Time Travel is Impossible

Miscellaneous History
21

There are several reasons why.

a) To explain is to give a reason, which is to give a cause. Hence, any explainable phenomenon is causal. This does not tell us that all phenomena are causal unless all phenomena are explainable which is, of course, not obviously the case. (In fact, I believe it is not the case that all phenomena are explainable by us, but more on that later). But we can at least say that acausality may never feature in any coherent explanation. Thus, to explicitly invoke acausality in an explanation is to engage in contradiction. This makes almost any video featuring Michio Kaku virtually unwatchable.

b) Causality implies conservation (if the world is causal, you cannot have entities and forces popping into/out-of existence). Conservation of all physical variables (except entropy) is perhaps the most well-established fact of physics. While this does not prove the antecedent, it is strongly consistent with it.

c) The most subtle aspect of the issue has to do with the complexity of explanations. We can rank explanations in order of their complexity and when explanations are so ranked, it turns out that there is a concrete reason why Ockham’s razor is the case - simpler mechanisms are more probable than complex mechanisms, ceteris paribus. In other words, if you have a set of phenomena A, and two or more explanations (mechanisms) that are consistent with A, the simplest mechanism is to be preferred because if we imagined mechanisms being assembled at random, the simplest mechanism is more likely to occur. I’m stating this in very imprecise language for the sake of communicating the essence of the argument. For more information, search “kolmogorov complexity” “chaitin” “solomonoff induction”, etc.

When applied to physical systems, this idea suggests that random phenomena (acausal phenomena) are the most improbable of all. This reinforces point a) above and gives it a more specific meaning… there’s a reason why we should treat random phenomena as incoherent… the implied “explanation” is maximally complex.

Finally, on the point of our inability to explain everything, this goes into the fact that a computation system of complexity X cannot fully explain phenomena of complexity greater than X. Again, I’m using extremely imprecise language (caveat). The brain is not infinitely complex and, thus, it can only explain phenomena of a certain complexity. There is no reason to suppose that the Universe itself (its fundamental operation) is less complex than the human brain. Hence, there is no reason to expect that we can explain all real phenomena. This has some implications to the nature of noise/randomness in physical theories.

Clayton -

22

I’ve thought about this a bit. Causality is absolutely dependent on the nature of time, on time being essentially a half-dimensional (meaning, moving forward at a steady rate in essentially a single direction, from one moment to the next).

If you think about one dimensional time, where you could move backwards or forwards (the classic concept of time-travel in most stories), causality breaks down entirely, effects can become causes, and you reach the typical time paradoxes. Also, many dismiss the question of god with the question “who created god” which is really a question about causality, but we know that time itself began with the big bang–as one of the consequences of special relativity (or is it general? meh, one of those), meaning there was no causality before time began, there could not be, which invalidates that question about god, significantly muddying the impact of such a question. God as the “causeless cause” makes perfect sense if you understand that time did not come into being before god.

On the next level is two dimensional time, where one could move sideways in time. It’s kinda hard to imagine this one. But, you could for instance, begin a conversation with someone, then shift sideways and go fishing for ten years, then come back to that same moment in the conversation and continue as if nothing had happened and your conversation partner would not experience 10 years as having passed, because for him it wouldn’t have, it would be just a moment.

Time in that concept would be fluid, and also causality breaks down there as well. Also, there may be no such thing as scarcity in different concepts of time. Each moment passes for us now and is lost, but in a two dimensional-time universe, each moment in time an object exists could be selected out of that moment and taken elsewhere, and each moment in time would be essentially infinitely divisible, thus if there’s one copy of an item at any point in time to any other point in time, that continuity could populate the rest of time-space with that object. Which is a pretty freaky thing to think about.

I can’t really imagine what a third dimension to time could possibly add to the mix. Possibly not much of anything.

23

Exactly how I’m approaching it.

24

No, causality exists regardless of time. True, time is how we perceive it, but take a light switch. If the switch is in the downward position and the light is off, and then I flip the switch and the light is on, what we know is that I caused the light to turn on. Granted we perceive a laps in time, an amount of time that allows me to flip the switch, but this perception is nothing more than a subjective measuring system to understand what actually happened.

Now it gets sticky when you think of sequence (which itself implies time too): could the light switch be off and on at the same time? Logically we know that it cannot. So one might say that there is a measure of time between the light being off and on; it would have to be since the light cannot be off and on at the same time. But there is the catch: …at the same time. Really what I’m saying is that objects or an absolute states of existence (both off and on or here and there or alive and dead or cat and dog) cannot be contradictory; basically, paradoxes cannot exist. My point, though, is that fluctuation (change) is constant, and there is no way to speak of this fluctuation except by way of time. It is a measurement to gauge the change.

