Part 1: Introductions

This is a thoroughly predictable companion to my review of Heinlein's prophecies for 2000 AD.  That old page already mentioned Clarke's rival forecasts (because Heinlein's own postscripts did), and it would have made sense to follow up with a 2001 page assessing them; but it's against the rules to start mocking a prophet during his lifetime, so publication of this page has been on hold.

Part 1: Introductions
Table of Contents
Part 2: Laws
Part 3: Essays
01 02 03 04 05 06 07 08 09 10
11 12 13 14 15 16 17 18 19 20
Part 4: Predictions
Col A Col B Col C Col D Col E
Part 5: Conclusions

The other problem with this comparison is that instead of being obliging enough to give a list of hard predictions as hostages to an eventual performance evaluation, the late Arthur C. Clarke was more cautious.  This may seem strange from someone who was prepared to use specific dates as the titles of some of his best‐known works of fiction; but his 1962 collection of futurological essays, “Profiles of the Future”, took a quite different approach – as indicated by its subtitle, “An Inquiry into the Limits of the Possible”.

Part 2: Laws

Oddly enough, the part of Profiles that has had most impact on popular culture wasn't part of the original text.  As first published, the book didn't include any numbered “laws”: those were an editorial addition for the French translation!  However, later revisions (in 1973, 1982, and 1999) adopted Clarke's Laws into their footnotes.

(Nor, by the way, does Profiles say that all revolutionary ideas pass through the three stages of “It's completely impossible – don't waste my time”, “It probably can be done, but it's not worth doing”, and “I knew it was a good idea all along!” – that's from The Promise of Space, 1968.)

Clarke's First Law:
When a distinguished but elderly scientist states that something is possible, he is almost certainly right.  When he states that something is impossible, he is very probably wrong.

This stereotype of authority‐figures declaring things impossible reflects Clarke's personal experience as an early advocate of astronautics.  Being fifty years younger naturally gives me a quite different viewpoint: when I was growing up, the space race was over, but government think tanks were predicting that given funding they could build a global missile defence network of X‑ray lasersats by the end of Reagan's term in office.  Most of it sounded like vapourware then, and another generation later it's evident that it was.  (Yes, I know there are people who can't face this fact.  I dare say they also still think that if 'Nam goes Commie the rest of south‐east Asia will fall like dominoes.)

Regardless of this clash of biasses, I have to acknowledge that it's a handy rule of thumb.  With a few caveats.

  1. That's science; it's the heretics' job to prove their novel idea works.  If cold fusion had been replicable in other labs, nobody would have cared that it seemed improbable.
  2. When a brilliant young scientist states that something is impossible even in principle, she may well be right.  Many of the most surprising discoveries of twentieth century science were limits; absolute caps on velocity, observation, calculation, and prediction.
  3. On the other hand, when a distinguished but elderly scientist from one specialised field starts declaring unlikely things possible in another, it's probably time for his pills.

And then there's Asimov's corollary:

When, however, the lay public rallies round an idea that is denounced by distinguished but elderly scientists and supports that idea with great fervour and emotion, the distinguished but elderly scientists are then, after all, probably right.

That mention of the public hints at the real issue, which is that this law isn't about technological progress so much as the way it's reported; and the journalistic prejudices it was designed to counterbalance are those of a bygone era.  These days if an undistinguished biotech company flack says that in principle you could genetically modify insects to secrete valuable pharmaceuticals, the risk isn't that it'll be disbelieved; it's that the labs will be besieged by a pitchfork‐wielding mob of tabloid readers convinced that scientists have already done that and need to be stopped before they start breeding giant baby‐eating drug‐hornets for the sheer hell of it.

Clarke's Second Law:
The only way of discovering the limits of the possible is to venture a little way past them into the impossible.

If what you're hoping for is clear‐cut predictions like Heinlein's, Clarke's Second Law is always going to look a bit of a cop‐out; he gets to churn out fantasies, taking the credit if they materialise but ignoring all the misses.  This is especially noticeable with the highly variable wish‐fulfilment level of the separate chapters (which were originally published as essays between 1959 and 1961).  But Clarke was always more interested in grand panoramas of things to come than in mapping current social trends, and it's not as if he wasn't up‐front about it.

