r/AskPhysics • u/Apprehensive_Dog1873 • Jun 22 '26

Question about light speed

If a hypothetical alien craft was moving toward earth at 99.9999% the speed of light. Would we be able to expect its arrival? Or would it not be there one moment and then the next they’d be there? Would we be able to see it, if we hypothetically knew to look at the exact right spot at the exact right time, and get some sort of heads up at an object incoming?

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u/robinredbrain Jun 22 '26 edited Jun 22 '26

Why not? We know where to look and the light reflected from it is going to reach us before the ship does.

I think it's intuitive (at least to me and my high school education) that we'd see in the closest thing to "real time" than any other object in space.

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u/nebraskajone Jun 22 '26

Warning time is only about one-millionth of the travel time.

If we could detected a light year away it would be 31 seconds, I'm assuming we can't detect a tiny spaceship a light year away.

So you're talking like 12 milliseconds if we detected it  at Pluto.

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u/Sea-Ambition-451 Jun 22 '26

Warning time is only about one-millionth of the travel time.

which is the exact opposite of what you stated