Can we colonise other planets? justify technically?

Not yet, were are limited to how far we can travel in space, because there is a lot of radiation out there. Check out the van allen radiation belts. After reading about it, you will learn how the u.s. never got to the moon, it is impossible at this point, we do not have the technology. Yet alone, go to another planet. The only thing we can get away from our planet is unmanned space craft. Anything alive will die instantly after ping through the radiation belts. Our ozone and magnetic field is really helping us out, without it, no life would survive on this planet.