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Old 03-03-2003, 08:23 AM
tonbo0422 tonbo0422 is offline
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What's the status of time travel?

I'm wondering if anyone is seriously investigating travelling in time these days. I'm also wondering how difficult this challenge is compared to, say, "transporting" someone a la Star Trek.

Seems to me time travel would be easier. I remember reading somewhere that someone thought of "reading the grooves" of ancient pottery like an old-style LP to "hear" the sounds of what was happening when the pottery was made.

Are there any serious studies being done about the possibility of time travel that anyone knows of?

I heard recently that scientists were able to "transport" an ion or something equally ridiculous, but I've never heard the they were able to go back or forward one second in time.
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Old 03-03-2003, 08:43 AM
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Lots of theories, but all the sensible ones say that it can't be done. There might be tiny picosecond reversals in time possible at the quantum level, which some parapsychologists think could be somehow amplified into a sort of perceptible precognition of a second or less...
but for real time travel you would need a Tipler Cylinder or a pair of Relativistically Displaced Wormholes- both of which are very difficult, if not impossible, to acheive. LINK
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Old 03-03-2003, 09:19 AM
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I can't answer this again. I just answered it tomorrow. I'll tell you what. I'll explain it yesterday. OK?
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Old 03-03-2003, 09:27 AM
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Last time I checked, no one had a working flux capacitor capable of generating 1.21 gigawatts of power.

Besides that, Hawking and others have wagers on the issue, and neither him nor his peers with whom he wagered have ponied up any money yet, so it's still undetermined.

I believe Hawking is on the 'can't be done' side of the fence.
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Old 03-03-2003, 09:33 AM
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Theoretically it would be possible to travel back and forth to the future through some sort of quantum mechanism (forgive me if I can't give you more details) but travelling back in time past the creation of the quantum mechanism is impossible. However, no one is even close to creating this mechanism.

My guess is that time travel will come around before Star Trek transportation, just because I have never even heard credible theories on how it would be possible to break matter up, send them at light speed through other matter and then reassemble them perfectly. And that's just non-living matter.

Hopefully a physicist will be around to fill in the details.
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Old 03-03-2003, 09:40 AM
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What's the status of time travel?

It's been delayed due to foreseen circumstances.
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Old 03-03-2003, 11:31 AM
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As far as physicists can tell with today's knowledge time travel is possible. There is nothing in the theories we have today that prohibits it. Of course, time travel brings up so many problems that most seem to think there must be something that prohibits it...we just don't know exactly what that something is yet.

Fortunately for our timeline time travel, even if it is truly possible, seems to be insanely difficult to pull off. Most ideas for workable time machines require negative energy (no one has a clue how that would be managed) and stupendous amounts of energy. Even if you did get your hands on the energy necessary to do this that amount of energy would likely kill anyone attempting to time travel anyway.

For all of that, as already mentioned, time travel seems to be a simpler problem than transporting people/things ala Star Trek. Star Trek transporters are likely truly impossible due to such things as the Heisenberg Uncertainty Principle which is a well established and proven concept in physics that would mess up any transporter system (there are a few other problems with transporting people as well...the Uncertainty Principle just being the main stumbling block).
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Old 03-03-2003, 11:40 AM
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RE: What's the status of time travel?

TBA
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Old 03-03-2003, 11:59 AM
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Moving along nicely here at 1 second/second.
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Old 03-03-2003, 12:29 PM
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Quote:
Originally posted by Philster
[B]Last time I checked, no one had a working flux capacitor capable of generating 1.21 gigawatts of power.
[nitpick]
The flux capacitor does not generate 1.21 gigawatts, it requires this much power to operate. As this is GD, you'd think we could stick to the facts.




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Old 03-03-2003, 12:41 PM
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As for why it's generally believed to be impossible, the classic example is the "grandfather paradox". Suppose that I invent a time machine, and go back in time to before my parents were born. I then kill one or more of my grandparents. Now, this means that my parents were never born, and therefore neither was I. But if I was never born, then who was the guy who went back and killed those folks? And if nobody did, then I do exist after all, so why can't I do it?

