Time travel

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Emmmm, chaps? Wasn't the whole point of inventing the pencil in the first place so that folks could indulge in the time honoured pursuit of describing Time Travel without inducing the left side of ones lobes to melt under the conflux of the sort of language generally used...?

I mean, pardon the obviousness, but as one of you has mentioned previously, language and talk of Time Travel rarely bode well as far as clarity of meaning becomes concerned. It's frankly murder on the past tenses.

The Universe is expanding. We move with that expansion. Events in History therefore occur at unique points in Time and Space specifically and no other. Not the space between objects which merely occupy the Universe, but in the fabric of space itself.

Hit that specific point in Time and Space and what History informs you was there is, because you have simply placed yourself there. As to this place actually being "The Past" as History informs you...

Frankly, it isn't. Where you end up may to all practical intents and purposes might certainly appear to be "The Past", but appearances would be deceptive. For one thing, you'd be in the Present. Not as far as your perception would tell you, you're perspective as a Time Traveller would always be informing you that where you are is in "The Past" - however, as far as reality would be concerned, where you'd be would be the Present moment, exactly no different from that you are experiencing now except "Now" is occurring at a point in Time And Space billions of miles distant from where it was previously.

Up is up, down is down, flip the light switch and the lights come on, random chance can occur.

Meaning the whole endeavour of travelling through Time just for the sake of Time Travel remains a completely useless affair serving no genuine purpose entirely.

It's useless. Utterly, utterly useless.

Bring about chronological displacement (Time Travel) through travelling relatistically through space as if one were travelling faster than the speed of light, but physically actually not obviously, and you effect a means by which interstellar travel becomes a viable proposition to undertake.

Use the same thing to travel back to witness History on the other hand and y'frankly may as well have stayed home and just read a book for all the actual good it'll ever do anyone...

 

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Personally speaking, I would like to go back during the time of the Neanderthals and hang out with them a little bit. You know, at night dance around the old camp fire, grunting, yelling and screaming insults at each other. Do some cave painting, a little boulder rolling, spear throwing and maybe even get in some wooly mammouth and bison hunting. Yea........it's a great way to spend some quality time with my good ole distant relatives again.

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Apology accepted.

I will see to it that you get many virgins upon your arrival.



Seriously, though. The reason I am certain that time travel is not possible is just like I am certain that objects with mass will never exceed the speed of light in velocity through space. Some things are just built into the basic concepts of the universe.

Travel to the past will never be possible because, on a funamental level, the past will never, ever, ever exist. As soon as particles move out of their current state, that is it. That past is lost forever. It isn't still "out there" waiting for someone to travel back to it. That sort of mass-buildup would turn everything into black holes immediately. And the whole concept is just silly.

The fact that this state changes at different speeds relative to the effects of accelleration and gravitation is meaningless to this basic point. Those states are still changing at the same "moment" that any base state is changing, just at its own rate. The "past" is still lost immediately.

And when physicists MAKE UP constructs like wormholes, they are doing this SOLELY to allow themselves to talk about Faster-Than-Light travel and Time-Travel. That is all they are doing. Creating their own little sci-fi tools so they can geek out over the implications. None of it is based on science.

I normally get very defensive when theists tell me that atheists and scientists rely on faith just as much as they do. The reasons this upsets me is for a different section of the forum.... but then there are things like Wormholes, 11 Dimensions of Space, String Theory... and I feel like the theists have a point. All of these things are as real as the Purple Dinosaur that lived in Carl Sagan's garage, and yet people accept that these things are even POSSIBLE. They aren't, and some really smart people saying so doesn't alter that.

With all respects... I hate that I'm coming across as an ass here, because I usually conceal that part of me really well.

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I just had to respond to this example to give my view. Pete, this goes back to my earlier attempts at trying to explain why it does make a difference whether you consider yourself moving, or the object that emitted the light moving and yourself the one 'at rest'. Please bear with me for a moment.

