The following is a fairly straightforward issue, in my mind, but I haven't seen it put elsewhere quite the way it's occurred to me. The issue relates to the question we often see asked in connection with time travel: If time travel is possible, why haven't we been visited by others from our future, or even our past? For the sake of this message, let us assume that the "many worlds" theory of quantum mechanics is correct.

The answer to the above question may be as follows: The reason that we see neither time travelers from the future, nor time travelers from the past, nor any effects from their visitations, is that this universe happens to exist in a central zone of probability where the anomalous effects of time travel have virtually no chance of prevailing.

In other words, as measured on a higher dimensional plane where all the possible instantiations of the universe may be visible, our universe occupies an infinitely large zone where time travel has no effect. (And the infinite nature of this preferred zone is not determined by its "centrality" as so defined, but by the fact that any zonal percentage, however defined, of infinity is also infinity.)

This would not mean that time travel is impossible in our universe; it would mean only that any time travel by any occupants of our universe would be to another, parallel universe that permits manifestations of the consequences of time travel.

Thus, in the future, occupants of our universe could avail themselves of time travel without the universe's ever being subject to its effects. The drawback to the time-travelproof nature of this universe is that any time travel by a given individual would result in the loss of that individual to this universe, and possibly the instantaneous retroactive, concurrent, and future-active reset of events throughout time to accommodate the disappearance of that individual.

As for the absence of time travelers from our past, it may be either that time travelers never existed, or that they did exist, but history reset itself to compensate for their travels to other universes.

The central thesis of this proposition is that our universe is time travel-proof, without being time travel-prohibitive.

Finally, the idea that history, the present, and the future must necessarily reset themselves upon time travel is not so strange, considering that some physicists contend that there is a cosmic censorship principle that prevents such things as the classic paradox where a time traveler kills his own parents before they can conceive him.

Here's a question - how come we haven't had a visitation from somebody from one of the other universes then? Unless you're saying that "our" universe is a special case and it's the only one that won't allow a future traveller to cross over?

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The plural of "anecdote" is not "data".

Here is one possible answer for you. Time travel into the past is not possible because it violates conservation laws. If you send yourself back in time you have added mass to the past. Time travel into the future would mean skipping over a segment of time, thereby creating a gap in your existence. Thereby creating a time period in the universe wherein mass was absent.

What mechanism establishes this putative "central zone of probability"?

What exactly is a "higher dimensional plane"? At the risk of starting a long and tedious debate, I must point out that any claim about the universe being infinite is an arbitrary assertion. Everything that exists exists as a definite quantity. If you are going to claim that something is infinite in extent, then you must prove why this is necessarily so. The burden of proof is on you in this matter. You are making the assertion.

The real problem is that the missing person's mass constitutes a violation of conservation laws.

Again, time travel into the future is yet another violation of conservation laws.

The cosmos hasn't a care about it. It does not censor anything. I can't. It does not think. It obeys physical laws. Those laws state that matter and energy are always conserved.

Yes, this is precisely the speculation I've put forth here. The current universe is one of the infinite set (let's called this "S sub-1") in the zone of probability that happens to be immune from the anachronistic effects of time travel.

Further, because our universe is one in a set of infinite universes, the changes in our universe are instantaneously accommodated so that the laws of causation are never changed, throughout the existence of our universe, from its beginning to its end, through the transformation / cross-universal transmigration of all affected events, down to the slightest iota of energy, matter, and time, from one S sub-1 universe to another.^1

Regarding the conservation of energy, alluded to in the message following the above-excerpted, there is no question in my mind that it applies to events that take place in this universe alone. But if the "many worlds" interpretation of quantum mechanics is true, there exists at least some violation of conservation of energy if for no reason than that there is an information transfer that results upon the occurrence of any precipitating event subject to the interpretation. If an instantaneous information transfer that allows such occurrences exists, then there is an intuitive argument that the transfer itself is not subject to conservation laws, if for no other reason than there is no cognizable way to explain it as a transfer of energy.

One can also speculate that quantum entanglement (teleportation, which has been evidenced in laboratory results) also results in an information transfer in much the same way. That is, entanglement changes in a local set of parameters results in an instantaneous change in a remote or separated set. The explanation for this effect is that each set is somehow linked, but this only places of the question at one remove: How are they linked? Are they linked purely and solely in the ordinary dimensions of this universe, or, for example, do they exhibit linkages across other instantiations of this universe? (Of course, the fact that we can notice the violations of ordinary physical laws of causation at all is problematical for my speculative theory, and I admit that, but then quantum entanglement is not time travel, strictly speaking.)

Regarding some of the questions in the third message, I hope to edit this message to address some of them.

I agree with you that this is simply an exercise in pure speculation. However, the idea of a higher plane in which various universes may be viewed is not a fictional postulate. For example, it is used in a recent book written by Dr. Lisa Randall, a Harvard physicist, entitled Warped Passages.

Your comments on the violation of the laws of conservation are also aptly made, and I hope that the above comments of mine directed to the first reply suffice to touch upon a proposed answer.