Related to this is the problem of djinns, or effects without external causes. Suppose, for instance, that I'm a little more peaceful in my intentions, and go back to visit Bethoven to discuss his music with him. Of course, I bring along a copy of his famous fifth symphony. But I go back to when he was only still working on the fourth. Well, he takes a look at the sheet music I show him, and he thinks that it's great. I give him permission to publish it as his own, and a few years later, he does. So where did that music come from?

In physics, the only known problem with time travel appears to be the amount of energy required. It's not that it would require too much, but that it would require too little: Specifically, less than zero. I've seen schemes which would only require negative a few grams or so, so we're not talking astronomical amounts, here. Nor is the time of creation of the device necessarily a factor: A Thorne wormhole time machine could only take you back to when it was first constructed, but an Alcubierre warp field, which is theoretically no more impossible than a Thorne wormhole, would not suffer from this restriction.

Finally, I should add that there are a few possibilities which could theoretically permit time travel, but which couldn't ever be built, even theoretically. A Gödel universe, for instance (one whose spacetime has a net angular momentum) would contain closed timelike curves, as would a universe containing a maximally-extended extreme Riser-Nordstrom black hole. But in order for either of these things to exist, they need to exist from the very beginning of the universe: Neither can have a beginning point (or an ending point) in time. So it's conceivable that we might get lucky and someday find such an object, but if we don't, there's nothing we can do about it.
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Old 03-03-2003, 12:43 PM
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Didn't we do this just recently? Try the search function.

It's easy to travel into the future. Hop aboard a spaceship going 99.9% the speed of light for 10 years and when you come home everyone you know will be dead. Add more 9's and you can return to earth 1000, 10000, or as many years as you like in the future.
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Old 03-03-2003, 01:07 PM
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We have to agree what we mean by time travel to the future and to the past. If by time travel to the future, you mean finding a way to leave a place, do something, come back and age less than the people who stayed in the place (e.g. you have a twin brother, and when you come back, he is ten years older than you), that is perfectly possible in principle, and in a sense it is done all the time, according to General Relativity. The catch, of course, is that with current technologies, the differences among the watches are truly small.

A more challenging question is whether it is possible to travel to the past (say, meet your parents before you were born). We don't have a proof that it is not possible, although I expect that to be the answer. The problem is that General Relativity does not seem enough to settle the question, since it is expected that quantum effects will play an importan role, and General Relativity is a purely classical (i.e. non quantum) theory.

On the other hand, we don't have a fully developed and accepted theory of quantum gravity, so it is not clear which tools we should use to attack the problem.

In the last post of this thread, I tried to address the question in more detail.
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Old 03-03-2003, 02:17 PM
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>>I can't answer this again. I just answered it tomorrow. I'll tell you what. I'll explain it yesterday. OK?


There should be a law as to people making other people laugh till they're in stitches.
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Old 03-03-2003, 02:32 PM
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Umm, sorry if this was part of another thread. I apologise for recreating it without searching. I'll remember not to do it again yesterday.

But I was thinking: why isn't time just like other physical phenomena like light, or gravity? It seems to me that if only someone could "crack" the equation, it would indeed be possible to fool with time. It is my suspicion—pathetic though it may be—that all these "phenomena" such as ghosts or UFOs can actually be attributed to someone in the future who has cracked time travel.

And I'll bet you his name is not McFly.
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Old 03-03-2003, 02:35 PM
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eburacum45, brilliant link, thanks muchly.
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Old 03-03-2003, 02:40 PM
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Chronos:

God-dayam! This is why I post on this board.
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Old 03-03-2003, 02:46 PM
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Quote:
Originally posted by Chronos
In physics, the only known problem with time travel appears to be the amount of energy required. It's not that it would require too much, but that it would require too little: Specifically, less than zero. I've seen schemes which would only require negative a few grams or so, so we're not talking astronomical amounts, here. Nor is the time of creation of the device necessarily a factor: A Thorne wormhole time machine could only take you back to when it was first constructed...
I thought you'd still need a great deal of energy to make a Thorne wormhole time machine. You use your negative energy to hold open the mouth of the wormhole but now you need to drag one end of it around at relativistic speeds...probably by towing a large gravitational object nearby to attract one end of the wormhole.

