Time travel experiment demonstrates how to avoid the grandfather paradox (Update)

Mar 01, 2011 By Lisa Zyga feature
This graph shows that, as the accuracy of the quantum gun increases (from 0 to 180 degrees) so that it is more likely to flip a qubit’s state, the probability of successful self-consistent teleportation (red dots) decreases. While the theoretical probability of teleportation of qubits in opposite states is zero, the experimental probability of qubits in opposite states (blue diamonds) is about 0.01. Image caption: Seth Lloyd, et al. ©2011 American Physical Society.

(PhysOrg.com) -- Among the many intriguing concepts in Einstein’s relativity theories is the idea of closed timelike curves (CTCs), which are paths in spacetime that return to their starting points. As such, CTCs offer the possibility of traveling back in time. But, as many science fiction films have addressed, time travel is full of potential paradoxes. Perhaps the most notable of these is the grandfather paradox, in which a time traveler goes back in time and kills her grandfather, preventing her own birth.

In a new study, a team of researchers has proposed a new theory of CTCs that can resolve the , and they also perform an experiment showing how such a scheme works. The researchers, led by Seth Lloyd from MIT, along with scientists from the Scuola Normale Superiore in Pisa, Italy; the University of Pavia in Pavia, Italy; the Tokyo Institute of Technology; and the University of Toronto, have published their study in a recent issue of . The concepts in the study are similar to an earlier study by some of the same authors that was posted at arXiv.org last year.

“Einstein's theory of general relativity supports closed timelike curves,” Lloyd told PhysOrg.com. “For decades researchers have argued over how to treat such objects quantum mechanically. We believe that our theory is the correct theory of such objects. Moreover, our theory shows how time travel might be accomplished even in the absence of general relativistic closed timelike curves.”

In the new theory, CTCs are required to behave like ideal quantum channels of the sort involved in teleportation. In this theory, self-consistent CTCs (those that don’t result in paradoxes) are postselected, and are called “P-CTCs.” As the scientists explain, this theory differs from the widely accepted quantum theory of CTCs proposed by physicist David Deutsch, in which a time traveler maintains self-consistency by traveling back into a different past than the one she remembers. In the P-CTC formulation, time travelers must travel to the past they remember.

Although postselecting CTCs may seem complicated, it can actually be investigated experimentally in laboratory simulations. By sending a “living” qubit (i.e., a bit in the state 1) a few billionths of a second back in time to try to “kill” its former self (i.e., flip to the state 0), the scientists show that only photons that don’t kill themselves can make the journey.

“P-CTCs work by projecting out part of the quantum state,” Lloyd said. “Another way of thinking about closed timelike curves is the following. In normal physics (i.e., without closed timelike curves), one specifies the state of a system in the past, and the laws of physics then tell how that state evolves in the future. In the presence of CTCs, this prescription breaks down: the state in the past plus the laws of physics no longer suffice to specify the state in the future. In addition, one has to supply final conditions as well as initial conditions. In our case, these final conditions specify the state when it enters the closed timelike curve in the future. These final conditions are what project out part of the quantum state as described above.

“Although one would need a real general relativistic CTC actually to impose final conditions, we can still simulate how such a CTC would work by setting up the initial condition, letting the system evolve, and then making a measurement. One of the possible outcomes of the measurement corresponds to the final condition that we would like to impose. Whenever that outcome occurs, then everything that has happened in the experiment up to that point is exactly the same as if the photon had gone backward in time and tried to kill its former self. So when we ‘post-select’ that outcome, the experiment is equivalent to a real CTC.”

To demonstrate, the scientists stored two qubits in a single photon, one of which represents the forward-traveling qubit, and one of which represents the backward-traveling qubit. The backward-traveling qubit can teleport through a quantum channel (CTC) only if the CTC ends by projecting the two entangled qubits into the same state.

After the qubits are entangled, their states are measured by two probe qubits. Next, a “quantum gun” is fired at the forward-traveling qubit, which, depending on the gun’s angle, may or may not rotate the qubit’s polarization. The qubits’ states are measured again to find out if the gun has flipped the forward-traveling qubit’s polarization or not. If both qubits are in the same state (00 or 11), then the gun has not flipped the polarization and the photon “survives.” If the qubits’ states are not equal (01 or 10), then the photon has “killed” its past self. The experiment’s results showed that the qubits’ states were almost always equal, showing that a qubit cannot kill its former self.

The scientists noted that their experiment cannot test whether an actual CTC obeys their new theory, since it is currently unknown whether CTCs exist at all. In the future, they plan to perform more tests to better understand paradoxes.

“We want to perform the so-called `unproved theorem paradox' experiment, in which the time traveler sees an elegant proof of a theorem in a book,” Lloyd said. “She goes back in time and shows the proof to a mathematician, who includes the proof in the book that he is writing. Of course, the book is the same book from which the time traveler took the proof in the first place. Where did the proof come from? Our theory has a specific prediction/retrodiction for this paradox, which we wish to test experimentally.”

Explore further: Could 'Jedi Putter' be the force golfers need?

More information: Seth Lloyd, et al. “Closed Timelike Curves via Postselection: Theory and Experimental Test of Consistency.” Physical Review Letters 106, 040403 (2011). DOI:10.1103/PhysRevLett.106.040403

4.6 /5 (42 votes)

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TabulaMentis
2.2 / 5 (21) Mar 01, 2011
Lisa Zyga appears to be a great fan of these types of articles. I am with her all the way, so the more of these type of articles, the better.
Teleportation is a futuristic word I like to hear. I wish wormholes had been mentioned as well. This tech will eventually allow people to see real life copies of loved ones who have passed away.
Shootist
1.7 / 5 (20) Mar 01, 2011
Lisa Zyga appears to be a great fan of these types of articles. I am with her all the way, so the more of these type of articles, the better.
Teleportation is a futuristic word I like to hear. I wish wormholes had been mentioned as well. This tech will eventually allow people to see real life copies of loved ones who have passed away.


