Time travel

[sarahtowny]

Well I was discussing this the other day with hubby I say we cannot do it, he says we will do one day. 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 so-called 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 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. Then once the velocity becomes greater than C time moves backwards and the traveller has entered the realms of negative time.

So, if you were not confused before you will be now! But I still say no... :0)

[Tigerblade]

it's been a while since i had a physics class that dealt with quantum mechanics, but... here's what i remember. not only does time slow down as your velocity V approaches the speed of light C, your mass M also increases exponentially, meaning that it becomes harder to accelerate closer to C. it requires more energy (think E=MC^2) than before.

time travel forwards is perfectly possible. time travel backwards is possible in a few situations. ONE. pick up a book and read it, you can go back in time to the era of the story. TWO. Look up at the night sky. Everything you see is the result of light being given off years ago. Even the sun is old news. Theoretically, the sun could explode right now and we wouldnt know for about 8 minutes.

there's also that whole paradox thing. no offense to Stephen Hawking, but i dont think he's always all that brilliant. sure there's a lot of things that were thought to be impossible years ago that are common practice now (like flying) but some things seem to be utterly impossible. i say it's possible that we achieve farther and faster space flight, it's possible we colonize the Moon/Mars/Mercury, it's possible we set up some kind of space fleet and space stations. as for going backwards in time... i've had too much physics to believe in that

[gossipingrae]

You know, since I never took physics in high school, I don't know much about energy and velocity and blah blah, but I will say this...no, I don't think anyone will ever be able to PHYSICALLY travel backwards or forwards in time.

Like Tom said, if you wanna go back in time, pick up a book. If you want to go forward in time, pick up a book. But in reality, I don't think we will be able to do that ever.

[Crazy Penguin]

I was having a read of Stephen Hawking the other day coincidentally enough.... and from what I gathered he suggested lots of ways that you could theoretically travel back in time, but all of which were fundamnetally impossible, requiring for example more energy then was in the universe to achieve it, or manouvering black holes and other theoretical white holes (which i've not seen any evidence that they exist)...

On the realities of time travel however, according to most physical laws, theoretically the universe could run backwards in time with no real change, so theoretically it is possible.

The method involving faster than light travel, well i don't think that could be achieved as to achieve faster than light speed in standard physics you require an infinite amount of mass and energy, which is clearly impossible, but with ever increasing technological knowledge it is possible we could circumvent that, or in fact find that our current models of the universe are incorrect and faster than light speed doesn't require infinite amounts of energy.

Anyway i'm generally of the opinion that we will never travel back in time, we will never go back into the past, however I think that there is a possibility that we will one day be able to create a machine which will allow timetravel back to the point at which the time machine was created, as many of the more feasible timemachines I have seen proposed all allow travellers to travel to the time when the machine was in existence but not before this, which cunningly avoids paradoxes such as the absence of timetravelling tourists.

Personally however I find time travelling to the future to be a much more attractive proposal than travelling to the past but that's just me...

<Crazy Penguin: Ponders on timetravel>

[Tigerblade]

this doesnt exactly fall under the domain of time-travel, per se, but since you mention black holes. there have been theories about traveling great distances through space in short amounts of time by navigating through wormholes, but they generally require the use of matter that as far as we know, doesnt exist. this hypothetical matter would have to be extremely dense and self-repelling, as it would basically be a stint in the torn fabric of space-time. it would have to hold open the wormhole and keep it from collapsing in on itself. travelling through this wormhole would allow ginormous (highly technical astrophysics term... yeah.) distances to be covered almost instantaneously, but it would still be sublight speed.
i found an interesting article here: http://www.aleph.se/Trans/Tech/Space...wormholes.html that i'm going to have to read more carefully when i have a little extra time to spare... it goes through time-travel, wormholes, all sorts of cool stuff like that.

as for actual time travel and CP's thoughts about traveling back or forward... i think traveling backwards (to any point, not just the creation of the machine itself) is impossible due to the difficulties of paradoxes and all sorts of timeline shifts, would could be cataclysmically devastating - you accidentally kill the great-grandfather of the guy who invented the time machine... poof there goes the machine. go back and risk messing up the timeline. go forward and you're subject to any number of timeline shifts that could occur because of changes in what's happening in your own time. who knows, maybe because you're not in your own time, someone else dies and suddenly the population changes just enough to create a chaotic butterfly effect in the future. stuff happens.

I think i'm revealing too much of my sci-fi fascination/geekiness here. time to be quiet.

[Crazy Penguin]

That article looks interesting, and I'll read it when I get the chance...

go forward and you're subject to any number of timeline shifts that could occur because of changes in what's happening in your own time. who knows, maybe because you're not in your own time, someone else dies and suddenly the population changes just enough to create a chaotic butterfly effect in the future.

I don't quite understand the logic of that, if you travel to the future (and since travelling back in time has been discounted you won't return) you will essentially be doing what occurs everyday, just at an accelerated rate, so you will have ALWAYS been absent from your own time after the point where you embark in a timemachine, the future may be different from the future could have possibly been if you hadn't embarked on a timemachine, but the future could be different as a result of any of the infinite number of choices people make, and so the future is inherently unstable since it doesn't actualy exist yet. If you could travel backwards in time admitedly paradoxes creep in, but i don't see how a paradox can creep in from travelling forwards in time?

I think i'm revealing too much of my sci-fi fascination/geekiness here. time to be quiet.

Revel in your innergeek!

<Crazy Penguin: Revel's in his inner geek>

[Tigerblade]

Originally Posted by Crazy Penguin

the future is inherently unstable since it doesn't actualy exist yet.

exactly my point. it's so unstable, it would be horrifically dangerous to travel to the future for any significant period of time.

[Crazy Penguin]

Yes.... but the present isn't unstable, and if you travelled to the future it would become the present... and you'd be stuck there for ever since you can't go back in time, this happens everyday, so why woudl it cause a problem?

<Crazy Penguin: Curious>

[Qwerty]

The present would be altered. You would be reading History books that would tell of them time when in 2025, a man from 2009 came.

Think about it.

[Crazy Penguin]

Yes but the present would not REALLY be altered... as if a man travelled forward in time this would have always been going to happen... i mean technically we can travel forward in time now, just not very far forward, getting in an aeroplane means that due to relativstic effects you've travelled a couple of milli-seconds into the future, going on any fast conveyance meahns you travel forward in time so in real terms travelling forwards in time will not cause any paradoxes.

<Crazy Penguin: Firmly in favour of travelling to the future>