So, don't you need both a 'little' (less than zero) and a lot of energy to make this happen?
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Old 03-03-2003, 03:05 PM
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Quote:
Originally posted by Philster
Last time I checked, no one had a working flux capacitor capable of generating 1.21 gigawatts of power.

Besides that, Hawking and others have wagers on the issue, and neither him nor his peers with whom he wagered have ponied up any money yet, so it's still undetermined.

I believe Hawking is on the 'can't be done' side of the fence.
I believe Hawking cites as "proof" the fact that as far as he knows, we've never had any visitors from the future.
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Old 03-03-2003, 03:11 PM
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The Time Lords from Galleyfrea have prevented all time travel technologies to be fully achieved within this Time continuum. Time travel is limited to a few species in this continuum's universe.
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Old 03-03-2003, 03:12 PM
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You need the status on time travel?? Wait, let me check......yes here it is....Nope, still impossible.
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Old 03-03-2003, 03:15 PM
eburacum45 eburacum45 is online now
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The Visser virtual particles will close the wormhole before you can kill /become your own grandfather.
(nice idea about the silver balloons- have to try that some time)
If Time travel can be done, it will change the past, and continue to do so until time travel is uninvented again.
You could call this the Hawking/Niven Chronological Protection Conjecture.
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Old 03-03-2003, 04:10 PM
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Quote:
Originally posted by Beelzebubba
[nitpick]
The flux capacitor does not generate 1.21 gigawatts, it requires this much power to operate. As this is GD, you'd think we could stick to the facts.





As this is actually GQ - not GD as you indicate - and you are being smarmy, you'd think you would check the fine details of your post.


Also, as per the script, the Flux Capacior GENERATES the 1.21 gigawatts.

"Marty: The flux capacitor?

Doc: It's taken me almost 30 years and my entire family fortune to realize the vision of that day. My god has it been that long. I remember when this was farm land as far as the eye could see. Old man peabody owned all of this. He had this crazy idea about breeding... pine trees.

Marty: This is, uh, this is heavy duty doc. Does it run like on regular unleaded gasoline?

Doc: Unfortunately no. It requires something with a little more kick. Plutonium.

Marty: uh, plutonium. Wait a minute, doc, are you tellin me that this sucker is nuclear?

Doc: hey, keep rolling, keep rolling there, No, no, no, No, this sucker's electrical, but it needs a nuclear reaction to generate the 1.21 gigawatts of electricity I need."


See, the nuclear reaction allows the flux capacitor to generate the 1.21 gigawatts.
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Old 03-03-2003, 04:28 PM
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Quote:
Originally posted by Chronos
As for why it's generally believed to be impossible, the classic example is the "grandfather paradox".
Actually, this is a classic example of fuzzy thinking. No offense intended to you, Chronos. I imagine you were just relaying the concept in the most commonly encountered form. But it's wrong, as presented.

The "grandfather paradox", along with all the other hypothetical paradoxes (not to be confused with a "pair o' doxies", hypothetical or otherwise), are reasons why it might be a bad idea, not reasons why it's impossible. They do not prevent us from attempting time travel, should it ever be possible. A paradox may be a bad thing, but it doesn't proactively enforce the laws of math, physics, or Murphy.
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Old 03-03-2003, 06:10 PM
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To answer the OP, Time Travel was finally perfected in the year 2107. I'm sorry, but I'm not allowed to tell you any more.

Wow, it's just so cute to use this keyboard and the internet. I've read about these in history books!
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Old 03-03-2003, 07:12 PM
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As the representative of the Celestial Intervention Agency of Galleyfrea, I place you, ianzin, under arrest! Stay at your present temporal coordinates. Do not attempt to activate your trans-temporal device. You are under arrest!
  #27  
Old 08-28-2018, 05:54 PM
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Originally Posted by Earthworm Jim View Post
[nitpick]
The flux capacitor does not generate 1.21 gigawatts, it requires this much power to operate. As this is GD, you'd think we could stick to the facts.




