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Physics World at 25: Puzzle 5

By Louise Mayor

It is time for the final and most fiendish challenge in the Physics World at 25 Puzzle. Have you got what it takes to figure it out? #PW25puzzle

Check out our round-up of the entire puzzle series where you can enter your answers to all five puzzles.


This question consists of a list of 55 words, plus one lone word. You have to work out where the lone word slots into the list. Each of the 56 words can be associated with another word and this second set of 56 words are in alphabetical order. The second set of 56 words divide up into seven sets of eight words, with the seven sets representing seven methods of pairing. The list reads from left to right, top to bottom.

Where does FLOW slot into the following list?




MOON          LANE          DAY           MAN


KING          SUN           GIBBS         INDUCTANCE

FREQUENCY     TIME          WATER         ENERGY

IO            MASS          CYCLOTRON     LANDAU

PHOBOS        WELL          LEVY          FERRIMAGNETISM


ROSE          GROSS         CONSTANT      CHARON

ARGON         NEUTRINO      FORD          TITAN   


POWER         DARCY         MODULUS

The answer needs to be entered as three words, in this order: the associated word of the listed word that precedes FLOW, FLOW’s associated word, and the associated word of the listed word that follows FLOW. The three words should be entered as a single string of text with no spaces.

Enter your answer here

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

    Many thanks to all the commenters who have been such good sports in the previous puzzles. It’s fun to see the discussions that arise and I’m sure this final and most fiendish puzzle will be no exception!

    • Andrew Wright

      And thanks to you and GCHQ for the great puzzles with which we’ve gotten so confused with!

  2. Mat W

    Step 1: understand the question. Step 2: solve the puzzle. Still on step 1!

    • Mark

      I think it means to alphabetise the pairings?

      • Dead or alive

        It says the SECOND set is in alphabetical order. So it doesn’t seem to matter if the second set word normally precedes or follows the given set…but what would I know!

    • Errol

      same here! still stuck in step #1!
      perhaps a clarification of the question is needed, or is that part of the puzzle?:)

      • Errol

        paging Ms. Louise! :)

      • Hi Errol! As with the other puzzles, figuring out the question is part of the challenge 😉 Some of your fellow puzzlers are doing well with the interpretation – see comments below by Adam and Michael, for example.

  3. Clive Thomas

    Yes, thanks to all involved for these puzzles, which have been most enjoyable over the past few weeks. Mat W’s method looks good but like him, I’m still at step 1!

  4. Andrew Wright

    I get the impression that the words are already in a particular order. Our first step is to figure out why and where FLOW fits into the list.
    I haven’t had any Eureka’s yet.

  5. Adam

    Wow – my brain hurts already!

    So I’m thinking “methods of pairing” in the instructions could be, for examples, synonyms, antonyms, homonyms, etc?

  6. Adam

    Here’s one initial thought I have – the directions mention that the second list of 56 words is in alphabetical order. I think this means that the word associated with METEOR is probably near the beginning of the alphabet, and the word associated with MODULUS is near the end? Or if those two aren’t near the beginning/end respectively, they’re at least closer to the beginning/end respectively than the words in the middle of the list?

  7. Leigh

    I think I know what I’m trying to do, though I haven’t identified any definite pairings yet and I definitely think a better physics knowledge than mine would be useful!

  8. Michael

    I *think* I get the question: each of the above 55 has an associated word. The list of associated words is in alphabetical order (so meteor’s begins with ‘a’, positron’s ‘b’, etc.) and ‘flow’ its somewhere amongst the first 55. If you can figure out where, you’ll know what it’s associated word begins with, or if you can figure out its word, you can find where it fits…

    I think.

    • Leigh

      That’s my interpretation, Michael. And I think I just found a set which is supporting the theory so far!

    • Leigh

      Grr, I feel like I’m really close now and I’ve got to go back to work :(.
      I’m pretty confident I’ve got 3 of the association types, and I’ve got a good idea of a forth which is proving difficult to google. I’m a bit lost on the rest at the moment, but it’s going better than last week so far!

  9. P. Peters

    i’m not sure i follow how the groups in ‘seven groups of 8’ can represent methods of pairing if theres 8 things in the group… but then, i’m no where near that yet anyway, still trying to get the alphabetised list of associated words, which is difficult enough seeing as each word has any number of words associated with it!

    • Andy

      The “method of pairing” relates to how, within that set, the given word relates to its associated word – it’s this pairing method that varies between sets.

      • p peters

        ah, I see. it’s kind of like an ‘only connect’ style thing… I think I’m a bit over my head on this one! should get back to work anyway 😛 may keep slogging away at it throughout the week though…

  10. Mark

    Are all associated words associated with physics?

  11. Chris West

    #4 for me! Anyone else put off the track by KING?

    • Chris West

      Have you forgotten to put the clocks back? Or is Physics World based somewhere in Europe?

    • Andrew Wright

      Off the track? I can’t even see a track yet!!!

    • Steve

      Yes, KING was a nice one, but got it now. In fact, of that group, KING was the one that gave it away to me. Sadly I still have one grouping I haven’t understood at all, but mostly filled out the other six.

  12. Greg Heath

    #7 though I still have a few gaps in the list … and haven’t solved week 3 yet!

  13. Kevin Smith

    #5 – But still stumped by METEOR and MODEL.

  14. Leigh

    #10!! OK, I’m a bit too excited about that, but it’s my best result of the challenge :). I liked that one, though I’ve still got some gaps to work out…

  15. Wow, I’m really impressed with the speed of the solvers today! A very well done to Philip Gibbs, Chris West, Kevin Smith, Greg Heath and Leigh!

    (As we’re not collecting details, I have no idea who the other five successful solvers so far are.)

  16. Chris


    Only got 6 of the 8 connections but it was enough to get the 3 words that I needed fortunately.

