"Turn him loose as a theorist..."

[elfprince13]

The fact that you think "Inaugurated Eschatology" actually means something--actually has value in conversation--is part of the problem. What do you expect to happen? You say "Inaugurated Eschatology," we then say, "Oh! Inaugurated Eschatology! Of course!" And then we can all go talk about cars? You called it earlier: Jargon.

It's a debate about philosophy and theology, I would like to imagine that people interested in such things are also in conversant in the jargon that comes with the territory - or at least have a wikipedia hotkey ready in their browser

I seem to recall that Einstein had once said that you need to be able to describe what you believe in a simple manner that your audience can understand, or you really don't understand it yourself.

Unfortunately I don't naturally combine my teaching and arguing modes I'm often told I should be a teacher by people who are trying to learn from me, but the subset of people who are both actively trying to learn from me and actively trying to invalidate my arguments is small, so I don't get much practice combining the two rolls.

I see you as hiding behind a HUGE string of $1,000 words. I'm impressed that you seem to have some facility with them, but they're useless to me. You and I (and you and the rest of the people here) do NOT share a common vocabulary if you are going to insist on talking that way, and insist that it somehow makes you easier to understand. In this environment, they're useless to you, too.

If jargon is the problem, then I can turn the jargon down (or at least turn up the number of explanatory links) if that would make this conversation more productive.

And you really need to come to terms with the fact that I don't really give a good god damn about Godel. You brought him up. I'm using him as the butt of my jokes--and that's about it.

Maybe I'm wrong--and when my mind is fresher, I'll seek to improve myself--but what you call "the foundational result in logic of the 20th Century" seems to me to be a high order refinement of more classical logic

To understand the significance, you have to understand what came before it - Hilbert's program, and Russell and Whitehead's work on the Principia.

(as I claimed before: the more classical approach is still valid for more than 95% of all discussions).

This principle works in every day physics. This doesn't work in every-day mathematics and computer science. Rice's theorem and similar results tell us that the vast majority of interesting questions are undecidable. Even without getting into index sets and formal grammars, you can see this trivially from the fact that there are countably many computers (they are Gödel-numberable) and uncountably many things to compute.

These new logics claim "We can't know all that there is"--fine, let's confine our discussions to the 99% we CAN know. And if we CAN'T know something, then don't go giving it qualities just because you need to insert those qualities into the world to give you comfort (namely: God).

There's a difference between something being unknowable, and something being unknowable through reason. Presumably, if God were to exist, and He were also omniscient, he would know the answers to questions that are undecidable by human reason - this is the difference in Christian theology between natural and special revelations. Note clearly that I am not denying the validity of reason here, I'm simply taking the fact that reason is necessarily incomplete and allowing it to be augmented by another source of truth. I hope that the obvious next question from here is why I would accept that there is another source of knowledge to augment and reason, and why I would accept it as trustworthy.

[Boothby]

Quick response, as I am really supposed to be on my way to work right now:

Yes, please: turn down the jargon

Please DON'T use links--rather, explain, in your OWN words (not Heidegger's, nor Godel's) what you mean. Peppering your discourse with dozens of links does NOT conversations more productive. Explaining in English (with an English speaking audience) does.

We're NOT all theorists here. We're regular people.

The Einstein quote was NOT used in reference to teaching or arguing. Don't re-frame.

We're not talking about mathematics and computer science. We're talking philosophy. Currently, we're talking physical vs. spiritual realities, and a little bit of good and evil tossed in to pepper the pot.

If "Rice's Theorem" says all discussion (or most of it) is pointless, then why are you here? ('Cause *I'll* be gone)

"reason is necessarily incomplete and allowing it to be augmented by another source of truth" <--YOUR BIAS IS SHOWING. "Another form of TRUTH"?? Really? You haven't even presented a good case that this other form of ANYTHING even exists, let alone that it has some value of "truth" (besides simple existence--again, not shown).


And on that note, I'm off to use modern engineering tools to create a better reality, today....

