1063: "Kill Hitler"

[chapel]

Apparently after you time travel, the windows on the machine disappear.

He changed history... obviously.

[Mistercharles]

why is every single good xkcd comic a direct pull from either the hitchhiker's guide to the galaxy or calvin and hobbes?

really,
randall

just kidding i loved this

[phrase]

I am of the belief that BHG didn't actually have a time machine. That aside; the mannerisms of the characters in this strip get me laughing every time I've opened it since Friday (which has been more times than usual).

[flicky1991]

Now, it wouldn't be out of character for BHG to lie, so really he could have done anything in there. So here's another theory: he killed his own grandfather to see what would happen. (Spoiler: he still exists.)

[snowyowl]

BHG's got his friend so well-trained that he just accepts the existence of a time machine and moves on.

Also, the first thing you do with a time machine is to send high entropy into the past and low entropy into the future, thus reversing the Second Law of Thermodynamics and producing as much energy as anyone could want.

Wait, that's the second thing you do with a time machine. The first thing you do is go to the future and buy a better time machine.

[philip1201]

Spoiler:

Is this testable? If yes, can you explain what it means? If no, can you explain why your statement is more valuable than a couple of meta-physics buzzwords strewn together by a herd of manatees?

From what I understand, it's a very vague description of the Feynmann sum over histories (testable, verified) with a lot of wrong (unscientific) terminology, perhaps incorporating the many-worlds interpretation of quantum mechanics (untestable as of yet).

I can explain what it means. I'm not certain if it's testable, but it's not aiming to be a scientific theory of time, it's a philosophical concept of time on the same level of abstraction as eternalism or presentism. And it is incorporating not the many-worlds interpretation of quantum mechanics per se, but the more general philosophical analogue of modal realism, although as I am a necessitarian physicalist (i.e. I take physicalism to be necessarily true) I take the only logically possible worlds to be physically possible worlds, and so the many worlds of quantum mechanics should correspond exactly to the many worlds of modal realism.

The thought stemmed from thinking about modal realism, which is the position that every possible world is just as real as the actual world; 'actual' is just indexical, like 'here' or 'now'. That got me to thinking that debates about modal realism are highly analogous to debates about the nature of time, particularly presentism vs eternalism; is only the present "real", or are all times, past and future, equally real, and "present" is just indexical, meaning "this time"? I realized that a much more acceptable way to affirm modal realism would be to say "other possible worlds are exactly as real as other times"; I mean, Julius Caesar doesn't exist, now, but in another time he did; and the Roman Empire didn't colonize North America, actually, but in another possible world they did. That got me to thinking, further, what real difference is there between another possible world and another time? Except that modal realism generally defines a world such that it includes all of its space and time, but perhaps a simplifying way to think of it would just be thus: a possible world is just a (instantaneous) possible configuration of the universe, a frozen picture of a way matter and energy could be arranged.

With that concept of a possible world, we can say that other times just are other possible worlds, which bear a particular relation to this one, namely of being past or present states of it. Which then raises the question of how do we define a past or present state. Entropy provides a nice convenient arrow of time (and I can go into more detail of my thoughts on why we perceive time with the directionality we do, and thus define the arrow of time that way, but I'm in a hurry now so I won't just yet). So let us call a possible world a future world if it is adjacent to the actual, present world in the phase-space of all possible worlds, i.e. it differs from this one as minimally as possible, and those differences are such that it is more entropic than this one; and likewise, a possible world is a past world if it is adjacent and less entropic; and future-ness and past-ness are transitive, so a future of a future of a future of the present is also a future of the present, and a past of a past of a past of the present is also a past of the present.

Note however the indefinite articles there. "A" future or past, not "the" future or past. There will almost always be multiple possible worlds minimally different from this one which are more entropic, and multiple possible worlds which are less entropic. However, due to the statistical nature of entropy, there will almost always be more more-entropic adjacent worlds than less-entropic ones. As a result, lines of adjacent possible worlds in the direction of more entropy (the future) will diverge, while lines of adjacent possible worlds in a direction of less entropy (the past) will converge; so even if there are multiple immediate pasts, on a long scale there is one definite absolute past for any given possible world (the nearest local entropic minimum) while there are many possible futures (all the many local entropic maxima). Think of it like a hilly countryside: from any given point, there are multiple ways to walk which will lead you uphill or downhill, but if you keep going uphill you will eventually hit a point where there is no more uphill for you to go, and if you go anywhere you're going downhill again, and that point is the definitive top of whatever hill you started on; while if you keep going downhill, you'll end up at any of the many points around the skirt of the hill and then you can wander around there all you want at the bottom without necessarily having to go back up again.

Let's take a simple thought experiment: Imagine the universe consists of two massive particles with parallel spin. They orbit each other in circular orbits. Therefore, their entropy never changes. However, the universe where the lighter particle's angular momentum vector is parallel to its spin is clearly identifiable from the universe where it's antiparallel. No quantum phenomenon can invert the orbit of a sufficiently massive particle (conservation of angular momentum), therefore universes exist which make physical sense but are not necessarily existent in the many world interpretation of quantum mechanics.

Continuing on the experiment, in that universe, the laws of physics will always choose the state where the particle continues its motion. Looking from the direction in which the spin points, if L*s=+1/2, the lighter particle will always rotate counterclockwise. dφ/dS=0 but dφ/dt=+1 always. The future will always have a larger value of φ than the past despite having an entropically identical value. Therefore your method of distinguishing past from future is insufficient. (L is angular momentum, s is spin, φ is the angle of rotation, S is entropy, t is time, the mass of the lighter particle is set to one).

Ignoring these errors, and assuming your Galilean description of time can be generalized to relativistic concepts, the only thing you appear to be saying is that you believe modal realism, that the laws of physics are true, and that existence is a subset of possible existences. Because of what is apparently my adherence to physicalism, I see ontological philosophy mostly as wordplay and semantics. As such, "modal realism" merely defines "reality" and "truth" in an odd way.

adjacent to the actual, present world in the phase-space of all possible worlds, i.e. it differs from this one as minimally as possible

If your phase space isn't discrete, this doesn't make sense. Why do you think your phase space is discrete?

