Question

how many light years it will take to cross our whole galaxy

Answer 1

Simple Answer : Zero time

Lets know few basics first:-
Diameter of Milkyway is 100000 Light Years.

Our Sun is 30000 Light years away from Milkyway center.

So Spacecraft traveling at Light Speed from Earth can travel across the Milkyway Galaxy only after 70000 Years of time for the person observing from Earth. But time taken to spaceship and people in it is ZERO time.

According to Einstein(Time Dilation), Time stops for any object traveling at Light speed. Yes, for us too our age stops when traveling at Light Speed.

MARK BRAINLIEST..

Answer 2

100000 (one lakh) light years