Parallel Universes

[Mighty Jalapeno]

Ok, one thing that's always bothered me about parallel universes:

Premise The First: It's a universe. The WHOLE universe. It's right in the name.
Premise The Second: Any action that could be taken in one manner is taken in a different manner in the other Universe.
Premise The Third: By default, there would be infinite numbers of these universes.

However, if it's the whole Universe, that means that every action an alien takes in another galaxy creates a parallel universe, including a parallel Earth, where things AREN'T different. Assuming every action in the ENTIRE universe creates a parallel, then there would be an infinite number of parallel universes which are, within the boundaries of our solar system, exactly the same.

The result, of course, is that if there is an infinite number of IDENTICAL parallel universes, then if you managed to go to one it would be exactly the same as this one in every respect, which means the 'you' in that Universe would have just moved to a parallel universe right when you did, which means you are now occupying the space occupied by HIM a moment ago. You would be in an utterly identical world, occupying the former space of an identical you.

End result: As far as you know, you didn't go anywhere and the experiment failed.

...

Also, just a good place to discuss parallel universe theory.

Hi!

BEST SUBFORUM EVER!

[Diadem]

Well, it's true that some of the parallel universes are identical to ours. But the fraction of identical universes is of course vanishingly small. So how are you going to find one of them? You need some sort of mechanism not just to travel between parallel universes, but to travel to a specific one. Secondly, why would you end up in the same place if you travel to another universe? You might be displaced by several lightyears. Or by several normal years. Hmm, you might even use that as a method for FTL travel

[Sungura]

How would you know which universe you ended up in and which you came from? And if there are infinity many, could you even find the one you came from again? That is what worries me. I'd never make it back to where I started. Unless they are all identical, and then what is the point because nothing changed, right?

[netcrusher88]

Sliders!

The problem with travel between infinite universes is that you won't discover travel between them in all of them therefore the number where you will is a finite fraction of infinity and anything divided by infinity is as close to zero as no matter so you're not going to discover travel between infinite universes.

QED, the multiverse is a figment of its own imagination.

[KrO2]

If a new universe is created by a choice by an alien in a distant galaxy, is that instantaneous, or is there a speed-of-light delay before the fact that it exists reaches us? Silly me, wondering about FTL when we're already traveling past the bounds of the Universe.

Unforewarned subject change: If there's an infinite number of universes, then anything that can possibly happen with a nonzero probability will happen, and will happen an infinite number of times. Where the "size" of the infinity is based on the probability of the thing happening. So there would be an infinite number of universes that are completely identical to ours, as well as an infinite number that are identical in every observable way. Diadem's point about how virtually no universes are identical to ours holds if universes are arranged randomly. I think in some works of fiction (hey, it's not like we have any real sources to go by), more similar universes tend to be "closer together," so any experimental interuniverse travel would appear to have failed rather than ending up in a visibly different universe. One thing I'm not clear on is, is saying that you end up in the same point but in a different universe assuming that there's a privileged reference frame? Otherwise, you're in the same point relative to what? Yourself?

[New User]

Well, it's true that some of the parallel universes are identical to ours. But the fraction of identical universes is of course vanishingly small.

If there is an infinite number of universes identical to this one, and an infinite number of universes that are different, the fraction doesn't seem to be vanishingly small to me. But it's my understanding infinity over infinity does not equal one.

[ssund]

what about just communicating with a parallel universe instead of traveling there? What effect would be made on the other universe if any?

[Virtual_Aardvark]

It begs the question of whether we could even travel to any universe. What if the only parallel universes we could travel to are the ones we created ourselves?

[phlip]

One thing I'm not clear on is, is saying that you end up in the same point but in a different universe assuming that there's a privileged reference frame? Otherwise, you're in the same point relative to what? Yourself?

Saying "same place" or "same time" requires a privileged reference frame, but "same place and same time" does not, in SR at least (and I'm pretty sure GR too).

[Yakk]

You can do away with infinities.

Suppose the universe is quantized. Every Planck time period in every Planck volume one of two things happen. Each of these fork the universe into two.

The volume of the observable universe is about E80 cubic meters.

A Planck length is about E-35 meters. So there are E185 cubic Planck lengths in the observable universe.

The universe is roughly E10 years old, or E18 seconds. A Planck time unit is E-44 or so, so the universe is E62 Planck time units long.