I don't see why phase space would have to be discrete for this to happen. Just take the limit of change. He's saying d[universe]/dt = f( d[universe]/dS )

[billyswong]

Why no mention of Asimov's "The End of Eternity"? It was the greatest novel of time travel!

My pet theory on BHG: If he changed the history too much, he would not be able to come back and see his friend waiting for him. So out of the many-world path, the only path that have BHG come back out of the machine and his friend waiting him is the scenario we see in the comic strip. Other branches of BHG killing Hitler earlier did exist, but they won't converge to BHG came back and meet his friend.

Oh BTW, the world is probably run by a class 4 algorithm, thus the convergence of timelines: most temporal changes will not propagate too wide too much, nor even propagate indefinitely.

Note: Stephen Wolfram, the inventor of Mathematica, divided cellular automata into 4 classes of complexities: repetitive, nesting, random, and random with localized structure. Class 4, random with localized structure, is the most complicated.

[ijuin]

Well, a posteriori, quantum mechanics suggests that any value which might change between two possible worlds can only change in discrete multiples of some minimum quantity (the Planck units), which would make the resulting phase-space discrete as well.

I don't think there's any reason to treat space and time themselves as discrete, even if things like energy and frequency are. The Planck units are convenient to work with, but if the Planck length and time are physically significant, afaik it's because reality is too fuzzy to be discerned at smaller scales, rather than that reality is actually discrete at those scales.

The Planck units do not require that spacetime be discrete at that scale--as said, they only indicate the smallest meaningful measurement.

The values of the Planck units derive directly from relativity and the principle of quantum uncertainty (specifically, the inversely-varying uncertainty in the position vs. the energy of a particle/wave).

Consider a photon with an arbitrarily short wavelength. Since e = m*c^2, and shorter wavelengths mean higher energy, eventually you will reach a point where making the wavelength any shorter will make the photon massive enough that it will collapse into a black hole due to its own gravity. The wavelength at which this happens is the Planck length, the energy of the photon is the Planck mass, and the time between peaks of the wave is the Planck time. Since greater precision in space requires lesser precision in energy, making any object or measurement smaller than the Planck length would require that its mass/energy be allowed to exceed the Planck mass (and thus that it be capable of collapsing into a black hole). Also, since no positive-energy body can travel faster than c, it is impossible to travel more than one Planck length in a single Planck time, which means that measuring shorter times than the Planck time would require also measuring shorter distances than the Planck length.

P.S.: Please note that the measurements of the Planck length, mass, and time are relative to whatever relativistic frame of reference is being observed, and thus is subject to relativistic differences of measurement. For example, a fast-moving particle would experience slower time, smaller distance, and greater mass from the perspective of a "stationary" observer.

[dp2]

You don't understand.

He went back and killed Hitler in the bunker!!! That's what you know NOW because that's what happened.
Before that, Hitler completed the development of a new weapon and won the war. In fact, xkcd was in German.
You can't remember that, he changed the whole world with that trip in time.

This wraps it up nicely - I'm surprise that it took more than one page of comments to get there.

Generally, there different ways time travel could work, and they fall in two broad categories.
In the first - timeline preservation - you simply can't change the past as it has already happened - as in the case of gkawa's reading of this comic. BHG, even if he had good intentions, simply couldn't have killed Hitler before he does what we know him for.
The second one - multiple timelines - you switch between/change/create timelines when you travel. If this was the case in the comic's multiverse and BHG did kill Hitler before his time - then upon the return trip he would find that no one has heard of Hitler and (a potentially worse) alternative history scenario has played out - if he only moves forward in time in the timeline he just created, that is. Maybe his original timeline exists in parallel, Hitler is alive and well and BHG never returns - unless the time machine actually transports him back to his original timeline. In this case, he'll be like 'hey, I killed Hitler, how come nothing has changed'. But then again, if he designed the time machine himself then he probably knows pretty well if it jumps between timelines or not.

Your take on the first one isn't quite right. It IS possible for BHG to kill Hitler and not change history. We assume Hitler committed suicide, but we don't actually know that. He may have been killed by Eva Braun, it may have been a ninja, maybe a Russian assassin, maybe a time traveler from the 21st century.

Or think of it this way: if someone from our future invents a time machine and goes back and kills Hitler in the bunker, then it has already happened. He was killed by a time traveler or he wasn't. It cannot be changed. But since the time traveler does not know the facts around Hitler's death, he has hope of being the cause.

In a broad sense, this means that from 1945 until the moment the time traveler leaves for the past in his time machine, there is a causal loop, where all events can be affected by events both past and future. e.g. everything that happens because of Hitler's death in 1945 is partly caused by the time traveler being born in, say, 1975.

But you are correct in that Hitler cannot be killed before the point where we know he was dead.

[J Thomas]

Well, a posteriori, quantum mechanics suggests that any value which might change between two possible worlds can only change in discrete multiples of some minimum quantity (the Planck units), which would make the resulting phase-space discrete as well.

I don't think there's any reason to treat space and time themselves as discrete, even if things like energy and frequency are. The Planck units are convenient to work with, but if the Planck length and time are physically significant, afaik it's because reality is too fuzzy to be discerned at smaller scales, rather than that reality is actually discrete at those scales.

The Planck units do not require that spacetime be discrete at that scale--as said, they only indicate the smallest meaningful measurement.

The values of the Planck units derive directly from relativity and the principle of quantum uncertainty (specifically, the inversely-varying uncertainty in the position vs. the energy of a particle/wave).

Consider a photon with an arbitrarily short wavelength. Since e = m*c^2, and shorter wavelengths mean higher energy, eventually you will reach a point where making the wavelength any shorter will make the photon massive enough that it will collapse into a black hole due to its own gravity. The wavelength at which this happens is the Planck length, the energy of the photon is the Planck mass, and the time between peaks of the wave is the Planck time. Since greater precision in space requires lesser precision in energy, making any object or measurement smaller than the Planck length would require that its mass/energy be allowed to exceed the Planck mass (and thus that it be capable of collapsing into a black hole). Also, since no positive-energy body can travel faster than c, it is impossible to travel more than one Planck length in a single Planck time, which means that measuring shorter times than the Planck time would require also measuring shorter distances than the Planck length.

