Q & A: Magic with mirrors

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Most recent answer: 02/22/2010
Q:
First off, thank you for answering my questions about light and magnets and diffraction and such, I very much appreciate it. You have both closed off a large section that my partner and I will not have to study, and guided us more towards the correct answer. I would now like to ask you to follow up on your last answer to my question, which you titled, "Light, Magnets and...Gravity" (or something like that). That question is about the mirrors that magicians use to make things ’disappear.’ First off, could you explain how they do this (such as set it up right, get the perfect angles, etc). Secondly, I would like to know (should it please you) if it has to be a large setup, using large mirrors and the such, or can it be made relatively small (such as ’being brought into class’ small). Again, thank you very much for answering my questions and helping our project. It’s difficult to find the information you need for this kind of thing on the internet.
- Jon Stoffel (age 15)
King’s Academy, The, Marion, Indiana, U.S.A.
A:
I hope you will continue to be interested in the properties of light -- electromagnetic energy is used for a great variety of purposes. Only a small number of these purposes are meant to deceive observers. As physicists and truth-seekers and skeptics, we don't specialize in deception, and in fact try to dispel it whenever it arises. Those who do specialize, "magicians" or more appropriatley termed "illusionists", hide their secrets very carefully so that their shows remain entertaining to people who do not know their secrets. I can only offer a few small tips on the subject (not being an expert):

1) Make it entertaining and quick and do not show the setup more than once to any particular person. The reson for this is that mirrors are often easy to detect because what people see in mirrors looks reversed, and often appears to be farther away than the object the mirror is attempting to conceal. Two mirrors can fix the reversing problem, but then the combined image degradation may spoil the illusion (i.e., if there is dirt on the mirrors or they aren't perfectly flat or if the edges aren't concealed well).

2) Reflect a bland, featureless background -- that way people will have a harder time noticing that it is a reflection they are looking at and not the real thing. The background may not be the same as the background the audience thinks it is looking at. For example, placing an object in a box with interior walls painted a bland, light color, and then inserting a mirror so that a viewer sees a reflection of a side wall instead of the back wall makes for a passable trick. But the viewer has to be convinced that he is looking at the back wall, which means he cannot see the edges of the mirror or any other defects. It also confines the whole demostration to the box. And you have to slide in the mirror when no one's seeing you do it (and that's the biggest trick of all). One thing you can do is have a box with one side missing for viewing, a mirror arranged diagonally so that the side looks like the back, and then conceal a heavy weight in the part of the box that is invisible. Then it looks like an empty box, but a person picking it up will be amused to find how much it weighs.

3) The mirror only needs to be as big as the object it conceals. You can make these as small as you like (but not smaller than the wavelength of the light -- see our answer on diffraction.)

The whole purpose of illusion is to make an observer think he's looking at something that really is different, and mirrors can help this by bouncing light in different directions. Use your own creativity to find uses for them!

Tom

(published on 10/22/2007)

Follow-Up #1: proper mirrors

Q:
Is it possible to build a mirror cabinet that will present the 'proper' image of a person standing in front? Proper because it is actually reversed .... The person would raise his right hand and see his image raise his hand also, but only on the left side of the mirror as he faces it. What say you??
- Mr. Crabtree (age 60)
Michigan
A:
You need to use at least two mirrors, and see the image reflected an even number of times. I just did this to read the label on the back of a busted washing machine. (That was stupid, because another label was easily readable near the door hinge, with zero mirrors, but that's another story.)

Mike W.

(published on 02/22/2010)