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PostPosted: Wed Mar 23, 2011 6:32 pm 
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Quantum electrodynamics is a complex stack of mathematics that purports to model the interactions of light and small particles well enough to agree with experimental observations. One key assumption is that cause must always precede effect : that nothing can travel from the future into the past, or faster than the speed of light. Even in experiments where it looks like a wave is tunneling through a barrier faster than light, it is assumed that no meaningful information can be transmitted in this way. The same goes for entangled particles - no meaningful information is thought to be transmittable this way, even though the effects between collapsing entangled particles are transmitted instantaneously across any arbitrary distance.

QE is just a theory, one that only a small number of people alive fully understand. There's no reason at all for it to be perfect, and past history would suggest it is probably slighly wrong in some essential way.

Well, there's a bunch of evidence (dozens of repeatable studies) that suggest it is wrong in a key way. There is now quite a bit of evidence saying that the human brain is very slightly sensitive to future states of said brain. Some people are much more sensitive than others. These people aren't at all seeing the future Mrs. Cleo style, instead what is happening is some mechanism is causing electric charge or wave function collapses to happen inside noisy, physical neurons arranged in configurations sensitive to this effect. This means that neurons can react to events that are going to happen a few seconds in the future more often than chance. This probably applies to all living creatures that use neurons, not merely humans - this 'esp' is thought to be a primitive sense that would apply to anything using neurons. A fly may be able to sometimes predict the flyswatter, a fish the bite of a shark, and so on. (and react to dodge the negative stimuli some of the time)

These studies verifying the effects show that not only does it require very carefully controlled conditions, but it only applies to stimuli that would light up huge areas of neural circuitry if encountered. Usually pornography. The brain will light up before it is exposed to pornography, in fact before a "random" number generator has decided to show pornography or not (probably because even a random number generator is actually somewhat deterministic according to our universe). This is because erotic images activate many systems in the brain, and out all of that electrical activity some of it is leaking into the past. Whether electrons are tunneling through a barrier between the future and the past, or some other effect is involved I do not know. *

We don't see this effect at all with digital systems, by the way, because we have designed computers to be immune to mysterious bursts of "noise".

Anyways, if these effects are real, and there's an awful lot of consistent, repeatable evidence that they are, then a faster than light radio could be built. One simple way would be to have predictive circuits on said radio that will be enormously stimulated when a particular bit arrives at some defined time in the future. So if a binary signal is sent from 5 light seconds away, a particular circuit element in this radio is GOING to be active at a 1/1 billionth of a second time slice in 5 seconds to receive the amplified One OR Zero that is going to arrive. Build the circuit element correctly, and you could read the one or the zero that will be showing up in 5 seconds...right now. In principle this would work over any arbitrary distance, and it might sometimes work before the radio at the other end has even sent the message yet. The "time machine" that was cooked up in this comic by Kevyn might be physically possible. Longer distances might also be workable : we have to assume that a perfect mechanism built to spec will work far better than whatever is happening in our brains.

Here's the article I read on the subject : http://dbem.ws/FeelingFuture.pdf

* Maybe Satan is sending a weak telepathic message to encourage humans to click on the porn. This explanation is for the devout religious folks in the audience.


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PostPosted: Wed Mar 23, 2011 9:20 pm 
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You'd think that FTL results would first appear in something like particle accelerators, where actual detectors and such could be used to find these mysterious "we have no theory for why they should exist" particles, rather than in people's brains, where they can't be directly observed but must be imputed from questionable experiments. I don't suppose you recall the titles and journals of any of these "dozens of repeatable studies" which we could look at to check for methodological flaws? And do you have a position on why a certain Mr. James Randi isn't $1 million poorer as a result?


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PostPosted: Thu Mar 24, 2011 12:53 am 
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Well for one thing, the effects are small. For another, we DO see unexplainable effects in physics experiments all the time. Why would quantum states collapse when observed? Why can you create a diffraction grating light years across but not send data faster than light? Why are we even here? Particle physicists see a dozen unexplainable events before breakfast. A mathematical model that matches the events and predicts future ones is not an explanation for why and how the universe even works this way, or why it's all even possible.

Sure I'll find the journal articles.


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PostPosted: Thu Mar 24, 2011 12:57 am 
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Also this is one of the first published studies that has ever been put in a major journal. This one is the first one that actually has all the trappings of legitimacy. Once the results are replicated, Mr. Randi just may have to cough up the million bucks.


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PostPosted: Thu Mar 24, 2011 1:35 am 
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Habeed wrote:
Quantum electrodynamics is a complex stack of mathematics that purports to model the interactions of light and small particles well enough to agree with experimental observations. One key assumption is that cause must always precede effect : that nothing can travel from the future into the past, or faster than the speed of light. Even in experiments where it looks like a wave is tunneling through a barrier faster than light, it is assumed that no meaningful information can be transmitted in this way. The same goes for entangled particles - no meaningful information is thought to be transmittable this way, even though the effects between collapsing entangled particles are transmitted instantaneously across any arbitrary distance.