Note on inevitable flux capacitor failures, as reported recently on Boston TV as main cause of airplane crash.
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Old 08-28-2018, 10:35 PM
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I suppose forward is in theory possible
we move forward now, just at the same pace.

If you can move someone at near light speed, send them out 3 years and back
not much time will have passed for them btu when they return much will have passed here.

or at least that is the theory.

If you leave earth in a light speed ship to some distant star, you may still be alive when you get there, but there wont be anyone you know left alive to return to
  #29  
Old 08-28-2018, 11:00 PM
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Depends on your model

Quote:
Originally Posted by Chronos View Post
As for why it's generally believed to be impossible, the classic example is the "grandfather paradox". Suppose that I invent a time machine, and go back in time to before my parents were born. I then kill one or more of my grandparents. Now, this means that my parents were never born, and therefore neither was I. But if I was never born, then who was the guy who went back and killed those folks? And if nobody did, then I do exist after all, so why can't I do it?

Related to this is the problem of djinns, or effects without external causes. Suppose, for instance, that I'm a little more peaceful in my intentions, and go back to visit Bethoven to discuss his music with him. Of course, I bring along a copy of his famous fifth symphony. But I go back to when he was only still working on the fourth. Well, he takes a look at the sheet music I show him, and he thinks that it's great. I give him permission to publish it as his own, and a few years later, he does. So where did that music come from?
The more general problem is sometimes called the "Changing the past objection to time travel." It's not as bad as it looks. Two solutions: the second is more compelling:

1. There are multiple world lines. Grandpa lives in one, dies in another.

A: That's not really time travel. That's cross multiverse travel, that only appears superficially like time travel.

Q: It is!

A: It isn't!

2. True, you can't go back in time and shoot Grandpa. But you can go back in time and wave at Grandpa, or even yourself. There's nothing contradictory in that.

Ok, what if someone is a great shot and wants to kill their Grandpa? Well who says they could pull it off? From the Stanford Encyclopedia of Philosophy:
In order to defend the possibility of time travel in the face of this argument we need to show that time travel is not a sure route to doing the impossible. So, given that a time traveller has gone to the past and is facing Grandfather, what could stop her killing Grandfather? Some science fiction authors resort to the idea of chaperones or time guardians... But it is hard to take these ideas seriously... Fortunately there is a better response—also to be found in the science fiction literature, and brought to the attention of philosophers by Lewis (1976). What would stop the time traveller doing the impossible? She would fail “for some commonplace reason”, as Lewis (1976, 150) puts it. Her gun might jam, a noise might distract her, she might slip on a banana peel, etc. Nothing more than such ordinary occurrences is required to stop the time traveller killing Grandfather. Hence backwards time travel does not entail the occurrence of impossible events—and so the above objection is defused.
Since this is philosophy, there's more to it of course, discussed here: https://plato.stanford.edu/entries/time-travel/ , eg "Another response is that of Vihvelin (1996), who argues that there is no contradiction here because ‘Tim can kill Grandfather’ is simply false (i.e. contra Lewis, there is no legitimate sense in which it is true)."

