Impossible Arch Puzzle

Impossible Arch Puzzle
Impossible Arch Puzzle

I found this image in my optical illusions folder today, and wondered why I never got the time to publish it. Look at the picture on your left. What do you see? There must be something strange going on here. No way that the arch shown here has the proper top. Or can it? I’ve also included a solution inside this post. You’ll have to click the expandable box to see it. I wouldn’t want to ruin your solving experience before you’re ready to see the answer. Anyway, by looking at the solution everything becomes clear. Why has our brain presumed the column is aligned differently than it actually is? I really can’t tell, but hope some of you will try and explain this through comments.

Yesterday I tipped you about new Facebook vanity URLs. Have you had the time to check them? Hope you managed to grab something short and unique to represent you, like I did. But it seems not many of you actually read what I post. Probably you check only the illusions, which is also fine. But I’m REALLY curious what names were taken by our audience. Would be very nice to see more and more of you using your facebook logins to post comments. Not only does this automatically shows your image next to your comment, but additionally you have an option to share your comment so it appears in your Facebook feed. This way you can help us reach more people (your friends will see that you left a comment on our site, if you approve it). What is your opinion on this?

[DDET Click To Expand the Solution]
archesb[/DDET]

49 Replies to “Impossible Arch Puzzle”

  1. wow. it actually works! (i hope i’m the first to write a comment ^^)
    it must be something at the top where the column is in front of the peak of the arch…i guess…o.O

  2. It think this illusions works because our brain prefers symmetry. So our brain assumes that the column is in the middle of the arch when in fact it is slightly to the right of the arch.

  3. the arch is extremely possible.
    its just improbable for someone
    to do it. kind of an odd choice
    to classify this as an illusion.

  4. It’s quite simple, the arches are shaped as paraboles. But the brain probably extends the arches in the same direction as the end. Also, because the column is off-centered and shaded darker on the left it creates the illusion of it actually being in the middle (the darkness somehow makes our brain think it is more voluminous).

    It’s also possible the two arcs in the backgroung help create the illusion because they seem to be arced differently than the ones in the foreground. The right one should have a much higher gradient because of perspective.

    And as said before, symmetry is always fun!

  5. Hey there!
    Mathias, I agree with you. The human brain is a weird “machine”…
    I’ve got my pic like facebook users do, but I use gravatar instead. Is this why it requires the e-mail to post a comment? I think so…
    Well, anyway, really cool one!
    Cheers!

  6. It’s because we can’t see it that our brain assumes that the apex of the arch is somewhere behind the column, but not on its left edge.

    This is probably the kind of thing our primitive brains have done for millions of years (and is therefore the stronger instinct). It’s only now with our modern brains do we start looking at things with a mathematical eye.

    Imagine how an animal might see it, they have no idea what a parabola is, but might still need to make a fair guess at where a semi-obscured escape-hole is placed.

  7. nice one.

    It has something to do with the column off-centered. the brain assumes it would be in the middle of the top of the arch, but we see that it’s not. therefore, we think it’s not aligned.

    besides that, it also occured to me that we assume that the most upper left brick would be a “full” brick, instead of the left half one of the top.

  8. actually the column starts on the top middle part of the arch. so it’s not really an illusion at all ;)

  9. Why has our brain presumed the column is aligned differently than it actually is?

    [b] BECAUSE THE POLE ISN’T IN THE MIDDLE OF THE ARC! IT’S ON THE SIDE!!! [/b]

  10. This appears to be a variation of the Poggendorf illusion. There is no one commonly accepted explanation. There are physiological ( Huble and Wiss), visual consistency and cultural explainations.
    Ther is no doubt that the length and intersection of Vertical lines accounts for the effect. Reduce or eliminate the intersection of the vertical and curved lines and the effect reduces. rotate the vertiacl lines and the effect reduces. this is one of the strongest illusions of its kind.
    There are a variety of of explainations here: .http://www.psychologie.tu-dresden.de/i1/kaw/diverses%20Material/www.illusionworks.com/html/poggendorf.html

  11. This is simply another Poggendorff Illusion: an illusion that confuses the human brain when trying to join a diagonal line when it is obstructed by a vertical or horizontal bar. The only difference is that this is in a real life situation where most Poggendorff illusions are just lines.
    This has nothing to do with symmetry Zwaan; the pillar is clearly off centre in this pic.
    Vurdlak you posted more of these Poggendorff illusions on 10th Feb ’09.
    Peace!

  12. Actually, no one above has noticed that the eye and the brain are both working normally here, and nothing is wrong at all with the misperception.

    Look at the right half of the arch, now look closely at the vertical support for it. Notice how it is shaded. Notice how the vertical support for the left side are not shaded.

    Shading, without any other clues such as just what is causing less light to reach the right side, naturally make the shaded item appear further away or smaller, but definitely NOT in the same plain as the unshaded side.

    Do note that the shadows case by the column in the middle ore not the cause. Its just the artist shading the right half and left half in different manners.

    It has nothing to do with the apex, or the offset of the obscuring column, its all in the shading of the right side vertical support. Our brains would naturally extend the line of the arch correctly, but for the shading, it doe snot make sense for it to be in the same plane.

    Without the column, the shading on the right side would be correctly perceived by the eye/brain as ‘wrong’.

  13. Dumb illusion. the column isn’t “tricking” us into thinking that the apex is behind the column. We’re expecting the arch to be circular instead of having a point, so when the point is hidden, we expect it to go a different way.

    It’s like putting something in the road that obscures a turn and saying “HA! The road turned, but you didn’t see it because something was in the way! What an impossible road!”

  14. You can also see that the center dividing column and the arch support columns on the right side have their shading on opposite sides, differing light sources. This also works to confuse the eye/brain.

  15. Hello! I don’t comment much, but I’m here every day. Love the site! I frequently use your illusion of the day for my wallpaper. Make it a little more interesting when people walk by.
    Thanks for keeping me entertained.

  16. Yea, I expected the solution. When I viewed it in igoogle, the image was smaller and I could not see anything wrong with the arches. But when I expanded the image, it looked off. Cool illusion!

  17. it’s probably because when the eye sees the curve or the arch the first thing we think is the arch is rounded. also because the column is in the middle we assume that it goes between the middle of the arch.

  18. Great!
    I think its confusing because the pole is not in line with the peak of the arch.
    ~Asianpearlkeeper

  19. It doesn’t really work. If you look very carefully, the red line in the bottom extends the right column to the empty space right beneath the left column and the top line extends the top of the left column to the empty space right above the right column. It is actually the connection that’s an optical illusion and not the initial picture.

  20. Not an illusion- not impossible either. It could be real, just with rubbish architects working on it. Could be a simple mistake. I could do it at home.

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