Time Travel

[steve_bank]

What is time travel? Stra Trek used it a number of times.

In the original movie version of HG Wells' The Time Machine you set a date and you go back or forward in the same place. Go forward in time, move the machine, go back in time and you are in a different spot.

There are conceptual problems. Wren you are standing on the Earth it is rotating, it is circling the sun, and circling the galaxy. Space-time.

If you are standing on the Earth and travel back in time you end up in space somewhere. If you travel forward you have to know in some coordinate system where you will be in the future.

The universe does not know time, it is in constant change. To me 'time travel' makes no sense. Matter changes positions, there is no past or future to travel to. For the scifi versions of time travel every moment of the past would have to persist forever. To travel forward in time would imply predetermination.

 

[Koyaanisqatsi]

Agreed. The only way one could “travel” through time would be if you could mask your body’s entire quantum “signature” (i.e., shield every particle that comprises your body from interacting with any particles that are not part of your body), somehow exit our time-space continuum (presumably by entereing into a higher dimension or alternate universe) and then be able to enter back into our TSC at some other point then when you left it.

It would require that the higher dimension or alternate universe somehow granted you the ability to see the entirety of our TSC—from the Big Bang to the Big Crunch (or whatever will befall it)—at the particle level and have mapped every single particle’s entire “journey” through the TSC, such that you would know where in spacetime to reinsert your shielded body.

But because you would necessarily have to remain shielded (lest the particles in your body interract with the particles in the “entry” point of the TSC and thus butterfly effect the lot), there would be no way for you to see, hear or really experience anything at all once rendered into the time stream, unless the technology of the shield somehow allowed every TSC particle to simply pass right through you as if you were not there (so, tachyon based, I guess?).

But even if that were possible, you’d still have the problem of not being able to use any of your senses (they are all particle-interractive based after all), nor could you have technology that would act as sensors for you, since that necessarily entail particle interraction as well.

So the best you could do is take the particle information from the higher dimension map of our TSC and load that into a super super computer and make a VR creation of our TSC and then just wander around in it all you like, but it would be you walking around in a hologram, basically.

Iow, there is no way to travel through time, as you noted, because time isn’t set; it’s a chaotic pachinko game of the now. There is no such thing as either “past” or “future.” Those are just virtual constructs we create as a side effect of being able to form maps and analogue selves.

Actual “time” is more like a burning fuse, only just the burning part. There is nothing feeding it and nothing left after it burns each nano-second away. The now—and thus the universe—is just a constant bombardment of particles. Only our brains animate it (i.e., create memories, which in turn allow us to derive the notion of a future, which is really just possible soon-to-become memories).

If you can picture just the burning part of a fuse—with all the sputter and the dance, only without any unburnt part feeding it—that’s what you’d be trying to “travel” so the whole idea is moot before one could even contemplate it. How can you travel something that has no road?

 

[bilby]

Agreed. The only way one could “travel” through time would be if you could mask your body’s entire quantum “signature” (i.e., shield every particle that comprises your body from interacting with any particles that are not part of your body), somehow exit our time-space continuum (presumably by entereing into a higher dimension or alternate universe) and then be able to enter back into our TSC at some other point then when you left it.

It would require that the higher dimension or alternate universe somehow granted you the ability to see the entirety of our TSC—from the Big Bang to the Big Crunch (or whatever will befall it)—at the particle level and have mapped every single particle’s entire “journey” through the TSC, such that you would know where in spacetime to reinsert your shielded body.

But because you would necessarily have to remain shielded (lest the particles in your body interract with the particles in the “entry” point of the TSC and thus butterfly effect the lot), there would be no way for you to see, hear or really experience anything at all once rendered into the time stream, unless the technology of the shield somehow allowed every TSC particle to simply pass right through you as if you were not there (so, tachyon based, I guess?).

But even if that were possible, you’d still have the problem of not being able to use any of your senses (they are all particle-interractive based after all), nor could you have technology that would act as sensors for you, since that necessarily entail particle interraction as well.

So the best you could do is take the particle information from the higher dimension map of our TSC and load that into a super super computer and make a VR creation of our TSC and then just wander around in it all you like, but it would be you walking around in a hologram, basically.