But it doesn't get us to Alpha Centauri, cure cancer or pay off the national debt..
SAntczak
4.7 / 5 (16) Mar 01, 2011
Lisa Zyga appears to be a great fan of these types of articles. I am with her all the way, so the more of these type of articles, the better.
Teleportation is a futuristic word I like to hear. I wish wormholes had been mentioned as well. This tech will eventually allow people to see real life copies of loved ones who have passed away.


But it doesn't get us to Alpha Centauri, cure cancer or pay off the national debt..


...yet.
pain
2.4 / 5 (11) Mar 01, 2011

But it doesn't get us to Alpha Centauri, cure cancer or pay off the national debt..

The people that work on these things don't worry about such tedious things like paying off the national debt... you speak as if these studies are absolutely useless which is completely ignorant. Wormholes could potentially get us anywhere in the universe and could become our main medium of space travel (granted they exist). Curing cancer on the other hand has most likely already be done...
Pyle
2 / 5 (13) Mar 01, 2011
CTC's are an artifact of a theory that needs revision. Godel identified the flaw. Who is working on the solution? This qubit gun nonsense stinks like Hawking radiation in a sound hole. Not that great physics can't come out of it, but the CTC analogy is a thought experiment probing a broken limit IMHO.

Then again I refuse to embrace entanglement too. I guess I've been strung along too long.
frajo
5 / 5 (5) Mar 01, 2011
CTC's are an artifact of a theory that needs revision. Godel identified the flaw.
Where can I read about it?
superpaul3000
not rated yet Mar 01, 2011
These CTC's are possible under relativity but unstable under quantum mechanics. It would be like a ball rolling around the rim of a crater. You can go back in time to the past you remembered but very shortly afterwards your world line will diverge from the CTC.
Lorax_2nd
5 / 5 (1) Mar 01, 2011
The graph of probability vs. angle is wrong, and a blow to their credibility, and/or shows my ignorance. How does one interpret a negative probability, as shown at angle 100 (and, considering error bars, at many other angles)?
Pyle
3.7 / 5 (3) Mar 01, 2011
Where can I read about it?
Just me being cranky. Pun intended.
If you want to read something? Go check out what the cranks are pushing at arxiv. You know where to look. When you get bored of MOG look at Cahill's 3-space/aether for s@$#s and giggles. Heck, do some math and try to fit in omr's repulsion and Tux's stellar factories.

Anyway, my point was just that we seem to be testing the unintuitive limits of relativity, so maybe we need some more people to try different theories. GR should be the marker.

(A World Without Time by Yourgrau was a decent read. Keep in mind Yourgrau's position that Godel was the second coming though.)
Raygunner
2.8 / 5 (5) Mar 01, 2011
I don't believe in time, just "now". The tests don't prove anything that I can see. They can't prove the qubit went "back" because it did not. So it can't kill itself because there are no temporal effects to begin with. Time is a crack-laced illusion that's all, Charlie Sheen will back me up on that!
Shootist
2.1 / 5 (7) Mar 01, 2011

But it doesn't get us to Alpha Centauri, cure cancer or pay off the national debt..

The people that work on these things don't worry about such tedious things like paying off the national debt... you speak as if these studies are absolutely useless which is completely ignorant.


Who're you talking to? I'd stop feeding orphans, on the government tax dime, before I'd cut research funding.
stealthc
3.1 / 5 (11) Mar 01, 2011
We need our political climate to evolve first before time travel should enter the scene. This technology would be abused by governments and big corporations alike, unfolding the world into an environment of total domination and surfdom by the elites.

No thanks.
MorituriMax
1.8 / 5 (4) Mar 01, 2011
Lisa Zyga appears to be a great fan of these types of articles. I am with her all the way, so the more of these type of articles, the better.
Teleportation is a futuristic word I like to hear. I wish wormholes had been mentioned as well. This tech will eventually allow people to see real life copies of loved ones who have passed away.


But it doesn't get us to Alpha Centauri, cure cancer or pay off the national debt..

If you set it up right, couldn't you go back in time to when Alpha Centauri was where you are now?
bluehigh
3.2 / 5 (11) Mar 01, 2011
If you travel in time and want to be anywhere near the same place you started you would have to travel in space too. A trip backwards even a few hours and you will miss the earth by millions of kilometers and arrive in empty space!
spaceviking
5 / 5 (5) Mar 01, 2011
I don't see how this experiment applies to relativity, or CTC. All it appears to show is what happens when you fire a quantum gun at entangled states. That is, the higher the likely-hood of the quantum gun polarizing the qubits, the lower the probability those qubits will be in the same state afterward.

Is there something I'm not getting?

Also, what exactly distinguishes the "forward" qubit from the "backward" one? Is it just that the "backward" one is the one fired upon?
Pyle
not rated yet Mar 01, 2011
@spaceviking: My point exactly.
@bluehigh: Don't get started with preferential frames. You tread close to the abyss. Noodle a little bit about conservation (mass, information, momentum) as well to give yourself a headache.
dumdogslickthemselves
1.4 / 5 (9) Mar 01, 2011
We need our political climate to evolve first before time travel should enter the scene. This technology would be abused by governments and big corporations alike, unfolding the world into an environment of total domination and surfdom by the elites.

No thanks.

I hate you 2D conspiracy nuts. Youre all paranoia and bile. Get out of your hovel. Go get some exercise. Throw that pic of Chairman Mao away.