QE is just a theory, one that only a small number of people alive fully understand. There's no reason at all for it to be perfect, and past history would suggest it is probably slighly wrong in some essential way.

Well, there's a bunch of evidence (dozens of repeatable studies) that suggest it is wrong in a key way. There is now quite a bit of evidence saying that the human brain is very slightly sensitive to future states of said brain. Some people are much more sensitive than others. These people aren't at all seeing the future Mrs. Cleo style, instead what is happening is some mechanism is causing electric charge or wave function collapses to happen inside noisy, physical neurons arranged in configurations sensitive to this effect. This means that neurons can react to events that are going to happen a few seconds in the future more often than chance. This probably applies to all living creatures that use neurons, not merely humans - this 'esp' is thought to be a primitive sense that would apply to anything using neurons. A fly may be able to sometimes predict the flyswatter, a fish the bite of a shark, and so on. (and react to dodge the negative stimuli some of the time)

These studies verifying the effects show that not only does it require very carefully controlled conditions, but it only applies to stimuli that would light up huge areas of neural circuitry if encountered. Usually pornography. The brain will light up before it is exposed to pornography, in fact before a "random" number generator has decided to show pornography or not (probably because even a random number generator is actually somewhat deterministic according to our universe). This is because erotic images activate many systems in the brain, and out all of that electrical activity some of it is leaking into the past. Whether electrons are tunneling through a barrier between the future and the past, or some other effect is involved I do not know. *

We don't see this effect at all with digital systems, by the way, because we have designed computers to be immune to mysterious bursts of "noise".

Anyways, if these effects are real, and there's an awful lot of consistent, repeatable evidence that they are, then a faster than light radio could be built. One simple way would be to have predictive circuits on said radio that will be enormously stimulated when a particular bit arrives at some defined time in the future. So if a binary signal is sent from 5 light seconds away, a particular circuit element in this radio is GOING to be active at a 1/1 billionth of a second time slice in 5 seconds to receive the amplified One OR Zero that is going to arrive. Build the circuit element correctly, and you could read the one or the zero that will be showing up in 5 seconds...right now. In principle this would work over any arbitrary distance, and it might sometimes work before the radio at the other end has even sent the message yet. The "time machine" that was cooked up in this comic by Kevyn might be physically possible. Longer distances might also be workable : we have to assume that a perfect mechanism built to spec will work far better than whatever is happening in our brains.

Here's the article I read on the subject : http://dbem.ws/FeelingFuture.pdf

* Maybe Satan is sending a weak telepathic message to encourage humans to click on the porn. This explanation is for the devout religious folks in the audience.



This is vaguely reminiscent of a QST Magazine (A Ham Radio Publication) April Fools article detailing the use of a "negative-resistance" in a super-regenerative receiver's feedback loop to make it pick up signals which had not yet been transmitted. The author used a similar circuit in a companion transmitter to send into the future. After several minutes' copying signals from a century in the future, he tentatively sent a "CQ" (calling any station) from his 20th century "location." Sadly, his receiver exploded as every future Ham attempted to contact him "simultaneously."

Thinking seriously, the memory structures of the brain use RNA molecules which are small enough to function as "quantum antennae." Quantum theory assumes that subatomic fluctuations are random, and all statistical tests which have been applied have failed to show a pattern. Unfortunately, this is not proof of randomness. I have personally verified the following assertion: if you take Pi to 1,000,000 digits and treat it as 100,000 10-digit positive integers, it will pass every statistical test for randomness. I have done this, and I can tell you that it does. There is no known statistical test which will tell you that those 100,000 positive integers were not randomly generated, but they were not. I'm told the exact same thing holds true for e, the base of the Naperian logarithm system, but I haven't tested it. In fact it holds true for an entire class of functions known as Riemann Zeta functions, and probably many others. Often, these functions are used as "pseudo-random number generators;" that is, generators of number sequences which appear random, but can be reproduced. This is often quite useful in testing which requires numbers which appear random. Sometimes it backfires--I read about a scientist who got very bizarre data from such a "random test," called a "Monte Carlo test." The data suffered from severe clustering. When he discussed this with the computer experts, he discovered that the "random number generator" employed a Riemann Zeta function of the exact same order as the function he was testing. The programmers wrote him a different pseudo-random number generator and he started getting reasonable numbers.

My whole point is that just because we have so far been unable to prove that Quantum Uncertainty in not random does not mean it is. To quote Death in Hogfather: "Mere accumulation of observational evidence is not proof."