Now of course we can induce change, such as my flipping the light switch from off and on. I have free will, so I can manipulate objects and change their states of existence. But what am I doing other than changing their states of existence? In other words, sequence doesn’t exist; only fluctuation. Concepts like time and sequence are our own constructs we use to measure fluctuation and communicate or conceive the concepts.

Any thoughts? I’m thinking out loud, never really gone down this route before, friends.

25

Doing well, TR. Time is just a measure of change (i.e., motion). Paradox is the hallmark of an incoherent theory. Clear definitions and modern physics are like oil and water.

26

Yet distances between objects can change, can’t they?

27

Ok so I was watching some videos on special relativity and time, both supporting and opposed to it. I’m not an expert by any standard, but it seems at a bare minimum there’s a definition game problem. It seems to be conflating perception of light with whatever definition of time supports the theory (the theory that time isn’t just a concept about difference and distance, but something mystical, simultaneously not-physical and manipulatable) in any given context.

Again, I could be confused and probably am, but that’s what I got from watching a few videos regarding both sides of the issue of special relativity and time.

28

Yes. If one can commit to the premise that there is no physicality to time, then one must admit that it does not exist. If it exists, it exists; if it does not exist, it does not exist. Sounds silly/sarcastic to say it like that, but I agree, hashem: time doesn’t exist, therefore time travel is impossible.

29

Reminds me of the time travel scene in K-PAX: Adios aloha

Time is implicit. If you talk about travel in it, the implicit one becomes an explicit one that you’re traveling in, and a new implicit one gives basis for the notion of travel in the explicit one. But the explicit one isn’t time anymore, just another dimension that can be moved freely in.

In your description above of two-dimensional time, you basically lay out a bunch of timelines, where you can jump across them. But then you describe a third dimension, the implicit time in which you move forward in one timeline, jump to another for a while, then jump back to the first timeline. This implicit time is then the only time in your example.

30

Clayton, do you know of any good books that go into all that?

31

Please expand on that; I can’t imagine that’s even close to true.

32

The subject is called “algorithmic complexity” “algorithmic information theory” “kolmogorov complexity” etc. It is very young (about half a decade), and some of its philosophical implications are hotly contested. I’ll give you a springboard to dig around but there really isn’t any single book I’m aware of that lays out the case as I’ve stated it above.

The single best proponent of algorithmic complexity - both in terms of explaining the subject and explaining its philosophical/physical implications - is Gregory Chaitin. I recommend buying one of his books (I own Meta Math! The Search for Omega and I also recommend his latest book on metabiology to give you an idea of how his ideas can be applied).

This page gives a fairly lucid translation between algorithmic information theory and the arguments I presented above.

While studying the topic - which goes far afield into computation theory, which seems to have no obvious implications to the structure of reality - there are some key things to keep in mind:

  • Computers can be built out of any substance… there are even “water-valve” computers.
  • A special kind of computer called a Universal Turing Machine (or any logical equivalent) is capable of simulating the operation of any other computer… it merely needs to be given a special encoding that specifies the logical operation of the computer it is to simulate
  • Because computers can be built out of any physical substance (including computers that are equivalent to a UTM) and because there are problems that are uncomputable (cannot be solved by a computer), it is trivially easy to prove there can be no physical theory of everything: Simply construct a physical computer that is configured to simulate the operation of a computer that is supposed to solve an unsolvable problem and set it running then ask “what are the laws of physics that govern the long-run behavior of this physical device?”
  • While the structure of reality itself does not appear to be “discrete”, there is no reason its apparent continuity could not be the consequence of very fine discreteness (think of a digital photograph which is made of discrete elements but appears to convey a continuous image). This subject of research is called digital physics or digital philosophy.
  • Even more fundamentally, there is no reason that continuous systems could not arise which are subject to discrete laws. For example, if we speak of the “set of all computable real numbers”, we are actually talking about an infinitely sparse subset of the “real number line” that mathematicians use. Nevertheless, there is no reason to suppose that mathematics could not be constructed completely on the computable real numbers (Godel went some way in this direction with his “constructible set theory”). Mathematicians feel there are “holes” between computable numbers but this could be because we haven’t chosen a more natural metric.
  • The laws of statistical physics (e.g. thermodynamics, statistical mechanics, aerodynamics, etc.) are governed by an entropy relation that is formally identical to the information theoretic complexity of abstract codes! This suggests that information plays a crucial role in the physics of the world, whether as a fundamental substrate of some kind or merely as a reflection of the proper way for scientists to circumscribe their own ignorance (uncertainty).
  • Ray Solomonoff’s theory of induction has put the Humean problem of induction to rest for all practical intents. While there are still some philosophical “hangnig chads” (see above regarding issues surrounding discreteness, etc.), the fact is that once you understand Solomonoff, you understand why these philosophical objections are irrelevant and miss the larger point.
  • Here’s the Bible of Algorithmic Information Theory. I’ve read a significant portion of the book but I can’t say that I’ve grasped more than 50% of it. A lot of it is simply advanced theorems as they apply to specialized research interests (e.g. the P=NP problem) but a lot of it is very important technical clarifications of the limits to which this subject can be applied (prefix codes, etc.)