Iow, there is no way to travel through time, as you noted, because time isn’t set; it’s a chaotic pachinko game of the now. There is no such thing as either “past” or “future.” Those are just virtual constructs we create as a side effect of being able to form maps and analogue selves.

Actual “time” is more like a burning fuse, only just the burning part. There is nothing feeding it and nothing left after it burns each nano-second away. The now—and thus the universe—is just a constant bombardment of particles. Only our brains animate it (i.e., create memories, which in turn allow us to derive the notion of a future, which is really just possible soon-to-become memories).

If you can picture just the burning part of a fuse—with all the sputter and the dance, only without any unburnt part feeding it—that’s what you’d be trying to “travel” so the whole idea is moot before one could even contemplate it. How can you travel something that has no road?

That cannot be the case; Relativity tells us that observers in different reference frames disagree on both the timing and sequence of events. So there cannot be a universal "present"; And therefore the past, or the future, or more likely both, must exist.

 

[bilby]

Time travel is easy. We al go forward in time constantly; To travel into the distant future one merely needs to arrange to sleep in conditions where the increase in entropy in your body is significantly retarded - sleep, anaesthesia, and (still science fiction for humans) suspended animation - all of which are, to the subject, indestinguishable from rapid (instantaneous) travel to a future time.

Travel backwards in time, or at a lower forward rate than others in your reference frame - including the special case of not traveling in time at all - now that's hard.

 

[James Brown]

Time travel is easy in the same way that space travel is easy. Every year we make a huge nearly-circular tour around a moving star, mostly in a shirt-sleeves environment.

 

[Koyaanisqatsi]

That cannot be the case; Relativity tells us that observers in different reference frames disagree on both the timing and sequence of events. So there cannot be a universal "present"; And therefore the past, or the future, or more likely both, must exist.

Well, I won’t pretend to be any kind of astrophysicist, but for shits and giggles, I would argue that’s precisely why it is the case. From your perspective the “now” would appear different from my perspective. But if we were both experiencing the same “now”—or, rather, if the “now” were some fixed point—we would indeed be experiencing the same thing, but because there are no such things as fixed points outside our maps of the external, it always appears differently.

Iow, we are the ones that fix points and perspectives, not the universe and that is why they can differ. Again, think of a burning fuse (and let’s further state it’s a five foot long fuse for the sake of the analogy). You remember it being lit; you remember seeing the flame travel along the length of the fuse; you could even remember each foot of the fuse as it existed prior to the flame consuming it.

And if I happened upon the fuse after it was already lit and had “consumed” a foot of fuse, then from my perspective I would have seen a four foot long already lit fuse, so my account of it would differ from your account.

But from the flames’ “perspective” it’s just burning in the now. There is no fuse behind it. It—the flame—did not travel along any pathway, eventhough that’s how it appeared to us (being fixed observation points relative to it). There is no past; no previous three foot point or four foot point or five foot point, etc.

Nor is there a future, in spite of the fact that there is at time T still more fuse to burn. All the flame is doing is burning, It can’t “see” anything—or experience anything—beyond that burn. I reallize this may be where the analogy breaks down, but it’s not the analogy’s fault; it’s our inability to properly conceptualize what we’re talking about precisely because we make maps; we take pictures and then animate them. But it is the animation that is the illusion.

We are—effectively—within a giant flame in the process of exploding, it’s just so tremendously large that from our perspective it takes billions of years, but just like a flame in the process of exploding, there is nothing left behind for us to travel too.

Just look up at the stars any given night. None of them exist anymore. Not in the state we currently see them. We are effectively looking at a photo of a past explosion, but even if we had the technology to instantly transport us to the spot we are looking at, when we popped out at the other end there wouldn’t be anything there (or at least not the object we had been looking at).

That “state” no longer exists. Hasn’t existed for billions of years, it just took that long for the photons to reach our eyes, so unless there is a way to instantly freeze all matter in the universe and then reverse engineer every single particle’s changes in state due to their interactions with all the other particles such that you could recreate Universe of Particles at State X—and that in turn be so finely calculated/tuned to correspond to a meaningful event like JFK being shot or the like—it’s not possible.

