A Time experiment

[quarky]

Back in psychedelic times, I pondered time travel.
It soon became obvious that if there was any possibility of it happening, it was already happening...and i might as well wonder how one would go about verifying this.

Suppose we are the distant past; part of a vision imported from a futurist, doing time travel.
We're like those extras in the sci-fi films, acting out the past, to the best of our knowledge, to accommodate the perceptual expectations of the time traveler from the future. We have no choice. We got entangled. The only escape is to become a time traveler.
Which we did. But now we forgot. And we lost our sequential sense, and don't know what time is home anymore.

 

[JJM 777]

Umm. You do realize, I hope, that one of the laws of nature which you refer to limits the transfer of information to the speed of light?

So, how exactly are we bound to the Andromeda Galaxy in a single and simultaneous moment of existence?

As I said, simultaneity is locally obviously quite absolute. How absolute it is between remote objects, this is debatable -- but not very unessential for time travel.

How we are bound to the Andromeda Galaxy, for example by the law of conservation of energy in universe. What energy and matter we occupy, is away from matter and energy available to the rest of universe. No conception of time can break the law of conservation of energy, neither can any conception of time put two different atoms in the same location in space simultaneously. Local absolute simultaneity of all possible time frames prevents it.

Some people here argue that we can travel in time compared to another object in universe. This is debatable, but any interaction is apparently simultaneous (= subject to the laws of nature) when the objects no longer are remote from each other. Each location in universe appears to have one moment of time only, no past or future, only the present moment.

Some others in this thread theorize that time is a dimension as simple as length or width, and the same object can move back or forth in its own history. This is a heaven and hell claim, this is the Hollywood fairy tale, a Back to the Future movie.

what is the difference between a postview of the past of 10,000 years ago, and a simultaneous now view of the Andromeda Galaxy which was emitted 2.5 million years ago?

No essential difference, they are simply light rays which once were emitted from objects to random directions.

 

[Dan O.]

This may simply be a misunderstanding of this experiment: http://en.wikipedia.org/wiki/Delayed_choice_experiment

Tricky things those photons. In their reference frame, what is time or space?

I did some searching and I believe the work of Alain Aspect in 1982 is at least related.

 

[Roboramma]

Some others in this thread theorize that time is a dimension as simple as length or width,

Time is a dimension. To deny that fact is to deny modern physics. Mind, it's also different from other dimensions in ways that are described by the mathematical framework underlying modern physics. Those differences explain why:

and the same object can move back or forth in its own history.

Is not true, at the least not in the way that you are suggesting.

 

[Rasmus]

http://xkcd.com/716/

 

[Dan O.]

http://xkcd.com/716/

Perhaps that whould explain what happened to John Cramer^WP and his Retrocausality Experiment which is remarkably similar to what I had envisioned over 2 decades ago. He was very clever though to use fiber optic cable instead of a precisely aligned optical path on the order of LIGO.

 

[JJM 777]

Time is a dimension. (...) different from other dimensions in ways

In a virtual setting, such as in a 3D video clip, the playing time indicator of the movie clip is fully a "fourth dimension". You can move back and forth along the dimension as freely as you can move along any of the physical 3 dimensions.

In real life, time is one-directional and forward moving -- there is no going back in time. As relativity theory puts it, the highest possible speed (the speed of light) brings time close to a halt at best, but cannot turn it rolling backwards.

Neither can you go forward in time, by any other means than waiting that the desired moment will arrive. (There may be ways how you can speed up the waiting process, from your own perceptional viewpoint.)

Time is not a dimension in any such way that you would have more than one option where to locate yourself along the dimension. Your location on the dimension is a given and unavoidable fact.

 

[Roboramma]

In real life, time is one-directional and forward moving -- there is no going back in time. As relativity theory puts it, the highest possible speed (the speed of light) brings time close to a halt at best, but cannot turn it rolling backwards.

That's right, we are moving through spacetime and can only alter our trajectory so much. What of it?

Neither can you go forward in time, by any other means than waiting that the desired moment will arrive. (There may be ways how you can speed up the waiting process, from your own perceptional viewpoint.)

Which is exactly what going forward is. How does that differ from going forward north for instance? In that case you also have to "wait for the desired place to arrive".

Better to look at yourself as moving from event to event in spacetime.

Time is not a dimension in any such way that you would have more than one option where to locate yourself along the dimension. Your location on the dimension is a given and unavoidable fact.

That's just false: I can see to it that I am present at event A at location X₁Y₁Z₁T₁, or event B at location X₂Y₁Z₁T₁, or event C at location X₃Y₃Z₃T₃, or any other event at a different spacetime location that is within my future lightcone. (well, maybe I am more limited than that, but not by the laws of physics. Certainly my "cone" of available spacetime locations is still cone-shaped, at any rate*).

