Backwards Time Travel: Breaking the Heisenberg Principle?

[Math Jeans]

I had a thought that I wanted to run by physicsforums so all of you can tell me that I'm wrong and make me feel better.

One of the main issues with the concept of time travel into the past is that we don't know whether is breaks any physical laws in the process.

Here is what I believe might be a law that backwards time travel actually breaks:

Suppose you are examining a particle at one point in time. At that point in time, you figure out that particles momentum.

Then, you hop in your time machine, and travel back in time, and measure the particle's position at the exact time the you measured its momentum.

Wouldn't that suggest that backwards time travel can break Heisenburg's Uncertainty principle?

 

[Nick89]

Who is to say that the particle behaves the same way after you traveled back in time than it did before you traveled back in time? In other words, perhaps you traveling back in time would change the 'reality' so that the particle behaves differently.

 

[Math Jeans]

Who is to say that the particle behaves the same way after you traveled back in time than it did before you traveled back in time? In other words, perhaps you traveling back in time would change the 'reality' so that the particle behaves differently.

But would it really change it?

Suppose you traveled about a day into the past before the experiment was done, and you aren't the one doing the measuring.

You time travel back into your house (from someplace far away from the lab) which is far away from the experiment.

You call your labmate who is on his way to the lab and tell him to measure position instead of momentum.

The argument in measuring a particle twice in Heisenburg's uncertainty principle is that you aren't measuring the same particle, but if you are able to time travel such that you do not effect the experiment, wouldn't you be breaking that law?

 

[Math Jeans]

My argument is that it might be possible.

 

[Nick89]

Well, either time-travel is possible and the uncertainty principle is invalid, or the uncertainty principal holds and time-travel is impossible. We probably won't know until we have tried it.

 

[Math Jeans]

Well, either time-travel is possible and the uncertainty principle is invalid, or the uncertainty principal holds and time-travel is impossible. We probably won't know until we have tried it.

And of course, which do you think is more pheasable?

 

[Nick89]

I am not extremely knowledgeable about both subjects so I'm going to leave that question for someone more experienced ;)

 

[pallidin]

With my limited understanding as well, one of the theories I heard is that traveling back in time does not permit interaction. A secret, passive observer if you will.
But who knows? I sure don't.

 

[Math Jeans]

Well, if you are just a secret, passive observer, that would make it even easier to measure the particle's position without altering the particle from where it was in the other timeline.

 

[ThomasT]

I had a thought that I wanted to run by physicsforums so all of you can tell me that I'm wrong and make me feel better.

One of the main issues with the concept of time travel into the past is that we don't know whether is breaks any physical laws in the process.

Here is what I believe might be a law that backwards time travel actually breaks:

Suppose you are examining a particle at one point in time. At that point in time, you figure out that particles momentum.

Then, you hop in your time machine, and travel back in time, and measure the particle's position at the exact time the you measured its momentum.

Wouldn't that suggest that backwards time travel can break Heisenburg's Uncertainty principle?

The uncertainty relations don't refer to single measurements. The HUP regarding measurements of position (x) and momentum (p) is: (delta x)(delta p) >= h. This says that the statistical spread around an average value for a large number of position measurements multiplied by the statistical spread around an average value for a large number of momentum measurements is greater than or equal to Planck's constant.

General relativity is a source of speculations about time travel. But those speculations are based on math and geometry that doesn't actually describe, in a qualitative sense, the real world.

Talking about physically traveling backward in time requires a general concept of what the word, time, means physically.

If we define time as motion, the changing arrangements or configurations, etc. of physical objects, and if we live in an evolving universe, then traveling backward in time is a physical impossibility, because it would require rewinding the evolution of the universe. Put another way, if there is an arrow of time, then there can be no backward time travel. Available evidence strongly suggests that there is an arrow of time.

 

[pallidin]

Something I find interesting is that it is proven beyond any doubt that we can view astronomical events which have occurred before our current time.
I do fully understand the process(and it's current limitations), and I'm not implying that it means anything more, but it is interesting.

