Time travel?

[Brethern]

Sadly that does not prove time travel, just proves that human stupidity is the greatest force in the known universe.

I doubt we will ever develop the ability to travle backwards in time. No mater how careful or how well regulated there would eventualy people that break the rules or just screw up and leave evidence behind that they were from the future. Its the clasic issue of security needing to succeed 100% of the time while the person breaking the security only needs to succeed once but the security needs to succeed for 100% of the attempts from all of humanity's remaining existence. eventualy the evidence would start showing up and we'd see time travlers. Lacking any evidence of time travlers to date implies that its probably impossible

Why would you assume time traveling would be easy? Perhaps the method to do it is as complicated and expensive as traveling to the moon. Therefore it would be self regulating.

[micha]

Why would you assume time traveling would be easy? Perhaps the method to do it is as complicated and expensive as traveling to the moon. Therefore it would be self regulating.

At the beginning, sure. Give it another X years of development (where X can be thousands..) and it should be as ubiquitous as mobile phones or plane travel is to us today. Unless there's a physical restriction, anything desirable will eventually become mass market, given a long enough stable civilisation.

[pg01202]

The only way I can see that reverse time travel would be possible is if time exists as a physical dimension, with information stored as energy. Even then, are you really going back in time or just reconstructing past events?

Eventually the evidence would start showing up and we'd see time travlers. Lacking any evidence of time travlers to date implies that its probably impossible

What would you be comparing it to? From our perspective the changes made by time travellers would seem to be the natural chain of events.

Edited February 12, 2015 by pg01202

[MircoMars]

Timetravel will lead to the discovery of what the Universe is for and why it is here.

There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable.

There is another theory which states that this has already happened.

[TheDarkStar]

Best alternate history novel I read was Pastwatch: The Redemption of Christopher Columbus by Orson Scott Card. I thought it was perhaps the best novel OSC has ever written, maybe even better than Ender's Game.

His Pathfinder series was pretty good, too; it also explores the possibilities of time travel more fully. It's not quite as realistic, though.

[Brethern]

At the beginning, sure. Give it another X years of development (where X can be thousands..) and it should be as ubiquitous as mobile phones or plane travel is to us today. Unless there's a physical restriction, anything desirable will eventually become mass market, given a long enough stable civilisation.

It's been what 50 years since apollo? I don't see rockets having the same power as a Saturn V but with half the size.

[Bill Phil]

It's been what 50 years since apollo? I don't see rockets having the same power as a Saturn V but with half the size.

Do you mean power as in Joules per second, or power as in payload capacity?

[Brethern]

Do you mean power as in Joules per second, or power as in payload capacity?

Choose whichever one is harder to get lower.

While I'm not going to say I believe in time travel I'm not going to jump on the not going to happen bandwagon until we see a solid study done on it.

[Carl Sagan The S Stallion]

Personally, I'm a "fixed timeline" kinda guy. Of course, this is ALL conjecture, for there is no conceivable way of testing this.

Perhaps the very act of travelling back in time is a part of time itself. Consider the following.

TRADITIONAL VIEW ON TIME TRAVEL

Hitler rises to power in 1936.

Hitler invades Poland in 1939.

Hitler commits suicide in his bunker in 1945.

70 years later you travel back in time to defeat Hitler.

Now...

You arrive back in time and assasinate Hitler before he rises to power.

No WWII (well, if you ask me, the war would have happened eventually, but that's besides the point).

No need, 70 years later, to travel back in time to kill Hitler.

Now...

PARADOX

"FIXED POINT" TIME TRAVEL

You arrive back in time to kill Hitler a week after he is born by replacing him with another child.

The child you replaced him with is Hitler.

Hitler rises to power in 1936...

yada, yada, yada.

70 years later, you travel back in time to kill Hitler.

OR

You arrive back in time to assassinate Hitler in 1936.

You fail, or you kill the wrong person.

Hitler rises to power in 1936...

yada, yada, yada.

70 years later, you travel back in time to kill Hitler.

