[QUOTE=Polerius]
Basically, it seems to me that there can be only one 1995.
[/QUOTE]
311’s “Down” will never be cool again. I will never be a freshman in high school again. :mad:
[QUOTE=Polerius]
One huge difference between quantum physics/SR/GR, and the multiverse idea, is that AFAIK the former ideas, even though “weird” by normal human standards, were proven experimentally “soon” after they were proposed (a physicist can confirm how soon this happened), while the idea of a multiverse with universes coming into existence and branching off of existing universes has been proposed a long time ago and there is not a shred of evidence to support it, and it’s not clear that there ever can be any experiment that will be able to verify it.
[/QUOTE]
That’s not exactly true. You see, while we can verify the predictions of quantum theory, we can’t verify the underlying mechanisms. Thus terms like “Copenhagen Interpretation” and “Many Worlds Interpretation”, referring the underlying nature of QM. The experiments, not to mention applications that support the mainstream interpretations of quantum mechanics ALSO support the Many Worlds Interpretation. No one has as of yet managed to perform an experiment to determine which is real; they all produce the same observed outcome.
[QUOTE=begbert2]
Your problem is with your definition of “you”; it’s too rigid to work with time travel. To solve all your problems, either relax your definition, or simply recognize that the “you” that travels into the past is not the same “you” that existed there previously; for practical purposes such as the ones you’re tripping over, you should think of them as being different people. Poof! All your conflicts vanish.
[/QUOTE]
Yeah, but the “you” for whom all conflicts vanish would be a different one than the one I start off as, which would mean I’d never know they had vanished, right?
[QUOTE=Polerius]
The many-worlds solution sounds more like science fiction and fantasy than science.
I would like to see some scientific evidence of the existence of other universes that branch out of our own, or exist parallel to our own, before we use the many-worlds solution to prove that time travel is possible.
[/quote]
The problem is, there’s no evidence either way on the question of whether each subatomic probability event causes our universe to bifurcate. Maybe it does, maybe it doesn’t. Either possibility, as I understand it, is equally consistent with the laws of quantum mechanics.
The many-worlds (branching) interpretation of those laws doesn’t ‘prove’ time travel is possible, of course. I fully expect that it’s impossible either way. But the assorted contradictions and paradoxes inherent in traveling back in time seem to be firmly rooted in the assumption of a single, linear time continuum, and vanish if we assume many-worlds.
[QUOTE=AHunter3]
My problem with time travel is as follows:
a) Time is a coordinate just as the spatial coordinates are coordinates.
b) At a certain longitude and latitude and elevation and time, some certain thing exists. You can “travel” on any of the four coordinates and thereby “go” somewhere else but any combo of all four coordinates brings up a specific reality. What’s there is there.
[/QUOTE]
Not to mention that movement through those time coordinates often appears to only travel in one direction. Hawking describes three “arrows”:
Thermodynamic arrow - Over time, objects tend towards entropy (disorder)
Cosmological arrow - Direction in the universe expands
Psychological arrow - Why do we remember the past but not the future?
So IOW, it seems to me that moving through the “t” axis is different from an object moving through the x, y, and z axis.
The feature of one particular multiple worlds theory that sounds good to me is that it says time travel is impossible but you can still have what amounts to time travel stories. There are infinite parallel worlds and we have this handy machine which can burrow through the boundaries which separate us from them. But we’re not really time traveling, see. It’s just very convenient for us that there is an identical universe which is X years offset from ours. So you can go to a universe where WWII is happening right now. But you couldn’t prevent it from starting in that time line. But you could go to another identical universe running in parallel where it’s 1939 or whatever and knock off Hitler and prevent it there.
[QUOTE=RTFirefly]
the assorted contradictions and paradoxes inherent in traveling back in time seem to be firmly rooted in the assumption of a single, linear time continuum, and vanish if we assume many-worlds.
[/QUOTE]
This whole many-worlds explanation of how time travel to the past might be possible is like if someone said
“Based on my analysis of how heavy the average pig is, there is no way to transport 100 pigs from point A to point B using that dolly”
To which someone else replies
“Yes, but if pigs could fly you could get 100 of them from point A to point B with no problem”
And this would be stated with no proof whatsoever that pigs can fly, no one ever witnessing a pig fly, and no one even hinting as to how to set up an experiment that would help determine whether pigs can fly.
“Pigs flying” == “Many worlds”
[QUOTE=CalMeacham]
The “Grandfather Paradox” is unusually invoked to show that Time Travel, as in the simple sort imagined in science fiction stories, can’t happen – otherwise, you;d be able to go back into the past to kill your own grandfather, thereby preventing you from building a time macine and going into the past in the first place. …
Robert Forward, physicist (and science fiction author) didn’t buy this. …
[/QUOTE]
Douglas Adams didn’t buy it either: One of the major problems encountered in time travel not that of becoming your own mother or father. There is no problem involved in becoming your own mother or father that a broad-minded and well-adjusted family can’t cope with. There is no problem about changing the course of history- the course of history does not change because it all fits together like a jigsaw. All the important changes have happened before the things they were supposed to change and it all sorts itself out in the end.
