I've searched this site, I found a similar question here but not exactly like mine.
So I can't understand the Twin Paradox when I use the "day" (bright time) and "night" (dark time) on earth as the age reference.
In the Twin Paradox it is said :
the traveling twin is younger upon return than the Earth-bound twin.
Suppose the twin are 40 years old and can communicate instantly during the journey and the travelling twin calculate his age from his brother on earth standard. Say, when the travelling twin reach a star, the remain-on-earth twin told him that 7300 days and 7300 nights have passed on earth. (So the age of both of the twin are the same, 60 years old if in our common standard).
When the travelling twin return and almost landed on earth, the remain-on-earth twin told him that (for example), 14600 days and 14600 nights have passed on earth. So they still have the same age, which is 80 years old if in our common standard.
So my question is:
What does it mean of "the travelling twin is younger" at the time they meet each other again - while each of them think the same that his age is 29200 days and 29200 nights ? (80 years old if in our common standard).
Is the answer like below ?
Yes, their age is the same, but their appearance is different---> the travelling twin LOOK much much younger than his remain-on-earth brother.