Is time travel impossible

[siarad]

If I could travel back in time 2 hours I would be in mid-Atlantic, well hardly I'd be thrown 60,000? miles out in space er, no the Sun is moving & the Milkyway hurtling towards the great attractor...<br />It therefore seems time travel can't happen without apace travel & surely the g force would crush me.<br />Aha now we're in Startrek territory where warp drive causes space to hurtle past saving the crushing. (Einstein spins in his grave)<br />So it seems time & space are inextricably linked & maybe we could travel to the stars merely by time travel & should concentrate on this rather than rockets.

 

[SpeedFreek]

Well, travelling forwards in time is easy - you are doing it right now!<br /><br />As for travelling into the distant future, it is theoretically possible using relativity. If you speed up and approach the speed of light, time slows down for you, so if you made a journey at 99.98% of lightspeed you experience time 50x slower than the people at home on Earth! If you journeyed for 2 years at that speed and returned to Earth, 100 years would have passed.<br /><br />But travelling backwards in time is another thing entirely and isn't allowed by any current theory. Travelling backwards in time messes with causality in a big way. And we have to ask the question, "If backwards time travel is ever invented, why don't we see time travellers appearing throughout history?!" <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[3488]

Perhaps this is better off in Phenomena.<br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[heyscottie]

No, it's a good question...<br /><br />The original post points out a feature of time travel that is given by almost all fiction dealing with it -- that the person would end up in the same place after travelling through time. "The Time Machine" has the traveller showing up in the same place on the globe. "Back to the Future" shows the DeLorean appearing in the same location it left 30 years ago, etc.<br /><br />But what IS "the same place"? Why would we assume that any time machine would relocate us on the same part of the globe we were on when we started travelling? Why not the same place in the solar system? Or galaxy? Or Universe? It seems that time travel would probably not prefer Earth-centered Earth-fixed coordinates.

 

[enigma10]

Time travel in general is a common question on this board. please search for other threads concerning this. <br /><br />..and yes, they often find their way away from real science discussions. <div class="Discussion_UserSignature"> <em>"<font color="#333399">An organism at war with itself is a doomed organism." - Carl Sagan</font></em> </div>

 

[derekmcd]

An often overlooked reason for disregarding time travel is one of the laws of thermodymanics.<br /><br />How can you account for your mass simply appearing in another time. I've never been offered a descent solution to this conundrum. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[vandivx]

<font color="yellow">If I could travel back in time 2 hours I would be in mid-Atlantic, well hardly I'd be thrown 60,000? miles out in space er, no the Sun is moving & the Milkyway hurtling towards the great attractor... </font><br /><br />you are assuming absolute space here, at least that's what you'd end up with if you followed your idea logically to the (bitter) end<br /><br />and it would be called space-time travel then and people only want pure time travel in their fantasies and wouldn't want to have it spoiled by the likes of you who try to probe into it somewhat logically, if you approach things that way you will be largely ignored anyway, people are not interested in real truth and how things really are, on this forum or wherever, they like to stick to their fantasies above all, that's why its useless trying to explain that time travel is pure impossibility and accordingly I won't try it, people don't want to hear it and so they won't listen and physics be damned for all they are concerned<br /><br />vanDivX<br /><br /> <div class="Discussion_UserSignature"> </div>

 

[siarad]

This isn't about time travel but it's <b>meaning</b><br />Going back in time must move you in space otherwise what I see of the Universe would be different from the indigenous person i.e. a different phase of the moon for a simple instance.

 

[oscar1]

Going back in time would also make you wake up the dead, for when they would speak to you, they would be saying something after they died.

 

[trumptor]

I am not trying to say travelling back in time is possible due to the problems with causality and all the paradoxes, but as far as accounting for mass, if it was possible, could the laws of thermodynamics be rewritten to say that the overall mass of a closed system remains constant over eternity. If a box contains 10lbs of mass then if it mysteriously weighs 20lbs for 10 minutes then it will have to weigh zero lbs for ten minutes somewhere else in the timeline to make up for the discrepency leaving the average weight 10lbs? <div class="Discussion_UserSignature"> <p><em><font color="#0000ff">______________</font></em></p><p><em><font color="#0000ff">Caution, I may not know what I'm talking about.</font></em></p> </div>

 

[dragon04]

Without some sort of duality, there's still a "net loss" of mass from one "timeline" and a "net gain" in another in the case of time travel.<br /><br /><font color="yellow">could the laws of thermodynamics be rewritten to say that the overall mass of a closed system remains constant over eternity.</font><br /><br />So rather than the term "eternity", you'd have to say "sum of histories".<br /><br />Although I'll be the first to admit that my lack of formal training makes my input on something so esoteric even "esotericer and esotericer". <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>

 

[derekmcd]

That's the problem. Two different timelines are not the same closed system. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[Leovinus]

We are actually travelling backwards in time right now. We are just unaware of it because are brains think of time going forward.<br /><br />Noodle on that for a while. <div class="Discussion_UserSignature"> </div>

 

[enigma10]

So if we turn around real fast several times and click our ruby red slippers just right, we'll be going the right direction to achieve optimal existance. <div class="Discussion_UserSignature"> <em>"<font color="#333399">An organism at war with itself is a doomed organism." - Carl Sagan</font></em> </div>

 

[siarad]

OK, we're moving towards interstallar light from the past, not the same thing though <img src="/images/icons/smile.gif" />

 

[1111person]

No I don't think so unless you can run all the interactions on the universe backwards.

