“The speed of an object through space reflects how much of its motion through time is being diverted. The faster it moves through space, the more its motion is being diverted away from moving through time, so time slows down”.

General relativity

Time travel is a concept which has been featuring extensively in fiction movies and comic books, alot of questions about the idea have been coming through, questions like; is time travel a possibility?. Have scientists invented the time machine?. Do wormholes exist?. Is time the fourth dimension?. Can someone travel to his past to correct his mistakes?. And much more, today I’m certainly going to answer most of these questions.

Some theories, most notably special and general relativity, suggest that suitable geometries of spacetime or specific types of motion in space might allow time travel into the past and future if these geometries or motions were possible. there is some theoretical basis to the idea. Arguably, we are always travelling though time, as we move from the past into the future.

Time travel concepts have been viewed in some science fiction movies and books like Avengers Endgame, The Tomorrow War, Zack Snyder’s Justice League, Interstellar, X-Men: Days of Future Past, Tenetand so much more

**Table Of Contents**

1. Time Travel Definitions

2. History of the concept

3. Terms Used in Time Travel

4. Time Travel theories and equations

5. Time travel, possible or not?

6. Conclusions

**Time Travel Definitions**

Time travel has been defined by several authors and scientists basing on the way they understand the concept.

“I can simply describe this concept as the ability of a body or particle to travel forwards into the future or backwards into the past by use of some mechanism, say a time machine. The size of the particle remaining constant”.

Amonison

“Time travel is the concept of movement between certain points in time, analogous to movement between different points in space by an object or a person, typically with the use of a hypothetical device known as a time machine”.

Wikipedia definition

**Other popular definitions**

“Time travel is a science fiction concept in which people are able to move backwards into the past or forwards into the future”.

Unknown author

“A journeying into the past or the future, as in science fiction”

Anonymous

**History of the concept**

The idea of time travel and time travel paradox stories have been in existence sice time immemorial. The idea was popularized in the 19th century at a time when novel classics such as *Looking Backward by Edward Bellamy* started digging deeper into the idea.

However, The first real work to envisage travelling in time was The ,*The Time Machine Book by H. G. Wells*, which was published in 1895.

The book tells the story of a scientist who builds a machine that will take him to the year 802,701 – a world in which ape-like Morlocks are evolutionary descendants of humanity, and have regressed to a primitive lifestyle. Because it described time travel solely to the future and back, The Time Machine did not involve any paradoxes.

In 1988, motivated by a request from Carl Sagan to provide scientific justification for the interstellar transportation used in his novel Contact, Caltech physicist Kip Thorne assigned his then-PhD student Michael Morris the task of constructing solutions of Einsteinβs field equations of general relativity that offer traversable wormholes linking otherwise disconnected regions of the universe. In general relativity, mass and energy shape the fabric of the spacetime manifold. The greater the concentration of mass in a region, the more distorted space and time would become. While the technology to assemble enormous quantities of mass into wormholes is far beyond our present capabilities,and requires a hypothetical substance of negative mass, called exotic matter, the physics community took Morris and Thorneβs proposal seriously. There were a number of follow-up proposals, similarly published in scholarly journals.

In 1905, Albert Einstein wrote down his special theory of relativity that showed space and time are intimately linked, and in 1916, Einsteinβs general theory of relativity showed that space and time are malleable β that is, they respond to the presence of matter or energy by warping, bending, expanding, and contracting. By extension, this means if one can imagine space being filled with some exotic form of energy, then space and time could warp in a way so that time, as well as space, could bend back upon themselves like circles, allowing one to move forward in a straight line and still return to oneβs starting point in both space and time.

This was also a major develop in time travel studies.

In 1994, physicist Stephen hawking pointed out in his book “Black holes and baby universes“ “The best evidence we have that time travel is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future.”. This was somewhat a setback into the study but that didn’t stop researchers from finding out more about the time machine.

James Webb telescope Launched on December 25, 2021 is the most recent development in space-time science, natizens have nicknamed it the time machine….

**Terms used in Time Travel**

time machine: A device for traveling backward in time. |

gravitational time dilation: The slowing of the flow of time near a gravitating body. |

Planck length: The Planck length is the length scale below which space as we know it ceases to exist and becomes quantum foam. |

spacetime: The four-dimensional “fabric” that results when space and time are unified. |

spacetime diagram: A diagram with time plotted upward and space plotted horizontally. |

spacetime curvature: The property of spacetime that causes freely falling particles that are initially moving along parallel world lines to subsequently move together or apart. |

Spacetime curvature: the influences in the motion of massive bodies. |

wapping: Same as curvature of spacetime. |

general relativity: Einstein’s laws of physics in which gravity is described by a curvature of spacetime. |

wormhole: A “handle” in the topology of space, connecting two widely separated locations in our Universe. |