P.S.: Please note that the measurements of the Planck length, mass, and time are relative to whatever relativistic frame of reference is being observed, and thus is subject to relativistic differences of measurement. For example, a fast-moving particle would experience slower time, smaller distance, and greater mass from the perspective of a "stationary" observer.

I consider Philip1201 the cause of this sidetrack. (Blame is too strong a word.)

Is this testable? If yes, can you explain what it means? If no, can you explain why your statement is more valuable than a couple of meta-physics buzzwords strewn together by a herd of manatees?

So Pfhorrest felt some obligation to explain. And if time is discrete, then it would make sense to think of "adjacent" moments, and all those discrete moments could fit onto a 1-dimensional line like the integers, or a 2-dimensional mosaic, or something else.

Meanwhile, as philip1201 pointed out, his idea could work with continuous time. If the phase space is (I forget the word, not ergodic but something else), so no two paths ever join, then it doesn't work. Pick a starting point and trace its path through phase space and anything on that path can't be on any other path. But there's no proof reality is like that. Maybe the paths diffuse and overlap with each other. In that case, given one particular present there are many pasts that could have led there, and that present could lead to many different futures.

Is this testable? If yes, can you explain what it means? If no, can you explain why your statement is more valuable than a couple of meta-physics buzzwords strewn together by a herd of manatees?

I can explain what it means. I'm not certain if it's testable, but it's not aiming to be a scientific theory of time, it's a philosophical concept of time on the same level of abstraction as eternalism or presentism.

So, did he just tell you that it is nothing more than a couple of meta-physics buzzwords strewn together by a herd of manatees? Or was he saying something else? I think something about this interchange insults one or the other of you, but I'm not sure which.

Words have meanings. Words have different meanings to each person who uses them, and their meanings change with changes in understanding. You both seem to assume that today's physics theory has a close relationship to reality. But why would you make such an assumption? Many physicists have assumed that in the past, and they were all wrong. What are the odds that this time they have it right?

Meanwhile, PFhorrest is a philosopher, dealing with tricky slippery concepts. How would you find out whether his ideas have any value in that domain? Or whether that domain itself has any value? It might be hard to tell for sure that philosophy is useless unless you venture onto those slippery slopes yourself. And yet the same argument could be made for scientology, and we all know that's wrong. So there must be something wrong with my reasoning, but I'm not sure what it is.

[gmalivuk]

adjacent to the actual, present world in the phase-space of all possible worlds, i.e. it differs from this one as minimally as possible

If your phase space isn't discrete, this doesn't make sense. Why do you think your phase space is discrete?

I don't see why phase space would have to be discrete for this to happen.

It doesn't have to be discrete for the overall account to be basically correct, but it does have to be discrete for words like "adjacent" to make sense. If it's continuous, then the limit of change is 0, which obviously doesn't give you a past or future instance.

[cburke]

for a second there, i thought he was going back in time to kill Vic Hitler the narcoleptic comic. Whew!

No, I'm sure he's still knocking them dead on Hill Street.

[Pfhorrest]

adjacent to the actual, present world in the phase-space of all possible worlds, i.e. it differs from this one as minimally as possible

If your phase space isn't discrete, this doesn't make sense. Why do you think your phase space is discrete?

I don't see why phase space would have to be discrete for this to happen.

It doesn't have to be discrete for the overall account to be basically correct, but it does have to be discrete for words like "adjacent" to make sense. If it's continuous, then the limit of change is 0, which obviously doesn't give you a past or future instance.

Just a thought along this line of thought (I'm not really in my best state of mind recently so this is more thinking out loud than any concrete assertion).

I actually think of these possible worlds in information-theoretic terms -- so that an adjacent world is one which differs by exactly one bit -- but I didn't want to talk about them as such in case that opened up a whole other can of worms. However, this discussion makes me wonder, if there are truly continuous variables in the universe, does that imply that there is no such thing as a fundamental physical bit of information, as there would be no such thing as a smallest difference between two possible states of the universe? If that is so, what implications does that have on how many bits of information is encoded in any substantial difference between two such states? Since there are infinitely many possible transitional states between those two states, does that imply that any substantial difference encodes an infinite amount of information?

(A possibly related question: how many bits of information are necessary to encode an arbitrary real number, like say an irrational number? It seems you would need infinite precision and therefore infinite information).

On a related point, if we're thinking of the universe in information-theoretic terms, or even more broadly just in empirical terms, how are the limits of measurement not also the limits of reality? If nobody could ever in principle measure a difference (say in position) smaller than one Planck unit, then two states which "differ" by that much are indistinguishable in principle and so by Leibniz' Law identical, unless we were to concede that there was something more to reality than what could in principle be observed of it.

[J Thomas]

.... However, this discussion makes me wonder, if there are truly continuous variables in the universe, does that imply that there is no such thing as a fundamental physical bit of information, as there would be no such thing as a smallest difference between two possible states of the universe?

If some things are either on or off, then those things could be expressed as bits. Other things might be expressed as qubits or something else.

If that is so, what implications does that have on how many bits of information is encoded in any substantial difference between two such states? Since there are infinitely many possible transitional states between those two states, does that imply that any substantial difference encodes an infinite amount of information?

I guess. The bit concept in information theory was a conceptual convenience. There was never much reason to think that it corresponded to reality very well. But sometimes maybe it does anyway.

(A possibly related question: how many bits of information are necessary to encode an arbitrary real number, like say an irrational number? It seems you would need infinite precision and therefore infinite information).

Yes, but in theory you would only need a countable number of bits.

On a related point, if we're thinking of the universe in information-theoretic terms, or even more broadly just in empirical terms, how are the limits of measurement not also the limits of reality? If nobody could ever in principle measure a difference (say in position) smaller than one Planck unit, then two states which "differ" by that much are indistinguishable in principle and so by Leibniz' Law identical, unless we were to concede that there was something more to reality than what could in principle be observed of it.

Well, suppose that there were things going on that you could not in principle observe, but at some later time they had consequences. Maybe sometimes you could reason back from the consequences to tell what the unobservable states were. Maybe other times you could use later data to set limits on what the unknown states must have been, but in principle it cannot find all of them.

What difference does it make whether there are unknown states, or merely unknown probability distributions? I'm not sure it matters.