Even then it isn’t you traveling “through” time; it’s you recreating a previous energy state of the entire universe and then having to hit “start” to have it all become active again for you—in your quantum shield suit—to watch (not interract with, just watch somehow without needing the photons to hit your retinae) it unfold in real time, but how could you hit the “start” button if you also did not have all of the previous energy states recreated in order for the proper trajectories/momentum to all coincide/collide in the exact same way to produce the next series of state changes?

Iow, it would require a meta recording—a DVD—of the entire universe’s energy state conditions and then at best all you could do is recreate a simulation of that universe, but not the actual one. Even if you were some sort of god that could manipulate matter at will, we’re not talking about mere manipulation; we’re talking about needing to reset an entire universe of particle states to a specific condition, stepping into that universe (without causing any butterfly effect in so doing) and then “starting” the universe up again without any impact on any particle trajectories.

Ioow, you’d have to be an Omni-capable ghost observer whose observation does not collapse any waves, which would certainly seem to be a fundamental contradiction.

 

[steve_bank]

In Cartesian rectangular coordinates there are 4 dimensions. (x,y.z.t). X, y, and z are in meters and t is in seconds. The word dimension mostly from scifi has subjective meaning.

We traverse distance in meters and the rate of change in distance is measured in seconds. It is as simple as that. You can say we move through space, but we do not move through time. Time is a measure of velocity through space. We move through space not through meters, we move through space measured by meters.

If time is somehow a reality unto itself, it needs another word and definition.

 

[bilby]

Relativity tells us that the rate at which an object moves through time is dependent on its velocity; Objects moving at c (eg photons) do not move through time at all as observed in their reference frame. A photon arriving at the Hubble telescope from a galaxy 5 billion light years away has, in its reference frame, traveled zero distance in zero time. From the photon's perspective, Lorenz contraction reduces the distance between the distant galaxy and the Earth to zero.

This counterintuitive fact can be demonstrated experimentally; The half-life of unstable particles moving rapidly appears (to a stationary observer) to be longer than when those particles are at rest relative to the observer - which is readily explained if the half life is unchanged form the perspective of the particles themselves, but that the rate at which they experience time is lower.

 

[Juma]

That cannot be the case; Relativity tells us that observers in different reference frames disagree on both the timing and sequence of events. So there cannot be a universal "present"; And therefore the past, or the future, or more likely both, must exist.

Well, I won’t pretend to be any kind of astrophysicist, but for shits and giggles, I would argue that’s precisely why it is the case. From your perspective the “now” would appear different from my perspective. But if we were both experiencing the same “now”—or, rather, if the “now” were some fixed point—we would indeed be experiencing the same thing, but because there are no such things as fixed points outside our maps of the external, it always appears differently.

Iow, we are the ones that fix points and perspectives, not the universe and that is why they can differ. Again, think of a burning fuse (and let’s further state it’s a five foot long fuse for the sake of the analogy). You remember it being lit; you remember seeing the flame travel along the length of the fuse; you could even remember each foot of the fuse as it existed prior to the flame consuming it.

And if I happened upon the fuse after it was already lit and had “consumed” a foot of fuse, then from my perspective I would have seen a four foot long already lit fuse, so my account of it would differ from your account.

But from the flames’ “perspective” it’s just burning in the now. There is no fuse behind it. It—the flame—did not travel along any pathway, eventhough that’s how it appeared to us (being fixed observation points relative to it). There is no past; no previous three foot point or four foot point or five foot point, etc.

Nor is there a future, in spite of the fact that there is at time T still more fuse to burn. All the flame is doing is burning, It can’t “see” anything—or experience anything—beyond that burn. I reallize this may be where the analogy breaks down, but it’s not the analogy’s fault; it’s our inability to properly conceptualize what we’re talking about precisely because we make maps; we take pictures and then animate them. But it is the animation that is the illusion.

We are—effectively—within a giant flame in the process of exploding, it’s just so tremendously large that from our perspective it takes billions of years, but just like a flame in the process of exploding, there is nothing left behind for us to travel too.