[Wind Swept]

Okay elf, your god and whatever heavenly host he hangs out with exist happily outside the knowable universe. I think you're deluding yourself, but I can't prove you wrong, so whatever.

I do think that any events in our universe that you attribute to an interaction by your god with quantum events could just as easily be attributed to an infinite number of other things. We could start with an infinite list of gods that aren't the one you think is out there and go from there.

I am curious to know how firmly you believe in the events of the Bible. I'm not sure how you explain away giant floods, plagues of frogs, and necromancy with philosophy and quantum mechanics.

[Syphon the Sun]

I seem to recall that Einstein had once said that you need to be able to describe what you believe in a simple manner that your audience can understand, or you really don't understand it yourself.

Pretty much exactly this. I've been trying to follow this thread, but I'll admit my eyes were glazing over during a lot of the jargon.

Unfortunately I don't naturally combine my teaching and arguing modes

I think this is part of the problem. Your "arguing mode" doesn't create value. I've spent a lot of time struggling with that concept myself. But this isn't a battle of attrition. You don't "win" if everyone gets bored and walks out. You haven't persuaded anyone to your point of view; not your opponent (who you may never persuade), but not your readers, either, because they gave up on even listening to your point of view long ago. Winning that way isn't profitable, unless the only value you're trying to create is the high-five you give yourself after everyone else gives up.

You have local knowledge. But that knowledge does us no good if you insist on presenting it in a way that ensures it will remain local.

Use a little syntactic sugar for us.

[elfprince13]

I do think that any events in our universe that you attribute to an interaction by your god with quantum events could just as easily be attributed to an infinite number of other things. We could start with an infinite list of gods that aren't the one you think is out there and go from there.

I am curious to know how firmly you believe in the events of the Bible. I'm not sure how you explain away giant floods, plagues of frogs, and necromancy with philosophy and quantum mechanics.

What I was not saying is that everything God does has to happen through quantum mechanics. What I was (and am) saying is that under quantum mechanics and the usual set of scientific assumptions (locality, CFD), strong causal closure is broken. Once we have that, it really doesn't matter what scale God intervenes at, because the universe isn't causally closed - as I already pointed out, from a scientific perspective, there is nothing to distinguish weak causal closure and no causal closure, except for the weird probability distributions involved for God to act on the macro-scale.

As far as the Bible goes, I believe pretty firmly in everything after Genesis 9. Before Genesis 9, I think we're dealing with the Hebrew perspective on a lot of the Mesopotamian traditions that would have been inherited by way of Abraham, rather than things that actually happened to Abraham and his descendants. I still think there is some basis in historical events, but it's quite clear that a lot of the story is missing.

Please DON'T use links--rather, explain, in your OWN words (not Heidegger's, nor Godel's) what you mean. Peppering your discourse with dozens of links does NOT conversations more productive. Explaining in English (with an English speaking audience) does.

Fair enough.

The Einstein quote was NOT used in reference to teaching or arguing. Don't re-frame.

The way you explain things to a student and the way you explain things to an academic peer are totally different. Einstein understood that, as does everyone in academia, or we'd be studying his papers on relativity in high school geometry classes.

We're not talking about mathematics and computer science. We're talking philosophy.

Moden mathematics is love child of philosophy of logic and physics. Computer science is math with strong applications to philosophy of consciousness.

If "Rice's Theorem" says all discussion (or most of it) is pointless, then why are you here?

There are still a countably infinite number of things which are decidable That's a lot of things to talk about (productively) - it's just not "most".

"reason is necessarily incomplete and allowing it to be augmented by another source of truth" <--YOUR BIAS IS SHOWING. "Another form of TRUTH"?? Really? You haven't even presented a good case that this other form of ANYTHING even exists, let alone that it has some value of "truth" (besides simple existence--again, not shown).

You're getting ahead of me. You just said everything I said in that section of my previous post, except with more indignation and failing to recognize the difference between ""this allows that" and "this is necessary and sufficient to show that".

Ultimately, of course, I don't think this subject is decidable through argument (at least, argument independent of personal experience), so I'm content if everyone involved recognizes that there are logically* defensible positions (subject to certain constraints) on both sides (physicalists, such as yourself; and theists, such as myself).

