Why do Hindus mourns for 13 days?

Question

The normal practice of hinduism is that the family of dead ones mourn for 13 days when someone dies. Is there any reason behind it? How did our ancestors decided 13 days time period to mourn? Why not for 3 days or 7 days? Why mourning for 13 days is a standard practice? Is there anything mentioned like this in vedas?

Answer 1

Funeral ceremonies and oblations have been mentioned in the dharmashastras which are derived from Vedas. Specifically For the day count reference specifically Vishnu Smriti Ch 19 and Ch 22.

First comes day 4.

10. On the fourth day they must collect the bones that have been left.

11. And they must throw them into water from the Ganges.

There is a period of impurity (chp 19)

13. While the term of impurity lasts, they must continually offer a libation of water and a ball of rice to the deceased.

14. And they must eat food which has been bought, or which they have received unsolicited.

15. And they, must eat no meat.

16. And they must sleep on the ground.

17. And they must sleep apart.

18. When the impurity is over, they must walk forth from the village, have their beards shaved, and having cleansed themselves with a paste of sesamum, or with a paste of mustard-seed, they must change their dress and re-enter the house.

19. There, after reciting a propitiatory prayer, they must honour the Brâhmanas.

From chp 22

6. During the period of impurity oblations (to the Visvedevâs), gifts and receiving of alms, and study have to be interrupted.

Now the term of impurity varies as per the varna of the deceased

1. The impurity of a Brâhmana caused by the birth or death of Sapindas lasts ten days.

2. In the case of a Kshatriya (it lasts) twelve days.

3. In the case of a Vaisya (it lasts) fifteen days.

4. In the case of a Sûdra (it lasts) a month.

Nowadays 12 days mourning followed by ceremonies on the 13th day (as mentioned in Chp 18) seems to be the norm irrespective of varna.

Answer 2

There are majorly five life forces driven by breath that keep us moving and alive. They are

1) Prana

2) Apana

3) Vyana

4) Udana

5) Samana

Each of the above leaves the body at certain time in the duration of two weeks. Firstly the Udana and Prana leaves the body. Udana is responsible for the buoyancy. So that is the reason that dead body feels much heavy. Prana is responsible for driving all the organs. Vyana keeps the parts fresh by producing new live cells. Vyana leaves the body within 2 weeks. So the rituals go on upto two weeks. Source: Sadhguru