NEW DISCOVERIES ON TIME TRAVEL
Throughout time, mankind has always been fascinated by the idea of time travel. From ancient myths and legends to modern science fiction, the possibility of changing the past or looking into the future continues to fascinate our imagination. However, now that science and technology have reached unprecedented levels, the question of whether time travel is really possible remains one of the most fascinating and mysterious aspects. The scientific community continues to explore the nature of time, conducting experiments and developing theories, but it is still unclear whether real travel into the past or future is possible from the perspective of modern physics and what risks lie behind such a possibility.
Time travel is the idea of the hypothetical movement of an object, person or information through different moments in time. The concept includes several variants of events, such as: travelling into the past and interacting with events that have already happened; travelling into the future – moving forward in time and interacting with events that have not yet happened; time lines – the idea that time travel can create different branches of reality or parallel time lines, where each reality corresponds to different choices and events, or closed time curves – a theoretical approach that assumes the existence of a different reality, or the existence of a different time line, or closed time curves .
Revolutionary in the context of time travel were Einstein’s theories of special and general relativity. They gave rise to the concepts of space-time and the closed time curve. The fundamental system of space-time considers space and time as interrelated elements of a single continuum in which each event can be described by four coordinates: length, width, height and time and is subject to gravitational forces. Space-time has become a key concept in modern physics, ranging from the theory of general relativity to quantum mechanics ..
The concept of a closed time curve can be thought of as a temporal loop describing the trajectory of a hypothetical observer who, always travelling through time from his own point of view, at some point finds himself in the same place and time from which he started. Such a curve can create potential time paradoxes, logical contradictions that arise as a consequence of past events that change or conflict with each other as a result of time travel .
Our common journey through time
Graphical representation of a closed time curve
Right now we are already travelling through time to our near future at the speed of one second per second. Einstein’s special theory of relativity, on which much of modern physics is based, states that the passage of time depends on how fast one is travelling. The faster one travels, the slower the seconds pass. An observer travelling at close to the speed of light will experience time with all its effects (boredom, ageing, etc.) much more slowly than an observer at rest . Einstein’s other theory, the theory of general relativity, on the other hand, states that gravity has an effect on the passage of time: the stronger the gravity in the vicinity, the slower time passes .
These two fundamental theories are perfectly illustrated by the example of the GPS global positioning system. With GPS, we know our exact position by communicating with satellites in high earth orbit. The satellites orbit the planet at a speed of 14,000 km/h and a distance of over 20,000 kilometres. According to the special theory of relativity, satellites move much faster than the terrestrial devices to which they transmit data and time passes more slowly for them.
For GPS satellites with atomic clocks, this effect is reduced by 7 microseconds, or 7 millionths of a second, every day. But according to the general theory of relativity, clocks closer to the centre of a large gravitational mass like the Earth tick slower than those further away. So the clocks on the GPS satellites go faster because they are much further from the centre of the Earth than the clocks on the surface, and the correction is plus 45 microseconds to the clocks on the GPS satellites every day. Recall the negative 7 microseconds from the calculation of the special theory of relativity and we get 38 microseconds more on the GPS satellite clocks.
The atomic clocks on board will not shift to the next day until 38 microseconds later than a similar clock on Earth. Such a shift forward in time seems really insignificant but, given the ultra-precision of today’s GPS technology, this makes all the difference . The Large Hadron Collider has regularly sent subatomic particles into the future, accelerating them to nearly the speed of light, thus moving their relative time 6700 times slower than stationary human observers.
If we transfer this idea to people as a concept and level the engineering component, we can assume that travelling into the future is quite possible. Suppose a person boards a spaceship capable of 99.995% light speed and heads for a celestial body 500 light years away: the journey will take 500 years, and the same amount of time will be needed to return. Adding 1000 years, the traveller finds himself back on Earth in the year 3024. But the speed of this journey would slow down his internal clock by a factor of 100 compared to Earth time, and the traveller would only age by 10 years. But there is a huge gap between what is theoretically possible and what is real . So far, the fastest spacecraft is only able to travel at 635,000 km/h, while the speed of light is 1,079,252,848.8 km/h, so we can only travel, at best, at just over 0.06% of the speed of light .