'Surfdom' -Is that in Malibu? Rincon? Waimea maybe?
bluehigh
2.5 / 5 (6) Mar 01, 2011
In general we move relative to our previous spatial position at perhaps 1 meter every microsecond and to the best of our knowledge have never been in the same spatial place twice and are never likely to be!

Kinda makes it very difficult to be killing grandfathers. Expect a photon with time travelling qubits embedded to get ripped to shreads.

Unless: time is bound to mass in such a way that local time moves with associated mass through space, if anyone can even imagine what that implies.

We've got space-time. Is there mass-time?

Ok ... i'll go take my medication!
Pyle
2.3 / 5 (3) Mar 01, 2011
@bluehigh: You are missing the subtlety of preferential frames. If there is no preferential frame you can say everything else is moving relative to the time traveling matter (or whatever it is). i.e. the rest of the universe is rotating around the spot on the Earth where the time traveler transitions. i.e. no shredding. But I oversimplify. It reminds me of one of my favorite fortune cookies - "Wherever you are, there you are." (Probably stolen from somewhere else, but I really got it in a fortune cookie.)
mass-time? May I suggest less medication?
bluehigh
2.9 / 5 (7) Mar 01, 2011
New Cookie - mmm love cookies.
Whenever you once were. Is wherever you are not now.

Preferential frames of reference don't change the fact that we are in a different location relative to and from everything.

.. its neither here nor there cause it doesn't matter.

jonfmac
not rated yet Mar 01, 2011
In relativity a spacial frame can move forwards or backwards. It can even be warped. The argument is that time also behaves the same way. I have never seen anything that has ever shown time to possess anything like the same properties of space. A time frame always moves in one direction. It can be stretched or compressed. Nothing has shown that this forward "motion" can be looped in one direction proceeding from the present to the past. I'm with "spaceviking". Gotta start looking at time as a different kind of field. Interesting thought experiment though.
Terrible_Bohr
5 / 5 (2) Mar 01, 2011
My favorite cookie-delivered fortune was "Keep your goals away from the trolls".
Ron_Alford
not rated yet Mar 02, 2011
This would explain why UFOs are so elusive and can never be proved. If they are observers from the future they cannot do anything that would actually prove their existence, or be in violation of the above quantum effect. Direct interference that might change the timeline would be physically impossible. Lights in the sky or surreal events, widely disbelieved, would not be impossible.

It's a relief anyway. If we went back in time we wouldn't have to worry about stepping on that butterfly, and changing all of reality in a butterfly-effect event.
Decimatus
not rated yet Mar 02, 2011
I would think if you can move through time, moving through space should be pretty simple.

And I have never believed in time paradoxes. If time travel is actually possible, you are killing someone else's grandfather, not your own. Not as in parallel(though this could be it also), but more along the lines of your present being further down the stream and never touching the "current" past.

For example:

Year 2011, you go back 21(1990) years, kill your father, and return to present. Your father is still alive(your 2011). Wait 21 years(2032), and return to 2011(changed 2011). You find that you father had died in this past, but is still alive in your present.

In this way you can forever change the past, and it will never catch up with your true present. But if you stay in that past, your true present will be forever unchanged, apart from you being absent from it(which would only occur if you stay in the past beyond your true present departure date).
Ron_Alford
5 / 5 (4) Mar 02, 2011
We need our political climate to evolve first before time travel should enter the scene. This technology would be abused by governments and big corporations alike, unfolding the world into an environment of total domination and surfdom by the elites.

No thanks.


They might have said this about the Internet. Yet the net, and cell phone cameras, have enabled us to see the full truth, unfiltered by mainstream media editorial decisions. This has led to a major revolt for freedom in the Middle East. Technology frees. Yes, it can be misused, but the people who know the most about technology are the smart ones, and they will always be one step ahead of the dummies who still think controlling people is a good idea.
SCMarkT
not rated yet Mar 02, 2011
Finally, the "Bill and Ted's Excellent Adventure" model of time travel wins out over the "Star Trek" and "Back to the Future" models of time travel.
Decimatus
not rated yet Mar 02, 2011
Another way to think about time would be to literally interpret it as the 4th dimension. Traveling through time is really only movement through this 4th dimensional substance, perhaps fluid-like.

Basically, think of a cube, which is the 3 dimensions, now picture the hypercube as the 4th dimensional version, with all Axis beyond the original 3 as time. So if you move up or down in the 4th dimension, you are moving into the past and into the future. You would need to move in a diagonal direction to return to a past event and also be in the proper segment in space.

Our problem is, we have no objective view of this 4th dimension because we are moving uncontrollably in one direction along it's axis. As if we came from an explosion and have no choice but to sail along our given time path.

To tear ourselves out of this time path, would require enourmous energies to reverse the momentum along this path.
Decimatus
not rated yet Mar 02, 2011
What would be the opposite of lightspeed and gravity that could possibly reverse our momentum down the time path?
AtomThick
not rated yet Mar 02, 2011
What would be the opposite of lightspeed and gravity that could possibly reverse our momentum down the time path?


Time has similarities with a dimension but I'm not convinced it's a real dimension (like the 3 dimensions of space) through which you can move. We detect time only becaue there are periodic processes to which we can relate, like day and night, the seasons, etc. Those periodic processes slow down if you move faster but i'm not convinced you can go back in time. If you could there probably would be no paradox because you will actually change everything and end up in another normal timeline just like an observer changes the outcome in the double slit experiment.
Cave_Man
1 / 5 (3) Mar 02, 2011
only problem with this is that if you were to "travel" back in time to an earlier point in spacetime that earlier point in spacetime is already a fixed point so therefore you would not be able to "change" anything relative to the future.

otherwise we would be seeing numerous examples of travelers from the future coming back and messing with us, and we don't see that at all.
Cave_Man
2.6 / 5 (5) Mar 02, 2011
What would be the opposite of lightspeed and gravity that could possibly reverse our momentum down the time path?


