Time travel theory avoids grandfather paradox

July 21, 2010 by Lisa Zyga report
P-CTC time travel

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This figure shows CTCs through (a) conventional and (b) post-selected teleportation. Image credit: Seth Lloyd, et al.

(PhysOrg.com) -- The possibility of going back in time only to kill your ancestors and prevent your own birth has posed a serious problem for potential time travelers, not even considering the technical details of building a time machine. But a new theory proposed by physicists at MIT suggests that this grandfather paradox could be avoided by using quantum teleportation and "post-selecting" what a time traveler could and could not do. So while murdering one’s relatives is unfortunately possible in the present time, such actions would be strictly forbidden if you were to try them during a trip to the past.

The model of proposed by Seth Lloyd, et al., in a recent paper at arXiv.org arises from their investigation of the quantum mechanics of closed timelike curves (CTCs) and search for a . In simple terms, a CTC is a path of spacetime that returns to its starting point. The existence of CTCs is allowed by Einstein’s , although it was Gödel who first discovered them. As with other implications of his theories, Einstein was a bit disturbed by CTCs.

In the new paper, the scientists explore a particular version of CTCs based on combining with post-selection, resulting in a theory of post-selected CTCs (P-CTCs). In quantum teleportation, quantum states are entangled so that one state can be transmitted to the other in a different location. The scientists then applied the concept of post-selection, which is the ability to make a computation automatically accept only certain results and disregard others. In this way, post-selection could ensure that only a certain type of state can be teleported. The states that “qualify” to be teleported are those that have been post-selected to be self-consistent prior to being teleported. Only after it has been identified and approved can the state be teleported, so that, in effect, the state is traveling back in time. Under these conditions, time travel could only occur in a self-consistent, non-paradoxical way.

“The formalism of P-CTCs shows that such quantum time travel can be thought of as a kind of quantum tunneling backwards in time, which can take place even in the absence of a classical path from future to past,” the researchers write in their paper. “Because the theory of P-CTCs relies on post-selection, it provides self-consistent resolutions to such paradoxes: anything that happens in a P-CTC can also happen in conventional quantum mechanics with some probability.”

However, the scientists note that prohibiting paradoxical events would cause unlikely events to happen more often. These “strange and counterintuitive effects” arise due to the nonlinear nature of P-CTCs. Like a movie hero who always manages to escape seemingly imminent death, the grandfather would always somehow manage to survive his grandchild’s murderous plots. “Some little quantum fluctuation would whisk the bullet away at the last moment,” Lloyd explained.

In addition to prohibiting the grandfather paradox, the P-CTC theory also has the advantage that it doesn’t require the distortions of spacetime that traditional time travel theories rely on. These spacetime distortions probably only exist in extreme environments such as inside black holes, making these theories nearly impossible to realize.

Although post-selected computations are nonlinear and have not yet been shown to be possible, some studies have shown that quantum mechanics may be nonlinear and allow post-selected computations, which would potentially make quantum computing a very powerful technique. Such a computer could more efficiently solve a complex problem containing lots of variables by running all possible combinations of values and post-selecting only the combinations that solve the problem. This strategy would work much better than the classical strategy of trying different combinations until you get one that works. On the other hand, other studies suggest that must be linear, in part due to the seemingly impossible things that post-selection allows.

Still, the scientists hope that future investigations will reveal whether or not their theory is correct. They explain that the effect of P-CTCs can be tested by performing quantum teleportation experiments, and by post-selecting only the results that correspond to the desired entangled-state output.

“P-CTCs might also allow time travel in spacetimes without general-relativistic closed timelike curves,” they conclude. “If nature somehow provides the nonlinear dynamics afforded by final-state projection, then it is possible for particles (and, in principle, people) to tunnel from the future to the past.”

More information: Seth Lloyd, et al. "The quantum mechanics of time travel through post-selected teleportation." arXiv:1007.2615v2
via: The Physics ArXiv Blog and Science News

© 2010 PhysOrg.com

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Hesperos
Jul 21, 2010

Rank: 3.9 / 5 (15)
In summary, travel to the past would be possible, but changing it would not. A "time traveler" would be able to view the past, but would not be able to interact with it.

We already have this. It's called movies.
Skultch
Jul 21, 2010

Rank: 3.4 / 5 (10)
In summary, travel to the past would be possible, but changing it would not. A "time traveler" would be able to view the past, but would not be able to interact with it.

We already have this. It's called movies.


You could confirm things accused of revisionist historical accounts. That's not nothin.
Husky
Jul 21, 2010

Rank: 3 / 5 (1)
there is a classic SF story that goes abvout nature preventing these paradoxes by repeately killing civilisations, just as they are about to invent a working timemachine, by unexpected explosion of the host star and that sort of things
Sonhouse
Jul 21, 2010

Rank: 1 / 5 (1)
In summary, travel to the past would be possible, but changing it would not. A "time traveler" would be able to view the past, but would not be able to interact with it.

We already have this. It's called movies.


You could confirm things accused of revisionist historical accounts. That's not nothin.


Also, there is nothing in this theory, at least I think so, that would prevent you from going into the past, knowing a winning lottery # and leaving a note to your previous self. Any holes in that idea?
podizzle
Jul 21, 2010

Rank: 3.3 / 5 (3)
so we can go back in time but we can't change the present by altering the past. hurry this up so i can employ my parallel selfs for more antimatter fuel. Nano age cant come soon enough.
michaelick
Jul 21, 2010

Rank: 5 / 5 (1)
there is a classic SF story that goes abvout nature preventing these paradoxes by repeately killing civilisations, just as they are about to invent a working timemachine, by unexpected explosion of the host star and that sort of things


http://xkcd.com/716/
malapropism
Jul 21, 2010

Rank: 2.5 / 5 (2)
So would it be possible to post-select for *only* the paradoxical events to propagate, eliminating the self-consistent results?