 

[Vanadium 50]

Something I find interesting is that it is proven beyond any doubt that we can view astronomical events which have occurred before our current time.

Why is this surprising? If you hear thunder you are also observing a terrestrial event that happened before your current time. Same idea, different scales.

 

[pallidin]

It's not surprising to me at all; I understand the physics of each phenomenon.
I just find it interesting.

 

[Gnosis]

Time travel into the past is utterly impossible and deserves no serious waste of thought and energy. It is best left to science fiction books and movies where virtually anything is possible, as well as entertaining.

The passing of time is marked by the orientation of all heavenly objects relative to one another. Their orientation is merely a singular and unique position on our infinite clock. Their relative orientations are never identical from one passing moment to the next nor will they ever be repeated in any future time frame due to expansion of the universe and the complex relative motion of all objects. Each moment of orientation is unique and the recorder of an instant in time.

Examine the Earth's motion through space. A year from now the Earth will be in almost the same orbital position around our Sun however, the Earth (and Sun) will NOT be in the same orientation in space nor will it be precisely in the same orientation relative to all other heavenly objects. This is because the Sun is streaking through the great expanse of space at roughly 12 to 12.5 miles per second (43,200 MPH to 45,000 MPH) and the Earth has no choice but to follow, as it has for eons now. A year from now, the Earth and Sun will have traveled roughly 378,691,200 miles deeper into space. The motion of all heavenly objects continually marks unique orientations in time that will NEVER be repeated.

So, anyone desiring to travel 100 years back in time to Earth as it were 100 years previously would have to travel 37.8 billion miles back through space to where the Earth was actually located 100 years previously (in which case, the Earth won't be there). In order for the Earth’s night skies to appear just as they did 100 years previously, EVERY viewable heavenly object would ALSO have to be returned to its 100 year previous orientation. Needless to say, this isn’t going to happen. A feat of this nature would require a magnitude of control over the entire universe that could only be comparable to that which is thought to be God-like and limitless in ability. We humans aren’t going to be pulling off such a feat, you can be certain of that. We can’t even live peaceably amongst ourselves on our own planet. Profit margins dictate which scientific products are feasible and which ones are deemed too costly to pursue.

The continually forward progression of all heavenly objects over billions of years has demonstrated that time advances in one direction only, and that direction takes us ever deeper into the universe. The past is gone forever, so make the most of the present to make it a memorable past…

 

[Nick89]

I can't see how the motion of heavenly objects has anything to do with time travel. Sure, time travel is probably impossible, but as far as I know it has never been proven impossible.

Suppose for a minute that time travel was possible. If you could somehow manipulate time so it runs backwards and you end up a few years before, than that action would automatically move everything back in time, even the heavenly objects you are talking about, and they would be in exactly the same position.

Of course this is all fiction, I have no idea how we could control time to run backwards. I am merely pointing out that IF you can travel back in time, than everything would have to travel with you (otherwise, you haven't traveled back in time, you have gone to another reality, dimension, whatever...)

 

[scupydog]

Time travel into the past is utterly impossible and deserves no serious waste of thought and energy. It is best left to science fiction books and movies where virtually anything is possible, as well as entertaining.

Travel into the past is permitted by the laws of physics and science fiction has a knack of becoming science fact all to often nowadays which i agree is very entertaining.

 

[scupydog]

I have no idea how we could control time to run backwards. I am merely pointing out that IF you can travel back in time, than everything would have to travel with you (otherwise, you haven't traveled back in time, you have gone to another reality, dimension, whatever...)

now that's food for thought, I love this forum

 

[Gnosis]

I can't see how the motion of heavenly objects has anything to do with time travel. Sure, time travel is probably impossible, but as far as I know it has never been proven impossible.

Suppose for a minute that time travel was possible. If you could somehow manipulate time so it runs backwards and you end up a few years before, than that action would automatically move everything back in time, even the heavenly objects you are talking about, and they would be in exactly the same position.

