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Physics World at 25: Puzzle 1

By Louise Mayor

Physics World at 25 Puzzle

This month is the 25th anniversary of Physics World – the member magazine of the Institute of Physics – and in addition to a special celebratory issue, we’ve decided to set you a challenge.

In fact, we have teamed up with GCHQ – one of the UK’s three Intelligence Agencies and home to some of the country’s hottest code-breaking talent – to create with us a set of five physics-themed puzzles. The puzzles have been devised by three GCHQ members of staff, who today we still know only as Colin, Nick and Pete. (Thank you, guys!)

Below is Puzzle 1, the first of the five. The rest will be released on successive Tuesdays throughout October on this blog. The first is the easiest – they only get harder from here on in!

You can check your answer for each puzzle using the box at the bottom of each post. If you enter the correct answer, you will be told you’re person number X to have done so. But will you be the first?

Once the fifth and final puzzle is released, then you’ll be able to check all your answers simultaneously in one master answer-checker, and see where you rank overall in solving in the Physics World at 25 Puzzle. We hope you enjoy the challenge and that, as there are no prizes, the satisfaction of completion will be a big enough reward.

Your first challenge lies below. #PW25puzzle


There is a word missing from the following. What is it? (Enter the answer in its encrypted form.)


Enter your answer here

This entry was posted in Physics World at 25 Puzzle and tagged , , , . Bookmark the permalink.
View all posts by this author  | View this author's profile


  1. Please be a good sport and DO NOT post the answer in the comments.

    By all means discuss the puzzle in the comments. You can check whether your answer is correct using the box above. Happy puzzling!


    Puzzle 2 is now live! What will you make of Schrödinger’s puzzling puss?

    All posts for the Physics World at 25 Puzzle can be found here.

    • Pete

      Unfortunately Louise, nobody posting comments is discussing it – simply preening themselves at how clever they are. Nobody would want to think themselves clever if they thought they were like this lot!

      • Stumped

        Im stumped. Ive read through all the comments, stared at the letters, researched ciphers and code breaking and I have NO IDEA how to solve this. Can someone please give me a hint or something more concrete to go on. Many thanks in advance.

      • Stumped, there has been some nice advice in the comments about how to start. I think reading what Andy Marshall said would be helpful. Don’t lose heart at not solving it straight away – it took me a good deal longer than most people who’ve commented here.

      • Susan Mc

        It took me a while but I got there eventually, I found it really helpful to look at some of the websites about letter frequencies. The most common letters and letter combinations in English gave me a place to start.
        Google’s great but I used

      • True! Absolutely agree.

    • antony r

      There was a tricky point about 1/3 to halfway through and I was stumped last night, but today it was obvious :)

      My tip, is to assume they aren’t trying to trick you or lead you down a false path – that should help some of you.

    • ray miller

      didn’t think i’d get the answer, but it turned out to be easier then I thought. 15 minutes and 2845. good answer!

    • Jack

      Loved the answer!

    • Matthew

      corrrrrr blimey!! that blew out the cobwebs from the Grey matter. got there in the end though, wont say how long it took, lets just say 14 years printing shirts didn’t help solve it 😀

  2. michael john

    neat answer!

  3. Leum Fitzgerald

    There are no ‘A’s or ‘O’s in the code

  4. MR

    12th !
    Nice puzzle.

  5. I solved this one in 20 minutes but I’m Italian, I live in Italy and I’m not a scientist; I’m a photographer. I’m including an hint on the title of my gallery to prove it 😛 ah ah …it was fun thanks!

  6. Hardly tricky, but a clever answer :)

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  10. David R

    299th and it took me an hour

  11. Joe I

    311th 😀
    that was fun. Took 15-20 minute?

  12. Andy B

    Took under half an hour, once I spotted the clue, That made it easier.

    Looking forwards to the next one :)

  13. Martin

    Fun – not done anything like this in a while. Took 20 mins – No: 341 Look fwd to the next one :)

  14. Bob Wakelam

    Very clever answer!
    Took me just under 20 minutes.

  15. Adrian Klemens

    Just saw the article on BBC website. Took 10mins. 371st. Looking forward to next week!

  16. Andras Zoltan

    Very cool.

    Was two hundred and something-th.


  17. Peter S

    408 spent ages getting the last letter instead of just thinking a little!