Also, I'd like to point out that at least one of Einstein's arguments against superluminal travel was the assumption that to exceed the velocity of light one must, at some point achieve it, and that an object with non-zero rest mass would require infinite energy to accelerate to C. I'd like to point out that Quantum theory contests that assumption; if you were to accelerate a neutrino to one quantum below C, the next energy level would not be C, at infinite energy, but one quantum above C; granted, this would result in the neutrino gaining an imaginary momentum relative to our reference frame, but if we truly live in a ten-dimensional universe, perhaps this is as simple as the momentum vector being along a currently-undiscovered vector which is orthogonal to the 4D space we perceive. Similarly, the imaginary Tau factor for mass and time dilation may simply represent a temporal vector orthogonal to our familiar temporal one. If I've visualized this correctly (I haven't done the math, although I should), the occupants of the ship would travel across the hypotenuse of a temporal triangle, while an observer in our 4D universe would observe their trip time as the cosine of their angle through "hypertime." Thus, for an FTL trip, it seems that the absolute minimum trip time to the occupants would be the distance in light years divided by C, i.e., 1 year per light year. To the outside universe, it would appear infinitely fast. I'll have to do the math to be sure.

I will point out that the last time I read about it, Stephen Hawking was of the opinion that FTL travel was possible, although possibly "non-trivial."

_________________
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"A sufficiently-advanced technology is indistinguishable from magic."
Arthur C. Clarke
"Sufficiently advanced magic is indistinguishable from technology."
Jack L. Chalker
"Magic is just another way of saying 'I don't know how it works.'"
Larry Niven


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PostPosted: Thu Mar 24, 2011 4:45 am 
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richv wrote:
Habeed wrote:
If I've visualized this correctly (I haven't done the math, although I should), the occupants of the ship would travel across the hypotenuse of a temporal triangle, while an observer in our 4D universe would observe their trip time as the cosine of their angle through "hypertime." Thus, for an FTL trip, it seems that the absolute minimum trip time to the occupants would be the distance in light years divided by C, i.e., 1 year per light year. To the outside universe, it would appear infinitely fast. I'll have to do the math to be sure.

I will point out that the last time I read about it, Stephen Hawking was of the opinion that FTL travel was possible, although possibly "non-trivial."


So if your spaceship also had stasis ability for the crew, you could effectively travel instantly anywhere?

Relativistic time-dilation is supposed to be the other way around - time slows for the people on the ship, but not for the outside observer. So at close to C, hardly any time would pass for the crew, on a round trip between Earth and Alpha Centauri, but when you got back, 8.6 years would have passed for the people at home.
But if you exceeded C, time would have to be "slower than stopped" for your crew...


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PostPosted: Thu Mar 24, 2011 11:03 pm 
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As I understand it, time for the traveler slows down as you approach C, approaching a full stop when you hit C. Once you exceed C... would time flow backwards for the traveler? Might make it difficult to remain above C... once you act to accelerate above C, your personal time-flow would reverse and you would un-act and decelerate. Or so goes my crude understanding of the subject. My crude understanding also suggests that an external observer is not possible, as such would require simultaneity, but I'm given to understand such is not possible.

The big stumper for me still, such as things go in relativistic and super-C travel has to do with the tachyon duel. How does travel faster than C equate to traveling back in time? Particularity when it comes to such small things as entropy -- Does my traveling faster than C permit me to to travel backward in time and thus observe personally an entropy flow opposite that of the universe as I'm observing it? Or would my entropy flow match that of the universe around me? ...

Hmm.

Assuming my understanding of the entropy is correct (I assume it is flawed), you will exceede light speed, bouncing above and below light speed, and arrive at the target as though you were in stasis (in truth, you were stepping forward in personal time below C, and backward in personal time above C)... and arriving there at what (to a stationary observer) would appear to be an infinite velocity (or rather, an series of the traveler appearing and disappearing...)
:boom:
//Torrenal


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PostPosted: Fri Mar 25, 2011 12:34 am 
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The fact that time slows down for the ship and everyone inside it is also a reason preventing the ship from ever reaching C.


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PostPosted: Fri Mar 25, 2011 2:08 am 
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Strictly speaking, nothing actually states faster than light travel is impossible, merely that faster than light travel is equivalent to time travel, and such time travel could then violate causality. If causality does not exist, then free will does not exist. So if you're willing to say causality doesn't really exist, as there's no scientific evidence that actually supports that it must exist, then FTL travel could again be possible. All this leads to 3 possible outcomes, all fairly plausible.
1. FTL travel is impossible, therefore, none of these problems can ever occur.
2. Causality doesn't actually exist, and neither does free will.
3. Some undiscovered mechanism prevents causality from being violated even in the presence of time travel.

Of these, #3 tends to make for the most interesting universe to set things in, if you want a "hard" universe.


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PostPosted: Fri Mar 25, 2011 12:31 pm 
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Or it could be so much simpler.

If you try to pick up a casaulity message breaking message from the future, the message will be extremely noisy because it is a superposition of possible futures. Said message doesn't break causality due to the noise.

If you pick up a message that isn't causality breaking, you'll find that the signal is much cleaner and it's possible to actually send meaningful data.


