The stars pass by slower than light speed, but they’re closer together (in the direction of travel). While everyone else in the galaxy explains the remarkably short travel time in terms of the people on the ship moving slower through time, the people on the ship attribute it to the distance being shorter. ![]() But relativity is a slick science length contraction and time dilation are two sides of the same coin. The speed of light is still a fundamental limit, so if you were on the ship you’ll still never see stars whipping by faster than the speed of light (which you might expect would be necessary to cross 100,000 light years in only 25 years). By the way, this trip (across the Milky Way, accelerate halfway, decelerate halfway, anti-matter fuel, photon drives) would require a fuel-to-ship ratio of about 10,500,000,000 : 1. ![]() According to every one else in the galaxy, you’d have been cruising at nearly light speed for the full 100,000 years. That said, if somehow you could accelerate at a comfortable 1g forever, you could cross our galaxy (accelerating halfway, then decelerating halfway) in a mere 20-25 years of on-board time. Even with antimatter fuel (the best possible source by weight) and a photon drive (exhaust velocity doesn’t get better than light speed), your ship would need to be 13 parts fuel to one part everything else, in order to get to 99% of light speed. The math isn’t difficult, but it is disheartening. In order to move faster, a rocket needs to carry more fuel, so it’s heavier, so it needs more fuel, etc. Rockets: in a hurry for a little while and then not for a long while. The big exception is ion drives, but a fart produces more thrust than an ion drive (seriously) so… meh. And those 8 minutes are why the shuttle weighs more than 20 times as much on the launch pad than when it lands. For example, the shuttle (before the program was shut down) could spend weeks coasting along in orbit, but the main rockets only fire for the first 8 minutes or so. Spacecraft in general coast ballistically except for the very beginning and very end of their trip (excluding small corrections). While this is definitely possible for a few seconds or minutes (“ retro rockets“), you’ll never see people building bridges on rockets, or hanging out and having a picnic for an afternoon or three on a hovering rocket. ![]() A rocket capable of 1g of acceleration for years is a rocket that can hover just above the ground for years. However! Leaving a rocket on until it’s moving near the speed of light is totally infeasible. However, the on-board clocks run slower (from the perspective of anyone “sitting still” in the galaxy) so the ship and everything on it may experience far less than 100,000 years.įirst, when you read about traveling to far-off stars you’ll often hear about “constant acceleration drives”, which are rockets capable of accelerating at a comfortable 1g for years at a time (“1g” means that people on the rocket would feel an acceleration equivalent to the force of Earth’s gravity). The far side of the galaxy is about 100,000 lightyears away, so it will always take at least 100,000 years to get there. On the one hand, it is true (for all intents and purposes) that if you travel fast enough, time will slow down and you’ll get to your destination is surprisingly little time. This is a good news / really bad news situation. Physicist: Yup! But sadly, this will never happen.
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