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  20. Quexlia

    The answer made me smile. Nice one. :)

  21. Dom M

    Found on BBC – not been a member for years – more’s the pity. 414th – took about 30mins. Chuckled at the answer the answer

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  23. 474th

    Nice puzzle.

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  25. Walter

    # 419. Answer was so cool I had to double check my decoding! Took me about an hour, including setting up a spreadsheet to do the VLOOKUPs.

  26. Just_Some_Bloke

    #500! I’m just proud to get a round number! took me 2 hours mainly because i thought it was deeper than it was!


  27. BB

    Cute – very cute, is that GCHQ job still going?

  28. TheWizardOfOz

    Nice code for beginners!

    The irony of the answer is appreciated too :)

    Good website explaining some encrypting basics:

  29. Hazel

    Number 555.
    Clever puzzle. Pleased with myself for working it out, although earlier comments suggesting it was easy may mean I have reached my limit.

  30. Jeffers

    Great answer! number 445, took roughly 20mins. All falls into place once a few words have been found!!

  31. Jean Delefrati

    I was #475…


    Thank you!

  32. schotten1944

    Nice puzzle; enjoyed it a lot. Once the penny dropped it was straightforward but I liked the twist with the keyword,

  33. Stephen


  34. Jean Delefrati,


    • Jean Delefrati

      Obrigado, Louise, vou esperar. Até lá!
      Thanks, Louise, I’ll wait. See ya!

  35. Tobicas

    Wow I did it in 26 minutes – I am astounded! I used to love this type of puzzle but it’s been a while, and yes the answer is pretty cool when you get to it! I was 704th in the universe, which for me, is now a magic number.

  36. Chris Wright

    Came from the BBC article and got 179th. Looks like that publicity has made a big difference since it had already been available for 2 days and we’re up to 704th already.

    Again, kudos for the answer. Nicely set up puzzle. Will be very interested to see the next ones.

  37. Jaki

    Ha ha. Great puzzle! My husband Fraser and I did it together in only around 5 minutes. Bring on the next one!

  38. The Delegator

    790th!!! think it took me about 5 mins to break, which was the time it took me to realise I wasn’t going to break it personally and to choose a different approach :)

  39. Cameron

    837 – took me longer than it should have done… didn’t read that the answer had to be encrypted and was swearing at my screen, convinced I was right and the webform must be broken… now I get it…

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  41. Paul Jeffreys

    I actually laughed out loud when I translated the missing word back into code. Much amusement lol


    • James

      “I actually laughed out loud when I translated the missing word back into code. Much amusement lol”
      Likewise – great fun Colin, Nick and Pete

  42. Alan Denton

    under the magic 1000 😀 (921st)


  43. anona bob

    confused myself at the end because i did remember it said ‘Enter the answer in its encrypted form’ lol

    very nice puzzle

  44. JULIE G

    Took me 30 mins. Not knowing any physics at all it didn’t make any sense to me until I searched online and, yes, it is clever and I would have solved it sooner had I taken Physics O level!

  45. Tom

    I’ve solved it (1037), but my method was horrendous, is there a simple way?

  46. Dickie

    Came via the BBC website, it was fun! 981st in about 30mins.

    As with Just_Some_Bloke – HYMP HMT PYN VSQN?

  47. Just got the lovely 25th anniversary edition of Physics World through the post today. Enjoyed solving the cipher, and a delightfully satisfying solution when I found it. I came in 1066th, and it took me just under half an hour (pen and ink method), but it’s not a race!

  48. Stephen

    1096 Embarassingly slow for a theoretical physics PhD

  49. KB

    1079th – very neat answer made me smile too :)

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  51. BH

    1219th, took about 15 minutes, nice answer!

  52. Matthew

    This is a fairly easy class of problem to solve. I wrote a computer program to do it automatically, because I had been reading The Order Of The Stick, where one of the characters has a mental breakdown and starts speaking in code. Have a look at the url

  53. Grant

    1159 and it took me about 15-20 minutes. Are we saddo’s or is this fun?

  54. Andrew Carnon

    Very clever!

  55. RR

    No. 1331. Took about 7 minutes. Looking forward to the rest. Clever answer!

  56. 1322 – I wish I heard about this puzzle earlier, it would have nice to have been one of the first to crack it. Used techniques I taught myself when I was 11.

  57. Jason

    Neat answer. Took me about 45 minutes I guess.

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  60. Heidar hardy

    You thought 2Y’s UR, 2Y’s UB, ICUR, 2y’s 4 me, but I got it anyway. Neat. Thought there had been a typo til I reread the question and found the word was MEANT to be missing!!!