Paradoxes of the past
Graphical representation of time in the universe
Theoretical options for past time travel abound, but they usually involve insurmountable paradoxes and are based on outlandish theoretical constructs such as wormholes, black holes and cosmic strings (which may not actually exist). The general theory of relativity predicts the existence of ‘wormholes’, a kind of tunnel in space-time connecting one point in a galaxy to another.
This idea is based on the concept of a black hole and gravitational deformation. Scientists have suggested that if a black hole is a region of space-time where gravitational attraction is so strong that even light cannot escape from there, i.e. it essentially acts as a vacuum, sucking in all matter, then theoretically there is also a ‘white hole’ that acts as a source that ejects matter . While black holes never let anything out, white holes never let anything in, and to create a wormhole you simply take a black hole and a white hole and connect them to form a tunnel between them.
But even if one theoretically imagines the existence of such a ‘wormhole’, it is very difficult to predict how ‘safe’ it would be and what would happen to the particle in it and whether it would not instantly collapse under the influence of gravity. According to scientists, stabilising such a wormhole would require a form of matter with a negative mass . And of all this hypothetically possible wormhole that could be a portal in space-time theoretically proven is only the existence of a black hole, the white hole and matter with negative mass remain only a hypothesis, which is allowed by the theory of relativity .
The idea of time travel in terms of theories of relativity often comes up against various paradoxes that cause logical or temporal contradictions. These paradoxes underline the complexity and ambiguity of the idea of time travel and are discussed in theoretical physics and philosophy. For example, the ‘grandfather paradox’ considers a situation in which one travels back in time and changes something, for example by killing the grandfather before the birth of the parent. It is about understanding how this affects one’s existence. If your parent is not born, consequently you will not exist either and you cannot go back in time. “Grundy’s paradox” describes a situation where you go back in time to avoid the death of your grandparent and make your own existence possible. However, if your grandfather is not dead, why would you want to travel back in time?
Or do we have, for example, the so-called ‘information paradox’: If information from the past is sent into the future, can this information change the course of events so that the future from which it was sent does not occur? This paradox has to do with the possibility of changing the future with information from the future . In any case, from a logical point of view, all paradoxes suggest that any change in the past will necessarily affect the future.
At the intersection of two theories
Wormholes are still a subject of science fiction today
While the theory of relativity describes the behaviour of large objects such as people, celestial bodies and even galaxies, quantum mechanics describes very small particles such as electrons and photons. At these subatomic scales, physics operates in ways that confound our intuition. According to the mathematical modelling of a young scientist at the University of Queensland in Australia, based on the postulates of classical dynamics, according to which having data on the state of a system at a certain point in time can tell the whole story of the system, travelling into the past is possible without paradoxes .
The scientist studies the effects of certain non-random processes on multiple regions of the space-time continuum and shows how closed time-like curves can conform to the principles of free will and classical physics . His work shows that space-time can potentially adapt to avoid paradoxes. Put simply, if a time traveller thinks he is preventing or changing something by any action, the system will react in such a way that events will adjust to be logically compatible with any action taken by the time traveller, so as to avoid paradoxes and alter the future. No matter what one does or how hard one tries, important events will adjust to avoid any inconsistencies .
A team from the University of Cambridge conducted a ‘thought experiment’ that modifies past events a posteriori, demonstrating efficient time travel, but at the quantum level . The scientists used the principle of quantum entanglement, a phenomenon that describes the state of two or more quantum objects, in which their properties become interdependent to such an extent that it becomes impossible to describe the state of each object separately, regardless of the distance between them. This means that a change in the state of one of the ‘entangled objects’ instantaneously affects the state of the other object, despite the physical distance separating them .
Quantum physics is always a bit confusing; this phenomenon can be understood with the example of pocket watches. To better understand, imagine that you have shared a pair of pocket watches that are confused: one copy is in your possession and the other you have sent to your friend on the other side of the planet. When you check the time on your watch and see that it reads 12:00, you immediately know that your friend’s watch will also read 12:00, even though the distance between the watches is enormous.
