Ask Astro: How briskly might a ship attain light-speed with out crushing its human occupants?

Due to the results of relativity, a light-speed traveler experiences much less time passing than an observer on Earth.

If a traveler might attain 99 % the pace of sunshine by accelerating at 32.2 ft/s2 (9.8 m/s2), they might expertise the journey from Earth to the middle of the Milky Approach in about 20 years. Credit score: Astronomy:
Roen Kelly

If a crewed spacecraft could possibly be constructed to journey at or close to the pace of sunshine, how lengthy would it not take to realize that pace with out crushing the human occupants? 

Lawrence Schwab
Phoenix, Arizona

Regardless of what science fiction might counsel, humanity won’t ever be capable to journey on the pace of sunshine. That mentioned, we might theoretically get shut. To trigger the fewest issues for our human occupants, it might greatest to take care of the acceleration our physique is accustomed to: Earth’s gravitational pull. On the floor of our planet, that’s 32.2 toes/second² (9.8 meters/second²). Accelerating at that fee, from the angle of the traveler it might take 2.65 years to achieve 99 % the pace of sunshine.

To raised recognize the end result, think about that such a traveler desires to achieve the middle of the Milky Approach. That’s practically 30,000 light-years distant. For half that distance, they’ll need to speed up at 32.2 ft/s² (9.8 m/s²) after which decelerate by that very same quantity for the remaining half of the journey. At that acceleration, it might take the traveler round 20 years to get there — 40 years for a spherical journey.

However some bizarre issues occur to time when shifting near the pace of sunshine. 

Whereas only some a long time have handed for the traveler, considerably extra time can have handed on Earth. Let’s assume the unattainable: The traveler manages to journey on the pace of sunshine all the approach. On this case, practically 30,000 years can have handed on Earth by the point they attain the middle of the galaxy. For the round-trip journey, 60,000 years can have passed by on the finish from Earth’s perspective.

Evidently, the traveler’s associates on the time of departure would now not be round after they return. This distinction in noticed time, or time dilation, is a consequence of Einstein’s particular relativity and illustrates his well-known twin paradox.

Stuart L. Shapiro
Professor of Physics and Astronomy, College of Illinois, Urbana-Champaign, Illinois