Time has similarities with a dimension but I'm not convinced it's a real dimension (like the 3 dimensions of space) through which you can move. We detect time only becaue there are periodic processes to which we can relate, like day and night, the seasons, etc. Those periodic processes slow down if you move faster but i'm not convinced you can go back in time. If you could there probably would be no paradox because you will actually change everything and end up in another normal timeline just like an observer changes the outcome in the double slit experiment.


if it were possible we would be flooded with travelers from other timelines, probably an infinite amount of them which would tear a hole in the spacetime continuum. i think this justifies the use of LOL.
Thingumbob
not rated yet Mar 02, 2011
If we and Lisa Zyga can solve this mystery, why, the whole key to the greatest mysteries of times gone by can be solved as well! Lets see...There's squaring the circle, transmuting lead into gold (Isaac take heed!), how many angels can fit on the head of a pin, the epicycles of the celestial spheres...All these can now be answered in relatively no time at all! Wunderbar!
Tachyon8491
2.9 / 5 (8) Mar 02, 2011
There is only minkowskian 4-D spacetime - you cannot "separate" space and time - the one becomes meaningless without the other. Getting back to your grandfather requires a spacetime shift (through space AND time) of a limited number of years but perhaps gigaparsecs in the reference frame. Shifting the macrocosmic ref frame from the visited past into the new state without a grandfather into an origin-future of the traveler, would require macrocosmic rearrangement of all ontological matter-energy resonances in the universe(think energy involved..) which is esoteric nonsense. The only alternative is a form of frame-splitting in a multiple-parallel-world theory, which also implies an energy conservation challenge. I.e. unless we consider extant, infinite number of mutually phase-isolated, non-entangled universal subdomains, which imply that universal energy (matter) is infinite, and not somewhere close to the 10^108 particles presently granted. That would be true only for one subdomain. FV
AtomThick
not rated yet Mar 02, 2011
@cave_man: Therefore there couldn't be an infinite number of timelines just one which can be changed. The double slit experiment gives you a feeling of what is like to travel back in time. What I mean is this:

You already know that if you don't observe the electrons they will behave like waves therefore you know the future result of the experiment. The next step is to perform the experiment again but this time observe the electrons. Because you have observed the electrons they behave like particles therefore you have a different result. Instead of performing the experiment twice you can imagine that you have performed the experiment once and after that you got back in time and performed the experiment by observing the electrons therefore changing the timeline.
bluehigh
1 / 5 (3) Mar 02, 2011
showing that a qubit cannot kill its former self.


This implies that no change to a timeline is possible where any interference, measurement or observation occurs.

Therefore backward time travel for physical objects is unable to be realised and that CTCs are a mathematical artifact.

Though I guess theres nothing to prohibit the arrow of time reversing but I guess time travel without knowing you have gone back in time is a bit of a fizzer.

If we could hit the rewind button on time, would we be dead before we are born?
tkjtkj
not rated yet Mar 02, 2011
If you travel in time and want to be anywhere near the same place you started you would have to travel in space too. A trip backwards even a few hours and you will miss the earth by millions of kilometers and arrive in empty space!

I think the idea of CTC's touches exactly on that: there *is* at least one route that would get ya back to the starting point, and that pathway is a CTC.

but then .. im just an ignorant layman ...
eurekalogic
2 / 5 (4) Mar 02, 2011
I doubt it is a path within the same timeline but a jump or skip to another time line. IE TV series Sliders. Maybe the reason they never got home. Even though they did have one episode where they did.
frajo
5 / 5 (5) Mar 02, 2011
IE TV series Sliders. Maybe the reason they never got home. Even though they did have one episode where they did.
TV is neither reality nor science modelling reality.
panorama
4 / 5 (1) Mar 02, 2011
IE TV series Sliders. Maybe the reason they never got home. Even though they did have one episode where they did.

I'm envisioning something more along the lines of "The One" with Jet Li. I like the idea that there are multiple panorama's out there and if I kill them I will have a quickening type event and get a little stronger.
Anthony_Milner
1 / 5 (1) Mar 02, 2011
These tests are invalid.

The entire premise for the current relativistic model is grossly incorrect.

Results will always vary directly ACCORDING to the laws of physics and action for any given Determinant of relative and RELEVANT differential change within a given envelope. I'm sure Schrodinger and Heiseburg would agree with me with my postulate.

They must and WILL always balance. The physics of Relativity theory today is (largely) valid for our observable universe, but sadly it's underlying Cosmology is often more fiction than fact. It's sad that so many $ and talented minds are wasted chasing Mother Goose at the base of our knowledge pyramid.
Pyle
1 / 5 (1) Mar 02, 2011
@bluehigh:
Preferential frames of reference don't change the fact that we are in a different location relative to and from everything.
They absolutely do. They mean you can consider any one frame as static. Consider yourself as you go through the day. Treat the universe as in motion around you and yourself as static. That's relativity. No shredding from relative motion.
Pyle
1 / 5 (1) Mar 02, 2011
@Tachyon
Shifting the macrocosmic ref frame from the visited past into the new state without a grandfather into an origin-future of the traveler, would require macrocosmic rearrangement of all ontological matter-energy resonances in the universe(think energy involved..) which is esoteric nonsense.
I don't think so. For purposes of time travel I believe you can hold the frame of the traveler as static and ignore the rest of the universe. The only problem you have is the actual matter of the time traveler. Where does it come from? Maybe a pile of goo that you push quantum state onto, like our quantum teleportation. Still an enormous energy bill. And also a vastly limited method of time travel.
However, IMHO, time travel isn't possible and CTCs are an artifact of an incomplete theory.
Pyle
1 / 5 (1) Mar 02, 2011
@jonfmac:
Nothing has shown that this forward "motion" can be looped in one direction proceeding from the present to the past.
Right, nothing except relativity theory itself. That is what Godel did with his Godel universes. He showed that there are possible universes within relativity theory that contain these CTC's. The implications of this, I think, are that either time doesn't exist, or the theory is broken. Note: Godel didn't go here. That is just me conjecturing, along with others.
Note 2: I think GR is great, but its limits show that it is incomplete (Godel again). Relativity's predictive power has been shown again and again. I just think there is more to it.
Userless_Id
5 / 5 (1) Mar 02, 2011
sounds like, 'there are no contradictions because they are not allowed." Or, a similar 'scientific' principle saying, 'the fine structure is constant is what it is because otherwise, we would not be hear to wonder why it is the way it is ...'