But then -- imagine that there are unknowable states for things, and at any time the unknowable states can shift things around in unpredictable ways. Like, they could at any time change the laws of physical nature to something we cannot predict. If that was true, then in principle we can never know what the laws of nature will be from second to second. The way to bet is that they will not change this second, but you never know.

Dueling aphorisms:
What you don't know, can't hurt you.
Anything you don't understand is dangerous until you do.

Clearly the first one is wrong. But it can be restated:
Anything which can never have any effect on you, can't hurt you.

Can you be affected by things you can't exactly measure?

[Pfhorrest]

Is this testable? If yes, can you explain what it means? If no, can you explain why your statement is more valuable than a couple of meta-physics buzzwords strewn together by a herd of manatees?

I can explain what it means. I'm not certain if it's testable, but it's not aiming to be a scientific theory of time, it's a philosophical concept of time on the same level of abstraction as eternalism or presentism.

So, did he just tell you that it is nothing more than a couple of meta-physics buzzwords strewn together by a herd of manatees? Or was he saying something else? I think something about this interchange insults one or the other of you, but I'm not sure which.

I got the impression he was trying to be insulting (or at least dismissive) but chose to ignore that.

Words have meanings. Words have different meanings to each person who uses them, and their meanings change with changes in understanding.

If you're getting at what I think you're getting at, then I think you're on the right track: the value of my statement is in its use for clarifying our conceptual frameworks, of understanding the relationship of different concepts to each other, specifically the concepts of time and possibility, and the reality of both. This is more than just affirming modal realism, as Philip read it; it is asserting a connection between modal realism and eternalism, and conversely between modal anti-realism and presentism, asserting that other times are a subset of other possible worlds rather than completely different unrelated kinds of things, and thus that the ontological status of one is linked to the ontological status of another, as they are the same kind of thing.

You both seem to assume that today's physics theory has a close relationship to reality. But why would you make such an assumption? Many physicists have assumed that in the past, and they were all wrong. What are the odds that this time they have it right?

I'm not assuming that physics as it exists at present is absolutely correct, only that reality is inherently physical, as in objectively empirical, as in subject to consistent observation and measurement across multiple observers. Present physics is of course merely the best explanation so far of observations made so far, though as any workable future physics will need to subsume that explanatory power over those observations (plus whatever else we haven't explained or even observed yet), just like relativity subsumes Newtonian mechanics, it's reasonable to say that present physics is in some sense on the right track, even if it is perpetually incomplete; as were its predecessors, like the aforementioned Newtonian mechanics.

Meanwhile, PFhorrest is a philosopher, dealing with tricky slippery concepts. How would you find out whether his ideas have any value in that domain? Or whether that domain itself has any value? It might be hard to tell for sure that philosophy is useless unless you venture onto those slippery slopes yourself. And yet the same argument could be made for scientology, and we all know that's wrong. So there must be something wrong with my reasoning, but I'm not sure what it is.

The difference is that in examining the value of philosophy or of some particular philosophical idea, you are inherently doing philosophy and tacitly granting it enough value to be worth doing. But in examining the value of Scientology (or any particular belief system, including any particular more-legitimate philosophical concept, like some concept of the scientific method), you are not necessarily doing Scientology or granting any value to it.

Well, suppose that there were things going on that you could not in principle observe, but at some later time they had consequences. Maybe sometimes you could reason back from the consequences to tell what the unobservable states were. Maybe other times you could use later data to set limits on what the unknown states must have been, but in principle it cannot find all of them.

What difference does it make whether there are unknown states, or merely unknown probability distributions? I'm not sure it matters.

But then -- imagine that there are unknowable states for things, and at any time the unknowable states can shift things around in unpredictable ways. Like, they could at any time change the laws of physical nature to something we cannot predict. If that was true, then in principle we can never know what the laws of nature will be from second to second. The way to bet is that they will not change this second, but you never know.

Dueling aphorisms:
What you don't know, can't hurt you.
Anything you don't understand is dangerous until you do.

Clearly the first one is wrong. But it can be restated:
Anything which can never have any effect on you, can't hurt you.

Can you be affected by things you can't exactly measure?

The only way we ever observe anything is by their consequences, so if something has observable consequences, it is observable.

[gmalivuk]

If nobody could ever in principle measure a difference (say in position) smaller than one Planck unit, then two states which "differ" by that much are indistinguishable in principle

But if A and B differ by less than one unit, and B and C differ by less than one unit, that doesn't mean that A and C differ by less than one unit.

[J Thomas]

Words have meanings. Words have different meanings to each person who uses them, and their meanings change with changes in understanding.

If you're getting at what I think you're getting at, then I think you're on the right track: the value of my statement is in its use for clarifying our conceptual frameworks, of understanding the relationship of different concepts to each other, specifically the concepts of time and possibility, and the reality of both.

Yes. If your words have value, that's where the value will be.

This is more than just affirming modal realism, as Philip read it; it is asserting a connection between modal realism and eternalism, and conversely between modal anti-realism and presentism, asserting that other times are a subset of other possible worlds rather than completely different unrelated kinds of things, and thus that the ontological status of one is linked to the ontological status of another, as they are the same kind of thing.

I can imagine that. I can also imagine it another way. Maybe the past (and possible also the future) are different from other "possible" worlds because they are worlds that really do exist at some time, while the other "possible" worlds are worlds that have never existed and never will. Is there a way we could tell the difference between those? If we could somehow travel among some of the worlds that would be solid evidence. There might be other worlds we could never travel to, but if we could travel to even one that was definitely different from ours, we would know that there is more than one.

But what evidence would we accept that somebody has gone to different universe? Is it enough to bring back photos? Rock samples? Memories?

I'm not assuming that physics as it exists at present is absolutely correct, only that reality is inherently physical, as in objectively empirical, as in subject to consistent observation and measurement across multiple observers. Present physics is of course merely the best explanation so far of observations made so far, though as any workable future physics will need to subsume that explanatory power over those observations (plus whatever else we haven't explained or even observed yet), just like relativity subsumes Newtonian mechanics, it's reasonable to say that present physics is in some sense on the right track, even if it is perpetually incomplete; as were its predecessors, like the aforementioned Newtonian mechanics.

