Category Archives: General

My memory of Stephen Hawking

Stephen Hawking was a Fellow of my college, and a familiar sight when I was a student: my first-year accommodation was in a block just next to his flat, and as I walked or cycled into town I would often see him in his wheelchair heading in the same direction.

I never knew him, though, or ever really had any interaction with him, but he did address a few words to me on one occasion. A very few words, actually — “Thank you” — after a friend and I had carried him, in his chair, up the stairs to the dining hall. I guess the lift must not have been working!

I do, however, have a lasting memory of a talk about ‘baby universes’ that he gave in that same hall soon afterwards, around the time that ‘A Brief History’ was published. We were all conscious, even then, that this was a rare opportunity, and the place was absolutely packed. Whoever was responsible for fire regulations must have been kidnapped and locked in a cupboard somewhere, I think, because the rules must all have been broken by quite large margins.

Anyway, I don’t remember very much about the talk, I’m afraid. He had prepared it in advance and it was played back in his well-known synthesised voice. Half-way through, there was a short pause, and then, “Please wait while I load the second half of my speech.” Disks whirred — probably floppy ones at that time — and then he continued.

At the end, he asked if there were any questions. Somebody asked one, and there was a pause while he composed the response. A long pause. A pause which continued and continued for perhaps two minutes or more as he went through the slow process of selecting words. And then the answer came; just a very short sentence.

I don’t remember much about the questions, or the answers, either. But one image is imprinted very clearly in my memory. A hall packed with hundreds of boisterous and energetic young students, crammed into every corner, having been crammed there for some time, with a bar open and waiting on the floor below… and yet, in the long intervals between a question being asked, and the short answer a considerable period later, you could absolutely have heard a pin drop.

-–

My nephew Matt is a very talented artist who works for a company that does animations, infographics and other creative graphical things, and I do like his one on “Stephen Hawking’s Big Ideas”, published by the Guardian as part of their ‘Made simple’ series.

It’s certainly more entertaining than most other explanations of Hawking Radiation I’ve encountered!

Android: How the other half live

I have had an epiphany. Living on a small boat with four strangers for five days is a great way to discover many things (including, in my case, what good company they were). One of the less aquatic things I learned, though, was probably very obvious and I should have realised it years ago.

One day, we were sharing photos of our adventures, and I sent a few of mine to a fellow shipmate. “Oh!”, she said. “You’ve sent them by text! You can use WhatsApp if that’s easier.” To which I responded that I had recently deleted my WhatsApp account.

This casual announcement, to my surprise, was met with blank astonishment.

Deleted WhatsApp?! Why on earth would you do that? I explained that I wanted to distance myself a bit more from Facebook (for reasons I would have hoped were reasonably obvious by now) and, having not missed my FB account since binning it a few years ago, I had decided to do the same with WhatsApp. They were kind and considerate, but I was clearly regarded as something of an oddity; much more so, say, than if I had announced I was a vegan. And it wasn’t until just after the trip, that I realised why.

You see, I, and almost everybody I communicate with regularly, are Apple users, and so for the last decade or so we’ve had access to iMessage, the chat service behind the ‘Messages’ app (formerly known as iChat).

For those not in this world, Messages basically provides a chat interface which sends and receives SMS text messages if your recipient isn’t an Apple user, but seamlessly switches to using internet-based messaging if they are. You use the same app, but SMS texts are shown in green whereas internet-based iMessages are shown in blue. As well as being completely free, of course, the latter allows Messages to provide group messaging, to work seamlessly across all my Apple devices, to provide delivery confirmation, and so forth.

So when WhatsApp arrived, I didn’t really see the point of it. I installed it, yes, because I had a few friends and family who used it, but it always seemed an inferior solution; in particular, it didn’t really work well on my desktop machine, laptop or iPad. You could do it, but this was clearly a botched afterthought and involved regular re-confirmation using your phone. Why, I wondered, would you want to type text-based messages on a little phone keyboard if you were sitting at a desk with a better one? Why would you want to make a Faustian pact with Mark Zuckerberg simply to send chat messages? And so on.