(Of course, in this case you may not see anything happen, since a paradox is involved but it might be feasible to devise an experiment to indicate an outcome of sorts.)
malapropism
Jul 21, 2010

Rank: not rated yet
Also, there is nothing in this theory, at least I think so, that would prevent you from going into the past, knowing a winning lottery # and leaving a note to your previous self. Any holes in that idea?

If you have won the lottery in your existent past then you may have done exactly this but if you have not yet won the lottery, surely the act of giving your past self a winning number combination changes the present?

However, it seems to me that if inconsistent, paradoxical events can be post-selected as well as self-consistent, non-paradoxical events then you could feasibly post-select for final-states where you have won the lottery despite not already having been a winner of the lottery in the past?

(Hence the point of my question above. The Arxiv paper seems to indicate that paradoxical post-selection may be allowed but I don't follow the math involved to know for sure; the authors seem to be unsure too, which makes me feel slightly better about my [lack of] understanding.)
DamienS
Jul 21, 2010

Rank: 4 / 5 (4)
"In quantum teleportation, quantum states are entangled so that one state can be transmitted to the other in a different location".

No, nothing is being 'transmitted', that's the whole point of quantum entanglement or 'spooky action at a distance'.
Starblade_Enkai
Jul 21, 2010

Rank: 1 / 5 (2)
Yeah I'd use that kind of time machine, but wouldn't it cause rips in the spacetime continuum?
malapropism
Jul 21, 2010

Rank: 3 / 5 (2)
"In quantum teleportation, quantum states are entangled so that one state can be transmitted to the other in a different location".

No, nothing is being 'transmitted', that's the whole point of quantum entanglement or 'spooky action at a distance'.

But surely it can't be stated unequivocally that nothing is transmitted until the mechanism for the "spooky action at a distance" is known?

My understanding (open to correction) is that we can't yet *detect* anything being transmitted and that the 'how' of entanglement and teleportation of entangled quantum states is not currently known. Perhaps nothing is transmitted (maybe what we see as the entangled particles are the 'end-points' of a string or something): it may one day be proved how the quantum state teleportation occurs but even if the 'how' never is proved and all known possibilities are eliminated, "nothing is transmitted" is also not falsifiable so can never be a definitively true statement.
malapropism
Jul 21, 2010

Rank: 3.8 / 5 (6)
Yeah I'd use that kind of time machine, but wouldn't it cause rips in the spacetime continuum?

Nah, according to the Dr, it's all complicated "wibbly, wobbly, timey-wimey stuff" and allows this sort of thing to happen anyway.
Skeptic_Heretic
Jul 21, 2010

Rank: 4 / 5 (3)
Truth is, viewing the past may be possible if you can track each and every particle that was present, reading their information and replaying it. Perhaps you can determine it with enough knowledge by simply following the laws of probability and "rewinding time", but, I highly doubt any form of travel will be possible based on the fact you'd probably have some form of feedback preventing the exchange of information without causality.
MorituriMax
Jul 21, 2010

Rank: 1 / 5 (1)
Why can't we just invent a time-camera that can film whatever is happening at a specific (down to the meter and second) place and time in the past? Filming it in 1080p detail and with night vision if needed?

I wonder if knowing the past in that kind of detail would make us god-like AFTER the fact?

Example 1: A bomb goes off on an airliner, killing everyone aboard. In a series of steps we use our time camera to go further and further back in time, narrowing down the events that led to the bombing. Eventually we identify all the people who planned and carried out the crime, track them down and arrest them. The time-camera evidence is presented and they are sentenced to life in prison.

Example 2: We film the murder of Ron Goldman and Nicole Simpson with the time camera. There is no obfuscating or misunderstanding possible as to what we see.

So would being able to see what HAS happened in the past be almost as effective a tool as seeing the future, ie what HASN'T happened?
MorituriMax
Jul 21, 2010

Rank: not rated yet
Wow, skeptic must have been reading my mind as I was typing.. heh
DamienS
Jul 21, 2010

Rank: 3 / 5 (2)
"Perhaps nothing is transmitted (maybe what we see as the entangled particles are the 'end-points' of a string or something)"

Even if a state is connected by a 'string', yanking at one end would not cause a tug instantaneously at the other - there would still be a propagation delay (much slower than c, the ultimate speed limit).

"it may one day be proved how the quantum state teleportation occurs but even if the 'how' never is proved and all known possibilities are eliminated, 'nothing is transmitted' is also not falsifiable so can never be a definitively true statement".

In fact it's proved. The quantum states are decided instantaneously, ie faster than c, but no informationn is exchanged, so it can't be used for communications.
nuge
Jul 21, 2010

Rank: not rated yet
The time-viewer concept is far from pointless. Read "The Light of Other Days" by Arthur C Clarke
jabo
Jul 21, 2010

Rank: 4.3 / 5 (3)
So it'd be the tv show Big Brother - Time Machine Edition. Or a history channel where you actually watch history. How do you choose a point of view for the 'camera', or how does one localize your viewpoint? I guess software would recreate the world and we would pan around in it? far out.
also, I guess there would be no barrier as to where we could look, so we could watch Kim Jung Ill sitting in a submarine from 1 second ago? I'd watch that.
daywalk3r
Jul 21, 2010

Rank: 3.5 / 5 (4)
So this is what they do @ MIT when they are bored?

Interesting..

..not the fact that they are talking time-travell, but that they are bored :D
toocool
Jul 22, 2010

Rank: 4.5 / 5 (2)
So this is what they do @ MIT when they are bored?

Interesting..

..not the fact that they are talking time-travell, but that they are bored :D


What? Who said they were bored?
daywalk3r
Jul 22, 2010

Rank: 1 / 5 (1)
What? Who said they were bored?
Alice & Bob obviously..

