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Time Travelling Computer

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Even if it's possible to create a time machine, it's unlikely that it will be built any time soon.

However, it may be possible to send a single particle back in time. Mathematically, an antiparticle is identical to an ordinary particle travelling back in time. Whether a positron is *actually* an electron travelling back in time, I do not know.

But if it were possible to send a single particle back in time, information (even if just a true/false value) could be sent back in time.

A Turing machine can calculate anything, given enough memory and time.

A computer could be built that upon completing a calculation sends the result back to itself before the calculation begun. This would, in essence, give you unlimited computing power, as any calculation would be performed instantly, without any calculating taking place.

[Edit: Once it has the answer, it waits a while and then sends it back in time to itself, completing the loop. Duh.]

mitxela, Jun 14 2012

Time Travel and Computing http://www.frc.ri.c.../1991/TempComp.html
[mitxela, Jun 14 2012]

Tachyons http://en.wikipedia.org/wiki/Tachyon
Tachyons are what they are. The wikipedia article even mention the tachyonic anti telephone, which is this idea. [bungston, Jun 16 2012]

Tachyonic antitelephone http://en.wikipedia...yonic_antitelephone
“According to the current understanding of physics, no such faster-than-light transfer of information is actually possible.” [ytk, Jun 18 2012]

[link]






       I'm fairly sure this must have been thought of before, but haven't been able to find anything.
mitxela, Jun 14 2012
  

       This is nifty. One hears plenty about the ansible or runcible or whatever that distance communicator / entangled particle thing is, but I have not heard this one. It should be easy to test if one can generate antiparticles reliably and if the generated particles maintain their temporal separation. You could send morse code.   

       Let us summon up some dissertation on this idea. Draw the pentacle... ok. Vernon, Vernon, Vernon.
bungston, Jun 14 2012
  

       [marked-for-deletion] Bad science. This would violate causality, plain and simple.
ytk, Jun 14 2012
  

       "What do we want?"
"TIME TRAVEL!"
"When do we want it?"
"IT'S IRRELEVANT!"
gnomethang, Jun 14 2012
  

       [unmarked-for-deletion] The science is merely unproven.   

       Causality can not be violated in an infinite multiple universe.   

       [bungston] you crack me up sometimes.   

       [ytk] If time-travel is possible, casaulity is violatable. Therefore, it's unreasonable to delete any time travel idea for that reason.   

       The fact that such a computer would have an infinte number of particles arriving at the same time, resulting in an implosion, on the other hand...
MechE, Jun 14 2012
  

       Matter, energy, and information are all different states the same thing. Computers effectively transmute energy into information. You do the same thing when you move an object from one place to another. Its matter is its physical form, the information is its location, and the energy applied moves its physical form from one place to another, changing the information.   

       Under this idea, you're trying to generate information without spending the requisite energy, thus violating the second law of thermodynamics. This is just as silly an idea as perpetual motion. Why don't we just create a pump that moves energy backwards in time, and use that energy to power the pump?
ytk, Jun 14 2012
  

       Ah, but if you accept the many worlds interpretation as applied to time travel, the energy is expended, it's just expended in a different reality.
MechE, Jun 14 2012
  

       But then you're just sending energy from one universe to another, which violates the first law of thermodynamics. Even in the MWI, each universe is considered to be a closed system within itself. So you can't just send information from one reality to another. And regardless, the entire multiverse is still considered a closed system, which implies that each universe's energy is multiplied by the probability of it existing, preserving the total energy of the multiverse. So it would be impossible to send energy with only a given probability of existing into a universe with a different probability, because this would change the total energy in the multiverse and now I have a headache.
ytk, Jun 14 2012
  

       // This would violate causality, plain and simple. //   

       Sorry, you have a problem with that ?   

       We think you should drop this conversation right now, and step away. You are on to something here, and if you carry on, we may have to do something about it which you will never know about as it involves going back in time and stopping this before it starts.
8th of 7, Jun 14 2012
  

       They said I was crazy for always carrying around a minigun loaded with high explosive rounds and never sleeping, but I'll have shown them one day!   