    Think I’ve spent enough time on it already, but might go back later to get the last two.

  17. Old Bob

    Curious – the magic box told me I was #12 – dead heat with Chris?

  18. Linus Schumacher

    14. That was tricky… The description was very misleading in one aspect.

  19. Amith

    Small example would have made things clearer, and easier too. Looks like many people are in Step 1. And the rest of them are experiencing ‘Fear of puzzles’ [did not get an equivalent word for this.] But I am in a state of superposition!

  20. Mat W

    That’s helpful ta. I’m learning a lot doing this week’s puzzle.

    • Mat W

      Odd, I thought I was replying to a specific comment. Must have been deleted. Cue X-Files music.

      • Hi Mat. You may have been replying to the comment that I removed. The comment I’m talking about gave a hint that I felt could have given the game away too easily for some people. We wouldn’t want anyone to miss out on the hard slog required to solve the final puzzle, would we? :)

      • Mat W

        Hi Louise. Thought as much. It was a bit of a giveaway I suppose (if you got the reference). Personally I’m still slogging!

  21. p peters

    regarding the second list, is it alphabetised in relation to the order the given list is in, or in relation to the groups they belong in… or both…?
    this is not the relaxing break from work I was hoping for! haha

    • Leigh

      If you write the associated word next to the original word as they appear above, the second list will be in alphabetical order.

      • Andrew W

        I really wish I had read this far back in the comments as I would have saved myself an awful lot of time. I sorted my pairings into alphabetical order – daft I know – and wondered why nothing seemed to fit. Had flows pairing too very quickly but dismissed it.

  22. confused

    Are the “associated words” that form the second set members of the given list of words?

  23. Old Bob

    “…this SECOND set of 56 words ARE in alphabetical order.” Seems to cover it.

    • Dead or alive

      Are all the words in the second set complete words that can stand alone?
      (Not a word fragment.)

  24. Robin S

    #17. This was the best one. No massive jumps of logic to get to the answer. Really enjoyed these puzzles!

  25. James

    I have 55 words in seven nice groups, and still I can’t work out what FLOW is. Frustrating. Is it a debatable spelling?

    • Leigh

      Remember there are 8 pairs in each group including FLOW and its paired word, so if you’ve worked out all the others you should be able to deduce which group it belongs to.

      • James

        I have the group its attached to (and had tried it in the other groups just in case) but none of them yields an obvious partner word (except one which could take many spelling variants, which I’ve tried exhaustively). It may be that detailed physics knowledge is required, but my question would be – if I have the group it goes in right, is the partner word obvious? Doesn’t seem like anyone else has got stuck at this point…!

      • Hi James. For me, the partner word is not something I’d have known off the top of my head. I definitely needed Google to figure it out.

      • Leigh

        I definitely did not know the word, but I found it quite easily with google and there was only one ‘correct’ spelling. If you think you’ve got the right word maybe you’re not entering your answer exactly as required? You need three words without spaces to validate the solution.

  26. FoxyV

    So I’ve got 2 out of 3, but kind of stuck now…

  27. Mat W

    #26. Not filled everything in yet, but plan to. Perhaps a bit trickier than some of the others for those without any science knowledge, but the answers are all out there if you know what questions to ask Google.
    Some lateral thinking needed…

  28. Tobz

    Finally got there and thoroughly enjoyed it. I had to figure it all out without guessing (unlike last week) as I needed the very last piece to solve it! #27 :)

  29. Ted

    I’m pretty sure I’ve got all the groups worked out, except that I can’t fit METEOR, MODEL, and FLOW into them. I have two empty slots in one of my groups and one in the other. It seems pretty clear where FLOW belongs (in the group that has two empty slots), but when I base my answer on that it doesn’t seem to work. There are potential issues with spelling / capitalization / different forms of some of the relevant words. I think I’ve tried all the reasonable possibilities, but it never comes out right. Any advice?

    • Mat W

      Tricky to advise without seeing what you have already, but there wasn’t any option that I could see with the spelling, and I entered the answer all in capitals. Might be worth revisiting which category you have for which word.

    • Don’t overlook “no spaces”.

    • Tobz

      Capitalisation is probably not an issue. Unlike Mat I entered my answer all in lower case without any issue.

    • Leigh

      Double check spelling and which three words you need to type in. I had the right solution and got it wrong 3 times forgetting spaces, typing FLOW as word one, then misspelling the real word one.

      • Ted

        I’ve sorted out MODEL (suitably embarrassed not to have gotten it before!) and I think I’ve got METEOR (which was quite obscure). That means I’ve got everything except FLOW, so (unless I’ve made a mistake, of course) I know what category FLOW must go into. It seems clear (to me, anyway) what the answer to FLOW must be, but evidently I’m missing something because the answer doesn’t come out right.

        I wish I could think of a suitable question to ask without giving things away … I’ll say a few things that I think are true, and if anyone can tell me what I’ve got wrong, I’d appreciate it.

        If I’ve got things right, then there are a few possible spellings for the word associated with FLOW (all of which I think I’ve tried). The preceding word is a proper name with (as far as I can tell) unambiguous spelling. The third word strikes me as having some ambiguity in what you’re supposed to write down: there’s a longer word involved, and it’s not totally clear whether you’re supposed to use that longer word or just part of it. Again, I think I’ve tried all the combinations of possibilities.

      • Andy

        Ted, I think you’re nearly there. You’re right about the first word, and the third is just the short part. The word associated with FLOW is, as far as I know, only spelt the one way, but there are similar words with different suffixes which may mean the same sort of thing. You’re looking for a 20 character string, if that helps.

      • Ted

        Andy’s comment got me over the hump. Thanks!

        In case anyone’s wondering, I had the right general idea for the category containing FLOW, but I didn’t have it exactly right, so the word I was trying to enter was different from (but closely related to) the right one.