On the other hand, if you assume that states vary continuously along these CTC (or any curves for that matter), then Deutch;s criteria follow follow as a mathematical necessity. And instead of treating CTC as some abstract quantum channels, if we treat them for what they are, i have a feeling even the post-selection criterion will follow mathematically from the set-up, rather having to have it imposed from above. And the continuity assumption is almost built into both the quantum AND the GR from the beginning.
Userless_Id
5 / 5 (1) Mar 02, 2011
ultimately, though, one would have to face the task of understanding space-time at 'quantum level', whatever that means. Because all these 'CTC as quantum channel' business is just our way of saying that we have not the slightest idea of what the hell is going on. Of course, such euphemistic treatment of scientific issues has been a fashion since 'Copenhagen Convention', 'main-stream' physicists should not feel compelled to feel perturbed by such curiosities.
Pyle
1 / 5 (1) Mar 02, 2011
@userless: Your first part sounds anthropic. Seems like a step too far in this context.
...Deutch;s criteria follow...post-selection criterion will follow mathematically from the set-up..
To paraphrase: basically the only time travel possible is internally consistent within the universe of its possibility? I don't think I am getting the reference to Deutsch. Please explain if I missed something. Thanks.
frajo
5 / 5 (5) Mar 02, 2011
I think GR is great, but its limits show that it is incomplete (Godel again).
Please don't try to marry GR to Goedel's incompleteness theorems. No intercourse is possible between them as GR is not an axiomatic system able to describe the natural numbers.
The heuristic incompleteness of our understanding of physics is fundamentally different from the proven, unchangeable incompleteness of certain axiomatic systems dealing with netural numbers.
This is because the objects of maths are different from the objects of physics.
Pyle
1.5 / 5 (2) Mar 02, 2011
@frajo:
Please don't try to marry GR to Goedel's incompleteness theorems.
I'm not capable to developing this properly but... I think you are limiting the implications of incompleteness unnecessarily. Godel himself limited the implications of his theorem to certain axiomatic systems, and even so dealt a fatal blow to positivism.
I believe the theorem can be extended to include any non-trivial system to a certain extent. Godel himself showed the conflict between GR and the intuitive with his Godel universes. I believe singularities are another example of the completeness problem within GR. It may be possible to limit the completeness problem in any system to the trivial, "this is a lie," but I still believe that ultimately any theory will have its limits. Our goal should be to push those limits to the absurd, thereby enhancing our predictive powers to any feasible situation.
Pyle
1 / 5 (1) Mar 02, 2011
To mix threads. I believe MOND fits into this discussion as well. Although not a proper theory, it helps plug a limit hole in GR if dark matter, in fact, doesn't exist. MOND is vastly more incomplete, maybe not even properly considered a system, but hopefully my point isn't lost in my erratic semantic freedom. Heck, I'm not even sure if I am making any sense.

Point being, CTC's, wormholes, singularities, etc. all seem to be unintuitive fallacies resulting from the limits of GR's ability to model/explain the universe.
Shelgeyr
2 / 5 (9) Mar 02, 2011
you speak as if these studies are absolutely useless which is completely ignorant.

They ARE absolutely useless, unless you're using some other, uncommon, definition of the word "use". Since I'm admittedly ignorant of how such studies could really actually be useful, please enlighten me.

And what's all this about killing your grandfather? As fragile and complex a process as conception is, going back and changing any aspect of your grandparents' lives earlier on "parent conception day" would change which sperm fertilized the egg, or even IF. Kill? Unnecessary. Heck, just hand him a $5 he supposedly dropped, or just strike up a conversation with grandma. Damage done.
Cave_Man
2 / 5 (4) Mar 02, 2011
quote


research the double slit experiment, you never hear more than the high school textbook version which is that when you measure something (could be any experiment) you change it, well its not the mental process of "observing the data" which makes it change its the measuring device which can never be 100% accurate without interfering with the thing it is measuring.
bluehigh
2 / 5 (4) Mar 02, 2011
@Pyle
However, IMHO, time travel isn't possible and CTCs are an artifact of an incomplete theory


Reasons aside, we agree on a conclusion.

Telekinetic
1 / 5 (6) Mar 02, 2011
We need our political climate to evolve first before time travel should enter the scene. This technology would be abused by governments and big corporations alike, unfolding the world into an environment of total domination and surfdom by the elites.

No thanks.

Get off this forum, you skinhead wannabe. Learn how to spell serfdom, you dunce.
Anthony_Milner
1 / 5 (1) Mar 03, 2011
Sorry for the late response Pyle I've been "relatively ill", and thanks. How to say this with brevity?