In their simulations, the research team first modelled the entanglement of two particles and then sent one of them to be used in an experiment. Once the experiment was completed, the scientists had new information that led them to act differently. Instead of settling for an unsatisfactory result or completely redoing the experiment, they manipulated the second particle to modify the past state of the first and change the outcome of the experiment. Even this simulation of modifying the past is not without error, as the experiment modifies the past with the new information only about 25% of the time . So, in any case, more often than not.
A result that is more than sufficient, for those who promote scientific research, both in the public and private sector, especially in the military field, to invest energy, know-how and large sums of money to continue this research, whose official justification, in western countries, is to find a solution to make interstellar travel possible and accessible within a reasonable timeframe .
Playing with light
Illustration of the experimental platform used to realise temporal reflection
Wave physics also has something to say about time travel. Researchers at the City University of New York have demonstrated a breakthrough in the creation of light-based time reflections. The usual spatial reflection of light occurs when the light stream encounters matter with optical properties different from those of air in its path, causing it to reflect, like a ping-pong ball bouncing off a wall. But if one changes the optical properties not at specific points in space, but along the entire path of the light beam, at a particular time, the light stream will bounce back in time, repeating its traces, like a ping-pong ball returning to the last player who hit it, thus demonstrating the concept of temporal reflection.
The scientists used a special material called matte, which consists of arrays of microscopic rods or rings that can be configured to interact with and manipulate light, changing the optical properties of the material in a fraction of a nanosecond. An example of such structural properties is also found in nature, for example in the shimmering iridescence of a butterfly’s wing. Using a waveguide that transmits microwave light, scientists dynamically modified the properties of the waveguide, creating time reflection effects.
This experiment revealed unusual effects, such as a change in the colour and frequency of light and the inversion of time components. It is as if one were looking in a mirror but saw the back of one’s head, which could also appear a different colour. The study also notes that the light rays that collide in this process behave in an unusual way. Normally, light behaves like a wave or a point-like projectile. This experiment showed that in time reflection, light can behave in both ways, depending on how the waves collide, giving scientists the ability to control the energy of wave interactions. This research has potential implications for the development of new technologies and the understanding of fundamental aspects of physics, but it does not propel us into the past or the future .
The use of metamaterials and the interplay of optical effects open up new possibilities in the physics of the interaction between light and matter. Scientists at Imperial College London have succeeded in creating a laboratory analogue of a metamaterial that collects and compresses photons; this type of photon compressor shares the characteristics of black holes .
An astonishing result. Nevertheless, the idea of time travel rests on two pillars: relativity and quantum mechanics, which, although they work very well for some aspects of the universe, are incompatible in the context of time travel. Almost all experiments are theoretical and only work on paper in the form of formulas and calculations. It is therefore important to realise that new discoveries and theoretical models of the interaction between matter and space-time do not mean that time travel will become a reality. Certainly these concepts have the potential to expand our understanding of the structure of time, but actual steps towards physical time travel currently remain a matter of pure fantasy and scientific speculation, rather than a demonstrable real possibility.
 A complex system of data: https://en.wikipedia.org/wiki/Array_(data_structure)
 https://www.scientificamerican.com/article/light-can-travel-backward-in-time-sort-of/ , https://www.nature.com/articles/s41567-023-01975-y.epdf?sharing_token=VdRKZY-D7oEepAbkw7kbIdRgN0jAjWel9jnR3ZoTv0P-Y1zeDeMZfN0XstvlFFPW623hzPpIf8TQ2PzpcixbQoiW0atH7fNn9OhbtvBWndwFiU9NzNt2vqXs29TWwJ-qND8EypHgsNnqb38-RxBpB1oNk_11u81xb1KQ-Y3OP_IaAeRdfVJmhM6kb5Qxx5BcdioHqYLncqIohrObW9aaVIHPDKi4vYhAZzKn8PWpedA%3D&tracking_referrer=www.scientificamerican.com