  61. Steve H

    1430 – in 20 minutes, cool answer.

  62. Mary

    Got it! 1434th person to break it!

  63. JC

    My 14 year old daughter just finished this in 20 mins!

  64. Carl Glynn

    Never studied physics in my life, so had never heard of the answer. I cracked the code with pure logic in 45 mins with my 3 kids aged 7, 4 and 2 distracting me.

  65. pat

    1460TH. Anyone else confused about the first letter of the answer (in code). I worked out what it must be, but get a different letter for the first by deduction?

    • veronicarose

      No, sorry. If you translate the original message correctly, the final answer makes perfect sense however you look at it. I didn’t know the physics, but made an educated guess and googled to check my missing word.

  66. andrew w

    #1427 took about 45 mins – what fun!

  67. mini falcon

    Never done anything like this before (and no physics for 20+years) but managed 1486 after seeing this on the bbc website. About 40mins but pretty quick once you get the hang of it! And a good answer….

  68. Jud R

    I am Number 1458 and found it fascinating fun, many thanks to the puzzle maker for your time and effort

  69. Rob Smithson

    1531 wasted a lot of time looking for a pattern in the code, once I just did it the old fashioned way it was much easier. Get a pen and paper out :-)

  70. Dermot

    Just found this from the BBC Website.
    I am number 1541 and like a previous subscriber I laughed with delight when I got the answer ! What a neat idea !

  71. Neil Stewart

    I came across this in an article in the i newspaper this evening. Never tried a cypher puzzle before or studied physics. Completed in an hour 1527th. I look forward to subsequent weeks to find my level of incompetence!

  72. Aidanr

    …YO FWD MIAE TUNLSRC QHP or I will rend thee in the gobberwarts with my blurglecruncheon, see if I don’t.

  73. Dingo

    1.5 hours, but proud to be number 1555.

  74. Dave

    Cant do it. No idea. Any clues?

    • Bob

      This cypher (NOT A CODE! Pedant here!) has word spaces. What common single letter words are there in English? Also 2 letter and 3 letter ones? This should give you a good crib to start!

      • I don’t think it’s fair to say this is not a code as I do recall the first encoding method similar to this was invented by Julius Caesar, and that was called Caesars CODE.

      • On second thoughts I thought it best not to rely on memory and check which was correct. There is a difference between codes and ciphers and technically cipher is more appropriate, but a cipher can use a code so the difference isn’t that big.

  75. Mishius

    Yay, #1648. Was tempted to give up and go to bed but glad I stuck with it. Satisfying solution.

  76. Les

    1621 got it after an hour-I might try this as a chat up line.Did you know_________?

  77. number 1675
    14 mins
    Nice answer

  78. Graham

    #1726, smiles all round, and round, didn’t think I was going to get it!

  79. jennifer

    Loved this and the twist at final word – it brought a smile to my face. Took me longer than others to complete but i am just pleased i completed it (Number 1716)

  80. mansie

    1655th – I’m happy with that! But I’ll be ready and waiting for the next one and not 10 hours late!

    Nice touch with the answer!

  81. sarah

    got it!!!

  82. Gurjit

    #1793: Clap Clap Clap. Waiting for the next.

  83. David

    Its good to keep the brain cells ticking over but as the month goes on hair might be torn out.

  84. peter vaughan

    good little puzzle. Pencil and paper was the best way. Took about 15 mins.

  85. o.n

    how many encoding methods have they used? (just substitution or a few others as well).

  86. Cary

    It can be done – just start small!!
    Also smiled at the answer

  87. Mike

    No idea how to start. Somebody please leave a clue!

    • veronicarose

      bob has already left a clue about 13 comments above your comment. Also, what are the most commonly used letters in the message? What are the most common letters in the English language?

      • o.n

        I take it its a simple substitution then?

      • Mike

        Doesn’t help! OK I can guess t,o,h,a an e but the code isn’t long enough for statistical analysis to get anywhere and the keyword does not obviously fit anywhere. Please give me some clues! I need to get some sleep!

  88. Ian Chapman

    1882 (also the year of birth of Max Born). I only just found the puzzle, but I made an inspired guess at the content straight away which took me about 5 minutes with a pencil and paper to confirm. :-)

  89. Medikon


    Good momentary distraction. About 15mins with pen and paper…

  90. o.n

    ok seriously for those of us with NO experience with codes what are we even looking for? Doing the common letter/word search helps narrow it down very slightly but it is not enough.