Of course this is all fiction, I have no idea how we could control time to run backwards. I am merely pointing out that IF you can travel back in time, than everything would have to travel with you (otherwise, you haven't traveled back in time, you have gone to another reality, dimension, whatever...)

If you were able to travel 100 years back into the Earth's past, its night sky WOULD have to appear just as it did 100 years ago or you wouldn't otherwise actually be experiencing the Earth of 100 years ago! The heavens in any other orientation indicates a progression in time has occurred and the time frame has changed.

Tonight's heavens will only appear precisely as they do on this night ONLY. Any other night in the past or the future will NOT provide the exact same orientation and naturally, the further into the past (or the future), the greater are the visible differences in their orientation. The past is only the past if ALL is actually as it once was and this includes the orientation of all heavenly objects or it's simply NOT the actual past.

 

[Nick89]

If you were able to travel 100 years back into the Earth's past, its night sky WOULD have to appear just as it did 100 years ago or you wouldn't otherwise actually be experiencing the Earth of 100 years ago! The heavens in any other orientation indicates a progression in time has occurred and the time frame has changed.

Tonight's heavens will only appear precisely as they do on this night ONLY. Any other night in the past or the future will NOT provide the exact same orientation and naturally, the further into the past (or the future), the greater are the visible differences in their orientation. The past is only the past if ALL is actually as it once was and this includes the orientation of all heavenly objects or it's simply NOT the actual past.

Of course. But that doesn't mean that it is impossible for everything (including the heavenly objects) to go back to the exact same 'state' as they were before. Note how I use the words "go back to" instead of "go to". Time traveling to the past indicates that you are changing TIME, not the 'states' of every single object in the universe.

You seem to think that, if it was possible that I could hit a button here which would make everything (including heavenly objects) become the same state as it was 5 seconds ago, that I traveled 5 seconds back into time? Of course not! I have merely changed every single object to reflect how they were 5 seconds ago, that does not mean I have changed time...

If you are actually changing TIME, than everything would AUTOMATICALLY follow and go back to the same state. If that is not true, than you are not changing time.

 

[Gnosis]

Of course. But that doesn't mean that it is impossible for everything (including the heavenly objects) to go back to the exact same 'state' as they were before. Note how I use the words "go back to" instead of "go to". Time traveling to the past indicates that you are changing TIME, not the 'states' of every single object in the universe.

You seem to think that, if it was possible that I could hit a button here which would make everything (including heavenly objects) become the same state as it was 5 seconds ago, that I traveled 5 seconds back into time? Of course not! I have merely changed every single object to reflect how they were 5 seconds ago, that does not mean I have changed time...

If you are actually changing TIME, than everything would AUTOMATICALLY follow and go back to the same state. If that is not true, than you are not changing time.

You're clearly not paying attention and you need to actually read what I've stated from the beginning. I stated that time travel into the past IS IMPOSSIBLE! You cannot travel into the past. You can travel whatever distance, but that isn't traveling into the past. Time travel into the past is impossible.

 

[Nick89]

Time travel into the past is impossible.

That is a pretty bold claim to made imo. As I've said, as far as I know the possibility (or impossibility) of time travel has not been proven yet. As far as I know the current laws of physics permit time travel.
Can you back your claim up with a source?

Even if your claim is true, then I don't see the need for your long explanation of heavenly objects. If time travel is already impossible, why would you want to show that by stating that heavenly objects cannot go back to the exact same position? Because if time travel WOULD be possible, they COULD.

 

[ZapperZ]

Travel into the past is permitted by the laws of physics and science fiction has a knack of becoming science fact all to often nowadays which i agree is very entertaining.

You need to be very careful in saying something like this. Many people have used that as a license to bastardize various aspects of physics, simply because "the laws of physics" permits such a thing. The laws of physics also permit a broken vase to reassemble itself back into its original form, but you don't see that happening, do you?