If every Planck time unit in every Planck volume, a single random bit is split into two possibilities, you get 2^(10^185) universe copies created per Planck time unit. Over E62 Planck time units, this generates a total of roughly 2^(10^247) parallel universes.

This is reasonably large, but not infinite. And you can count and divide and generate probabilities.

---

Going further, we could apply the holographic principle, and say that the two copies of the solar system in which the solar system is the same, but all signals from the rest of the universe are identical, are actually the same solar system -- and similarly, the universes where the solar system varies but the boundary condition of what is emitted from the solar system stays the same is the same solar system. Ie, boundary conditions are what we care about.

In essence, whatever happens where you cannot observe it, everything happens. This sort of (in a hand-wavy sense) explains Quantum Mechanics -- when two things aren't interacting, or are carefully isolated from each other, the boundary conditions between them permit multiple states in each other, so these multiple states are real.

In this case, you are in effect in every parallel universe where the solar system is identical. You cannot "travel" there, because they are the same place.

[mister k]

You can do away with infinities.

Suppose the universe is quantized. Every Planck time period in every Planck volume one of two things happen. Each of these fork the universe into two.

The volume of the observable universe is about E80 cubic meters.

A Planck length is about E-35 meters. So there are E185 cubic Planck lengths in the observable universe.

The universe is roughly E10 years old, or E18 seconds. A Planck time unit is E-44 or so, so the universe is E62 Planck time units long.

If every Planck time unit in every Planck volume, a single random bit is split into two possibilities, you get 2^(10^185) universe copies created per Planck time unit. Over E62 Planck time units, this generates a total of roughly 2^(10^247) parallel universes.

This is reasonably large, but not infinite. And you can count and divide and generate probabilities.

---

Going further, we could apply the holographic principle, and say that the two copies of the solar system in which the solar system is the same, but all signals from the rest of the universe are identical, are actually the same solar system -- and similarly, the universes where the solar system varies but the boundary condition of what is emitted from the solar system stays the same is the same solar system. Ie, boundary conditions are what we care about.

In essence, whatever happens where you cannot observe it, everything happens. This sort of (in a hand-wavy sense) explains Quantum Mechanics -- when two things aren't interacting, or are carefully isolated from each other, the boundary conditions between them permit multiple states in each other, so these multiple states are real.

In this case, you are in effect in every parallel universe where the solar system is identical. You cannot "travel" there, because they are the same place.

What Yakk said. I've yet to be convinced that our universe isn't depressingly discrete, which would indeed lead to a really, really large number of parallel universes. Not that traveling betwixt them would make much sense. I would certainly imagine you'd have the sliders effect- effectively bouncing from one universe to the next, I don't see how one could directs one path sensibly (I want to go to the universe where I kissed that girl when I was 16. Now where the devil is the setting on my universe jumper for that?)

[SlyReaper]

And that's to say nothing of all the universes where the Earth never even managed to form. You'd go through your wormhole and emerge in the empty vacuum of space. Can't breathe! Or it formed in the same place, but has a radius 500m smaller than ours. WHEEEEEEEEE *splat* Or 500m bigger? "Bugger I'm stuck, can't move."

Of course this could be solved if you just sent a probe ahead of you, and could move the far end of your wormhole around. But where's the fun in that?

[Cobramaster]

See Slyreaper this is why you find a nice empty pocket of Space and hope nothing is different in the other universe, say somewhere outside of Pluto's orbit, which should not be a problem considering if we had the tech to bridge the gap of a few light hours to make it "home" Assuming of course you do not end up in an entirely separate region of space due to some rotation of the matter spread compared to our universe, given that a few degrees(or even minutes and seconds if we are far enough from the center) would equate from hundreds to millions of lightyears difference in where all of matter ends up with theoretically no real difference. That is of course if you look at the universe represented in a 3D grid, that is held in relation to all universes. And now for the ultimate horror the one universe that never expanded, just sitting there infinitely compressed energy and matter waiting forever to be released. Oh god the things you realize must be true if you fully accept the theories thrown around.

[MrConor]

However, if it's the whole Universe, that means that every action an alien takes in another galaxy creates a parallel universe, including a parallel Earth, where things AREN'T different. Assuming every action in the ENTIRE universe creates a parallel, then there would be an infinite number of parallel universes which are, within the boundaries of our solar system, exactly the same.

