Traveling Back in Time

Time is a merciless companion every moment that passes in our lives is transitory because as soon as it happens it has already become a memory at some point or another we have probably all wished we could relive precious past moments maybe it is to visit a historical moment or person to solve a mystery that baffles the annals of history or maybe it's visiting a missing friend just for the chance to share one more moment together or maybe you wish you could go

back

and type the wrong message. from your past to undo a mistake that haunts you every day of your life.

Physics reveals that

time

and space intertwine to form a unified fabric for our universe, but

time

is not like those other dimensions, although we can easily move in any spatial direction we want. We seem driven to advance only through time, neither stopping nor going

back

, but human will and ingenuity have broken Impossibles before, whether flying through the sky, eradicating smallpox, breaking the sound barrier, or running the mile. four minutes and yet reversing time would have been too much. deeper ramifications for our existence and our understanding of the way the universe operates, could it then be that the universe bans reverse time travel altogether?

In 1905, a young German physicist named Albert Einstein fundamentally changed our understanding of the universe by proposing that space and time were intimately connected. He was inspired by the experiments of Mickelson and Morley, who had measured that light travels at the same speed in both summer as in winter. This observation perplexed many at the time, as it had long been known that the Earth orbited the Sun to explain. Due to the movements of the planets, then the Earth must move in different directions between the seasons. Normally we would expect to catch up or fall behind something in motion, but Einstein proposed that the speed of light is a constant for all observers, no matter how fast or what it is. direction in which they are moving now the speed is simply the distance traveled per unit of time and therefore to keep the speed of light constant, Einstein's theory implied that time and space have to bend to accommodate this rule, this means that a clock moves relative to you.

Experimental tests of these time dilation effects have consistently verified the extraordinary predictions of relativity, to the point that we now, in fact, regularly use the theory to correct for time. There are variations between clocks on Earth and those aboard GPS satellites and yet, despite Einstein's union of space and time, they remain persistently distinct, we have three dimensions of two-way space but only one. dimension of unidirectional, why not some other combination? Well, the reason for this may simply be that it could not have been any other way. Now string theory invokes many more dimensions of space but these are microscopic dimensions rolled up so small that we cannot even perceive them.

Several physicists have shown that if there is only one time dimension then Adding more microscopic dimensions of space to the three known leads to unstable planetary orbits and even unstable atoms necessary for life, so there could be an ocean of dead universes out there with no one born into them to observe its existence in less than three spatial dimensions. is more viable, but here, then there simply wouldn't be enough complexity enabled within said universe to allow an intelligence like ours to one day evolve, for example, if you were put on a plain, your nerves would actually have to pass through each other approximately. time, if there were two dimensions of time, one could rotate around the plane they form just as we do in space, this would make time travel to the past trivial, one could simply turn around in time and visit the past or the future.

Cosmologists Max Tegmark argues that intelligent beings who developed technology would not arise in such a universe, since it would be impossible for them to make even simple predictions about their future, so it is perhaps not surprising that we find ourselves living in a universe that we make one of. in which we are. We are forced to move inexorably and exclusively through time, and yet we are forced to ask ourselves: can we bend these rules? Are they really immutable truths or just flexible guidelines? Maybe, if we really put our mind to it, maybe there is a way back to fix our problem. errors to correct mistakes of the past to save the moments we lost you looking for a time machine we first turn to Einstein to know his theory of general relativity or simply gr represents our best understanding of space and time gr imposes certain rules such as the fact that nothing has a positive Mass can move through space faster than light and allows us to calculate precisely how much time different observers perceived it passing depending on its relative speed and location.

Now it is encouraging that nothing in the theory says that things cannot go back in time and that fact represents Perhaps our greatest hope is that perhaps one day we will make this dream come true, but before we start designing our time machine, it is important to remember the limitations of gr, since this theory was conceived to explain the behavior of macroscopic objects, such as stars and planets, from microscopic objects, their behavior is described by quantum theory and the unification of these two remains elusive, It is one of the most sought after goals in theoretical physics and so what this means is that whatever opportunities GR may present as a means of

traveling

back in time, it is important to be aware of it. which remains incomplete as a unified theory of the mechanics of the universe, yet physicists have shown that within gr there are numerous examples of so-called closed time curves;

Those are methods of

traveling

into the past, for example you could build an infinite rotating cylinder as suggested by Frank Tipler which would require an infinite amount of mass or a wonka trip inside a rotating black hole but you would never be able to escape from it. its scope or that it could be constructed as the so-called Godel universe, one that rotates around a central axis with a perfect balance between mass and dark energy, as can be seen from those examples, there are certainly theoretical gaps for traveling back in time, but none of them are really useful for practically building a time machine someday, possibly the most plausible idea is a wormhole at two points in space.

