# "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:** 12\ **Page:** 4
**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:** [September 11, 2023, 7:59pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/61 "2023-09-11T19:59:57Z")
> [@TriPolar](#): > > There was an arcade ‘game’ made with that principle. I’m guessing this is the one you’re thinking of: > **[Time Traveler (video game)](https://en.wikipedia.org/wiki/Time_Traveler_(video_game))** > > Time Traveler or Hologram Time Traveler is a LaserDisc interactive movie arcade game. It was designed by Dragon's Lair creator Rick Dyer, and released in 1991 by Sega. Its plot is that an American old west cowboy named Marshal Gram travels to various timelines to rescue Princess Kyi-La and defeat the evil time lord Vulcor. The game is best known for its arcade cabinet which displays a "holographic" like projection, produced using optical technology from Dentsu. > In 2001, a home version was publis... ---
**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:** [September 11, 2023, 8:09pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/62 "2023-09-11T20:09:13Z")
Yes, there were several made but I think that one got the most exposure. The size of the mirrors, resolution, and limited viewing angles didn’t make for a great gaming experience. I’m sure someone must have tried a larger scale hi-res version. There are plenty of ‘mirror box’ illusions and also a [therapy for amputees](https://en.wikipedia.org/wiki/Mirror_therapy) that provides visual feedback of a missing limb to help relieve phantom-limb symptoms. ---
**Author:** ![Drum\_God](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drum_god/32/44_2.png) [@Drum\_God](https://boards.straightdope.com/u/Drum_God)\ **Post date:** [September 11, 2023, 8:18pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/63 "2023-09-11T20:18:55Z")
Since we’re here, how does a broken mirror work? If I look in my bathroom mirror, I see my handsome mug smiling back at me. However, if the glass is broken, I’ll see two of me. Both of the “new” mirrors are in the same plane as the original unbroken mirror. Why does the crack in the glass matter? ---
**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:** [September 11, 2023, 8:23pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/64 "2023-09-11T20:23:21Z")
That’ll only happen if the pieces are tilted relative to each other. Which is likely to be true if something broke the mirror by bashing into it. But if the pieces remain perfectly planar, you’ll just see one of you (with a small gap where the crack is). It takes only a tiny tilt to give you multiple images. Mirrors are very flat by default. ---
**Author:** ![Atamasama](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/atamasama/32/12961_2.png) [@Atamasama](https://boards.straightdope.com/u/Atamasama)\ **Post date:** [September 11, 2023, 9:09pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/65 "2023-09-11T21:09:08Z")
> [@Spectre\_of\_Pithecanthropus](#): > > I wonder now if larger versions of this are ever used in stage magic. ISTM it ought to be very easy to make a large object vanish when the real object was never in view of the audience at all. It only works when you look at it from a particular angle. A small one on a table that you’re looking down at works well. A huge one on an elevated stage that people below are looking at wouldn’t work. They wouldn’t even see the “floating” object. It would ruin the illusion. It’s a neat trick that you could probably use very well in close-up magic, but I don’t think it would ever work for traditional stage magic. ---
**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:** [September 11, 2023, 9:27pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/66 "2023-09-11T21:27:51Z")
> [@Spectre\_of\_Pithecanthropus](#): > > If some people can’t understand how an ordinary mirror works, then what would this thing do to their little minds? Many college physics departments have a large parabolic mirror, which can produce a similar effect. One of my professors liked to start class by swinging a baseball bat through a lightbulb that wasn’t there. > [@Spectre\_of\_Pithecanthropus](#): > > I wonder now if larger versions of this are ever used in stage magic. Disney’s Haunted Mansion uses similar tricks, as well. ---
**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:** [September 11, 2023, 9:35pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/67 "2023-09-11T21:35:59Z")
The Exploratorium has a nice one that they keep clean enough that it’s hard to distinguish from reality… except that it’s positioned such that everything is flipped upside-down. Aside from that, it looks totally convincing, with depth cues and everything else looking normal. ---
**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:** [September 11, 2023, 10:52pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/68 "2023-09-11T22:52:27Z")
> [@Dr.Strangelove](#): > > You can get those devices fairly cheaply (like \<$20). Search for “mirascope”. They are pretty neat. There’s one on Amazon for 7.99 ---
**Author:** ![Atamasama](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/atamasama/32/12961_2.png) [@Atamasama](https://boards.straightdope.com/u/Atamasama)\ **Post date:** [September 11, 2023, 11:14pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/69 "2023-09-11T23:14:11Z")
I was tempted to buy one of those things for my 9-year-old daughter, I still might. She loves stuff like that. I remember when I bought her a prism so she could make her own rainbows, you’d think I bought her a functioning magic wand. ---