Newton decided that light comes in corpuscular quanta. But he couldn't explain diffraction and interference. Later physicists decided that light came in waves, but they couldn't explain why atoms seem to emit and absorb quantized amounts of light. They decided that atoms are quantized, and charges are quantized, and particles are quantized. With QM they decided that light is quantized, and Feynman said that quantized light and quantized particles both travel exactly like waves except they're quantized particles because he says they are. I don't want to say these guys are on the wrong track when I don't have a better model myself, but I don't see any particular reason to assume they're on a right track.

Meanwhile, PFhorrest is a philosopher, dealing with tricky slippery concepts. How would you find out whether his ideas have any value in that domain? Or whether that domain itself has any value? It might be hard to tell for sure that philosophy is useless unless you venture onto those slippery slopes yourself. And yet the same argument could be made for scientology, and we all know that's wrong. So there must be something wrong with my reasoning, but I'm not sure what it is.

The difference is that in examining the value of philosophy or of some particular philosophical idea, you are inherently doing philosophy and tacitly granting it enough value to be worth doing.

No. People tried to do this same bullshit about physics, and it was wrong then too.

Most people have a sense of what they value, what they think is worth doing or worth having etc. They don't think much about why they have that sense or how they got it or whether it's right. They assume it's right because it's what they value. Philosophy includes a lot of careful thought about how people get values and how they ought to get values and how we can rationally tell which values are good, correct, pleasing, etc. But people do not need to do philosophy to have values any more than a beaver needs to study civil engineering to build a dam. You can argue that to have values they must do philosophy, just like you can argue that to throw a baseball they must do calculus. But it's bogus.

Very often, people who instinctively know what their values are start to get confused when they try to justify their opinions with philosophy. Before, they just knew. But logical snarls can persuade them they don't know. "A man with one clock knows what time it is. A man with two clocks is never sure." So deciding whether philosophy is valuable is not the same thing as doing philosophy. It's a cynical sophist's trick to pretend it is.

To my way of thinking, you don't find out what an idea is good for unless you try it out. To do it right, you have to get the idea and try out believing it. Get a full sense of who you are when you believe it. Then compare what it does for you versus who you were before. And choose. If somebody says "Life is too short to worry about essence and existence so philosophy is not worth doing" you can say that he's being a philosopher because he has made a philosophical choice. But I say he has rejected philosophy. You won't do philosophy unless you decide that the ideas are worth thinking about. If you decide they aren't worth thinking about and you refuse to think about them, then you are not a philosopher. Maybe you could practice zen or something.

Similarly, I criticize scientology without trying it. I read a lot of the Dianetics book in the school library and it looked like it had a lot of good stuff. I just can't see myself trying out scientology and paying larger and larger amounts of money for advanced courses. I like to think I wouldn't, but a lot of people do. it's the same reason I won't try hard drugs. I think I wouldn't keep using them enough to get addicted, but how can I know without risking it?

But in examining the value of Scientology (or any particular belief system, including any particular more-legitimate philosophical concept, like some concept of the scientific method), you are not necessarily doing Scientology or granting any value to it.

If you aren't willing to grant value to it to find out where that leads, then you haven't tried it.

Can you be affected by things you can't exactly measure?

The only way we ever observe anything is by their consequences, so if something has observable consequences, it is observable.

No, the consequences are observable. Or maybe that's the consequences of the consequences that are observable? Or the consequences of the consequences of the consequences? Maybe it's turtles all the way down.

The more elaborate the indirection, the more likely you are to get silly results. So for example, neutrinos are almost undetectable. Every now and then something happens that you can assume would not have happened unless a neutrino intervened at precisely the right moment, so that's your evidence that a neutrino was there. But people calculated the number of neutrinos they expected to see from the sun, and they didn't get that number. They got about half as mny. They could have assumed this meant there was something about the sun they didn't know. But instead they assumed that the sun's neutrinos oscillate between a form that is rarely detectable and a form that is completely undetectable. And the fact that at any given time half of the neutrinos are completely undetectable has profound implications. It's possible that all this is clearly the right way to think about it when you have enough background information. But from where I sit it looks like assumption piled on top of assumption. The observable consequences are too far removed from the hypothetical causes.

[Pfhorrest]

But what evidence would we accept that somebody has gone to different universe? Is it enough to bring back photos? Rock samples? Memories?

We can ask the same question about other times, and that's part of what got me on this line of thinking. You can't do an experiment on the past or the future, you can't go visit them and then come back, you can't observe them from where (when) you are, any more than you can other possible worlds. We can only observe the present, and from evidence in the present we infer that certain things have been, will be, might be, might have been, could be, could have been, etc. The only logical contact with other times and other possible worlds we have is as hypothetical other configurations of the world which factor in to our models of the actual present world.

I'm going to reply out of order now because this segues into something else you talk about later...

No, the consequences are observable. Or maybe that's the consequences of the consequences that are observable? Or the consequences of the consequences of the consequences? Maybe it's turtles all the way down.

It is turtles all the way down.

All we have to go off of as to the contingent nature of the actual, present world (as opposed to pure logic which doesn't tell us much of any material import) are our immediate observations. And I mean the raw sense-data, not things like "I see a bird"; that perception is already laden with hypotheses about the existence of birds and what they look like and when and where it makes sense to expect the sensations which compose them looking like that. Everything else, including the existence of "directly observable" objects like said birds, is hypothetical to some degree, part of some explanatory framework which helps make sense of those observations. It is all just noticing patterns in the observations and seeing how well those patterns hold up. We can never be certain that any of those hypotheses are true. Strictly speaking I can't rule out that I might not be sitting on my room typing this on my computer, but instead I might actually be a Brain in a Vat in the Matrix being deceived by an Evil Genius. But we can have various degrees of confidence in the reality of those hypothetical objects which form parts of the overall models which make best sense of our observations, based on the success of those models in making sense of our observations.

So, are neutrinos only detectable half the time? If that is what the best possible explanation of all possible observations says, then yes. To the degree that we're not sure the current explanation is the best possible one, then maybe not. Am I really writing this on a laptop in my room? Most probably; any model which hypothesizes that I am not would have to go through some crazy contortions to explain all my other observations adequately, and I've no reason to buy those crazy contorted models over much simpler ones unless further observations warrant them; but still, to the extent that I can't rule out some day making such observations which would warrant the acceptance of those contorted models (or the existence of such observabilia and my contingently just never happening to observe them), "most probably" is the best answer I could ever give.