Then again, as any advertising executive will tell you, the limits of the possible aren't always relevant.  The Reagan‐era Star Wars schemes influenced the course of the Cold War regardless of their feasibility, while on the other hand there are plenty of technologies that have been developed, proved workable, and abandoned, like dirigibles and supersonic passenger jets.

Clarke's Third Law:
Any sufficiently advanced technology is indistinguishable from magic.

This law is another one that lends itself to corollaries and parodies, of which my favourite is “any technology is indistinguishable from magic to the sufficiently retarded”.

And of course it's presented as upbeat, since again it's a justification for flights of fancy – the point being that you can't rule a technology impossible just because you can't imagine it as a practical engineering project.  However, the down side is that you can't make useful forecasts about something you're writing off as magic, so any sufficiently steep technological slope necessarily creates an “event horizon” for prophecy.

While that's a problem for writers of futurology, it has at least given us a whole new subgenre of fiction that takes seriously the idea of an exponential technological growth‐curve.  “Singularity” SF, such as Accelerando (which of course I'm plugging only so that I can casually mention that I was briefly Charles Stross's Systems Administrator while he was writing it), follows naturally from the view of the future described in Profiles.  So it's striking how completely different it is from the subgenre Clarke himself was most comfortable writing, with its sweeping cosmic vistas in the tradition of Olaf Stapledon's Last and First Men.

Clarke's Fourth Law:
For every expert there is an equal and opposite expert.

You didn't hear about the fourth law?  Well, yes, he did promise to stop with the third (like “both the Isaacs”), but the nineties edition of Profiles added this blatant contravention of the standard do‐everything‐in‐threes protocol.  That said, I think I'm going to declare from this point onward that the 1999 revised version doesn't get to count here, since for all I know it might have been inspired by my Heinlein page!

Part 3: Essays

Next up, quick highlights from each chapter of Profiles, with comments.  Instead of three laws, the book starts with two “Hazards”, each of which gets a chapter to itself.