*Except that the big thrust of my argument (which I haven't made yet) on the logical constraints of physicalism, is that it is logically inconsistent for a physicalist to accept human reason as being anything more than evolutionarily useful; and that, in fact, only (mono)theism sets up human reason as something capable of making objective truth claims.

And on that note, I'm off to use modern engineering tools to create a better reality, today....

On that note, I'm off to use modern mathematical tools to further our understanding of nanoscale self-assembly.

[neo-dragon]

If I may take several steps back; personally, I've often struggled with the notion that the universe can't be deterministic. The usual argument against derterminism begins with, "well, quantum theory says..."

Unfortunately, I don't have the physics or mathematics to understand quantum theory beyond the basic application of describing electron orbitals. I certainly don't know how to apply the concept to the universe at large in any meaningful way, so maybe someone could explain to me in very simple straightforward terms how it rules out determinism rather than just meaning that effects often have causes that are too small and numerous to ever account for.

[Boothby]

Elf,

Your mention of "another source of TRUTH" was what I was pointing out. You chose that (coded) word. Not "energy," not "information," not "causal impetus," but "Truth."

In other words:

There's something in the universe, and we don't know what it is.

Let's call it God.

Let's assign it all these attributes to make it match the God of our hearts' desire.

Therefore, our God exists.

[elfprince13]

If I may take several steps back; personally, I've often struggled with the notion that the universe can't be deterministic. The usual argument against derterminism begins with, "well, quantum theory says..."

Unfortunately, I don't have the physics or mathematics to understand quantum theory beyond the basic application of describing electron orbitals. I certainly don't know how to apply the concept to the universe at large in any meaningful way, so maybe someone could explain to me in very simple straightforward terms how it rules out determinism rather than just meaning that effects often have causes that are too small and numerous to ever account for.

This is what Bell's Inequality (or Bell's Theorem) is used to prove. Essentially, particles are defined by a complex-valued (a + bi, or, more commonly in physics, k*e^(i*t)) "wave function" which defines a probability density (you can sort of think of this like the square-root of a probability). If we know the wave function we can calculate the probabilities that the particle will be in different states, but it really isn't determined until you make a measurement and "collapse" the wave function to a spike at a certain point. And even then, there are certain conjugate pairs of values, like position and momentum, or time and energy, and the more accurately we measure one of them, the less accurately we can measure the other. Bell's Inequality shows that apparent randomness of the wave function actually has to be random (in the true sense of the word), unless we're willing to throw away certain other principles that most scientists think are even more important. The three popular interpretations of quantum mechanics each throw out one of those assumptions, and are adopted by different scientists, depending on which interpretation has the implications with which they are the least uncomfortable. Most people find it much more disturbing to reject locality or counterfactual definiteness, so determinism is the popular candidate to be disposed of.

Your mention of "another source of TRUTH" was what I was pointing out. You chose that (coded) word. Not "energy," not "information," not "causal impetus," but "Truth."

I'm talking about logical propositions here, and in any self-consistent system, these are true or false. The incompleteness theorems say that any self-consistent system is also incomplete, so there will be propositions which have a truth value, but whose truth value can't be determined through logic using the rules of that system. There is nothing to prevent you from arriving at a conclusion (correct or not) about the truth-value of those propositions, you just can't verify through logic that your conclusion is correct. If we call a black box (we don't care how it works, just what it does), which takes in propositions and returns truth values, an oracle; then an omniscient oracle, which always provides the correct answers, is just as allowable as a random one. Oracles are (cleverly named) theoretical constructs used for certain classes of proofs in math and computer science (random oracles are important in cryptographic proofs, others are useful in complexity theory); and I'm not demanding that one exist - I'm simply pointing out that if one did exist (and we had reason to trust it) it would be a valid supplement to logic as a means to knowing truth.

[neo-dragon]

If I may take several steps back; personally, I've often struggled with the notion that the universe can't be deterministic. The usual argument against derterminism begins with, "well, quantum theory says..."

