Or are mindbogglingly slow.
If we can reach 90% of lightspeed we would have a good Lorentz number to travel the whole milkeyway in a few weeks. We would see a very different earth though when we come back.
To travel 87,400 light years at near light speed, in a subjective time of a month requires a dilation of 87400 years * 12 months / year = 1048800, with a speed of:
(1-(1/1048800)²) c = 0.9999999999990908 c
which is about 0.27 mm/s slower than the speed of light.