Time is connected forming a potentially traversable tunnel. If we ever manage to build a wormhole between two points in space, then automatically we will have also managed to build a time machine, that's because you can always take one of the mouths and put it on. a different gravitational potential or accelerated at high speed and then a time shift would be introduced between the two inputs. Wormholes are familiar to us from many books and movies, but they have also been studied extensively by many of the best-known names in physics. such as Einstein John Wheeler Stephen Hawking and Kipps according to our current knowledge is that the construction of a wormhole would require the use of negative energy, this is because positive mass and energy curve spacetime in such a way that they cause Particles converge into a black hole. hole, so escaping the other end requires divergence and therefore negative energy.

Now many point to small quantum effects like the Casimir effect as an example of negative energy that could perhaps serve this purpose that could keep a wormhole open, but remember that quantum theory and general relativity have not yet been theoretically unified and Therefore it is not clear if this would actually work, perhaps we are missing some piece of the puzzle that somehow prevents this from happening and therefore at this time we cannot prove that a time machine is physically possible nor we can actually prove that it is impossible to use physics alone if we can't use physics maybe we can use logic through a reduction argument and impossible to assume that time travel is allowed and then calculate whether the consequences of that assumption are Logically consistent, backward time travel comes with the possibility of apparent logical self-contradiction paradoxes.

Two of the most important types of paradoxes in temporal mechanics are the grandfather paradox and the causal loop; The first is perhaps the most familiar to us, where we travel back in time and kill our grandfather before he has children. as a result of this action he never has children unless you are never born and therefore you never make the trip back in time to kill him so he stays alive and therefore you are born and then eventually you come back and kill him, and so it goes. endless cycle of self-contradiction, we are trapped in an endless paradox that seems to have no resolution if the universe were a simulation, as some have suggested, this is the kind of thing that would probably crush the code, perhaps ending the program, assuming this doesn't it's true.

The grandfather paradox appears to violate the premise of a logical, self-consistent universe and this undermines the very framework upon which theoretical physics is built. It is unacceptable to physicists that this is the case. The other important paradox is the causal loop or bootstrap paradox. In the movie somewhere in time a student named Richard receives a watch from an old woman in the year 1972 contact me eight years later he manages to travel back in time to 1912 where he falls in love with the same woman when she was much younger than him. he gives the saying "watch" before he travels back to 1980 and she keeps that watch until 1972, when she finally returns it to young Richard, completing the causal loop.

Now the paradox here lies in the origin of that watch because he never ventured near a watch factory during his entire timeline, so where did it come from? It appeared seemingly out of nowhere, a brute fact that was somehow written into the timeline, but who can extend this paradox to information? What would happen if someone traveled back in time and gave Beethoven everything? his music before he wrote it Beethoven copies the songs, history remembers his work and then the time traveler sends it back, so where did those symphonies really come from? The Princeton physicist and God takes this paradox to the extreme by suggesting that the Big Bang was the creation of the universe itself may represent an example of a causal loop perhaps the answer to what created the universe is the universe with the example of the causal loop paradox applied to a clock that goes round and round through time is falsifiable on the basis of entropy because each time this clock goes round and round it should suffer a few more scratches, a few denser ones, until finally completely falls apart, so the only way this paradox makes sense is if the lady is somehow able to accurately repair each of them. atom that moves inside this clock in each loop because if entropy breaks the clock then she can't give it to her lover and therefore he can never go back in time and give it to her in the first place, so we have essentially a grandfather paradox.

In this scenario, the grandfather paradox is the real pea moth to deal with because if time travel to the past is possible then apparently there is nothing stopping us from doing it and it doesn't have to be limited to murdering our ancestors, where this paradox can arise from. There are much more benign and ethical motivations, and that motivation could be as simple as trying to undo a past mistake, if given the chance to go back, who wouldn't be tempted to change their past, undo their arms to help his younger self or save someone we lost, but if we succeed, we will never feel the need to go back in time to save him unless we were never meant to save him.

The fundamental paradox is that the change is not recorded in history. It seems forbidden from the beginning. The resolution of these paradoxes is to invoke multiple timelines, multiple universes that are separated from each other in this way, when we travel backwards, we will never be able to change our own past, only start a new timeline with a different story or together, it is a simple solution, but Of course, it doesn't actually allow us to go back and change our past nor do we have any good reason to be suspicious of this multitude of infinite timelines, so let's keep trying to find a resolution here in our own universe, a solution clear.

The paradox is that it is simply impossible to change the past in a different way than it already happened. This means that before you get on yourtime machine you could look in a history book and read exactly what. Plus, you already did it in the past, assuming the story was accurate, so no matter what you can't deviate from that script, like a record being played over and over again, you can't kill your grandfather because your future self He didn't do that and that. it is an immutable fact your actions are governed by fate you believe in fate no why not because I don't like the idea that I am not in control of my life I know exactly what you mean this forms the basis of Novikov's self -principle of coherence and yet from the beginning this may seem immediately unsatisfying to us because it tells us that certain actions are prohibited but doesn't really explain why we can't deviate from the script after all, don't we have free will okay?

