# Question-Thought Experiment about point of reference when moving near speed of light

1. Jun 15, 2012

### SpeedSpaceman

I have a question (thought experiment) that pertains to the speed of light and point of reference. I'm just interested in thinking about this subject and I can't quite get my head around this. I'm sure the answer is probably simple. Thank you for your help. By the way, if the answer involves math at all it will be lost on me.

An Astronaut and a Scientist agree to conduct an experiment. The Astronaut will be launched into an agreed upon orbit (Orbit X) around the Earth in a spaceship traveling near the speed of light. The duration of his flight, from his point of reference will only last sixty seconds. However, from the point of reference of the Scientist on Earth, the Astronaut will not decelerate and return to Earth for 500 years.

Now, the Astronaut and the Scientist agree that a "day" after the Astronaut leaves on his trip (a "day" after in the point of reference for the Scientist) the Scientist will begin to launch massive amounts of space trash into Orbit X, and that his predecessors will do the same for 500 years. They will try to “hit” the spaceship.

So, the Astronaut has the course laid out, accelerates for sixty seconds and then decelerates, returns to Earth and it is 500 years later. Or does he? Does he manage to make his 60 second/500 year voyage safely? Or did the space trash the Scientist threw into orbit hit him? If it did hit him, did he crash and eject to Earth in 20 seconds, 33 seconds and then land on Earth 200 years or 300 years later?

I guess the point I am trying to wrap my head around is that I always hear about points of reference in relation to the speed of light and time travel. However, “where” does the point of reference begin and end? Does the material making up the spaceship only endure 60 seconds of physical strain since it is accelerated at tremendous speeds? Okay, if so, the space debris, space trash and asteroids, etc that are crisscrossing our Astronauts path are not moving this quickly, and there are 500 years worth moving around that orbit, the same orbit in space as the Astronaut, but why does it not hit him? Is the problem that I should be thinking of two discreet “spaces” as well as two “times”?

Note: All numbers and times are just arbitrary. I don't know exactly what speed or what time this would all work out to. I understand that we can't build a ship like this. I often hear this same type of scenario in physics shows meant for a general audience, but they don't really explain what happens "during" the time periods for each person, and how space interacts and functions.

2. Jun 15, 2012

### BruceW

Re: Question-Thought Experiment about point of reference when moving near speed of li

hi, speedspaceman. Welcome to physicsforums :)
If they launched the space trash in the right speed and direction so it collides with the spaceship, then it will hit the spaceship. In the reference frame of the earth, the space trash is fired after one day. And in the spaceship's reference, the trash is fired after some different time interval. There is no problem with this because the two reference frames will measure time intervals and spatial lengths differently.

3. Jun 15, 2012

### ghwellsjr

Re: Question-Thought Experiment about point of reference when moving near speed of li

Speedspaceman, the simple answer to your question is that if the Astronaut hits a piece of debris after say 30 seconds of his time, then it will be after 250 years of earth time. Is that all you are concerned with?