International Youth Day

On 17 December 1999, in its resolution 54/120, the United Nations General Assembly endorsed the recommendation made by the World Conference of Ministers Responsible for Youth (Lisbon, 8-12 August 1998) that 12 August be declared International Youth Day.

This year’s International Youth Day is a particularly important day for youth around the world. In December 2009, the United Nations General Assembly adopted resolution A/RES/64/134 proclaiming the Year commencing this International Youth Day (12 August 2010) as the International Year of Youth.

In line with the theme for the International Year, the theme for this year’s International Youth Day is “Dialogue and Mutual Understanding”. The choice of theme reflects the General Assembly’s appreciation of the value of dialogue among youth from different cultures as well as among different generations.

Quark epoch - Big Bang

In physical cosmology the quark epoch was the period in the evolution of the early universe when the fundamental interactions of gravitation, electromagnetism, the strong interaction and the weak interaction had taken their present forms, but the temperature of the universe was still too high to allow quarks to bind together to form hadrons. The quark epoch began approximately 10⁻¹² seconds after the Big Bang, when the preceding electroweak epoch ended as the electroweak interaction separated into the weak interaction and electromagnetism. During the quark epoch the universe was filled with a dense, hot quark-gluon plasma, containing quarks, leptons and their antiparticles. Collisions between particles were too energetic to allow quarks to combine into mesons or baryons. The quark epoch ended when the universe was about 10⁻⁶ seconds old, when the average energy of particle interactions had fallen below the binding energy of hadrons. The following period, when quarks became confined within hadrons, is known as the hadron epoch.