Answer: Our future does not exist, just like alien invasions do not exist either.
Explanation: We build our own future, in the present with plans, which will become true if we work hard. Alien invasions can only exist in our mind, just like future only exists in our minds at the present. Do not let your mind be "invaded" by "aliens", invade your mind yourself with amazing plans.
Happiness. If you live longer but have a worse life it’s not worth it. If you live shorter but have a better life it’s the better option
Completely unrelated, but that is a great sentence, I want that painted as a quote on my wall.
Also, the punctiation seems right to me. But you might be able to use a ";" instead of a comma, im gonna check that real quick.