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PostPosted: Sat Mar 26, 2011 1:10 am 
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Habeed wrote:
If you try to pick up a casaulity message breaking message from the future, the message will be extremely noisy because it is a superposition of possible futures. Said message doesn't break causality due to the noise.
Your solution, while being a proposed subset of #3, has a flaw: It is possible to create a chain such that no individual message violates causality but the ring together does. For instance, say I transmit a message "instantly" to distance world far away. The receiver there can receive this message and transmit a response back, which I receive shortly later. This doesn't violate causality. A receiver in a fast-moving spacecraft can transmit to another similarly moving spacecraft and this, too, does not violate causality. The problem occurs when I transmit this message to a distant world like so, and this distant receiver uses a conventional radio, to transmit to the moving spacecraft, which then transmits to the other spacecraft using FTLcomm. This other spacecraft, however, due to the quirks of special relativity, is in my past. So you have now created a ring of valid messages that nonetheless would violate causality. But each step in the chain is perfectly valid taken alone, yet together, a giant mess results.

In short, either true FTL is impossible and you get some kind of many-worlds dimensional-hopping instead as a magical preventative measure, or causality doesn't exist because effects can occur before their causes, and even be a loop, and therefore, free will doesn't exist. This is a valid explanation consistent with known science, but the idea that free will doesn't exist makes for some rather uncomfortable stories.


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PostPosted: Sat Mar 26, 2011 5:57 am 
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Fishman : I think that the necessity of having to set up links beforehand, possibly using particle entanglement, would prevent this from working. Any two points would have to meet before instantaneous links could be created. And your transmission from the stationary world would have to travel at the regular speed of light - it might never catch up to a spacecraft that is in your past.

And even if it does, the message has to make it's way back to YOU, without superposition of signals forced on it, BEFORE you sent it, for causality to actually break. Doesn't matter if it reaches a starship in your past - that ship has to be in your light cone. In theory that's impossible - any chain of messages that gets to your past must come from a multitude of futures and it would be impossible to distinguish them from noise.

Instantaneous com links would have an important distinction between them and wormholes. Wormholes link the same point in space and time, which creates all kinds of causality breaking problems. Instantaneous com links simply let you read a conventional message transmitted to you before it actually arrives.


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PostPosted: Sat Mar 26, 2011 2:08 pm 
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Fishman wrote:
2. Causality doesn't actually exist, and neither does free will.


That conclusion does not follow for me. Could you explain it?

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PostPosted: Sun Mar 27, 2011 1:35 pm 
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Quote:
2. Causality doesn't actually exist, and neither does free will.


I would think that a lack of free will is linked to causality, and by eliminating the possibility of causality, you create the possiblity of free will.

How? Causality requires that any event have a cause. If causality does not exist, one could freely act in response to...nothing. You would likewise not be bound by necessity to react. You would be free to act as you will.
//Torrenal


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PostPosted: Sun Mar 27, 2011 5:16 pm 
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As I understand it, "causality" means "every event must have a cause."

As I understand it, "free will" means that a person is "capable of reacting to a given event in any chosen manner, regardless of whether said course is wise, rational, moral, legal, obedient to $DIVINIT(Y|IES), etc."


1) Let's assume our universe obeys causality. An event happens; there is a cause, but I don't know what it is. Do I have free will in how I respond to it?

2) Now let's assume our universe does has mandatory non-causality. An event happens; it has no cause. Do I have free will in how I respond to it?

3) Now let's assume our universe has optional non-causality. An event happens; it may or may not have a cause and I don't happen to know which is the case. Do I have free will in how I respond to it?

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PostPosted: Mon Mar 28, 2011 12:17 am 
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Whitehawke wrote:
Fishman wrote:
2. Causality doesn't actually exist, and neither does free will.
That conclusion does not follow for me. Could you explain it?
In relativistic causality, the cause must preceed the effect in all inertial reference frames: If causality does not exist, then an event in the future can influence the past. If events in the future influence the past, then this means the future is predetermined: The cause an effect we observe in the past or present is in the future, yet it already "happened" or "must happen". Thus, free will does not exist: Our behaviors are now deterministic: We have no actual input in our actions, like characters stuck on a railroad plot run by a bad DM.

If "true" time travel is possible, not merely of the "many worlds" variety, then I can, and indeed, have, retroactively altered the past if I were to go back in time and change something in the past. That change already happened. Indeed, in the future, I now MUST do so, because this event already "happened". I can no longer choose not to do so. Free will doesn't exist.

So, does this rule out the possibility that we live in a universe where causality doesn't exist? No, but it makes for some very uncomfortable ramifications. Consider what it means if we were to discover that free will doesn't exist and therefore, people have no actual ability to alter their behavior, because the future is predetermined.


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PostPosted: Mon Mar 28, 2011 3:33 am 
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The huge difference here is that if you can't send yourself to the past, only information (and you can't encode yourself as information for a reason I will explain in a moment) then said information will arrive in the past even if you don't actually send it in the future. There just has to be a chance of the information arriving and it will, with a signal strength proportional to the probability of a particular future occurring.