The result, of course, is that if there is an infinite number of IDENTICAL parallel universes, then if you managed to go to one it would be exactly the same as this one in every respect, which means the 'you' in that Universe would have just moved to a parallel universe right when you did, which means you are now occupying the space occupied by HIM a moment ago. You would be in an utterly identical world, occupying the former space of an identical you.

End result: As far as you know, you didn't go anywhere and the experiment failed.

There appears to be a problem here. You've moved from "a distinct universe which is identical to our own within the boundaries of our solar system" to "a universe which is identical to our own". The two parallel universes aren't the same: one of them is our own, and one of them is our own except for the consequences of the alien's action. There is an important distinction between being identical and merely appearing to be identical. You don't know what's going to happen in the future as consequence of the alien's action - he might have fired a rocket into space which after billions of years of travelling hits the Earth and kills everyone on it.

I find that, when considering parallel universes, it's better to consider them atemporally. Rather than thinking of a parallel universe as "another three-dimensional space which is somehow different from our own" think of it as a complete, discrete unit - a series of events beginning with a point of creation and ending in some kind of universe-death scenario.

[Eddie Editor]

It's nonsensical to say that when a decision is made 'a parallel universe is created.' (It's also massively egocentric to believe we have the power to create a parallel universe merely by deciding whether to have a cup of coffee or a cup of tea!).
Whatever happened to the law that energy cannot be created or destroyed?
A phrase that drives me mad is "an infinite number of...."
When we put the word 'number' and 'infinite' together, we reinforce the misguided notion that infinity is simply a very very very big number. It's not. The concept of infinity is in a category of its own. To relate it to our feeble understanding of incredibly high numbers is pointless and misleading. You can't have an infinite number of monkeys. You can however, have 'infinite monkeys' - it might seem the same but it isn't. The word universe means everything there is - you can't have an infinite 'number of universes,' but you can have an infinite universe.
The infinite universe you can have however, can be a lot more interesting than the worn out sci-fi 'Sliders' type concept of parallel universes. The infinite universe can be simultaneously exploding in the big bang, compressing to nothing in the big crunch - and also at every other stage between those two extremes (including what we think of as the present moment). Yeah, okay, in order to think about that, it might be useful to imagine the old idea of 'infinite parallel universes', all slightly younger or older than each other, and all identical to the one we see, except at different stages of its development. It's useful to imagine them this way, yeah, just as long as we keep in mind that this way of looking at it is purely mental aid, a model in which we can try to get to grips with it because - it's all the same universe really.
What does this do for us? Well, as it's all one universe, IF it's imperfect, then leakage of data from the older or younger universe, might occur. This might, at least in the realms of fiction, explain the sensation of deja vu, when data leaks through from slightly older 'universes' (or to be correct, from the older stage of the universe).
In the case of data leaking into our perception from younger 'universes', (the younger universe), we might see the phenomena that we describe as 'ghosts.' (Whoops, there goes God and life after death, dammit!).
But - if in fiction terms, you really don't want to shake off this notion of the existence of slightly or very different universes - you can still have them.... you just can't 'create' them by making a decision. They must already exist. Every conceivable version must already be in existence, from big bang through to big crunch. Can't rule that out because if everything is infinite, then it could all be there right 'now'. But you can't.... (no matter how hard you try!) 'create' a universe, by making a decision.
PS I agree with the original poster who postulated that we could be constantly jumping into parallel identical universes, and not be aware of it. Clearly that's exactly what we're doing, by moving forwards at a rate of one second per second through what we erroneously call 'time.'

[Sweeney_Todd]

If you assume parallel universes to be true, then what determines why our consciousness occupies this universe? For example, say you face a crossroad, and you turn right. A parallel universe exists in which you turn left the second you turn right. If that universe is exactly the same, save for your direction change, why don't you experience turning left?

[Yakk]

Broad definition of consciousness:
You do experience turning left (as well), but those parts of your "consciousness" are no capable of reaching each other than two rocks on the opposite side of the world can rap together?

Less broad definition of consciousness:
Because consciousness is a classical phenomena? And each "branch" is a complete classical universe. As consciousness dwells within such a universe, it doesn't notice the branches.

There are simply multiple classical consciousnesses that remember being the consciousness that was there before the "branch". Which one is "you"? /shrug, that depends on what "you" you are talking about. If you are talking about the "you" before the branch, the question is simply meaningless -- or the answer is "all of them are that consciousness, at a later time". If you are talking about one of the "you"s after the branch, then it is clear which one is "you".

