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Time Travel
June 17, 2005 6:31 PM   Subscribe

Back to the FutureDrawing Board
posted by Pretty_Generic (42 comments total)

 
I'd swear this was a double post.
posted by I EAT TAPES at 6:33 PM on June 17, 2005


I just want my damn time machine already. Is that too much to ask?
posted by cmonkey at 6:34 PM on June 17, 2005


Well, I'd go back and try to save that kitten.
posted by DeepFriedTwinkies at 6:40 PM on June 17, 2005


I wish I was a quantum mechanic. It seems like a lot of making shit up to gullible folks for shits and giggles. Actually that seems like what auto mechanics do too.

Anyway, you can have your time machine when I get my hoverboard, dammit.
posted by Stan Chin at 6:42 PM on June 17, 2005


The explanation of the theory does sound incredibly childish to me. The idea that by going back in time, you lose your free will and "will always choose to" maintain the future as it was... doesn't it really indicate that going back in time is logically impossible?

And, uh, is the City University of New York a good university?
posted by Pretty_Generic at 6:44 PM on June 17, 2005


Quantum behaviour is governed by probabilities.
Sounds like the way Douglas Adams explained the Infinite Improbability Drive. (Oops. A vase of flowers just fell to the ground next to me.... AAAAAAAAH! WHALE!!!!)
posted by wendell at 6:50 PM on June 17, 2005


You need a strong cup of tea.
posted by Pretty_Generic at 6:52 PM on June 17, 2005


This is not news. I read about this in Flatterland three years ago.

This looks like SoftNewsFilter to me. (no offense, PG; I blame the BBC.)

I've always figured that paradoxes are unstable waveforms, and therefore collapse. In other words, the reason nothing impossible has happened is not that it can't happen, but simply because of all the infinite possibilities at any one point in time, only the stable ones manifest as reality (the others die out within Planck-moments). We are here because it is possible and probably for us to be here (wherever we happen to be at any point in time).
posted by Eideteker at 6:53 PM on June 17, 2005


Wouldn't the Butterfly Effect negate all possibility?
posted by Gyan at 6:56 PM on June 17, 2005


I saw this stupid damned theory being bandied about last time I was in 2005 and I couldn't stop the bastards printing it then, either.
posted by Decani at 7:00 PM on June 17, 2005


I'm with Stan i think--it takes all the fun out of time travel if you can't do stuff or interact at all.

CUNY's good for some things, Pretty--it all depends.
/proud 2nd-gen. graduate
posted by amberglow at 7:04 PM on June 17, 2005


Eideteker, many things aren't really that probable tho, and if you look back thru history, i think you see tons and tons of really improbable things.
posted by amberglow at 7:05 PM on June 17, 2005


This idea was put forward some time ago by Harlan Ellison in his short story "Go Toward the Light", which was published in the anthology Slippage.

If time travel is allowed but renders a self-consistent universe, we can't progress in any other way but in a deterministic fashion. So much for free will.
posted by Rothko at 7:08 PM on June 17, 2005


Eideteker, by your reckoning, would someone going back in time be doomed to instant death? Or could they live on in an alternate future of their own?
posted by Pretty_Generic at 7:09 PM on June 17, 2005


So much for free will.

This isn't anything new.

Think of yourself as a function of the universe. It puts a little smile on my face and makes me feel a little less lonely on these long friday nights at work when all my friends are out imbibing cell-damaging substances.
posted by angry modem at 7:32 PM on June 17, 2005


Wouldn't the Butterfly Effect negate all possibility?

Nope. You can always fulfill the future rather than negating it -- it all pieces together like a jigsaw puzzle. (Also, you should read Greg Egan's "The Hundred-Light-Year Diary" (in Axiomatic), which takes this time travel theory to its ulitmate psychological and sociopolitical conclusions).
posted by Tlogmer at 7:51 PM on June 17, 2005


amberglow: Improbable is like an entire mountain turning to gold. I'm not saying it couldn't happen, but it's very improbable. I'm not talking about things like Bush getting reelected or a small independent film winning multiple Oscars. I'm talking physical (quantum) improbability.