Quantum Realm: an amalgamation of two different dimensions from the comics |

special relativity: Einstein’s laws of physics in the absence of gravity. |

singularity: A region of spacetime where spacetime curvature becomes so strong that the general relativity laws break down and the laws of quantum gravity take over. |

quantum mechanics: The laws of physics that govern the realm of the small Particles(atoms, molecules, electrons, protons). |

curvature of space or spacetime: The property of space or spacetime that makes it violate Euclid’s or Minkowski’s notions of geometry; that is, the property that enables straight lines that are initially parallel to cross. |

mouth: An entrance to a wormhole. There is a mouth at each of the two ends of the wormhole. |

event: A point in spacetime; that is, a location in space at a specific moment of time. |

field: Something that is distributed continuously and smoothly in space(electric field, the magnetic field, the curvature of spacetime, and a gravitational wave). |

gravitational wave: A ripple of spacetime curvature that travels with the speed of light. |

hyperspace: A fictitious flat space in which one imagines pieces of our Universe’s curved space as embedded. |

Newtonian laws of physics: The laws of physics, built on Newton’s conception of space and time as absolute, which were the centerpiece of 19th-century thinking about the Universe. |

quantum gravity: The laws of physics that are obtained by merging general relativity with quantum mechanics. |

time-warped field: A self-contained filed in which time rates within the field may be accelerated or decelerated relative to time rates outside of the field. |

world line: The path of an object through spacetime or through a spacetime diagram. |

**Time Travel theories and equations**

According to Albert Einstein’s famous equation, E = mcΒ² , time travel is possible, at least in one direction.

Proof from E=MCΒ² explained with worked examples

The equation that tells us by how much mass appears to increase due to speed is:

Where:

m = relativistic mass, i.e. mass at the speed it is travelling.

m0 = “rest mass”, i.e. mass of object when stationary.

v = speed of object.

c = speed of light.

Also note that the mass increase isn’t felt by the object itself, just as the time dilation of Special Relativity isn’t felt by the object. It’s only apparent to an external observer, hence it is “relative” and depends on the frame of reference used. To an external observer it appears that the faster the object moves the more energy is needed to move it. From this, an external, stationary observer will infer that because mass is a resistance to acceleration and the body is resisting being accelerated, the mass of the object has increased.

Kinetic EnergyNext, we need to look at the energy involved in very high speed movement. We have seen that as an object gets faster its mass appears to increase, and the more mass an object has the more energy is required to move it. The standard equation for the energy of movement (kinetic energy) is:

That is, kinetic energy is equal to half the mass multiplied by the velocity squared. This is often called Newtonian kinetic energy. Note that the velocity term is squared. This means, for example, that it takes far more than twice the energy to travel at twice any particular speed. We can see this by working through the equation for two values of v, where: v = 50 ms-1 and v = 100 ms-1 respectively, both with the same mass of 10 kg:

This equation is fine at low speeds,

From this equation we know that mass (m) and the speed of light (c) are related in some way. What happens if we set the speed (v) to be very low?

This equation seems to solve the problem. We can now predict the energy of a moving body and take into account the mass increase. What’s more, we can rearrange the equation to show that:

This result is fine for low speeds, but what about speeds closer to the speed of light? We know that mass increases at high speeds, but according to the Newtonian part of the equation that isn’t the case. Therefore, we need to replace the Newtonian part of the formula in order to make the equation correct at all speeds. How can we do this?We know that E β mc2 is approximately equal to the Newtonian kinetic energy when v is small, so we can use E β mc2 as the definition of relativistic kinetic energy:

We have now removed the Newtonian part of the equation. Note that we havenβt given a formula for relativistic kinetic energy. The reason for this will become apparent in a moment. Rearranging the result shows that:

It can now be seen that relativistic energy consists of two parts. The first part is kinetic and depends on the speed of the moving body, while the second part is due to the mass increase and does not depend on the speed of the body. However, both parts must be a form of energy, but what form? We can simplify the equation by setting the speed (i.e. the relativistic kinetic energy) of the moving body to be zero, thereby removing it from the equation:

We now have the famous equation in the form it’s most often seen in, but what does it mean?Einstein therefore concluded that mass and energy are really different manifestations of the same thing, i.e. that any mass is really tightly packed energy. At the time he saw no mechanism for releasing the energy from the mass, and was in fact sceptical of the idea that it could ever be achieved. This didn’t really matter to Einstein, however. As a theoretical physicist he was happy that his equations were consistent and he had a model to predict what happens to a body moving at very high speeds.

**Time travel, possible or not?**

Relativity theory says that time and space are linked together. Einstein also said our universe has a speed limit i.e nothing can travel faster than the speed of light (186,000 miles per second). according to this theory, the faster you travel, the slower you experience time. Scientists have done some experiments to show that this is true.

One of the experiments involved two clocks set to the exact same time. One clock stayed on Earth, while the other flew in an airplane, all planes moved in the same direction. After the airplane flew around the world, scientists compared the two clocks. The clock on the fast moving airplane was slightly behind the clock on the ground. So, the clock on the airplane was traveling slightly slower *in time* than 1 second per second.

“time travel is indeed a real thing. But it’s not quite what you’ve probably seen in the movies. Under certain conditions, it is possible to experience time passing at a different rate than 1 second per second”

Space place(NASA Science)

But we can’t use a time machine to travel hundreds of years into the past or future. Maybe this will be possible in many years to come.

**Conclusions**

*We can go into the future. Time travel to the future is possible under Albert Einsteinβs general theory of relativity. But time travel to the past is impossible*

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A concept that has fascinated man almost from the very beginning…Thank you for following CarolCooks2 :)…

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Wow, thatβs extensive! Looking forward to seeing more analyses!

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Informative post and thanks for following meπ

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