Just not sure which one was from the future, and which one from the past ;-)

"Bored" as in "nothing better to do" ..
Or did they come up with it durring the lunch break?

In that case, Bon appetit! :-)
taka
Jul 22, 2010

Rank: 1.3 / 5 (3)
How do we know that the Time is coordinate? Most likely it is not, just math the Einstein use MODELS it like coordinate. To travel into past the past must still exist, where? Where come all this energy to retain a copy of everything for a cease somebody want to travel into past?

I is also not possible to recreate the past by tracing all and every particle in the present. It is not possible to track into past even if you have just three ideal point particles, equations of there movements give infinitely many possible solutions for rather resent past.
taka
Jul 22, 2010

Rank: 1 / 5 (5)
And how we know that c is ultimate speed limit? We do not, it is just speculation and belief that if even light cannot then also information should not. It is also not clear that the space itself is real. Again, it is MODELED as coordinate system, but what is it really? It may be that space is just created by mass. You know, if there is a mass near bay the space become denser. So, if there is no mass, the space density can be just zero. Space is noting else then time the light need to travel throw it, meaning aktually there is nothing between, just light is slowed down by mass.
Husky
Jul 22, 2010

Rank: 5 / 5 (1)
it is possible to recreate a previous state for a simple system, like reordering a pack of shuffled cards, but when the system/entropic state gets more complicated, like unbreaking eggs, the amount of information about the system and energy needed to reshuffle billions of particles grows way above our heads, we can either roughly replicate a system on macro level, by recycling/melting broken glass to make it look the same for the casual viewer, or handle a system on nano level, comprising of just a few quantum dots, shielded/"delocalized" from the environment
taka
Jul 22, 2010

Rank: 1 / 5 (4)
Past cannot be reconstructed from present not because there is too much information needed. Any information about present is not enough as there are probabilistic processes involved when present is generated. Some information just gets lost in the process.
Magus
Jul 22, 2010

Rank: not rated yet
Why is it that we assume that the Paradox is even a problem? What if traveling back is more like just popping into existence in that particular time. My lack of knowledge "is" the reason I am asking.
CSharpner
Jul 22, 2010

Rank: 2.3 / 5 (4)
Regarding paradoxes: 8t would seem that free will is "suspended". Physics might allow for this, but only for outcomes that didn't already produce a paradox. You would be able to interact with the past (assuming physics allowed for this type of travel), but you'd discover how your actions were part of the "past" that you're now experiencing. Any attempt to change anything would fail; because it already did... you're just now discovering how you failed. You may even discover that in your attempt to change history was the very catalyst that caused it to turn out the way it did.
Skeptic_Heretic
Jul 22, 2010

Rank: 4.8 / 5 (6)
Regarding paradoxes: 8t would seem that free will is "suspended". Physics might allow for this, but only for outcomes that didn't already produce a paradox
Nothing in physics requires free will. Everything is predetermined based upon the rules of nature and prior occurances through causality.
CSharpner
Jul 22, 2010

Rank: not rated yet
Skeptic, well said.

I hope no one read "physics may allow for this" thinking I meant "may allow for free will". It was "may allow for this type of time travel".

I'm skepticle that physics would allow for any kind of time travel, but if it did, I'm certain it'd have to be without paradoxes (hence the necessity for no free will). It would be a good example to demonstrate how free will really doesn't exist.
flhu
Jul 22, 2010

Rank: 3 / 5 (1)
If T-travel into the past is possible, ALL possibilities should be reset, not just the ones you interact with. Like the lottery winner scenario, if you got the daily numbers from yesterday and then went back in time to purchase the ticket, as you travel forward (either by machine or by just sitting it out) when the lottery numbers are drawn, they will be chosen at random again. The chances of winning /something/ are potentially greater, but winning the jackpot would not be a slam dunk.
Donutz
Jul 22, 2010

Rank: 4 / 5 (1)
For one of the best stories on past-time viewing (IMO) get "The Light of Other Days" by Steven Baxter and AC Clarke.

Anyway, this theory isn't really new. Lots of SF stories have handled variations on it. It goes like this:

You go back and kill your grandfather. That creates a timeline where you didn't get born, so you didn't go back and kill him, etc. Because there's some inertia in the time dimension, these loops actually execute consecutively. Because of quantum uncertainty, they're never exactly identical. Eventually a loop happens where the gun blows up and kills you instead of your grandfather, and the paradox disappears and the timeline stabilizes. So *any* paradox loop will execute until it self-heals. All we "remember" is the last loop with the unlikely save.
VOR
Jul 22, 2010

Rank: 3.5 / 5 (4)
oh but then there's the more sound idea that all of this is utter nonsense. Forward travel is more interesting since it's actually possible. The arguments against backward are much stronger than for. And its annoying the way the theory is about the quantum level, but everyone loves to apply it to the macro world. Its only with math you can show it, not reality. For example you can have a negative number but you can't literally have negative items.
People talk and theorize about this because its popular, not because it has potential to produce direct results. But it could accidently acheive something unrelated.
Sir_Bedivere
Jul 22, 2010

Rank: 5 / 5 (4)
I can't accept this idea. Maybe its because I don't understand the full theory but this sounds a little too much like a "God" theory.

How would the universe correct itself? When would this countermeasure begin and what triggers it? Why would the universe correct itself? Why does it only accept specific events? Is the universe self aware? Wouldn't going back in time to begin with change the universe? When I emerged from my time vehicle and made my first steps would countermeasures be in place to prevent me from disturbing the ground? What if I went back in time to kill someone else, would those countermeasures prevent me from doing so?

Just way too many meta questions can be created when you apply this to something bigger than time travel between quantum states of two particles.
0c4pnh4nk
Jul 22, 2010

Rank: 5 / 5 (1)
Yeah I'd use that kind of time machine, but wouldn't it cause rips in the spacetime continuum?


