New Delhi: Till the end of the 20th century, scientists expected the universe to accelerate rapidly immediately after the Big Bang, and then slow down the expansion with the passage of time. Two independent teams of scientists came to the same dramatic conclusion in 1998, that the rate at which the universe is expanding was accelerating, instead of slowing down. Now to measure the rate at which the universe is expanding, it is necessary to measure distances in space, which is comparable to attempting to guess the distance to a city on the ground from an aircraft flying overhead at night.

To estimate these distances, scientists use what is known as the cosmic distance ladder, that are objects of known luminosities, known as standard candles. Based on the brightness of these objects, the cosmic distances, and the rate of expansion can be determined. Young stars with predictable variations in luminosities, as well as Type Ia supernovae are used to build this cosmic distance ladder. An emerging problem in astrophysics is that the rate of expansion determined from observations of the cosmic microwave background (CMB), caused by fluctuations of some unknown field........

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