Here’s the thing, you see: never having used Android, I had just assumed there was some equivalent service built in to that system. After all, ICQ and AOL Instant Messenger were long gone, so I just assumed that Android had always included an iMessage-like system of its own that everybody else was using. It probably had a Windows interface too, but I hadn’t really used Windows this millennium either, so didn’t know what people did there. I just assumed the the Microsoft/Google fans had some Android Chat system of their own, and only used WhatsApp because it picked up their Facebook contacts or something. In contrast, if I want to start a group discussion with, say, my mother, wife, and niece, I just use the same app as if I were sending them an individual text. It’s built-in, it’s the default, and they all have it on all of their machines and could answer anywhere.

So enlightenment only struck when I found myself on this boat and in the unusual situation, for me, of being in the minority as an iPhone user. I may even have been in a minority of one. So when I sent them all a message full of photos as a group, they all got it as SMS texts, and had no way of replying to the group, or even of knowing that they hadn’t each been the only recipient. (SMS messages have a Bcc-like facility, but not a Cc-like facility.) So it’s no wonder they all used and relied on WhatsApp: the poor things didn’t really have anything else! And it’s no wonder they were all astonished at my giving it up. As far as I can gather, it has done for Android users what iMessage started doing for Apple users all those years before (though still, it seems to me, in a markedly inferior way).

Now, don’t get me wrong, it’s not that I’m ignorant of other messaging systems. I used AIM, ICQ, and then Skype chat for years, Slack for a while, and I currently use Zulip and Signal every day to communicate with other groups of friends and work colleagues. Even Teams, when I have to. I love chat systems. I just hadn’t realised that Android didn’t have a default group-messaging solution built in, or that you had to choose between sending texts and doing something radically different on a third-party app for free messaging or for groups. Now I know, and I understand better why WhatsApp is so much more compelling for others than it ever was for me.

I could, of course, have just emailed them, and that would probably have been the best solution, but I think email has one key disadvantage: it’s still slightly less convenient to share your email address with someone than it is your phone number. If all email addresses were 11-digit numbers, it would be easy to call them out to somebody on the other side of the deck in a stiff breeze, and for the recipient to type them in on a simple numeric keypad while hanging onto a halyard with the other hand. Perhaps the solution, these days, is just to have my email address in a QR code stuck to the back of my phone, which anybody could scan quickly if they wanted to communicate with me…

In the meantime, if you do want to use an end-to-end-encrypted messaging system which supports groups, is based on phone numbers but works nicely on machines with keyboards, works on Android, iOS, Mac, Windows and Linux, and doesn’t involve selling your soul, I’ve been finding Signal to work very well.

Rockin’, Rollin’, Ridin’

“Model railways”, someone once told me, “are a lot like breasts. They’re meant to be there for the children, but it’s always the men who want to play with them.”

Well, though I’ve always liked and admired them, they’re not something I ever went in for very much myself. Model railways, I mean.

It must be much more fun these days, though, since I gather you can get engines with cameras in them, giving a driver’s-eye view of your carefully-constructed world. I’d love to see one of those in action!

But, lest you should think that model trains are purely frivolous, Tom Scott’s latest video shows that they can have serious uses too.

Now that must have been great fun to build! And, as Tom mentions, and as some of my colleagues in the Computer Lab discovered a few years back, users exhibit a lot more engagement with something if there’s likely to be a physical crash when they get it wrong or lose concentration. Even if that crash only involves a model, it’s a great deal more compelling than a simulator on a screen.

I don’t think, by the way, that I’ve ever seen one of Tom’s YouTube videos that wasn’t worth watching. Subscription definitely recommended.

Eye in the Sky

I had owned my little drone for a while before I discovered one of its cleverer tricks: taking 360 panoramic views. You just put it in the right mode and press the button, and it turns round on the spot taking 26 photos at various pitch angles, then stitches them together. In some ways I find these interactive views more compelling than videos.

This was one of my first: Houghton Mill, on the River Great Ouse. (If you just see a blank space below, I’m afraid you may need to try another browser, and if you get these posts by email, you’ll probably have to view it on the web.)

Or here’s a view of the University’s Computer Lab, where I used to work back in the days when we had physical offices. The big building site opposite is the Physics Department’s new Cavendish Lab (the third of that name), which is also known as the Ray Dolby Centre, since that little button you used to press on your cassette deck is paying for a lot of this:

People who are interested in the West Cambridge Site may want to look at other shots from the same evening. And people who remember when cassette decks started having Dolby C as well as Dolby B may be inspired by the title of this post to hum tunes from the Alan Parsons Project.