3. Addenda: The Steins;Gate franchise applies a hybrid model of time travel.

Last edited by Measure for Measure; 08-28-2018 at 11:00 PM.
  #30  
Old 08-29-2018, 02:13 AM
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Note on inevitable flux capacitor failures, as reported recently on Boston TV as main cause of airplane crash.
That darn flux capacitator [sic], always failing when you least expect it.
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Old 08-29-2018, 02:21 AM
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Ok, what if someone is a great shot and wants to kill their Grandpa? Well who says they could pull it off? From the Stanford Encyclopedia of Philosophy:
In order to defend the possibility of time travel in the face of this argument we need to show that time travel is not a sure route to doing the impossible. So, given that a time traveller has gone to the past and is facing Grandfather, what could stop her killing Grandfather? Some science fiction authors resort to the idea of chaperones or time guardians... But it is hard to take these ideas seriously... Fortunately there is a better response—also to be found in the science fiction literature, and brought to the attention of philosophers by Lewis (1976). What would stop the time traveller doing the impossible? She would fail “for some commonplace reason”, as Lewis (1976, 150) puts it. Her gun might jam, a noise might distract her, she might slip on a banana peel, etc. Nothing more than such ordinary occurrences is required to stop the time traveller killing Grandfather. Hence backwards time travel does not entail the occurrence of impossible events—and so the above objection is defused.
Since this is philosophy, there's more to it of course, discussed here: https://plato.stanford.edu/entries/time-travel/ , eg "Another response is that of Vihvelin (1996), who argues that there is no contradiction here because ‘Tim can kill Grandfather’ is simply false (i.e. contra Lewis, there is no legitimate sense in which it is true)."

3. Addenda: The Steins;Gate franchise applies a hybrid model of time travel.
Lewis clearly stole this from an old Superboy comic, where he goes back to save Lincoln but is thwarted. I hope he gave the comic a reference.

The problem is that if she failed she could try again later, and again, and again. And sometimes the presence of an additional factor is likely to change the past. The only stable situation is one where there is no time travel. See Asimov's End of Eternity.
Anyhow, the real proof against time travel is the lack of ticket stubs dropped by time travelers at significant events.
  #32  
Old 08-29-2018, 02:37 AM
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tonbo0422, I'm not sure why you brought up in the OP the matter of playing the grooves of ancient pottery to hear the sounds of what was happening when the pottery was made. There's nothing about doing that that remotely challenges present science. It may be very difficult, but it's just as much a part of present science as playing the grooves of a record. Time travel, on the other hand, requires a major revision of modern bases of physics.
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Old 08-29-2018, 03:58 AM
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tonbo0422, I'm not sure why you brought up in the OP the matter of playing the grooves of ancient pottery to hear the sounds of what was happening when the pottery was made.
It should be noted that tonbo0422 last visited the SDMB in 2006, so he's not likely to answer you.
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Old 08-29-2018, 09:04 AM
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I suppose forward is in theory possible
we move forward now, just at the same pace.

If you can move someone at near light speed, send them out 3 years and back
not much time will have passed for them btu when they return much will have passed here.

or at least that is the theory.
It's a theory in the sense that gravity is a theory. Time dilation has been proven experimentally. GPS depends on it.
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Old 08-29-2018, 09:14 AM
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Well, maybe tonbo0422 is a time traveler from the far future who went back to 2003 to start this thread. To tonbo0422, 2003 and 2018 are so long ago that the two years are almost the same amount of time in the past. tonbo0422 has decided to experiment with ancient methods of recording, first checking out pottery grooves and then online message boards. Both are incredibly primitive to tonbo0422.
  #36  
Old 08-29-2018, 11:16 AM
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Time traveling zombies would be a great idea for a movie!
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Old 08-29-2018, 02:09 PM
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Originally Posted by Weisshund View Post
I suppose forward is in theory possible
we move forward now, just at the same pace.

If you can move someone at near light speed, send them out 3 years and back
not much time will have passed for them btu when they return much will have passed here.

or at least that is the theory.

If you leave earth in a light speed ship to some distant star, you may still be alive when you get there, but there wont be anyone you know left alive to return to
It is not theory. That is how it works.

Indeed the GPS system in orbit around the earth needs to take relativistic time into account in order to provide accurate data for the system to work. In other words, they are moving through time at a different rate than you and I are and they need to account for that difference.