       (Oh, and they said the exact same thing about every single one of my ancestors, before you get any bright ideas.)
ytk, Jun 14 2012
  

       We never said that. You're certainly not crazy, just well-prepared and insightful. We like the way you think, and also the way you hide in the shrubbery, twitching and muttering.
8th of 7, Jun 14 2012
  

       //This would violate causality, plain and simple.//   

       Once the machine receives the answer to the problem, it waits a short while, then sends it back in time to itself. The answer would appear as if from nowhere, but would be correct.
mitxela, Jun 14 2012
  

       The Pope's already got one of these, right ?
8th of 7, Jun 14 2012
  

       You can't generate information without expending energy. If you have information that comes from nowhere, you have energy that comes from nowhere. You can't have energy that comes from nowhere. So you can't have information that comes from nowhere.   

       Even assuming you could somehow actually do this, as soon as you received the information in the past, and therefore did not expend the energy necessary to obtain the information, it would cease to exist. You're just restating the grandfather paradox here.
ytk, Jun 14 2012
  

       There are different kinds of information. Does it take energy to know if a number is a prime? It's a prime whether you do the calculation or not.
mitxela, Jun 14 2012
  

       I have found an article which discusses this idea [link]. Although I haven't yet worked out what the conclusion is as to whether this would work at all, clearly this has been thought of before, so I suppose this is baked. Or as baked as it's ever going to get.
mitxela, Jun 14 2012
  

       // suppose this is baked. Or as baked as it's ever going to get //   

       Well essentially, both. We refer you to Dr. Dan Streetmentioner's "Time Traveller's Handbook of 1001 Tense Formations " which you may find of some assistance. Or have found of some assistance.   

       Or possibly both. Or neither.
8th of 7, Jun 14 2012
  

       I believe that [ytk] knows of what he speaks. Reducing the idea to a perp motion machine demonstrates that this idea is WIBN. So, m-f-d after all.
sqeaketh the wheel, Jun 14 2012
  

       // It's a prime whether you do the calculation or not. //   

       But you have to collapse the wave function to determine that.   

       // So, m-f-d after all //   

       <pedant>   

       "marked-for-deletion" or "marked-as-deleted" ?   

       </pedant>   

       You really do need to be precise about these things. Please, do try to keep up.
8th of 7, Jun 14 2012
  

       // you have to prove that dark matter is not the injection of energy from another multi-world //   

       No, you have to prove that in a rational Universe, there's a reason for the existence of Kylie Minogue.
8th of 7, Jun 14 2012
  

       You are [Beanangel], and we claim our five dollars.
8th of 7, Jun 14 2012
  

       //Does it take energy to know if a number is a prime?//   

       To know if a number is prime? Yes, of course. Some being has to contain that knowledge.   

       //It's a prime whether you do the calculation or not.//   

       Well, now you're confusing information with the structure of the universe. Mathematics is simply an abstraction of the physical properties of the universe, and it happens that in this abstraction, certain numbers are what we call "prime". Can you change the primality of a number? No, of course not, because primality has no physical form. So it's not information. That prime numbers exist is not information. That we /know/ about them is. This is true about any property of the universe. That matter is made up of atoms isn't information—it's simply a physical property of the universe.
ytk, Jun 14 2012
  

       You are [Beanangel] as well, and now we are ten dollars up and are thinking about which bar we are going to spend it in.
8th of 7, Jun 14 2012
  

       Cram it, Borg, before I Happylong your pasty metal ass.
ytk, Jun 14 2012
  

       "You lookin' at us ? We said, are you lookin' at us ?"   