    • Mike

      It is a substitution cipher but with no keyword., The colon is the missing word, not punctuation and the plaintext isn’t on any web page. Don’t give up, it’s very satisfying when you get it.

  91. A fun distraction while I’m waiting for my sequence alignment to finish. #1973

  92. Andy

    1998th! Under 2000, counts as a win… took a good 20 mins and a hastily-assembled excel sheet…

  93. Harry Willis

    1995. Groaned at the answer. I thought from the comments that it would end up being some awful physics joke… y’know, the “neutron walks into a bar” sort.

  94. Mark

    Good fun. 1999.

  95. Phil Rippingale

    #1980 – fun puzzle and a nice answer. However, some very few of the comment entries above remind me why I left Mensa…

  96. Cliff Jones

    A little too easy – I expected aces to represent a letter and a letter a space. Does the fact that one answers without submitting an email address indicate that gchq already know who I ami? Will I be in trouble for pressing submit 100 times?

  97. Frustrated

    Somebody please give me a clue. I have run into a wall. Is there a keyword?

  98. Paul Wolfram

    20 mins. I liked the twist in the anwser.

  99. Bruce James

    I was number 2028.

  100. Chris Clark

    2047, but at 30 minutes I’m getting past it…(next person to solve it gets to be number 2^11!). Nice twist as the answer though.

  101. Rothcoe


    • Mike

      Got it! Dead chuffed but I think that’s my limit.

      BTW I think you mean MSS PEE NMLD.

      Smug mode – Select

    • Mike

      Apologies. No misspelling. Nice pun. Understand why you found it easy and I took 3 hours. Enjoy the next one, I almost certainly won’t!

  102. Carlos

    Clever answer. Took 5mins. No. 2085 (2nd set of digits minus first set are the last two digits of my year of birth). vynnut!

  103. James Grant

    2095 Took about 20 mins. Nice puzzle guys.

  104. Conor Casey

    Very nice puzzle! Looking forward to the rest!

  105. Ryan Hynd

    Took 15min on tablet with incredibly cumbersome office replacement. Should have used pen and paper!
    Answer made me chuckle

  106. Jez

    Took me nearly an hour. Was hoping it would be a Caesar cipher. No 2121

  107. Daithi


    I had the basic idea almost immediately after I remembered a code book from school days. Unfortunately my astrophysics ain’t what it used to be hence it took me a while to figure it all out.

    Fun little answer though :)

  108. Steve

    FINALLY! Not until I reread the instructions did I realise I had to answer the question in cypher. Doh!

  109. Malc Cox

    Took me a while, but very proud to sort it. Good brain food, thanks for the challenge. 2150th the only way is… Up.. Down or sleep. Ttfn

  110. tuftyaurelius

    This drove me crazy because my poor vision due to diabetic retinopathy caused me to mix up certain letters eg. “N” with “M” etc but I eventually got it!!!!!!! Not a “law” from Newton but the other guy…

  111. Andy Marshall

    Number 2149 to solve… code broken in 30 minutes, then wasted an hour encoding the missing word using the codes ‘the wrong way around’… when I finally tried it the right way around… DOH!!!

    To Frustrated, how I started was as follows:
    start small and build from there. The smallest word is 1 character in length, so how many words in English do you know that are character in length? That will lead you to your first letter, and then that letter appears several times in the code, so you have a foothold in a number of words. Next look at the words that are 2 letters long. There are more 2-letter words in English than 1-letter words, but make some educated guesses, then try substituting letters based on your guesses. Just keep building one letter at a time, and as you get more letters and substitute them into the code, you’ll get closer to solving the whole thing.

  112. Jason Gow

    Good fun, looking fwd to the next one. #2157

  113. Neo Dog

    No. 2158, but only after 3 attempts.
    Failed attempts due to inability to read the requirements correctly. D’oh!

    1) Missing word only, not the whole sentence
    2) Missing word to be encrypted.

    Nice distraction from work though. Thanks!

  114. Ilan Filondz

    Number 2188!!! WOOOHOOO

  115. S.D.R.

    No. 2220! Did not take all that long!

  116. Claroid

    No. 2223 enjoyed the challenge.

  117. Pete

    #2227. great answer! I was looking for a pattern in the reverse encryption, but then of course the result was it. Some quick excel formulas helped too. Cant wait for the next.

