Einstein’s general relativity, a system of equations, presents solutions that appear to allow travel into the past. In other words, there could exist a universe, permitted by these equations, where going back would be possible. Is it ours? Nobody knows anything about it. These solutions do not demonstrate that we are in the universe in question, but it would be necessary to demonstrate that they are incompatible with other characteristics of our universe to invalidate them. Astrophysics is not currently capable of this. There remains therefore an extremely precarious hypothesis on the feasibility of time travel, barely more solid than the existence of magic. The films that exploit it are more esoteric than science fiction.
Especially since there is a fatal logical flaw in this hypothesis, neglected by physicists who love equations to go back in time. Let’s start with the most common philosophical objection to time travel, which is the grandfather paradox. You climb into your H.G. Wells machine, jump back 150 years, and meet your grandfather, at the cradle, to shake his claw – or it could be that of a mollusk ancestor if you jumped much further. Patatras!! You let go of the baby and he fractures his skull! Your mother will not be born, and neither will you. You don’t exist. So what are you doing here?
Top thinkers have tackled this problem, including Stephen Hawking, who developed “timeline protection conjectures,” a sort of conspiracy of the laws of physics to prevent infanticide and other temporal paradoxes. However, there is no need to indulge in conspiracy theory. The idea of a paradox is false from the start.
This is due to the very nature of the universe described by general relativity, whatever the solution adopted to its equations. In all cases it is a block universe, where time does not “pass”. It is as still as a straight line in the spatial frame. Or rather a circle. Because if time doesn’t pass, it could bite its tail. This is where the hypothesis of the journey lies, which does not even require getting into Wells’ machine. Just take the appropriate timeline and presto! Here we come back to our past, to relive it again.
But relive the same. Not change it. Change is based on the concept of an absolute time that passes, which cuts through the universe in the present and replaces the past puck with the future puck. If you go back to the same place, why not decide differently and change the future? But in fact, this is perfectly impossible in the block universe. It exists from the outset “from all eternity”, if one can thus designate the absence of “time of time”, of an elsewhere where the temporal lines themselves could be manipulated. The block universe is already entirely woven. Impossible to change a single wire.
General relativity inherently forbids any “transformation” over time. What travels is, in fact, the theorist’s imagination, nothing more. This is, in fact, a serious flaw in Einstein’s theory. It leaves no room for this imagination, nor for the impression of time passing. It is impossible for it to claim the status of a complete theory of reality, except for a reductionist who sweeps our personal experiences under the rug, dismissing them as illusions.
Time travel is easy… but not within the framework of general relativity. Simply recall your memories, read an old story, and mentally reconstruct the scene. This time machine belongs to the realm of the psyche, not the physics, and general relativity is incapable of explaining its workings. To understand this, read Temporium, of which this article is a sequel.
In short, there are no time travelers in the Einsteinian block universe because it cannot accommodate any travelers at all. There is no “movement” or transformation, strictly speaking, within a block, only a sequence of predetermined states. The sensation of movement could only arise from something that experiences the succession of states. But since everything in the block consists solely of the states themselves, this something must be foreign, external to it. This is the fatal flaw of the Einsteinian universe, which renders it unsuitable for describing reality. Its proponents are blind to this flaw because they are unaware that they have placed themselves outside the theory, in the position of the creator God.
But this is rather good news for inventors of time machines. Since general relativity forbids them, but this theory is incomplete, will a truly comprehensive theory allow them to exist again? Phew, at least our imaginations have escaped the block. The sirens wail in unison! A murderess is on the loose. Will she try to kill her grandfather again?…
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