So you are in a spaceship…. In interstellar space…
Obviously you have no nearby points of reference…. Say maybe stars light-years away….
Is your spaceship moving? Yes? No?
How do you authoritatively know without nearby external points of reference that allow you to track your motion?
In this context, what does moving mean? Perhaps relative to something? Then you are always moving because there are a lot of somethings to compare against.
Measure the doppler-shift of the light from our sun. If there’s a measurable red-shift then relative to it, you’re moving away.
Assuming you’re travelling in the direction of another system (a fair assumption, i would think) – a blue shift in the the spectrum would indicate you’re moving towards it (relative, of course, to its current vector).
Hope this helps
🙂
jettison something out the airlock and see which way it goes. 😛
Thats answered by Einstein and Special Relativity.
If you are moving with constant velocity, you don’t know when you are moving, there is no absolute reference frame you can check against.(http://en.wikipedia.org/wiki/Special_relativity)
If you accelerate/decelerate, you feel the forces.
Regarding dopplershift
Measuring the dopplershift tells you not that you are moving, it can equally be that the sun is moving away and you remain at your place.
>mdm-adph Says:
>March 27th, 2007 at 8:21 am
>jettison something out the airlock and see which way it >goes.
Sorry, no go. Anything jettisoned from the airlock is travelling at the same speed you are. Unless you’re currently accelerating or decelerating it’ll just hover calmly at your side due to the lack of friction to slow it down.
(Although the presence of the smilie may suggest you already knew this)
Oh come now, we have all seen star trek, we know there are a hundreds of tiny little glowing particles per sq kilometer in space, you’d know you were moving by these zipping past. 🙂
In all seriousness though, it is the same issue that early astronomers faced, they thought the earth was stationary as the stars move in a uniform arc, the only clue was the wanderers (aka planets) with there damned retrograde motion.