Again, yours is the mainstream of thinking, and I concede that. But there are also physicists who speculate that if time travel is possible, the universe prohibits any violation of causality. This prohibition is the "cosmic censorship principle" to which I referred.

I also agree with you that it is absurd to believe that the universe actively "thinks" at all, in any human sense.

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1. An illustration of cross-universal rectification may be as follows: Suppose there is a secret laboratory somewhere that is working on a time portal. Suppose, further, that yesterday at 2:00 p.m. local time, the time portal was fired up for the first time and that at 2:01 p.m. yesterday a mouse was attempted to be sent back in time to a point one minute prior to the time at which the time machine was first activated -- i.e., to 1:59 p.m. It is discovered at 2:02 p.m. that the time machine has done nothing more to the mouse than apparently turn it into a brilliant flash of light and gamma radiation. Did the mouse in fact die? In our universe, it may have; we cannot tell. All we know is that the animal disappeared. But under this speculation, it is possible that the mouse did travel back to 1:59 p.m., but not to that point in time in our universe, nor to any parallel universe in which the anachronistic, anti-causal effects of time travel are, strictly speaking, impossible, but instead to a universe in a set of universes (possibly S sub-1, as defined above) in which the effects of changes in the spacetime continuum may be causally accommodated. For example, the mouse might have been transferred to a universe where, the time portal was turned on at 1:59 p.m., replacing the mouse there that was, unfortunately, microwaved by the machine into "nonexistence".

There is an important epistemological issue here. When you say universe, that includes everything. It leaves nothing out.[/quote]

There is only one universe and everything that exists is in it. So if you want to talk about "other universes" then what you are really talking about is other large sections of the universe. See what I'm saying? The word universe stands for a particular concept. It symbolizes everything, not just some things, everything. So why would one section of the universe be immune to conservation laws?

I suppose this will do for the techno-babble of a science fiction piece, and it might even work if you have a decent plot and theme to weave around it, but is by not a workable theory by any stretch of the imagination.

Unless Doctor Randall is providing us with evidence, it is speculation or, conceivably, a hypothesis at the very best.

Well, perhaps you think I am mainstream thinker, but I think you had better check with the mainstream thinkers before you leave that label stuck to me. Speculation is speculation irregardless of who might indulge in it. It may or may not give rise to a working hypothesis. So far, I haven't seen anything in what you are proposing that makes for a good hypothesis. Others may judge it otherwise.

Okay, so far, so good.

But we are, once again, up against conservation laws. Why would the destruction of a mouse by converting the poor creature to gamma radiation in one part of the universe create an intact mouse in some other part of the universe at time in the past? See the dilemma? We converted mass into energy in one place and then sent the same mass back into and into another location. It still violates the conservation laws.

One might get around the conservation laws by sending only a signal (which might be as weak as one pleases). However, this would not obviate the paradoxical nature of time travel.

Suppose I build an appliance which I will be able to use only once, receiving a signal next monday which I plan to send next tuesday. I also plan the signal to be a natural number: say, a sequence of N tiny blips. And I intend to send one blip more on tuesday than I received on monday, so if I received N, I will send N+1. (If I receive nothing at all, I will send just one blip.)

To accommodate this, a countable infinity of different "worlds" must come into existence between now and next wednesday.

We still fall afoul of conservation laws. First, the blip itself had to be a something, it otherwise would not be sensible at all, nor could it have an effect on events. Secondly, by creating whole new worlds, we've created large quantities of mass. I can't see how this is workable. Others may.

My apologies if my comments appeared to depict you as either mainstream or not; I had hoped simply to characterize the ideas, not the man. Perhaps I failed to make that clear.

However, regardless of the foregoing, my idea of what is mainstream, what is preposterous, and what, in the middle, is permissible speculation is well evidenced by a similar approach taken by Dr. Michio Kaku. I will link a particularly pertinent article of his as follows:

http://www.mkaku.org/articles/hyper_sci_odyssey.shtml

What is evidence? What is logical empiricism's role in the discussion of anti-mainstream thinking?

The issue of epistemology was raised hereinabove, and I acknowledge that science cannot produce knowledge, qua knowledge, without the rigor associated with a firm foundation and some reasonable degree of certitude regarding the ontology of a particular claim. No one takes science fiction seriously as science fact, and similarly no one should confuse my speculation with any pretense at knowledge. It is, at best, a reasonable chain of logical links that do not depart too radically from received knowledge. Hence, from my point of view, it is (conveniently, I may add) the case that I do not have to meet an empirical understanding, nor even a mathematical one, of my postulates in order to state them.

In fact, it is my hope that those who are familiar with logical empiricism who desire to comment on this speculation can do both of the follow: (1) Disprove the postulates I have set forth (1.) by (a.) empirical means or (b.) mathematical logic (2.) in a manner that makes intuitive sense. The laws of conservation that you cite are obviously the considered result of empirical and logical analysis of the most reliable sort, and have withstood all manner of observation. I do not question them as they are (although, for reasons presented in the next paragraph, I do not agree that they must prevail in every speculation that does not claim to be truth).