Imagine you had a crystal seed in sub-zero liquid water. When you put the crystal into the water, it spreads.

Now, arrange it so that the crystalization only spreads in one direction by arranging for a temperature gradient or something -- say, left to right.

Next, melt the crystal on the left behind the wave of crystallization.

Now we have a propagating pattern of ice, going left to right in some body of water.

Clearly this propagating ice is the same pattern of ice moving, even though the water it consists of is not the same over time or space.

Lets add channels -- the water splits into multiple different channels that are not connected. At each split, the ice starts out connected -- but then the wave of melting catches up, and it splits.

Which of the various split ice flows is the original flow of ice?

If consciousness is a classical pattern of information processing, then a universe split just continues that classical pattern in multiple different verses.

The word universe means everything there is - you can't have an infinite 'number of universes,' but you can have an infinite universe.

Semantics are uninteresting.

In this context, multiple universes means "multiple versions of what we naively perceive to be everything, ie, what we'd call the universe without that assumption". The fact that you are defining the term "universe" to be incompatible with the context is both uninteresting and not useful.

A more interesting system would be to, say, use the term "verse" to mean "a classical macro-scale universe instance", and "multiverse" to mean "the collection of all verses". This avoids the annoyance of having to deal with people who get semantically caught up on the term "universe", in addition to being more clear about what you are talking about.

But - if in fiction terms, you really don't want to shake off this notion of the existence of slightly or very different universes - you can still have them.... you just can't 'create' them by making a decision. They must already exist. Every conceivable version must already be in existence, from big bang through to big crunch. Can't rule that out because if everything is infinite, then it could all be there right 'now'. But you can't.... (no matter how hard you try!) 'create' a universe, by making a decision.

Yes, that's wrong. By that I mean what you wrote above.

Your use of the word "must" in particular. Building a model where there aren't enough copies of verses to be "already there" for all future splits is not the only way to do it, despite your claims. If you have a reason why this "must" be the case, please clarify.

[Xanthir]

If you assume parallel universes to be true, then what determines why our consciousness occupies this universe? For example, say you face a crossroad, and you turn right. A parallel universe exists in which you turn left the second you turn right. If that universe is exactly the same, save for your direction change, why don't you experience turning left?

Mu.

[Copper Bezel]

Your use of the word "must" in particular. Building a model where there aren't enough copies of verses to be "already there" for all future splits is not the only way to do it, despite your claims. If you have a reason why this "must" be the case, please clarify.

Point of fact, it defeats the purpose, because parallel universe don't really mean much if they don't diverge. I mean, the idea only exists to explain where the things that don't happen go.

But your, or some alien's, "choice" is beside the point, isn't it? I thought the divergences are only supposed to happen as a result of differing outcomes at the quantum level.

[reglow]

who knows are we asking ourselfs the same in the parallel univere..

[Yakk]

The non-forking model, where there are a countable number of identical parallel universes who evolve non-locally and probabilistically, is nigh-indistinguishable from the forking parallel universe model. And if you identify with the pattern of information processing rather than any physical particles, you could say that the pattern exists over multiple causally disconnected universes, and forks itself.

My personal favorite parallel universe model is a computational one. Each cell of Planck size is simulated fully with all boundary conditions for a period of Planck time (where I assume reality is discrete on Planck time / Space units). Then, possibly needlessly, 8 such cells are glued together (such that they agree on the seams) and their evolution is simulated (which is nearly a noop in a sense, as the possible evolutions of each cell was already calculated). Then 8 such cells are glued together...

As no actual simulation really need be done past the first stage, in a sense the first simulation implies a full simulation of every reality that consists of only the original Planck sized cells and the evolution rule. . . We (the patterns that make up people) can be found in the dust of the original computation.

A classical computation results in a physics model that contains information patterns that perceive reality as being non-classical. How is that for a brain in a vat?

[letterX]

The non-forking model, where there are a countable number of identical parallel universes who evolve non-locally and probabilistically, is nigh-indistinguishable from the forking parallel universe model. And if you identify with the pattern of information processing rather than any physical particles, you could say that the pattern exists over multiple causally disconnected universes, and forks itself.

My personal favorite parallel universe model is a computational one. Each cell of Planck size is simulated fully with all boundary conditions for a period of Planck time (where I assume reality is discrete on Planck time / Space units). Then, possibly needlessly, 8 such cells are glued together (such that they agree on the seams) and their evolution is simulated (which is nearly a noop in a sense, as the possible evolutions of each cell was already calculated). Then 8 such cells are glued together...