There may be more of these to come.

When not to Excel

Back in about 1993, I was doing the bookkeeping for a big project being undertaken by my local church. Donations were flooding in, and we needed to keep track of everything, send out receipts, forms and letters of thanks, and note whether each donation was eligible for the UK tax relief known as ‘Gift Aid’.

I was keeping track of this using on a PC running the now long-gone Microsoft Works, which, for those less familiar with last-millennium computing, was a software suite incorporating basic and much cheaper versions of the things you found in Microsoft Office: a word-processor, database, and spreadsheet. If your needs were simple, it worked rather well.

Anyway, at one point I was printing out a list of recent donations on my dot-matrix printer, and I noticed what appeared to be some data corruption. In the midst of the sea of donors’ names, there were a couple of dates being printed out. Was this a software bug, or was my database file corrupt? I started investigating, while wondering just how much data I’d entered since my last backup and whether I could recreate it…

In the end, the answer was simple, and I breathed a huge sigh of relief. I tried recreating the entry for one of donors and the same thing happened again, at which point I dug a bit deeper and discovered a ‘feature’ of the app. The lady’s first name was ‘June’, and, though it displayed just fine on the data-entry screen, behind the scenes, it had been turned into 1/6/93! I skimmed quickly through the congregation to find the other problematic record, and found it was for a donation from a lady named ‘May’!

When I came back to doing some scientific computing in academia a few years ago, I was surprised and slightly worried to see several of my colleagues processing their data with Excel. It’s a wonderful program and very appealing, because of the ease of viewing, checking and plotting graphs of your results, but it comes with lots of problems of its own and shouldn’t be used as a substitute for a proper database (if you’re a church accountant), or for something like Jupyter Notebooks, if you’re a scientific researcher, unless you’re exceedingly careful. Last year, more than a quarter of a century after my issues with May and June, 27 human genes were actually renamed because of the number of errors caused in scientific papers by the use of Excel by researchers. The genes’ previous names were things like ‘SEPT1’.

All of this came to mind when reading Tim Harford’s enjoyable piece in yesterday’s FT, The Tyranny of Spreadsheets. Harford follows the origins of spreadsheets, double-entry bookkeeping and other ways of keeping track of things, up to the famous case last year where 16,000 people weren’t promptly told they had positive Covid test results, because somebody had used Excel’s old XLS file format, which can only store about 64,000 rows of information, instead of the newer XLSX. That’s not really a problem; the problem is that Excel doesn’t give you adequate warning when it’s discarding data, or changing it in an attempt to be helpful. And the results can be serious.

To quote the article:

Two economists, Thiemo Fetzer and Thomas Graeber … decided that no catastrophe should be allowed to occur without trying to learn some lessons. They combed through the evidence from Public Health England’s mishap. And by comparing the experiences of different regions, they concluded that the error had led to 125,000 additional infections.

Fetzer and Graeber have calculated a conservative estimate of the number of people who died, unknown victims of the spreadsheet error. They think the death toll is at least 1,500 people.

Think about that, as you click ‘Save As…’ and pick your data format.

(Thanks to my sister-in-law Lindsey for the link to the Harford article, which also traces some of the origins of spreadsheets from the 14th century; that’s before even I was using them!)

Anchors aweigh

It came to my attention, when renting a small boat last year, that I didn’t really know much about anchors: how best to use them, how long the rode (the cable) should be, and so forth. The little dinghy I sailed in my youth had a mud-weight, but a proper anchor? No, I’d never really had to use one of those myself, certainly not in any situation where it might matter. This gap in my knowledge was brought to mind again today as we listened to the audiobook of We Didn’t Mean to Go To Sea. Connoisseurs of quality children’s literature will understand the relevance.

Now, the wonders of modern life allow you to find out all sorts of things in all sorts of situations, and so it was that, relaxing in the bath after a hard day’s domestic labour, my thoughts naturally turned to things aquatic. I had my trusty iPad to hand, and so was able to watch a range of YouTube videos from people in exotic parts of the world explaining the different kinds of anchor, how long the rode should be for a given depth of water, why it’s important that the bit that attaches to the anchor should be a chain even if the rest of it is rope, and so on. Time passed, and I became simultaneously cleaner, more relaxed, and better-educated.