Your reply, is why I said Einstein's buddies would agree with me. But there-in lays the problem. As humans, we always digress from our own view point.
COCO
1 / 5 (3) Mar 03, 2011
I cannot believe all the attention being payed here w/o a squeak about Charlie Sheen!
LarsKristensen
1 / 5 (3) Mar 05, 2011
Time can not be changed.
Twin Paradox does not exist.
Give both the twin task that they must keep track of how many times Venus has surrounded the sun, to meet each other again.
Change their time, one will have a different number of Venus' circle the sun than the other and they have good reasons for not having it. It is therefore not possible to change the time.
Have the twins' clocks time different, at least one of the clocks going wrong.
hush1
1.3 / 5 (3) Mar 05, 2011
This is because the objects of maths are different from the objects of physics.


Frajo. Your quote of Wittgenstein's Adage:
"The limits of your languages are the limits of your world"
comes to mind. (The original you understand, as well)

Of course, being human is "the proof in the pudding" to this adage. And, of course, the 'language' of physics and the 'language' of math are just that - two languages. And, of course, we both don't regard languages as 'merely' languages. We regard them as 'extensions' to our personal vocabulary.

The heuristic incompleteness of our understanding of physics is fundamentally different from the proven, unchangeable incompleteness of certain axiomatic systems dealing with netural numbers.


Surely there exists a 'translation' between both languages, both vocabularies, that is able to 'satisfy' both camps of meaning:
Physics and Math.
Where translation is possible, no matter how poor, "fundamental differences" decline at a half life rate.
hush1
2.3 / 5 (3) Mar 05, 2011
Show compassion. That is understanding. I feel sorry for all human words. They bear the assigned weight and meaning everyone assigns to them. Meaning reduced to the size of vocabulary.
Skeptic_Heretic
4 / 5 (4) Mar 05, 2011
Surely there exists a 'translation' between both languages, both vocabularies, that is able to 'satisfy' both camps of meaning:
Physics and Math.
The language of physics is math. Your dichotomy is false. Physics is a description of our reality. Our reality is made in such a way that our mathematics are as they are.
Pyle
5 / 5 (1) Mar 05, 2011
Oh goodie!! Can we start another thread debating the validity of the statement math = language??? Math is transcendent!!! Who wants to start?

Physical phenomenon follow mathematical relationships. That math can be used to describe our physical world is inherent. Math started with quantity. That it can be used to predict the outcomes of interactions between forces is astounding. Math is not a language. We use language to describe math so we can study and discuss it, but math is math. We use the language of math in our description of physics because of math's universal applicability.

That was a huge post of nothing!!! I love it.
Pyle
5 / 5 (2) Mar 05, 2011
I actually had a point though. Back to the incompleteness.
We create logical systems, theories, to describe the interactions in our world. Godel showed that within an axiomatic system there are statements that are true but unprovable and that the consistency of the system is not provable.
Within GR we can create situations with CTC's, singularities, etc. These are intuitively not possible, I think. In addition to searching the possibility of these, I think we should be exploring other adaptations of the theory that eliminate them. Any system will have limitations.
Yoaker
2 / 5 (1) Mar 05, 2011
If we think a bit outside the box, a time-travel cosmology is actually less paradoxical than a non-time-travel cosmology: Without time-travel we would be slaves to the deterministic progress of the guiding laws, we would not have the brain power to solve NP-problems, and there would be no way to travel back to the Big Bang and set it off (at the end of the technological singularity in the future).

Quantum time-travel is not the answer though; quantum mechanics is a mathematical epiphenomenon evident in its reliance on complex numbers, which are not real, but a result of a very unfortunate turn away from geometric algebra in the last century.

Holographic time-travel is however predicted by the holographic correspondence between 4D and 5D space-times. The natural 5D space-time in this correspondence has two dimensions of time (and therefore allows time-travel), but is usually unwrapped to a fourth dimension of space, because of difficulty accepting time-travel; big mistake?
hush1
1 / 5 (3) Mar 05, 2011
The language of physics is math. Your dichotomy is false. Physics is a description of our reality. Our reality is made in such a way that our mathematics are as they are.


You are free.
To interpret math as you wish.
hush1
1 / 5 (3) Mar 05, 2011
We use language to describe math so we can study and discuss it, but math is math. We use the language of math in our description of physics because of math's universal applicability.


"...because of math's universal applicabliity."

You are free.
To interpret math as you wish.
Skeptic_Heretic
3 / 5 (2) Mar 05, 2011
The language of physics is math. Your dichotomy is false. Physics is a description of our reality. Our reality is made in such a way that our mathematics are as they are.


You are free.
To interpret math as you wish.

Actually, no, you're not. Hence why mathematics is usable to describe reality as it arises from reality.

Math is an abstract of measurement without true definition beyond what is agreed upon, however, changing the symbols does not alter the validity and expression of the fundamental existence of the construct. Pi is always Pi in our universe, and perhaps beyond it, but to sstate that it transcends reality as some of you are is unfalsifiable, meaning opinion without evidence.
hush1
2.5 / 5 (4) Mar 05, 2011
Your dichotomy is false.

You misunderstood because I did not state clearly:
There is only one language for humans. The human language.
There is no dichotomy. Of course, the 'parts' of the human language have been given 'names' - oddly enough, more often than not - the names of the region or countries from whence the 'parts' supposedly originated.

...but to sstate that it transcends reality as some of you are is unfalsifiable, meaning opinion without evidence.


Yes. There is no way to transcend to a reality beyond the limits (if the limits exist)of the human language, if that were the only means to convey meaning.