Just look up at the stars any given night. None of them exist anymore. Not in the state we currently see them. We are effectively looking at a photo of a past explosion, but even if we had the technology to instantly transport us to the spot we are looking at, when we popped out at the other end there wouldn’t be anything there (or at least not the object we had been looking at).

That “state” no longer exists. Hasn’t existed for billions of years, it just took that long for the photons to reach our eyes, so unless there is a way to instantly freeze all matter in the universe and then reverse engineer every single particle’s changes in state due to their interactions with all the other particles such that you could recreate Universe of Particles at State X—and that in turn be so finely calculated/tuned to correspond to a meaningful event like JFK being shot or the like—it’s not possible.

Even then it isn’t you traveling “through” time; it’s you recreating a previous energy state of the entire universe and then having to hit “start” to have it all become active again for you—in your quantum shield suit—to watch (not interract with, just watch somehow without needing the photons to hit your retinae) it unfold in real time, but how could you hit the “start” button if you also did not have all of the previous energy states recreated in order for the proper trajectories/momentum to all coincide/collide in the exact same way to produce the next series of state changes?

Iow, it would require a meta recording—a DVD—of the entire universe’s energy state conditions and then at best all you could do is recreate a simulation of that universe, but not the actual one. Even if you were some sort of god that could manipulate matter at will, we’re not talking about mere manipulation; we’re talking about needing to reset an entire universe of particle states to a specific condition, stepping into that universe (without causing any butterfly effect in so doing) and then “starting” the universe up again without any impact on any particle trajectories.

Ioow, you’d have to be an Omni-capable ghost observer whose observation does not collapse any waves, which would certainly seem to be a fundamental contradiction.

Then how do you explain the pole/barn example: a very fast runner, while holding a pole (like a pole vaulter: in the direction he runs) runs through a barn through two open doors. In a referens system at rest with the barn the pole is so long that it extends through both doors: it doesnt fit in the barn. But if the runner runs fast enough the relativistic length contraction will make the pole shorter relative the barn (for an observer that is at rest relative the barn) and thus may fit within the barn.
That means that the events: ”pole end A leaves barn” and ”pole end B enters barn” will occur in different order for the runner and the farmer resting in the hay.

This thus events behaves like points on a line when viewed from different angles.

 

[Koyaanisqatsi]

Then how do you explain the pole/barn example...This thus events behaves like points on a line when viewed from different angles.

Same issue. Human perpective. Regardless, there is no recording of the energy states. Unless all “events” (i.e., energy states) co-exist simultaneously and we—humans—are merely the animators creating the illusion of continuity and we are all actually stationary as the “slide show” from one set of “pictures” of the universe’s particle energy state to the next clicks by or something.

Which, in an infinite space (or whatever the hell space is) could be possible, I guess—that the universe is actually static and every single energy state of every single particle just exists at Point X like some gigantic diorama or something—but then there is the same problem of stepping out of that set-piece and then re-inserting one’s self back in without altering anything in order to be more than just a blind ghost, if you will.

 

[Koyaanisqatsi]

Relativity tells us that the rate at which an object moves through time is dependent on its velocity; Objects moving at c (eg photons) do not move through time at all as observed in their reference frame. A photon arriving at the Hubble telescope from a galaxy 5 billion light years away has, in its reference frame, traveled zero distance in zero time. From the photon's perspective, Lorenz contraction reduces the distance between the distant galaxy and the Earth to zero.

This counterintuitive fact can be demonstrated experimentally; The half-life of unstable particles moving rapidly appears (to a stationary observer) to be longer than when those particles are at rest relative to the observer - which is readily explained if the half life is unchanged form the perspective of the particles themselves, but that the rate at which they experience time is lower.

Well, the “stationary” part is the problem. As I understand Lorentz (and that’s poor at best), any object traveling at relativistic speeds is contracted in the dimension it is traveling in as seen from the stationary reference (i.e., if horizontally relative to the stationary reference, it contracts horizontally, but not vertically). The amount of contraction of the object is dependent upon the object's speed relative to the observer.