I hope you find that helpful. Feel free to ask for further information/guidance as needed.

Clayton -

33

I typed up a long reply and it’s pending moderation.

Clayton -

34

When I was younger I used to believe that time didn’t exist, but that what we called time was rather simply the passing of events.

Now I’m older and I hear of things in physics proving that time and space lie on some continuum. I’m not a scientist, so I have no idea, really.

35

Definitely, hashem, it’s a definitions game. The theories are held up by malleable definitions that are changed flexibly as needed to support whatever claim is being made at the time. When traveling through space, space=nothing, but when talking about gravity, space=physical object that can bend. Getting a clear definition out of a modern physics proponent is like playing whack-a-mole.

And absolutely, TR, time does not exist. Timing (the action) happens.

36

Erratum: “half a decade” should be “half a century”

ugh.

Clayton -

37

If time’s flow weren’t a physical feature of reality, you’d have absolute time, where nothing could affect it’s speed of flow.

However, that’s not what we see. We see gravitational time delay, where atomic clocks running at different altitudes run at different speeds despite using the same unvarying periodic phenomena to meter the passage of time. The slowing of one of those clocks over another cannot be due to any physical interference apart from the property of time itself.

38

Again, traveling into the future by slowing your own time-frame -is- possible by the following means:

There are various ways in which a person could “travel into the future” in a limited sense: the person could set things up so that in a small amount of his own subjective time, a large amount of subjective time has passed for other people on Earth. For example, an observer might take a trip away from the Earth and back at relativistic velocities, with the trip only lasting a few years according to the observer’s own clocks, and return to find that thousands of years had passed on Earth. It should be noted, though, that according to relativity there is no objective answer to the question of how much time “really” passed during the trip; it would be equally valid to say that the trip had lasted only a few years or that the trip had lasted thousands of years, depending on the choice of reference frame.

This form of “travel into the future” is theoretically allowed (and has been demonstrated at very small time scales) using the following methods:[24]

  • Using velocity-based time dilation under the theory of special relativity, for instance:
    • Traveling at almost the speed of light to a distant star, then slowing down, turning around, and traveling at almost the speed of light back to Earth[56] (see the Twin paradox)
  • Using gravitational time dilation under the theory of general relativity, for instance:
    • Residing inside of a hollow, high-mass object;
    • Residing just outside of the event horizon of a black hole, or sufficiently near an object whose mass or density causes the gravitational time dilation near it to be larger than the time dilation factor on Earth.

Additionally, it might be possible to see the distant future of the Earth using methods which do not involve relativity at all, although it is even more debatable whether these should be deemed a form of “time travel”:

39

The relativity theorists are very confused indeed. They say that one clock based on unvarying periodic phenomena ran slower, but they cannot possibly visualize this without selecting a reference frame in so doing, thereby privileging one frame. Either that or they visualize the situation from a god-like absolute vantage point, but then they could see no variance in the clocks, violating the conclusion.

Perhaps you can visualize a movie of two clocks running at the same unvarying rate while also NOT running at the same unvarying rate, but I cannot, and therefore can only treat such utterances as incoherent.

Whatever causes the purported differences in the clocks, I hope we can all agree it is not square circles, no matter who claims it or how many people agree that it has been “proven.” An incoherent theory is no theory at all.

40

It’s interesting that there are basically two separate notions of “time” which have been discussed in this thread. One can be described as something like “simultaneity or non-simultaneity of observations”. The other can be described as “causality”. Relativity theorists use the former notion of “time” exclusively, although they still accept the existence of causality.

Interestingly enough, while relativity theorists think that the simutaneity or non-simultaneity of multiple observations is dependent on the observer’s frame of reference, IIRC they conversely think that causality is not. The question then is whether Newton’s notion of “absolute time” is actually analogous to causality rather than simultaneity.