*4-dimensional cone, of course

 

[JJM 777]

That's just false: I can see to it that I am present at event A (...) Certainly my "cone" of available spacetime locations is still cone-shaped

Yep, but your "cone" is not "time", it is "time-space". Omit the space factor and consider (a moment of) "time" only -- is each moment a thin layer across the cone then. You cannot avoid reaching those moments of time. You can choose "where" you are, but "when" comes automatically and irresistibly upon you.

 

[WhatRoughBeast]

Yep, but your "cone" is not "time", it is "time-space". Omit the space factor and consider (a moment of) "time" only -- is each moment a thin layer across the cone then. You cannot avoid reaching those moments of time. You can choose "where" you are, but "when" comes automatically and irresistibly upon you.

Now you're just being silly. Of course you can choose "when". By moving away from the event at llight speed you can put off encountering the cone indefinitely (according to a "stationary" frame of reference).

 

[BTMO]

I tried it. It works. So I did it again and again and again. Eventually, I got to the point where it became boring.

Even fleets of hookers and nose candy lose their thrill eventually. So I took up fishing instead.

Turns out I like the uncertainty.

The machine is still in the garage if anyone else wants a turn?

 

[JJM 777]

you can choose "when". By moving away from the event at light speed

But wherever you move, at whatever speed, there you will perceive time in a similar way as anywhere else, and each next moment will keep coming upon you at the same perceived rate as always everywhere, you cannot avoid that. Perhaps not compared to "the event" from which you move away, you can avoid some local events, by going away from them.

 

[Roboramma]

But wherever you move, at whatever speed, there you will perceive time in a similar way as anywhere else, and each next moment will keep coming upon you at the same perceived rate as always everywhere, you cannot avoid that.

What does it mean "each next moment will keep coming upon you at the same perceived rate as always everywhere"?

It is possible for me to experience the elapse of more time than you between two events, both of which we are present at:

We meet at event A and synchronize our watches.
We separate as some relativistic velocity.
I alter my trajectory or speed such that we will come to meet again at event B
We meet at event B and check our watches: We find that I measure less elapsed time that you.

Alternatively:
We meet at event A deep in a gravity well and snychronize our watches.
I climb out of the gravity well at non-relativistic velocity and spend some time there.
I return at a non-relativistic velocity and my path intersects yours at event B, again deep in the gravity well.
We check our watches and find that I measure more elapsed time than you.

I don't know if this contradicts your statement, because it's not really clear what you are saying, but I suspect it does.

 

[TubbaBlubba]

As I said before, this was in a November issue of Scientific American in the 80’s. I don't have access to their archives so this will probably entail a trip to the library to look up.

I'm amazed that you remember that it was a November issue, but not with year to any accuracy closer than a decade.

 

[Manopolus]

Okay!
Here’s a thought experiment I dreamed up.

Let’s say that you have invented the first time machine (!) -
and you decide to go back in time to win last week’s lottery! - having first memorised the winning numbers.

Will the winning numbers be the same??
Will the slight effect of you going into the past, alter the past to such an extent that the numbers will be different and the journey a waste of time??

This is assuming that a random output will be exactly the same in the reality that you go back to. What if it's just as random the second time around as it was in the first version?

I think it's a mistake to think that travelling back in time, you will experience random/chaotic events happening the exact same way as they did the first time around. I'd bet the opposite, actually. I suspect that borderline decisions that folks made in that past time might be made differently, as well... leading to different sports scores, possibly a different political direction... etc.

All this without the time machine owner doing a single thing. The concepts of randomness, indeterminism, free will, etc would still exist in this past reality, thus not forcing anything to occur in the exact same way.

If we can travel to the past, then the past must be mutable... not just by direct manipulation, but in its own natural course. Time travel would disprove universal determinism, IMO. This would also automatically make it impossible for our time traveler to go "home" by travelling to the future, as he has landed at a point where the future is not yet determined.

Also note that from a relativity standpoint, the question of whether you moved yourself to a different location upon the timeline, or reversed the universe itself to a prior point would be an impossible question to answer. One point of reference is as good as another, in this circumstance. This also erases a paradox. If you hit the rewind button, and it's the universe that changed (rewound), not the time traveler... there is no paradox when the future does not produce the time traveler the next time around.

Another way to look at it: It's just a matter of cramming two distinct time-period entities together, with one of them quite small (the time traveler/machine being much smaller than the universe). See? No paradox. But again, there's no going "Back to the Future," or at least not to an identical future. That future effectively ceases to exist for you the moment you "travel" to the past.

Since this scenario creates no paradoxes, I would say that it is the most likely if time travel is possible. This would make time travel necessarily linked to a form of non-determinism.

Alternate realities, anyone?