As no actual simulation really need be done past the first stage, in a sense the first simulation implies a full simulation of every reality that consists of only the original Planck sized cells and the evolution rule. . . We (the patterns that make up people) can be found in the dust of the original computation.

A classical computation results in a physics model that contains information patterns that perceive reality as being non-classical. How is that for a brain in a vat?

You want to explain that a bit more? It sounds technical enough that you're likely not just stringing fun words together (in addition to the fact that you're in the class of forumites that doesn't usually do that), and that there's an actual model/theory behind it, but... I can't at all figure out what it is you're saying...

[Yakk]

Suppose you have two universes that are absolutely identical. Then one (due to chance) behaves differently at a point.

How do you distinguish this from one universe that forked? Really, you don't.

Second, suppose consciousness is what information feels like when it is processed. And that these information processing patterns are more concrete than platonic -- if you do the same information processing at two different spots in space-time, that is the same information processing, not two instances of it.

Ie, suppose if I simulate your consciousness, that actually is your consciousness. Next, suppose I simulate it at 1/2 speed. How about on a time sliced system, where I simulate it 100 times a second for 1/1000th of a second each, running at a speed factor of 10 times faster. That would seem to the consciousness to be an almost continuous experience, yet each simulation step is divorced from the one before.

Now, suppose there are shortcuts, and we can simulate the consciousness out of order. We can simulate the 10th second before we simulate the 1st second of an experience, in a sense. Or, we take a consciousness simulation and run it backwards -- the consciousness would experience things forward, even though it didn't occur.

How about if, instead of simulating the entire consciousness, we break the consciousness up into sub-processes, and simulate each sub-process for a tenth of a second each. These maintain boundary conditions and approximate what the other parts of the consciousness will do, then they hash up their boundary conditions and determine which are consistent, and then discard the ones that don't sync up. In this case, the information processing done locally doesn't line up with the "global experience" that the end-consciousness experiences.

We could even do this over a distributed computation network, where each sub-chunk is run for seconds, then synchronized with the other sub-chunks. We now have the information processing going on over relatively vast and separate points in time and space, quite possibly out of order -- but the consciousness, if it is what information feels like when it is being processed, won't notice anything out of the ordinary if you are also simulating an environment for it.

Going further, imagine a computer that runs forever running each possible program one step at a time in a huge traversal. Far, far down this path, the program (well, many of them) that describes simulating your consciousness within a virtual environment exists. If that computer runs forever, that program will run to "completion", but each step will occur eons apart from the previous step.

Next, we build our computer in a system with local computational rules. And instead of running each step at a time, we simulate all possible events of "radius 1" for a period of 1 cycle, and record their boundary conditions. We then repeat for radius 2 for 2 cycles, radius 4 for 4, radius 8, etc. Each of these ends up using the previous computation, which isn't completed, to determine how it evolves, rather than running the actual steps. This, divorced in space and time, ends up computing all of the results from the "program that runs all programs". Does your consciousness run here? And is the stitching step necessary, if all of the information is already encoded in the radius 1 period 1 case, just not organized?

Throw in a dash of holographic universe (that the boundary conditions of a region of space completely describe it), and you could imagine a classical computer being able to completely describe a quantum universe through the complete simulation of the Planck size (in time and space) region of space's evolution. Every verse in the multiverse described by our physics would be completely described by this in a sense -- might consciousness find itself in that description, or does it actually have to run on actual hardware in the "right" order for it to experience consciousness?

[MHD]

Well, it gets trippy for me when the "splitting" propagates at c through space...

[Eddie Editor]

Semantics are uninteresting.

This is rather dismissive and the tone of some of what followed bordered on the insulting. My knee-jerk response would undoubtedly have been rejected by the site moderator.

Instead I’ll say this.

Semantics in themselves may seem to be ‘uninteresting’, but I didn’t mean my comment to be interpreted as a kind of ‘that apostrophe is in the wrong place’ sort of statement. I’m not concerned about the misuse of the English language in itself. What I meant was this; our understanding of anything is necessarily limited by the language we have available to us, because words transfer meaning. If we don’t have the right words for something, then we can never fully understand it and we end up thinking about things in the wrong way and wasting a lot of time. That’s a problem we’re just stuck with.