       COME ON THEN, IF YOU THINK YOU'RE HARD ENOUGH …
8th of 7, Jun 14 2012
  

       Madness. Jim would be impressed if he hadn't died giving an automated tube sweeper a kicking.
rcarty, Jun 14 2012
  

       //COME ON THEN, IF YOU THINK YOU'RE HARD ENOUGH …//   

       Whoa whoa whoa whoa whoa. I think you have me confused with some other sort of bloke here.
ytk, Jun 14 2012
  

       //Does it take energy to know if a number is a prime?//   

       Yes. That is why there are only 24 Prime numbers known - as I didn't have the energy to calculate any further. (Seems odd that "24" isn't Prime itself, but there ya go).
AusCan531, Jun 14 2012
  

       //No, you have to prove that in a rational Universe, there's a reason for the existence of Kylie Minogue.//   

       The video for "Come Into My World" was actually pretty damn cool. I'd be willing to believe the universe allowed Ms. Minogue to exist for the sole purpose of enabling that video to come into being.
ytk, Jun 15 2012
  

       This might explain the autoboner, it's merely the anti-particle of a bun travelling back in time and colliding with my posts?
not_morrison_rm, Jun 15 2012
  

       But if you get the answer before the question, how the hell do you know what the question was.   

       Mother......
S-note, Jun 15 2012
  

       So the idea will be marked for deletion in the future, and that information has been transmitted back to us just now.
tatterdemalion, Jun 15 2012
  

       //if you get the answer before the question, how the hell do you know what the question was// Perhaps you could also send the question just a little further back in time?
pocmloc, Jun 15 2012
  

       //Bad science.//   

       Bad science or maybe just quantum strangeness. This is analogous to the idea of the delayed choice quantum eraser, which implies retrocausality. From Wikipedia: "In other words, something that happens at time t apparently reaches back to some time t - 1 and acts as a determining causal factor at that earlier time."
ldischler, Jun 15 2012
  

       Even so, you simply can't have two events that cause each other.
ytk, Jun 15 2012
  

       "you simply can't have two events that cause each other."   

       That's more philosophy than science.
ldischler, Jun 15 2012
  

       // you simply can't have two events that cause each other. //   

       I disagree. Beyond our mode of perception, time is non- linear. If that beggars the mind, then imposing artificial organization makes it recursive at best. Thus, while it is indeed nigh impossible to make the statement (a-->b) = (b-->a), it is certain that every event is intrinsically the cause of every other event. No two things are unconnected.
Alterother, Jun 15 2012
  

       //the idea will be marked for deletion in the future   

       Yes, but by who?   

       Is this Skynet trying to prevent humanity stumbling on the one idea that can prevent the rise of the machines?   

       Or could it be the last surviving halfbaker trying to prevent the ideas that inexorably leads to the Rotating Superconducting Cheese Fondue Set in 2014 that awoke Chulthu?
not_morrison_rm, Jun 15 2012
  

       //the idea will be marked for deletion in the future // Yes, but by who?   

       I sent your inquiry ahead, but the response indicates no knowledge of the idea in question, since it never existed.
tatterdemalion, Jun 15 2012
  

       Following the link, I checked the replier's HB profile and when translated from the original chittering, it quite distinctly mentions "......how beautiful my tentacles look, reflected in the light from the burning human city".   

       I find myself quite concerned.
not_morrison_rm, Jun 15 2012
  

       //Once it has the answer, it waits a while and then sends it back in time to itself, completing the loop.//   

       And if it doesn't wait, bad things happen.
ldischler, Jun 16 2012
  

       No, the bad things have already happened. All it's done is cause them.   

       Please, do try to keep up.
8th of 7, Jun 16 2012
  

       I think that positrons do not travel backwards in time. If they can be generated, and distinguished from other particles by the curve of their paths, that implies they are temporally moving just like electrons but with opposite charge.   

       There is some other particle that is supposed to move backwards - I read some sort of theory that this particle always travels faster than light. But there is a boatload of SF up in there jostling with half-remembered stuff. Let me see if I can link that up.
bungston, Jun 16 2012
  

       //simply can't have two events that cause each other. //   

       Is that true? When heat moves to a cold area the hot area becomes cool and the cool area becomes hotter. When lightning strikes the exchange of electrons causes rapid polarity changes. Two events that cause eachother. When a dog unconsciously wags his tail he chases it and wags his tail more out of fun. I think my point is that when two mutually dependant things happen simultaneously then you view of linear causality is questionable.
rcarty, Jun 16 2012
  

       //temporally moving just like electrons but with opposite charge.//   

       But the argument works both ways. If you film me reversing the Bentley round a corner, and then play the film backwards...   