Unfortunately, I don't have the physics or mathematics to understand quantum theory beyond the basic application of describing electron orbitals. I certainly don't know how to apply the concept to the universe at large in any meaningful way, so maybe someone could explain to me in very simple straightforward terms how it rules out determinism rather than just meaning that effects often have causes that are too small and numerous to ever account for.

This is what Bell's Inequality (or Bell's Theorem) is used to prove. Essentially, particles are defined by a complex-valued (a + bi, or, more commonly in physics, k*e^(i*t)) "wave function" which defines a probability density (you can sort of think of this like the square-root of a probability). If we know the wave function we can calculate the probabilities that the particle will be in different states, but it really isn't determined until you make a measurement and "collapse" the wave function to a spike at a certain point. And even then, there are certain conjugate pairs of values, like position and momentum, or time and energy, and the more accurately we measure one of them, the less accurately we can measure the other. Bell's Inequality shows that apparent randomness of the wave function actually has to be random (in the true sense of the word), unless we're willing to throw away certain other principles that most scientists think are even more important. The three popular interpretations of quantum mechanics each throw out one of those assumptions, and are adopted by different scientists, depending on which interpretation has the implications with which they are the least uncomfortable. Most people find it much more disturbing to reject locality or counterfactual definiteness, so determinism is the popular candidate to be disposed of.

That helps... somewhat. Thanks.

I'm familiar with the Heisenberg Uncertainty principle and the basic Schrodinger stuff, but the part that I have difficulty wrapping my head around or perhaps I'm misunderstanding it all together is the idea that "collapsing" the wave function somehow solidifies the state of the particle, whereas prior to that it existed in various states at once. Like Schrodinger's cat being both dead and alive up until you open the box and make it either one or the other. How can we say that reality doesn't exist in a certain state (or that it exists in every state) until we observe it in one state or another? Does a book have infinite endings until you actually read it, or did it have one all along?

[elfprince13]

I'm familiar with the Heisenberg Uncertainty principle and the basic Schrodinger stuff, but the part that I have difficulty wrapping my head around or perhaps I'm misunderstanding it all together is the idea that "collapsing" the wave function somehow solidifies the state of the particle, whereas prior to that it existed in various states at once. Like Schrodinger's cat being both dead and alive up until you open the box and make it either one or the other.

Without getting into the technical aspects of it, that sounds about right.

How can we say that reality doesn't exist in a certain state (or that it exists in every state) until we observe it in one state or another? Does a book have infinite endings until you actually read it, or did it have one all along?

There's one saying about quantum mechanics, which is that nobody ever really understands it, they just get used to it. And there's another, dealing with the many interpretations that have been offered, which is "shut up and calculate". Both reflect just how brain melting it is to try and understand a universe which is non-determinate. The best answer I can give you is that particles exist in a combination of possible states, but aren't uniformly distributed across them.

[Boothby]

There's one saying about quantum mechanics, which is that nobody ever really understands it...

So, not only can we NOT understand the universe, we can never even know WHY we can't understand it.

[elfprince13]

There's one saying about quantum mechanics, which is that nobody ever really understands it...

So, not only can we NOT understand the universe, we can never even know WHY we can't understand it.

That was physicist humor. "I think I can safely say that nobody understands quantum mechanics." is a Feynman quote. I'm not sure who first tacked on the "you just get used to it", but it gets tossed around a lot. Same thing with the "shut up and calculate". We have pretty good models for quantum mechanics, and we have good bounds on some of the implications (Bell's Theorem), but mathematical descriptions don't always translate to physical intuitions. Inverse square laws make sense, when you think about density and the surface area of a sphere with increasing radius. Minkowski space and special relativity and the Lorentz transformation make geometric sense, once you have the right mental model. But the idea that a particle exists as a superposition of states is strongly counter intuitive, and not really something you can visualize mentally, even if you know how to describe it. The fact that firing one particle at a time towards a pair of slits and forcing it to choose one still causes a wave interference pattern should mess with your head.

