Just come across this combination of two great illusions to create a stunning new effect. Believe it or not, the two horizontal lines in the picture below are the same length…

Do you know which psychological principles are at work here? Have a good day!


  1. Ah yes, the principle of unquestioning gullibility. We are told something is an illusion, and we say, “Huh. Interesting, that’s amazing”.

    Those lines aren’t even close to the same length! It’s easy to meaure them on the screen.

    April Fools?

  2. I would note that it is April 1 (nearly) making it clear which psychological principles are at work here. (Gotcha! for one.)

  3. Psychological principle: Er..Bullshit?

    On my computer, the upper line is 42 cm, the lower is about 60 cm.

    Perhaps you are trying to teach us not to trust authority figures?

    1. LOL, A nice size screen with terrible resolution…unless you meant millimeters. If I measure in millimeters, I get approximately 42 and 60.

    1. And if you want I’ll even sell ya that prime location…..you can see the beach from your front door too! Location, location, location…….

    1. Good point! Perspective view could be a way of seeing two lines with equal length. Otherwise its just April fools day 😉

  4. April fool games.

    ”Believe it or not, the two horizontal lines in the picture below are the same length…”

    “Not” is my answer.
    This is new.

    Which psychological principles are at work here?

    The concept of experience.

  5. The lines are the same length, though measuring them with a ruler on your monitor will not give you an accurate reading, due to the variable width of pixels used by different monitor manufacturers.

    This just highlights the need for a standard pixel length to be implemented………

  6. the whole is larger than it’s parts. whole patterns are perceived before detail. results in preconceived proportions.
    ‘ow’s that for a theory ?

  7. enlarge picture, leftklick upper line,drag it down to lower, then up again. that experience amazes me. am i pixillated ?

  8. Perhaps the only way to deliberately see them equal is to assume that the red triangle be a path of fixed width (like a red carpet or something )and viewed at such an angle and these horizontal lines were marked on it…..

    otherwise …………….. no chance

  9. Nice Illusion, Richard. I had to use a rule to confirm what you said. Having said that both traces are identical, my inner visual correction mechanisms should have used the triangle behind to correct the perceived lengths of the lines… No way, although I confirmed that the lines has the same vanishing point as the triangle, I still see their “vanishing point” considerably below the right one. The illusion messed considerably with my perspective sense, although I don’t know how to describe the psychological principles responsible for that, as you challenged.

    PS.: Nice fool’s day joke too… not may perceived you were talking seriously. 😀

  10. The lines are, in fact, exactly the same length. It’s an optical illusion. You have to stare at the screen, try not to focus your eyes on anything, just keep them relaxed. Then you’ll see it.

    If it doesn’t work, just stare longer. You’ll get there!

  11. Did you see he wrote “the same length…”

    Notice the elipsis, indicating there were more words to come. Possibly “…whether you view as a .jpg or .png”

  12. Ahh yes. I was puzzled when I got a pen cap to compare the two lengths, and found something rather different than what you said, before I realized the date.

    1. I know for certain it is. I also know a bunch of people are gullible enough to go look it up. Nice try though. Seriously.

  13. Brilliant. I had to actually measure them on my screen with a pen to make sure I wasn’t losing my mind 😀

  14. Great! measured it too with my fingers.

    Funny, i didn’t aspect an April Fools day joke from Richard. Maybe because he is a scientist. But he is always misleading with illusions and such. This is a logical consequence.

  15. Given: The “red road” is defined by 2 parallel lines stretching off into the distance.

    Observe: The distance from the end points of each line to the road edge is equivalent.

    Conclude: The lines must be the same length.

    Principle at work: All space/time constructs are relative. Given the right perspective, all things are equivalent. Somewhere, everyday is April 1st.

  16. Actually, they’re exactly the same length. It is the very act of measuring that makes them unequal. If you don’t measure, everything is working perfectly.

    Great illustration of the “homeopathy principle” at work here.

  17. I LOVE THIS! So far I’ve caught two children and a husband using this bait. Thanks, and keep on tricking!

  18. What a weaselly comma-splice! Replace the comma with a colon and the wind-up is starkly illumined.

    Good one, Richard. Happy April 1.