01) Hazards of Prophecy: The Failure of Nerve
The first reason people fail to foresee things, Clarke says, is that even when given all the relevant information they refuse to face the implications (compare Asimov's Third Law).
Anything that is theoretically possible will be achieved in practice, no matter what the technical difficulties, if it is desired greatly enough.  It is no argument against any project to say: “The idea's fantastic!”
It's some sort of mark of how things have changed that he needed most of a chapter of examples to lead up to something that today reads as a truism.
02) Hazards of Prophecy: The Failure of Imagination
The second reason prophets fail is more forgivable (“and more interesting”): the failure to acknowledge that there might be crucial facts yet to be discovered that convert the impossible into the trivial.
From their very nature, these breakthroughs can never be anticipated; but they have enabled us to by‐pass so many insuperable obstacles in the past that no picture of the future can hope to be valid if it ignores them.
Personally I would add a third Hazard of Prophecy: the Failure of Cynicism.
03) The Future of Transport
A chapter about automated cars, Concorde, and Heinleinesque pedestrian beltways, from which I unfairly pluck this one sentence to quote:
In the cities, of course, the weather will be fully controlled before another century has passed; and outside them, even if we cannot control it, we will certainly be able to predict it and make plans accordingly.
Meteorology is a good example of a field where unanticipated breakthroughs (in this case in the mathematics of nonlinear systems) have pushed hitherto plausible technologies back towards infeasibility: even with supercomputers and satellite data, we can't tell whether it'll be raining this time next week.
04) Riding on Air
This is full of enthusiasm about Ground Effect Machines (by which he means hovercraft); and I'll admit I wish they'd got off the ground.  But the get‐out clause is there:
It is only fair to point out that the large‐scale use of private or family GEMs may not be a very practical proposition while we have to depend on the petrol engine. […] But the petrol engine is on its way out, as any petroleum geologist will assure you in his more unguarded moments.
My hovercraft is full of electric eels.
05) Beyond Gravity
On Cavorite, cities in flight, and the exploration of Jupiter.  Jupiter?  Wouldn't that be a job for automated probes?
I doubt this; in any event, there are always going to be cases where robots get into trouble and men will have to get them out of it.
So far we haven't bothered with anything even as fancy as robots – just remote‐controlled vehicles with a trivial amount of local processing capability.  When one gets into trouble, we radio it a software upgrade.
06) The Quest for Speed
This starts with a table illustrating the curve of the world speed record over recent decades (from 100+ mph trains to 10,000+ mph orbital flights).  Although refusing to envisage atomic rockets (“I do not believe that uranium and plutonium‐fuelled devices should be allowed off the ground”), he projected this trend continuing:
Man's love of record‐breaking will presumably lead to ultra‐high‐speed circuits of the globe as soon as they become technically feasible.
Not detectably; back in 1969, Apollo 10 hit 24,791 mph (that's 11 km ⁄ s), and it still holds the record for fastest‐ever manned vehicle to this day.  Since then we've given up on supersonic passenger transports, and we're retiring the space shuttle fleet.
07) World without Distance
This chapter starts by taking teleportation fantasies seriously and seeing where they lead.  It ends with visions of a society transformed by perfected transportation.  In between is a short interlude mentioning the possibility that on the other hand perfect communications would reduce the need for physical travel, since
Telecommunication and transportation are opposing forces
Thus once you've got the Internet, you can “telecommute” in to work, do your shopping online, and join your MMORPG team‐mates for a night on the virtual town without once setting foot outside your room.  Of all the topics Clarke prognosticated about, this for some reason is the one Heinlein chose to pick a fight about… demonstrating that not only could he not make decent predictions, he couldn't recognise them either.
08) Rocket to the Renaissance
Seen in retrospect, the pro‐astronautics propaganda in this chapter is way over the top.
The road to the stars has been discovered none too soon.  Civilization cannot exist without new frontiers; it needs them both physically and spiritually.
If reckless, unsustainable expansionism is a prerequisite for civilisation, what was Imperial China?  As far as I'm concerned, people who go to places just so they can say they were the first to leave footprints there are no more admirable than the ones who get in the record books by attaching clothes pegs to their faces.
09) You Can't Get There from Here
Dealing with journeys to the centre of the earth, the surface of the sun, and so on.
A man‐carrying, nuclear‐powered “subterrene” is a nice concept for any claustrophobe to meditate on.  For most purposes, there would be little point in putting a man in it; he would have to rely entirely upon the machine's instruments, and his own senses would contribute nothing to the enterprise.
And more importantly, he wouldn't get to leave footprints.
10) Space, the Unconquerable
On the fact that even with magic stardrives, space is still too big for space‐opera galactic imperialism.
Vega of the Lyre, twenty‐six years away at the speed of light, near enough the point‐of‐no‐return for us short‐lived creatures […] For no man will ever turn homewards from beyond Vega, to greet again those he knew and loved on Earth.
