The Naked Scientists

The Naked Scientists Forum

Author Topic: Why do mirrors reverse but not invert images?  (Read 4511 times)

Offline thedoc

  • Forum Admin
  • Administrator
  • Sr. Member
  • *****
  • Posts: 511
  • Thanked: 12 times
    • View Profile
Why do mirrors reverse but not invert images?
« on: 10/09/2013 13:05:15 »
If one looks in the mirror, the left and right side is reversed, so we see a "mirror image". However, the top and bottom is not. Why do we see left and right swapped around but not top and bottom?

Regards
Mark
Asked by Mark Faesen


                                        Visit the webpage for the podcast in which this question is answered.

 ...or Listen to the Answer or [download as MP3]

« Last Edit: 10/09/2013 13:05:15 by _system »


 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 12001
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Re: Why do mirrors reverse but not invert things?
« Reply #1 on: 04/08/2013 19:20:37 »
It doesn't swap anything. Put yourself in front of it and then blink your right eye, you will find that the (reflected) light goes directly, from your eye, to the eye blinking in the mirror, and all in a straight line. So how would the mirror swap? What you are thinking of is rotations, not swapping. And you're not the only one :) One might be able to argue that as most of us do seem to think in this manner, we're all instinctive geometric mathematicians. because what you are doing is comparing your reflection to what would happen if it was you there instead, 'rotated for real'.

You having rotated yourself, looking in the opposite direction.

It's less confusing if you think of it that way. In fact it is you, presuming that the mirror must fit your idea of what really should happen if you were to turn around, not any strange physics about it. And that's also what make us 'instinctive geometric mathematicians' in my eyes :) Although, applying logic I'm sure you agree on that there's no swapping happening.

You can also take a look at The Mirror Question for some more cool discussions about rotations.
 

Offline David Cooper

  • Neilep Level Member
  • ******
  • Posts: 1505
    • View Profile
Re: Why do mirrors reverse but not invert things?
« Reply #2 on: 04/08/2013 20:30:27 »
It does swap things around, but it's the front and back that get switched round rather than left and right. The reflection of your left side is still on the left just as the reflection of your head is still at the top, but if your face is facing east in the real world, in the reflection it is facing west - that is what has been reversed.
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 12001
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Re: Why do mirrors reverse but not invert things?
« Reply #3 on: 04/08/2013 21:01:34 »
Assuming you was the one looking out from the mirror then David? We have this ability to imagine ourselves into something, like 'steering by ones pants' placing ourselves where we're not. Although to me that mirror image doesn't look at anything, it's a reflection, a depiction of the 'light paths' taken from you and your surroundings to the mirror, then reflected back to your eye. You can create rotations of something, as in the link above, but that's not the same, to me, as a mirror image would be. Because if you did a real rotation, then moving your left hand indeed should be the right, looking at 'yourself' in some weird space.
 

Offline syhprum

  • Neilep Level Member
  • ******
  • Posts: 3826
  • Thanked: 19 times
    • View Profile
Re: Why do mirrors reverse but not invert things?
« Reply #4 on: 04/08/2013 21:21:50 »
Its because your two eyes are side by side and not one above the other, if you want to see things inverted vertically lie on your side and look in the mirror
 

Offline David Cooper

  • Neilep Level Member
  • ******
  • Posts: 1505
    • View Profile
Re: Why do mirrors reverse but not invert things?
« Reply #5 on: 05/08/2013 17:56:42 »
There is no rotation. It's a simple front-back reversal which is being mistaken for a left-right reversal. You don't make the mistake of thinking it's a top-bottom reversal because you aren't symmetrical in that direction (unless you lie on your side in front of the mirror, at which point you will mistake the front-back reversal for a top-bottom one).
 

Offline bizerl

  • Sr. Member
  • ****
  • Posts: 279
    • View Profile
Re: Why do mirrors reverse but not invert things?
« Reply #6 on: 06/08/2013 05:26:28 »
If it is a flat mirror, the paths of light will simply reflect without crossing paths. For true inversion/reversal you would need a parbolic mirror (like in a telescope) which would invert both vertical and horizontal.

I guess you could play around and parabolise (if that's not a word, it should be!) the mirror horizontally and not vertically, then you would see yourself as others see you and it would be very disconcerting.
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 12001
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Re: Why do mirrors reverse but not invert things?
« Reply #7 on: 06/08/2013 17:10:37 »
Sort of fun isn't it? On one plane it is what most expect to be 'correct'. On the other tentacle you would have this nagging feeling of being conned somehow.
 

Offline chiralSPO

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 1880
  • Thanked: 145 times
    • View Profile
Re: Why do mirrors reverse but not invert things?
« Reply #8 on: 11/08/2013 01:52:07 »
If you say left and right are switched, I think it is fair to say top and bottom are switched as well. Left and right are only switched from what you would expect by rotating 180 degrees about the vertical axis (ie. if you turned around). Similarly, top and bottom are reversed from what we would expect by rotating 180 degrees  about the horizontal axis (ie. if you turn upsidedown).
 

guest

  • Guest
None
« Reply #9 on: 19/04/2014 17:57:11 »
well for instance if you hold a card that says A when you hold it in front of the mirror its inverted so why dont we see ourselves inverted??????????????
 

The Naked Scientists Forum

None
« Reply #9 on: 19/04/2014 17:57:11 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length