Maybe I can explain my position by the following example. I definitely am not as articulate as Zimmerman!

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Consider a fictional star exactly 5 lightyears in distance from the mailbox in your front yard, no relative velocity difference between the two, in other words the star and your mailbox are co-moving or 'at rest' wrt each other. Let this star emit two photons, travelling side-by-side but some distance between them. You have one clock/detector that can register the one-way speed of light on your mailbox and another identical one in your hand. While standing beside your mailbox, both clock/detectors would measure the speed of the two photons as 299,792,458 meters/sec. assuming the atmosphere didn't slow the photons. Both clocks would measure identical arrival times for the photons, a five year time-of-flight for the photons. Now assume two more photons were emitted from the star, but this time you are travelling 1000 meters/sec away from the star and mailbox. One of the photons will still hit the mailbox detector exactly five years after it was emitted, say at 01:00:00 pm, and the detector will record the one-way speed of the photon as 299,792,458 m/s. If you have been travelling for 2 seconds when the photon hit the mailbox clock/detector, the other photon will hit your clock/detector at 01:00:02 pm. Consider that your detector may register the speed of the photon as 299,791,458 m/s. If you incorrectly calculate the relative velocity as 299,791,458 m/s for the entire 5-year journey for the photon, the results would be skewed as you mentioned. But in truth, the only part of the photon's journey that was at a relative 299,791,458 m/s was during your 2-second travel time, the part I have always referred to as the linear Sagnac effect. If you calculate the same example and assume the star is the one in motion and you are 'at rest', then you have to use SR's 'constant c' for all observers, or the 1,000 m/s relative velocity difference would skew the results.

I may have misinterpreted your reference about simply 'walking' causing a one-day delay in photon arrival, so I apologize if I have. Please don't think I am trying to 'talk down' to you or something in this post, I just tried to put it in as simple of terms as I could because I seem to have a problem getting others to understand what I am discussing sometimes.

Excellent post, Mr Anonymous.
Edit: Whoops, I made an error in the 'arrival time' on your moving detector. You weren't travelling at the speed of light, so in two seconds you would have only moved 2,000 meters from the mailbox. Your clock would have read less than 7 microseconds after 01:00 pm.

 

Do you see a problem here?
SR says that our detector should register the speed of the photon as 299,792,458 m/s.

The small change in velocity (walking) makes a large difference in when occur a long way away.

If you and I walk past each other on the street, and at that very moment in my current inertial reference frame something happens millions of light years away, then SR suggests that it might not happen in your current inertial reference frame for a day or two, or it might already have happened a day or two ago.

 

Odd you should actually pick that as a thing to do. It's funny but, as an actual Time Travelling activity, it's possibly one of the few sorts of activities you could conceivably undertake to indulge in which wouldn't unduly alter the subsequent outcome of "history" as you'd know it to be.

You'd never get to return to the place where you originally started, but in travelling forward back to the point in time that corresponds to when you originally left, you'd conceivably find a reality with a history so close to our own as to be negligibly any different to the one you originally started out from - this one.

Of course, this would all rather depend on the notion that, in the History of Ever, you should turn out to be the only Time Traveller in the universe that ever managed to travel back through Time: however, that in itself remains a notion only possible to begin with if we consider the idea that incidences of Time Travel have never actually yet occurred.

Should reality indeed allow incidences of Time Travel to occur in the first place no one, most especially a Time Traveller themselves, could ever be certain of the fact that events as either Histroy records or they themselves actually witness first hand unfolding them are indeed actually the consequence of what merely simply "happened" as a consequence of "natural" occurring events.

If one could place ones self physically in "The Past", as it were, they'd be no prohibitation whatsoever on others having been exactly as successful in doing exactly no less the very same - including within the reality ones self as a Time Traveller originally starts out from

Presumably this one....

Kind of goes towards the whole "Time Travel Is Useless, Really - Read A Book Instead" argument in a nutshell really.

Fun, possibly. But do you ever really get to go back?

You're terribly kind. Thank you for saying so.