What, not even if his journey takes him a subjective (time‐dilated) week of hibernation, and his friends back home are AIs and immortals?  This may yet turn out to be a Failure of Nerve.
11) About Time
Various wibbly ideas with a lot of hedging, but including:
If we ever learn to control gravity, we may also learn to control time.  Once again, titanic forces would be required to produce minute time‐distortions.  Even on the surface of a White Dwarf star, where gravity is thousands of times more powerful than on Earth, it would require very accurate clocks to reveal that time was running slowly.
You'd think he'd have been in a hurry to update this once the existence of black holes was established, but even the eighties edition only added a line about neutron stars.
12) Ages of Plenty
This chapter on natural resources was optimistic on principle (the final revised edition kept things positive by bringing in plenty of new material about Space Elevators).  But already in the early sixties he included provisos to the effect that we'd better get nuclear fusion working before it's too late.
If, as is perfectly possible, we are short of energy two generations from now, it will be through our own incompetence.
Who's “we”?
13) Aladdin's Lamp
On universal constructors, written long before anybody expected self‐replicating “Santa Claus machines” to be the killer app (let's hope not) of nanotechnology.
It is certainly fortunate that the Replicator, if it can ever be built at all, lies far in the future, at the end of many social revolutions.
He meant the kind of atom‐perfect Star Trek replicator you could put a human being through, which is indeed a tall order, but “3D photocopiers” are coming along faster than anticipated.
14) Invisible Men, and Other Prodigies
This chapter is a string of ever‐more‐unlikely fantasies, ending with the wild idea that a fourth spatial dimension might be a neat way to account for recent anomalous discoveries in particle physics such as parity violation.
In a Four Dimensional universe the distinction vanishes, and so, accordingly, does the paradox now worrying the physicists.  The Nobel Prize committee can contact me through my publishers.
Sorry, Sir Arthur – modern cutting‐edge physics postulates at least half a dozen more dimensions than that!
15) The Road to Lilliput
On the limits of biological miniaturisation.
We can dismiss, therefore, those ingenious stories of midget (or even microscopic) spaceships as pure fantasy.  If you are ever persistently buzzed by a strange metallic object that looks like a beetle, it will be a beetle.
Or a nanotechnological mothership; just not a spaceship with flesh‐and‐blood crew.
16) Voices from the Sky Cosmic Engineering
The original version of this was an explanation of how telecommunications satellites were going to work, so for later editions he had to replace it with something still in the future.  For instance, on satellite TV:
The very profusion of available channels, each capable of being received by most of the human race, will make possible services of a quality and specialized nature quite out of the question today.
Now that's Failure of Cynicism.
17) Brain and Body
A chapter larded with gullibility: Clarke thought hypnotically recovered memories were eidetically accurate, attributed fire‐walking to autosuggestion rather than simple physics, and fell for the Russian Sleep Machine scam.  But then there's this:
It is hard to think of any invention that would be more valuable than the device which science fiction writers have called a Mechanical Educator.  As depicted by authors and artists, this remarkable gadget usually resembles the permanent‐wave machine at a ladies' hair‐dressers, and it performs a similar function – though on the material inside the skull.  It is not to be confused with the teaching machines now coming into widespread use, though one day these may be recognised as its remote ancestors.
Teaching machines?  [2009 PS: oh, like these!  Skinner‐box‐tastic.]
18) The Obsolescence of Man
Clarke could see that the future would feature mighty mechanical brains; unlike many, he even saw that they were ultimately going to be tiny mechanical brains.  The imminence of networked commodity PCs still blindsided him, but:
For a few generations, perhaps, every man will go through life with an electronic companion, which may be no bigger than today's transistor radios.  It will “grow up” with him from infancy, learning his habits, his business affairs, taking over all the minor chores like routine correspondence and income tax returns and engagements.
The only part of this that now seems ludicrous is the assumption that you'd stick with the same PDA/PA your mother bought you, back in the days when quantum computers were a novelty!
19) The Long Twilight
Odds and ends.
Our Galaxy is now in the brief springtime of its life – a springtime made glorious by such brilliant blue‐white stars as Vega and Sirius, and on a more humble scale, our own Sun.  Not until all these have flamed through their incandescent youth, in a few fleeting billions of years, will the real history of the universe begin.
So we're not entitled to penalise Clarke for auguries that fail to come true before the sun goes out…
20) Chart of the Future
There is no Chapter 20 – this is another list that stops at 19.  However, there's an appendix featuring a timeline of 1800–2100 with forecasts for coming decades, and I thought this would be a good place to mention that the introduction specifically says:
And because I am trying to visualize ultimate goals, there is little discussion of timescales (apart from a light‐hearted “Chart of the Future” to be taken no more seriously than all such predictions).
Okay, so now I've clarified that I can get on with ripping it to shreds.