**Author:** ![Sage\_Rat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sage_rat/32/399_2.png) [@Sage\_Rat](https://boards.straightdope.com/u/Sage_Rat)\ **Post date:** [September 11, 2023, 11:19pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/70 "2023-09-11T23:19:47Z")
> [@Drum\_God](#): > > Since we’re here, how does a broken mirror work? If I look in my bathroom mirror, I see my handsome mug smiling back at me. However, if the glass is broken, I’ll see two of me. Both of the “new” mirrors are in the same plane as the original unbroken mirror. Why does the crack in the glass matter? If you have a flat wall and throw a ball at it really hard, the ball will bounce back at you. Aim a little to the side and it’s going to bounce, come back, miss you, and keep going off into the distance behind you. But, curve that wall or put a corner in it and you might have a second or third location where you could chuck the ball and have it bounce back to you. For example, you stand in a corner with two walls that are at a right angle to one another and there will be a spot on either wall where you can aim and catch the ball on the bounce-back. Likewise, if you’re in the bottom of a cylindrical well, you can basically throw the ball in any direction you want and it’s going to come back to you (if you’re standing in the dead center). How ever many places there are in a wall that you could throw a ball real hard and have it come back to you, that’s how many copies of yourself you would see if you painted the wall with mirrors. “bounce” and “reflect” are just synonyms (for this discussion). Now, as the others say, when you break a mirror, you’re basically creating a very small corner with two flat pieces that are at small angles to one another. If those angles are just right, they might both angle back at you perfectly that they reflect back to the same center point. If you break a wall into bits and angle the parts so they all aim back at you, you can bounce a ball back to yourself in as many ways as you want to. You haven’t done any magic, you’ve just aimed things appropriately so that the bounces go in that direction. ---
**Author:** ![MrAtoz](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@MrAtoz](https://boards.straightdope.com/u/MrAtoz)\ **Post date:** [September 12, 2023, 1:08pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/71 "2023-09-12T13:08:23Z")
> [@Chronos](#): > > Disney’s Haunted Mansion uses similar tricks, as well. The Haunted Mansion, as I understand it, uses a technique called [Pepper’s ghost](https://en.wikipedia.org/wiki/Pepper%27s_ghost). It’s a very old trick that’s been widely used in theatre, amusement parks, and magic shows. It actually uses not a mirror, but a sheet of glass, which makes the “ghost” appear translucent. The glass is reflecting something that’s in another room which is hidden from the audience. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [September 12, 2023, 1:49pm UTC](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224/72 "2023-09-12T13:49:50Z")
Pepper’s Ghost appears to be what was used in a circa 1900 illusion called _The Fatal Marriage_. I know about it because it was used the first year at Wonderland Park, which I wrote a book about. The beauty of the illusion is that _it works from all angles_, at least all angles where you can look into the glass serving as a mirror. And since it works for all angles, it means that objects have the correct parallax and appear properly three-dimensional. The illusion using the parabolic mirror also works for all lines of sight that let you look into the mirror. And, again, it gives you a true three-dimensional image. As such, it _could_ work for stage magic, but only for a restricted range of angles. The “Mirage” illusion is a third case of one that givers perfect three dimensional images. > **[Amazon.com: ComputerGear 3D Mirror Scope Illusion Creator Mirage 3-D Hologram...](https://www.amazon.com/Illusion-Creator-Hologram-Parabolic-Reflector/dp/B001TFV4BE)** > > Create your own 3D hologram with this amazing 3D Mirror Scope Illusion Creator. How does it work? Place your object in the center bottom of two parabolic mirrors and watch as it is projected as a solid object above the opening in the top mirror. Try... > **[Amazon.com: Toysmith: 3-D Mirascope, 6" Instant Hologram Image Maker, Includes a...](https://www.amazon.com/Toysmith-79747-3-D-Mirascope-6-Inch/dp/B000N5T8KA)** > > Product Description Transform ordinary objects into awesome holograms with the Toysmith 3-D Mirascope. The mirascope takes small objects and uses an optical illusion to create a 3D holographic projection. The mirascope includes a plastic... This one is different from the single parabolic mirror, in that it requires two parabolic mirrors, each placed so that its vertex coincides with the focal point of the other. Of course, you have to cut a hole in the upper one. This illusion has such a restricted range of viewing that you treally can’t use it on stage. It’s a “close-up” magic thing. A fourth trick gives you a _reduced_ image of the object. It was popular in the early 20th century, and is called _Tanagra Theater_. I wrote an article about it. Although people tried to use this one on stage (It was used in one production of Karel Czapek’s **R.U.R.** ), it really has such an angularly restricted range of vision that it can only be seen b y a small group of observers, close in. It was used in a Ford promotion at World’s Fairs in the 1930s. There’s still one with a “mermaid in an aquarium” at Bimbo’s Bar in San Francisco > **[The Legendary Brio of Bimbo's 365 Club](https://www.7x7.com/the-legendary-brio-of-bimbos-365-club-1786889694.html)** > > As the legend goes, guests visiting Bimbo’s 365 were subjected to a scandalous visage. They called her Dolfina, the woman in the fishbowl, and her appearance was part optical illusion made possible by strategically placed mirrors, and part burlesque... > **[Dolphina at Bimbo’s 365 Club](https://www.weirduniverse.net/blog/comments/dolfina_at_bimbos_365_club)** > > Bimbo's 365 Club is still an active music venue in San Francisco. But, according to news on their own website, they seem to have abandoned a (I know they’re still running the mermaid, because I queried them not that long ago, and they replied that it was still up and running) Various bars used this illusion up until about 1960, but Bimbo’s appears to be the only one still working. The illusion isn’t really perfect, because the image is “squashed” front to back by the same magnification factor, but most people don’t notice this. There are other “shrunken mermaid” illusions, but they generally don’t use mirrors. [Previous page](https://boards.straightdope.com/t/how-does-the-mirror-know-the-ball-is-there-oh-my-god/989224.md?page=3)