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i'm going to do an experiment and i need

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your help

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i'm going to show you two videos and

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this is the first one

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look at it carefully it shows a white

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object

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shaped like a tic tac moving over a

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background or fence

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but is it moving what's actually moving

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left and right up and down here

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is it the object the camera or maybe

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both

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obviously the camera is rotating to

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track the object but is the camera

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moving

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now the second video is the same object

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but this time we're looking down over

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the water

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again the camera rotates to track the

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object but what's moving left

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right up and down here the camera the

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object

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or both can you even tell

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think about what your answer is before

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continuing with the video

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feel free to write down your answers for

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both videos in the comments before

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continuing

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okay spoiler alert make sure you have

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your answers because i'm about to pull

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back the curtain

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the answer is the camera is moving

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but the object is not

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i shot both videos with an iphone

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mounted on a gimbal

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the gimbal is set to track the object so

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it remains fixed in the middle of the

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screen

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i cropped the scene to remove 3d objects

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that would give the game away

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and i added a bit more stabilization

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using adobe after effects to lock the

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object in the middle

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in both cases the model was about

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halfway between the camera and the

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i asked about this on twitter with this

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exact same videos and i got some

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interesting replies

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with the fence experiment most people

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seem to think that both camera and

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tic-tac were moving

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although i might have messed up the

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question there by suggesting it was a

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real tic tac

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it's actually two inches long for the

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pool experiment

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which are worded a bit better there was

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quite a mixed set of responses

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and rationales for those responses but a

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majority of people thought the object

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was moving

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some thought both the object and the

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camera were moving and a few people got

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the correct answer

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what i was trying to demonstrate was

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just how compelling the illusion of

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motion can be if you don't know how far

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away an object is

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the pool example is particularly

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compelling i was surprised that there

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was a real sense of the object moving

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around even without cropping and

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stabilizing the image

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so there's a general point of don't let

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your brain trust what your eyes are

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telling you

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but there's a more specific point about

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camera systems that track

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objects parallax can be a very

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compelling illusion with an object

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tracking camera

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even an undetectable illusion you can

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make things look like they are moving in

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a direction that they are not

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we see this with various ufo videos like

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gimbal and go fast

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but i think you can also apply to direct

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visual observations

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if you don't know how big something is

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then you can't judge distance

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like with this model over the pool the

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natural impression is that it's low and

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close to the water when it's actually

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much higher

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this is a very natural and

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understandable illusion that anyone in a

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particular position above an object of

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unknown size might make

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in a plane in that position with two

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pilots both pilots would see the same

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illusion

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and if there was another plane higher up

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they might see a different version of

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the illusion

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but still not say things as they really

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are

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it's something to keep in mind when

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looking at accounts of normal objects of

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unknown size

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if you don't know where it is how do you

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know how big it is

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do you know how far away it is

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and if you don't know where it is or how

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big it is and you are moving

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then how do you know if the object is