'Yugas' means period.

The dark period is called 'Kali Yug' in which we are living today witnessing all the negativities around, its more of Rajsik qualities (totally conditioned, disturbed and more of selfish thoughts and behavior) and Tamasik qualities (harmful thoughts, which lives in illusion and does not have harmony with nature) in your thoughts and action.

Meditation takes you above kaliyug to 'Dwapara Yuga' where you see basic changes, progressive activities and physical change, that is industrial revolution.

Deeper you go you will touch a 'Treta Yuga' where you see mental change and connect to the higher intelligent consciousness. It is more of creative happening in physical world.

This higher intelligence will lead you to the period of happiness and joy, which is called 'Sat Yuga'. In this yuga we will witness everything in equanimous state, the state of 'Samadhi', which has bliss all around. Positivity envelopes you all around thus no negativity can touch you. It is full of divine light, truth and responsibility for everything and everyone. There is only growth and prosperity.

All these yugas exists in this universe itself. This universe is within you. It is up to you how and whom you want to connect, no person is bad or evil on this level of silence (Meditative quietness of mind). Evil is made by the way you think only. So you have all the power to bring 'Sat Yuga' again by simply connecting to your basic meditative nature. That is reconnecting to self and fall in love again within. Purity of this love will connect you to the 'Sat Yuga', which will reflect back in the outside universe as unconditional love and compassion. 'Sat Yuga' is including everything and everyone as you.