  118. david ramage

    Great little puzzle. Took me a while, started off with completely wrong approach.

  119. tatang ng klase



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  121. Terry P

    Nice. :) Enjoyed that but bet the rest won’t be a doddle. 😀

  122. Joe Godfrey

    It might help if I actually read the question, cracked the code and spent ages putting in loads of stuff, then read the question properly.
    Neat answer

  123. D.

    Wow,I’m 2300!!! The coded answer makes the puzzle worth solving!

  124. allan

    That was satisfying, didn’t think I was going to be able to do it, but in the end it just sort of rolled out with a bit of logical thinking and using excel, in about an hour. Came it a #2306, but who cares it was fun. Suspect they will get rapidly more complex than this though as they come out.

  125. DM

    That wasn’t too hard. No 1335

  126. david j

    Finally got round to looking at the BBC web-site. 15 minutes and a cup of coffee. Neat! Many hours spent with the “i” codeword puzzles helped with this one.

  127. Alex Y

    #2501, spent far too much time playing with spreadsheets, slept on it, 5 mins this morning (though 2 hours last night).

  128. Ho

    pen & paper > spreadsheet
    c15 mins or one and a bit episodes of Adventure Time

  129. Great puzzle – got the missing word but how do you get the rest of the alphabet??? stumped – can’t see the pattern!

  130. One commenter mentioned a clue and a few people have been wondering what that person meant. I have no idea either!

    • Brian QUinn

      Might this have been the two words starting ZSM? This narrows down the possibilities for MUD which then becomes one of a small number of possible suffixes.

  131. Nearly 24 hours in and we’re really chuffed that so many people have been enjoying the puzzle. If you don’t want to miss the remaining four puzzles, you could subscribe to our newswire, Twitter feed or Facebook page, or just put the dates in your diary: 8, 15, 22 and 29 October – all the remaining Tuesdays this month.

    Congratulations to all solvers so far! For those yet to complete the puzzle, don’t lose heart if it’s taking you longer than the fast times people are reporting here. I enjoyed it very much and took longer than most people who’ve commented.

  132. wilder001

    #2605 – Wondered why all the “neat answer” comments – but it is a good answer. Letter frequency is the key I think.

  133. BRIAN

    2621, great puzzle

  134. Paul A

    Read far too much into the complexity of this.
    About 30 minutes with a false start .. fun though.

  135. Justin Davies

    Quick spreadsheet helps speed this up.
    great fun, looking forward to next week now!

  136. Usalman

    2667, happy with that, nice little puzzler :)

  137. Iain Forbes


  138. Jamesp

    2679th. Got there in the end, but hope someone can explain how to crack it quicker.

  139. Chris B


  140. Sunil

    2726 …. the fun part was the missing word’s encrypted version 😛

  141. Mark C

    Was thinking too deeply to begin with, but once I worked out the solution, took me about 25 mins. Was #2723.

    Looking forward to the next puzzle.

  142. Not sure whether I should consider using a computer as cheating? Wrote it down, started guessing a few letters, then got impatient so brute forced it. #Fail? #2765

  143. Dazza

    I wasnt the first person to get it in my department, but I did get it :)
    Nice puzzle – and loved the answer :)

  144. Elias

    2817! ahhahha nice!

  145. Stumped –
    Start as I did by assuming that the phrase is in English.

    Then there are several 1-letter words: there are only 2 possible letters used in 1-letter words in English “I” & “a”.

    Then there are some 3-letter words: the commonest 3-letter word in Englsih is “the”. Try subsituting for each…

    Thst should get you going.

  146. Alex

    2846th, hylvy lt tquzultlrsd she l sylra

  147. Alex

    Really there should be another word at the start but that would have needed m zettnttlfn mzelpuezyn. I suppose punctuation like that would have made it much easier.

  148. reverend jayne

    My goodness!! Wasn’t going to give up.. Started this when people were numbering in the low hundreds yesterday… Just solved now, I’m number 2930th !! I am “TEEEE ZUEQI” :)

  149. Hi, I desire to subscribe for this blog to obtain newest updates, therefore where can i do it please
    help out.

    • Scott, check out the blue box at the top-right of this page that says “Free weekly newswire”. You can click through there to sign up. Thank you.

  150. Greek geek

    Nice puzzle. Number 2941. Only just saw it and took around 15 mins when I realised that it was famous. Tip : don’t go around in circles trying to solve it!

