Topic: Future interstellar travel and plantary colonization won't work
Well for a long, long time. Why? Here's why:
The vast distances between stars, moons, and planets making long journeys, even past our solar system, incredibly time consuming (Even our fastest probe, Helios 2, would take thousands of years just to reach the nearest star system alone and ships that can reach even just 1/10th the speed of light are decades, if not centuries away, but it doesn't matter anyway because when you factor in relativity at those speeds it means that all of your family and friends and the whole system itself will be long dead or really, really old by the time you return home).
The lethal radiation given off by stars
The below freezing temperatures
Space debris, micrometeorites and other hazardous material, especially when you want to fast, which we'll need to do to get to anywhere beyond the sun.
The negative effects of little gravity on the human body
The psychological effects of traveling through space for such a long period of time
The lack of aid or supplies if something happens while millions of miles away from Earth
The slow response of communication from Earth the further we get from the planet. Alpha Centauri, the closest star system to our solar system for example, is almost four and half light years away from Earth, meaning it'll take roughly four and half years to get a signal to future astronauts and four and half years to get a return signal. So it'll take roughly nine years to get just two messages across. If something happens to the astronauts or they discover something they're practically on their own.
And if in an emergency where we need to leave the planet now (such as a in the events of a gamma ray burst, severe global warming, the death of the sun, or a extinction level asteroid) we have to find a planet suitable for human colonization, something like Mars, but even that runs into problems such as:
Finding a planet about the same size and gravity as Earth. Mars is about have the size of Earth with only 38% of our gravity. Some gravity is useful, but for long term use it doesn't seem good. Venus is about the same size as earth, but it's problem is that too hot, acidic, and it's atmospheric pressure would crush you in seconds.
Finding a planet with an atmosphere similar to ours. Mars is no good seeing it only has an tiny atmosphere composed mostly of carbon dioxide. Venus is the same.
The time will be different on the new planet. Life depends on the 24 hour cycle of Earth. We may be able to adapt to a slightly changed time scale, but most other animals won't.
Finding a planet with a moon. Most organism on Earth depend on the moon for hunting, travel and other means.
How do you manage politics on a interplanetary scale? If one planet or planets needs help how do send aid, troops and supplies there in time?
Finding a planet with the continents positioned in a way that allow certain weather patterns for irrigation and other function for our survival to work. On a slightly similar note having a planet with a similar axial tilt that allows the season to happen.
Finding a planet with similar geological composition as ours. We could try to irrigate Mars but its soil are toxic to plants, plus the radiation would probably kill them even if they had a chance to survive that long.
If all of those problems are absent and we do find a planet similar to ours (in the case of the "Earth Similarity Index," as close to a 1 as possible) hopefully we don't infect the possible life on the planet with our viruses and bacteria and vice versa.
Those are just my thoughts. Feel free to chip in.