As to that last, you are most certainly bang on the money. There isn't anything sillier. Sorry to interject here, by the by, I do hope y'don't mind I was just reading. It's just this picture you describe of the Past as being somehow "waiting" as y'put it and therefore the whole notion of Time Travel being impossible as a consequence.

You're right. The notion of the Past somehow hanging around waiting to be visited is indeed a nonsense - however, I don't think anyones actually saying that such would be the case.

Rather, that in travelling through Time & Space to a specific point in it, at that point the events which History record exist because this is where they happened and you as a Time Traveller have placed yourself in that exact same point in Time & Space when this is actually true.

The effect would be simply no different than that which you experience now, this minute, without Time Travelling. This moment begins with the Earth being at one specific point in the fabric of Space and ends with it being compelled by expansion to have moved through space some considerable distance in the meanwhile.

Over the normal course of events both you and the Earth you're on will never return to the exact points in Space where as previously it has both existed and is continually compelled to move through and beyond - the Universe is continually expanding and the stuff, such as you, I and the world, are constrained to continually move ever outward in a given direction with that continual process of Universal expansion.

But think of specific instances of History as events occurring at specific and points in Space and and simply hitting them accurately, at the correspondingly correct point in Time, and what was their is simply because, at that point in Time & Space, that's exactly where things actually took place.

And when.

... It's probably easier just squinting at the diagram in the post above.

The point is, you're right in the sense that the last thing the past is doing is hanging around waiting for someone to visit it - the actual Past itself very much is is gone for ever and indeed, no. Travelling to the actual Past as was really is impossible.

Nevertheless. At a given point in Time & Space, at a given point in Time this is where the Earth was and, if you can get yourself too it, you get to be there too because, at this specific point in Time & Space this is where the Earth actually is.

That would conform to a Time Travellers perspective of "History": but to physically be there would be an experience no different from any other point in Time. Causality isn't bound by events yet to occur. Random chance exists.

This one could never describe as being The Past. It's a The Present, constrained by the perspective of a Time Traveller to certainly correspond to The Present As Was from their way of looking at it - but as far as reality is concerned you have simply arrived in The Present.

Both your perception of Time and Realities can only encompass The Present moment. Whenever that happens to be. Blink and its gone forever. All the Time Travel in the Universe never changes any of that full stop.

And, yes. It is a silly business. Very silly.

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This is precisely why people avoid doing it. Or, possibly more accurately, this is probably why people avoid deliberately trying. Time Travel for simply the sake of Time Travel is useless. However, we live in hope that one day we can undertake to travel to the stars in such a fashion as to make such an undertaking not simply possible, but viable to undertake.

The instant mankind does that mankind has access to all the tools necessary to facilitate instances of Time Travel in that Wellsian sense of travelling through Time. One can argue all the prohibitation to such activities as one likes, the point is that Future is not within our means to either wield or control.

Should mankind progress to do the Star Trek thing for real that means a future where navigational errors will, inevitably, occur. As mankind progress further and beyond our grasp of the Universe may increase a thousand fold. Our understanding of the processes involved, the discovery of fauna and flora on on others worlds - all that happy shit may inform us of so much more than we of today are only now dimly begging to grasp.

But what non of that is ever going to actually tell is is what really happened here on this particular planet that gave rise specifically to us. What did we actually come from? All the fossil evidence in the world is but fragments, forensic samples from the scene of a crime millions of years committed. Tagged, bagged, catalogued. A glimpse of the truth.

Time is the ultimate Serial killer. And it loves nothing better than taunting those who care about what it has done.

Here in the real world Quantum Mechanics dictates that we must abide with a Universe at its fundamental level which makes a happy riot of even the very basic notions we hold of what is sensible and common sense. We can't even look at the universe on a fundamental level because to do so would require the use of other, equally fundamental particles, and this in turn would undoubtedly influence the behaviour of the very things we would most wish to see clearly and directly.