Pretty_Generic: Think about this: Would someone going back in time continue to perceive time forwards for just himself? If so, then he hasn't really gone back in time; he's gone forward in time for himself (unless there is some sort of meta-time). So by going "back" in time, you've already entered a different set of conditions then the place you were attempting to go. It is not the same reality by virtue of your presence. Whether it is an "alternate universe" is irrelevant; it's not the same place you came from. You literally can't cross the same river twice (even if you travelled "back" in time through a method that looked like reversing the video tape, it's still just the one crossing). What the article is saying is that you can't go back in time unless you already went back.
posted by Eideteker at 7:59 PM on June 17, 2005


What the article is saying is that you can't go back in time unless you already went back.

There are other theories that work out by way of multiple universes.

For example, the "murdered father" paradox can also be resolved by way of two universes where you exist in one but not the other, and you continually flit in and out of existance.

This "new" theory is nothing too special. There are many ways to resolve paradoxes in time travel.
posted by Rothko at 8:06 PM on June 17, 2005


Tlogmer: Nope. You can always fulfill the future rather than negating it -- it all pieces together like a jigsaw puzzle.

The point is that you're adding a new piece to the puzzle. The only other way, as I see it, is that the possible time-travel vectors are constrained and must happen, hence always being part of the past.
posted by Gyan at 8:08 PM on June 17, 2005


Whether it is an "alternate universe" is irrelevant

Well, it seems important to know whether you would be alive or dead if you attempted it... what would this theory indicate would happen if you did try to alter the future (and none of that "your victim would always be in a different room" nonsense)?
posted by Pretty_Generic at 8:24 PM on June 17, 2005


Although quantum physics proves that reverse time is possible, I think forward time, or cause and effect is the only relationship that conscious beings can understand. Maybe we select cause and effect relationships in a static universe of infinite possibilities, thereby creating time in our heads. If time is an illusion resulting from our selection of the only "events" that make sense, then time travel is an illusion composed of the events that don’t make sense.

The principle of least action is an interesting paradox. If light obeys our notion of time, how can it possibly refract through a denser medium on the optimum path to reach a destination in the least possible time without knowing the destination in advance? Don't tell me it's due to the index of refraction, since we derive that index from the light’s path.
posted by weapons-grade pandemonium at 8:45 PM on June 17, 2005


PG: I'm assuming you made it "there" alive; there was no mechanical malfunction that killed you. If you made it there alive, you would not be where you thought you were (unless you were there originally). Unless you were present there the first time, your presence has altered the quantum waveform of that universe so that it is not the one you departed from. Anything you do affects your future, and the future of those around you, but it cannot affect your past or the past of those you left. You are still travelling straight-forward on a line.

If you went back to 1955, it would still be 2005 for you. You might as well have stood still while they changed the scenery around you to look like 1955; it's still 2005 as far as your timeline is concerned. The only way for you go back to that time would involve you physically regressing to the age you were then (assuming you were alive; I just picked 1955 at random since things probably looked a bit different then), and in that case, you would lose all the memories you'd stored in that time. Nothing would have changed, because you'd be in the same exact universe (a = a, all physical condtions identical), so you would not be able to change anything (barring a discussion on freewill; you'd basically have to make the same choice a different way).

I don't want to be condescending, but I like metaphors. Imagine a buffet at a really well-run restaurant. Every time you go back to the buffet, it's completely stocked. In fact, it looks the same as the last time you went up. But it's not the same, because you've already eaten that food. The food you eat the second time is not the same as the first, nor the third. If you go up the third time and decide that this time you want to get tartar sauce with the shrimp instead of cocktail sauce, you're not actually changing what you already ate. You're changing what you are eating, at best.
posted by Eideteker at 8:52 PM on June 17, 2005


WGP: We perceive time in the direction of the flow of Entropy. The reason we perceive things the way we do is that our memories are actually a result of an entropic function in our brains. Light doesn't have to worry about this; time is reversible for objects with no memory and therefore no concept of the flow of time.
posted by Eideteker at 8:59 PM on June 17, 2005



I asked God
Do one thing for me
Send me back in time
Send me to Seattle
Let me go
Find Kurt Cobain
Take away his gun
Take away his bullets
Talk to him
Make him wanna live
Tell him how we love him
Help him see his glory
God Said No
If I sent you back
If you really found him
You would only ask him
If he could
Help you get a deal
If he knows a lawyer
If he can help you
God Said No


--Dan Bern, from the song "God Said No"
posted by extrabox at 9:02 PM on June 17, 2005


Eideteker, isn't this a circular argument, like my index of refraction point? Entropy is a notion based on time that we create in our heads. By your reasoning, entropy doesn't have memory, so it is reversible.