Q could fix it.
Donutz
Jul 22, 2010

Rank: 1 / 5 (1)
How would the universe correct itself?


Read my post again. I specifically deal with this. Doesn't require a god or a self-aware universe. It's just a feeback cycle that continues until one of the iterations *happens* to damp out the paradox.

And VOR: Even if you don't believe in the possibility, it's still fun to talk about. You do understand *fun*, right?

frajo
Jul 22, 2010

Rank: 4 / 5 (4)
Nothing in physics requires free will.
Sure. But that's not sufficient to state there is no free will. As nothing in physics requires human beings.
Everything is predetermined
"Predetermined" is different from "determined" and "determinable" but is unfortunately associated with "predestination" which is a religious term.
based upon the rules of nature and prior occurances through causality.
Radioactivity? Which rule of nature predetermines which particles in a macroscopic radioactive body decay first, second, etc?
Prior occurrence? What is the series of prior occurrences leading to the event of "inflation" in the standard model of cosmology?
Causality? The QM phenomenon of entanglement violates the principle of locality. This cannot be modelled using the concept of causality.
Ritorix
Jul 22, 2010

Rank: 2.8 / 5 (6)
The grandfather paradox is just silly. If someone killed their own grandfather, they would return to their place in the new timeline and no one would know who they were. They don't exist in the new timeline, but its one hell of a leap to assume the actual time traveler somehow ceases to exist at all. Energy cannot be destroyed and the time traveler continues to exist, even if he traveled back in time only 5 minutes and killed himself.

Not that it matters. There is no going back.
rwinners
Jul 22, 2010

Rank: 5 / 5 (1)
I cannot believe that 'physicists' are spending time even considering this. What a waste.
braindead
Jul 23, 2010

Rank: not rated yet
Eventually a loop happens where the gun blows up and kills you instead of your grandfather, and the paradox disappears and the timeline stabilizes. So *any* paradox loop will execute until it self-heals. All we "remember" is the last loop with the unlikely save.

Whoops - I just killed myself back then so how am I back here now?
james11
Jul 23, 2010

Rank: not rated yet
People need to decide what gets funded and where money goes. There are war veterans on the street while people are trying to go back in time...
frajo
Jul 23, 2010

Rank: not rated yet
Not that it matters. There is no going back.
It's one of those cases where a mathematical solution (in a model) doesn't translate into physical reality. Like the tachyon, like the BigBang singularity.
It's one of those decision problems which are not (yet?) computable but need human interpretation.
Syzygy
Jul 23, 2010

Rank: not rated yet
I can accept that the time dimension of the past and future exists, but does an 'image' of our time-frame still exist on that line for us to travel to that point in time? If you say 'yes' then it suggests that energy within the universe is infinite to maintain every moment in the past, if you say 'no' then if you travel back in time you will be the only thing existing in that time-frame, but the energy balance will be maintained.

The same for travelling into the future, does our future exist, or are there infinite predefined futures. Again time may exist as a dimension but is there anything on it outside of our own time-frame?

Skeptic_Heretic
Jul 23, 2010

Rank: 2.3 / 5 (3)
Sure. But that's not sufficient to state there is no free will.
Causality effectively removes the entire concept of free will, as your will is not free but bound by limiting chemical interactions.
Radioactivity? Which rule of nature predetermines which particles in a macroscopic radioactive body decay first, second, etc?
The strong and weak nuclear forces for the most part.
Prior occurrence? What is the series of prior occurrences leading to the event of "inflation" in the standard model of cosmology?
Causality? The QM phenomenon of entanglement violates the principle of locality.
How exactly does this violate causality? Your first question is just silly. Something caused inflation, not knowing what it was doesn't prevent causality.
This cannot be modelled using the concept of causality.
Just because you don't know the cause doesn't mean there was no cause.
Syzygy
Jul 23, 2010

Rank: not rated yet

To travel into future or past isn't so difficult, as quantum fluctuations are doing it all the time: they're "breathing" and expanding and collapsing less or more irregularly like density fluctuations inside of gas.


With such irregularity our past must no longer exist in a recognisable state, supporting the idea that time travel to our own past must be impossible.

At a quantum level particles may permeate time but each time they pass though my time-frame they will be different. So even if I could time-travel at a quantum level I would not come back the same being.
Skeptic_Heretic
Jul 23, 2010

Rank: 3.7 / 5 (3)
Your opinion is based on the assumption, all hidden states are really distinguishable each other for us.
My "opinion" is based on causality. Nothing can occur without a cause.
If you want to talk about the philosophy behind free will and apply science to it there is only one method that is congruent with all observation. Materialistic Determinism. In order for you and I to have this conversation, we must have been born first. If all of the chemical reactions, and yes they are incredibly numerous, occur exactly as they had prior, then you and I will be having this conversation.
Skultch
Jul 23, 2010

Rank: 5 / 5 (3)
It still amazes me how many "educated" people have never discussed the free will vs god's omniscience problem. It's probably the most straight forward philosophical argument out there. Some people just believe what they want to believe.
Skeptic_Heretic
Jul 23, 2010

Rank: 1.7 / 5 (3)
It still amazes me how many "educated" people have never discussed the free will vs god's omniscience problem. It's probably the most straight forward philosophical argument out there. Some people just believe what they want to believe.
Why would you even go there? A creatorless creator while demanding a cause for the Universe is enough to create a logic loop that is inescapable.

