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2nd November 2023
02:30pm GMT
In news, that will no doubt confuse Marty McFly and Dr. Emmett Brown and a host of time travellers on TikTok, scientists have concluded that time travel isn't in fact possible - in case there was any doubt.
The concept, made famous by movies like the Back to the Future franchise and TV shows like Dark and Loki - see Rotten Tomatoes list of best time travel shows here - time travel, has, sadly, been found to be impossible. Even with the use of a flux capacitor.
The conclusion to the debate - no one was probably having - is based on the well-established phenomenon of what happens when light passes through an interface. This could be anything from glass or water.
While the solution to the query has been known for some time, scientists have now found something rather interesting going on in the middle, Unilad reported.
As light goes through the interface, we know that speed often changes - though that doesn't explain what actually happens at the interface.
Scientists have put forward an equation in the case of a universe with one space dimension and one time dimension.
Lead author of the study assistant professor Matias Koivurova, from the University of Eastern Finland, said: "Basically, I found a very neat way to derive the standard wave equation in 1+1 dimensions. The only assumption I needed was that the speed of the wave is constant. Then I thought to myself: what if it’s not always constant? This turned out to be a really good question."
The team behind the study, published in full in the journal Optica, delivered the expected solution on either side of the interface.
But there was one crucial requirement to achieving it. It required time to only move forward.
While the equation may be one-dimensional, it has solved a long-standing controversy that has stumped scientists.
Study lead Professor Marco Ornigotti explained that in physics there is a "very famous debate" called the Abraham-Minkowski controversy.
He continued: "The controversy is that when light enters a medium, what happens to its momentum?
Minkowski said that the momentum increases, while Abraham insisted that it decreases.
"We found that we can ascribe a ‘proper time’ to the wave, which is entirely analogous to the proper time in the general theory of relativity."
The upshot of the breakthrough is that the arrow of time is always going in one direction, making time travel impossible.
The study reads, in a review of "our understanding of time".
"In everyday experience, time always seems to have a preferred direction. That is, time always moves towards the future and away from the past.
"However, there is no concrete reason why this should be. As Sir Arthur Eddington wrote: “Let us draw an arrow arbitrarily. If as we follow the arrow we find more and more of the random element in the state of the world, then the arrow is pointed towards the future; if the random element decreases, the arrow points towards the past. That is the only distinction known to physics.
"This was how Eddington coined the term “arrow of time,” and tied it explicitly to the second law of thermodynamics. Up to now, this has been the best explanation for the existence of a preferred direction of time. Nonetheless, it is only an observation of the behaviour of macroscopic objects, and not an actual law of nature."
The study paper explains: "The solutions have a preferred direction of time, therefore establishing the microscopic arrow of time. We then continue by concentrating on the special case of electromagnetic waves, and show that an electromagnetic wave that has a varying speed will experience relativistic effects. Moreover, when the wave is moving along a geodesic, its energy and momentum are conserved. This has important implications on one of the longest standing debates in photonics."
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