Part 4: Predictions

Clarke's Chart of the Future had five columns, which I'll handle one by one.  Later revisions of Profiles left the five categories unchanged, but rescheduled and reorganised a lot of the contents; dates in the following with insertion or deletion tags indicate emendations, usually in the 1981 edition.  For obvious reasons, I'm ignoring the retrodictions placed before 1960, but I'm including only the items that were (at some stage) due before 2060.  Later decades were for all intents and purposes the futurological equivalent of “Here Be Dragons”.

Column A:
Spaceship (1960s)
Manned vessels capable of getting out past low Earth orbit are one of those technologies we've developed and then (at least temporarily) abandoned.
Space Lab. (1970s 1990s)
For my money, this was already fulfilled before Clarke rescheduled it.  In the process he pluralised it to Space Labs, but we get to count Skylab plus Mir as two…
Lunar Landing (1970s)
Down as a successful projection; later versions renamed it Moon Landing, but never corrected the decade!
Nuclear Rocket (1970s)
One he must have been glad to cancel.
S.S.T. (1970s)
Supersonic passenger transports, inserted retrospectively as an unforeseen development, and (like a lot of the pre‐1960 entries) as a sort of a “springboard” for later predictions, in this case Hypersonic Transport.
Planetary Landings (1980s 2000s)
The eighties revision substituted a reference here to imminent Space Probes, clarifying that the late‐running prediction was for manned missions.
Colonizing Planets (2000s 2050s)
This plummeted down the chart and changed title to Space Colonies, which I suppose would include low‐orbit villages.
Earth Probes (2010s)
With our hunger for new petrochemical reserves you'd think we'd be hearing a lot about mechanical moles, but we aren't (unless you watch the movie “The Core”, which I don't recommend)… do news editors always file it under “boring”?
Interstellar Probes (2020s 2100+)
This is a remarkable retreat, given that “Space Drive” was due by 2070!  It's not as if it would need a human pilot… or even cost anything, once you've got Fusion Power plus Space Mining plus Replicators.
Hypersonic Transport (2020s)
The only things that need to be transported at Mach 5+ are WMDs, but people occasionally claim they're going to build these any decade now.
Deep Sea Probes (2030s)
A couple of decades later than Earth Probes!  Couldn't you simply steer your subterrene under the Mariana Trench and raise a periscope?
Lunar Settlements (2030s)
This was inserted to accompany (and help excuse the delay of) Colonizing Planets (originally above).
“Space Drive” (2050s 2060s)
The kind fuelled by pixie‐dust.
Column B:
Communication Satellite (1960s)
Clarke's big successful prophecy, which became familiar enough that he eventually got to abbreviate it to Comsats.  Mind you, he was visualising space‐stations full of radio engineers…
Pocket Calculators (1960s)
Inserted after the fact as an unforeseen development, and as a springboard for later predictions.
Video Recorders (1980s)
Ditto – but this is now something of an abandoned technology.  Twenty years ago, most ordinary UK households had the facilities for automatically storing a week's supply of some favourite soap opera on portable, reusable cassettes.  These days VCRs are vanishing from the shops, but the nearest thing to a replacement is the programmable DVD player/(re)writer, a gadget most households don't have.
Translating Machines (1980s 1990s)
Delayed and then cancelled; but those jokes you're thinking of were about the seventies implementation – there are handheld devices on sale today that'll take a stab at this.  What could possibly go wrong?
Personal Radio (1980s 2000s)
The eighties version calls it Universal Radiophone, which more clearly matches “global mobile phone networks”.
Pocket Educators (1990s)
This isn't the same as the Mechanical Educator he had scheduled for the 2060s, so if it's not that and it's not books, what did he mean?
Artificial Intelligence (2000s 2020s)
And yet Machine Intelligence Exceeds Man's is off in the 2090s, instead of beginning as soon as that first AI starts getting hardware upgrades… [2022 PS: bear in mind that this was written back in the days when “AI” meant “Turing-testable machine mind” rather than “neural‐net plagiarism app”.]
Global Library (2000s 1990s)