Finally, feeling that the bathwater was getting a bit cool, and it was time to move to a different berth, and I was now equipped to handle most anchoring situations I was likely to encounter before bed, I sat up, reached for the plug-chain, and gave it a tug. It seemed to stick for a moment and then came free, and I wound it in, only to discover a situation for which none of my training had prepared me…

The plug had remained in the murky depths. There was nothing on the end of the dangling chain.

It only takes one bit of data…

A few days ago, I created a new Facebook account. Not for myself, of course; I’m not stupid! (I deleted my own account many years ago and haven’t looked back.) No, it was because my company was writing some software that connected to Instagram, and doing that requires you to have a Facebook account in order to get ‘Developer’ access and for testing.

So, I set up a new email address and registered with a somewhat fake name, logged in and started browsing a generic here-are-some-feeds-you-might-be-interested-in type of experience. No personal details… all nice and anonymous.

The following day, I couldn’t log in. “Your account has been blocked.” Had I been rumbled? Ah, no, they just wanted to check I was really a real human by sending a text to my phone. I put in my phone number, got the text, filled in the code, and I was back in again. Jolly good. I logged out and went back to work.

A few days later…

The following Tuesday I logged in again, and there was a picture of my cousin, listed as someone I might want to connect with. Nice picture, I thought. And then, “Wait a minute! How do they know about her?”

I scrolled down, and sure enough, there were my friends, family, past work colleagues… dozens of ’em, all just waiting to welcome my ‘anonymous’ account into the fold. And then I remembered…

I still have a WhatsApp account. I seldom use that, either, but it’s there. And so, I presume, the act of entering my phone number for a security confirmation on my test account gave Facebook access to my entire graph of social contacts. Or, and perhaps in addition, lots of people with Facebook apps on their phone will have my phone number in their contacts. Facebook know exactly who I am, and all about me. Sigh. Should have used a ‘burner’ phone! Meanwhile, my friends have probably all received invitations to befriend a strangely-named new account and thought that the Facebook algorithms had gone a bit squiffy. Oh no. They’re working perfectly.

There is, however, something that still intrigues me. A noticeable aspect of the front page was the range of dog-related material. If this came from WhatsApp, how did they know I liked dogs? I guess it might be an Instagram link, but I really don’t have many dog pictures there either. Mmm.

No, I suspect this must be because I used my spaniel Tilly as the profile pic on the company account, just for fun. (Her modelling fees are very reasonable, and can be paid entirely in Bonios.) Anyway, if that is how they made the connection, then I can’t help wondering what other analysis they might be doing of people’s profile photos…?

Of course, I thought, I may be imagining it; they may just have decided that dogs were a cute and safe bet for the populace as a whole.

But I notice that there weren’t any pictures of cats on my page.

The Alpine Butterfly Knot

As someone who has done a fair amount of sailing in my youth, I like to think I’m more familiar with knots than the average bear. But there was one that I’d heard of in the past but knew little about: the Alpine Butterfly Knot (or Loop). It looks like this:

and it turns out to be jolly useful, but if you just look at it, it’s very tricky to work out how to tie it quickly.

There are lots of different techniques and lots of different YouTube videos about them, but today I found the method I liked the best:

Important YouTube Changes

In October, I wrote about my enjoyment of and use of YouTube, but I predicted that, at some point, people might want to shift some of their content elsewhere.

Well, that hasn’t happened yet, but there’s a small step today which might make people think more about it: the new Terms of Service, which take effect on 1st June. These include the following:

Right to Monetize

You grant to YouTube the right to monetize your Content on the Service (and such monetization may include displaying ads on or within Content or charging users a fee for access). This Agreement does not entitle you to any payments. Starting June 1, 2021, any payments you may be entitled to receive from YouTube under any other agreement between you and YouTube (including for example payments under the YouTube Partner Program, Channel memberships or Super Chat) will be treated as royalties.

Now, for most viewers, this won’t make much difference. We’re used to seeing ads on YouTube videos; in fact, quite a few of mine have them, and I earn enough from the ads to keep me in coffee beans. (I only use skippable ads at the start of the video, since I think those are the least annoying. You get more money if you allow others.).

