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Throughout the ages, outstanding physicists, to the movies, to some of the greatest science fiction novels of all time, have pondered the idea of time-travel. The thought of actually being able to travel to another time or universe has long since enthralled, enveloped, and overwhelmed some of the greatest minds in the history of physics. No one person can actually prove any of their theories, but a few actually make sense. Meaning that they do not violate the laws of physics.
One of the main theories suggested, are wormholes. Wormholes are considered to connect two regions of flat space-time, two universes, or two parts of the same universe. There is a lot of theoretical evidence that wormholes exist, with an equal amount of evidence that they do not exist. However, no matter what one's belief is, the existence of wormholes still makes you wonder...
What is a Wormhole? Basically a wormhole is an approach to time travel, involving black holes. The equations of relativity suggest that pairs of black holes may be connected by "tunnels" that make a short cut through space-time. These tunnels are known as wormholes.
It is postulated that for all forces, there is an equal, yet opposite force. So, a black hole's equal but opposite force would be a white hole. White holes expel light and matter, rather than pulling it in. A wormhole is the connection between a black hole and a white hole.
Einstein himself, working at Princeton with Nathan Rosen had discovered that the equations of relativity actually represent a black hole as a bridge between two regions of flat space-time, a phenomenon known as the "Einstein-Rosen Bridge." Later on, in 1963, the New Zealand mathematician Roy Kerr found that if a black hole is rotating, a singularity still forms, but in the form of a ring, not a point. It was believed that in principle, a particle may be able to fall towards the singularity, but if at some point moved through the hole instead of the ring, the particle may not be lost forever. Therefore, with these theories in mind, a particle falling into a black hole will fall through the ring that the singularity has become, then going through the Einstein-Rosen Bridge, eventually being spewed out of the white hole into another space-time continuum. Problems with White Holes In relativity, a white hole can exist, however it conflicts with the second law of thermodynamics. The second law of Thermodynamics gives a precise definition of a property called entropy.
Entropy can be thought of as a measure of how close a system is to equilibrium; it can also be thought of as a measure of the disorder in the system. The law states that the entropy, that is, the disorder, of an isolated system can never decrease. For example, it entails, that unless work is don't, heat cannot be transferred from a region at a lower temperature to one at a higher temperature. A machine that would do work like that while violating the second law is called a "perpetual-motion machine of the second kind", since, for example, it could draw energy continually from a cold environment to so work in a hot environment at no cost. However, since perpetual-motion machines are said not to be impossible to create, then a white hole is also possible to create, or o already be in existence. Problems with the Kerr Hypothesis Roy Kerr's theory on the rotating black hole, along with the rotating singularity seemed to convince many, even before black holes were not believed to exist.
However, modern work published in late August 1998 by Plan and Shahar Hod has seemingly ended this idea. They used complex computer simulations to study how an electrically charged black hole might form and how the singularity would behave. They showed that a process known as 'mass inflation' violated the Kerr hypothesis. When a particle moves towards the black hole, the apparent mass of the hole increases to infinity as observed by the object. Thus, causing the singularity to go through the entire system, not leaving any hole through which matter may pass. Problems with the Einstein-Rosen Bridge While writing a novel in 1985 Sagan turned to Kip Thorne for advice, at CalTech.
Sagan wanted a method of moving a character faster than light, though not in a manner violating Relativity. Thorne set two of his PhD students, Michael Morris and Uv Yurtsever, the task of working out some details of the physical behaviour of 'wormholes'. Morris and Yurtsever's work found that this widely held belief was wrong. The problem is that in order to traverse an Einstein-Rosen bridge from one universe to the other, a traveler would have to move faster than light at some stage of the journey. Another problem with this, is that the wormhole is very unstable. The way Morris, Yurtsever, and Thorne set about the problem posed by Sagan, was the opposite of the way everyone before them had thought about black holes.
They worked backwards and started out by constructing the mathematical description of a geometry that described a traversable wormhole. They then used the equations of the general theory of relativity to work out what kinds of matter and energy would be associated with such a space-time. The difference here being that they did not look for an object and try to describe the effects it may have. More over they looked at the effects and tried to extrapolate to an object that might create them. Stephen Hawking believed that while wormholes might be created, they cannot be used for time travel. The Einstein-Rosen Bridge is so unstable, that even one particle entering into it would cause it to collapse.
Yurtsever and Thorne found that gravity tends to create singularities, and pinch off the throat of an Einstein Rosen Bridge. The equations said that in order for an artificial wormhole to be held open, some form of matter must thread its throat, or some form of field, that exerts negative pressure, and has antigravity associated with it. Types of Einstein-Rosen Bridges There are two main types of wormhole of interest to physicists: Lorentzian wormholes, relating to general relativity, and Euclidean wormholes relating to particle physics. Lorentzian wormholes are essentially short cuts through space and time but they close instantaneously unless some form of negative energy can hold them open.
It is possible to produce small amounts of negative energy in a laboratory by a principle known as the Casimir effect. Unfortunately, this is very far removed from the kinds of energy required to keep the 'throat" of a wormhole open. A by-product of Lorentzian wormholes would be that objects passing through them would not only be moved spatially but also temporally. This effect of Einstein Rosen Bridges led Stephen Hawking to promulgate his Chronology Protection Conjecture.
According to this conjecture, quantum effects will conspire to effectively prevent time travel even when it looks like classical physics might allow time travel to occur. Euclidean wormholes are even stranger given that they live in 'imaginary time' and are intrinsically virtual quantum mechanical processes. These Euclidean wormholes are of interest mainly to the particle physicists (quantum field theorists). Paradoxes of Wormholes Stephen Hawking explained wormholes as something that creates a bridge between two regions of space. These wormholes are shorter than the actual distance between the two regions. Space can be thought of as a piece of paper being folder over and over itself.
It could have many layers to it. Wormholes might simply connect two regions of space that seem to be millions upon millions of miles apart from each other. Going through a wormhole would allow you to reach a point before you actually left. If you leave the wormhole to come back you would come back to your point of origin before you actually left to go anywhere. You would then be in your history.
There is a lot of controversy over what would happen to you at this point. Stephen Hawking gave many points: Would you become helpless as history took you over? Would you have no control over what you did as you would simply be acting out the past the way it was supposed to be? Or would you be completely independent in your actions? If you did travel through history why was is not written in before it happened? If one did travel through space it would already be written in time of what happened.
An example given was what would happen if you travel back in time and killed your great-great grandfather. This would cause a ripple in time. If this happened it would have been written in time and you would go back in time and be unable to control yourself as you are just acting out history as the way it is written. If you did kill your past relative you would end your life yourself, thus making the event never happen. You still continue to exist though, so how could you have killed him? This is a paradox of what would happen.
If time travel is possible, how come no one from the future has given us the secrets to do so? Is it because the future has not been acted out yet? Or has it been, and we are simply the past, seeing it as the present? Time travel has been a long debated subject. One such debate is, can it even be done?
Many models of the big bang suggest that it can, while the theory of relativity says that it cannot be done. We see the universe because we are who we are, and where we are. That is the only reason we can question the facts of our existence. Sometimes we answer questions that were never supposed to be addressed. Space-time has always been in question. Time travel would give mad unlimited powers.
One could act as god, change the world the way He wanted. If the outcome did not meet satisfaction, then travel back in time and re-work the problem until satisfaction. With our primitive ways and violent acts, why would we give ourselves this weapon of infinite power? Maybe that is why we have not been told of how to build a time machine. However, the people in the future didn't think.
If they have created a time machine and are hiding it from us, then eventually we will stumble upon this discovery, since we are their past! -A. R. G.
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