If you send yourself, well -a living being has an almost infinite number of future states. The way the communication device works, all those states are overlaid on each other - you cannot distinguish which one came from a particular possible future. Thus the message will lack the coherency needed to send a living being.

UNLESS...the other case is if you have a radio receiver that will pick up a message from a star light years away. Now, that message has already been sent - so as far as the universe is concerned, the message you receive IS predetermined. You just normally cannot receive it - but it might be possible to read it ahead of time.


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PostPosted: Mon Mar 28, 2011 9:36 pm 
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Whitehawke wrote:
As I understand it, "causality" means "every event must have a cause."

This includes reactions.
Whitehawke wrote:
1) Let's assume our universe obeys causality. An event happens; there is a cause, but I don't know what it is. Do I have free will in how I respond to it?
2) Now let's assume our universe does has mandatory non-causality. An event happens; it has no cause. Do I have free will in how I respond to it?

An event happens. There is a cause. Do I have free will in how I respond to it? That depends: Am I bound to give a specific response? (ie: is my response predetermined by the inputs) Or am I free to chose my own response (ie: Am I free to chose my response, regardless of the inputs?).

In a causal-universe, give me the same event an infinite number of times, and I will give the same response an infinite number of times.
In a non-causal universe, give me the same event an infinite number of times, and I will give an infinite number of different responses.

I can even argue that our own universe is non-causal.
I could look to various examples (Schrodinger's cat, slit experiments, etc) but instead, I will look at a single atom of Radium-226.

Neat stuff, Radium. With a half life of 1601 years for this particular isotope. Long compared to some radioactive materials, but short compared to others. Lets look at the nucleus, where we have four nucleons held tightly in place by the nuclear force. Well, mostly tightly. Were these four nucleons to be just a bit further away from the nucleus, the nuclear force would be overpowered by the electromagnetic force, but they are tucked away securely in the nucleus. I'll put my atom on the shelf and leave it sit for a few years. At some point, those four nucleons will find themselves just a bit further away from the nucleus (credits to Quantum Tunneling) and... an alpha particle is born. An event without a cause. No action was taken on the atom, it decided all on its own, without external inputs, to decay into Radon-222.

Habeed wrote:
The huge difference here is that if you can't send yourself to the past, only information (and you can't encode yourself as information for a reason I will explain in a moment

Um. What is a person but information? What is a floppy disk but information? What is a pile of sand but information? Or is time travel limited to the transmission of light, which (I would think) cannot be made to travel fast enough to enable time travel.

Whitehawke wrote:
If "true" time travel is possible, not merely of the "many worlds" variety, then I can, and indeed, have, retroactively altered the past if I were to go back in time and change something in the past. That change already happened. Indeed, in the future, I now MUST do so, because this event already "happened". I can no longer choose not to do so. Free will doesn't exist.

I cannot go back in time to alter the past if it has already been altered. Instead, I can go back and maintain the status-quo. In short, you have a paradox: A circular loop of events, where A causes B causes A, but nothing causing the loop. This cannot come to pass, unless altering past events is actually possible, and some other event then caused the loop to exist.

Assume for a moment I can send information both forward and backward in time. Lets say on January 1st, 2012 I send a message to myself on January 1st, 2011, containing the day-by-day stock prices. So starting on January 1st, 2011, I start trading on the market, and quickly become wealthy. My mere act of trading causes the present to deviate from what my future-self reported to me. But at the end of the year, I can still send back the stock market data -- updated by the effects of my trading on it, thus allowing me to trade using information that includes the effects of my trades, thus altering the outcomes of the market.... Things revolve in a circular flow. My sending the information back has churned a figurative pool of 'spacetime', and it will continue to roil and flow until it settles down in one of three states:
A static, linear flow: From an exertion of free will (curse you Radium-226!), I find myself leaving the airport in England, looking left as the bus drives up from the right. Owch.
A series of alternate flows that flipflop: I get rich in the market, and lack motivation to invent time travel, thus I don't send the information back in time, thus I invent time travel and send the market results back... don't send the info, do send the info, don't send the info, do send the info... etc. (inherently unstable. I'll bet some random radium atom in my brain will at some point spit out a helium atom, shifting a decision of mine to take a trip to England...
A closed loop: I get rich on the market, and send the information back in time so that I can do same.

As I see it: The universe is not causal, thus free will exists, and time travel is at least plausible. I however remain dubious as to time-travel being possible.
//Torrenal


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PostPosted: Mon Mar 28, 2011 11:13 pm 
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Terry Pratchett explored this in an interesting way in "I Shall Wear Midnight," the latest, and probably last, Tiffany Aching book. In it, a 17-year-old Tiffany has a talk with a much older Tiffany and asks why it's necessary; the older Tiffany responds "Because I remember it." She also notes that while an older and younger Tiffany will talk together "throughout time," they won't always say the same things to each other. The future changes the past, which ripples forward, then ripples back, which actually makes sense. Time doesn't really have an arrow--our language only assumes it does. Causality is only conserved because we use the measure of entropy to measure time. That's a trap, because entropy increases with time, but entropy is not time. You need to be able to think in four dimensions.

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Arthur C. Clarke
"Sufficiently advanced magic is indistinguishable from technology."
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"Magic is just another way of saying 'I don't know how it works.'"
Larry Niven


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PostPosted: Tue Mar 29, 2011 5:16 am 
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torrenal wrote:
An event happens. There is a cause. Do I have free will in how I respond to it? That depends: Am I bound to give a specific response? (ie: is my response predetermined by the inputs) Or am I free to chose my own response (ie: Am I free to chose my response, regardless of the inputs?).
Which is how Free Will works, yes...

torrenal wrote:
In a causal-universe, give me the same event an infinite number of times, and I will give the same response an infinite number of times.
A universe with causality may stil be devoid of free will. However, a universe without causality...

torrenal wrote:
In a non-causal universe, give me the same event an infinite number of times, and I will give an infinite number of different responses.
But here's the catch. In a non-causal universe, the thing which causes your reaction can be you, in the future. In which case you are constrained to react this way, because if you do not, the you of the future that causes this reaction will never be able to cause this reaction, and therefore, you will not be able to react. Thus, free will does not exist.

torrenal wrote:
I'll put my atom on the shelf and leave it sit for a few years. At some point, those four nucleons will find themselves just a bit further away from the nucleus (credits to Quantum Tunneling) and... an alpha particle is born. An event without a cause. No action was taken on the atom, it decided all on its own, without external inputs, to decay into Radon-222.
No, the alpha particle is born because the atom decayed. The event has a cause, one that comes before the event. That's what causality means. With a closed time-like curve, causality can be violated: An item or information can return to its own past, and therefore, could cause a paradox, if not for the fact that this already happened. But if this already happened, then everything is already predetermined, and you cannot change it.

torrenal wrote:
Assume for a moment I can send information both forward and backward in time. Lets say on January 1st, 2012 I send a message to myself on January 1st, 2011, containing the day-by-day stock prices. So starting on January 1st, 2011, I start trading on the market, and quickly become wealthy. My mere act of trading causes the present to deviate from what my future-self reported to me.
Ah, but here's the catch: Some time before January 3rd, 2011 (1st and 2nd are weekends and the market isn't open), you receive a message from a mysterious stranger claiming to be yourself from the future. Or maybe not so mysterious, if you, like me, have an authentication protocol you use to identify yourself from the future. Either way, for whatever reason, you follow this guy's advice, which somehow seems curiously resistant to everything you do, even if for some reason you attempt to derail the plan out of pure contrariness, which probably just ends up making you less rich than you could have gotten had you not done that. Sometime in the future, however, you discover the ability to transmit messages to the past. At that point you realize you MUST transmit that message, or else none of this would have happened. But it DID happen, so you can't NOT do so. Even if you attempt to defy destiny and not transmit the message, it ends up happening anyway...just like it did. Because in a non-casual universe, FREE WILL DOES NOT EXIST. Your actions, including going back in time, are predetermined by events in the future.

torrenal wrote:
A series of alternate flows that flipflop: I get rich in the market, and lack motivation to invent time travel, thus I don't send the information back in time
Flipflopping universes is "many worlds", though: In some worlds you are motivated to invent time travel, in others you are not. This is not "true" time travel. In TRUE time travel, you are motivated to do it, or perhaps do so on accident without motivation, or perhaps someone does it for you and you merely exploit it, specifically because you ALREADY DID, in your future-future self's past. In response to the fact that you DID receive this help from the future, you become motivated to invent, discover, or maybe just stumble upon, time travel. You can't avoid this, because it already happened. The fact that the universe is non-causal results in predestination, which necessarily implies a lack of free will, because you don't choose your actions, they're already determined. The ability to "change" the "past" is moving into "many worlds" territory in which you are altering *A* past, but not your OWN.

richv wrote:
Time doesn't really have an arrow--our language only assumes it does. Causality is only conserved because we use the measure of entropy to measure time. That's a trap, because entropy increases with time, but entropy is not time. You need to be able to think in four dimensions.
Time may not necessarily have an arrow, but we don't know what the hell it DOES have. Without causality or the "many worlds" escape hatch, though, time is like a book that is already written and then posted onto the Internet: Unalterable and indelible, even if you set the book on fire, and indeed, attempting to set the book on fire makes it stick around forever.


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PostPosted: Tue Mar 29, 2011 5:39 am 
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torrenal wrote:
Um. What is a person but information? What is a floppy disk but information? What is a pile of sand but information?


A person is a real entity - and a conscious one at that, with his or her own feelings and point of view. Even the pile of sand is a real thing, something the information is about. And some other real entity is being "informed" of those real things by getting the information.

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Or is time travel limited to the transmission of light, which (I would think) cannot be made to travel fast enough to enable time travel.


Send the light through a wormhole? It goes at its constant speed through the space its moving in, like a train moving along a track, but said track is curved back through a "shortcut" into another space or time.


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PostPosted: Tue Mar 29, 2011 7:05 am 
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Quote:
QE is just a theory

Arrrrrrrgh. Every time I read "just a theory", I die a little inside. There is no such thing as "just" a theory. Being a theory means having met a certain standard of evidence and falsifiability.

Anyway. Let's run this through the Pathological Science checklist, shall we?
  • The maximum effect that is observed is produced by a causative agent of barely detectable intensity, and the magnitude of the effect is substantially independent of the intensity of the cause.
  • The effect is of a magnitude that remains close to the limit of detectability, or many measurements are necessary because of the very low statistical significance of the results.
  • There are claims of great accuracy.
  • Fantastic theories contrary to experience are suggested.
  • Criticisms are met by ad hoc excuses. [can't be bothered to see how Mr Bem responds to his critics]
  • The ratio of supporters to critics rises and then falls gradually to oblivion. [likewise]

Anyway. Here's some more reading:
http://www.talyarkoni.org/blog/2011/01/ ... lly-wrong/

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PostPosted: Tue Mar 29, 2011 9:29 am 
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gnolan : don't forget this effect is also observed with fMRI studies, and it's a lot stronger there. The brain really does know sometimes when something is just about to happen. But given the incredible noise in the circuitry, one would fully expect for the effect to always be very small, at least when referring to brains. Some experiments in quantum physics have much stronger 'impossible' results.


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PostPosted: Tue Mar 29, 2011 1:15 pm 
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Referring to (weak) fMRI effects makes me especially suspicious.

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PostPosted: Tue Mar 29, 2011 5:20 pm 
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torrenal wrote:
Whitehawke wrote:
If "true" time travel is possible, not merely of the "many worlds" variety, then I can, and indeed, have, retroactively altered the past if I were to go back in time and change something in the past. That change already happened. Indeed, in the future, I now MUST do so, because this event already "happened". I can no longer choose not to do so. Free will doesn't exist.



@torrenal: For the record, Fishman was the source of that quote about "If 'true' time travel....", not me.

-----

This discussion reminds me of something I read once...I wish I could remember the author or title. IIRC, it goes like this:

*) FutureSelf shows up, hands PresentSelf a note, then leaves.

*) TeacherGuy tells PresentSelf "you don't need to bother writing the note, just leave it for yourself"

*) PresentSelf (confused) says "but where did the note come from?"

*) TeacherGuy says "It exists on a closed time loop. It came from the same place that the other side of the paper goes when you twist it into a Möbius strip."

This was science (fiction / fantasy) of course, but I find myself wondering if there is anything in the math that forbids something like this from happening -- does everything have to follow the same timestream, or is it possible to have a "one world" situation where there are still multiple timestreams that overlap / interact with each other for limited segments?

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PostPosted: Tue Mar 29, 2011 6:07 pm 
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gnolam wrote:
Referring to (weak) fMRI effects makes me especially suspicious.


That is the most wonderful of all studies. Thank you for linking to that.

Whitehawke wrote:
This was science (fiction / fantasy) of course, but I find myself wondering if there is anything in the math that forbids something like this from happening -- does everything have to follow the same timestream, or is it possible to have a "one world" situation where there are still multiple timestreams that overlap / interact with each other for limited segments?


Just as a thought experiment, using your note example:

Say there is a year between your present and future selves. When future you hands you the paper, it is at least one year old. When you age a year, and take it back to (now past) you, the paper is now 2 years old. Next time through the loop it's 3, then 4, then 5 . . . and each time it's been touched by more pairs of your hands, exposed to another year of light/humidity/air . . . after a few hundred or thousand trips through the loop, the paper will be in faded, tattered ruins, with nothing left to hand to your past self. Without the introduction of outside information (a new piece of paper), the loop eventually evaporates itself away.

A similar (but not identical) problem presents itself with "I'm my own grandpa" time-travel scenarios, involving the degrading of DNA over time. I think.


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PostPosted: Wed Mar 30, 2011 3:05 am 
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Well, current models of what would allow time travel of any form to occur may exclude physical objects, since all of them seem to involve forces and energies that would destroy any such object. Thus it seems unlikely that a physical note would survive the attempt to time travel without being crushed into subatomic paste. Causality violation does not require that a physical object be used, however.