  151. Aydin Deger

    fantastic puzzle!


  152. Jen

    3012 – took me an hour but that was interrupted by phone calls. Good puzzle

  153. Stuart Bradshaw

    Yep good puzzle (#3036) – you will be in no doubt when you get the right answer. It was the word just before the colon that unlocked it for me – I spent quite a while orbiting the answer and not really getting any nearer, but I got it quite quickly after that.

  154. Jo

    Well thought out puzzle. :)

  155. Gerrit Wessendorf

    #3171 – That was fun! Can’t wait for the next one :)

  156. Brian Quinn

    PEE YMUI GEU KN without help from Poe’s The Gold Bug and some of the coded posts. Number 3192, done in two sittings. I’ll take that.

  157. Snehal M. Shekatkar

    Didn’t think that I would go so much back in time with this! :)

  158. James


  159. Karen

    Puzzled over this late into the night…worked on it again just now and managed to crack it, just as my husband walked in from building an astronomy exhibition at HoP. Am triumphant…and not a Physicist or in Mensa, just a lowly TA.

  160. girish


  161. n0tMaRK

    that was hard, I thought the wrong way! two hours but I did it! 3288th

  162. Ecaterina

    No 3054 :)

  163. Ashish

    3407… just happy that was able to complete the puzzle 😛 looking forward to the next ones..

  164. Tobeyjd

    # 3434 :)

  165. IBuxton

    lovely pencil and paper job. see also Simon Singh’s ‘The Code Book’ for something in a similar VEIN.

  166. vimal

    #3440 Wasted a lot time thinking is a caesar cipher as commented above when actually its not the case. Reminds me of a word game on the ipad. For those struggling start with deciphering M EG PE & PYMP, that will give you enough to get started. The missing word is indeed very clever.

  167. FrankM


  168. amy

    I find the meaning of whole sentence….struggling for that particular word in sentence….
    wasted a whole day…
    plz give me some clue or hint that i can find the missing word…plz help me…

  169. Bahman

    My number is 3539 for 3 min. :)

  170. Ezekiel Romero

    3566! :) LP HML HEUPW PWN NGGEUP! :)

  171. AndyT

    I enjoyed that, and the enciphered solution was an elegant touch. Looking forward to the next one. :)

  172. JohnJFAR

    That’s a beautiful answer. I did an out loud smile when I got it.

  173. Blauco

    Barely one min. Nice.

  174. Chris F

    Fab answer!

  175. CLC


  176. John Payton

    Enjoyed puzzle and completed it in 30 minutes but no idea how to decode ABBC GOW ?

  177. Jorge

    #3771,laughed so hard at the answer, i wish i could have seen this before.

  178. Ben

    Oh very cute! Took about 5min after the first couple of substitutions

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  180. Sixties Sailor

    No 3752 – about 5 hours in total. GCHQ will have to wait. Cracking this “simple” code makes me look at the exploits of Turing, Tutte and Co with even greater admiration.

  181. Francis G

    #3780 Now that was good, made some stupid mistakes that made me laugh out when I actually realised. Love the answer to.

  182. Parky

    Happy with that i dont do these problems often but did this in about 20 mins with help from a crossword solver and google to get the missing word (cheating or using initiative??)

    Started looking for obvious vowels then double letter cobinations then used the crossword solver for ideas. no.3783

  183. Rivet N

    Interesting to note that the first word in code is an anagram of INVERT :)

    • Clive T

      Yes, I also spotted the anagram of ‘invert’ in the first word and it sent me off on a bit of a tangent for 5 minutes as I thought it might be an instruction…

  184. Beth Wales

    The last time i did one of these was 50 years ago,but enjoyed this simple cipher so much ,I might even attempt the next.(if it doesn’t send me bananas first)Thanks to the setters.Good fun

  185. Tintin

    3892, i’m getting old

  186. sam

    took me about two hours, was good fun 3939th. looking forward to the next one!

  187. Matt S

    Each letter represents another letter, the phrase is in english, so is relatively simple with a logical approach. Took about 15 mins (using of Excel to decode, and Google to search the phrase)

  188. Simon

    Woop, 4005… Helps to encode the answer the correct direction

  189. Clive T

    An excellent first code, and I loved the answer! Only found this today so I’m 4017th, but will hopefully get in quicker with the next one.

  190. John

    Just found this on the bbc link today. Great little puzzle and a clever answer.