Science fiction also has a knack of having something that hasn't been shown to become science. We don't hear about those, do we? It's like a psychic highlighting only the things he/she predicted that actually happened. All the other misses, no one ever mentioned them.

So just because science, as we know it now, permitted them, and just because it is in science fiction novels, do not have any bearing on whether it is valid.

Zz.

 

[Gnosis]

That is a pretty bold claim to made imo. As I've said, as far as I know the possibility (or impossibility) of time travel has not been proven yet. As far as I know the current laws of physics permit time travel.
Can you back your claim up with a source?

Even if your claim is true, then I don't see the need for your long explanation of heavenly objects. If time travel is already impossible, why would you want to show that by stating that heavenly objects cannot go back to the exact same position? Because if time travel WOULD be possible, they COULD.

Nick89 respectfully, the fact that you miss the correlation between the orientations of heavenly bodies and the time frames they represent makes it apparent that you don't fully comprehend that which constitutes the nature of the past, or even the present.

The orientation of heavenly objects defines a time frame. Each time frame is a tick in the clock of the universe having its own unique orientation. All heavenly objects travel continually deeper into space, never to repeat any previous orientations, therefore, never to traverse the same time frames nor traverse any previously traveled space. There’s simply no going back in the past because there’s no Earth in those previous time frames to go back to. The Earth is in our present time frame and continually traveling deeper into space therefore, ever forward into the great expanse of the universe and ever further from its orientation in the past. As far as we can tell, it has been doing this for many billions of years now.

There are a host of other reasons why traveling into the past is quite literally impossible, but the blaring reason that makes it self-evident is the unique orientations of all heavenly objects per their time frames, as well as the relentless forward motion of the Sun and Earth through ever-deeper space.

Once you finally realize that the motion of all heavenly objects will never duplicate any previous orientations, you may finally come to the realization that there is no Earth to go back to in a year from now, 100 years from now, 1,000,000 years from now. There is only this unique time frame called “the present”. We can make references to the past, as well as the future, but the Earth that we’d need to travel to past (or future) exists in the present and nowhere else.

“IF” you were able to travel into the past (though, you emphatically CANNOT), you must realize that you are leaving from THIS time frame (the present) whose heavenly objects are in a precise orientation relative to one another. These heavenly objects will NOT coincide with their orientation in the past that you wish to travel to unless you physically move them into those positions and even then, moving them into their past orientations wouldn’t make it the past because you’ve used the present to manipulate the heavenly objects to the orientations of the past.

The major point that should be realized here is; there’s no Earth to go back to in the past. The space that Earth traversed in the past has been left far behind and the Earth will never return to that space, neither will it ever be in the same heavenly orientation ever again...

 

[phi-lin good]

The Uncertainty principle will uphold, you going back in time to measure the position of the particle would mean you changed the momentum at the same time you measured the momentum particle, making your measurement obsolete. If you went back in time and it created a second time line, then there are two particles you are measuring, so you have a 50/50 chance of the second particle having the same momentum.

 

[Nick89]

snip...

So, what you are saying is, that if I were to travel back in time 10 years right now, I would end up in the middle of empty space, where the Earth was 10 years ago? That doesn't make sense to me... Oh well, I'm going to give this up.

 

[ThomasT]

So, what you are saying is, that if I were to travel back in time 10 years right now, I would end up in the middle of empty space, where the Earth was 10 years ago? That doesn't make sense to me... Oh well, I'm going to give this up.

He's saying essentially the same thing that I said in my previous message -- which is that traveling back in time would require reinstating the configuration of all the material objects in the universe, because any particular time of the universe is the relative positions of all the material objects in the universe.

And if we live in an expanding, evolving universe, then it's not just a technical problem -- it's, in principle, an absolute physical impossibility.

It can be a bit misleading to say that the laws of physics permit backward time travel. The basic equations of motion are time-independent. So, it's just that if the universe did suddenly start rewinding and things sort of deevolved, then the sets of differential equations that are applied to the evolution could also be applied to the deevolution.

