In the hypothetical case that we were able to build the prototypes of spacecraft devised by NASA, capable of moving at relativistic speeds, and gather the indecent amount of energy needed to propel them, the journey would not be as pleasant as it seemed to be aboard the Millennium Falcon. And is that the main impediment to an interstellar journey is not the technological part, which we could dominate in a matter of centuries, but the dangerous space environment, as astronauts well know, which once again highlights the fragility of the human body.
If we moved at the speed of light (300,000 kilometers per second) through outer space, we would die in a matter of seconds. While particle density is very low in vacuum, at high speed, the few hydrogen atoms per cubic centimetre would hit the bow of the vehicle with an acceleration similar to that achieved in the Large Hadron Collider (LHC) thus acquiring an energy of 10,000 sieverts per second. Considering that the lethal dose to a human being is about 6 sieverts, this beam of radiation would damage the ship and destroy any trace of life inside it.
According to measurements by scientists at Johns Hopkins University, no frontal shielding would be able to rid us of ionizing radiation. A 10-centimetre thick aluminium partition would absorb less than 1 percent of the energy, and its size could not be increased unlimitedly without compromising the energy needs of the propulsion system. In addition to atomic hydrogen, the ship would have to resist the erosion of interstellar dust, which would increase the chances of seeing its pulverized structure considerably. As a solution, we would be content to reach speeds of only 10 percent the speed of light, which would hardly allow us to travel to the nearest star, Proxima Centauri, within the span of a human life, as the 4.22 light-years away would turn into 40 years of travel.
Cosmic radiation is therefore an insurmountable obstacle to journeys at the speed of light, which, if overcome in the distant future, would allow us to witness the most incredible spectacle of our life. At that speed, time would dilate and we would age more slowly (ISS astronauts age 0.007 seconds less every 6 months than people on Earth) and our field of view would curve as if it were a tunnel, And we would advance into a flash of white light, without a trace of stars, while leaving behind the most absolute darkness.