According to this principle, you can travel back and visit your grandfather, you can even share a meal and talk together, but you are somehow prevented from killing him because that would be inconsistent with your presence there, so after finishing your delicious meal and conversation together, your grandfather walks. across the room and maybe start dusting off an old photo you raise your gun slowly but surely and point it at the back of his head at that moment what's stopping you from pulling the trigger what force is stopping you this paradox Complicated when it involves apparent free will and decision human, as we perceive ourselves to be the architects of our own agency, but perhaps that is just an illusion, three Caltech physicists, including Kip Thorne, considered a simpler version of the grandfather paradox, one involving a single ball billiards rolling towards a time machine.

They use a wormhole here, but that's not strictly necessary. The initial conditions are chosen so that the ball should apparently roll into the wormhole and then emerge. from a nearby exit a little back in time, if we place this other wormhole perpendicular to the ball's initial trajectory, then the older ball would have to crash into itself, which would prevent the younger version of the ball from entering to the wormhole and thus would establish a grandfather paradox: The setup is attractive because it involves any simple classical physics and there is no free will, no problems of human agency here now, as said, it is logically inconsistent, it is a grandfather paradox , but physicists at Caltech discovered that there is, in fact, a physical, self-consistent solution to this puzzle.

Well, consider exactly the same initial starting position and velocity for the ball now that, as it rolls forward, it encounters an older version of itself a little earlier than in the paradox case; However, the angle of the older ball is such that the impact is just a skim enough to gently push the ball to the side and so the younger ball continues its path towards the wormhole but ends up falling into it. at a slight angle when it emerges in time, then it still has this slight angular deviation and so this actually explains why the impact that occurs was bordering on a beautiful, self-consistent, perfectly logical solution in the first place.

In fact, the Caltech team discovered that there was not just one solution to this paradox; in fact, there were many, in fact, actually infinite. number of resolutions and therefore this is somewhat unpleasant for physicists because we expect classical physics to be deterministic after all, if not how the universe decides which of these resolutions to actually use; However, the team showed that Novikov's self-consistency principle can solve the paradox, but this was only with an idealized classical billiard ball, did this work show that the self-consistency solution explains more complicated scenarios? What if you connected a device that could detect if and if there were ever two balls present on the surface? somehow trapping is one of them either it closes the wormhole resulting in a paradox again or maybe you could just replace the ball with a bomb that detonates once it emerges from the exit of a wormhole and then In fact, if you go a little further and start replacing these balls with people then we are back to this free will dilemma.

Wormhole expert Professor Matt Visser describes the novel self-consistency principle as ad hoc and remains largely unacceptable to physicists, and wormholes run into more problems than simple paradoxes against which they are unstable. even a single photon passing through them, consider two wormholes facing each other, let's imagine holding a single particle between the two and releasing it to fall into one of the holes, the particle re-emerges in the past and then take another turn. In fact, it keeps going around and around and around, if the time delay between wormholes is the same as the distance divided by the speed of light, we essentially end up duplicating infinite versions of the photon.

Time creates a loop where an infinite number of photons in other words an infinite amount of energy appears in just one interval of time, with infinite energy trying to force its way through the wormholes they will collapse and therefore , it appears as if wormholes essentially collapse instantly. The late Stephen Hawking argued that even random quantum fluctuations will trigger these catastrophic cascades, making wormholes impossible and this brings us to Hawking's alternative solution to these paradoxes: the chronological protection conjecture Hawking argues that situations like This will always prevent us from building a useful time machine, no matter how smart we are, physics always will. conspire to protect causality because if it weren't, the universe would be unstable and we should be here, so we can't prove this conjecture to be true or false, not until we have a unified theory of quantum theory and general activity at the same time. less, but it is currently considered the most quietly acceptable solution to these paradoxes in the sense that it is really simply the Novikov principle taken to the extreme.

Hawking's solution is certainly self-consistent because time machines simply do not exist. Time is over. The chronological protection conjecture posits that causality is sacred and that it is fundamentally impossible for us to go back and change the past. This is our best guess at how the universe works right now and what it means is that our dreams go back in time and change the past, only the dream means we can't go back and save those we lost, we can't undo All the mistakes we have made and we will never relive moments from our past For some of you, this may seem like a disappointment, but There is another way to look at it because what it means is that each day can only be lived once, that each moment can never be lived again. happen again, we have all made mistakes, we have done things we wish we could undo, but the nature of time is such that we have to live with our past we cannot change what happened we can learn from it instead of looking back and wishing for a hobby different forces us to look forward to choose a tomorrow makes us realize how precious the days we have left really are, that our lives must be lived with a sense of urgency, this is it, so whatever You want it to be your life, you may be running out of time if you don't do it now, maybe at the end of time the lack of mercy is actually a compelling gift.

Let's make the most of the remaining days to fully experience what awaits us.