You want to remove the whole God aspect from a discussion ask a simple question: Why would God have been so localized. He seems very interested in what happens to the Jewish people while not even mentioning other people, let alone other planets, stars, galaxies, etc. It's useless to debate God jsut as it is useless to debate santa claus.
Skeptic_Heretic
Jul 23, 2010

Rank: 1 / 5 (1)
Indeterministic, statistic character of quantum mechanics violates this view.
No it doesn't. Show an example where QM violates causality.
otto1923
Jul 23, 2010

Rank: 2.3 / 5 (3)
Truth is, viewing the past may be possible if you can track each and every particle that was present, reading their information and replaying it. Perhaps you can determine it with enough knowledge by simply following the laws of probability and "rewinding time", but, I highly doubt any form of travel will be possible based on the fact you'd probably have some form of feedback preventing the exchange of information without causality.
Yeah, information is apparently the one thing that never dies-
otto1923
Jul 23, 2010

Rank: 2.3 / 5 (3)
Radioactivity? Which rule of nature predetermines which particles in a macroscopic radioactive body decay first, second, etc?
One of the ones we havent discovered yet.
Prior occurrence? What is the series of prior occurrences leading to the event of "inflation" in the standard model of cosmology?
The series we havent discovered yet.
Causality? The QM phenomenon of entanglement violates the principle of locality. This cannot be modelled using the concept of causality.
No, not with the tools we have developed to date. Doesnt mean we wont EVER do so, or that we need to draw conclusions NOW.
otto1923
Jul 23, 2010

Rank: 3 / 5 (2)
It still amazes me how many "educated" people have never discussed the free will vs god's omniscience problem. It's probably the most straight forward philosophical argument out there.
Yeah it is pretty straightforward. God doesnt exist. So its a non-argument.
Some people just believe what they want to believe.
Some base their beliefs on evidence and some base theirs on selfish desires- the desire to avoid death, to have wishes granted, to feel special enough to warrant special treatment. The desire to manipulate others by exploiting their own selfish desires is a big one.
Skeptic_Heretic
Jul 23, 2010

Rank: 3 / 5 (4)
@SH: Did you hear about uncertainty principle?

You cannot never measure the pair of conjugate variables with unlimited precision - the rest is simply indeterministic there. From the same reason we never measured quantum function directly.

Don't try to use it as evidence for your stance if you don't understand it.

In quantum mechanics, the Heisenberg uncertainty principle states by precise inequalities that certain pairs of physical properties, like position and momentum, cannot simultaneously be known to arbitrary precision.

Now this doesn't mean that nothing can be known, it simply means, the more precise your measurement of one attribute, let's say speed, the less precise your conjugate measurement, example position, can be. Meaning you would not be able to determine speed and location instantaneously with perfect precision of both measurements. This means nothing in terms of post measurement. Again, practical knowledge is key here.
Skeptic_Heretic
Jul 23, 2010

Rank: 3.7 / 5 (6)
Some base their beliefs on evidence and some base theirs on selfish desires- the desire to avoid death, to have wishes granted, to feel special enough to warrant special treatment. The desire to manipulate others by exploiting their own selfish desires is a big one.
It's primarily based on fear. The god fearing don't fear god, they fear dying and leaving behind a lilfe that was utterly worthless in the scope of the world. Some people need a purpose to be given to them because they're afraid to develop their own.

Religion is for the fearful, that's about all there is to it.
Skultch
Jul 23, 2010

Rank: not rated yet
It still amazes me how many "educated" people have never discussed the free will vs god's omniscience problem. It's probably the most straight forward philosophical argument out there. Some people just believe what they want to believe.
Why would you even go there? A creatorless creator while demanding a cause for the Universe is enough to create a logic loop that is inescapable.


I go there because of the social situation I find myself. I choose not to escape these beliefs, because I enjoy debates with religious people who also enjoy debate. I feel limited if I ignore all the debates that I am "beyond," and I also enjoy enlightening others with pure logic.

My post was not meant to further the specific debate in this thread, but to see what others like me(?) feel about the refusal of logic in the human community. Thanks for your input.
Skeptic_Heretic
Jul 23, 2010

Rank: 1 / 5 (1)
this doesn't mean that nothing can be known.

This doesn't mean, I'm saying so...:-) I'm saying, something will remain always unknown/hidden by quantum mechanics. I.e. not everything - if you can spot the difference.

For example, superluminal speed of information spreading means, you cannot detect its source with certainty.

http://www.physor...526.html

So you're not saying it but you are saying it...
First, nothing travels at superluminal speed. Not even information (as far as we know).
Second, you haven't provided an example, and it appears you haven't done so because you're unable to.

The only thing that will never be known with any sort of certainty is whether you're actually trolling or just that bad at reading. Quantum Mechanical determinism isn't a philosophical question, it is a mechanical question. You're inventing possibilities that have no observational evidence. You cannot use those developments to create your own reality.
Skeptic_Heretic
Jul 23, 2010

Rank: 1 / 5 (1)
I feel limited if I ignore all the debates that I am "beyond," and I also enjoy enlightening others with pure logic.
So would you think arguing whether the sky was blue is a worthy pursuit?

Everything can be argued, not everything is worth arguing.
croghan27
Jul 23, 2010

Rank: not rated yet
there is a classic SF story that goes abvout nature preventing these paradoxes by repeately killing civilisations, just as they are about to invent a working timemachine, by unexpected explosion of the host star and that sort of things


There is another one where a time tourist squashed a bug .... as they return they can see the lights on thweir civilization flickering out, one by one ... (Ray Bradbury? Theodore Sturgen?)
otto1923
Jul 23, 2010

Rank: 1 / 5 (1)
It's primarily based on fear. The god fearing don't fear god, they fear dying...

Religion is for the fearful, that's about all there is to it.
"Fears of dying, growing old,
We ran the race, the race was run, by running slowly." -Jethro Tull

-We're all fearful of something or other I suppose. Religionists lack patience and courage to a significant degree. And the ability to accept the inevitable, and to cope with it. Yes?

They became distrustful of reality at some point, maybe because they never knew it very well; enough to abandon it for the comfort and companionship that fantasy could provide. Hordes of mickey mice.