Of course, nature could just make it so you can't actually time travel. It could be that creating a portal back in time would create so much feedback it would annihilate itself or dissolve.

[tuckjohn]

Sadly that does not prove time travel, just proves that human stupidity is the greatest force in the known universe.

I doubt we will ever develop the ability to travle backwards in time. No mater how careful or how well regulated there would eventualy people that break the rules or just screw up and leave evidence behind that they were from the future. Its the clasic issue of security needing to succeed 100% of the time while the person breaking the security only needs to succeed once but the security needs to succeed for 100% of the attempts from all of humanity's remaining existence. eventualy the evidence would start showing up and we'd see time travlers. Lacking any evidence of time travlers to date implies that its probably impossible

Signs would start to show up? I bring you the 7 great wonders of the ancient world. I bring you extra-terrestrial-like UFOs (not weather balloons). I bring you the free masons. And finally I bring you the fact that first civilizations appeared everywhere on the planet within a 100 year period.

[Rakaydos]

Why would civiliaations appearing at the same time be evidence of time travelers, even if true?

[tuckjohn]

Why would civiliaations appearing at the same time be evidence of time travelers, even if true?

It is true(Go here and scroll down to the chart at the bottom), and I am just pointing out that it is an unexplained occurrence. Who knows? Possibly the time travelers pushed civilization into existence in multiple places at roughly the same time in order to allow to their own existence...

[Voyager55]

^ ^ ^ A possibility. But I personally don't think time travel to the past will ever be possible for one reason. If backwards time travel ever becomes possible, there would be a near infinite amount of time after the discovery wherein over the next few billions of years anyone who ever is or is going to travel to this exact point in time would have already done it. I have no idea how to explain it..... i'm done, before I risk sounding any dumber

[Stargate525]

^ ^ ^ A possibility. But I personally don't think time travel to the past will ever be possible for one reason. If backwards time travel ever becomes possible, there would be a near infinite amount of time after the discovery wherein over the next few billions of years anyone who ever is or is going to travel to this exact point in time would have already done it. I have no idea how to explain it..... i'm done, before I risk sounding any dumber

No no, it's another perfectly valid argument; the whole Time Tourist Paradox. If we eventually get time travel, where are all of the visitors to great historical events? I recall reading a rather neat short story about a time-vacation to see the Passion of Christ and, through an accidental outing of one of the members of the group, they discover that the ENTIRE crowd shouting for Jesus' death are actually time-travelers.

Avoiding that particular issue is why I prefer the splitting timelines version; you go back in time, and that action immediately shears off a parallel timeline. From the future perspective, there's never a functioning time Machine (as nothing changed, and your traveler never returns) and from the traveler's perspective, well... you can't ever get back to 'your' time. Kinda depressing.

[dryer_lint]

Or what if they gave bears and Native Americans Ak-47s?

The possibilities are endless!

If they're advanced enough to invent time travel, then they're probably able to rain down AK-47s from the sky.

[micha]

It's been what 50 years since apollo? I don't see rockets having the same power as a Saturn V but with half the size.

Rocketflight is not desirable to the masses. At least, not yet. Hence no major incentive to pour development effort into it.

Cars, planes, mobile phones, movies are all counterexamples.

Also I didn't suggest you'd have a TARDIS, just as most people don't have their own plane, but planetravel is certainly accessible.

[Thiagobs]

Time travel is an interest of mine, not in a scientific, but a fictionalized way....

One issue that I often mention when talking about time travel is a sort of "Universal coordinates". Traveling back in time, let's say, 10 years, would put you in that exact spot in space 10 years ago, but because the Earth, the Solar System our galaxy moves about, you end up in space, in the middle of nowhere...

About the "objective of travel" paradox, I believe it wouldn't be an issue if you're going back in time to act as an observer. Since you don't change anything, you're just acquiring knowledge for your post-timemachine self, the paradox doesn't kick in. But I wonder how thing would go if you unintentionally changed the course of history. Accidentally killing baby Hitler wasn't your objective, so it wouldn't affect your need to build a time machine, but you end up changing history.