Great poem, extrabox.
But what did God say to Eric Clapton when he asked to see his boy?
posted by weapons-grade pandemonium at 9:18 PM on June 17, 2005


Blah, this is just a matter-of-fact resolution of paradox mixed with the waveform collapse of quantum uncertainty. It's nothing terribly new, just putting two disparate pieces together that may not even fit.

The explanation of the theory does sound incredibly childish to me. The idea that by going back in time, you lose your free will and "will always choose to" maintain the future as it was... doesn't it really indicate that going back in time is logically impossible?

Yeah, that is dumb. I think what they were actually going for originally is:
i) all changes in time (if such is possible) have worked themselves out "already" -- obviously. Someone goes back in time and cleans off my desk, it won't suddenly "become" clean. It will be clean already.
ii) waveform collapse is permanent. I look in the box and see that the cat is dead (or alive), and when you look later, you always get the same result. Always.

But this business of "murdering your father" if you don't know he's alive... strikes me as a bit odd. What if someone else knows he's alive? The waveform doesn't respond to particular personalities, but to any conscious observation.
posted by dreamsign at 9:54 PM on June 17, 2005


I'm really interested in WGP's question about the behaviour of light in different mediums. Does anyone have more links I can look at to read up on this? It's one of those deceptively simple "of course it does" kinds of things, but when you really think about it, it doesn't make the slightest bit of sense without destroying the entire notion of a universe without fate, without a predetermined future, i.e., it requires an entirely complete universe.
posted by odinsdream at 10:54 PM on June 17, 2005


Google least action for more of this, odinsdream.

Here's the double slit paradox, where a single photon seems able to go through two slits and create an interference pattern with itself. If one observes which slit the photon goes through, the interference pattern disappears.
*cues Twilight Zone music*
posted by weapons-grade pandemonium at 11:52 PM on June 17, 2005


First, as mentioned, there are several quantum interpretations and we don't know which is correct. The leading ones being copenhagen and many worlds. The transactional interpretation is gaining ground in light of recent tests.

Second, it's been demonstrated, very convincingly, that while wormholes are quite plentiful at the quantum foam level, it's impossible to make the amount of negative energy that would be necessary to maintain the negative space-time curvature at the waist of the wormhole on a macroscopic level.

Finally, even if you could somehow extract that much exotic negative energy, you still wouldn't be able to travel any further back in time then when the wormhole was created--there wouldn't be a past to alter, rather, you would just be "altering" the future.

Like faster than light travel or that singularity crap, it's just not going to happen.
posted by cytherea at 12:17 AM on June 18, 2005


wgp: The spooky thing about the double split paradox is the fact that even if you send only one photon (or electron) at a time, say, once a week or so, you'll still get an interference pattern. This is odd, since there's nothing the photon/electron could be intefering with, except itself or possibly the photons/electrons sent weeks before.
posted by sour cream at 12:23 AM on June 18, 2005


weapons-grade pandemonium : "If one observes which slit the photon goes through, the interference pattern disappears."

If Afshar's experiment has a mundane explanation. It seems it probably does.

cytherea : "The leading ones being copenhagen and many worlds"

I believe some informal surveys indicate that Many-Worlds is now the preferred interpretation.
posted by Gyan at 12:29 AM on June 18, 2005


wendell writes "Quantum behaviour is governed by probabilities.
"Sounds like the way Douglas Adams explained the Infinite Improbability Drive. (Oops. A vase of flowers just fell to the ground next to me.... AAAAAAAAH! WHALE!!!!)"


