Based on today's knowledge and technology.
However, I suspect that five hundred years from now we will have solved that problem.
Imagine 500,000 years from now… We’ll being flying around the galaxy and colonizing every planet… But wait… they would have already done that millions of years ago… Right?
I always ask for the best evidence. Show me the most convincing artifact you have. If that doesn’t convince me why would I have to hear a string of less-convincing arguments?