  191. Ernest

    Nice, but since I only found this half an hour ago I am 4073rd.

  192. Nate D

    cracked the code in 10 min, found it fairly easy, but then proceeded to miss read the code when encryting the answer.. took me a further hour or so to try everything i could think of before realising my mistake! looking forward to the next one.

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  194. Hank

    Well played! I needed a break from a deathmarch software effort and this made a good one. I made the computer do a lot of the work — revenge is sweet. I’ll keep an eye out for the next one.

  195. Steve

    4190th. Took me longer than I’d care to admit, but good god, the satisfaction

  196. Puzzle 2 is now live! What will you make of Schrödinger’s puzzling puss?

    All posts for the Physics World at 25 Puzzle can be found here.

  197. Simon

    Took about an hour and had to learn how to decipher. haha

  198. Dave W

    Finally!!! 4872nd, awesome

  199. Marco

    I couldn’t figure it out… So I ended up writing a quick piece of code that substituted every possible letter combination with another letter combination one word at a time, putting out a massive txt file. Then I used a dictionary program to check spelling and deleted nonsensical words until I got the answer…. I guess that’s cheating (but I wrote the program to help me cheat, so does that count?)

  200. Me

    I liked the twist in the answer, but the system is telling me that I have it wrong. I tried one word, and the word encrypted. Guess I’m a better codebreaker than physicist.

  201. Corrigan

    Thanks to the creators of this enigma for the pleasure I derived from solving it. Roll on two.

  202. Lloyd Dawes

    Took me a while (about an hour), but a couple of assumptions and a leap of faith got me quickly to the end.

  203. Shy

    Wow! I am person 5057!!!
    It took me less than an hour to decode it BUT it took me overnight to determine what the missing word was.. WHEW!!

  204. Kumaran

    I am 5155 .. it took many hours..and finally I solved it after solving second puzzle. :)

  205. Dominic

    Spent 2 hours writing a substitution-cypher decoder based on a brute force dictionary checking algorithm I designed.

    Once I’d started it running I did a back of the envelope calculation to guess how long it would take, and decided 10^22s was too long.

    Once I started it by hand, took around 10mins. Nevermind, I enjoyed my Python programming.

    I also chuckled at the answer.

  206. Dominic Cook

    Good challenge. I relly enjoyed it, im 13 years old and came 5199. look at PYN PYMP M and PE for a start. :-)

  207. Robi

    Just got the magazine this morning (live in the US), 12 minutes – all in my head! On to number 2.

  208. 5227 – but I did not get to page 88 of Physics World till 9.30 last evening. Made much quicker progress this afternoon after re-reading the instructions.
    Lovely puzzle!

  209. Glenton Jelbert

    Here’s a spreadsheet to help you:

    Go to this page, click File – Make a copy.

    Should be self explanatory from there.

  210. Took me longer than I would have liked (5338). My (admittedly weak) excuse: I was looking for more complexity than required! Impressed that some of the (younger) posters got it so quickly.

    [Thanks to Glenton Jelbert for convenient Google Spreadsheet !]

  211. Colin L

    Left it after an hour last night hacking with a Python program. Tackled it again this evening and cracked it with fresh mind and pen and paper. Good one. Got 5392.

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  213. Jack Rawlinson

    Yes! Cracked it at last, and I see only 246 folks did so before me! :-)

    Figuring out the link from the coded phrases to the picture was relatively easy with a bit of Googling. That gave an obvious connection that had me haring off down the wrong path for far too long. When I finally found the “joke” I actually remembered my old physics tutor referring to it.

    If anyone wants help/hints email me at, letting me know how far you’ve got…

  214. Jack Rawlinson

    Err… i was talking about puzzle number 3, by the way. Dumb me managed to post under the wrong one!

  215. Ricardo Fieldini

    5479. I may even be the last :) but I am happy. Started with no real knowledge but just plodded. Good things really do come to those that wait. Thank you.

  216. Robc

    I am loving these problems, even if time consuming, I believe I have all information for question 3 in front of me…but can I see the answer?

  217. Adam Lewis

    That was fun! Illustrates how you can compromise a cypher fatally just by not encrypting the space character.

  218. James Bamford

    Finally! Number 5588. Spent a couple of hours going down the garden path before realising it is simpler than i thought! Paper and pen win every time.

  219. Johnathon

    I figured out what it stands for, but I don’t know how to submit my answer. Help?

  220. Disha

    love the answer. :)

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