A sane and intelligent man does not wish to enter any of the material planets because the four conditions of material miseries exist on all of them. From Bhagavad-gītā we can understand that even if we enter Brahmaloka, the highest planetary system of this universe, the four principles of misery will be present. We learn from Bhagavad-gītā that the duration of one day on Brahmaloka is millions of years of our calculation. That is a fact.
Even the highest planetary system, Brahmaloka, may be reached, but scientists say that it will take forty thousand years at sputnik speed. Who is prepared to travel in space for forty thousand years? From the Vedic literature we can understand that we can enter any of the planets, provided we prepare for that purpose. If one prepares himself to enter into the higher planetary systems, which are said to be inhabited by demigods, he can go there. Similarly, one can go to a lower planetary system, or if one desires he can remain on this planet. Finally, if one desires, he can enter the planet of the Supreme Personality of Godhead. It is all a matter of preparation. However, all planetary systems within our material universe are temporary. The duration of life on certain material planets may be very long, but all living entities in the material universe are eventually subject to annihilation and have to again develop other bodies. There are different types of bodies. A human body exists one hundred years, whereas an insect body may exist for twelve hours. Thus the duration of these different bodies is relative. If one enters the planet called Vaikuṇṭhaloka, the spiritual planet. however, he then achieves eternal life, full of bliss and knowledge. A human being can attain that perfection if he tries. That is stated in Bhagavad-gītā when the Lord says, "Anyone who knows in truth about the Supreme Personality of Godhead can attain to My nature."