Thus back on the subject of other times and other possible worlds, they are the same kind of thing if and only if the best explanatory framework considers them the same kind of thing. The rest is argument over what is the best explanatory framework.

You can argue that to have values they must do philosophy

But I'm not. I'm arguing that if they are arguing about values, they are doing philosophy. Including arguing about the value of philosophy. If they just say "philosophy is bull", and upon being asked why say "it just is, and arguing about why is stupid", then they are not doing philosophy, they are just asserting an opinion about the value of something. But if they say that, and upon being asked why, give reasons, and then rebut counterarguments against those reasons, and so on... then they are doing philosophy.

Very often, people who instinctively know what their values are start to get confused when they try to justify their opinions with philosophy. Before, they just knew. But logical snarls can persuade them they don't know.

The self-important people Socrates went around asking questions of said the same thing. "Stop asking questions, you're confusing me!" I think that is the value of philosophy. It stirs things up and makes you ask the right questions, and keeps you from making the wrong assumptions or jumping to the wrong conclusions. Of course, after a while it will get you questioning everything and never coming to any conclusions. But then, more philosophy will make you question what to question, and clear up what kind of assumptions you should make.

I heard it put once, and I'm sorry I don't have proper attribution for this paraphrase, "Before you walk the path to enlightenment, tables are tables and tea is tea. As you walk the path of enlightenment, tables are no longer tables and tea is no longer tea. But once you have reached enlightenment, tables are again tables, and tea is again tea." And I would add, the difference at the end is now you understand what tables and tea are and are not, and why they are as they are and not as they are not. And perhaps also that the practical value of this, for someone who already saw tables and tables and tea as tea, is for when you come across someone calling a chair a table or calling coffee tea, and need to set him straight about what a table is and why coffee doesn't count as one.

[philip1201]

But what evidence would we accept that somebody has gone to different universe? Is it enough to bring back photos? Rock samples? Memories?

We can ask the same question about other times, and that's part of what got me on this line of thinking. You can't do an experiment on the past or the future, you can't go visit them and then come back, you can't observe them from where (when) you are, any more than you can other possible worlds. We can only observe the present, and from evidence in the present we infer that certain things have been, will be, might be, might have been, could be, could have been, etc. The only logical contact with other times and other possible worlds we have is as hypothetical other configurations of the world which factor in to our models of the actual present world.

All information we receive concerns the past. Neurons have finite speed, light takes time to travel and it takes a good long while for new observations to coalesce and be presented to the frontal cortex for analysis. If we want to consider anything true beyond "cogito ergo sum", we have to accept past data as valid. And we can only do experiments in the past and future, by looking at the received data and checking them against predictions, or by designing an experiment which will occur in the future, which for a future you will be the past.

The present is only an infinitesimal point in spacetime, possibly extended into an arbitrary 3D spatial volume depending on the velocity of the observer. The only logical things which can have an influence on the state of a particle in the present are all events in the particle's past lightcone. Interaction with the present is physically impossible, because instantaneous interaction violates causality for moving observers. What you are saying is physically wrong.

You can argue that to have values they must do philosophy

But I'm not. I'm arguing that if they are arguing about values, they are doing philosophy. Including arguing about the value of philosophy. If they just say "philosophy is bull", and upon being asked why say "it just is, and arguing about why is stupid", then they are not doing philosophy, they are just asserting an opinion about the value of something. But if they say that, and upon being asked why, give reasons, and then rebut counterarguments against those reasons, and so on... then they are doing philosophy.

Again with the semantics, everyone. Pfhorrest is defining ethics as the discussion of worth, and J Thomas is defining it as a discussion of worth which is philosophical, where philosophy is a specific method of reasoning which not all rational discussions of worth fall under.

But you are correct in that Hitler cannot be killed before the point where we know he was dead.

(Assuming general relativistic wormholes in a single non-splitting spacetime) The arrow of causality is always towards the future in spacetime. By traveling back in time, some of the "past" becomes your future, and your interactions with that future do not change your experiences in the past. Therefore you can kill Hitler before you know he was dead. However, the you who does that will be erased by the next iteration, unless you ensure the dead Hitler iteration of yourself goes back in the past to kill Hitler, who then might kill him slightly differently, meaning that you' has to convince you'' to go kill him in exactly the same way you or you' did, et cetera. Eventually, the timeline will converge, and for an outside observer (i.e. a future one) Hitler will always have been killed by a time traveler, or the time traveler will never have had a chance because the timeline converged differently, but that's no different from any action perceived by a future observer. So you most certainly can go back in time and kill Hitler before it was known he died, even if you have only a single timeline.

Arguing that Hitler was killed in his bunker in unknown circumstances is merely hiding the problem. Per chaos theory, your father's sperm might have swam in a slightly different formation because there was one less oxygen atom which damaged a protein in one sperm's tail because the time traveler breathed it, leading to a different genetically coded you who decided to kill Hitler slightly differently, leading to "a different timeline" if you want to call it that. After a few gazillion reiterations, the timeline converges exactly, but each and every last one of you has a choice as free as any other choice you make. Determinism is weird that way.

[Eriskay91]

This was an interesting comic, and all the time-warpy responses have been equally intriguing.

I just want to share a thought not originally thought of by me, but by the vlogbrothers over at youtube and the Nerdfighter community. See, there really is no need to kill baby Hitler. The proper solution to this problem is to kidnap him, and take him to an orphanage for evil babies aptly titled The Evil Baby Orphanage. Where baby Hitler will receive therapy, and all will be well.

This is, of course, not a perfect solution to the problems of the world; what kind of therapy should we go for, how do we decide exactly who's evil enough to earn a spot and how do we even take anyone but Hitler there given that this comic only allowed for one journey in time? Not to mention the already much discussed time-warpy issues. But it is a thought that I think is worth putting into this whole equation of making the world a better, more paradoxal place.

[iamspen]

What if you do that, and Hitler is still elected into office, except this time he's good Hitler? What if he eventually forms a coalition government with the communists and socialists in the German government? What if that allows an easier alliance with the Soviet Union? You've doomed Western civilization, sir, by putting Hitler into an evil baby orphanage!