Anyone who maintains that backward time travel is a possibility, no matter how remote, is doing so in the face of overwhelming evidence to the contrary.

 

[zwest135]

Hm...this is all interesting. I think someone briefly mentioned this, but what about looking at time as a dimension?

As in, all moments in time exist equally. Just because we are not aware of them right now, doesn't mean they don't exist. This theory on time kind of creates an implicate order where everything is in a constant state of flux. Everything is everywhere at the same time, and our awareness creates the explicate order which we perceive. Our awareness would be of just a tiny, tiny slice of reality in this theory.

We can only be aware of our brains one moment at a time, and being aware of our brain at that one moment we are aware of all its memories and naturally feel like we've lived all of those memories. How our brains function, makes the illusion of an arrow of time I think. I mean If you could pick any moment and be aware of your brain...you wouldn't know the difference. This might be the first moment I've ever been aware of my brain, and because I'm given all its memories I falsely conclude I've always been aware of my brain.

Remember that we have NEVER exprienced what reality is. We only exprience what's inside our minds. Whats out there could be anything...but we only see the surface.

Now, maybe in the future we could build a device that can perceive a different slice of time. Maybe it can be aware of a different location in the dimension of TIME. It could pick up on the implicate universe, not the universe our brains pick up. I doubt it would be able to interact with it though.

Science gets really tricky when you talk about our awareness of our brains, a lot of people avoid it because it sucks, but we are talking about perception and awareness here, i think almost... beyond physicality. :( You can't talk about time without talking about our awareness of our brain, in my opinion.

If you contemplate our awareness too much I think you'll run into the paradox that each of us, individually, exist as an infinite universe, but are only aware of one single, limited, part of it...and I mean this even when not considering this theory on time.

 

[Lojzek]

After measurement of momentum the wavefunction colapses into an eigenstate of momentum operator. After measurement of position the wavefunction colapses into an eigenstate of position operator. Those two eigenstates are always diferent. So even if we had a time machine, it would be imposible to measure both observables in the same moment. We can not put a sistem into two different states at a single time.

 

[Math Jeans]

Hm...this is all interesting. I think someone briefly mentioned this, but what about looking at time as a dimension?

As in, all moments in time exist equally. Just because we are not aware of them right now, doesn't mean they don't exist. This theory on time kind of creates an implicate order where everything is in a constant state of flux. Everything is everywhere at the same time, and our awareness creates the explicate order which we perceive. Our awareness would be of just a tiny, tiny slice of reality in this theory.

We can only be aware of our brains one moment at a time, and being aware of our brain at that one moment we are aware of all its memories and naturally feel like we've lived all of those memories. How our brains function, makes the illusion of an arrow of time I think. I mean If you could pick any moment and be aware of your brain...you wouldn't know the difference. This might be the first moment I've ever been aware of my brain, and because I'm given all its memories I falsely conclude I've always been aware of my brain.

Remember that we have NEVER exprienced what reality is. We only exprience what's inside our minds. Whats out there could be anything...but we only see the surface.

Now, maybe in the future we could build a device that can perceive a different slice of time. Maybe it can be aware of a different location in the dimension of TIME. It could pick up on the implicate universe, not the universe our brains pick up. I doubt it would be able to interact with it though.

Science gets really tricky when you talk about our awareness of our brains, a lot of people avoid it because it sucks, but we are talking about perception and awareness here, i think almost... beyond physicality. :( You can't talk about time without talking about our awareness of our brain, in my opinion.

If you contemplate our awareness too much I think you'll run into the paradox that each of us, individually, exist as an infinite universe, but are only aware of one single, limited, part of it...and I mean this even when not considering this theory on time.

I like this theory. Like a *section* of consciousness that moves through a 4 dimensional plane.