God is a big teddy bear.
Jigga
Jul 23, 2010

Rank: 1 / 5 (3)
nothing travels at superluminal speed. Not even information (as far as we know) ...you haven't provided an example..
From article above linked by VestaR:

..."After performing multiple tests on two entangled photons, physicists have yet again found that the photons seem to be communicating faster than the speed of light - at least 100,000 times faster. The researchers hope that their results might encourage theorists to come up with new explanations for the strange quantum mechanical effect. "...

Religious people like you don't require any evidence, actually. If they get it, they're simply ignoring it like ghosts.
Husky
Jul 23, 2010

Rank: not rated yet
by definition, paradoxes don't exist, just like we don't find that barber that shaves all men that don't shave themselves, we will never find that grandfather to kill, the implication is that we cannot do a full rewind of the tape, maybe we can recreate more or less a cloned grandfather, but his grandson is not you
otto1923
Jul 23, 2010

Rank: 3.7 / 5 (3)
I bin bitch-slapped by jigga and vestaR on the same post- 2 avatars of one -?- I guess aether religionists are most afraid of derision. Be strong alizee- like khreisst. Present your other cheek for to being slapped.
Skeptic_Heretic
Jul 23, 2010

Rank: 3 / 5 (2)
Religious people like you don't require any evidence, actually. If they get it, they're simply ignoring it like ghosts.
Quote mining a popsci article, ha.

Information isn't being transmitted, nothing is transmitted during entanglement. Thank you for again showing that you're unable to decipher what you're reading.
Skultch
Jul 23, 2010

Rank: 5 / 5 (2)
I feel limited if I ignore all the debates that I am "beyond," and I also enjoy enlightening others with pure logic.
So would you think arguing whether the sky was blue is a worthy pursuit?

Everything can be argued, not everything is worth arguing.


If it concerns the relative neurological underpinnings on the perception of color, then maybe. Nice snarky comment, though.

True, but life's a journey, not a destination. For me, sometimes a good old fashioned god's existence debate is fun. Sure, I've come to my own atheistic conclusions (probably very similar to yours), but sometimes I enjoy crushing a theist in debate. Maybe it's my arrogance, maybe I like teaching philosophy 101 with youngsters. Whatever.

For me, it's not always about finding a fundamental truth in every argument. Sometimes I'm just in the mood for a pointless, yet fun argument with someone who thinks differently than me. Why do you continue your "debates" with Jigga/VestaR?
james11
Jul 23, 2010

Rank: not rated yet
Does God exist? Does a squirrel go to heaven? A dog? A monkey? No.
Skultch
Jul 23, 2010

Rank: 5 / 5 (2)
Does God exist? Does a squirrel go to heaven? A dog? A monkey? No.


Monkeys go to normal heaven, dogs go to animal heaven. C'mon, everyone knows this. :)

What if a monkey goes back and kills his grandfather. He doesn't have a soul, so who cares, right? The monkey just disappears the moment his existence becomes impossible.

Or..... maybe every moment (quanta?) of time is independent from the previous or the next, time and space are just reference points, there is no such "thing" as spacetime, and Einstein was trying to make math for physics extremes easier and it just "seemed" like he was discovering more reality.
Jigga
Jul 23, 2010

Rank: 1 / 5 (5)
Actually it turns out, the God is another archetype, which could have its rational meaning in connection to existence of hidden reality (aether, extra-dimensions or parallel Universes). Just compare the omnipresence of deity with omnipresent character of quantum fluctuations and/or the fact, the high information density appears like random chaos from low-dimensional perspective.
james11
Jul 24, 2010

Rank: 1 / 5 (2)
Anyone wanna switch it up and talk about or share dreams? Or has anyone ever felt like there is another you out there? Or maybe the possible abilities a species could gain evolving on a different type of planet? I am very bored.
james11
Jul 24, 2010

Rank: 1 / 5 (2)
I dont know what to call it but one time this guitar solo made me dream while I was awake and it was very powerful. No I wasnt on any drugs.
CSharpner
Jul 24, 2010

Rank: not rated yet
In summary, travel to the past would be possible, but changing it would not. A "time traveler" would be able to view the past, but would not be able to interact with it.


A time traveler could interact. If they attempted to change anything they know happened, they'd discover how they originally failed. They may even discover that they were directly or indirectly part of the events that lead up to the event they were trying to prevent. In short, they were already part of that history before their younger self was aware of it. And now, they're simply discovering how they originally played a part in it.

This is how non-paradoxical time travel would work.
CSharpner
Jul 24, 2010

Rank: not rated yet
Many newbs to QED (myself inluded earlier on), when learning of the delayed choice experiment, fathom using it to transmit classical info back in time. To the dismay of them all (well, the ones that research it in a little more depth) learn that one must "wire up" a coincidence counter to separate the early receiced "receptor" photons from the noise ones and this information cannot be known until after the future time when the "signal" is sent back, meaning you can't decode the future signal (or even know if one was sent) until adter the future signal is sent.