When you view a YouTube video with ads, the revenue is typically split between YouTube and the creator. This revenue-sharing partnership is available to creators who have enough followers and sufficient viewing hours. In some circumstances, if you’ve included other material (such as commercial background music for which you don’t have a licence), rather than blocking you completely, YouTube will allow it to be posted, but you can’t monetise it: ad revenues are shared with the music copyright owner instead. The 360-degree video I recorded of my campervan trip to the Dordogne is an example: it does have ads, and the proceeds go to the creators of the background music I occasionally include. That seems reasonably fair to me. Doing this does have risks, though, if you’re thinking of trying it: firstly, you need to check whether it’ll be allowed for the tracks you’re thinking of including, and secondly, if the music publisher changes their policy in the future, your video may be removed.

Anyway, this new change will allow YouTube to put ads on the videos where I haven’t enabled them, perhaps to include more of them, or different types, and not necessarily share the proceeds of these extra ones with me. What’s more, if I had a very popular video, I think they could decide to put it behind a paywall.

As well as being detrimental to the viewing experience, this could be important, say, for universities who don’t want advertisements on their lectures, or software developers who don’t want competitor’s ads popping up over their tutorials. There will be ways around this, no doubt, involving payments to YouTube.

But this is just a reminder to make sure you keep copies of all the videos you upload in preparation for the day when you might want to move them somewhere else because your friends and family can’t watch them without a YouTube subscription.

YouTube is an amazing service, and a phenomenally expensive one to run, and most of us get it for free. So the fact that they are always looking for extra sources of revenue should come as no surprise. Especially to readers of Status-Q!

The uncomfortable truth about tithes

Many religions, especially those with Mosaic/Abrahamic connections, embrace the concept of ‘tithing’: giving one tenth of your income to the church. Originally, of course, this referred primarily to agricultural produce; in more recent years it tends to focus on Standing Orders and Gift Aid. Jesus himself apparently said little or nothing about it, which has allowed different groups of his followers to put differing degrees of emphasis, or compulsion, on on the concept since. But it is, of course, generally regarded by church leaders as desirable, and in my youth, sermons pointing out the biblical distinction between ‘tithes and offerings’ were not uncommon — the former being expected and, in effect, already belonging to God; the additional voluntary contributions constituting virtue (as long as both were done in secret).

Over coffee, after one of these sermons, I sympathised with the preacher. How obvious it was, I said, that very few people took these biblical directives to heart. He made some remark about how he was fortunate to have a generous congregation, and I fear I may have emitted something like a snort as I looked around at the gathered multitudes. I was very fond of them too, and many of them were very generous people, but I pointed out the mathematics…

In the Anglican church, for example, if people took tithing seriously, then every nine parishioners could support one vicar, who would then have the same average standard of living as his flock. (That got his attention!) You would need ten in your congregation if the vicar tithed too (which I guess would allow ten vicars to support one bishop, and so on).

OK, and you have to maintain the church buildings, do some good works, etc. So perhaps you need a congregation of about 15 people per priest for the church and clergy to lead a comfortable life. (That’s assuming your church doesn’t have any other income from land, bequests, indulgences or whatever…)

In the 35 or so years since that conversation, church attendance has declined so rapidly that many parishes will be doing this kind of maths for themselves. The average C of E congregation is something like 30-40 at present. But back then, though, I fear I may have left him contemplating his congregation of around 150 a bit less favourably than when he started his mug of coffee.

Location, location, location (or, ‘How technology saved me a few hundred quid yesterday’)

Yesterday, I lost my glasses. This is perfectly normal, and happens on a regular basis. One of my roles in life is to provide the opticians of South Cambridgeshire with a healthy and predictable revenue stream. What was much less typical about yesterday, though, was that I found them again!

Despite some of my recent posts, this was nothing to do with Apple AirTags, because I don’t currently have those attached to my spectacles. (I thought I looked rather dashing with them dangling about the ears, and many of the chaps at the Drones agreed, but I noticed that Jeeves had become particularly frosty recently, and found himself unable to extract me from a dashed sticky situation involving Madeline Bassett… but I digress. No AirTags currently adorn your correspondent’s brow.)

Anyway, yesterday afternoon, I was out walking Tilly, in a gentle rain, and I decided to take a photo of the view across the field in the mist. “This shot would be easier to compose”, I thought, “if I were wearing my glasses”, and I reached into the pocket of my coat… to discover that they weren’t there.

