TIME TRAVEL

(1)  Time travel, everybody would love to time travel, if it were possible. Go back, maybe change a few things, sounds like science fiction but what if it wasn't, what if it could be done. Well I think it can be done, we just need the means to do it. The ideas of how to time travel are out there but turning those ideas into a reality is going to prove to be a bit difficult to say the least, but lets look at ways that we could time travel if we had the means to do so.

There are a number of theories on how it could be possible to time travel, one of those theories is to travel at the speed of light or near to the speed of light. From what I have learnt about physics and the laws of physics, which I may add is next to nothing but from what I gather, the laws of physics will not allow anything to travel faster than the speed of light. Why this is so I do not know but at some point I will find out and when I do I will blog the reasons why but for now lets assume my facts are correct and it is only possible to travel up to 99.9% of the speed of light, a cosmic speed limit will prevent you from going faster.

In order to have some comprehension of the speed of light think about these examples: :- If you had two people standing side by side and another person standing a distance away, down the road lets say (the distance away is irrelevant in this example). One person has hold of a torch and switches it on to shine a light in the face of the person down the road, if you can get to that person before the light from the torch reaches that person's face, then you have travelled faster than the speed of light.

Another example of the speed of light is the one we all know, thunder and lightning. Light travels faster than sound so you see the flash of the lightning before you hear the sound of the thunder.  It is only one event that is happening but it appears to be two events, one being the lightning and the second being the thunder. The reason for this is because the light has reached us before the sound but thunder and lightning is actually a single event.

By travelling at the speed of light you are transporting into the future. Stephen Hawkins best describes how :- Imagine a track that goes right around Earth, a track for a super-fast train. We're going to use this imaginary train to get as close as possible to the speed of light and see how it becomes a time machine. On board are passengers with a one-way ticket to the future. The train begins to accelerate, faster and faster. Soon it's circling the Earth over and over again.

To approach the speed of light means circling the Earth pretty fast. Seven times a second. But no matter how much power the train has, it can never quite reach the speed of light, since the laws of physics forbid it. Instead, let's say it gets close, just shy of that ultimate speed. Now something extraordinary happens. Time starts flowing slowly on board relative to the rest of the world. Everything on the train is in slow motion.

This happens to protect the speed limit, and it's not hard to see why. Imagine a child running forwards up the train. Her forward speed is added to the speed of the train, so couldn't she break the speed limit simply by accident? The answer is no. The laws of nature prevent the possibility by slowing down time on-board.

Now she can't run fast enough to break the limit. Time will always slow down just enough to protect the speed limit. And from that fact comes the possibility of travelling many years into the future.

Imagine that the train left the station on January 1, 2050. It circles Earth over and over again for 100 years at the speed of light before finally coming to a halt on New Year's Day, 2150. The passengers will have only lived one week because time is slowed down that much inside the train. When they got out they'd find a very different world from the one they'd left. In one week they'd have travelled 100 years into the future.

So having a cosmic speed limit can actually aid time travel. By slowing down the speed of time on-board the train enables the passengers to time travel into the future. Then maybe we are suppose to time travel, as it looks to me as if the universe has given us a way of doing it by giving us a cosmic speed limit.

One of the biggest problems to overcome with time travelling at the speed of light, besides the challenge of inventing a vehicle that can travel that fast, is the fuel it would take to power a vehicle to travel that fast. The faster you go the more fuel you use so to go on the theory that you need to travel at the speed of light to time travel then we would have to find a different source of fuel.

WORMHOLES

Another theory on how it could be possible to time travel is the possibility of wormholes, even though a wormhole has yet to be discovered, scientists believe they are there. Before black holes were discovered scientists had an idea that they existed and they were right, so there is a very good chance that wormholes exist, we just need to find them and I believe we will.

In 1957 John A Wheeler, a theoretical physicist, coined the phrase, "wormhole" in his simple analogy of a worm that eats through the apple and comes out the other side, creating a short-cut through the apple. If you use this analogy in space and a wormhole has been created, in theory you could jump through the wormhole and come out the other side, "a short-cut". You would go in through a black hole and come out through a white hole. The rest of us would be moving along in time, living each second, going through a wormhole would transport you into the future.

Hypothetical wormholes

The Einstein-Rosen bridge, first laid out by Albert Einstein and his colleague Nathan Rosen in 1935, is a scientific explanation of a wormhole. Imagine space as a two-dimensional (2D) surface, imagine this surface is folded along a third dimension, it allows you to picture a wormhole "bridge" similar to the above picture of a hypothetical wormhole.

As I have said there is no visual evidence for wormholes, but on a theoretical level there are valid solutions to the equations of Einstein's theory of general relativity which contain wormholes. The first type of wormhole solution discovered was the Schwarzschild wormhole which would be present in the Schwarzschild metric describing an eternal black hole, but it was found that this type of wormhole would collapse too quickly for anything to travel through it. Wormholes which we could actually travel through, known as traversable wormholes, would only be possible if exotic matter with negative energy density could be used to stabilize them.

TRAVEL BY BUBBLE

The final theory on time travel that I am going to talk about is a more resent theory and that is to travel within a bubble in space. Two physicists suggest that a future spaceship could fold a space-time bubble around itself to travel faster than the speed of light. The idea involves manipulating dark energy,  the mysterious force behind the universe's ongoing expansion,  to propel a spaceship forward without breaking the laws of physics. "Think of it like a surfer riding a wave," said Gerald Cleaver, a physicist at Baylor University. The ship would be pushed by an existing bubble that occurs in space which is travelling faster than the speed of light but the space craft within the bubble is not moving faster than the speed of light. The ship would be carried along on a wave. Although if you have ever tried to surf, which I haven't but I would hazard a guess that it is pretty difficult to catch a wave on the sea, so I guess it may prove difficult to catch a wave in space.

Strange as it sounds, current evidence supports the notion that the fabric of space-time can expand faster than the speed of light, because the reality in which light travels is itself expanding. Cleaver and Richard Obousy, a Baylor graduate student, tapped the latest idea in string theory to devise how to manipulate dark energy and accelerate a spaceship. Their notion is based on the Alcubierre drive, warp drive, which proposes expanding space-time behind the spaceship while also shrinking space-time in front.

The Alcubierre drive, as it's known

A spacecraft could travel at warp velocity 

Some scientists believe that a total of 10 dimensions exist, including height, width, length and time. The other six dimensions exist largely as unknowns, but everything is based on hypothetical one-dimensional strings. A newer theory, called M-theory, suggests that those strings all vibrate in yet another dimension. Manipulating that additional dimension would alter dark energy in terms of height, width, and length. Such a capability would permit the altering of space-time for a spaceship, taking advantage of dark energy's effect on the universe.

The dark energy is simultaneously decreased just in front of the ship to decrease (and bring to a stop) the expansion rate of the universe in front of the ship. If the dark energy can be made negative directly in front of the ship, then space in front of the ship would locally contract.

This loophole means that the spaceship would not conflict with Einstein's Theory of Relativity, which states that objects accelerating to the speed of light require an infinite amount of energy.

However, the Baylor physicists estimate that manipulating dark energy through the extra dimension requires energy equivalent to the converting the entire mass of Jupiter into pure energy, enough to move a ship measuring roughly 33 feet by 33 feet by 33 feet. That is an enormous amount of energy. We are still a very long way off before we could create something to harness that type of energy.

So there you have it, 3 possible ways of time travel. It will never happen in our life time but for our future descendants who knows.