# "How does the mirror know the ball is there?" Oh my God **URL:** \ **Category:** The BBQ Pit\ **Created:** [August 28, 2023, 12:13pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224 "2023-08-28T12:13:41Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [August 28, 2023, 6:15pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/21 "2023-08-28T18:15:45Z")
> [@RickJay](#): > > 40% or more of all commenters on Facebook honestly do not get it. In this video it is literally one troll who posted dozens of times. Every other person got it and tried patiently explaining it to him. ---
**Author:** ![ThelmaLou](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/thelmalou/32/390_2.png) [@ThelmaLou](https://boards.straightdope.com/u/ThelmaLou)\ **Post date:** [August 28, 2023, 6:26pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/22 "2023-08-28T18:26:22Z")
It might have been a Thermos…it might have been Andy Griffith… 😉 ---
**Author:** ![suranyi](https://avatars.discourse-cdn.com/v4/letter/s/e36b37/32.png) [@suranyi](https://boards.straightdope.com/u/suranyi)\ **Post date:** [August 28, 2023, 6:32pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/23 "2023-08-28T18:32:36Z")
For good or bad I’m on social media a lot. There are a tremendous number of incredibly stupid people online. It would take me ten lifetimes to correct even the dumbest, so I just don’t bother anymore. ---
**Author:** ![Stratocaster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/stratocaster/32/16393_2.png) [@Stratocaster](https://boards.straightdope.com/u/Stratocaster)\ **Post date:** [August 28, 2023, 6:45pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/24 "2023-08-28T18:45:33Z")
Well done, @SenorBeef! ---
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [August 28, 2023, 6:58pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/25 "2023-08-28T18:58:12Z")
Also, some/a lot of people like playing dumb just for lols, so I wouldn’t take the comment section as being wholly sincere. To be honest, I never thought about this or why it works, nor would I able to explain it (nor do I even care about the explanation.) ---
**Author:** ![Shoeless](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/shoeless/32/7099_2.png) [@Shoeless](https://boards.straightdope.com/u/Shoeless)\ **Post date:** [August 28, 2023, 7:33pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/26 "2023-08-28T19:33:22Z")
> [@Briny\_Deep](#): > > > [@ThelmaLou](#): > > > > One of the catch phrases in my marriage to my late husband was, “But how do it _know_?” It comes from a shaggy dog/country boy story told by (I think) Andy Griffith. Talking about how an insulated chest will keep hot things hot and cold things cold. _“But how do it KNOW?”_ > > Also a commonplace in my household, but we thought it was about a Thermos. I didn’t know it was from Andy Griffith, thanks for that! “What do you have in your Thermos?” “Hot coffee, and a Popsicle!” ---
**Author:** ![ThelmaLou](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/thelmalou/32/390_2.png) [@ThelmaLou](https://boards.straightdope.com/u/ThelmaLou)\ **Post date:** [August 28, 2023, 7:44pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/27 "2023-08-28T19:44:06Z")
🤣 Good one! ---
**Author:** ![velomont](https://avatars.discourse-cdn.com/v4/letter/v/8491ac/32.png) [@velomont](https://boards.straightdope.com/u/velomont)\ **Post date:** [August 28, 2023, 7:49pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/28 "2023-08-28T19:49:34Z")
> [@Stratocaster](#): > > Well done, @SenorBeef! Your two-mirror model really made it intuitive. Thanks for that. I remember this stuff from grade 9 or 10 science, with the various angles. But I was, TBH, having trouble with the first diagram with the dashed lines and one mirror. ---
**Author:** ![Buck\_Godot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/buck_godot/32/6573_2.png) [@Buck\_Godot](https://boards.straightdope.com/u/Buck_Godot)\ **Post date:** [August 28, 2023, 7:54pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/29 "2023-08-28T19:54:28Z")
In spite of the fact that I consider myself a pretty smart guy and understand optics it took me a minute or so to figure out what was going on. > I was wondering if looking at video was throwing people off so I went in the bathroom to try it with a book and a Dixie cup. I think what was happening was more obvious since I had to lean over the sink and get my head close to the mirror to get the angle right. But if you have no clue what’s happening that may not help. I think one of the things that helps the illusion is that it photographed with a single cell phone camera that could be placed right next to the mirror. In real life you have two eyes one of which is going to have to be fairly far from the mirror so its easier to see what it going on. ---
**Author:** ![digs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/digs/32/14889_2.png) [@digs](https://boards.straightdope.com/u/digs)\ **Post date:** [August 28, 2023, 8:39pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/30 "2023-08-28T20:39:08Z")
> [@Pleonast](#): > > But our brains want to interpret the image as another person, and our bilateral symmetry causes us conflate the image’s left hand with another person’s right hand. I remember a time travel episode from some tv show in the 60s, where Present Day Protagonist says “You look exactly like me… except your hair is parted on the wrong side!” Future Protagonist says “I’m you. You’re just used to seeing yourself in a mirror.” ---
**Author:** ![digs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/digs/32/14889_2.png) [@digs](https://boards.straightdope.com/u/digs)\ **Post date:** [August 28, 2023, 8:40pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/31 "2023-08-28T20:40:54Z")
> [@suranyi](#): > > For good or bad I’m on social media a lot. There are a tremendous number of incredibly stupid people online. It would take me ten lifetimes to correct even the dumbest… …but less time to start a thread here with some of the most inadvertently hilarious. ---