  30. Frank

    #31 yay!

    I learnt a lot today. Google must be sick of me!

    Big thanks to PW and GCHQ. It’s been a lot of fun!

  31. Phil

    Number 33! Managed to improve on the 1800 I got with the first one.

    That was fun to solve, but quite frustrating as I had two parts of the answer a couple of hours ago, but the third proved pretty tricky.

    Thanks for these puzzles, they’ve been great.

  32. Laura

    #35! That took a lot of research, but came together nicely. Now I have to go finish solving the rest.

  33. Eric

    #36 – best yet! got it just as I was about to give up for the day. lovey puzzle! (only 1 word I didn’t get – that will have to be for tomorrow!

  34. Natasha

    #38 Found this a lot easier than puzzle 4. Definitely helps having a physics background and access to Wikipedia!

  35. FoxyV

    #39….Better do some work now..

  36. Paul

    #40. I’ve certainly learned how much I don’t know about physics! Very many thanks to Louise and the team who have put these together. Great fun.

  37. Tim P

    I’ve got 16 words left including FLOW and missing 1 or 2 from some of the categories, I know the associated words for 3 or 4 of them but for the life of me can’t think of the last 2 links. Any hints regarding the categories gratefully received at

  38. Ezekiel Romero

    Go to get some shuteye now! :)

  39. Mike W

    I agree with Natasha. Being a physicist certainly helped on this one – not much need for Googling. I thought this was the second easiest after #2. Great fun all of them.

  40. Leigh

    Based on the other comments I think my answer for MODEL must be wrong, unless you’d only kick yourself over it if you’re a physicist…

    • Steve

      If it’s what I think it is (not guaranteed) then it should certainly be familiar to any physics, and maybe chemistry, undergraduate, but not necessarily to others. It might also be mentioned in the A-level syllabus, or rather it might have been many years ago when I did it, so not necessarily still the case.

  41. Andrew W

    Have been plugging away at this today, and have grouped the the words into 7 sets; very unsure about UNIVERSE (‘aggregates’ rather than ‘has’ its sets attribute) and MARS (rejected classical/planetary went the Sherlock Holmes elementary route) but they are in their respective slots tenuously linked nonetheless. Reasonably comfortable about the associated word with FLOW.

    Tried plugging in the answer and getting no where. The second word has several suffixes so tried various combinations.

    Clearly I am doing this wrong and with no logic in sight in this puzzle its very frustrating.

    So backing up and taking stock: Does the second list of 56 words contain a) 56 unique words or b) 7 unique words with 8 repeats of each?

    • Tim P

      56 in strict Alphabetical order, the 3 you want are very close together.

      • Andrew W

        Hi Tim, thanks I appreciated they are in alphabetical order but are they rearranging the original 56 words (with Flow included) or am I suppose to be adding my 7 words that are what I think are my set attributes. Not really understanding how the answer is suppose to be presented.

      • Andrew W

        Sorry for the typo.

      • Andy

        Andrew, you should end up with 56 pairs of words, which can be split into 7 sets of 8 pairs, each set having its own distinct pairing rule. The new 56 words are in alphabetical order – and you’re looking for FLOW’s partner, bracketed by the words immediately before and after it.

      • Andrew W

        Ok in trying to understand puzzle #5 by way of a(highly contrived) example:

        Where does FLY fit in to the following list?

        Lets say ‘FLY’ is the fifth word inserted between APPLE and SWIM.

        The list together with associated words in alphabetical order


        The sets are
        fruit – APPLE, BANANA, PEACH
        travel – FLY, SWIM, WALK
        SWIM, SWIM-WALK. Using diagonal links in some cases.

        What form does the answer take?
        3)fruittraveltravel (i.e. by set categories)

        Presumably the answer is in the form of either 1 or 2. Only ask as my categories are wrong in the real puzzle but not sure what to try next…

      • Andrew W

        Oops that example should have read fruit – APPLE, PEAR, PEACH for the first set not banana. Its late I am going to bed!

      • Andy

        Andrew, the second set of words is different. Example, where does PLYMOUTH fit into CREWE ANTONY TROILUS ROMEO CRYSTAL? Sets are football teams and Shakespeare plays, so associated words are (crewe) ALEXANDRA, (plymouth) ARGYLE, (antony) CLEOPATRA, (troilus) CRESSIDA, (romeo) JULIET, and (crystal) PALACE. The text to be entered would be ALEXANDRAARGYLECLEOPATRA

      • Andrew W

        Andy, thanks that has helped.

        Will look at this again later on today.

  42. Stewart H

    Having joined the game about 8 hours late, am really pleased to be #64 after a bit of trial and error with words 2 and 3.
    Louise – thanks a lot for these great puzzles. This one was by far the best, combining Physics knowledge and the seven groups akin to the Only Connect wall.
    Presumably there will be another set of puzzles next year – please !

  43. uszkanni

    #71. Took longer than it should have and I think I’m wrong on the categories of a couple of terms (eg, in my scheme TEMPERATURE would have worked out better than MASS).

    Fun and thanks for all the fish! 😉

    • Steve

      Excellent point about TEMPERATURE. I agree that to my mind that would have worked better. The word I matched to MASS (if I’ve got it right) did give me some doubt as, while it fits in some sense, it doesn’t have all the features of the other 7 matches in that group.

      And if, like me, you got the category wrong for flow, then commiserations. I was stuck for over 24 hours with mostly correct words, but FLOW in the wrong category and therefore position. My match was obscure, but some of the correct answers are also pretty obscure too!

      • uszkanni

        I think we’re thinking along the same lines in terms of this particular grouping. My assumption was that I had miscategorized MASS or couldn’t get the correct matching term rather than it being a problem in the coding (it’s never a bad idea to assume I’m wrong ;-)).

        I was able to fill up 6 categories so I had FLOW narrowed down to a particular category with high confidence. I had a wrong idea of what that category was, however, and it took an “a-ha” moment to realize the key aspect which led to the correct word.

        I assume the correct solutions to all the puzzles will be posted soon, it’ll be interesting to see where I may have gone wrong.

  44. Graham W

    #78 Ouch. Lots of physics I didn’t know, thanks google!

  45. Gerrit Wessendorf

    Hm.. this one is giving me more trouble than the previous puzzles :) Not sure how to continue or ask for a hint without revealing what I got so far.

    I found one grouping quite easily where one “child” word is associated with exactly one matching “parent” word using one single pairing method, and there were exactly 8 of them in the list of 55/56. Check :)

    Similarly, I have another grouping with six (possibly seven) elements of a common kind for which I found a good match using a single pairing method. I found one item that could fit the category but not the same method of pairing I applied to the other six/seven elements.

    If this looks familiar to you – can a word in this group match even though it doesn’t strictly fit the pairing method?

    And after that it all falls apart. Lines get very blurry. Whatever I’ve tried, I either ended up with more than 8 elements that fit my method of pairing, or less than 8, or I found countless other words I could countless pairs with. Am I looking for methods that result in 8 and only 8 pairings, or is it possible that I could find, e.g. 12 fruits and 4 vegetables and build one group of 8 fruits and one with mixed foods?

    Have to get back to work now.. will have to try this again later tonight!

    • Andrew Wright

      Hi Gerrit, I’m in the same boat as you. I have a few possible groups, only 2-3 that I’m sure about. Apart from that there are a few other ideas for groups but i can’t figure out all 8 words or find all the matching words.
      I even have one group that i thought was very neat that has a very easy to confirm 8 elements but I have no idea what the linked words could be.
      I’ve been working on and off with this since it was released so i feel a bit dumb :(

    • Steve

      You should definitely get groups of 8 in the end. It is true that some could initially fit into more than one category, but that’s all part of the puzzle setters plan to fool us, I guess. In the end, I think the members of each group all do fit their category quite nicely. I think this is a tough puzzle if you don’t have some background in physics, as you may find getting a foothold in some of the groups difficult. For example, the group containing KLEIN I found easy, but only because I work in that area of physics and immediately recognized the likely pairing. Having got that one, I could Google the rest quite easily, but none of the other 7 were at all familiar to me.

      • Andrew W

        Yes my physics ‘O’ level not too much help, so struggling, pairings done but several are wrong. Interesting for KLEIN I have two German gentleman and I ended up selecting the one who was born the earliest of the two as I was overflowing with candidates for one set. Guessing you may work in the field associated with the other I picked the eponymous one. Did I crash land here?

      • Steve

        On Klein, let’s just say: remember this is a physics blog, not a mathematics blog. I’m afraid popular science will probably lead you down the garden path here (ie towards an incorrect two word mathematical association). And it’s nothing to do with fashion either, but you probably knew that already.

      • Andrew W

        Hi Steve, yes you are right this is tough. Of the two Germans I originally rejected the mathematician, but looks as if the other German Hermann does not fit either from what you say so perhaps should I be thinking of a prize winning Polymer Physicist instead?

      • Steve

        Ah yes, you’ve definitely not got the right Klein yet. This one comes from a bit further North than Germany, and the pairing is the most well know ‘thing’ associated with him. But I’d be surprised if he or the ‘thing’ are at all familiar to anyone who hasn’t taken certain options in an undergraduate degree, or continued as a post-doc in the field.

      • Gerrit Wessendorf

        Thanks everyone for your thoughts – I’ll start over, maybe I let my convictions lead me into the wrong direction. The group with KLEIN is my group for which I thought I had a very solid method of pairing but found only 7 words that matched the category and method. I was convinced he was born not far from where I used to live and that his “thing” was 1.5 km deep :) Is my method of pairing, although matching 7 words beautifully, not correct after all?

      • Steve

        I don’t want to stress KLEIN too much, there are other groups that will help you more. I was really just illustrating that I think this group is particularly difficult as many of them are pretty obscure (even to a physicist) but once you know the form of the matching, they are all actually quite easy to find with google and eliminate from your search. I was just lucky that the correct match for KLEIN is something I’m very familiar with.

        But yes, I’m afraid the KLEIN ‘thing’ is definitely not 1.5 km deep. Perhaps I should say that while KLEIN is a physicist, and the ‘thing’ is definitely what I’d class as physics and definitely not pure mathematics, one might consider it as rather mathematical. Maybe doubly so.

        Oh dear, that’s probably just going to confuse you more, sorry, but don’t want to give too much away.

        On the other hand, the group which contains KING is difficult in a different way. This one should be OK for physicists and non-physicists alike, but as others have commented, requires a little lateral thinking.

      • Andrew W

        Hi Steve, thanks for your help.

        I added a comment at the end of the general thread – still stuck but have swapped and amended some of my classifications.
        Without giving anything away does finding flows match also require lateral thought?

        Also I think I have the right Klein and therefore field -has something in common with a certain EW at Princeton?

      • Steve

        Not sure this hinting is getting us far! Here’s something that should definitely be helpful. I think this web page is particularly useful:

        Along with its companion page on astronomers, it includes the matching word (and original word) for about 30 of the matches in some form or other. It also includes the link between the two in many cases, though certainly not all. It should at least get you a bit further with KLEIN.

    • Paul

      Gerrit / Andrew – It sounds as though you are on the right lines. I think that the key is to get the definition of each category right.
      If your thinking process is like mine, there was one quite obvious group, where the associated words came mostly with general knowledge and a couple of Google searches to find the more obscure ones. (Interestingly, one of the associated words in this group is also a main word in another group. Do not be misled by this – it is a Red herring!) The associated words in this group are usefully scattered across the alphabet, which helps to fix the others.
      On the second group you mention, does the exchange between uszkanni and Steve above help? The extra word does fit if you define the category slightly more simply and broadly.
      Beyond that, it was mostly Google searching for me.
      But this is a physics puzzle, so there are some ideas and people which you might expect to see – and there are clues or references to them !

      • Andrew W

        Paul, thanks for the confirmation of the red herring and that is in my first group! Now feel confident about how the puzzle is designed to work. I have 56 pairings some more plausible than others. Of the placements for flow and its associated word I have three alternatives:

        In one case both the previous and following associates are proper nouns. Flows associate could take several forms (to be clearer two choices both with several variations).

        In the next case, of the three associated words the last is the shortest, the first the longest with some ambiguity over flows associated word which seems as if it should be two words so here I have taken only the first. These 3 are in the first half of the alphabet.

        In the last case the first word is a proper noun. Flows associate is very specific uncertain of the third and they are all in the latter part of the alphabet.

        Nothing I tried is correct.
        Rejected mythology as category as no clean fit.
        Also someone mentioned answer as a 20 character string.
        Two pairings not included above relate both to moon and sun but in different ways.
        Delorean and star came to mind at some point.
        All my categories are science based.

        Copious excel workings but very hard to validate any work in progress. Is any of this on track? Clearly something is wrong. I appreciate it is difficult to comment without giving the game away.

      • Andrew W

        Regarding the discussion between Steve and uszkanni I can see how that could link in with either my first case above or the last one. What the third word aMounts to I am not sure.
        Frustrating feel I am close and yet so far.

  46. Stu_P_id

    Its 40 plus years since I did any Physics, so the comment that you receive about being a committed puzzler rings very true.

    Having said that I got lucky because I was only really confident of 5 of the sets.

  47. Martin

    I have four groups of eight and one group of seven that I am fairly sure. I have started a sixth group but the connections seem a lot more tenous than the others. Does this sound like I am now clutching at straws?

  48. Les

    #90 at last!Understanding the exact definition of the pairing method for the group containg FLOW,was the eureka moment for me.All the other word pairings fell into place as well for this group[I’d got some wrong and some missing]Great puzzle.

  49. Mat W

    Andrew W: Are you still stuck? I’ve not read all the previous comments but the key thing is to get the class that FORD belongs to, which for me unlocked all the words that seemed to have nothing to do with physics.
    You have probably got the first two right.
    My earlier lateral thinking comment applies to FORD. It does not apply to FLOW or to NEUTRINO.

    • Andrew W

      Hi Mat W, just read your comment, yes I am still stuck.

      The logic puzzles for me are far easier trouble is with this puzzle is there seem to be too many pairings and my Physics knowledge is lacking.

      Looks like I need to rethink Ford from where ‘he’ is placed, as I went with an obvious Wikipedia connection. Steve above has indicated I haven’t the correct Klein either. Will cogitate further..thanks.

      • Mat W

        You might want to compare the way I capitalised FORD with the way you did. I could equally have written it all in lower case.

      • yaputyay

        Hi Andrew,
        I haven’t quite got the damn thing out yet either. If you want to compare groupings, drop me an email at yaputyaDOTleftleginATgmailDOTcom
        I think I have 7 out of the 8 right.

  50. James

    So no comments since the day the puzzle came out eh? Does that mean everyone trying it has got it or given up (apart from me who just got round to attempting it but already feel like giving up)?

    I think I have 3 groups but am beginning to show Signs of Lunacy Equating the other 4. (You may be able to tell which 3 sets I believe I have solved.)

    Any clues that keep the puzzle interesting but offer a little insight would be much appreciated. At least this is harder for me than the last 4!

    • James

      Ops. Didn’t see above that there are later comments. For some reason my PC shows the last comments and replies as from the 29th Oct.

      • Mat W

        It’s not just your PC. It’s partially my fault, I replied to a comment that was subsequently deleted and it mucked up the comment threading!

  51. Paul

    James – Do you mean SIgns? If so, you are on the right track.

    Andrew – It is not easy to reply to your post of last night without knowing what groups you have in mind.

    But in one respect the instructions are misleading: in one of the groups, not all the associated words are “words” in the strict sense (see Dead or alive on 29.10 @ 7.55).

    All the other words are English words (not, for example, Greek ones). Although some of them may be obscure to those not working in the field.

    • James

      Thanks Paul,

      Yes I meant “SIgns” of “Lunacy” “Equating” but didn’t want to be too obvious. There are still 4 I have absolutely no idea about. And I work in the finance industry so I’m certain that “some of them may be obscure”.

    • Andrew W

      Of all the People Brigadier Lethbridge-Stewart would be familiar with one group.
      My lunacy is bipolar (no disrespect intended to anyone).
      Conveyancying the meaning of particulars of others is hard although I may have an idea bulb pop.

  52. Woohoo!

    #94! Very proud. I’ll be feeling smug all day!

    Some helpful reassurance from the comments above got me through. I’ve still got three words that I can’t pair up, so I might have another look, or I might wait for the answers.

    Google was definitely my friend for this puzzle. Thanks to Louise and all at GCHQ/PW for giving my poor arts grad brain a good workout. I hope we do get more next year.

  53. Dan

    #95. Turns out not all of the “associated” words are real words. Still don’t know what the word that goes with METEOR is.

    • Paul

      I also struggled with the associated word for METEOR, but today I have found a word which fits, if METEOR is understood in its strict sense (and not as the object which the word is often used to refer to).
      The word I have found does have the same Hellenic roots which the other associated words in that group share.

      • Leigh

        I’ve got something on my spreadsheet for METEOR, but the link is somewhat tenuous so I doubt it’s correct. I’ve got it in the same category as MARS.
        The only thing I’ve got nothing on is COINCIDENCE, and no one else seems stuck on that one!

