Every film is ultimately a deception, some lies are just more obvious than others. The success of a film rests on how much you enjoy the deception; how convincing it is, is almost secondary. James Ward Byrkit’s Coherence, a mind-bending psychological thriller with a premise apparently based on the mathematical thought experiment Schrodinger’s Cat, succeeds in the first instance as a hugely entertaining story that barely stops to let you know that it’s all nonsense. It’s only after the film has finished that you realise the title was, perhaps, aspirational. Hugh Sullivan’s The Infinite Man, an ultra-low budget time travel film about a man who tries to mend a relationship by travelling back a year to when it all went wrong manages the miraculous feat of being both completely entertaining whilst still maintaining a logical consistency within its own rules.

Coherence is about an awkward dinner party between old friends with a tense romantic history that is made more awkward by a comet fracturing the fabric of reality. As events escalate from curious to disturbing and inexplicable, the tensions in the group rise to the surface and each character is forced towards introspection, and big questions are asked of each of them – what makes them uniquely them? What really makes Coherence work is that each character is established effortlessly, with convincing dinner dialogue showing the quirks and anxieties of each of this slightly mismatched group of friends. Aside from an annoying tendency to cut to black when a scene has run out of steam, the opening scenes are effective in building up tension before the psycho-sci-fi elements have really come into play. When things do kick off, there’s a bit too much SCIENCE exposition dialogue, a futile task when the plot is largely inexplicable, but the mystery builds with an intensity that leads to almost total insanity by the end. It makes a virtue of its low budget by setting it all in one house and using this to intensify the claustrophobia, forcing the characters to confront each other and themselves. The big, bonkers idea at the centre of it all works not because it makes logical sense – it doesn’t – but because it asks big questions of the main players. The Schrodinger’s Cat plot forces the characters to ask themselves whether they can ever change, even within infinite possible worlds.

The Infinite Man has an even lower budget than Coherence – it is set entirely in a disused motel, has only three actors and very little in the way of special effects. Dean is a man who tries to control every element of his anniversary weekend with his girlfriend Lana, but things go wrong when their motel has closed down and one of Lana’s old flames turns up. Dean’s solution is to travel back in time with Lana a year later to try and fix things but this ends up being more complicated than it first appeared. As with Coherence, it’s best to know as little as possible before going into the screening. At the centre of it all is an incredibly funny, subtle performance from Josh McConville as Dean. His character’s arc moves from pathetic to slightly less pathetic over the course of the film, and McConville captures every shift, even through a slight change in his posture or the way he walks. It’s a perfectly judged comic performance that also hits the emotional notes when needed. Hannah Marshall and Alex Dimitriades round out the tiny cast with equally strong performances that really help the big ideas land. The last time time travel mechanics melded so seamlessly with daft humour, it ended with Johnny Be Goode. It’s obviously far more low key than Zemeckis’ masterpiece, but it has a similar spirit of embracing the inherent silliness of time travel while still spinning out a compelling plot that uses its central conceit to great dramatic and comic effect.

At film festivals like Edinburgh, low budget is often king, but that means the quality of the films on show can range from the dazzlingly inventive to the painfully amateur. The Infinite Man and Coherence were both made for the approximate cost of a train fare to the set of Star Wars, yet both demonstrate that big ideas, a sharp script and probing questions about humanity can totally transcend lo-fi trappings and budgetary limitations to become something very special indeed.

Coherence is playing on the 25th and 28th June and The Infinite Man is showing on the 26th and 27th June at the Edinburgh Film Festival.