The major problem is quite simply one of grammar… Separately (quite), Hawking doubted whether time travel exists, because if it did there we would have noticed crowds of tourists bussed in from the future by now. Another commentator, possibly Paul Davies, speculated that time travel could still be possible, if it was also extremely expensive, and therefore only used for serious purposes by big governments or maniacal quadrillionaires.
[QUOTE=Polerius]
This whole many-worlds explanation of how time travel to the past might be possible is like if someone said
[/QUOTE]
Naw…it would be more along the lines of something like this:
‘Why is the universe all lumpy? Why isn’t it uniform?’
‘Well, we posit that perhaps there were irregularities in the singularity that existed before the Big Bang, and those irregularities formed…’
‘Wait! How do you know this?’
‘Well, we don’t…it’s a theory…’
‘Ah ha! And whats a singularity exactly?’
‘Well it’s a place in space time where the gravitational field becomes infinite. Basically a point mass…like beyond the event horizon of a black hole. You see…’
‘Hold on a second! How do you know what’s in one? Infinte gravity?? Sounds like bullshit to me…nothing is infinite!’
‘Well, we don’t know for certain. It’s a theory…look, do you want me to show you the math?’
‘Hell no! Math schmath! Lets talk about flying pigs!’
sigh ‘Ok…’
The thing is…there is nothing in our current understanding of quantum mechanics or cosmology that rules out the multi-worlds interpretation. Respected physicists both support and deny it. The math seems to work out…but it’s a theory. It’s not made up science fiction but based on real theoretical physics and back up by the math.
Does this mean it’s right? Hell no…we may never know if it’s true or not. But it’s not creationism or dowsing for water either.
And afaik there is nothing in the ACTUAL physics or the math that precludes time travel either…
-XT
I wonder about the granularity of the many worlds. Say there’s this guy, Zeno, whose home is a certain distance from the Elea town market. There is another world exactly like this one except Zeno’s home is 50% closer to the market. There’s yet another where his home is 75% closer, and yet others where it’s 87.5%, 93.75%, 96.875%, 98.4375%… closer. Would there be some granularity limit or is it the case that there is no world in which Zeno’s home is closest to the market?
[QUOTE=xtisme]
The thing is…there is nothing in our current understanding of quantum mechanics or cosmology that rules out the multi-worlds interpretation. Respected physicists both support and deny it. The math seems to work out…but it’s a theory. It’s not made up science fiction but based on real theoretical physics and back up by the math.
Does this mean it’s right? Hell no…we may never know if it’s true or not. But it’s not creationism or dowsing for water either.
And afaik there is nothing in the ACTUAL physics or the math that precludes time travel either…
-XT
[/QUOTE]
I am not familiar with this math or these theories and have a question about them: in them, are the various alternate universes created by the time traveler, or do they already exist all the ‘time’ before that (like in marshmallow’s proposal)?
[QUOTE=begbert2]
I am not familiar with this math or these theories and have a question about them: in them, are the various alternate universes created by the time traveler, or do they already exist all the ‘time’ before that (like in marshmallow’s proposal)?
[/QUOTE]
I doubt there is a theoretical model for this question. I was actually talking about the multiple universes theory (to which there IS math underlining it…though like you I’m not conversant in it either. It is FAR beyond my meager abilities to grasp).
My WAG on your question would be that IF one could actually move from this universe to an alternative universe where time flowed differently and it was, say, 1939, then that universe would already be there…i.e. it wouldn’t be created by the time traveler but part of an infinite number of related but different universes that are constantly being created (or destroyed…not sure about this part)…sort of like soap bubbles that almost touch but not quite.
Understand that I’m no physicist. I may be completely or partially mis-representing the basic theory (in fact, I am almost certainly doing so)…or conflating various sci-fi books I’ve read along with the very limited grasp I have of the actual physics. My point in all this was to try and show that there ARE possibilities that real physicists (who actually do know this stuff) acknowledge. The multi-worlds/multi-universe interpretation is an acknowledged possibility among physicists, not just sci-fi or pigs flying or whatever. It’s a working theory. Whether it’s main stream (I THINK M-Theory is pretty main stream and that seems to lend itself to this interpretation) or not I couldn’t say…and whether it’s true or not I REALLY couldn’t say. And neither could the physicists who endorse this possibility as at this time there is no way to test it to see.