[queueingtheory]

This was an interesting comic, and all the time-warpy responses have been equally intriguing.

I just want to share a thought not originally thought of by me, but by the vlogbrothers over at youtube and the Nerdfighter community. See, there really is no need to kill baby Hitler. The proper solution to this problem is to kidnap him, and take him to an orphanage for evil babies aptly titled The Evil Baby Orphanage. Where baby Hitler will receive therapy, and all will be well.

This is, of course, not a perfect solution to the problems of the world; what kind of therapy should we go for, how do we decide exactly who's evil enough to earn a spot and how do we even take anyone but Hitler there given that this comic only allowed for one journey in time? Not to mention the already much discussed time-warpy issues. But it is a thought that I think is worth putting into this whole equation of making the world a better, more paradoxal place.

Actually, the bigger danger is that you fail to spot the evil cacopediatric therapist before his army of evil takes over the world (and destroys all the time machines, obviously).

[Pfhorrest]

All information we receive concerns the past. Neurons have finite speed, light takes time to travel and it takes a good long while for new observations to coalesce and be presented to the frontal cortex for analysis. If we want to consider anything true beyond "cogito ergo sum", we have to accept past data as valid. And we can only do experiments in the past and future, by looking at the received data and checking them against predictions, or by designing an experiment which will occur in the future, which for a future you will be the past.

The present is only an infinitesimal point in spacetime, possibly extended into an arbitrary 3D spatial volume depending on the velocity of the observer. The only logical things which can have an influence on the state of a particle in the present are all events in the particle's past lightcone. Interaction with the present is physically impossible, because instantaneous interaction violates causality for moving observers. What you are saying is physically wrong.

This is very much what I was saying to JThomas about everything being an observation of the consequences of the consequences of the consequences ... etc ... of the hypothetical event we model to be the cause of that observation. Instantaneous nonlocal interaction violates causality, so anything you are not immediately observing i.e. directly, locally interacting with, anything which you are indirectly observing, is a hypothetical cause in a hypothetical past of another hypothetical cause in another hypothetical past of whatever it was you locally interacted with. And that's all for whatever system we consider to constitute "you", discounting the measurement apparatus you use to do the observation by proxy, the light you use to observe that measurement apparatus, and quite plausibly your eyes, optic nerves, and whatever else could theoretically be discarded and replaced with some more direct transmission of the signal to whatever bundle of neurons finally counts as 'sensing' that signal.

As far as you can be absolutely certain, not only might the phenomena you think you're observing not be occurring but instead you have some kind of faulty reading, but the apparatus you're using might not exist, it could be an optical illusion of some kind, or maybe there's not even any light reaching your eyes, maybe you don't even have eyes and are a brain in a vat, or maybe you don't even have a brain and are software in some kind of simulation running in a universe whose laws are completely unlike anything you think they are, maybe you were just booted up right now and all your memories of seeming to have seen a reading of some phenomenon on some instrument are false to begin with -- your memories are just something you're immediately perceiving too. The supposition of all of that stuff in the causal chain of you observing some phenomenon which just occurred a moment in the supposed past is all just part of your best explanation of why you are having the perceptions you are having now, including the memories you seem to have. And you set up experiments to be done in a future which you suppose to exist because you are acting in confidence of that explanatory model, but for all you know your incomprehensible not-even-alien programmers will shut your program off in a moment before any such future can occur, even in simulation.

I'm not trying to cast any substantial doubt on the veracity of these common suppositions that we have brains and optic nerves and eyes and that light is actually reaching those eyes after bouncing off of instruments that actually exist and actually measure real phenomena -- in fact I'd argue very strongly in favor of those hypotheses -- but just making a point about how we relate to time and cause and for that matter space and matter too. Strictly speaking it is all hypothetical. I can make an argument about why assuming that there is some kind of space, time, matter, and causation is a necessary hypothesis to make any sense out of anything, but the particulars about them all are always up for debate.

[J Thomas]

I'm [...] just making a point about how we relate to time and cause and for that matter space and matter too. Strictly speaking it is all hypothetical. I can make an argument about why assuming that there is some kind of space, time, matter, and causation is a necessary hypothesis to make any sense out of anything, but the particulars about them all are always up for debate.

Let's take it a step further -- we all know that we heavily censor the perceptions we use to understand the world. A whole lot of what we experience does not make sense, and when it does not make sense we assume it is a dream. People who don't make that assumption are assumed to be hallucinating and there are medications that are supposed to help them fit into society, or at least to cause less harm.

I cannot stress enough how convenient it is to dismiss anything that does not fit our preconceptions as a dream.

[Pfhorrest]

I'm [...] just making a point about how we relate to time and cause and for that matter space and matter too. Strictly speaking it is all hypothetical. I can make an argument about why assuming that there is some kind of space, time, matter, and causation is a necessary hypothesis to make any sense out of anything, but the particulars about them all are always up for debate.

Let's take it a step further -- we all know that we heavily censor the perceptions we use to understand the world. A whole lot of what we experience does not make sense, and when it does not make sense we assume it is a dream. People who don't make that assumption are assumed to be hallucinating and there are medications that are supposed to help them fit into society, or at least to cause less harm.

I cannot stress enough how convenient it is to dismiss anything that does not fit our preconceptions as a dream.

Quite. Dreams -- as in, the theory of dreams, the hypothesis that when people sleep mental processes happen which resemble waking perception but in fact are not, rather than that people are actually mentally transported somehow to another body in some other world where everything is very different and then returned to their bodies in this world, or some such -- are just another part of our attempts to make sense of a series of observations. Just watch any science fiction for some (albeit far-fetched) hypothetical scenarios where the veracity of that hypothesis might be called into question (i.e. "I thought it was just a dream, but in fact aliens were communicating with me", "I thought it was just a dream, but I was actually transported to another dimension and back", etc). The theory that our dream-perceptions are caused by the psychological and neurological processes we think they are is totally falsifiable. It's just that so far, nobody's come up with credible evidence favoring another theory more strongly, and it looks improbable that anyone ever will.