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PostPosted: Wed Mar 30, 2011 3:47 pm 
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Time travel is obviously possible. We are all travelling in time in what we define as "forward" at very nearly 1 second/second, which is lightspeed (C), in time. As an object approaches C in 3 Space, its velocity in time approaches zero. Photons, which travel at C, do not travel in time at all. The question that's really being asked is "can one travel in time at speeds greater than 1 sec/sec or less than zero?" Maybe the people asking the questions think it's obvious, but in science, you have to ask very specific questions if you want meaningful answers. If you could figure out how to build an engine that accelerated the entire universe, except your spaceship, up to lightspeed, you'd see Einstein's Twin Paradox in reverse (and have a whopping fuel bill). You'd age while the rest of the universe didn't. From your inertial reference frame, time would remain the same and "universal time" would slow down.

If you exceed C, Tau, the time dilation factor, becomes imaginary. Effectively, time is rotated orthogonal to the normal timelike vector. That's OK; there are three known vectors orthogonal to T: X, Y, and Z. Thus, one possible solution is that one of the spatial vectors becomes timelike, and the temporal vector becomes spacelike. What the crew perceives as movement in time, observers in the outside universe see as movement in space, while what the crew perceives as movement in three spatial dimensions, observers from outside see as a complex 3-vector with two spatial and one temporal component. Thus, FTL travel does involve time travel, but so does all travel; it takes time to get there from here--put two atomic clocks in supersonic planes and fly them in opposite directions around the Earth, and they'll have a measurable difference when they land where they started. I've seen some interpretations of FTL travel which imply that if you traveled to Alpha Centauri at FTL speed, you'd get there before you left here. On the return trip, would you return even earlier? That would violate not only causality, but Conservation of Mass-Energy, too, which seems counter-intuitive to me. It seems more likely to me that the logical result, that travelling at 430C would get you to Alpha Centauri in about 3.65 days from outside, and I'll have to calculate what the time-dilation for the crew is.

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PostPosted: Wed Mar 30, 2011 8:40 pm 
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richv wrote:
Time travel is obviously possible. We are all travelling in time in what we define as "forward" at very nearly 1 second/second, which is lightspeed (C), in time. As an object approaches C in 3 Space, its velocity in time approaches zero. Photons, which travel at C, do not travel in time at all. The question that's really being asked is "can one travel in time at speeds greater than 1 sec/sec or less than zero?" Maybe the people asking the questions think it's obvious, but in science, you have to ask very specific questions if you want meaningful answers.
Okay, fair point. When we talk about time travel, we're clearly discussing these cases, though.

richv wrote:
I've seen some interpretations of FTL travel which imply that if you traveled to Alpha Centauri at FTL speed, you'd get there before you left here.
Well, I don't think there's any interpretation of time travel which allows you to, in a single jump, travel into the absolute past. What WOULD happen is that you would exit the light cone at your origin, but if you were to then transmit any non-FTL message back to your original location, which has not moved FTL, that message would never arrive before you left, so you would not be in the "past". The messed up stuff happens if you then accelerate or otherwise do something to change your reference frame, and then jump: Since all inertial reference frames are equally valid, you can now arrive in the past when your spaceship returns home or your hyperspace email returns to sender. There is no particularly good way to escape this: The science strongly indicates that if FTL travel is possible, this happens. Therefore, either FTL travel is impossible (boring), FTL travel involves some kind of fancy dimensional hopping which prevents causality violations because you're actually violating a parallel universe, or causality, and therefore, free will, do not truly exist. Of course, it's possible for free will not to exist even in a causal universe, but that's a different story.


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PostPosted: Wed Mar 30, 2011 9:57 pm 
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Seriously, fellows, you're rehashing old arguments. I just mentioned a fairly mundane but relatively uncommon explanation for what happens with faster than light travel, and you ignore it in favor of arguments that are 60 years old.

So, again, here's what happens :

If you try to RECEIVE a message or a physical object from a future that YOU can affect (meaning you have a way to get something to that future before it happens, limited by the speed of light) you will NOT receive a discrete message or object. You'll receive a SUPERPOSITION of possible messages and objects, INCLUDING ones that could only be generated if you acted on said information or object from the future.

Probably when you try to observe the object or message, the universe randomly chooses a possible state for it from the solution space.

Suppose you are receiving a coffee mug from a future self that could potentially put anything into the wormhole in any orientation. Most futures you put in a coffee mug, but lots of other possibilities are there. You'll receive a mess of plasma composed of all possible states of the coffee mug as well as samples of everything else your future self might have sent, including things that would only be sent if a past self received something specific.

This wouldn't be very useful a device, and in fact it might destroy itself from the energy surges mentioned above due to virtual particles using your device to amplify themselves.

HOWEVER, it still would be incredibly useful as long as you filter the inputs and outputs properly. For example, this machine would work PERFECTLY for receiving stuff as long as you CANNOT physically interfere with the sending based upon what you received. So long distance travel and communication would work fine, as long as you carefully synchronize all the long distance com channels and wormholes to prevent the above paradoxes from being possible.

Again, paradoxes are no big deal, because I don't think they can happen like it does in the movies. You cannot kill your grandfather, because if you try to travel into your own past you'll come out the wormhole as a cloud of plasma of superimposed future selves.


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