[Tiny genius]

But the idea that a particle exists as a superposition of states is strongly counter intuitive, and not really something you can visualize mentally

Lucky for me, I'm blind. This thread has taken off more than I thought it would and it would give me eyestrain and a headache just to read all the posts to follow the argument(s).

[Tiny genius]

I see you as hiding behind a HUGE string of $1,000 words. I'm impressed that you seem to have some facility with them

The prolongated use of a polysyllabic vocabulary invariably exercises a deleterious influence on the fecundity of an argument.

[neo-dragon]

There's one saying about quantum mechanics, which is that nobody ever really understands it, they just get used to it. And there's another, dealing with the many interpretations that have been offered, which is "shut up and calculate". Both reflect just how brain melting it is to try and understand a universe which is non-determinate.

I don't think I'll ever quite get used to it. I understand what quantum mechanics is saying even if the technical aspects go over my head, but I can't shake the idea that there is no such thing as true randomness. Everything has a cause. Quantum mechanics just seems to be saying that when we look deep enough it's impossible to see the cause without influencing it, so we just say "it is because it is".

The best answer I can give you is that particles exist in a combination of possible states, but aren't uniformly distributed across them.

Like with electron orbitals. That much I know since I teach chemistry.

[elfprince13]

I understand what quantum mechanics is saying even if the technical aspects go over my head, but I can't shake the idea that there is no such thing as true randomness. Everything has a cause. Quantum mechanics just seems to be saying that when we look deep enough it's impossible to see the cause without influencing it, so we just say "it is because it is".

The Uncertainty Principle says that, to an extent, but unfortunately (for your perspective, fortunately for mine), Bell's Theorem is stronger than that. Keep in mind that discarding locality to preserve determinism doesn't "fix" the chain of causality in any tidy way. If information can propagate faster than the speed of light (propagate across spacelike intervals, if you have any background in relativistic physics), then causality is broken in a different way. Instead of getting "links" in the chain which have no predecessor, you introduce the possibility of loops.

Like with electron orbitals. That much I know since I teach chemistry.

Right. The electron orbitals represent the possible states (more specifically, the spherical harmonics governing them form an orthonormal basis for the Hilbert space of square-integrable functions), but the probability distribution is governed by the energy.

[neo-dragon]

If nothing else you've given me some things to look into when I have the time, Elf, and I appreciate that.

[Boothby]

The prolongated use of a polysyllabic vocabulary invariably exercises a deleterious influence on the fecundity of an argument.

Heh, heh. You said "fecundity."

[Tiny genius]

Assuming you got the joke, I can't see the humor in the word "fecundity".

[Boothby]

(Bad Beavis and Butthead reference)

[Tiny genius]

What do you guys think about the possibility and implications of time travel? I know this is a much discussed topic everywhere but I'd like your opinions and insights.

[Boothby]

I doubt that Time Travel exists, or we would have seen some evidence of it....unless it only starts to exist the moment it is first invented (Read James P. Hogan's wonderful novel, "Thrice Upon a Time")

I'm also a big DISbeliever in the "parallel universe" approach to time travel--where every change, every decision, SPAWNS an entirely new universe. Do you know how much ENERGY is required for each and every universe? And what would be the MECHANISM to create a universe every time a quantum uncertainty collapses this way or that? Personal opinion: Utterly ridiculous.

[elfprince13]

If nothing else you've given me some things to look into when I have the time, Elf, and I appreciate that.

Glad to have been of service.

What do you guys think about the possibility and implications of time travel? I know this is a much discussed topic everywhere but I'd like your opinions and insights.

Depends on what you mean by "time travel". Everything you interact with is traveling through both time and space simultaneously.

Almost certainly can't happen unless it is somehow possible to adjust the topology or connectedness of space (wormholes of one sort or another). In relativistic physics we would refer to this as the creation of a closed timelike curve (technically, it's only closed for you if you return to your starting point, but one would nonetheless exist) .

Tachyons (particles which traverse spacelike, rather than timelike curves) are mathematically interesting, but when you attempt to interpret the results physically, you discover that they can't exist for any length of time long enough for them to be useful (this is a phenomena known as tachyon condensation). They also have REALLY weird behavior (if they were to exist), like moving faster at lower energies.