If it is apparently *impossible* to re-orientate heavenly objects, then what exactly happens to these *irreversable* movements of orientation when you go faster than the speed of light?
Assuming the existence of tachyons, and that we are somehow able to observe and use them. Could we theoretically hop onto one of them and travel back in time through speeds greater than the speed of light?
Because mass cannot exceed the speed of light, what happens when you attach yourself to something that is already moving over that magical speed?

Or what about negative mass? If the existence of negative mass were discovered (it would have to be artificially created because if it exists it all went to the edge of the universe), could we 'cancel' our own mass and accelerate to the speed of light using a total mass of 0?


These are just some examples of why I think exotic matter is very fun.

 

[zwest135]

I like this theory. Like a *section* of consciousness that moves through a 4 dimensional plane.

If it is apparently *impossible* to re-orientate heavenly objects, then what exactly happens to these *irreversable* movements of orientation when you go faster than the speed of light?
Assuming the existence of tachyons, and that we are somehow able to observe and use them. Could we theoretically hop onto one of them and travel back in time through speeds greater than the speed of light?
Because mass cannot exceed the speed of light, what happens when you attach yourself to something that is already moving over that magical speed?

Or what about negative mass? If the existence of negative mass were discovered (it would have to be artificially created because if it exists it all went to the edge of the universe), could we 'cancel' our own mass and accelerate to the speed of light using a total mass of 0?


These are just some examples of why I think exotic matter is very fun.

Wow, I've spent a while now imagining traveling on negative mass or on a tachyon. I've never heard of it, but it seems like its possible. Its weird imagining two masses with opposite arrows of time, because it seems like time travel would be relative, just like velocities are. To each mass the other mass would appear to be going in reverse, if they were observing each other. I guess the one who did the accelerating and decelerating (or hopping on and hopping off rather) would be the one who expirienced the time travelling. Its similar to the twin paradox.

There seems one weird little thing bothering me though. If you hopped on one of these faster than light, (negative?) masses and traveled a good distance and than hopped off. You would end up in the apparent past, and you could turn around and see the mass you just traveled on traveling backwards with you on it. With a telescope you could see your self living in reverse... and if you watched yourself all the back up until the point where you hopped on, what would you see? Would you see your duplicate dissappear? and does this violate the conservation of matter by the creation of this duplicate self?

 

[ZapperZ]

This is always the risk whenever a topic like this starts. It appears that this thread is also heading in this direction.

May I remind everyone involved of the PF Guidelines that you have agreed to. In particular, our policy on speculative post is very clear:

Overly Speculative Posts:
One of the main goals of PF is to help students learn the current status of physics as practiced by the scientific community; accordingly, Physicsforums.com strives to maintain high standards of academic integrity. There are many open questions in physics, and we welcome discussion on those subjects provided the discussion remains intellectually sound. It is against our Posting Guidelines to discuss, in most of the PF forums, new or non-mainstream theories or ideas that have not been published in professional peer-reviewed journals or are not part of current professional mainstream scientific discussion. Posts deleted under this rule will be accompanied by a private message from a Staff member, and, if appropriate, an invitation to resubmit the post in accordance with our Independent Research Guidelines. Poorly formulated personal theories, unfounded challenges of mainstream science, and overt crackpottery will not be tolerated anywhere on the site. Linking to obviously "crank" or "crackpot" sites is prohibited.

If this thread dives further into such speculation, it will be locked, and subsequent thread on this "time travel" topic will be severely curtailed. So you decide the fate of this thread.

Zz.

 

[scupydog]

You need to be very careful in saying something like this. Many people have used that as a license to bastardize various aspects of physics, simply because "the laws of physics" permits such a thing. The laws of physics also permit a broken vase to reassemble itself back into its original form, but you don't see that happening, do you?

Science fiction also has a knack of having something that hasn't been shown to become science. We don't hear about those, do we? It's like a psychic highlighting only the things he/she predicted that actually happened. All the other misses, no one ever mentioned them.

So just because science, as we know it now, permitted them, and just because it is in science fiction novels, do not have any bearing on whether it is valid.

Zz.

Thx ZapperZ for your reply i quite understand your reasoning.