Interestingly the clocks on the satellites run faster than those on earth. Because they are moving so fast that slows their clocks down but that is overwhelmed by them being further out of earth's gravity well which means their clocks speed up. Their speed slows the clocks down by about 7 microseconds/day while being further out of the gravity well speed them up by 45 microseconds/day so the net result is they run 38 microseconds/day too fast. If not compensated for your reported location would be off by about 10km each day.
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Old 08-29-2018, 03:49 PM
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2. True, you can't go back in time and shoot Grandpa. But you can go back in time and wave at Grandpa, or even yourself. There's nothing contradictory in that.

Ok, what if someone is a great shot and wants to kill their Grandpa? Well who says they could pull it off? From the Stanford Encyclopedia of Philosophy:
In order to defend the possibility of time travel in the face of this argument we need to show that time travel is not a sure route to doing the impossible. So, given that a time traveller has gone to the past and is facing Grandfather, what could stop her killing Grandfather? Some science fiction authors resort to the idea of chaperones or time guardians... But it is hard to take these ideas seriously... Fortunately there is a better response—also to be found in the science fiction literature, and brought to the attention of philosophers by Lewis (1976). What would stop the time traveller doing the impossible? She would fail “for some commonplace reason”, as Lewis (1976, 150) puts it. Her gun might jam, a noise might distract her, she might slip on a banana peel, etc. Nothing more than such ordinary occurrences is required to stop the time traveller killing Grandfather. Hence backwards time travel does not entail the occurrence of impossible events—and so the above objection is defused.
Since this is philosophy, there's more to it of course, discussed here: https://plato.stanford.edu/entries/time-travel/ , eg "Another response is that of Vihvelin (1996), who argues that there is no contradiction here because ‘Tim can kill Grandfather’ is simply false (i.e. contra Lewis, there is no legitimate sense in which it is true)."
This can be simply stated as: "You can't go back in time to kill your Grandfather, because you didn't. If you had, you would have. But you didn't, so you won't and didn't." Or another way to put it is that any changes to the past have happened already. They aren't changes to the past, they've always been the past. If you go back in time and step on a butterfly, you already stepped on that butterfly.

Another theory is that you can travel into the past and change the past and this creates a whole new timeline. This happens all the time, but no one notices because when the past is changed it is the new present. So people go back to stop Hartler, then they go back to stop Schneider, then they go back to stop Xrrph, then they go back to stop #*!)(<. Then eventually somebody goes back in time and makes a change that coincidentally results in the time machine never being invented. This is the timeline we live in. Time travel is possible, but it's never going to be invented, because if it was someone would eventually change the timeline enough that time travel would never be invented, and that's the only stable timeline.
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Old 08-29-2018, 04:25 PM
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This can be simply stated as: "You can't go back in time to kill your Grandfather, because you didn't. If you had, you would have. But you didn't, so you won't and didn't." Or another way to put it is that any changes to the past have happened already. They aren't changes to the past, they've always been the past. If you go back in time and step on a butterfly, you already stepped on that butterfly.

Another theory is that you can travel into the past and change the past and this creates a whole new timeline. This happens all the time, but no one notices because when the past is changed it is the new present. So people go back to stop Hartler, then they go back to stop Schneider, then they go back to stop Xrrph, then they go back to stop #*!)(<. Then eventually somebody goes back in time and makes a change that coincidentally results in the time machine never being invented. This is the timeline we live in. Time travel is possible, but it's never going to be invented, because if it was someone would eventually change the timeline enough that time travel would never be invented, and that's the only stable timeline.
And this would explain the Fermi paradox. The only stable timeline is one where no civilizaton lasts long enough to figure out time travel. This does not bode well for us.
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Old 08-29-2018, 04:41 PM
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Back when the LHC was firing up, it had a number of setbacks and failures due to a variety of perfectly mundane but nonetheless odd and quirky failures. Some physicists suggested, mostly-facetiously, that a full-power LHC would destroy the Universe somehow or another, and so we were only seeing the a priori improbable timelines where it didn't reach full power.
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Old 08-29-2018, 05:04 PM
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What's the status of time travel?