A response to the above may be that it is not up anyone but me to advance any proof, since my claims are extraordinary, and as I have presented none. But my statements in this thread, as to the speculative theory, extraordinary as they are, do not include that the theory is true. The speculation is, at best, a hypothesis that may be subject to some form of productive discussion.

If I am wrong in using concepts such as higher dimensional planes or assumptions that logical, mathematical, or even intuitive links of thought have some validity in hypotheses, then, of course, your position on this matter would rule the day. It is because I do not claim that my theory is knowledge, but merely informed speculation, that I believe that it does not.

On another note, I would say that the term "universe" is a semantic thorn in the side, and I would simply avoid the problem of monism (the reasonable idea that "universe" means "everything") by using the often-advanced notion that the "universe" is everything that can be observed, rather than everything that is possible.

Regarding the issue of the creation of possible universes advanced in another reply in this thread, it seems to me an answer that in a "meta" sense, every universe in every possible instantiation already exists, and that we are simply witnessing the course of our own universe through each of them.

I was highly amused rather than offended. My opinions are very often in the minority of any given forum.

I'll take some time to read this and offer commentary for you--assuming you're interested.

As much as physicists are inclined to dislike philosophy and tend to be mistrustful of it, there is no escaping it. Answers to these questions have surprising variations depending upon one's philosophical outlook.

Speculation is completely safe from them.

Fair enough.

Here we still get into trouble. That which imagines is also part of the universe. The universe really is. Our existence or knowledge of it is not a requirement.

Okay, but we still want for a plausible explanation of how this can be. The Copenhagen School never really provided us with one.

Okay, about the concervation laws. What if the time traveller wouldn't just disappear. What if there will be a VERY energetic explosion triggered each time a time traveller leaves for the future?

In the receiving end some kind of apparatus would also need to be energized with high amount of energy, which would be turned into our time travelling hero... and probably also quite a lot of sound energy, heat and what have you.

Now here's a question... would this be time travelling or just... well... conservation of a life form in an energy state

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I have many of 'em mental powers

That still violates the conservation laws. In effect, the scenario doubles the mass of the time traveler.

Please forgive me for selecting out only one of your several paragraphs in reply, but because of time limitations, I wanted to address what was to me the most intriguing part of your message.

You say that "[t]hat which imagines is also part of the universe." I agree -- because from a physicalist standpoint, that which imagines is seated among biological strata (neurons, which themselves are situated and supported by other life processes). I will go even further and say that the "mind" may be nothing more than a holistic, self-generated "projection" of such neurons.

But then you say, "[o]ur existence or knowledge of it is not a requirement." Now, I'm not sure what is meant by that statement. "Our existence" is clearly a requirement for any sufficiently descriptive account of the universe, however defined, since it's clear that we exist. Secondly, "our knowledge" of the universe is precisely at issue here, since what I've proposed does dance around the peripheries of knowledge and presumes that knowledge does exist. Or are you saying that "knowledge" cannot be any requirement of the universe at large? But that's a little like saying that perceiving the universe is not a part of the universe. Without running into the issue of whether "collapsing the wave function" (a la Copenhagen) is important to consider, surely the fact that we perceive is part of the universe? And surely our acts are predicated on our perception?

In fact, isn't a monistic theory of the universe dependent on the question of what it is that is perceived? This is without prejudice to the question of Berkeleyan or Spinozan idealism. From the point of view of even the logical positivist, that which is not observable or implied from the facts, cannot truly be known to exist. How is this possible without first acknowledging the existence of perception?

The importance of this is that if one's imagination or perception -- or, to move out beyond that into a less intangible or amophous field of inquiry -- if one's logical reasoning or mathematical postulations -- lead one to believe that something is possible, then that in itself is part of the universe. And, further, if the concept of more than one universe is arrived at through some form of persuasive reasoning, then how can it not be possible to ascribe the existence of other universes? How would we know for sure that not only is "universe" impermissibly defined except monistically, if our perception and our logical reasoning suggest that it might not be?

Thank you, as always, for your responses.

Let me put it simply. The universe exists independently of consciousness. Another way of looking at it is to crawl up on a cracker barrel and announce, "Wishin' won't make it so, folks!" I do that sometimes just annoy some of my stuffy colleagues.

Ah, thank you. There is, as you have proved, an advantage to succinctness.

But I'm afraid that I don't quite understand why realism must at every instance prevail over theory, particularly when realism may be limited by our perceptions, which I also believe to be real. (How can the processes (rather than the result) of perception be false?) Further, realism is defined, I think, by the limits of technology. Were quarks no less real before they were recently found, would be one question.

I think your position in the text I excerpted, posted as it was after my words,

is fully consistent with a skeptical view toward the efforts of many theoreticians.

Thus, upon your earlier invitation, I would indeed like to read your views on Dr. Michio Kaku's article, if you would be so kind as to provide them.

Thank you in advance.