 

[Dan O.]

I'm amazed that you remember that it was a November issue, but not with year to any accuracy closer than a decade.

It's the way memory works. By reconstructing an event the memory of it becomes stronger. I had previously hunted down this issue by recalling that it was the night of Halloween while I was visiting friends when I read through the new issue that had just arrived. So not only do I have the original memory to draw from, I have the reconstruction. Unfortunately, remembering the actual year of the issue wasn't necessary, I just flipped through the back issues and found it.

The implication of that experiment was immediately obvious to me. Either there was a loophole that allows faster than light transfer of information or the old universe had another trick to keep everything sane. The next experiment was undoubtably already under way so there wasn't much to do but wait for it to happen.

But we had fun that night designing the first time machine using existing technologies, examining the limitations of the machine and its implications.

I've been waiting a long time to see the results from the next phase of the experiment.

 

[JJM 777]

What does it mean "each next moment will keep coming upon you at the same perceived rate as always everywhere"?

Your clock will tick at the same perceived rate. The next second will come in a second for you. You cannot choose to avoid the next second that is coming at your clock, nor can you move back to the previous second, nor can you skip over a second in your clock.

It is possible for me to experience the elapse of more time than you between two events

This does not contradict my statement that time is one-directional, and comes at you without you having any other choice about it than possibly delaying or hastening the rate a bit -- comparing to time perceived at some other location, but not comparing to time perceived at your own location (where "your own location" is always your current location). In that sense you have zero choice to have any effect on your local time, your wristwatch will tick the way it does, no matter where you go with it and how fast.

 

[Roboramma]

Oh, okay, yeah, that's correct. Similarly if I'm on a train and I measure how far I've travelled, it doesn't matter if I use a piece of string, counting the passing mile markers, a radar gun and a watch, or some other method, they'll all measure the same value.

 

[JJM 777]

Oh, okay, yeah, that's correct. Similarly if I'm on a train and I measure how far I've travelled, it doesn't matter if I use a piece of string, counting the passing mile markers, a radar gun and a watch, or some other method, they'll all measure the same value.

The discussion has reached some of its objectives, if we finally agree about these conclusions:

You cannot tweak your local time, your "wristwatch time", in any possible way. If you travel in time or space, and your wristwatch travels with you, your travelling does not affect your perceived and biological local time experience.

Hence: your biological clock, as well as your personal life clock, are forward moving timelines, where time moves at a constant perceived speed (and physically / atomically measured speed, locally). Call it a dimension if you want, but you cannot choose where to locate yourself on your local timeline (biological or personal life): there is no going back in your local time, neither is there slowing down your local time, neither is there going forward to the future in your local time by any other means than waiting for the perceived (and biologically and physically real, locally for you) amount of time difference.

 

[Roboramma]

The discussion has reached some of its objectives, if we finally agree about these conclusions:

You cannot tweak your local time, your "wristwatch time", in any possible way. If you travel in time or space, and your wristwatch travels with you, your travelling does not affect your perceived and biological local time experience.

All you are saying here is that all clocks measure the same time. Yep, we agree.

Hence: your biological clock, as well as your personal life clock, are forward moving timelines, where time moves at a constant perceived speed (and physically / atomically measured speed, locally).

Again, what you're saying is basically that if I have two wrist watches that I carry with me at all times (and keep arbitrarily close together), I can't get them to disagree with each other. Sure. But they can disagree with watches that are in other places.

Similarly, if I have two rulers and keep them stationary relative to each other, and aligned in the same direction, they will always measure the same distance, regardless of how I move. But, if I take one of those rulers and move it relative to the other, it will measure a different distance (due to length contraction.

I agree, but don't really understand why you think it's interesting to point this out.

Call it a dimension if you want, but you cannot choose where to locate yourself on your local timeline (biological or personal life): there is no going back in your local time, neither is there slowing down your local time, neither is there going forward to the future in your local time by any other means than waiting for the perceived (and biologically and physically real, locally for you) amount of time difference.

Now you are just playing with words: what does "slowing down your local time" mean if not slowing it down relative to something else? That the percieved flow of time doesn't change is no more interesting than the fact that I can't change my state of motion relative to myself. The fact that I can't be anything other than stationary relative to myself doesn't mean that I can't move relative to other things, and neither does the fact that I have only one proper time mean that I can't slow the rate at which my proper time flows relative to other things.

What is true is that if I choose a particular reference frame (for instance, one in which I'm stationary now) I can do something such that my proper time is different than the proper time measured in that reference frame. Similarly, if I choose a particular reference frame (such as one in which I am stationary now) I can do something such that I am moving with respect to that frame of reference, but I never move with respect to myself.

Moreover, I can note that between event A and event B I less more time on my watch than I would have had I remained at rest.