigh air, and state the tides:                 

  Instruct the planets in what orbs to run,                          

  Correct old time and regulate the Sun;                              

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EPR Paradox

 

      Quantum Mechanics are the laws of Physics that were discovered through the study of atoms and subatomic particles. Nobody understands Quantum Mechanics(QM)! There are Physicists who do not care about understanding QM. They just use it to understand other subjects like Quantum Optics, condensed matter Physics. Some other Physicists are trying to understand QM. No matter what they try QM still surprises them.

      When I talk about the  crazy aspects of QM you will most probably say “Ha! How can this be! I do not believe it”. This is because QM does not agree with your common sense. But how was your common sense formed? Your common sense is based on your experience with the world around you. Your common sense is based on the properties of objects from .01 metres to 100 metres. You see a cricket ball bouncing and you “feel” that an electron should bounce too. You see a cricket ball spinning and you think that when we talk about electron spin it means the same thing! Is the electron doing off spin or leg spin 🙂 ?!

How can you apply the common sense acquired from your narrow vision of the world from 10^(-2) metres to 10^(2) metres to everying from 10^(-15) metres to 10^(15) metres? But QM still haunts us. It shatters our cosy world. Many Physicists are still struggling to overthrow it and form a more intutive theory.

      One such scientist was Albert Einstein. He devised a lot of thought experiments to disprove QM. A thought experiment is a theoretical Physicist’s tool. The experiment may not be performed. But the situation is analysed logically and mathematically. In 1935 Einstein, Podolsky and Rosen published a paper that many thought would destroy QM( Physical Review 47,777(1935)). Before we go into the description of the EPR paradox I would like to remind the VERITAS readers that according to QM you cannot measure the spin of a particle along two perpendicular directions. So if you measure the spin along x axis you cannot measure it in the y axis. Uncertainly principle.

      So this is what EPR suggested: Take a particle with 0 spin. Let it disintegrate into two particles A and B. Now law of conservation of spin says that A and B will have opposite spins along each direction. Now the crazy thing that QM says is that A and B do not have definite spin util they are measured. So if A and B go light years apart and you measure the spin of A along the x axis and you find that it is +1 then immediately the spin of B becomes -1. If you had measured A’s spin and found that it is -1 then the spin of B would have become +1 immediately( even if they are now on opposite sides of the universe).

      EPR suggested this situation and raised the following points:

1) QM seems to be non local. How can particle B know what A’s spin is. How can information go from A to B faster than light?

2) EPR in this paper tried to define reality! They said that if a particle has a property independent of observation then that property is said to be real. SInce the spin of  particle B is dependent on the measurments on A then this property is not real.

3) If instead of measuring the spin along x axis you had decided to measure it along y axis then particle B’s y spin would have attained a value opposite to A’s measured spin. So the observer(measurer) decides which component of B’s spin has to be made real.  

( Note that I am just giving you a simplified version of the experiment. There is much more in it)

   Please note that particles A and B do not have fixed spins when they are created. The spins are set only when one of them is measured.

   To most Physicists it seemed that EPR had found a hole in QM and proved that the theory is not sound. Bohr( one of the greatest defenders of QM) analysed the experiment for weeks and then found inconsistencies in the EPR arguments. But we do not have time to go into these today. Maybe in some later VERITAS.

      The world is stranger than you think. So why watch thrillers or mystery movies. Why not do Physics instead and take part in the ultimate adventure???

kanwar

 

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  Go, wondrous creature! mount where Science guides:                 

  Go, measure earth, weigh air, and state the tides:                 

  Instruct the planets in what orbs to run,                          

  Correct old time and regulate the Sun;                              

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