Delayed.
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Old 08-30-2018, 11:44 AM
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Absolutely no progress has been made. Theoretical physicists think about time running backwards in their equations, perhaps to amuse themselves, wow the public, or they really think it might (or some combination). I would say: we don't really know what time is. I have never read any physics in which it is more than just a parameter in an equation with no definition. I am convinced it never and can never run backwards. Not just for people, but also for any of the physicist's postulated things that actually exist. I think I read that virtual particles are postulated by some to travel bacwards in time. I don't believe virtual particles even exist in any sense, and they just help the equations, where the more accurate description would involve waves in an "ether".
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Old 08-30-2018, 01:48 PM
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Well, since the OP was written, I've traveled into The Future! And it's glorious! It's everything we ever dreamed about.




Except for flying cars. Where are the flying cars?
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Old 08-30-2018, 01:58 PM
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I read an interesting book called, "The Science of Star Trek", and an amazing number of things they do are actually possible if - and it's a gigantic IF - you can generate enough power which, at this particular time, is way beyond anything we could possibly muster. However, the one thing that is impossible is the Transporter because of the Heisenberg Uncertainty Principle in Quantum Physics.

Time travel continues to remain in the realm of Science Fiction only.
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Old 08-30-2018, 02:04 PM
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Well, if there's an aether, where is this aether? What is the nature of the aether? What's it like? What is it made of?

The problem with the aether theory is that all the experiments made to investigate the aether instead showed that no such thing could exist. So there's that.
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Old 08-30-2018, 02:08 PM
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I read an interesting book called, "The Science of Star Trek", and an amazing number of things they do are actually possible if - and it's a gigantic IF - you can generate enough power which, at this particular time, is way beyond anything we could possibly muster. However, the one thing that is impossible is the Transporter because of the Heisenberg Uncertainty Principle in Quantum Physics.

Time travel continues to remain in the realm of Science Fiction only.
David Brin invented a much more plausible version of the transporter in one of his short stories. It involves a chemical bath that separates every cell in the body into a slurry, the cellular slurry is then pumped down to the planet surface by long tubes, and reassembled at the new location.
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Old 08-30-2018, 04:23 PM
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The Uncertainty Principle is only a problem for a transporter if, for some reason, you restrict yourself to classical information channels. And even then, it might or might not be an insurmountable problem, depending on how much fidelity you need (which I don't think is a settled question).
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Old 08-30-2018, 05:15 PM
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I find the argument "If time travel is possible, where are the time travellers?" not quite persuasive. It could be that time travel is expensive, uses considerable resources, and requires considerable time to accomplish, all of which would prevent casual time travel tourism.

Time to accomplish you say? It seems that most SF time travel assumes that the traveller remains in the same relative location on Earth. But all celetial bodies, including Earth, are in constant motion. If someone goes back 100 years, he/she would end up somewhere in outer space. So now he/she would have to take the time to travel to wherever Earth was at that point. And reverse that trip when he/she wanted to return. That simple logistic requirement could be enough to prevent any time travel from happening, even if its possible.
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Old 08-30-2018, 05:40 PM
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I find the argument "If time travel is possible, where are the time travellers?" not quite persuasive. It could be that time travel is expensive, uses considerable resources, and requires considerable time to accomplish, all of which would prevent casual time travel tourism.

Time to accomplish you say? It seems that most SF time travel assumes that the traveller remains in the same relative location on Earth. But all celetial bodies, including Earth, are in constant motion. If someone goes back 100 years, he/she would end up somewhere in outer space. So now he/she would have to take the time to travel to wherever Earth was at that point. And reverse that trip when he/she wanted to return. That simple logistic requirement could be enough to prevent any time travel from happening, even if its possible.
But where in space would you end up? If you say "where the Earth was located at that time" how would that spot be determined? Since there are no privileged reference frames isn't any location relative? In the case of time travel, relative to what?
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Old 08-30-2018, 05:46 PM
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But where in space would you end up? If you say "where the Earth was located at that time" how would that spot be determined? Since there are no privileged reference frames isn't any location relative? In the case of time travel, relative to what?
All very good questions! And they better be answered before we spend the expense and resources to send that spaceship back through time!
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