On the Nature of Time and Time Travel

[tt137]

For whatever reason, time has an apparent direction that follows the path of increasing entropy. It seems to be a one way street from the past to the future. So, what are the prospects for actually controlling the movement through the 4th dimension?

Travelling Forward
No one disputes the concept of travelling forward in time. This type of time travel relies on an effect called time dilation. As you approach the speed of light, time contracts. So, a person moving at 0.9 times the speed of light might experience 1 year pass by but to an outside observor (who is stationary with respect to the moving person) they would experience 2.3 years. In affect when the travelling person comes to a stop, they would have travelled 1.3 years into the future. There are no foreseeable problems with this type of time travel as it doesnt affect what we percieve as the past. This type of time travel isnt theoretical. It is experimentally verified. For example, scientists know the lifetime of certain particles generated in the upper atmosphere from cosmic rays. This lifetime is much shorter than the time it would take the particles to reach the surface where they are detected. Since the particles are highly energetic (travelling near the speed of light), they are able to make it to the ground due to this time dilation effect which to an outside observer(the person detecting them) makes their lifetime seem longer. In reality, the particle still experiences the same lifetime.

Travelling Backwards
This form of time travel only exists within a few special(extreme) theoretical models. The thing all of these models seem to have in common is they require immense amounts of energy or matter. Most of them are toy models in that they are nonphysical and are only investigated for the purpose of looking at how the physics works in them. There are a few which might actually be conceivable. One such model uses Einstein-Rosen bridges (wormhole) and time dilation to create a link between the past(when the wormhole is created) and present(where the other end of the time dilated wormhole ends up). The problem with these models is it isnt possible to go back beyond the point where the time machine was created. So for example, you could never witness the Pyramids being built or prevent the JFK assasination. There might be other problems also but a quantum theory of gravity would be needed to understand them. One possible problem is that the wormhole might collapse if anything tries to pass through it. Even though the equations of stable wormholes work on paper now, there isnt a guarantee they will be possible once you incorporate quantum theory with general relativity.

Paradoxes
A lot of good stories have centered around the possible inconsistencies that travelling back in time might create. The classic example is the Grandfather Paradox. In this paradox, a person travels back in time and prevents their grandfather from producing their father. The paradox is said to exist because the time traveller shouldnt exist to go back in time to prevent the birth of his father at that point. It is my belief that paradoxes do not occur. That the only reason we believe there will be a paradox is because of a linear mindset with regard to time. If you look at the amount of energy needed to actually generate a portal back in time, it seems to me that it is causing a different excitation of the universe. Just to explain what I mean here. Most mainstream scientists do not think that the multiple universe vision of quantum mechanics is true. For example, Roger Penrose thinks that once you include gravity that mass will cause multiple states to collapse into a definite state. So, you will not have the superposition(a system being in multiple states simultaneously) of macroscopic objects (see Schrodinger's cat thought experiment). So, at any given moment of time there are an infinite number of possible states for the universe to be in. However at that moment, it actually only exists in very few. By excitation, I am saying that backward time travel is essentially pumping energy into the earlier universe so that a particular state is populated(realized).

 

[norn_iron]

interesting post, kind of lost me towards the end but my small brain cant handle it all. ive read shrodingers cat many times but even seeing it mentioned causes my head to implode, never mind thinking about it in relevance to anything else.

clearly im no scientist, but i think the idea that if you wher to build a time machine and you cant go further back than its production; is the only plausabile way of going back. it is also my belief that paradoxes dont occur, simply because they are just a good way of showing that time travel to the past isnt possible. i will always be under the belief that travelling back is impossible. im quite happy to believe time is linear, i also believe ther are other things in this universe besides us, and if us or them had discovered time travel we'd have messed with it, it would have got in the wrong hands and somebody would go back and do something.
i found it interesting in another post someone put up the idea that hitler etc maybe have been a time traveller, going back to change the time line for their own gain. an interesting thought, as i suppose it fits with the fact that if you wher to go back and change something, then thats the way it would always have happened in the first place so we would be unaware the past had been altered.
but comeon, how many of you can actually say you believe that one day it will be possible to go back; i cant get past the idea that if it where possible, it would have already happened and we'd already know about it. plus the paradox idea, they dont exist because they cant. if i where possible to time travel backwards, the pure thought of killing my grandfather should kill me! paradoxes imo are a nice way of saying "going back in time is impossible"

 

[tt137]

Just because we have not seen a vister from the future doesnt mean that travelling back in time is impossible. The current models show that travelling back beyond the point at which the time machine was created isnt possible. So once someone makes a time machine then you might expect to have a vister from the future.

The point I was trying to make with the no paradoxes was this. People perceive a clear cause and affect relationship because of a linear mindset. The problem with the Grandfather paradox is people believe that the Grandfather must produce the father in order for the grandson (time traveller) to exist. What I was saying was that the energy needed for travelling back in time basically is what is producing the grandson (time traveller in the past). That going back in time itself changes the past state of the universe and that particular changed state is independent of any future changes to the universe. So when the grandson (time traveller) stops the grandfather, the grandson doesnt cease to exist. I know at first it might seem strange or even disturbing to think that at any moment in time there are infinite number of possible states. The keyword is possible since clearly only a few or even one state is realized at a given moment. What does this mean? Well, I am saying that there are possible states with you existing in the past with the knowledge you have now. However, making these states populated(realized) may or may not be physically possible.

 

[jm1372]

Ah I see where you are coming from now, you create a wormhole in the past and then it appears in the present, then you go through it to the past. Thus it is limited to the time the device that created the worm hole was invented and used.

Would traveling back in time this way effect the theories of philosophy. It seems most of them would not be ruled out simply by such a scientific explanation on how it would be possible.

If in your world you created a machine to create a worm hole to the future either someone would come through it at some time, or you would have to wait until the time that it appeared in the future and then go through. Either way there would be two worlds coexisting at the least. If no one came through the worm hole and you had to wait until the time that it opened to become the first time traveler your world would be on the edge of time, (as long as it acutally worked and you did not just get vaporized accounting for the reason the first guy did not come through). Nothing would exist ahead of your time. If someone did come from that wormhole you created you are at least the 2nd world to exist and you could ask the first if someone came from his machine and if his world was on the edge. He would either say this question has been asked x amount of times or has been asked forever or never and they are the edge of time.

If such a thing existed would freewill actually exist, or would it have existed in the first world on the edge of time and we are just going through motions already decided by others in order to create a place for them to originaly travel to.

At any rate I am going to go hit some baseballs, I think this choice is free will, but who knows?

 

[zerubbabel]

Hi Guys,

Other than a few romantic notions you might have about tt, you are basically on the right track. The romantic notions that have to go away are: grandfather paradox, physical bodily transfer from point to point, limitation (per creation of time machine as only limit to access to the past), ramifications (per observation of past/future events), ...and the list goes on.

Current facts show that if we could ride upon a "particle" of light we would be able to travel back into the past. The double-slit experiments prove this. The romantic view would have us adding an immense amount of energy to get us into the past and all that kinetic energy being transferred into the past. Virtual time travel upon quantum "ships" (providing we can "map" the spagetti-like vortexes) is as close as the next quantum-leap of computers. With the approaching technology, only a few quanta of energy will be needed to travel multiples of c. Just as radio waves will bounce off the upper atmosphere and send ghost signals back to us, all the forms of radiation that make up "us", also bounce back at us from the outer fringes of interconnected spacetime/matter systems---going back to first cause. It doesn't matter which way you go--past or future, you end up at first cause. Now combine that technology with the tactile tech that is being developed for virtual reality and, presto, a virtual time machine that just may have real-world applications.