      • uszkanni

        Leigh, the word associated with METEOR very clearly links to the category. There will be no doubt when you get it. It does belong to the same group as MARS. I am not giving away anything when I say that it is the first word in the list and, hence, very early in the alphabet.

        COINCIDENCE was pretty obscure (to me anyway) but like MARS it fits the category perfectly. It does not belong to the same category as MARS.

      • Dan

        Paul, thanks for the tip. I’ve found a word, which happens to be a fairly obvious anagram of another word in the list.

      • Leigh

        That sounds like the same word I’ve got, Dan, though I’m a bit discouraged as no amount of googling is bringing up those two words together!

      • uszkanni

        The word I have for METEOR is 13 letters long and doesn’t look like it would easily anagramize to another word in the list.

      • Leigh

        Thanks uszkanni! I’ve been going a bit mental on that one. Dan, our word was very close to the correct word, and though wikipedia let me down on this one, Wiktionary was far more enlightening!

      • Dan

        Hmm. I think I’ve found that 13-letter word, but its definition suggests it’d go better with “meteorite” than with “meteor”. I’ll stick with what I’ve got for now.

      • uszkanni

        Leigh, YW. This word was the one that gave me the clue to finding FLOW’s companion word.

        Dan, I don’t know what word you and Leigh had and it’s certainly possible that I am wrong. TBS, some definition may point towards “meteorite” vs “meteor” but if you decompose the 13 letter word into its root parts then it works out well (and with a strict and narrow reading of those root parts actually excludes “meteorite). Just my opinion, of course, and we’ll have to wait until the Jan 2014 issue of PW for the official answers.

  54. david

    Just to keep the messages going as they seem to have tailed off I am number 96 used the clues of 20 chars+beginning with a proper name and ending with a part word not many then to check. Just using lateral thinking with the flow. Try basic aspects of the subject.

    • Andrew W

      Hi David, thanks, I too had been trying with these constraints. Tried a few more. Most of these fit my classification scheme but although I have tried 16 patterns now still the answer is not among them. Very surprised to still be out on a limb. Flows associates regions tried fhmpsv. Most of my combinations lay in m.

      If this was a game of battleships would that be a hit or miss?

      Looking for inspiration.

      • david

        Hi Andrew flow is not around the letter you suggested try a bit further down

      • uszkanni

        Andrew, what you’ve listed as, presumably, possible starting letters for words associated with FLOW are not correct. You may not have the category exactly correct or may not have narrowed it down sufficiently. I don’t want to give too much away but there is a very definite commonality between the words in that group; I’d suggest you study what feature the words in that group share.

        A big(gish) hint follows. Read at your own risk. :-) Louise, feel free to delete it if you think it goes too far.

        P.S. I don’t know if this blog allows the tag. If it does, the hint will be hidden unless you drag your mouse over it. If not, the hint will just be visible.

        If I had included one of the words in the above paragraph in quotes you’d get it right away :-)

        –END HINT—

      • uszkanni

        Just to be clear, the hint refers to something in the first paragraph.

        Evidently, the “color” tag doesn’t work.

      • TheBigBean

        It probably is a huge hint, but I still can’t get it.

        I’ve made no progress in several days.

      • uszkanni

        BigBean, how many of the 7 categories have you figured out? Even if you can only narrow FLOW down to 2 or 3 possible categories you can search assuming it’s in category A, then B, etc.

        The word is not at all familiar (at least not to me) and I think people need to get some handle on the category and use it in the search for FLOW’s associated word.

      • TheBigBean

        I think I have six of the seven categories. I’m missing two items from one of the categories. I’m fairly surely that FLOW should be in the missing category, but I’ve been stumped for days on what that category is.

      • uszkanni

        Bean, Paul on 1 Nov at 6:25 posted some useful information which can serve as a starting point to getting the group characteristic. Apply that hint to the words in the category and then expand what you get so that you have actual words. When you do that you will see some common feature in the words which can be used to search the Intertubes to identify the missing words, including FLOW’s companion.

      • Andrew W

        uszkanni, thanks for your hint to me, well that helped narrow a category which now lines up nicely, which I had almost from day one. (quotes not shown).

        I have all 8 categories pinned down (I hope!).

        I have Flows associate in the group which I think you are alluding to in your reply to Ben, which is nice confirmation. (Thread with Steve Oct 31 8:21 helped shake this category down re KLEIN conversation)

        Thing is I cannot find the 3rd word nothing seems to fit. (Even looked through a dictionary for inspiration).

        Thinking that flows associate is wrong I also tried the category mentioned in paragraph 1. (in many cases we are still in the same region of the alphabet but not for all).

        Exhausted many many options.

        So I think the first 2 words are ok but not the third. Ideally the 3rd word looks to be a few characters. Difficult as I don’t seem to have any obvious gaps – (or at least any that will have much impact anywhere else but I have something wrong somewhere).

        Other categories not mentioned above NAMAKA gave me one, UNIVERSE, WATER, MAN are grouped in another as parts along with METEOR, SIgns as hinted elsewhere in another and I will stop there for now.

      • uszkanni

        Andrew, YW.
        MAN does not belong in the same group as UNIVERSE, WATER and METEOR. If you move MAN out of that group it may push something else out of its group and into the group associated with the third word. It may result in a chain reaction of re-assignments depending on how you’ve got your groupings.

        Once nice thing about the net is that you can search for lists of word fragments as well as complete words.

      • TheBigBean

        uszkanni, many thanks for your help. I’ve finally solved it!

        Now I realise which word in your original hint was such a big clue…

      • uszkanni

        Bean, YW and congrats. I probably oversold the “bigness” of my hint but I think it’s actually more satisfying for it to be confirmatory rather than leading.

