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New way of getting sense of time flow

Date: 11 February 2020 Tags: Miscellaneous


A Professor from the Physics Department of IIT Kanpur has come up with a different way of defining the arrow of time.



Time, as we experience it, flows only in one direction – forward. We cannot easily reverse the ‘arrow of time’ as it is called.



  • The laws of elementary particle physics remain the same when time is reversed. That is, take the questions which govern gravitational, electromagnetic and strong-nuclear forces and replace “t” by “–t” and the equations are invariant.

  • We do not see it in practice, hence there must be something defining the arrow of time. This is the second law of thermodynamics, which says that a quantity known as the entropy of the system will either remain a constant or increase with time. 

  • The entropy is directly related to the disorder in a system. So, the direction of increasing entropy determines the arrow of time. This is a popular way of defining the arrow of time.

  • Such alternative definitions of arrow of time are needed, for example, in cosmology to explain cosmological models like the oscillating universe.

  • The second law of thermodynamics encounters difficulties in explaining cosmological arrow of time for oscillating universe. However, energy transfers can predict the arrow of time for the collapsing universe.

  • In a gravitating system, such as the collapsing universe, cluster or star formation is somewhat similar to the formation of cyclones or hurricanes. For such systems, the clustering or structure formation is in the forward direction of time.

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