  19. Maybe I’m missing something here. I measured the two lines separately on my screen and the bottom line is longer.

  20. Perhaps the psychological principal at work here is the power of suggestion. The lines do not measure as the same length but a check on today’s date shows that it is All Fools Day once again!

  21. good one! Snagged me with intended effect. As I was familiar with the classic version of this illusion I assumed this was an enhancement.

  22. Ah yes, Feinmark’s Principle of You’re Gonna Have to Do Way Better Than That to Fool the Kind of People Who Read Your Blog, Mr. Wiseman!

    Happy April Fool’s!

  23. If the red is treated as a simple triangle face-on, then the lines are obviously different.

    This would be an ‘April Fool’ (Poisson d’Avril in France).

    However, if the red triangle is, for example, a red carpet of infinite length disappearing into the distance (Perspective), then the two lines (I’m imagining Stair rods) would be of the same length, laid on the carpet.

    If you don’t believe me, place a straight edge at the vanishing point and run it to one end of the ‘longer’ line – it will touch the end of the ‘shorter’ line, thus showing, in perspective, the lines are indeed the same length!

    I waited until today to comment, in case anyone thought my ‘Perspective’ answer was an attempt at an April Fool.

    Is it an April Fool joke? Yes OR no! (It depends on how you think!)

    1. You waited too long. See my comment in the morning of the day before. And yes, I think is was an April’s fool: Richard convinced a lot a of people he was playing an April’s fool with the illusion when he was not… 🙂

  24. I didn’t buy it for a second. I said “No way!”. I realized that my eyes didn’t just move vertically to jump from the left end of one line to the left end of the other (the same with the right).
    I measured with a paper clip, but only to see the actual difference.

    That’s my story and i’ll stick to it. ¬_¬

  25. Ahah but they really have the same length, it’s not an April Fool.

    Just a perspective view. Think in 3D view, not as a 2D image. It’s not a triangle, it’s a long red road ending at horizon.

    So, the line have same length!

  26. The psychological principle which works here is…er… we tend to exggerate the ones close to us! No? Then perspective. :))

  27. Brilliant! Had me fooled twice… first, I thought, “no way are the lines the same length, oh it’s a clever April Fool’s Illusion.” Then I read some comments, and realized the Perspective angle, in which case they are indeed the same length. I love it!

  28. I agree. In reality the lines are quite different in length. As seen in the perspective of the triangle they look to be the same length. Perspective is an illusion used by artists to make things look as they might look as they recede into the distance.

  29. The lines are the same length. It’s just that Ariel perspective fools the brain. If you were travelling (walking) along a road, and measured the first line length, you would find that as you approached the second line its length would seem to increase up to the same as the one now behind you. If you look back, you will see that that one now looks shorter!

    1. The lines are indeed the same length. And I agree with Anthony.. The line in the distance looks shorter but it’s actually the same length if you approach it. If you look behind your back then the first line is shorter. The triangles on both sides of the lines are fooling the brains as the first line seems to be shorter but reality it isn’t!

  30. Funny as it may seem, the anwers thus far are not only incorrect but indicative of the psychological factor involved in the puzzle. They are all exhibiting something not unlike the “ladder of inference”, where the observer believes they previously solved this puzzle, but, in fact, it is not the puzzle they have seen.

    The puzzle is that it is NOT the puzzle they knew so well, but something that looks quite like it. They strive to explain the answer they have for the other puzzle (an optical illusion), yet the answer is wrong.

    Unfortunately, I can not remember the psychological term for this. XD

    Damon Lyon

  31. Very good. This is confusing yet simple. The are very equal. Perspective, imagin that this is a long road…..heheheheh

  32. Well nominaly there effectively not same length. But if you use THALES’s geometrical tool box (can’t find the name in english sorry) you can see that if you devide the length of the shorter black line by the legth of the longer one it’ll give you roughly the same result as if you do the same but extend it to the border of the triangle.

    So just as with the man eaters we can say that this statement is true AND false. If you mesure it it’s false but if you try to represent something in 3D (perspective) it’s true.

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