There is still hope. That 'our' 'construct' will always fall short - short of fundamental and short of existence. Or in the words of Godel: Be incomplete.
Skeptic_Heretic
not rated yet Mar 05, 2011
There's a hint of Derrida in your phrase, very poor choice.
hush1
1 / 5 (2) Mar 06, 2011
We agree. There is no poorer choice than Derrida.
The 'inventor' of 'deconstruction' using an army of translators to translate his original works.
And the definition, as well as the meaning and personification of the word: charlatanry...is
Derrida.

And I don't even know his work. Tell me now.
If I am to die, never knowing him, tell me, I am not missing a thing. Do me the favor. Save me the time. So we can discourse over more important meanings.
frajo
5 / 5 (2) Mar 06, 2011
There is only one language for humans. The human language.
That's neither the colloquial nor the scientific meaning of "language". It's your idiosyncrasy only.
frajo
5 / 5 (3) Mar 06, 2011
There is still hope. That 'our' 'construct' will always fall short - short of fundamental and short of existence. Or in the words of Godel: Be incomplete.
"Incomplete" is not Goedel's word. "Be incomplete" is not Goedel's postulate.

One should understand Goedel's incompleteness theorems before trying to exploit the fame. Otherwise, one may use the word "incomplete" but one must not refer to Goedel in that context.
hush1
1 / 5 (3) Mar 06, 2011
To understand Goedel's incompleteness theorems, one must refer and exploit the vocabulary the theorems were written with originally. All translation morphs meaning.

"Incomplete" is not Goedel's word. "Be incomplete" is not Goedel's postulate.


Correct. Absolutely.

That's neither the colloquial nor the scientific meaning of "language". It's your idiosyncrasy only.[q/]

Provide us with the scientific meaning of "language'.
frajo
5 / 5 (1) Mar 06, 2011
To understand Goedel's incompleteness theorems, one must refer and exploit the vocabulary the theorems were written with originally.
No. You are confusing mathematics and metamathematics. The mathematical meaning of mathematical theorems is independent of the metamathematical meaning of the words used for expressing the theorems in different human languages.
All translation morphs meaning.
Not the mathematical meaning of mathematical theorems.

There is only one language for humans. The human language.
That's neither the colloquial nor the scientific meaning of "language". It's your idiosyncrasy only.
Provide us with the scientific meaning of "language'.
Not necessary. The science of linguistics deals with more than one language.
ERW
not rated yet Mar 06, 2011
The Article states "The experiments results showed that the qubits states were almost always equal, showing that a qubit cannot kill its former self." Doesn't the word almost imply that the qubit sometimes kills its former self? It there were exceptions, the how is the theory proven ?
hush1
1 / 5 (2) Mar 06, 2011
The mathematical meaning of mathematical theorems is independent of the metamathematical meaning of the words used for expressing the theorems in different human languages.


What is the purpose of discussing the mathematical meaning of mathematical theorems? No metamathematical meaning of the words used for expressing the theorems in the different human languages has equivalency to the independency.

All translation morphs meaning

Not the mathematical meaning of mathematical theorems.


So the 'independency' means no translation is available for the mathematical meaning, at least in any other language we know?

You, yourself, have stated, other languages are merely an extension of one's vocabulary. I share that sentiment. Why regard the 'dealings' of a 'science' that regards one's vocabulary as many languages as scientific? As if every language had an underlying independence structure.

nanolouizos
not rated yet Mar 07, 2011
Loyd has made his miracle again! I really love his approach to science, especially when it comes to quantum mechanics. His solution to time travel paradox also conserves the information n our universe...
Ludwig
not rated yet Mar 07, 2011
The 4th dimension isn't time. It is the length that light has traveled in the lapse of time during which you observe your system.
ZipWizard
1 / 5 (1) Mar 07, 2011
From what I can figure out, nature does not allow pure paradoxes. Therefore, when you time travel to the past...it is not YOUR past you travel back to and start expressing your knowledge of the future. You can time travel all you want, interact all you want, as it becomes your own personal time bubble of existence.

In fact, I think the phenomena may be localized within a field. When you travel back in time through a wormhole, you only influence your local field that you come in contact with.

The reason we do not see folks from the future in OUR current time is, there is some kind of field inertia that prevents them from extending their influence to objects or characters outside some kind of Karmatic existence, within our individual temporal experiences. The Prime temporal flow, we normally exit in, cannot be touched.

Once you drop yourself into one of these new Quantum existences...it is virtually your OWN universe that you are expressing in, which cannot harm the PRIME you left.
ZipWizard
not rated yet Mar 07, 2011
Besides my comment about a PRIME temporal flow, I think successful time travel is also directly related to mass.

If CTC's exist, they can only perform because they are of low mass, and less interactive. The nearly infinitely larger mass of a human dictates a much larger wormhole than for individual particles.

As this larger mass is a slave to Quantum variables in every millisecond of its existence, it and the TIME it is brought back into are in constant flux. Therefore the record of history will be different each time the event is visited, but due to the Prime's temporal inertia, the Prime is not effected.

I also believe you can return to the prime at the instant you left, via a wormhole left in space - and carry back your experiences locally, perhaps even objects that have enriched you, but you cannot return to the exact same Quantum Reality you temporarily experienced.

It could be a great way to renew your tissues by borrowing from your past self, if YOU can be found.
ZipWizard
not rated yet Mar 07, 2011
My more profound theories:
Yes, there can be mild inter-dimensional influences once communications are open, but all major influences must originate from the Prime...making conservation of original energy and animus reactions the results of actions in Prime...to add to its history.

If the object originated in Prime, it can return there, and has the option of pulling matter to Prime with it as it exits.

Prime Quantum Reality can initiate an origination temporal wormhole that can reach the Big Bang, given enough mass and energy. Such a wormhole is a white hole with nearly infinite energy available, much like the sought after zero point energy.

