My original plan for this piece was to tackle two history and archaeology-specific aspects of time travel, but in the process of researching it, I’ve ended up writing a basic guide to ‘real’ (i.e. theoretical) time travel, for which, see below. Still, my main focus is to tackle what have become known as ‘Time-Travelling Tourists’ (TTT) and ‘Out-Of-Place-Artefacts’ (OOPArts) such as the c.80 BC Antikythera Mechanism. The former are mostly outside my remit, as such characters are invariably supposed to have originated from our own future, rarely seem to spend much time in our own past, and are coming back to warn of us something or other (the laughably fake ‘John Titor’ is the grandfather of them all). Having said that, we actually do have some strong pieces of evidence against the idea that time travellers have visited us from the future. Famously, theoretical physicists (notably Stephen Hawking) have held parties for time travellers (invitations going out only after the party has happened), and no-one turned up. Obviously there are lots of problems with that sort of stunt; plenty of reasons why people might not break cover. More compellingly, people have actually looked online for time travellers. No, not cranks like ‘John Titor’ (by the way; JOHN TITOR – JOHN connor from the film TermInaTOR, anyone?) but people typing things that they could not possibly have known at that time (using Google Trends and Twitter searches) and also (like Hawking) inviting time travellers to respond to them (from the future, creating anachronistic messages obviously, not just ‘yes, I am a time traveller!’). This had the advantage of only requiring the transmission of information back in time, not people (which would be more difficult). They came up completely empty on both counts (which, by the way, I can’t help being disappointed by). Finally, there’s a real show-stopper for TTTs that I deal with at the end of this article, one which applies to all forms of time travel that we have so far conceived of.
Let’s move on to OOPARTs, which are more firmly within my proverbial wheelhouse. As a jumping-off point, I took this article from Time Travel Nexus (who have some great material on TT fiction, but seem a little credulous when it comes to the ‘real thing’) as a case study of sorts. There is also this recent article at Ancient Origins, but it’s behind a paywall (I can’t be sure that it postulates time travel, but I’d be surprised if it doesn’t given the remit of the site and the track record of author Ashley Cowie). The big problem with TT claims surrounding these artefacts is that they are usually unfalsifiable. There’s no way to prove the negative, and the onus should be upon the claimant. However, having spent a LOT of time reading about TT theory, I don’t think people realise just how impossible it really is, despite periodical news headlines to the contrary.
Basically, time travel into the past is impossible. That might sound like a bold statement, but hear me out. There are hypothetical ways to achieve backwards time travel, but they are even less likely to happen than interstellar space travel. You should really watch this fantastic lecture by theoretical physicist Sean Carroll and/or read this short article, but to summarise the state of the time travel art, there are only a handful of ways that scientists can even conceive of achieving backwards time travel. These are (each with links to firstly a simple explanation, and then the original academic paper in brackets);
1). Tipler cylinders (Frank Tipler, 1974). Create a 100km+ long 10km wide cylinder of exotic matter, as dense as the sun, rotating extremely rapidly. You’d also have to find a way to even approach it without being killed in order to fly around it in a spacecraft to go back in time. There’s an interesting predecessor of these in Van Stockum’s 1937 version (covered in these Kip Thorne lecture notes) which differed in being made of ‘dust’ and being necessarily of infinite length (and therefore not physically possible). It’s the weakest of the three.
2). Cosmic strings (J. Richard Gott, 1991) – Find and somehow modify/relocate two of these equally hypothetical objects, 10 million billion tons per cm dense and stupidly long (infinitely so, if the universe is indeed infinite in size), and somehow get them moving past each other very, very quickly.
3). Wormholes (Kip Thorne et al, 1988). Find or create a wormhole and somehow stabilise it with more exotic matter (with ‘negative energy’). Move one end near a black hole or neutron star or accelerate near the speed of light for a period of time in order to get one end of the hole effectively into the future (by aging differentially). You’d then be able to go the other way through the wormhole to back in time. This seems to be our best hope, and yet achieving all of this would be no mean feat. Thorne himself lists the many reasons why Stephen Hawking was probably right about his ‘Chronology Protection Conjecture’ in this easy to read article (see here for Hawking’s original, less easy to read one). Spoiler alert – there’s a good chance that even attempting this solution would cause the wormhole to self-destruct; ‘…an explosive flow of gravitating fluctuational energy through the wormhole at precisely the moment when time travel is first possible — at the moment of time machine activation.’
All three of these are theorised to produce ‘Closed Time-Like Curves’, the only agreed upon mechanism in theoretical physics for time travel, but a mechanism that is still not proven to even exist. To quote one paper, ‘it is Aside from this issue, and those already listed above, there are some pretty serious drawbacks to all three.
A quick aside – there’s also another theoretical method that you don’t often come across in fiction, which is just going really, really fast. Although more straightforward than the above three, it’s still very confusing. You can read about it here, along with a good explanation of what ‘tachyons’ actually are (beyond being a go-to SF technobabble word). There is apparently a maximum backward time travel limit of just one year, and that’s if you can achieve a speed of 10 times the speed of light. Unfortunately, it is quite simply impossible to travel faster than light, hence the mental gymnastics that physicists have had to resort to in order to come up with the ‘big three’ above. However, I’d love to see it done in fiction, partly because of the bizarre visual effects that would result in showing multiple (not just present and future versions) of the time machine visible at the same time.
