WHAT’S OUR REACH?

If you started to travel, via a spaceship moving at 25,000 miles per hour, to Pluto when you were 25-years old, it would take you about 22 years to reach Pluto, and another 22 years to return. You would be 69 years old when you got back: a near-lifetime of travel, mostly surrounded by darkness. Most likely, this is not what you expected.

Only light, or other waves that have no intrinsic mass, can move at the speed of light. As an object (like a spaceship) approaches the speed of light, its mass rises ever more quickly, so that it takes more and more energy to speed it up further. It can never reach the speed of light, because by then, its mass would have become infinite, and by the equivalence of mass and energy (E = mc squared), it would have taken an infinite amount of energy to get there.

Thus, the science-fiction-generated fantasy (so prevalent in movies!) of humans traveling at the speed of light, from galaxy to galaxy, is not to happen!

THE VASTNESS OF SPACE

The universe consists of a million trillion trillion cubic light years and growing each second. [One cubic light year is enough to encompass our solar system]. 

Suppose you could select anyone of the cubic light years in space to explore, how would it look? 99 times out of a 100, you would find a pristine vacuum embedded in total blackness. Absolutely nothing would be visible to the unaided eye. The universe is almost entirely empty space. Galaxies, stars, and planets are scattered here and there in a lumpy way, not in a uniform way. 

Source: A manual written by me [circa 2010], for my college-level, introductory course for “Earth and Space Science for Liberal Studies Majors.” I taught this course for many years.