One would think this would put everyone off the notion of progressing any further with studying the basic stuff out of which all things are made of - but it doesn't. We work around the problem.

It doesn't mean that we solve the problem. We just work around it. Make the problem acceptable.

The essential nature and problems associated with Time Travel are exactly no different to those which go hand in hand with modern day Quantum Physics.

If we do in practice develop and progress as the technological culture we imagine ourselves to be capable of - sooner or later our species finds in its hands the means to longer have to ask such questions as "what really happened?" and "why?".

When really doesn't matter. It's Time Travel. Time Travel makes a nonsense out of everything. But, on a fundamental level, so too does our present day concept of the fundamental nature of the universe - so what difference does a spot of nonsense actually make?

If the Universe on a fundamental level doesn't actually give a stuff - why really should we? That's never in the history of anything ever stopped us in the past, it's hardly likely to change anything in the future....

A

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Great read. I even enjoyed reading the bits I disagreed with. How rare is that?

 

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... It's been said, I have a way about me.

You're awfully generous, my regards.

A

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Pete,

I don't wish to hijack the the point of this thread too much, but the 'time travel' hypothesis comes about mainly because of Special Theory's predictions of time itself changing due to relative motion and Einstein clock synchronization precedures.
As the Special Theory of Relativity was originally formulated by Einstein, yes, it does predict all detectors should register the one-way speed of light as 'c', which is now defined as 299,792,458 m/s. However, it is now known that doesn't hold true. The modern interpretation in advanced physics is that the speed of light is 299,792,458 m/s in co-moving reference frames. Special Theory has been altered from its original state, but it is still considered to be Special Theory.
I can give a link to the abstract of a paper submitted by NASA's JPL division in which they tested the one-way speed of light invariance. I haven't found access to the full paper, but I have read 'summaries' of the results by such noted physicists as Clifford Will, one of the fathers of GPS and a recognized authority on time. Here is the abstract and a link:

http://prola.aps.org/abstract/PRD/v42/i2/p731_1
The abstract does not mention what I am going to say, but I have read the remarks by C. Will in other locations.
The test showed an anisotropy in the speed of light passed through the fiber optics cable. Extremely accurate hydrogen masers recorded different travel times for light between the two clocks according to the direction the signal was travelling. After all the motions of the Earth were accounted for, there was still a discrepancy that amounted to 300 km/s left over. That 300 km/s is the Earth's velocity through the universe relative to the rest frame of the Cosmic Microwave Background. Light seems to travel at 299,792,458 m/s relative to the rest frame of the universe, the rest frame of the CMB. A detector moving relative to the rest frame of the CMB will not measure the velocity of light as 299,792,458 m/s, the detector's own motion can be measured.

I have also found out that pulsars are being used to test the changes in the transition cycles of atomic clocks. The favorite seems to be the highly stable Millisecond Pulsar PSR 1937+21. Move the clock to different locations and you affect the clock's cycle rate, but not the Pulsar's. Besides gravitational potential, many other factors alter the rate at which cesium clocks cycle, such as temperature and magnetic fields. Does everyone realize that clock cycle effects due to temperature changes are considered 'relativistic' effects also? Does 'time' slow in a cold enviroment and speed up in a warm one, or is it only a 'clock effect' that affects the measuring device itself?

 

no, pure time dilation is the discrepancy, left when all physical influences on teh clock have been accounted for. If you put a grandfather clock on a spceship, which goes really fast and then the clock falls over and breaks, obviously time has not stopped because the clock isnt ticking. Time dilation accounjts for all physical influences.

by the way, time dilation has been measured not only by atomic clocks but also the radiocative deacy or half life of certain substances such as muons. Whne acclerated to near light speeds, their half lives are considerably longer, so they "age" more slowly becauase their relative time is slowed.

 

Has anybody got the time? My watch is running a little slow today. I guess I'll have to replace that plutonium battery again. It only lasts about 400 years if I'm lucky.