However... a problem we can do something about is a misuse of the words that lead us to misunderstand the meaning of something. For example, if we continually put two words together that don’t belong together, we limit our thought processes to the dynamic of the twinning of those words, and we corrupt the meaning of one or both of them.
e.g. ‘Time’ and ‘Travel’. We pointlessly debate whether this is possible. We pointlessly debate whether our mathematics and theoretical physics allow for its possibility. Putting these two words together anywhere outside the sphere of fiction corrupts our ability to know our place in existence. ‘Time’, is a convenient term that we need, in order to understand our lives and the universe we see. It’s needed to bring order to our lives and it’s needed to make the mathematical equations we use to predict the behaviour of the physical world. But let’s not lose sight of the reality. What actually exists is ‘change’.... not ‘time’. The universe and everything in it changes. Developed, sentient beings that we are, we understandably need to quantify the change. We need to examine the change and relative change of one event with another. ‘Time’ is the term that we use to do this. It might be convenient to our limited thought processes to consider time as the fourth dimension; helpful in documenting events relative to what we call ‘the present’, but we need to remember that no matter how convenient it is, time as a ‘thing’ does not exist. It cannot be travelled through. It might seem elegant but it's meaningless to say that we 'travel' through time at a rate of one second per second. Can we ‘travel through’ change? No, we can’t. We just change.

Another example of how the use of a word can limit our examination of the world...
Here’s the phenomenon.... data in the wrong place. No – nothing to do with the latest version of windows, this is the sort of data we carry in our heads. We call it memory. The phenomenon is memories in the wrong brain. Mmm, sounds interesting... worthy of scientific examination maybe? Giving the phenomenon the wrong name in this case, means that people’s approach to it will be polar.... there will be no spectrum of thought about this subject (well, nothing to speak of anyway). The word it got lumbered with is ‘reincarnation.’ This gives rise to a polar approach. At one end of the scale, the people that call it ‘reincarnation’ have pretty much declared where they stand on the subject. At the other end of the scale, if you can call it a scale, will be the scientific heads that say reincarnation is nonsense. And in the middle of the scale? Are there any rational minds approaching it purely as a phenomenon that needs investigating? Nope.... nobody there..... all quiet on the western front.

Likewise, I was not merely being pedantic when I said that ‘an infinite number’ misleads us. I think it is important to be aware that ‘infinity’ is utterly in a class of one. Beyond our primitive mathematics, it has nothing to do with very big numbers.

To better understand our universe, our language needs to evolve. The problem is, our language (understandably) tends to follow our understanding rather than to lead it. Until we can catch up with Robert Heinlein’s Valentine Smith – and ‘grok’ the things around us, I guess it’ll stay that way. In the mean time, if we can use the words that we actually do have in the right way, then we might at least get a little closer to understanding.

[Yakk]

I'm dismissive because your level of certainty is overly high for your level (as expressed) of knowledge. You are picking your favorite use of a language term and dictating that others use it, and dismissing other uses as being wrong. You aren't doing this as part of a technical discipline or domain specific sub language as far as I can tell -- you are doing it personally. It is ridiculously arrogant and non constructive. I suspect I'm witnessing the expert paradox -- the more knowledgeable you are about a subject (physics, mathematics) the less certain you are about being right about things. You act extremely certain.

When you go on about "what actually exists is 'change' ... not 'time'", what you have done there is made language less useful. People have a grasp of what they call time, and they have at least a vague grasp of what they would call "time travel". You claim that "what actually exists" as if your claims have merit that is unassailable -- that is patently ridiculous, arrogant, and non constructive. You do not know if time is a "4th dimension", or if the "universe just changes" -- well, you might think you know, but you are wrong about your knowledge. Your certainty is in error.

I'm relatively certain about your error, because I know that I don't know if time exists as a physical dimension or not, and I know why I know I don't know that. And your behavior doesn't seem to indicate any reason to doubt my own doubt.

So, why do I have doubt about if time really exists as a dimension? Well, we can build 2 and 3 dimensional physical models that do not change in time, yet have a time-like direction behavior in one of the spacial dimensions. We can build thought constructs (or computer models) that have 4 spacial dimensions and contain within it, to the interior "perception", a time-like dimension and 3 space-like dimensions. Some current work in physics is building pairs of models in which one acts as a "hologram" of the other -- a different dimensional physics model that captures the evolution of the other. In a sense, both models refer to the same modeled "reality" insofar as the interior perception of what is going on would be, yet are modeled completely different.