Just a musing note:
Extreme caution needs to be handled when opening temporally deep (Big Bang Event) wormholes beyond particle size (CTC), because if a null time event rips open wide enough, it could get extremely dangerous. Near the Big Bang event, the energy amount in our Sun could be squeezed into the size of an atom.
bimachakti
not rated yet Mar 08, 2011
I believe time traveler was not possible..
ODesign
5 / 5 (1) Mar 09, 2011
Misunderstanding Godel,

@frajo: It may be possible to limit the completeness problem in any system to the trivial, "this is a lie," but I still believe that ultimately any theory will have its limits.


I would advise against using boolean logic to resolve quantum conundrums. The existence of indeterminate quantum phenomena seem to invalidate boolean logic and therefore Godel's theory A Priori.

I don't think Godel was claiming that EVERY system it is possible to create will be incapable of proving everything. In fact we can recursively apply Godel's theory to say that Godels theory itself may be part of a system (boolean logic) that is incapable of proving everything. Godel's theory also allows that there may be some other theory existing where it is possible to prove everything, although obviously in this other theory Godel's Theorem would not be provable since it would be false.

aliby
not rated yet Mar 09, 2011
So we are in 2011, we achieved lots of technological development, but the fundamental questions have not found yet an answer. We talk about Big Bang, black holes, and so on, we make a lot of theories, but the experiments are so limited. Sure our life is much better in terms of comfort but what is really going on right now, can t be explained. So why do you think things happen in this way, why we find in this specific way clues, the nano field is the first now.
aliby
not rated yet Mar 09, 2011
Maybe in a few years we ll be whitenesses to lots of beautiful technological achievements, we could improve our life, our health, we could live longer, and solve another mysteries, so could we travel in the future? in the past? It is a possibility, maybe it will come a time, when we could do this, but what if this have been achieved and between us are people who use this technique, to travel back in time, travel in future, and maybe these people are the ones who give us clues of solving different problems in medicine, biology, physics, economy...A lot of things happen right this time, but time does it really exists?
Pyle
1 / 5 (1) Mar 09, 2011
@ODesign:
I would advise against using boolean logic to resolve quantum conundrums. The existence of indeterminate quantum phenomena seem to invalidate boolean logic and therefore Godel's theory A Priori.

While I agree that Godel was way too careful to reach beyond the explicit implications of his incompleteness theories, I don't think that isn't because they are thusly limited. There was a discussion a couple of months ago regarding this on physics forums - physicsforums.com/showthread.php?t=455641.
Ultimately the anti-Godel argument had a stronger position in the thread, but I am not persuaded.

btw, where did Boolean come from? I thought BL was complete and not a Godel qualifying axiomatic system. It is with the natural numbers that we encounter incompleteness and where I see opportunities to expand the theories to broader systems.
Pyle
1 / 5 (1) Mar 09, 2011
Ultimately new axioms can be added to address the incompleteness, narrowing it. My belief is that GR has reached its limits when we discuss singularities, inflation, CTC's, wormholes, etc. and modifications and additions need to be made to the system to complete it. (Now you can attack my semantics as I start throwing well defined terms into the buzz saw of colloquialisms and ambiguous usages. I am obviously not a scholar.)
frajo
not rated yet Mar 09, 2011
While I agree that Godel was way too careful to reach beyond the explicit implications of his incompleteness theories, I don't think that isn't because they are thusly limited. There was a discussion a couple of months ago regarding this on physics forums - physicsforums.com/showthread.php?t=455641.
Ultimately the anti-Godel argument had a stronger position in the thread, but I am not persuaded.
Thanks for the link. "Mathman" in PhysicsForums is right:
Godel's theorem is a mathematics foundation subject. It has nothing to do with physics (TOE).
But a lot of physicists obviously are not mathematicians.
(How could they, doing renormalizations all the day?)
Ian_Sandoval
not rated yet Mar 10, 2011
It seems so logical, and in some ways unnecessary. As an eleven year old I could have told you that you cant go back in time and kill yourself. I can also answer the question at the end of the article. You can't add info to a book from the same 'future book,' unless the book would have gotten that info without help from its future self. Basically, we cannot change the past. It's just simple logic. I guess the fact that people don't grasp that does give these experiments some necessity.
Skeptic_Heretic
not rated yet Mar 10, 2011
It seems so logical, and in some ways unnecessary. As an eleven year old I could have told you that you cant go back in time and kill yourself.
That's great, but you may indeed be wrong.

Typically when someone says "wow, that's so easy a child understands that" they point out that they have a gross misunderstanding of what science is and how it works.
MRBlizzard
not rated yet Mar 11, 2011
For stealthc,
I've given this some thought and the only ones I'd trust are Doctors Without Borders. And they would have to keep their heads down so the powers that be wouldn't twig on their prescience.
denijane
2 / 5 (1) Mar 24, 2011
The main problem in time traveling is actually non-physical. Because it is actually related to free will. "What if the traveler decides to kill X?". Physics doesn't work with free will. Every particle is confined to its configuration space and it moves trough it in a certain way that is directed by the forces around and/or space-time geometry. The problem of choice is simply irrelevant. It sounds like "what will happen if the Earth decides to stop spinning". The Earth cannot decide such thing, because it is directed on physical laws. Such event can happen under certain conditions, but not on a whim.
So the actual question in time travel is "what will stop you from killing your ancestors". Or what laws will keep the causality of events and are there any ways to break them. Because it's not free will that we should care about, it's causality. Free will is a fiction anyway.
JustJeff
not rated yet Mar 29, 2011
Why would one want to kill his grandfather anyway, it don't make sense to me.I subscribe to the theory that if time travel ever does become practical, one could ONLY travel back to the point that the "Machine" was invented, therefore it would be impossible to travel back and kill one's grandfather.

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