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2inq,
This thread is about time travel, and the nature of time. The relevance of relativity to the thread is whether it is compatible with the presentist point of view.

If you want to discuss the compatibility of SR with experiment, please start a thread. If you do, I'll be happy to discuss your understanding and memory of Professor Will's comments on that experiment.

 

There have been a number of ideas presented in the thread regarding how time travel would or wouldn't work, with various proponents apparently completely convinced of the reality of their own POV.

Why? The nature of time has long been a staple of metaphysics. Why would anyone have the arrogance to think their own point of view on something untestable like this is the One True Reality?

While it would certainly be folly to commit to the notion that time-travel will one day be possible, there doesn't seem to be any value in damning the notion as absurd either.



Wormholes are an interesting solution to GR mathematics. While their potential physical realisation is pure speculation, it is an educated speculation. There is nothing to say that they cannot exist.

Black holes began as interesting solutions to GR mathematics, without good models of how they might be physically realised. The idea of their potential physical realisation was soundly condemned for good reasons... that later turned out to be not so good after all.

 

Possibly because ones own point of view would be all a Time Traveller could apply to the matter - and because of the fundamental nature of Time Travel it wouldn't do them the slightest bit of good.

You can prove this with a simple coin. Say I have in my hand a shiny, new, freshly minted pound coin and I offer you a wager: "Call it, and it's your's."

You call Heads.... Oh, jolly bad luck. The coin comes down Tails.

Still, not to worry. Splendid fellow that I am I chuck you the keys to my Time Machine and in so doing present you the opportunity to use your first hand knowledge of History to pop back momentarily into "The Past" and win the coin. You're knowledge of History informs you that the coin is going to come down Tails, and so back you trot.

As I say: "Call it," you reply Tails and Tails it is. Jolly good show, you're a pound better off...

Leaving aside the obvious fact that in order to accomplish this you'd have to have travelled back more than just a few mere seconds in Time. You're "Past Self" would be present, this is all about Time Travel. There being two of you present in the same room at the same time might tip the nod to the more observant that something decidedly dodgy might be afoot.

Lets also leave aside such questions regarding exactly what sort of person is it that goes to such extraordinary and contrived lengths just to win a measly quid....

That way lies Terry Pratchett. And hilarity must, therefore, ensue. It's a Law.

Let's just stick with the coin.

As you know, over and above the physical forces that compel a coin when flipped up into the air to come down, the odds of it landing one side over the other remain more or less even. 50/50. Random Chance. The out come of any one specific toss has absolutely no bearing or influence on the outcome of the next. The odds remain more ore less exactly even. 50/50 straight down the line. Doesn't matter how many times you do it.

Certainly there's very little in physics to dictate that the outcome of the flip of a coin can be governed by the outcome of one subsequent to the coin being flipped. Were this the case, Random Chance wouldn't exist. Causality as we understand and experience it would no longer be the case either. Effects would no longer be the consequence of what simply happened previously, but predetermined by the events of some Future we have yet to arrive in and constrained to occur in order to facilitate the advent of this exact, predetermined Future.

Codswollop, as Einstein would have put it.

So, you as a Time Traveller travel back through time. You're experience and foreknowledge of the Future informs you that the outcome of the flip of the coin will be Tails and, in applying that knowledge, Tails it is...

The question is: do you actually win the coin because of you're unique foreknowledge of the Future, or is it just the consequence of random, simple, plain, blind, bog-ordinary, dumb luck?

A Time Traveller has absolutely no means of being able to determine which to be the case.

One might indeed, when it comes witnessing the outcome of the toss of a coin, observe the same outcome as ones knowledge of "History" dictates - equally one might observe the exact opposite. The odds remain exactly no different than if one had simply never bothered Time Travelling in the first place and just gone for Best Out Of Three instead.

Since a Time Traveller, in being present in "The Past" for certain would know that an instance of Time Travel has occurred, they may infer, that in witnessing a change in outcome from what their knowledge of "History" informs them (the coin coming down Heads instead of Tails for example) that possibly the actual act of Time Travel itself may have caused some fundamental degree of change to the outcome of "History"...

