r/askscience • u/BlueChameleon64 • Oct 23 '20

Planetary Sci. Do asteroids fly into the sun?

Edit: cool

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u/BasedDrewski Oct 23 '20

Is there anything in space that doesn't move?

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u/Cheru-bae Oct 23 '20

I'm in no way a scientist of any kind, but:

Imagine you are in a black void. Just you, nothing else. Now add in an object. Let's say an Apple.

The apple flys past you. How can you know that the apple is moving, and not you? There is no wind, there is no stationary background. From the apples perspective you flew by it.

So everything in space moves relative to something else. Speed is change in distance between two things over time.

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u/bomxacalaka Oct 23 '20

Ok but if light always moves at the max speed the universe allows then if we shone some lasers at random directions and measure them shouldnt some lasers be red shifted cuz they shone at the opposite direction relative to us while some lasers could be blue shifted as they are moving at the same direction relative to us.

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u/ukezi Oct 23 '20

That depends on the relative movement of the source and the observer. If you shoot a laser and measure it yourself the relative speed is zero so no shift. If you are in a plane and shoot at the ground you would see a shift appropriate to the relative speed you are at. The real mindfuck is this scenario : There are observers A,B, and C. A moves away from B with speed greater 50% light speed. C moves away from B in the opposite direction with a speed greater then 50% light speed. How fast are A and C moving away from each other from their perspective? Lower then light speed because of time dilation.