John Cramer gave an explanation of how to differentiate early received, entangled photons from noise photons. In theory, he should be able to transmit actual, classicle data back in time and decode it before it was sent. He accepted private donations (~$30,000) to set up the experiment. He dissapeared off the net a year or so before it was to be done. I'd love to hear what the results were. Even failing should teach us.
frajo
Jul 24, 2010

Rank: 3.7 / 5 (3)
I bin bitch-slapped by jigga and vestaR on the same post- 2 avatars of one -?
Yes, it's the cheater at work. It's his way to answer your comment "Usually you are doing quite well".
Ravenrant
Jul 24, 2010

Rank: 5 / 5 (1)
ANY kind of time travel to the past requires that the exact state of every particle in the universe at every instantaneous moment throughout all time is not only still here but accessible. BS, time travel to the past ain't happenin and people that theorize about it are idiots.
Skeptic_Heretic
Jul 24, 2010

Rank: 4 / 5 (4)
@skultch,

You're right, it was a little snarky, my apologies.
For me, it's not always about finding a fundamental truth in every argument. Sometimes I'm just in the mood for a pointless, yet fun argument with someone who thinks differently than me. Why do you continue your "debates" with Jigga/VestaR?
To prevent people from accepting his pseudoscience as fact.
Jigga
Jul 24, 2010

Rank: 1 / 5 (5)
To prevent people from accepting his pseudoscience as fact
You can demonstrate my factual errors instead - it would be a much more effective, then the some obstinate downvoting without arguments. I'm just trying to prevent people from accepting of my theory as pseudoscience with using of arguments and explanations. You cannot win without any arguments at all.
otto1923
Jul 24, 2010

Rank: 4.2 / 5 (5)
You can demonstrate my factual errors instead - it would be a much more effective, then the some obstinate downvoting without arguments.
I think theyve been through the 'factual errors' stage without effect, passed through the 'rational argument' stage with no reasonable response, and are now trying to demonstrate that your nefarious posting methods belie an inherently untrustworthy poster with compulsive-neurotic tendencies and perhaps a schizoid personality. Again, I'm just trying to clarify things here.

When you look in the mirror sir, what do you see? Is it you or only someone who looks like you?

And again, its 'than' rather than 'then'. The rest of the sentence needs a total rewrite.
otto1923
Jul 24, 2010

Rank: 3.7 / 5 (3)
Has anyone here ever seen disagreement among with alizee/jigga/vestaR etc personas? Now that would be entertaining.
From article above linked by VestaR:
Although he does reference himself- thats a start- but otto has also done that. Otto however knew it was himself he was referencing- does jigga realize this same thing or no?
Husky
Jul 25, 2010

Rank: 5 / 5 (1)
true timetravel would imply that all obejcts/events in the known universe would have to be reset to their previous state, this takes energy, and as the universe has a habit of seeking the lowest energy state, it would mean we have to push the whole universe back uphill, this would take more energy than contaqined in the universe itselve?
Audai_Louri
Jul 25, 2010

Rank: not rated yet
The real question, is time travel by its self a paradox. Let's say I go back in time to change something in my life, now back in the present the reason I traveled back in time does not exist, therefore I do not have a reason to travel back in time. Does that mean time travel never occurred.
MadPutz
Jul 25, 2010

Rank: not rated yet
The only feasible type of "time-travel" would be simulating the entire universe, then entering an instance of a certain time. It would be a copy, a virtual reality, but that doesn't matter - it will still play out with realistic consequences if the universe is truly simulated.
Skeptic_Heretic
Jul 25, 2010

Rank: 4.2 / 5 (5)
You cannot win without any arguments at all.
Then why do you keep trying to? Your "theory" makes no arguments, observations, or refutations of more complete and compelling theories. You're a 9/11 conspiracy theorist amongst structural engineers in your debates.
Erik
Jul 25, 2010

Rank: 5 / 5 (2)
John Cramer's "A Transactional Interpretation of Quantum Mechanics" contains an explanation for a "post-selection" mechanism.

He cites an example where a photon is emitted (event 1) & later absorbed (event 2). If each event emits psi waves that travel both forward & backwards in time, then the backward traveling wave from event 2 will modify event 1 & the modified event 1 will create a modified forward traveling wave that modifies event 2 ad infinitum. Thus, you get an infinite series of such waves that sum to zero before event 1 & after event 2, but in between events, they form a 4D space-time standing wave.
Erik
Jul 25, 2010

Rank: 5 / 5 (2)
John Cramer's "A Transactional Interpretation of Quantum Mechanics" continuation:

It resolves spooky action at a distance as signals between the entangled particles spend half their time traveling backwards in time to the moment they were created & half their time then traveling forward to the other entangled particle. This would create the appearance of instantaneous action even though none of the signals ever exceeded the speed of light.

This also resolves delayed choice experiments as the delayed choice is still before event 2 occurs & thus, blocks one of the possible 4D space-time standing waves. So it appears as if the particle wave made a post-selection to not travel along the path the ends up being blocked.

If one was to link multiple events together, it seems to me that Cramer's model would automatically lead to the sort of post-selection needed in this article to prevent you from killing your own grandfather. (FYI Cramer works at the University of Washington - iirc.)
james11
Jul 25, 2010

Rank: 1 / 5 (2)
Ravenrant-BS, time travel to the past ain't happenin and people that theorize about it are idiots.

I feel the exact same, as I said before there are people on the streets that have fought for this country while other people are completely wasting time on things like going back in time and looking for habitable planets that are too far away in the first place. We need to focus our brilliant minds on the tasks at hand.
Husky
Jul 25, 2010

Rank: not rated yet
one can simulate an entire copy of a small universe if you make a cloned image of your hard disk, if later on, after changes, you restore the image, it looks as if your little desktop universe has traveled back in time. Now lets think of our image as the Grandfather, included in the image is a Grandson, a timed program that is set to delte the complete harddrive, including the image. It is entirely possible for this grandson to carry out this action, because no true time travel has happened the events actually play out in the future, in a cloned version of the past
frajo
Jul 25, 2010

Rank: 1 / 5 (3)
there are people on the streets that have fought for this country
Only for the upper ten thousand of the country.
mgenest001
Jul 25, 2010

Rank: 4 / 5 (4)
This theory seems to only take into account one possible universe. However, if the multiverse theory is correct, than the paradox can be overcome because it isn't a paradox at all.

Perhaps the Grandson can exist in both possible universes with both possible outcomes at the same time, that is, the Grandfather being dead and not dead. Schrodinger's cat. It's not a paradox, because the Grandson still exists in another universe where his Grandfather did not die. His past is already written. He is only changing his 'future' by going into what seems to be his past, which by doing so, ceases to become his original universe and becomes another where his Grandfather is dead. In fact, if time is not linear, than this would be an instance of the future influencing the past.