“Bother!”, said I, contemplating the last couple of miles that we had walked, the branches I had ducked under and the ditches I had leaped, any of which might be clues to their likely location. But then I remembered I’d received a phone call just a few hundred meters back, and had been able to read the name of the caller with ease, so I must have been wearing them then. I started to retrace my steps, gazing without much hope at the long wet grass, and thinking how easy this would have been if it weren’t for Jeeves.

After a couple of further passes over the relevant stretch, in the fading light, with a bemused (but useless) scent-hound trotting behind, I was about to give up hope, when I suddenly remembered: Hang on a minute! I had taken one other photo! It was after the call, but before I had noticed the glasses were missing. Surely I must have been wearing them then, and removed them afterwards because of the raindrops gathering on them. I bet I dropped the glasses at the location of the photo!

The problem was that it hadn’t really been a great photo; not many distinguishing features in the view. I was along one side of a big field, on a wide path, and I had paid little attention to my surroundings. Looking back at it now, I realise that I could probably have got those two rows of distant trees in the same relative alignment and located my former position quite accurately, but I was trying to view it on a small and decidedly damp screen… without my glasses. I was having enough fun just trying to tap on the right photo.

However, of course, all my photos are geotagged. I spent a while trying to work out how to see its location in the Photos app: not easy, even when you can read the text and make out the icons. (Hint: you need to swipe up from the bottom.) But eventually I found it. Not entirely helpful for precise location.

By tapping random blurry things, I managed to get into satellite view, and that was much better:

However, you have to remember that, at the time, it looked more like this:

And there are quite a lot of bends in the path with big trees beside them.

The Photos app doesn’t show your current location, only the location of the photo. I switched into Google maps, where I could see the moving blue dot, but the trees and crops looked completely different; the photo had been taken at a different time of year, several years before. Not much help.

But Apple Maps, of course, used the same satellite imagery as Apple Photos, and I was able to switch to and fro between the apps as I walked, until the blurry image with a blue dot seemed perfectly aligned with the blurry image with a yellow square.

I looked down, and there, nestled in a tuft of long grass, were my glasses. I had passed them three times that afternoon since dropping them, as had Tilly, who can track a pheasant at a considerable distance, but takes little notice of her master’s most valuable possessions right under her nose.

“At last!”, said she. “Come on! It’s dinner time.” And we scampered off towards the car.

Unwanted Corkpull

This is a lovely essay by Kelly Pendergast, brought to my attention by Andrew Curry on his Just Two Things newsletter.

It’s beautifully written and an enjoyable read, which is quite an achievement when it’s talking about consumerism, supply chains and waste management. Don’t let that put you off. Lots of good stuff there.

She talks about the admirable Oxo corkscrew she was given by a friend.

I suppose I should be happy to own such a perfectly functional piece, no muss, no fuss, no danger of injury, but what can I say? It’s ugly and I don’t like it.

You may not be surprised to hear that it was a gift. Life would be simpler if it had never entered the house, but between the gift-ness and its unfortunate excellence at performing its single task, I haven’t been able to get rid of it. Marcel Mauss, in his inquiry into the anthropology of the gift, asks “What power resides in the object given that causes its recipient to pay it back?” The gift corkscrew is freighted with a psychic weight that can’t be directly repaid, but can’t be forgotten.

She includes a memorable quote from Robin Nagle, anthropologist of material cultures and anthropologist-in-residence at the New York Department of Sanitation. (Now, that’s a job title to conjure with!)

“Every single thing you see is future trash.”

She talks about the other kinds of emotional weight we attach to objects, (or, sometimes, don’t, when we should do), and a feeling of guilt about being part of the flow of manufactured items on the way from raw materials to the grave…

Anyway, as Andrew Curry said, it’s hard to do it justice in excerpts; just read and enjoy.

On that topic, having referred to my late friend Martin King a couple of days ago, I will do so again today.

I remember that we were buying furniture for one of our companies’ offices, and he was spending some time seeking out used, good-quality, basic tables and chairs, which also seemed rather expensive to me. I probably said something about it being easier and cheaper to get them from Ikea.

“Yes”, said Martin (who, despite his considerable wealth, generally shunned anything that looked like luxury), “but we buy quality things because we don’t want to be responsible for creating rubbish in the world.”

That was a phrase that stuck with me.

© Copyright Quentin Stafford-Fraser