Apparently meaning something rather like the WWW, given that it's one of the few climbers (though oddly he retitled it to plain Libraries).  Okay, so he didn't anticipate Facebook or YouTube, but this is still more or less the only feature of Tomorrow's World that I've ever looked forward to and then ended up getting.
Telesensory Devices (2010s 2020s)
That is, remote sensing equipment you can patch into your nervous system.  Already slightly available if you're willing to risk being Kevin Warwick.
Logical Languages (2020s)
I'm hoping that the reason this one vanished was that he realised it was worthless.  People have devised speakable languages with algorithmically parsable grammars, and you can still translate Jabberwocky into them.
Robots (2020s)
By which I surmise he meant something more than production‐line automata; it's not obvious why he cancelled the prediction.  After all, Artificial Intelligences sound like prime customers for perambulatory machine bodies – assuming HAL won't always blow every penny of his pocket money on RAM.
Contact with Extra‐Terrestrials (2030s)
This of course requires them to be available for contacting.  Wait, though – if these are advanced, friendly ETs, why don't we get Matter Transmitters until 2090?  Maybe that's why later editions watered it down to “Discovery of Extra‐Solar Intelligence”.
Memory Playback (2050s)
The eighties revision left this in the same decade but changed the name to Memory Recording, to match Video Recording… unless maybe he was hinting that playback will take another century to develop.
Column C:
Efficient Electrical Storage (1970s 1980s 1990s)
Battery technology made purely electric cars feasible quite a while ago, but we're only now approaching the stage where it's possible to get anybody to sell you one.
Solar Energy (1980s)
This more or less counts, though it's taken a long time to get people to start using it.
Ocean Thermal Power (1980s)
Decades of experimental plants have yet to make this cost‐effective.
Fusion Power (1990s 2010s)
Perpetually a generation away, and still looking good for being up and running in only another twenty or thirty years.
“Wireless” Energy (2000s)
Running late, but there seems to be optimism that we'll have it someday, if only with strings attached; so why was it cancelled?  [2020 PS: younger readers may need a translation here – for Clarke, “wireless” meant “broadcast from the transmitting station many miles away”.]
Sea Mining (2000s)
Manganese nodule mining was a handy cover‐story for Cold War spook stuff, but it still isn't quite profitable.
Non‐Cryonic Superconductors (2010s)
It's unclear what temperature Clarke was thinking of, but the current record (−135 °C, −211 °F) is already above the level of what's now officially called “cryogenics”.
Weather Control (2010s 2030s)
People have been trying cloud‐seeding since the 1940s, but “control” is a long way off.
Space Mining (2030s 2050s)
Digging a rich seam of vacuum?  What he meant of course was asteroid mining – economically viable if there's a nearby market (i.e. lunar colonies).
Transmutation (2040s 2060s)
Of elements, industrially; one to start daydreaming about after we've got Fusion Power working.
Planetary Engineering (2050s 2090s)
Terraforming and so on; the eighties revision leapfrogs it down past Climate Control (which makes more sense).
Column D:
Protein Structure (1960s)
Dropped, and not because it's a failed forecast; maybe it was just a dull one.
Genetic Code (1960s)
This was hardly a prediction even when he made it, but it's another “springboard” entry.
Organ Transplants (1970s)
Inserted as an unforeseen development, and as a springboard for Brain Transplants.
Cetacean Languages (1970s 1980s 1990s)
This is another of those things you only get to discover if they're there to be discovered.  The eighties revision vagues it down into Animal Languages, but still, you might as well foretell the discovery of animal team sports.
Exobiology (1980s)
Yet another thing you only get to discover if it's there to be discovered.  Clarke continued to list Planetary Landings, so the fact he dropped this one (which would be fulfilled by, for instance, unambiguous signs of biochemistry on Titan) is an interesting shift in worldview.
Cyborgs (1990s)
Was this cancelled on the assumption that people would get Organ Transplants instead, or was it only because it's so hard to define?  There are people walking around with increasingly sophisticated prosthetics and artificial organs, but how routine and how obtrusively cybernetic do they need to be to count as fulfilling the prediction?
Cloning (2000s)