But we would not be static observers looking at the photon, we would be “travelers” on the photon, if you will. So, if we were somehow in a spaceship that traveled at the speed of light, would it take us zero distance and zero time to travel five billion light years? And even if that were true, we wouldn’t be traveling back in “time” we would simply be traveling five billion light years.

 

[Tom Sawyer]

If time travel were possible, wouldn't we see things like drunk teenagers coming back in time and pretending to be Russian agents or something and fucking with election results to stop Hillary Clinton from becoming President and have whats-his-name (that reality tv star who ran against her) win just for the shits and giggles of seeing what would happen?

 

[bilby]

Relativity tells us that the rate at which an object moves through time is dependent on its velocity; Objects moving at c (eg photons) do not move through time at all as observed in their reference frame. A photon arriving at the Hubble telescope from a galaxy 5 billion light years away has, in its reference frame, traveled zero distance in zero time. From the photon's perspective, Lorenz contraction reduces the distance between the distant galaxy and the Earth to zero.

This counterintuitive fact can be demonstrated experimentally; The half-life of unstable particles moving rapidly appears (to a stationary observer) to be longer than when those particles are at rest relative to the observer - which is readily explained if the half life is unchanged form the perspective of the particles themselves, but that the rate at which they experience time is lower.

Well, the “stationary” part is the problem. As I understand Lorentz (and that’s poor at best), any object traveling at relativistic speeds is contracted in the dimension it is traveling in as seen from the stationary reference (i.e., if horizontally relative to the stationary reference, it contracts horizontally, but not vertically). The amount of contraction of the object is dependent upon the object's speed relative to the observer.

But we would not be static observers looking at the photon, we would be “travelers” on the photon, if you will. So, if we were somehow in a spaceship that traveled at the speed of light, would it take us zero distance and zero time to travel five billion light years? And even if that were true, we wouldn’t be traveling back in “time” we would simply be traveling five billion light years.

Consider the twin paradox. By instantaneously accelerating to c, and instantaneously decelerating at the target, a photon achieves the boundary condition of that model, in which the stay at home twin ages x years, while the travelling twin ages x - x = 0 years. So yes, if you were a passenger on a spaceship at the speed of light, you would experience zero years (and therefore zero distance traveled) for any journey, no matter how long.

Your ship (including passengers) would either need to have zero rest-mass, or infinite propulsive energy, in order to make such a journey though.

And no, that would not be time travel. Just an aside to the demonstration that the past must exist, because different observers have different assessments of the sequence and timing of events. If we don't agree on what is in the past of what, then the idea that there is only the present leaves us asking 'whose present is the only one?'

 

[steve_bank]

By time travel I meant by a device of some kind, as in scifi.

The Lorentz Time Dilation is not really time travel. A ship leaves Earth accelerating to say 0.5c. Observer on Earth and on the ship see each other aging at different rates.

Time dilation was demonstrated in the 60s using clocks. The inference is that biological processes will vary in accordance with dilation, but that has not been demonstrated.

 

[Koyaanisqatsi]

By time travel I meant by a device of some kind, as in scifi.

Well, again, the biggest (or one of the biggest) problems is the quantum “signature” of both the device and the traveler within it. Just picture dropping a rock in a stream. Its presence alters the course of the stream. So, even if somehow you could go “back” in spacetime (itself a misnomer), the instant you re-entered the stream, so to speak, is the instant you change everything about the original timeline.

It’s not just a matter of you stepping on a butterfly, you have trillions of particles that make up your body (and the device) that would all suddenly be where they previously were not, so all of the photons, for example, that did not previously bounce off of you and your device would now alter their courses/states, which in turn would cause incalculable, exponential alterations for every other particle in the entire universe eventually (including your own at a distance).

 

[bilby]

Pretty much that. Another way of looking at it is that it is only possible to travel back to the past, if the past already contains you having travelled back to it. So a prerequisite for doing it is that you already did it. That's difficult to pull off, and really only a many-worlds hypothesis, in which travels back in time take you to a different timeline (from which there can be no return) could reliably resolve the problem.