Now, I wonder about two possibilities:

1- You can travel back in time, but once there, you cannot travel forward (back to the present). Basically, if you make any significant changes to the past, you alter the course of history. There's a possibility that your life would be different, so when traveling back to the new present, who lived your different life? An automaton, a husk of yourself? Think about 'Back to the Future', when Marty goes back to his alternate family, where his father and siblings are successful, he gets there without knowing this, like he missed all those years, but his family acknowledge him as being part of their history, so... who was living his life? To prevent that, you can't go back to the present, once in the past, you're stuck there.

2- You can go back in time, change history and live there to see the outcome of your meddling, but once you come back to the present, you're back to your 'original timeline', where the changes you made never happened and everything is back as it was before. Can create some interesting mechanics there...

Anyway, I'm starting to ramble...

[KerikBalm]

It is true(Go here and scroll down to the chart at the bottom), and I am just pointing out that it is an unexplained occurrence. Who knows? Possibly the time travelers pushed civilization into existence in multiple places at roughly the same time in order to allow to their own existence...

That chart proves nothing, it does not show the start of the civilizations... it only goes back to 3000 BC

From your own link:

"The Mesopotamian civilization of Sumer emerges in the Ubaid period (6500-3800 BC)"

"Evidence also indicates human habitation in the southwestern corner of Egypt, near the Sudan border, before 8000 BC"

"It has been suggested that as a result of these changes, around 2500 BC early tribes from the Sahara were forced to concentrate along the Nile river where they developed a settled agricultural economy and more centralized society."

"By 4000 BC, a pre-Harappan culture emerged, with trade networks including lapis lazuli and other raw materials. Urban centers during this phase spanned what is now Pakistan and western India. The Harappan phase is known to have comprised several large cities, including Harappa (3300 BC)"

"The earliest archaeologically verifiable dynasty in recorded Chinese history, the Shang Dynasty, emerged around 1750 BC"

"The Yellow River was irrigated around 2205 BC, reputedly by Yu the Great, starting the semi-mythical Xia Dynasty."

Doesn't fit in so well with your claims... does it?

[pg01202]

I think there's a lot of anthropocentrism that prevents us from analysing time travel properly. We see it all the time with laws of nature, seen as immovable and implacable, but remember that they apply to closed systems. When you leave your linear time you leave the closed system and the laws don't have to remain consistent. Physical laws only describe what the universe has been capable of doing on its own. If you find a way to force interaction in ways that the universe has not been able to do on its own then you need new laws to describe what you're doing.

Edited February 14, 2015 by pg01202

[tuckjohn]

That chart proves nothing, it does not show the start of the civilizations... it only goes back to 3000 BC

From your own link:

"The Mesopotamian civilization of Sumer emerges in the Ubaid period (6500-3800 BC)"

"Evidence also indicates human habitation in the southwestern corner of Egypt, near the Sudan border, before 8000 BC"

"It has been suggested that as a result of these changes, around 2500 BC early tribes from the Sahara were forced to concentrate along the Nile river where they developed a settled agricultural economy and more centralized society."

"By 4000 BC, a pre-Harappan culture emerged, with trade networks including lapis lazuli and other raw materials. Urban centers during this phase spanned what is now Pakistan and western India. The Harappan phase is known to have comprised several large cities, including Harappa (3300 BC)"

"The earliest archaeologically verifiable dynasty in recorded Chinese history, the Shang Dynasty, emerged around 1750 BC"

"The Yellow River was irrigated around 2205 BC, reputedly by Yu the Great, starting the semi-mythical Xia Dynasty."

Doesn't fit in so well with your claims... does it?

All of those dates are withing ~3000 years of each other, which on a timeline of the earth, is relatively small. Why did all of these civilizations appear at relatively the same time without any kind of communication with each-other? Currently the leading ("sane") theory is that naturally human evolution caused the civilizations to emerge because all humans had the need for civilization at the (relatively) same time.