  55. TheOldRic

    It’s my birthday! For a present I would like a hint about what category “KING” is in. I’ve got 3 groups, an uncertain 4th and a deficient 5th but the rest are a scatter.

    • Paul

      Happy birthday, TheOldRic! KING is in the group in which some of the associated words are not full words. (The word associated with KING is a real word, but fairly uncommon.)

  56. Joe

    You are one committed puzzler…you have just solved the fifth and final puzzle! A big congratulations to you for solving the hardest puzzle in our series – you are person number 99 to have done so.

    Top 100 (just) Thanks for the puzzles, lots of fun. Can I have my life back now? Best result of the 5 but least favourite puzzle. No. 4 was best.

  57. Ian P

    #101. All done. Really excellent puzzle.

  58. Vasia T

    Any help with FORD at would be very appreciated.

  59. Dartmoor Graham

    Got there! #104. Still haven’t got METEOR though. Will await the published answer with interest. Thanks, Louise et al

  60. Vasia T

    #107! Finally! Many thanks to Steve and Paul for saving me the rest of the weekend :)

  61. Maria

    #109 thanks Ted and Andy for the hints.

  62. Martin

    It is difficult to ask for help with this puzzle without giving away spoilers so how about this? Can someone who has solved it tell me if the number of true statements in the following list is odd or even?

    NEUTRINO is in the same group as HOLOGRAPHY
    MAN is in the same group as KLEIN
    TRITON is in the same group as ARGON
    NUMBER is in the same group as MODULUS
    MOON is in the same group as HAMAKA
    FORD is in the same group as ROSE
    FLOW is in the same group as CONSTANT
    LANE is in the same group as PRESSURE

    • Andy

      Martin, you’ve got an even number of true statements there.

      • Martin

        Thanks Andy. I haven’t solved it yet but that has extracted me from the loop I’ve been in for the last couple of days.

  63. Martin Kimber

    #116… I love it. Very nice set of 5 puzzles… but I had to get my wife (not a physicist) to help me with this one.

    Thanks for a super set of puzzles!

  64. Neil

    I think I’ve got three full groups of eight, one with seven (or maybe eight if “lines” is in the same group as “holography”), and another with five (or six if “day” is in the same group as “universe”). I’ve got three more that could go together in a group and another two that have some similarity to each other for a seventh group.

    I’m sure that ought to be enough to enable me to get an answer by a bit of guessing, and yet, nothing I’ve tried for my answer which fits in my scheme has worked.

    • Steve

      Difficult to know exactly which groups you’ve got, but just to resolve some of your uncertainties there, assuming I’ve got my groups right: ‘lines’ is not in the same group as ‘holography’. I suspect I can guess which one you’re missing from that group, as it’s one of the more obscure ones. If you’ve got the ‘universe’ group right, you’ve done well, and that should really help you find the final solution. However, ‘day’ is definitely not in that group. This is a group you’ll have to crack before getting the solution, but once you’ve seen the trick (and there is a bit of a trick here) then all eight are quite easy. I’ve give you one clue about the group – the words are all rather short, and there’s a good reason why they have to be. Other hints elsewhere in these comments may help with this group.

      • going nuts

        I have these left over after the rest seem to fit consistently. Are they all in one group, or have I misplaced one or more. (I guess you have to misplace them at least 2 at a time!)
        METEOR MARS UNIVERSE SUN TIME WATER FRICTION FLOW. There doesn’t seem to be any pattern in them, not Greek mythology etc.

      • Paul

        goingnuts – Take heart, you are not going nuts, in fact you are nearly there. There is a pattern in those words. Keep thinking “logically” along Greek lines.

      • Neil

        OK solved. But I still have five words unpaired. (I don’t want to say what they are because four of them are in the same group – the same group as “number”).

        But I also have one missing from the same group as “holography” and none of my remaining words looks like it even has the necessary property to belong there.

      • Leigh

        Thanks Neil! I thought I had that group and when I went to check for you I realised I’d miscoded something on my pretty spreadsheet and was trying to cram my last word into totally the wrong group! So I think I have a complete set now and you’re probably missing the same one I was. Try looking at the words you’ve got left and see if any of the broader ones yield results when you look at them in the context of physics alone. Don’t know if that helps!

  65. John

    This one has beaten me. I think I have one group and bits and bobs of others. I think I’ll have to give up and go back to watch Strictly – I think thats more my level !!!

    • uszkanni

      John, don’t give up just yet. Go back over the comments. In particular:
      – Steve on 1 Nov at 10:10 posted a link to a site which gives more than half the associations. I believe you can complete three groups with that info and maybe a bit of searching.
      – Several comments refer to SIgns.
      – going nuts’ post on 3 Nov 8:45 is another (and significant) one. Consider along with Paul’s 1 Nov 6:25 comment and perhaps my comment on 2 Nov 9:56.

      Other hints:
      – Sometimes physicists/mathematicians do not work alone.
      – You don’t get in this group by finding one of these in a box of Cracker-Jacks. 😉

  66. Dartmoor Graham

    going nuts – You are definitely on the right lines. Don’t look for a link between them, though, but rather something that can be applied to all.

    • going nuts

      Is there a sensible link to physics between all the pairings in this group? It seems so different to the other six groups or do I just have a mental block?

      • going nuts nomore

        #124 – I made a silly spelling mistake last Wednesday – dropping the second ‘e’ out of the “horserider” word. So I was chasing ghosts all this time!
        Thanks to those who helped make me finally realise something simple must be wrong.

  67. Andrew W

    #125. A big face palm moment for me – I was finding associates and then sorting that list into alphabetical order, so was trying to solve a slightly different puzzle. It was only the mention of the associate to METEOR at the beginning of the alphabet that it hit me. Just found the wording of the puzzle very confusing.

