- #1
Gerinski
- 323
- 15
Let's take a star 500 light years away from Earth, let's call it Star X. To make round numbers let's say we are in Earth year 2000.
We set a manned space mission to Star X, the spaceship will travel at 0.5 light-years per year (0.5 c) so it will reach there in 1000 years. Let's not worry about the longevity of the travellers, let's assume they are superhumans who live more than 1000 years.
Upon departure in year 2000, the travellers obviously see Star X how it was 500 years earlier, in Earth year 1500. When they will arrive there 1000 years later, in year 3000, they will see how Star X looks like in year 3000.
So if they look forward towards Star X during the trip, in 1000 years of travel they will see the evolution of Star X in 1500 years. The travel time plus "catching up the delay" in light travel time from Star X to Earth. In other words they will perceive time running faster than normal, precisely 1.5 times faster than normal (while looking towards Star X, they will see 1500 years of the star's history condensed in 1000 years of their time).
Oppositely, if they look back towards Earth during the trip, on departure they see how Earth looks like in year 2000. When they arrive at Star X in year 3000, the Earth is 500 light years away so its light takes 500 years to reach them. They will see how Earth looked like in year 2500.
So they will perceive time running slower than normal, in the 1000 years of travel time they will see the evolution of Earth during 500 years. Time will appear to run at half its normal rate while looking back towards Earth.
This perception of time running faster or slower than normal, due to one's velocity towards / away from the light source, what is this effect called? Is it just time dilation? Is it relativistic Doppler effect? Does it have another name?
Thanks,
We set a manned space mission to Star X, the spaceship will travel at 0.5 light-years per year (0.5 c) so it will reach there in 1000 years. Let's not worry about the longevity of the travellers, let's assume they are superhumans who live more than 1000 years.
Upon departure in year 2000, the travellers obviously see Star X how it was 500 years earlier, in Earth year 1500. When they will arrive there 1000 years later, in year 3000, they will see how Star X looks like in year 3000.
So if they look forward towards Star X during the trip, in 1000 years of travel they will see the evolution of Star X in 1500 years. The travel time plus "catching up the delay" in light travel time from Star X to Earth. In other words they will perceive time running faster than normal, precisely 1.5 times faster than normal (while looking towards Star X, they will see 1500 years of the star's history condensed in 1000 years of their time).
Oppositely, if they look back towards Earth during the trip, on departure they see how Earth looks like in year 2000. When they arrive at Star X in year 3000, the Earth is 500 light years away so its light takes 500 years to reach them. They will see how Earth looked like in year 2500.
So they will perceive time running slower than normal, in the 1000 years of travel time they will see the evolution of Earth during 500 years. Time will appear to run at half its normal rate while looking back towards Earth.
This perception of time running faster or slower than normal, due to one's velocity towards / away from the light source, what is this effect called? Is it just time dilation? Is it relativistic Doppler effect? Does it have another name?
Thanks,