       Of course, if the petrol guage were visible in the movie, you would be able to tell. On the other hand, positrons do not have petrol guages. Nor do they have reversing mirrors, of course, because they are not built by English craftsmen.
MaxwellBuchanan, Jun 16 2012
  

       //If you film me reversing the Bentley round a corner   

       Hey, where's my Bentley? Police! Police!!
not_morrison_rm, Jun 17 2012
  

       Yes. Classically it is described as a paradox because this computer could not only give you the answer to an incredibly complicated question, it could do it so fast that you got the answer even before you started building the computer, thus making ever building a time machine a completely foolish endeavor because the first thing you would do with such a machine, were it's construction possible, is go backwards in time far enough to make construction of the machine redundant.
WcW, Jun 17 2012
  

       //Is that true? When heat moves to a cold area the hot area becomes cool and the cool area becomes hotter. When lightning strikes the exchange of electrons causes rapid polarity changes. Two events that cause eachother.//   

       Those sound suspiciously more like two descriptions from different perspectives for the same event to me.
RayfordSteele, Jun 18 2012
  

       A conflict of perspectives as great as a hurricane.
rcarty, Jun 18 2012
  

       ...yet as subtle as a butterfly flap.   

       //When heat moves to a cold area the hot area becomes cool and the cool area becomes hotter. When lightning strikes the exchange of electrons causes rapid polarity changes. Two events that cause eachother.//   

       Two simultaneous events can be caused by an independent third factor. In the case of heat transfer, the cold area becoming hot and the hot area becoming cold are both caused by whatever made the heat transfer occur in the first place. Same thing with the lightning. Just because two events cannot exist without each other doesn't mean they spontaneously cause each other. It just means that both events must be caused to happen simultaneously, or neither of them.   

       //When a dog unconsciously wags his tail he chases it and wags his tail more out of fun.//   

       Here you have a series of events that happen in series, with each event causing the next. The dog wagging his tail in the beginning causes the chase, which then causes him to wag it further, which causes him to chase it further, and so on. But he's not wagging his tail /because/ he's about to chase it. Even if he decides to wag his tail for the express purpose of chasing it, the initial wagging, and therefore the chase, was caused by the dog getting the notion to do so in the first place.   

       //I think my point is that when two mutually dependant things happen simultaneously then you view of linear causality is questionable.//   

       These things are mutually dependent on some third factor, not each other. That's the difference.   

       Regardless, this is still bad science. As [bungston] points out, this is just a description of the tachyonic antitelephone (link), which has been shown to be physically impossible. “A device capable of "telegraphing into the past" was later also called "tachyonic antitelephone" by Gregory Benford et al. According to the current understanding of physics, no such faster-than-light transfer of information is actually possible. For instance, the hypothetical tachyon particles which give the device its name do not exist even theoretically in the standard model of particle physics, due to tachyon condensation, and there is no experimental evidence that suggests that they might exist. The problem of detecting tachyons via causal contradictions was treated scientifically.”
ytk, Jun 18 2012
  

       The problem with trying to catch something that goes backward is that by the time it's outrun you, you've only just started chasing it, but if you simply sit down and wait for one, it's already been and gone.
Alterother, Jun 18 2012
  

       //Even so, you simply can't have two events that cause each other.
— ytk, Jun 15 2012 //
  

       Bollocks! Which came first, the chicken or the egg?
UnaBubba, Jun 18 2012
  

       The egg.
Alterother, Jun 18 2012
  

       I've long believed it was the rooster, or the egg would never have been fertilised.
UnaBubba, Jun 18 2012
  

       No, it was definitely the egg. One of your all-time classic modes of reproduction, the egg is. It's been in use since before the new-ecosystem shine was all worn off of the Earth. The chicken, however, is a much more recent evolutionary development.
Alterother, Jun 18 2012
  

       Except for that one universe where it's chickens all the way down.
Fowl universe that one.
  

       //Which came first, the chicken or the egg?//   

       By the egg, I assume you mean the chicken egg. Otherwise, the answer is clearly the egg, as [Alter] points out.   