Even an Alcubierre warpdrive, which we sort of understand the physics of, and falls somewhere between the two possibilities mentioned above (it creates a tachyonic bubble of spacetime) is terrifyingly impractical for several reasons. First, to create one big enough to transport a human would require the resources of a civilization ranking above Type-III on the Kardashev scale. Secondly, once inside, it would be impossible to navigate or communicate with anything outside the bubble. Thirdly, decelerating the bubble back to sublight velocities would unleash a cosmic death-ray obliterating anything in its path.

[Boothby]

Please don't go referring to the "Alcubierre Warp Drive" as if it is, somehow, an actual thing. It isn't.

http://en.wikipedia.org/wiki/Alcubierre_drive" onclick="window.open(this.href);return false;

"The Alcubierre drive (or Alcubierre metric see: Metric tensor) is a speculative idea based on a valid solution of the Einstein field equations as proposed by Miguel Alcubierre by which a spacecraft might be accelerated to speeds greater than the speed of light in order to achieve the objective of interstellar flight."

(Though I did make extensive references to it in my chapter on "The Technology of Ender's Game" in the "Authorized Ender's Companion"--as a FICTIONAL construct)


"Kardashev Scale"??? Really? More jargon. (Or, maybe it's me--vote? How many here knew what the "Kardashev Scale" is, without looking it up? Type I? Type II? Type III?)

Though I am intrigued by the concept of a cosmic death ray shining backwards as an Alcubierre Drive decellerates...really makes for some severe penalties if you're going to try interstellar travel!!

[elfprince13]

Please don't go referring to the "Alcubierre Warp Drive" as if it is, somehow, an actual thing. It isn't.

I thought it was fairly clear from what I said that the hypothetical thing to which that name refers is almost certainly not constructable.

"Kardashev Scale"??? Really? More jargon. (Or, maybe it's me--vote? How many here knew what the "Kardashev Scale" is, without looking it up? Type I? Type II? Type III?)

This is ostensibly a forum full of people who appreciate sci-fi literature. I thought I was safe with that one...but for those who don't know, the Kardashev scale is used to measure how advanced civilizations are based on the energy/resources that they have available to them. A Type I civilization is one which makes FULL use of the resources of their home planet. Type II is the same thing for their solar system/home star. Type III is whole galaxy. There isn't a standard beyond that, but Type IV has been used to refer to, for example, Gallifreyan civilization before the Time War in Doctor Who.

Though I am intrigued by the concept of a cosmic death ray shining backwards as an Alcubierre Drive decellerates...really makes for some severe penalties if you're going to try interstellar travel!!

As I understand it, the cosmic death ray would be projected forwards (though conditions inside the bubble could also get nasty), but obviously there are similar problems with return voyages if you ever want to come home. If you want to read up on it, the kindly people over at phys.org have a nice article. The really math-heavy version of the paper is over on Universe Today.

[Boothby]

(You would have been better served to have used the future imperfect tense, rather than the present tense. That's all I'm sayin'...)

[neo-dragon]

Of course, even if time travel is possible, it would have to be accompanied with some pretty nifty means of directional travel to be useful, as of course planets and stars and everything else are always moving. (Forgive me if someone has already brought up that obvious fact. I haven't had a chance to fully read the last several posts).

And I actually did know what the Kardashev Scale was... after I looked it up. I knew the concept and classifications, but didn't recognize the name.

[Boothby]

I don't think the positional requirements are typically dealt with. The closest I've seen an author come to acknowledging secondary effects like this is Larry Niven, regarding his teleportation disks. The earlier versions had a hard time taking care of potential energy differences between disks located at different heights. Heaven forbid you teleport to the surface of a planet from a ship in orbit!

Back to time travel: James P. Hogan (in "Thrice Upon a Time") shoots tachyons back in time, using the computers associated with the tachyon "transceivers" as temporal "relay links" in order to get messages back to the first machine that was ever turned on. But that's his backwards limit. He send messages forward in time by encrypting them on the same computers, with an associated "open on" date code.