    Things a became a little more straightforward after that. Still a few key hints were needed so a big thank you to all involved.

  68. Andrew W

    This is what I had for Meteor,

    “Airy meteors are such as are bred of flatuous and spirituous exalations as winds”

    Universal Etymological Dictionary of 1749 – N Bailey

    Not sure it is what the puzzle setters had in mind but it fits.

  69. Fed Up

    Any hints on NEUTRINO’s associate word please? proper “noun” or proper “name”?! No names seem to fit.

    • Andrew W

      This is a more straight forward one and the Wikipedia entry for Neutrino helped. Also Steve on Nov 2 10:10 has a useful link.

      • going nuts nomore

        I misspelt the one for NEUTRINO, just one missing letter stuffs up the answer. (The right answer is close to a noun.)
        That caused me to doubt all the rest, which was actually right all along.

  70. Fed Up No More

    #127 Thanks to all for posted hints. I was stuck as flow’s associate is not as exact a match as the rest of the words in its group. Going with the e x a c t match led nowhere.

    • Fed Up No More

      I rephrase so as not to mislead anyone: not as exact as some (or all) of the words in the respective group. They could all be e x a c t matches or not without much change. But not FLOW. See Going Nuts comment Nov 4th.

  71. Elias P.

    #129 The last and most difficult puzzle solved by my wife (Vasia T), since I’m more into ciphers etc. Thanks to the GCHQ team who make me realize (once again) how bright she is.. :)

  72. Loggzy

    #132. So relieved to have got it in the end. Took hours to get the link for the last set of 8 words. The clue someone gave above of Hellenic got me there in the end. Thanks!

  73. James

    Finally #133 – Ouch, getting wrong answers that seem right can really put you off track!

  74. Andrew Wright

    #141. That was more of a struggle than it could have been. I was hanging around the correct answers for a very long time.
    Kicking myself and asking those who know me to have a good kick as well.
    Having said that, there are still a few gaps in my list…

  75. L

    So I had most of it quite quickly, and then wasn’t able to look at it for several days and then I got stuck with the connection with the last group, which I finally got and got the answer phew!

    But I still have two words that I’m struggling to fit and get the partner word: model and force. I have the connections in the two groups (one missing in each), know more or less in the alphabet and still cannot figure it out. And they both would seem to fit in the same group, rather than one having to go with holography, etc. It seems way too general for that group. Have I gotten more things wrong and this is why I’m stuck? Or maybe I’m just blind.

    I enjoyed this one a lot more than 4, that’s still frustrating me!

    • Andy

      L, I definitely had those two in the same group – maybe check the seven you already have and see if any fit with holography, the answer may surprize you.

    • Vicky G

      L, I would go with just alphabet – not groups. Since you got the answer, you have the essential groups sorted out. Associate words should appear just by looking at the alphabet. If my list is right, think Europe but not Greece for model and think of technicalities for the other word.

    • uszkanni

      MODEL and FORCE could belong to the same category as HOLOGRAPHY but it would require the loosening of the criteria for inclusion. There are also sufficient other associations that fill the group and are less likely to belong to any other group. I believe that MODEL and FORCE do belong in the same group, though.

  76. Michael McLaughlin

    #152 I just started yesterday. I thought this was easier than the third Cipher in Puzzle 4.

  77. Michael McLaughlin

    I got all the ascociated words except METEOR and LEVY. Can’t get those even though I know the categories they are in. Still, it doesn’t stop you getting the three words.

  78. Michael McLaughlin

    Oh. I didn’t get FORCE either.

    • Andrew W


      METEOR: there is quite a discussion in the earlier comments by several others. I also added an amusing definition. That category I defined more loosely than the hellenic association. Not sure if it is correct but all the pairings seem to fit nicely.

      LEVY: a colourful pair

      It took me some time to find the pairing for the other listed word you mentioned but not quite a week.

      Also re puzzle #4 you have a couple of replies to your comment regarding the logic behind the ciphers, hope they help – I referred to statements #1 and #2 and Dan referred to #3.

    • Vincentio

      FORCE is given away by its position at the end of the alphabet.

      It doesn’t belong to the same set as MODEL – in my version anyway – but fits very neatly in to another category – perhaps not a physical force in the Newtonian sense but then again there is another word you probably have that is used often in Newton’s laws that has another sense in this puzzle. They are both in the same set

  79. Vincentio

    158th and yes, I did find it a slog. A fiendish puzzle that had me thinking for many (read many many) days.

    Hats off to the puzzle setter and hope the setting was as much fun as the solving.

  80. JW

    Made it at last #160! Steady improvement over 5 weeks. Pleased as punch – not bad for a Mech Eng., 34 Yrs after physics A Level.

  81. David P

    Can’t believe I actually got it after all this time. Thought I had it several times but finally flowed into the final word. Ended up with nine categories of eight with key terms shifting about. Several hints were confirmatory but not defining, therefore good hints.

  82. David P

    METEOR was rather problematic. Maybe would have been better after POSITRON, depending on your answer, but could also have been a replacement for MARS.

    One prominent association was missing which could have been used to identify one of the two associations with LANE.

  83. LH

    Woohoo! #168. This weeks is much easier than last, only took a few hours once I got back from hols. Now to go abck and try 4 again!

  84. SDR

    #174. Surprised that it is almost a week and the puzzle has not been solved by a thousand people! I took a few days. But puzzle 4 was harder, and I have to go back and try it again.

  85. Chris_Switzerland

    Wow, taken forever but finally dropped into place. Still surprised after this long to make #182!

    Great work Physics World and GCHQ. Now for a rest……

  86. Martin

    NEUTRINO caused me no end of problems because it does not fit as neatly into its category as the other in the same one!

    Really enjoyed solving these puzzles over the last couple of days

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