# Under certain physical conditions, could I catch my own shadow?
**URL:** https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699
**Category:** Factual Questions
**Created:** [April 17, 2011, 4:56am UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699 "2011-04-17T04:56:52Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)
#### Post date: [April 17, 2011, 4:56am UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/1 "2011-04-17T04:56:52Z")
The question was prompted by a cute YouTube video of a kitten trying to pounce on its own shadow.
I’m thinking if I were made of some semi-transparent medium, and a second beam of light tracked me, or …
I can’t get my head around this. I’m sure I can’t catch my shadow, because that would imply some sort of time travel?
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### Author:  [@Joey\_P](https://boards.straightdope.com/u/Joey_P)
#### Post date: [April 17, 2011, 4:59am UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/2 "2011-04-17T04:59:51Z")
I think you’ll have to define what it means to catch your shadow. I could cast my shadow onto a piece of paper and hold that in my hand. Is that catching it?
Hell, I could just cast my shadow directly onto my hands and hold ‘it’ just like I was holding a person. Would that count? Beyond that, I’m not really sure what you mean.
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### Author:  [@EvilTOJ](https://boards.straightdope.com/u/EvilTOJ)
#### Post date: [April 17, 2011, 10:26am UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/3 "2011-04-17T10:26:04Z")
No, you can’t. Your shadow is the absence of light. So in a very real sense, nothing is there to catch.
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### Author:  [@Autolycus](https://boards.straightdope.com/u/Autolycus)
#### Post date: [April 17, 2011, 11:58am UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/4 "2011-04-17T11:58:26Z")
> [@EvilTOJ](#):
>
> No, you can’t. Your shadow is the absence of light. So in a very real sense, nothing is there to catch.
Poppycock. Everyone knows all you need is simply a needle and some thread.
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### Author:  [@Fubaya](https://boards.straightdope.com/u/Fubaya)
#### Post date: [April 17, 2011, 3:13pm UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/5 "2011-04-17T15:13:34Z")
I’m not sure what catching your shadow means, but a shadow would move at the speed of light so you can’t do anything that would be faster than your shadow. It would be like trying to do something in the mirror to trick your reflection.
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### Author:  [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)
#### Post date: [April 17, 2011, 3:34pm UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/6 "2011-04-17T15:34:46Z")
> [@Fubaya](#):
>
> I’m not sure what catching your shadow means, but a shadow would move at the speed of light so you can’t do anything that would be faster than your shadow. It would be like trying to do something in the mirror to trick your reflection.
Shadows can move at any speed, infact they can move faster than the speed of light.
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### Author:  [@The\_Tao\_s\_Revenge](https://boards.straightdope.com/u/The_Tao_s_Revenge)
#### Post date: [April 17, 2011, 3:45pm UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/7 "2011-04-17T15:45:46Z")
> [@These are my own pants](#):
>
> Shadows can move at any speed, infact they can move faster than the speed of light.
Okay I have to ask, how would a shadow move faster than light?
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### Author:  [@The\_Tao\_s\_Revenge](https://boards.straightdope.com/u/The_Tao_s_Revenge)
#### Post date: [April 17, 2011, 3:49pm UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/8 "2011-04-17T15:49:44Z")
> [@Leo\_Bloom](#):
>
> The question was prompted by a cute YouTube video of a kitten trying to pounce on its own shadow.
> I’m thinking if I were made of some semi-transparent medium, and a second beam of light tracked me, or …
> I can’t get my head around this. I’m sure I can’t catch my shadow, because that would imply some sort of time travel?
Catching your own shadow is easy. Whatever happens to the shadow’s source affects the shadow. Therefor put yourself in a cage and your shadow will be trapped in a shadow cage. Stand with light directly overhead and your shadow will stuck under your feet.
Edit: your shadow is always stuck fallowing you. The real challenge is setting it free.
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### Author:  [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)
#### Post date: [April 17, 2011, 4:11pm UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/9 "2011-04-17T16:11:22Z")
> [@The\_Tao\_s\_Revenge](#):
>
> Okay I have to ask, how would a shadow move faster than light?
A shadow is not a physical object, nor does it carry information between the surfaces on to which it is projected when it is moving (rather infomration goes from the source and the object that casts the shadow to the surfaces) so it can move faster than the speed of light.
Try using a light source and seeing if you can create a shadow that moves a lot quicker than the object casting it. It shouldn’t be difficult, then you should be able to work out for yourself what sort of simple set-up you’d need to create a FTL shadow.
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### Author:  [@The\_Tao\_s\_Revenge](https://boards.straightdope.com/u/The_Tao_s_Revenge)
#### Post date: [April 17, 2011, 4:27pm UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/10 "2011-04-17T16:27:53Z")
> [@These are my own pants](#):
>
> A shadow is not a physical object, nor does it carry information between the surfaces on to which it is projected when it is moving (rather infomration goes from the source and the object that casts the shadow to the surfaces) so it can move faster than the speed of light.