 

[vandivx]

I used to muse ala young Einstein what it would be like if one could travel FTL, for example you could fly out away from Earth and you could look back at it and see it as it was in the past, if you kept it up long enough you could see the Earth as it was before people started roaming about it...<br /><br />so the question 'Is time travel impossible' could be translated into another one 'Is FTL travel possible'<br /><br />vanDivX <div class="Discussion_UserSignature"> </div>

 

[nyrath]

<blockquote><font class="small">In reply to:</font><hr /><p>so the question 'Is time travel impossible' could be translated into another one 'Is FTL travel possible' <p><hr /></p></p></blockquote><br />Yes. According to relativity, time travel and FTL travel are two words for the same thing.<br /><br />Which is why most physicists are hostile to the idea of FTL travel.<br /><br />

 

[SpeedFreek]

Quite true, but there are also ideas that sidestep the light barrier completely, without violating causality.<br /><br />Unfortunately none of them allow backwards travel in time, but they do allow <i>apparent</i> FTL travel. I'm talking about wormholes and such exotic methods, pure hypothesis so far.<br /><br />They sidestep the light barrier in the same way as the expansion of space allows galaxies to recede at superluminal speeds. They are not about moving faster than light, but are about manipulating space. <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>

 

[nyrath]

<blockquote><font class="small">In reply to:</font><hr /><p>but there are also ideas that sidestep the light barrier completely, without violating causality.<br /><br />Unfortunately none of them allow backwards travel in time, but they do allow apparent FTL travel. I'm talking about wormholes and such exotic methods<p><hr /></p></p></blockquote><br />That turns out not to be the case. <img src="/images/icons/wink.gif" /><br /><br />Didn't you read the link?<br />http://www.theculture.org/rich/sharpblue/archives/000089.html<br /><br />If a worm hole or whatever allows an object to travel from point A to point B faster than a ray of light, it is FTL travel. Not <i>apparent</i> FTL travel, no it is full-blown blatant take-THAT-Einstein FTL travel.<br /><br />And FTL travel and time machines are the same thing. At least if you accept Einstein's relativity. Therefore it does not matter how the FTL travel manages to travel faster-than-light, it will also violate causality.<br /><br />The only way out is to postulate some sort of weird law of physics that makes it impossible to use FTL-travel/time machines to violate causality.

 

[derekmcd]

"<i>no it is full-blown blatant take-THAT-Einstein FTL travel. </i>"<br /><br />Relativity doesn't exlude FTL travel. Einstein never postulated that FTL travel is not possible. Wormholes are a direct consequence of relativity. Relativity states that an object with mass can not be accelerated to or beyond the speed of light.<br /><br />An object traveling through a wormhole is not being accelerated at or beyond the speed of light within it's frame of reference. Only to observers outside the wormhole would it appear that they have travelled FTL. Hence the term "apparent" and it's proper use by speedfreek.<br /><br /> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[nyrath]

<blockquote><font class="small">In reply to:</font><hr /><p>An object traveling through a wormhole is not being accelerated at or beyond the speed of light within it's frame of reference. Only to observers outside the wormhole would it appear that they have travelled FTL. Hence the term "apparent" and it's proper use by speedfreek. <p><hr /></p></p></blockquote><br />I stand corrected.<br /><br />But this does not change the fact that wormhole travel, like all other FTL methods, cause failure of simultaneity at a distance. This means they are time machines. <br /><br />The old saying goes: <i>"Causality, Relativity, FTL travel: chose any two."</i> You cannot have all three.

 

[paintwoik]

There is no faster than light travel. There are no wormholes. There is no direction for time.<br /><br />There are no ifs ands or buts about this.

 

[siarad]

<blockquote><font class="small">In reply to:</font><hr /><p>Time has no direction<p><hr /></p></p></blockquote><br />Yes I think it's so.<br />Perhaps time doesn't actually exist, I think of it like temperature, a measurement of 'state'.<br />Temperature has no direction but what it measures does.<br />Shake a bottle of water & it increases in temperature & can't be unshaken by use of energy. Likewise time can be gained by supplying energy but can't be so lost. Flying in an aircraft gains you time no matter in what direction you fly.

 

[thebigcat]

<b>nyrath</b>: <i>The old saying goes: </i>"Causality, Relativity, FTL travel: chose any two."<i> You cannot have all three.</i><br /><br />In that case I'd like a Relativity with a side order of FTL Travel, hold the Causality. <div class="Discussion_UserSignature"> </div>