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id say if you were conciously aware of the object, it could go as fast as an object could go and you'd still be able to see it the only problem is perhaps you are physically unable to keep up with the object's speed (eg it zooms past you, you cant turn your head fast enough) but the human eye itself, i would think could detect it, for example, if it were to spin in a small circle but at very very high speeds, it would be visible


also, even if something is traveling very fast, if it is at a distance, it is no longer traveling as fast in your perception


also, if the object is a massive massive object, it'd be pretty hard to miss it no matter how fast it was (eg a train, you stare directly ahead, but you keep seeing the train zooming past, and if its infinitely long, no matter how fast it travels, you'll keep seeing it

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Thanks for reply biggs, I really appreciate it. I was thinking up a scenario. If you were standing about 25ft from an object (let say a car at rest), and if it could reach top speed of 10,000 mph almost instantly. Is it possible for your eye to perceive such a motion?


My understanding is, as long as the object is under light speed, it should be seen by a human eye considering that photons are faster and should be able to bounce off of the car and repel back into the observer's eye to be registered as an image.

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  • 1 month later...

the question isn't really whether the human eye can keep up with it; that's just a question about the mechanics of the eye. The upper speed your eye can track is (to a decent approximation) a function of the mass, size, and shape of your eye, the amount of force your eye muscles can exert, where they're attached, how far away the object is, the relative path it's going on (to know the tangential compent of its velocity), the mass, size, and shape of your head, how much force they can exert... you get the picture. In the end, the number's pretty freaking high because your eye is very small, nearly spherical, and almost frictionless. Also, your eye muscles are (relatively) pretty strong. But this doesn't answer the real question, which is whether you'll perceive it. After all, you must perceive it to "track" it. This doesn't have much to do with focus speed or the speed of light, or anything like that. It's more a question of

a) how much light is the object putting off,

b) how much of it reaches your actual eye, and

c) which part of your eye these photons land on.


imagine yourself staring straight ahead and an object appears out of nowhere. Before you "see" it, enough photons must reach the photosensitive cells in your eye to activate it. If enough of these cells are activated, it generates a signal strong enough to actually register in your brain (assuming you're not focusing on something else), which causes your eyes to turn to focus on it and elevates it to conscious thought. That's the order for most things: it registers on a rod or cone cell, their activation registers in your brain, you turn your eye to it, and a small fraction of time later this whole thing registers in consciousness. The irony is that we usually think of it as "Oh, I saw it and turned to look at it..." which is completely wrong.


It also depends on where the light first hits your eye: in the center our eyes have way more resolution (especially color), but near the outside the cells are much more sensitive to light.


Okay, I'm going to stop and sum up the answer. The speed at which "the human eye can no longer keep up with it" is more than just the human eye's movements speed, but also out ability to track it. That's dependent on whether it gets registered (so our eye actually turns) which is dependent upon how much light from the object reaches our eye and where it hits. Hope this helps!

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hmm i jsut skimmed through this thread mgiht of missed it but seems like people jsut balbbering on and didnt help at all....i think the answer your looking for is around 24 frames per second

actually what i think the correct answer is 24.5 frames per second....... lol

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