Split off in the eighties revision from Bio‐Engineering.  If he meant Dolly the sheep, it's quite accurate.  If he meant the start of the Clone Wars, less so.
Time, Perception Enhancement (2000s)
The eighties version retitles this Consciousness Expansion.  Given that he still put it decades in the future this seems a misleading label for things like accelerated perception.  A miss.
Control of Heredity (2020s 1980s)
Replaced by the obviously imminent technique of Gene Splicing, which gets it onto the “confirmed” list by ignoring the question of whether we'd ever use it to control human heredity.
Brain Transplants (2030s)
The problem with this eighties addition is, if you can splice a brain into a foreign nervous system, presumably you can also fix broken connections inside a living brain.  So where are you going to find body‐donors with unsalvageable brains?
Bio‐Engineering (2030s 2050s)
The eighties version clarifies this to “Artificial Life”, while moving it down the list against the tide of biotech optimism.  That's still a fuzzy target, but people have already produced bacteria with synthesised genomes.
Intelligent Animals (2040s 2020s)
Meaning animals with engineered IQ upgrades (mind you, uplifted dolphins aren't Turing‐testably intelligent, because they can't type).  At present our efforts are working on the principle that we can increase the average intelligence of the animal kingdom by wiping out everything but rats.
Suspended Animation (2050s 2010s)
The results of the latest experiments on animals (using either cryonic or chemical approaches) are getting less and less revolting, so maybe this will turn up on time.
Column E:
Nucleon Structure (1960s)
Given that this was treated as a confirmed hit, it must mean the discovery that nucleons were made of quarks.
Pulsars (1970s)
A particularly obvious example of a thing you only get to discover if et cetera et cetera (though in this case it's an unforeseen discovery, inserted in the eighties edition).
Strange Particles (1970s)
Gravity Waves (1980s 1970s 1990s)
Binary pulsars provide good evidence of gravitational waves, so everyone's sure they're there to be discovered, but we still haven't managed to catch them.  Clarke moved this up from prediction to confirmed past event and then back to the future as the early claims for direct detection crumbled.
Subnuclear Structure (2000s)
By which he meant sub‐quark (i.e. superstring/brane) theories, I deduce.  If theoretical models count, we were early; if he wanted brane surgery we're likely to be very late (hence the item's disappearance, perhaps).
Super‐Heavy Elements (2000s)
Yup, steady progress has been made up through the transactinides; elements around 120 may even turn out to be stable enough to occur in nature.
Magnetic Monopoles (2010s)
These are still up in the air, though it's suspected that they're prohibitively high‐energy.
Nuclear Catalysts (2020s)
This would essentially mean cold fusion.  In fact we've had muon‐catalysed tepid fusion since the eighties… but unfortunately it consumes more energy than it generates.
Gravity Control (2050s)
This had a whole chapter to explain how remote the prospect was, so it was no surprise to see it vanish.  See also the following.
Space, Time Distortion (2060s 2050s)
For some reason this timewarps its way up the chart from nonsense territory and strengthens from Distortion to Control, just as Gravity Control vanishes – some sort of merger?

Part 5: Conclusions

What, were you expecting me to end by awarding him a score?  That's a tricky one.  Well, let's focus on the predictions from the chart that were for a future decade when they were made, but which we are now in a position to evaluate; by my tally there are about two dozen.  Of these, how many have come true?  I'd say there are at least half a dozen definites plus about as many arguable or partial hits.  There's no obvious way of organising deductions for late arrivals (come to that, do early arrivals give a bonus or a penalty?), so at present my best estimate is that Clarke should get something like 35±10 %.

However, that's only an interim appraisal.  As time goes by and more decades on the chart become judgeable, we can expect the figures to rise and (past 2060, especially) fall.  Eventually it will be possible to divide the list into prognostications that arrived early, promptly, late, or never, and award a final score on that basis.  But I'm not going to be so foolish as to pretend I can predict how soon that day will arrive!