These models seem to have an internal complexity that is "reality-like" to some extent. And there doesn't seem to be a magic barrier between them and the models we have of our reality (which, as it happens, is currently best modeled by a physics that includes time as a dimension...)

And in many of these models, yes, one could build "time travel" in that behaves vaguely like various forms of science fiction.

For a toy example, start with a 1 dimensional binary finite automata with a diameter 3 evolution rule. This can easily generate time-like behavior in the y direction (with entropy and such). Such systems are easily made Turing complete, and (presuming something analogous to the Church-Turing thesis holds) we should be able to set up initial conditions for a sufficiently large (ridiculously so) system to contain the computation of intelligent life, whose existence is described completely in a 2 dimensional computation that is (once finished) unchanging.

We then add in a diameter n>3 "time travel" rule, where if a particular pattern occurs, we go "backwards" (or leftwards) and change the state of an "earlier" bit.

Make that n large enough and the pattern obscure enough, and one could arrange it so that it would extremely rarely happen. Alternatively, one could use it as a core part of the computation of the results, where it happens on small scales all of the time, but it takes an extremely contrived pattern for it to back-propogate more than a trivial distance.

I don't know if we could pull this off, but I don't see any reason why we couldn't. And the difference between the experience of "beings" within such a model universe and ours would be one of degree, not kind. Now, Occam's razor says I shouldn't presume such a contrived example: but our best simple physics models keep on permitting time-travel like behavior (if under ridiculous circumstances!)

Now, on top of those reasons to doubt what you hold to be certain, there is your claim about "we must travel at one second per second". We can change the rate at which we travel through time. It is called relativity. We can, in a geometric sense, change our rate of travel through time relative to each other.

We even seem to have particles going backwards through time in our models of certain subatomic events. Maybe there is a simpler way to work out these problems without that -- but I'm not going to take your word for it.

Likewise, I was not merely being pedantic when I said that ‘an infinite number’ misleads us. I think it is important to be aware that ‘infinity’ is utterly in a class of one. Beyond our primitive mathematics, it has nothing to do with very big numbers.

I can name multiple different infinite cardinalities. This might not match what your use of the term infinite is, but at this point, why should I care?

Your claims of absolute certainty about things does not generate confidence that you know what you are talking about.

So yes, I still hold, Semantics are uninteresting. Your level of certainty illuminates your lack of knowledge.

[Sandor]

For a toy example, start with a 1 dimensional binary finite automata with a diameter 3 evolution rule. This can easily generate time-like behavior in the y direction (with entropy and such). Such systems are easily made Turing complete, and (presuming something analogous to the Church-Turing thesis holds) we should be able to set up initial conditions for a sufficiently large (ridiculously so) system to contain the computation of intelligent life, whose existence is described completely in a 2 dimensional computation that is (once finished) unchanging.

If I've read that correctly, then Greg Egan's novel Diaspora contains an example of this type of system, based on Wang tiles. But you probably knew that already.

[yurell]

I'm a bit unsure of how parallel universe work (since I've only done up to third-year QM); I thought that they were based on Everett's Many Worlds Theory saying that we're all quantum mechanical object in a universal wavefunction, and we're only seeing things which are consistent with our little 'outcome-set' of all possible tests to this point of the entire superposition, and a parallel 'universe' is just another part of the superposition where at least one quantum result would have 'collapsed' differently had it been observed by a classical observer.
Or am I completely mistaken? I found this section rather confusing.

[RaptorRider]

Yes, that is correct, though that is just one theory about the multiverse. some of the others, as outlined earlier in this discussion are: that there are already in existance every possible configuration for the particles, and we just are passing from one to another, giving the impression of time; another, is that for every different "decision" that is made "creates" a new verse.
One that has not been mentioned yet, is that of there are the different 3D verses suspended within "4D" verses and so on. In the verses within our 4D verse, they all have related geometries and physics, but in other verses the laws governing the verses can be entirely different. There are more levels and properties that I can't remember at this time. - this is from my memory as well as it serves me. I read this in Scientific American

[Yakk]

There is also the large universe, which is large enough that (more than) all arrangements of particles exist in some region, and in those particles they evolve by the laws of physics.

So there would be individual probabilistic evolution, but the alternatives would also occur somewhere else.