In his story, alternate universes are (magically) created every time a message is sent back and acted upon.

[Boothby]

Re. "Kardashev," I figured that was what it was, but didn't recognize the names, or know what the various categories (types) included. Not without looking it up!

[Tiny genius]

I doubt that Time Travel exists, or we would have seen some evidence of it

Douglas Adams thought that we were. Every time you try to claim on insurance and that precise thing is somehow, mysteriously and DELIBERATELY exluded by the company policy.
As for the Kardeshev scale, I gussed the concept but not the actual categories. I figure IV would have to be galactic cluster and V super cluster.

I reckon that the whole Acubierre death ray would be exellent punishment using time travel to commit crimes (i.e. pre-emptively killing Hitler's mother).
I think that time travel (by which, neo-dragon, I mean moving through time at significantly different speeds relative to the majority of reality) is possible but can't go back past (or rather before) the time it was made. I think this was mentioned earlier but it is a sensible view.

[elfprince13]

I reckon that the whole Acubierre death ray would be exellent punishment using time travel to commit crimes (i.e. pre-emptively killing Hitler's mother).

(And also probably most of the population of Northern Europe, if not the world, depending on how long the flight had been).

I'm also a big DISbeliever in the "parallel universe" approach to time travel--where every change, every decision, SPAWNS an entirely new universe. Do you know how much ENERGY is required for each and every universe? And what would be the MECHANISM to create a universe every time a quantum uncertainty collapses this way or that? Personal opinion: Utterly ridiculous.

This is a mostly sensible view. The many-worlds interpretation of quantum mechanics is fairly well accepted (though I heartily disagree with it), but it definitely should not allow for time travel, since it is the one of the three mainstream interpretations explicitly designed to maintain a well-defined causal structure.

[Tiny genius]

Mmm... I don't think that new universes are literally CREATED every time a decision is made. There are just infinitely many universes that play out all of the possibilities and outcomes to decisions. As for the question of energy, where did the energy for this universe come from?

[elfprince13]

Mmm... I don't think that new universes are literally CREATED every time a decision is made. There are just infinitely many universes that play out all of the possibilities and outcomes to decisions. As for the question of energy, where did the energy for this universe come from?

There are different things that people mean when they talk about other universes, depending on the context, but if it has anything to do with your actions spawning another one (which is the only context I've ever seen someone who vaguely knew something about physics attempt to tie into time travel), it's the Many-Worlds Interpretation of quantum mechanics (or a variation thereupon). And like I said, that connection really doesn't make sense when you look at it more closely, because the MWI is something you go for if you're really concerned about "nice" causal structure.

I don't even know where someone would begin trying to talk about time-travel being connected to other universes in the context of M-theory or the more general context of theories pertaining to "things outside our Hubble Volume (observable universe)"

[Tiny genius]

Point taken. Universes that already existed don't make much sense in the context of causal relationships and time travel. Unless you decide that any universes being spawned by your actions have an "immediate history" so to speak so that they are caused as the alternative to decisions but then have already existed. That would have implications for time travel as the effect would date back to before the cause.

Hang on, I am assuming that if I raise my hand then the universe where I didn't spawns at that moment but also exists from that moment. Silly me . Much better if it just spawns a new universe which starts at the beginning and has a fixed history until the part about hand raising.

What I can't stand is some of the kuzo people get to saying when they don't comprehend time travel. I tried explaining something about a cricket ball flying out of a wormhole (having come from the near future) and you catching it. You subsequently throw it into the other end of the wormhole from where it goes back to the near past. Thus the ball is stuck on a loop, it's existence is confined to that space and time, no creation or anything. The response I got was: "But when it kept landing in the past, the person surely wouldn't make the decision to throw it back in EVERY TIME!" Somehow, apparently, they got to thinking that it was going round continuously on a loop, landing AGAIN each time.

[elfprince13]

This video is very much relevant to this particular topic's title, and very interesting watching. (Warning: huge doses of physicist humor in here, ask me if you don't understand why people are laughing)