>
> Try using a light source and seeing if you can create a shadow that moves a lot quicker than the object casting it. It shouldn’t be difficult, then you should be able to work out for yourself what sort of simple set-up you’d need to create a FTL shadow.
Well a rotational reference frame, with a long enough radius the shadow’s movement would seem to move faster than light.
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### Author:  [@Triskadecamus](https://boards.straightdope.com/u/Triskadecamus)
#### Post date: [April 17, 2011, 4:30pm UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/11 "2011-04-17T16:30:51Z")
Just stomp on it’s foot.
Tris
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### Author:  [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)
#### Post date: [April 17, 2011, 4:36pm UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/12 "2011-04-17T16:36:21Z")
> [@The\_Tao\_s\_Revenge](#):
>
> Well a rotational reference frame, with a long enough radius the shadow’s movement would seem to move faster than light.
The reference frame doesn’t need to rotate, we can have the source or the object casting the shadow rotating.
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### Author:  [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)
#### Post date: [April 17, 2011, 4:42pm UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/13 "2011-04-17T16:42:58Z")
edited to add: not that the source or the object casting the shadow have to rotate to get a FTL shadow. The surface on to which the shadow is cast is also a factor.
Though it’s quite possible to achive such a shadow with an object moving in a staight line in front of a point source projecting a shadow on to a flat surface
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [April 17, 2011, 5:17pm UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/14 "2011-04-17T17:17:45Z")
> [@](#):
>
> Poppycock. Everyone knows all you need is simply a needle and some thread.
Hm, that does sound like it’d work a lot better than soap.
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### Author:  [@Nanoda](https://boards.straightdope.com/u/Nanoda)
#### Post date: [April 17, 2011, 5:50pm UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/15 "2011-04-17T17:50:09Z")
You lose internet points for mentioning cute kitten videos without a link, but I’ll try anyway…
The [speed of light](http://en.wikipedia.org/wiki/Speed_of_light) isn’t totally constant; for example, through glass light will go 2/3 it’s “normal” speed.
What this means is that if you set up a big block of glass, and stand in front of it casting a shadow _through_ it, then you only have to run faster than 200,000 km/s around the glass block in order to rest in your own shadow.
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### Author:  [@PlainJain](https://boards.straightdope.com/u/PlainJain)
#### Post date: [April 17, 2011, 6:24pm UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/16 "2011-04-17T18:24:38Z")
> [@Chronos](#):
>
> Hm, that does sound like it’d work a lot better than soap.
Unlike the black hole thread, this _does_ seem to be your area of expertise.
😉
.
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### Author:  [@Fubaya](https://boards.straightdope.com/u/Fubaya)
#### Post date: [April 17, 2011, 6:35pm UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/17 "2011-04-17T18:35:12Z")
> [@These are my own pants](#):
>
> Shadows can move at any speed, infact they can move faster than the speed of light.
Right, I’m still not sure what “catching a shadow” means, but I think he is asking if he can move faster than the shadow that he is casting and the relationship between you and your shadow changes at the speed of light. If you raise your arm and cast a shadow, then move your arm an inch to the left, you are moving out of the way of the light and the shadow will change in the time it takes light to travel from your arm to the shadow. An FTL shadow, well, I doubt he can catch that.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [April 17, 2011, 8:46pm UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/18 "2011-04-17T20:46:39Z")
With a moving light source, your shadow could move slower than you, or even not at all.
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### Author:  [@The\_Tao\_s\_Revenge](https://boards.straightdope.com/u/The_Tao_s_Revenge)
#### Post date: [April 17, 2011, 9:01pm UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/19 "2011-04-17T21:01:30Z")
> [@Fubaya](#):
>
> Right, I’m still not sure what “catching a shadow” means, but I think he is asking if he can move faster than the shadow that he is casting and the relationship between you and your shadow changes at the speed of light. If you raise your arm and cast a shadow, then move your arm an inch to the left, you are moving out of the way of the light and the shadow will change in the time it takes light to travel from your arm to the shadow. An FTL shadow, well, I doubt he can catch that.
People catch cheetahs, falcons, and dolphins by using traps, not brute speed.
If the OP stands in a mirror box wouldn’t his shadow be reflected right back into his needle and thread, and soap wielding mits?
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### Author:  [@Fubaya](https://boards.straightdope.com/u/Fubaya)
#### Post date: [April 18, 2011, 12:42am UTC](https://boards.straightdope.com/t/under-certain-physical-conditions-could-i-catch-my-own-shadow/578699/20 "2011-04-18T00:42:24Z")
I think I am interpreting the question differently than everyone else. Maybe the OP can clarify what he means?
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