**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\ **Post date:** [August 28, 2023, 8:49pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/32 "2023-08-28T20:49:01Z")
> [@Left\_Hand\_of\_Dorkness](#): > > What may seem intuitive or obvious to the OP is really hard for me to wrap my head around, even with diagrams; I accept that it works, but struggle to comprehend it intuitively. You just explained my dismal failure in college physics classes. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 28, 2023, 9:08pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/33 "2023-08-28T21:08:58Z")
> [@Roderick\_Femm](#): > > I don’t much like that diagram, it makes it look as if the eye is looking through the mirror at an actual object. I think it could be more confusing than helpful. Yup, and that’s exactly how mirrors work. They act like windows into another room with the same stuff in it. Little kids (like, 3 years old) get this. But older students often don’t. I think this is largely because our modern world is full of things that act in some ways sort of like mirrors, but not really. On a TV or computer screen, the surface of the screen is where the image is, and so people assume that that’s how mirrors work, too. But the image from a mirror really is actually behind the mirror. > [@Pleonast](#): > > It’s similar to people thinking mirrors switch left vs right. There’s no switch. When you see the image of yourself in a mirror, your right hand is still on the right and your left hand is still on the left. Right, what mirrors actually reverse is front and back. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [August 28, 2023, 9:11pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/34 "2023-08-28T21:11:01Z")
> [@Buck\_Godot](#): > > I think one of the things that helps the illusion is that it photographed with a single cell phone camera that could be placed right next to the mirror. In real life you have two eyes one of which is going to have to be fairly far from the mirror so its easier to see what it going on. I think that’s part of it, the camera and the objects are moving in a way that enhances the illusion. Doing it yourself in the mirror you can move you head and the objects side to side and catch the angle where the hidden object is being reflected in the mirror, and then tilt it back to see it disappear. Nothing can be done with the people who ignore the explanations and only watch the videos. ---
**Author:** ![RickJay](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@RickJay](https://boards.straightdope.com/u/RickJay)\ **Post date:** [August 28, 2023, 9:24pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/35 "2023-08-28T21:24:47Z")
> [@Exapno\_Mapcase](#): > > In this video it is literally one troll who posted dozens of times. Every other person got it and tried patiently explaining it to him. I do note in the OP this was not the Facebook video I am referring to when I say a lot of people don’t get it. That is just a video of the effect I found quickly on Youtube. I didn’t want to like to Facebook. ---
**Author:** ![RickJay](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@RickJay](https://boards.straightdope.com/u/RickJay)\ **Post date:** [August 28, 2023, 9:26pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/36 "2023-08-28T21:26:19Z")
> [@Pleonast](#): > > It’s similar to people thinking mirrors switch left vs right. There’s no switch. When you see the image of yourself in a mirror, your right hand is still on the right and your left hand is still on the left. > > But our brains want to interpret the image as another person, and our bilateral symmetry causes us conflate the image’s left hand with another person’s right hand. Wasn’t it The Perfect Master himself who explained that mirrors don’t reverse left to right, they reverse **front to back**? ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [August 28, 2023, 9:30pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/37 "2023-08-28T21:30:36Z")
Just saying that not everybody on the internet is an idiot. ---
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [August 28, 2023, 9:33pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/38 "2023-08-28T21:33:38Z")
What I want to do now is make a trick video using similar angles where the mirror doesn’t show the apple in the reflection. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [August 28, 2023, 9:37pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/39 "2023-08-28T21:37:55Z")
> [@JRDelirious](#): > > It’s our own brains tricking us into perceiving the image is emitted from “inside” the mirror. There’s no trick, though. From an electromagnetic perspective, the virtual image really is there (assuming a perfect mirror, etc.). There’s no experiment you can perform with just photons that can distinguish a real image from a virtual mirrored image. It has nothing to do with our brains. ---
**Author:** ![Babale](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/babale/32/15666_2.png) [@Babale](https://boards.straightdope.com/u/Babale)\ **Post date:** [August 29, 2023, 2:28pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/40 "2023-08-29T14:28:02Z")
> [@RickJay](#): > > Wasn’t it The Perfect Master himself who explained that mirrors don’t reverse left to right, they reverse **front to back**? We all like @Chronos, but yeesh, get a room! > [@Chronos](#): > > Right, what mirrors actually reverse is front and back 😛 [Previous page](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224.md?page=1) [Next page](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224.md?page=3)