       The answer to your question, though, is that the chicken and the egg came at the same time. It wasn't a chicken egg until it had a chicken in it, and it wasn't a chicken until it was in an egg. But although the existence of each is conditional on the existence of the other (they are biconditional), you can't say that they cause each other. In fact, both were caused by a third event—namely, a genetic mutation in the offspring of the ancestor species that gave rise to what we now call a chicken. The existence of the chicken and the existence of the egg, while dependent on each other, did not cause each other.

Let's look at it symbolically:

Let A be "A chicken exists".
Let B be "A chicken egg exists".
Let C be "Some event has occurred that causes a chicken to exist"

To prove that A and B are caused by some single event, we need to prove C <-> (A & B)

1) A <-> B (Given: A and B are dependent on each other)
2) C -> A (Given: If some event has occurred to cause a chicken to exist, then a chicken exists)
3) ~C -> ~A (Given: If no event has occurred that causes a chicken to exist, then a chicken does not exist)
4) ~A -> ~C (Step 2, modus tollens)
5) ~C <-> ~A (Steps 3 and 4, restatement)
6) C <-> A (Step 5, inverse)
7) C <-> B (Steps 1 and 6, substitution)
8) C <-> (A & B) (Steps 6 and 7, conjunction)
QED

Note that we have not proved the nature of this event, only that some single event is the cause of both A & B, and that single event is the sole cause of A & B. Therefore, since neither A nor B can have multiple causes, and must both have the same cause, they cannot cause each other.
ytk, Jun 19 2012
  

       For some reason I keep getting the funny feeling that this idea should be redundant with itself somehow...
RayfordSteele, Jun 19 2012
  

       //1) A <-> B (Given: A and B are dependent on each other) 2) C -> A (Given: If some event has occurred to cause a chicken to exist, then a chicken exists) 3) ~C -> ~A (Given: If no event has occurred that causes a chicken to exist, then a chicken does not exist) 4) ~A -> ~C (Step 2, modus tollens) 5) ~C <-> ~A (Steps 3 and 4, restatement) 6) C <-> A (Step 5, inverse) 7) C <-> B (Steps 1 and 6, substitution) 8) C <-> (A & B) (Steps 6 and 7, conjunction//   

       I got the chicken and egg exist at the same time. The chicken needs to keep the egg warm, or else the egg is fetid ooze.   

       The fetid ooze comes first. Now I must bring forth a fetid ooze of my own lest there is a chick to recieve it.
rcarty, Jun 20 2012
  

       Again, I would point to my observation that the rooster had to come first, or any egg would be sealed in a shell and remain infertile.
UnaBubba, Jun 20 2012
  

       A ROOSTER IS A CHICKEN YOU COCK!   

       Your reference to the substrate excited me.
rcarty, Jun 20 2012
  

       That may be, [rcarty]. However, a cock is not always a rooster... though it may prove to be a chicken, or at least look like part of one, at times.
UnaBubba, Jun 20 2012
  

       I think the idea is interesting, but instead of providing "free" or "unlimited" computing, I think we might instead be condemning untold future generations to a life of manning the machines.   

       It's a kind of physical debt transaction where in order for someone benefitting today, they are relying on the endeavours of someone in the future.   

       If you can imagine an analogy to the current economic situation today where for the next decade we can expect to be paying off the lending of the last 30 years, and applying it to data processing.   

       Someone's got to do it sometime.
zen_tom, Jun 21 2012
  

       I do seem to recollect a much earlier post on eggs. Basically, almost everything we eat is an egg (wheat, rice etc)..so the actual egg greatly precedes the chicken.
not_morrison_rm, Jun 21 2012
  

       //Those sound suspiciously more like two descriptions from different perspectives for the same event to me//   

       Every single "social" event occurs in at least two subjective parameters, bus as many as society can allow before the simultaenity hurricane begins.
rcarty, Jun 21 2012
  

       In order to travel back in time we will need to require the lightness of less than nothingness that we will become.
rcarty, Jun 21 2012
  

       // What kind of establishment serves egg as a starter and then keeps you waiting for the main course ?   

       Eggsactly..sorry I just couldn't resist it.
not_morrison_rm, Jun 23 2012
  
      
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