Travel forwards is much easier; it's indistinguishable from suspended animation, deep sleep, or anaesthesia.

 

[Juma]

Then how do you explain the pole/barn example...This thus events behaves like points on a line when viewed from different angles.

Same issue. Human perpective. Regardless, there is no recording of the energy states. Unless all “events” (i.e., energy states) co-exist simultaneously and we—humans—are merely the animators creating the illusion of continuity and we are all actually stationary as the “slide show” from one set of “pictures” of the universe’s particle energy state to the next clicks by or something.

Which, in an infinite space (or whatever the hell space is) could be possible, I guess—that the universe is actually static and every single energy state of every single particle just exists at Point X like some gigantic diorama or something—but then there is the same problem of stepping out of that set-piece and then re-inserting one’s self back in without altering anything in order to be more than just a blind ghost, if you will.

no. its not a human perspective. its same for anything, not just concious creatures.

 

[steve_bank]

The past does not exist.

 

[Koyaanisqatsi]

Then how do you explain the pole/barn example...This thus events behaves like points on a line when viewed from different angles.

Same issue. Human perpective. Regardless, there is no recording of the energy states. Unless all “events” (i.e., energy states) co-exist simultaneously and we—humans—are merely the animators creating the illusion of continuity and we are all actually stationary as the “slide show” from one set of “pictures” of the universe’s particle energy state to the next clicks by or something.

Which, in an infinite space (or whatever the hell space is) could be possible, I guess—that the universe is actually static and every single energy state of every single particle just exists at Point X like some gigantic diorama or something—but then there is the same problem of stepping out of that set-piece and then re-inserting one’s self back in without altering anything in order to be more than just a blind ghost, if you will.

no. its not a human perspective. its same for anything, not just concious creatures.

Aside from the fact that you couldn’t possibly support such an assertion, it doesn’t matter due to all of the other reasons given. There is no such thing as a “past” event. That is a construct of human thought due to our capacity for memory and how our brains map the external world. Iow, only we “record” events and place them into a chronology, but the events themselves—the universe—does not “record” any such events, like a film and its individual frames.

But, again, even if that were the case and the universe and every single energy state/change in energy state exists as a whole—like a DVD in your hand contains every single moment of, say, the Terminator—and you could thus fast forward or reverse through the film to a particular point, then you’d still have the problem of entering into that film and yet at the same time not be any part of the film.

Once you enter a river, you change the river. So even if it ultimately turns out that every single particle energy state/change in energy state exists as a giant recording somehow—or the “true” nature of the universe is that it is really a static collection of every single particle’s energy state and “change” is really our illusion as we move amongst all of those states (including our own body’s particle’s energy states)—there is no way to interract with those energy states (and that would include mere observance) without changing every subsequent state.

Thus, even if you could “travel” to some specific section of some fully complete Universe of Every Sngle Particle’s Energy State that was as accessible to you as a DVD of a film, once you “entered” that section of the UESPES you’d instantly alter the whole thing forward of that point X. It would become UESPES + You and the exponential changes caused by just the introduction of your body’s particles’ energy states at point X forward would be way beyond anything “macro” that you would hope to accomplish (like preventing JFK’s assassination or killing Hitler or the like).

You would be the cause of uncountable trillions of “butterfly” changes in UESPES + You from Point X Forward that it would be the creation of an entirely knew universe overwriting the previous one, not merely creating an alternate timeline. Without doing anything but appearing at Point X, you would have simultaneously created and destroyed two universes, so any “good” you thought you’d accomplish by killing Hitler would be utterly dwarfed by the “bad” you accomplished in destroying uncountable trillions of creatures of all manner in the effort.

 

[untermensche]

A body is composed of matter.

A body is made up of matter that has existed for longer than the body has existed. In the past the matter that now makes up a body was scattered in many places.

If the body goes back in time either the matter existing in the past that eventually makes up the body must instantly disappear or you have the creation of matter.

Both seem absurd.

The idea that the past is sitting somewhere for somebody to return to it seems absurd too.

The whole idea of time travel seems too absurd to take it seriously. It is a comic book fantasy.