People are currently concerned with global disasters and pollution and other problems.
We can learn to overcome all of these problems which are caused by old and inferior technology and processes.
Air and water pollution are mostly from 18th century coal and oil for energy and dirty industrial processes.
We can convert to closed cycle nuclear fission and solar power. Closed cycle nuclear fission is where we use up all of the uranium and plutonium with onsite or offsite reprocessing or with new nuclear reactor designs.
Nuclear fusion has been difficult to solve but there are solutions with exawatt laser pulses.
Molecular nanotechnology, nuclear fusion, high volume production and usage of antimatter are all achievable.
By 2070, all of this technology should be mature and widespread.
Those technologies would not only be infinitely sustainable but would also enable easy production of spaceships with speeds of over 70% of lightspeed.
Exponential colonization of the galaxy would then occur at nearly that speed. Galactic colonization could occur within 150,000 years.