Of course, this is a simplistic thought experiment which, to make sense, would probably need to assume that universes are more like infinite dimensions that can exist simultaneously.
frajo
Jul 26, 2010

Rank: 3.7 / 5 (3)
However, if the multiverse theory is correct, than the paradox can be overcome because it isn't a paradox at all.
It's not a theory; it's one (of many) interpretation(s) of the theory known as quantum mechanics. You may like it, you may prefer it to other interpretations of QM, but you'll never convince the majority of scientists for several reasons.
One of these reasons is that you never can be sure whether it is correct or wrong as it is not falsifiable.
Another reason is its violation of the reasoning in Ockham's razor: You have to avoid unnecessary entities.
Skultch
Jul 26, 2010

Rank: 3.7 / 5 (3)
@skultch,

You're right, it was a little snarky, my apologies.
For me, it's not always about finding a fundamental truth in every argument. Sometimes I'm just in the mood for a pointless, yet fun argument with someone who thinks differently than me. Why do you continue your "debates" with Jigga/VestaR?
To prevent people from accepting his pseudoscience as fact.


No worries about the snark. :) I find it unavoidable, myself, sometimes.

I couldn't thank you enough for your fight vs his BS. I'm new to PhysOrg and learning more every day about how people behave here. I initially wondered why people didn't just ignore those posts, but I now see how relentless he is. You fight the good fight. :) He appears to have a theistic theory that he works back from, which, in a way, is the opposite of science.
CHollman82
Jul 26, 2010

Rank: 1 / 5 (1)
Radioactivity? Which rule of nature predetermines which particles in a macroscopic radioactive body decay first, second, etc?


Not knowing how/why something happens is NOT evidence that it is impossible to know that.

Prior occurrence? What is the series of prior occurrences leading to the event of "inflation" in the standard model of cosmology?


None.

But the point you are trying to make is fallacious because it assumes the standard model of cosmology is both complete and correct.

Causality? The QM phenomenon of entanglement violates the principle of locality. This cannot be modelled using the concept of causality.


And again you are using what we don't know as evidence for something, which is blatantly fallacious.

We do not know that the effects of quantum entanglement are instantaneous, and we never will, because it is impossible to measure instantaneous change as instantaneous, unless you want to arbitrarily put an upper limit on time resolution...
Jigga
Jul 26, 2010

Rank: 1 / 5 (3)
..we do not know that the effects of quantum entanglement are instantaneous, and we never will
Never say never.

Scientists at Geneva in Switzerland began with entangled pairs of photons, or packets of light. These pairs were then split up and sent over fiber optic cables provided by Swisscom to stations at two Swiss villages some 11 miles (18 kilometers) apart from each other. The stations confirmed that each pair of photons had remained entangled.

For any hidden signal to travel from one station to the other in just 300 trillionths of a second, any such x-factor had to go at least 10,000 times the speed of light.

http://www.nature...038.html
Skeptic_Heretic
Jul 26, 2010

Rank: 3 / 5 (4)
..we do not know that the effects of quantum entanglement are instantaneous, and we never will
Never say never.

Scientists at Geneva in Switzerland began with entangled pairs of photons, or packets of light. These pairs were then split up and sent over fiber optic cables provided by Swisscom to stations at two Swiss villages some 11 miles (18 kilometers) apart from each other. The stations confirmed that each pair of photons had remained entangled.
Which simply means we don't know how it happened. It does not prove superluminal speed. One can jsut as easily infer that hyperspace exists, or that the two particles created a wormhole and violated space time but neither of these two possibilities are proved by the experiement and subsequent observation.
CHollman82
Jul 26, 2010

Rank: 2.3 / 5 (3)
Never say never.


That's great and all, but my point was to the impossibility of measuring something to be instantaneous... Due to the fact that for any distance from the origin to the destination and for any resolution of time that you can detect there is always a longer distance and finer resolution measurements of time.

Furthermore, even if we detect an effect that that would have to propagate at 10,000x C or whatever ridiculous speed that is still assuming that our current model of the nature of reality is correct and that there isn't some mechanism to subvert distance in our perspective of 3 dimensional space that it only appears to have traveled a great distance from our limited perspective when in fact it moved a very short distance on another dimensional plane...

Or, any number of similar possibilities that we cannot rule out.
Bog_Mire
Jul 27, 2010

Rank: 2.3 / 5 (3)
Um, dogs go to heaven, cats go to hell
Skultch
Jul 27, 2010

Rank: 3 / 5 (2)
VestaR/Jigga/Alizee is a bot. That's my theory. Some bored grad student with access to a super computer is performing the Turing test on us. There! I just figured you out. Back to the drawing board. :)
Peanuts
Aug 06, 2010

Rank: not rated yet
God so loves us, that we know that most of us do not like the current time frame. Thus with wisdom and understanding, and some patience, we invent/create time travel to find a multi-verse parallel universe where each one of us can order what we want there. Thus blinking out and blinking in with our less then amoeba-sized brains compared to All. These time travel theories engage us to compare where we are at in time.
Peanuts
Aug 07, 2010

Rank: not rated yet
And as Richard Gott stated in his book "Time Travel in Einstein's Universe", we do look at the Past everytime we look up into the Universe. Every amatuer, professional astronomer knows this. So like Richard Gott said in the book that if a mirror was out there about 10 lightyears away and reflected back to the Earth, we would see how the Earth was doing in the Past. The only thing affecting this Past viewing is the resolution that can be obtained. Spacetravelling some place far away brings the Time up to the present as you approach that star or planet. The Time Frame catches up to the Present Time Frame, but before was the Past Time Frame.
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