It may, after all be absolutely nothing at all of the sort and simply the consequence of straightforward, honest-to-goodness random chance.

It's perfectly conceivable that if oneself could Time Travel in this fashion, others undoubtedly too could have done the exact same and what the Time Traveller is witnessing may actually be the outcome of other, undisclosed explorers, scholars and nefarious near-do-wells such as themselves prepared to go to any lengths, no matter how patently absurd, simply just to win a silly wager.

The point being: the Time Traveller themselves has absolutely no way of making an accurate determination regarding what they find themselves physically present to observe whatsoever.

This essentially gets to the very nub of the matter concerning why Time Travel, simply for the sake of travelling back into "The Past" to witness it is singularly useless. Despite what it might say on the box ones Time Machine comes in, one could never be certain that events one would witness would in fact be those that actually transpired in "The Past" as one thinks of it or simply events as they could have happened because the potential for them to occur in the manner one witnesses allows that series of unfortunate events to occur in the fashion one see's.

Travel back to the same point in Time again and observe the exact same Historical event. It may unfold the way you saw it the first time, it may conceivably not.

The concept of History in the broadest possible strokes, unless in being deliberately altered, are probably likely to occur has ones knowledge of History dictates: specifically what and when would likely occur each time one were to view it.

But in observation one might conceivably observe changes to the actual mechanics of History as one perceives them to have been: what happened and when may still be events which transpire, but the reasons concerning how and why may actually be observed to alter simply because there exists a degree of Random Chance at play concerning the mechanics and outcome of any given event, at any point in Time, irrespective of weather one travels back through it or not.

One never has to take anyones word in the slightest regarding such matters.

All one ever has to do is simply flip a coin and observe...

A

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They call in to the Art Bell show all the time. They never seem to give out any lottery numbers, though.

 

It is a problem. Changing ones own past in such a way is flat nonsense. If it's happened, it can't be changed. If I called Heads, and it came up Tails, then that's the way it is/was/willould... (bloody grammar)

But what if..
Say you have in your hand a shiny, new, freshly minted pound coin and you offer me a wager: "Call it, and it's your's."

I start to say Heads, but looking over your shoulder I pause before gleefully crying "Tails!"

The coin comes down Tails.

I pocket your pound and give you a warm embrace to comfort you on your loss, taking the opportunity to slip the keys to your Time Machine from your pocket. Along with that spare fiver. (Thanks!)


You see, when I was about to call heads, I saw myself tiptoe into the room behind you carrying a large sign saying "Call Tails! The time machine keys are in his right-hand jacket pocket, and a fiver in the breast pocket. His wallet is empty."

So, I duly prepare said sign and pop back into the past to fulfil what I know happened.


So, there was only one coin toss. There was (wissan?) no chance for a different outcome, because there was (wasill be?) only ever a single outcome.

Of course, this raises all sorts of hairy questions about free will and what not, but that's a more serious question.

H'rm, that may be so for a single 50-50 coin toss. Perhaps a more difficult test is appropriate?

Here's your pound back - let's take it down to the casino.
We'll collect the roulette results for the evening from the letterbox on the way out. Remind me to jot the results down while we're winning, and tomorrow I'll pop back to today and slip them into the letterbox!



But, there are problems involved. As soon as we put people into the mix things get very hairy indeed.
With my penchant for carrying pens with no ink or getting carried away at the bar, there's a high likelihood that I won't reliably write those numbers down so we won't find that list in the letterbox after all. And if we did, then why would I bother to write it again? Wouldn't it be easier to slip the same list back the letterbox :bugeye

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Perhaps we should have a little fun with a game of wormhole marbles instead.

 

Time travel is not possible because 'time' is an idea.

 

I guess by your definition, my watch is just an 'idea' too.

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Penguins and monkeys don't eat mangos during the summer solstice.

 

Unless they are very very hungry. Right? Right!

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