So, back to those ‘big three’. Firstly, none of them has ever been even proven to exist, let alone observed in nature. They would have to be discovered and manipulated or made from scratch, and then exploited. That’s the first hurdle. To do this would then require infinite amounts of energy or ‘negative energy’. Not ‘lots’, not ‘more energy than we’ve ever generated previously’, not ‘energy levels requiring cold fusion’ but literally infinite amounts of energy. In other words, an impossible amount. Physicist Ken Olum says that all known hypothetical methods would require the use of negative matter or matter with negative energy which, if it even/ever existed in sufficient quantities, would blow up the universe.
You’d then have to work out how to safely navigate the wormhole or other gravitic anomaly without being “spaghettified” by the tremendous forces involved. Let’s throw this into the overall unimaginable engineering challenge of finding or making these theoretical features in the first place, manipulating them into position and, in the case of wormholes, enlarging and stabilising them such that they can be traversed. Not to mention engineering and building the spacecraft and equipment to attempt all of this, and of course to convey passengers to the finished ‘time machine’ (also known as ‘the easy bit’).
To quote Carroll;
‘We can imagine making time machines by bending spacetime, but we don’t actually know a foolproof way of doing it.
Nor do we have a proof that it can’t be done.
The smart money would bet that the ultimate laws of nature simply don’t permit travel backwards in time.’
Carroll, Olum, Thorne and Hawking’s pessimistic views are further supported by another proof by Kay, Radzikowski and Wald (1996) that says essentially that the laws of physics will break down as soon as the time machine is activated. Here’s another quote from Kip Thorne, champion of the wormhole time machine;
‘When we physicists have mastered the laws of quantum gravity (Hawking and I agree), we will very likely discover that chronology is protected: the explosion always does destroy any time machine, when it is first activated.’
Hawking himself puts it best when he states his ‘chronology protection conjecture’ at the end of the original article;
‘The laws of physics prevent the appearance of closed time like curves.’
The final kicker is that, even if we can engineer one of these machines, *and* power it, *and* if it actually works, we would only ever be able travel back as far as the moment that the time machine was activated. The movie ‘Primer’ (which is excellent, but rather flawed), gets this right, as does my personal favourite ‘Cronocrimines’, but precious few others do because of the narrative limits that this choice places on events. Ironically perhaps, our single best bet for time travel would be some ‘arbitrarily advanced civilisation’ (as the theoretical physics and philosophy literature tends to call it) having created a time machine for us that we can use. Of course, if they had done so, it would be a long, long way from us, requiring a long, long journey and super-advanced spacecraft of our own to even begin to think about making use of it.
All of this (especially that last point) rules out the Antikythera mechanism as an out-of-place artefact, and in fact all other ‘OOPArts’ and indeed all time-travelling tourists into the bargain. It is all, frankly, bollocks – and makes a mockery of real history. Why is it so hard for us to accept that one person could have achieved something that was within their theoretical ability to produce, and yet so easy to accept something (time travel) that may not even have a theoretical basis? It’s pretty depressing. We even have other evidence for advanced technology of this sort from the period, notably that made by Archimedes. It’s not as though this thing was beyond the ancients either conceptually or technically. Even the superficially modern-looking gears have been shown to be made using hand tools. Although I suppose that wouldn’t rule out a ‘time traveller’ teaching ancient people how to make geared mechanisms, without having access to steam or electrical power. But why not foot or animal-powered machinery? For that matter, why no future metallurgy (the mechanism is wholly copper alloy and wood)? Why no actual (say) 19th century clock buried in some ancient stratigraphy? Why is the mechanism manually operated and not spring-powered? Why not teach them how to make screws? Why are there no out of place personal effects from whoever taught them? There’s no actual evidence of time travel here, just a piece of technology that they COULD, in fact, have made without any future knowledge? To quote from the article linked above; ‘The surviving features of the Antikythera Mechanism, particularly the lunar anomaly mechanism, support the idea that our proposed planetary mechanisms were within the engineering capacity of the makers of the Antikythera Mechanism—but only just.’ That article does a great job of explaining the astronomical/astrological functions of the mechanism, as does this superb lecture from former Science Museum curator Michael Wright (there’s a short explanation from him here, although it’s very low res). See also this Skeptoid podcast. In another blow to the idea that it could only have been made with future knowledge, all of it is also consistent with what we know of ancient Greek knowledge – there is nothing there that we didn’t already know that they knew. The mechanism has been thoroughly studied by actual academics since the 1950s, initially culminating in the article ‘Gears from the Greeks. The Antikythera Mechanism: A Calendar Computer from ca. 80 B. C.’ by Derek de Solla Price (Transactions of the American Philosophical Society Vol. 64, No. 7 (1974), pp. 1-70). Needless to say, none of the many people who have seriously studied the thing think that it is beyond the capabilities of the ancient Greeks.
Regardless, the mechanism remains an absolutely wonderful feat of engineering and craftsmanship. No doubt something similar will come to light in the future, only to be dismissed by cretins as proof of time travel rather than of the long tradition of human ingenuity.
So there you are – Doc Brown was, unfortunately, a quack.