Even if it IS true that doesn’t necessarily mean we could go from this universe to another. Perhaps there is some mechanism that would prevent this. The thing is that no one in this thread REALLY understands either the conceptual parts of R/GR or QT or the other related subjects let alone the underpinning mathematics…at least no one that I’ve seen in the thread so far. ‘Logic’ and common sense are really out the air lock when you start talking about quantum physics and relativity…they simply don’t work in a logical, common sense way to most of us.
-XT
Some food for thought if time travel might work similar to the OP
Imagine you have a box with a red light, and a green button. Everytime you press that green button, the red light blinks, but does so – not in the present – but 3 seconds in your past.
Every time you saw the red light blink, you KNOW you’re going to press that button 3 seconds from now. What would happen if you saw it blink and tried NOT to press it 3 seconds later. I tell you, madness lies there.
And I love Lemur866’s logic in post #30. Disappointing conclusion, but makes complete sense to me.
[QUOTE=cmyk]
Some food for thought if time travel might work similar to the OP
Imagine you have a box with a red light, and a green button. Everytime you press that green button, the red light blinks, but does so – not in the present – but 3 seconds in your past.
Every time you saw the red light blink, you KNOW you’re going to press that button 3 seconds from now. What would happen if you saw it blink and tried NOT to press it 3 seconds later. I tell you, madness lies there.
And I love Lemur866’s logic in post #30. Disappointing conclusion, but makes complete sense to me.
[/QUOTE]
Right - madness lies there, assuming that your timeline is sensitive to “paradox”; that is, that your timeline requires that when the dust settles, all the causes and effects still line up and all the time travel departures and arrivals all match up perfectly.
If you make no such assumption, then seeing a green light would only tell you that you would have pressed the button in three seconds, had you not seen the green light. By pressing green button in the ‘future’, you [del]killed your grandfather[/del] changed your decision making environment about pushing the button, and thus changed the future, possibly into one where you didn’t push the button. Which needn’t bother the universe at all, for all I know.
I’ve always assumed physical time travel isn’t possible. On the other hand, what if it is possible to alter one’s perception of the present? If memory could become reality?
If you could look out of your own 17 year old eyes, and speak with your 17 year old mouth? Could you alter the past?
I don’t recall if it’s been posted in this thread yet, but The Master has weighed in on this question already. I’ve seen other theoretical time machines that work in other ways than this as well.
-XT
…effects cannot preceed cause. Simply put, you and I are the results of our parent’s sexual acts. If you were to travel to a point BEFORE your birth, the atoms making up your boddy existed in totally different confugrations. Plus, chemical reactions don’t run backwards. However, I just had a thought: if past present and future can exist simultaneously, then viewing the past is possible (like Scrooge viewed his past and future). Scrooge was able to alter his futre, but not his past. Maybe we are thoughts in the mind of God!
[QUOTE=ralph124c]
..effects cannot preceed cause. Simply put, you and I are the results of our parent’s sexual acts. If you were to travel to a point BEFORE your birth, the atoms making up your boddy existed in totally different confugrations. Plus, chemical reactions don’t run backwards. However, I just had a thought: if past present and future can exist simultaneously, then viewing the past is possible (like Scrooge viewed his past and future). Scrooge was able to alter his futre, but not his past. Maybe we are thoughts in the mind of God!
[/QUOTE]
I think the minute you start to posit time travel at all, you explictly are denying that effects have to follow causes; so your protest sounds kind of like “You can’t make a machine that can fly!” “Why not?” “Because things that are unsuspended in the air fall down!” Such an argument doesn’t really seem all that strong to me, even if we don’t have time-traveling birds around actually proving that your assumption is wrong.
From what I hear, even hypothetical Einsteinian time travel will only let you travel back to the time the time machine was invented. Find the This American Life podcast for reference.
[QUOTE=Polerius]
This whole many-worlds explanation of how time travel to the past might be possible is like if someone said
“Based on my analysis of how heavy the average pig is, there is no way to transport 100 pigs from point A to point B using that dolly”
To which someone else replies
“Yes, but if pigs could fly you could get 100 of them from point A to point B with no problem”
And this would be stated with no proof whatsoever that pigs can fly, no one ever witnessing a pig fly, and no one even hinting as to how to set up an experiment that would help determine whether pigs can fly.
“Pigs flying” == “Many worlds”
[/QUOTE]
That analogy doesn’t work. We know that the pigs get from point A to point B, but we don’t know how. We can’t prove that there IS a dolly to carry them. We know they get from point A to B; we know that there are certain ways that can be achieved; but we have no evidence as to which way is being used. Perhaps a dolly. Perhaps a catapult ( so they ARE flying ). Perhaps they just walk.
At our present state of knowledge, the many worlds theory is no more or less implausible than any of the alternatives.
[QUOTE=ralph124c]
..effects cannot preceed cause.
[/quote]
Define “precede”. If time travel is possible, a cause in the future could precede one in the past, because then past events would no longer automatically precede future ones.
And maybe we are all in the Matrix. :rolleyes: