MaTTsWoRld
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time travel
Time Travel ... is it really possible?
So, where do we start? How about time? What is time? The Oxford English Dictionary defines time as "a limited stretch or space of continued existence”, or “as the interval between two successive events". We glance at our wristwatches and notice the second hand slowly counting the passing seconds. We are in our own time machines: Our hearts are pumping blood, we're breathing; we are existing through time (at least until our own personal time machines seriously malfunction).
What are the possibilities of moving through time at a rate different to one day per day? Common sense tells us that it's all nonsense  time travel is impossible. However, common sense is not always such a good guide. Some hundred years ago common sense said man could never fly; now we travel all over the world.
The commonest objections to time travel are the socalled paradoxes. For example, if we could travel through time, imagine what would happen to a time traveller if he (or she) travelled back in time and killed their own grandmother at birth. In theory the time traveller will therefore never be born, so the journey could never have been made in the first place; but if the journey never occurred then the grandmother would be born which means the time traveller would have been born and could make the journey ... and so on and so on. This is a paradox.
There are two possibilities to resolve this paradox. The first is that the past is totally defined, i.e. everything that has happened or must happen, including the time traveller’s attempt to kill his grandmother, cannot be altered and so nothing will change the course of history. In other words, the time traveller will experience endless "mishaps" in trying to kill their grandmother and will never achieve the murder, thus keeping time (or at least events) intact.
The second possibility is more complex and involves the quantum rules which govern the subatomic level of the universe. Put simply, when the time traveller kills their grandmother they immediately create a new quantum universe, in essence a parallel universe where the young grandmother never existed and where the time traveller is never born. The original universe still remains. Stephen hawking believes he can explain the origin of our universe as a variation of this parallel worlds theme.
Having explained these paradoxes how does one travel through time? The secret is to travel at speeds close to the speed of light. The main text of the web site explains this in greater detail. The obvious problem with travelling very near the speed of light is that as you approach C (the speed of light) time slows down until at C time stops. How can you go faster if time has stopped? The answer involves a complex process called quantum tunnelling and is discussed at length in the main text of this web site. Then once the velocity becomes greater than C time moves backwards and the traveller has entered the realms of negative time.

you smile because iam different,i laugh because your all the same

Oct/1/2007, 3:50 pm

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MaTTsWoRld
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Re: time travel
An Introduction to Time Travel
Time and space have fascinated man since the dawn of civilisation. People have spent aeons thinking about these concepts and the ideas behind them. The Greeks, the Romans, the English, all have stared at the heavens and wondered. And not without reason! As the boundaries of physics are pushed back and back it is becoming clear that whoever understands the laws of physics best will be able to travel through time and space, easily gaining a dominant position in the known Universe. Indeed that race which can move from universe to universe will get to control all universes! We must therefore double our efforts to ensure that it is we and not some other race who gains understanding first! Or we will end up playing second fiddle for rest of time!
Pythagoras into Einstein in Two Easy Steps
So where do we start? Well let us start with one of the greatest triumphs of the human mind, the great theorem of Pythagoras, a true pillar of all mathematics and physics. The theorem, which is applicable to right angled triangles in flat Cartesian (Newtonian) space takes the form of:
c2 = a2 + b2
where a, b and c are the lengths of the sides of the triangle.
Next we will jump straight to Einstein's theory of Relativity which states that neither time, length, or indeed mass remain constant additive quantities when approaching the speed of light c. Our simple ideas of time and space come from the fact the we are so used to living in a three dimensional universe. Einstein showed that this was simply not true and in fact all the "foundational" three laws of Newton have to be fudged by the Lorentz factor
Lf = (1  v2/c2) 1/2
Elementary Guide to Relativity
There are, however, certain quantities that do remain constant. These constants are related to fourdimensional quantities known as metric tensors. From this Einstein proved that space and time are two aspects of the same thing and that matter and energy are also two aspects of the same thing. From the second of these concepts we get the most famous equation in physics
E = mc2
Now since time and space are aspects of spacetime and we wish to travel through time and not build atom bombs we will leave E=mc^2 for the moment. To illustrate this, look at the extension of Pythagorean theorem for the distance, d, between two points in space:
d2 = x2 + y2 + z2
where x, y and z are the lengths, or more correctly the difference in the coordinates, in each of the three spatial directions. This distance remains constant for fixed displacements of the origin.
In Einstein's relativity the same equation is modified to remain constant with respect to displacement (and rotation), but not with respect to motion. For a moving object, at least one of the lengths from which the distance, d, is calculated is contracted relative to a stationary observer. The equation now becomes:
d2 = x2 + y2 + z2 (1v2/c2)1/2
and this implies that the distances all shrink as one moves faster, so does this mean there are no constant distances left in the universe? The answer is that there are because of Einstein's revolutionary concept of spacetime where time is distance and distance is time! So now
s2 = x2 + y2 + z2  ct2
and this new distance s (remember s stands for Spacetime) does indeed remain constant for all who are in relative motion. This distance is said to be a Lorentz transformation invariant and has the same value for all inertial observers. Since the equation mixes time and space up we have to always think in terms of this new concept: spacetime! This means that time isn't constant and that by simply increasing the velocity (to close to the speed of light for it to have an affect) significant time dilation effects can be seen. It will be a very long time indeed before we have the capability to build a time machine and travel the universe.
Where are the Time Travellers?
We now know that the theoretical evidence for time travel is considerable. There is, however, one question we have avoided until now. If time travel is possible, where are the time travellers? There are a number of possibilities. The most obvious and pessimistic of these is that life on Earth may simply not survive long enough for the technology to evolve. Nuclear wars, giant asteroids smashing into our planet, quantum instabilities developing within the Sun etc. could all stop mankind (or any other race) in its tracks.
Yet the absence of time travellers need not indicate anything nearly so sinister. It is possible that they have been here, and are here right now, but have been discreet about their presence in order to ensure that they return to something closely approximating the future universe of their departure. A further possibility is simply that none has arrived in this particular universe! Many conspiracy theories are based on the possibilities of time travelling aliens having the ability to control all world events on Earth while managing to remain completely hidden from our view. The CIA may be stranger than you think.
So to summarise, we have seen some simple ways of travelling vast distances and have noted some of their drawbacks. We have also looked at some of the more exciting possibilities, but some more real breakthroughs are required. New mathematical methods need to be developed and new physical models of the universe must be conceived. Not a job for the faint hearted! Fortune it is said favour the brave. Nowhere will that be more true than in the race to understand the ultimate laws of physics. The race that achieves that first will go straight to top of the premiership of civilisations. Lets make sure it's going to be us!

you smile because iam different,i laugh because your all the same

Oct/1/2007, 3:50 pm

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Blue Jeanz
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Re: time travel
Okay, I think my head just exploded....
Actually time travel is something I like to think about even though it can be mind boggling.
What I believe is much more simplistic. First, time actually doesn't exist, it's an illusion. Time "exists" for us when we are living a linear life in the physical body.
And, people can already time travel astrally, many do it all the time. No machine necessary, just detach from the physical and you can go back and forward anywhere you want.
Also, you can only be an observer.
See, simple. No exploding head.

Oct/2/2007, 10:07 pm

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