I would like to also point out a really good book series that I read that deals with that^ issue, and other unexplained "things" (everything from the pyramids to "foo fighters" from WW2). The "Area 51" series by Bob Mayer. Yes, it has a cheesy title, and yes, it is filled with conspiracies, and yes, it is a really good read. I will warn any readers that the beginning pages chuck a lot of names and characters at you, but then very little is introduced in the following pages/books.

EDIT: A link to the book series for the lazy: http://www.amazon.com/gp/feature.html?ie=UTF8&docId=1000869311

[monophonic]

I have a couple of hypothesis of my own on the subject.

1) You can go back in time, and you can do anything and everything you want, and go back. That changes nothing, because the future you came from was already the result of all the (mis)deeds you did in your past.

2) Travel back in time requires a receiving station. Therefore no-one can travel back to earlier than when the first time machine was switched on, and even then travel is limited because the receiver has a limited bandwith.

[pg01202]

1) You can go back in time, and you can do anything and everything you want, and go back. That changes nothing, because the future you came from was already the result of all the (mis)deeds you did in your past.

What would be the physical law that requires this? Depending on your mode of relativistic effects, this either violates conservation of energy or is rendered meaningless by Lorentz covariance, since the local effects in a single point of general relativity aren't directly related to the global effects of special relativity. As I was saying above, it's very unlikely that general relativity would apply beyond a single point in spacetime (which I think you are alluding to), so what you do in the past would simply cut you off from the time you came from. Linear (general relativistic) time would need to obey the laws of conservation, so going forward from the point you changed would maintain the information that you altered.

Information from the time you originally travelled from wouldn't disappear, you simply wouldn't have access to it.

[KerikBalm]

All of those dates are withing ~3000 years of each other, which on a timeline of the earth, is relatively small. Why did all of these civilizations appear at relatively the same time without any kind of communication with each-other? Currently the leading ("sane") theory is that naturally human evolution caused the civilizations to emerge because all humans had the need for civilization at the (relatively) same time.

3000 years is a big change from a hundred years.

You shouldn't used the timeline of the earth... but rather the emigration of modern humans from africa + the end of the ice age and other climactic factors to "synchronize" things... plus there were interactions among groups, and ideas can spread far further than people (at least back then).

See someone using a spear at the west end of your normal range... make yourself a spear... someone at the east end of your range sees you, does the same thing... etc.

I don't see any great paradox to be solved by time travel or gods or aliens...

[monophonic]

What would be the physical law that requires this? Depending on your mode of relativistic effects, this either violates conservation of energy or is rendered meaningless by Lorentz covariance, since the local effects in a single point of general relativity aren't directly related to the global effects of special relativity. As I was saying above, it's very unlikely that general relativity would apply beyond a single point in spacetime (which I think you are alluding to), so what you do in the past would simply cut you off from the time you came from. Linear (general relativistic) time would need to obey the laws of conservation, so going forward from the point you changed would maintain the information that you altered.

Information from the time you originally travelled from wouldn't disappear, you simply wouldn't have access to it.

Umm... Sorry, I don't speak Physics so most of what you say is way beyond my understanding. Was hypothesis too strong a term to describe my idea? Maybe my phrasing was off? I meant that when travelling back in time you could not actually change anything because those changes were already part of the history when you left for your time trip. So all you can do is go and act out things that must happen exactly as they happened. The same fixedness would then likely extend the other way into future as well. This would have big metaphysical implications too, like completely eradicating the concept of free will.

But, well, yeah... It is mainly idle thinking, there is no serious theory behind it.

[eddiew]

Taking advantage of time dilation isn't really time travel, because you don't disappear then reappear in the future; you're always present somewhere in the universe, just travelling really fast or near a really big gravity well.

Quantum physics + multiverse theory would suggest that you can potentially travel back in time, to when there were less universes in the multiverse... However you can't then go forward into the same one that you started, because you've caused a new branch. The one you started in is unchanged, it's the one you're in now that is different. You're more dimension hopping than you are time travelling.

My 2p on the subject anyway