It was a bowl of petunias... Bloody amateurs!
posted by benzo8 at 3:18 AM on June 18, 2005


Clearly, the present never is changed by mischievous time-travellers: people don't suddenly fade into the ether because a rerun of events has prevented their births - that much is obvious.

Like, dude, how would we know?
posted by cccorlew at 8:00 AM on June 18, 2005


Wow. Talk about making a statement noone can disprove. I mean really. "Prove I'm wrong, penisbreath!" You can sit smug knowing that your discreditors would have to invent a time-travelling device to do so, and then you could take credit for inspiring them in the first place.
posted by Busithoth at 8:53 AM on June 18, 2005


Don't tell me it's due to the index of refraction, since we derive that index from the light’s path.

We don't say the "index of refraction" causes light to bend: it is just a number, a parameter.

We observe different materials having different indices, and saying light bends differently is down to this index is just a turn of phrase.

Light doesn't "know" to bend. It just does as it goes through the material. The material has a particular index, which we can ascribe to the material by way of observation.
posted by Rothko at 9:42 AM on June 18, 2005


Yes, and that was my point, Rothko. But in thread some months ago, someone discounted least action by invoking the index of refraction. I was trying to defuse a common circular argument. When I asked how light can bend "without knowing the destination in advance", I wasn't implying that it did know. There must be another explanation, as in: "How can the blind read without seeing?"
posted by weapons-grade pandemonium at 10:25 AM on June 18, 2005


"...we derive that index from the light's path."

We can observe it from the light's path, but we derive it from the dielectric constant. Which, to be fair, is also a response to electric energy. But for many media it can be purely theoretically solved for. It's not just an empirical parameter.
As I understand it, and the physicists can correct me if I'm wrong, the light bends because it is entering a material which slows it (or allows it to go faster, as the case may be), and the bending occurs in order for the wavefront to remain coherent.

Back to topic, I was surprised when BBC put this up today; I didn't think it was new. It's just the claim that any time travel would be self-consistent.

ccccorlew: I thought that too. They wouldn't just cease to be, they would cease to ever HAVE been. How WOULD we know?
posted by solotoro at 6:21 PM on June 18, 2005


I really can't tell from reading that whole piece whether it's just the writer who's clueless or the people she's talking to as well. The whole point of a paradox to time travel and killing somebody is to kill someone whose death would make you not exist, therefore unable to go back in time and kill anybody, etc. That's why it's usually not your father but your young grandfather (hence the term "Grandfather Paradox"), whose death would assure you didn't exist.

Not only is none of that mentioned, but it gets worse: Talking about not knowing whether your father is still alive is evidence of a profound misunderstanding of this basic paradox: Whether your father is currently alive, or whether he died at any arbitrary point in the past, is completely irrelevant - it's whether you're alive in order to go back in time that is at issue. If you're standing around wondering whether your father's currently alive, the central question has already been answered.
posted by soyjoy at 8:34 PM on June 18, 2005


In the 'many worlds' theory, which I personally prefer when enjoying temporal physics type science fiction stuff, any and all possibilities are in existence. ALL of them.

The real mental zinger here is, when you go back in time, your presence doesn't create that alternate reality. It was always there. Or rather, it was always meant to be there, because if you are successful in going back in time, you were always meant to do it. You were also always meant to fail, so there's at least one alternate reality in which something bad happens on the way into the past that caused your death, and there's an alternate reality that plays that out.

There's alternate realities 'out there' where your every dream has been fulfilled, provided it was even remotely possible your dream could have happened. There's realities out there where the worst possible things that could happen to you have. There's also realities out there where everything in between existed. If you stubbed your toe on March 13th 1978, there's realities out there where you didn't. Every person reading these words and every person not reading them, it's true for them too. At least, in theory.

Every possible outcome has/is/will happen. That's what infinity means. It's literally incalculable. Einstein woulda had a cow.
posted by ZachsMind at 10:56 PM on June 18, 2005


...and if you're right, he did.
posted by weapons-grade pandemonium at 11:29 AM on June 19, 2005


absolutely! =)
posted by ZachsMind at 1:11 PM on June 19, 2005


that many worlds stuff is so Sliders. : >
posted by amberglow at 1:17 PM on June 19, 2005


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