I dream rather strangely, myself. For years I slowly got into lucid dreaming. At first it was cool; I would realize I was dreaming and do cool stuff in the dream. Over time at some point all of my dreams (that I remembered upon waking at least) became lucid dreams. And it stopped being a novel phenomenon. I don't go "holy shit I'm dreaming!" and go for a fly or something. I just watch the interesting things pan out, and about the only intervention I ever do is to rewind and rewatch some part of it, or occasionally to "rewrite" the story, just deciding that things happen differently, without causing them to do so in-character in the dream. As a consequence, dreams no longer feel like anything distinct from daydreaming to me. I'm lying there imagining something that I am continuously aware is just a product of my imagination. When compared to something as mundane as daydreaming or imagination, dreaming doesn't really seem such an odd phenomenon at all. We visualize unreal things all the time, every time we think of the way something could be but isn't, or used to be but isn't anymore, etc. The only qualitative difference with non-lucid dreams is that we lose track of the fact that we are doing so.

[J Thomas]

A whole lot of what we experience does not make sense, and when it does not make sense we assume it is a dream. People who don't make that assumption are assumed to be hallucinating and there are medications that are supposed to help them fit into society, or at least to cause less harm.

I cannot stress enough how convenient it is to dismiss anything that does not fit our preconceptions as a dream.

Quite. Dreams -- as in, the theory of dreams, the hypothesis that when people sleep mental processes happen which resemble waking perception but in fact are not, rather than that people are actually mentally transported somehow to another body in some other world where everything is very different and then returned to their bodies in this world, or some such -- are just another part of our attempts to make sense of a series of observations. Just watch any science fiction for some (albeit far-fetched) hypothetical scenarios where the veracity of that hypothesis might be called into question (i.e. "I thought it was just a dream, but in fact aliens were communicating with me", "I thought it was just a dream, but I was actually transported to another dimension and back", etc). The theory that our dream-perceptions are caused by the psychological and neurological processes we think they are is totally falsifiable. It's just that so far, nobody's come up with credible evidence favoring another theory more strongly, and it looks improbable that anyone ever will.

I was thinking more of the dreams that are almost like reality, but not quite. Like the one where your boss calls you in to explain about the new project. You will be central to it, and if you fail the project fails. She talks vaguely about the great rewards for success, and plainly about the great penalties for failure. You go back to your office and rough out a preliminary schedule, and it looks rough. Too many unknowns. You start getting info on each of them, and each time the answer looks bad. It starts to look impossible. But if you can subcontract the different parts, maybe you can hide the problems enough to pawn them off onto somebody who can take the blame. You take that to the boss and she says no subcontractors. As you learn more about the problem it keeps looking worse. The only possibility is to simplify the interfaces, have fewer layers of indirection. That has its own problems but maybe a ruthless simplicity might reduce it to something your team can do on schedule. You take that to the boss and she says absolutely not. No Forth. And she says a little more about the rewards of success. If you succeed at this, you can have her job. You feel more paranoid. Is this her way of saying she won't let you win? Why were you chosen for this job? Who hates you? Or is she hinting that the company is in such deep trouble that she's bailing and you'll be left trying to solve all the problems she couldn't? You go to sleep wrestling with it all and when you wake up you don't know whether it was a dream. Except it was late autumn in the dream and it's summer now. And you still have all the details of the Aldiss project in your head, and as you try to focus on it some of the details of the new project don't quite make sense. Oh, thank god, it must have been a dream.

When your wife talks about the great movie she saw with you, and it's a movie you've never seen. Did she see it with somebody else and remember it with you? Does she have a secret lover she confuses with you? Or did she remember a dream?

That kind of thing.

[Pfhorrest]

Actually I was going to write something on that subject and forgot about it by the time I finished my last paragraph. I don't think it makes any difference in what we've been talking about, but it is an interesting subject. About the only dreams which feel like dreams to me anymore are the mundane ones like that. My boss is mad at me. I'm getting pulled over for an illegal left turn. Oh god. How can this be happening to me. I can't afford a ticket. What if I get fired. Then what will I do. Panic. I wake up... thank god it was just a dream. On the other hand, a skeletal winged tyrannosaurus tries to eat me and I just pause or rewind and decide how I want the story to proceed from here. A part of me really wants to know how I would react if something really fantastic happened in real life, like aliens invade or something... whether I would assume it was a dream or what.

The most disconcerting "mundane" dream I had was one Sunday I got home from my normal weekend activities, did my normal evening stuff on my computer, went to sleep, woke up Monday morning, went to school, went to work, went to my other classes after work, came home, played around on the computer and so on in the evening as usual, went to bed, woke up the next morning, went straight to work as usual for a Tuesday morning, and my boss wanted to know what I was doing there so early on a Monday, did I not have class? That really threw me for a loop.

[ijuin]

The more elaborate the indirection, the more likely you are to get silly results. So for example, neutrinos are almost undetectable. Every now and then something happens that you can assume would not have happened unless a neutrino intervened at precisely the right moment, so that's your evidence that a neutrino was there. But people calculated the number of neutrinos they expected to see from the sun, and they didn't get that number. They got about half as mny. They could have assumed this meant there was something about the sun they didn't know. But instead they assumed that the sun's neutrinos oscillate between a form that is rarely detectable and a form that is completely undetectable. And the fact that at any given time half of the neutrinos are completely undetectable has profound implications. It's possible that all this is clearly the right way to think about it when you have enough background information. But from where I sit it looks like assumption piled on top of assumption. The observable consequences are too far removed from the hypothetical causes.

To put it in the simplest terms that I am able, it upsets known physics a lot less to assume that half of the neutrinos become undetectable than to assume that they were never created in the first place. Assuming that only half the expected number of neutrinos are produced by the Sun would mean that either 50% of fusion reactions produce zero neutrinos while 50% produce one neutrino (even though the reactions ought to all produce either exactly one or exactly zero), or else there are only 50% as many fusion reactions going on inside the Sun, in which case said reactions release twice as much energy each as we believed while happening only half as frequently, which completely upends our understanding of fusion and the internal processes of stars.

As an aside, let's look at the implications of the "half as many fusion reactions, therefore half as many neutrinos" hypothesis. Not only does this mean that we are getting twice as much energy from each reaction as we thought (which OUGHT to show up in H-bomb tests and fusion reactor tests producing more energy than anticipated), it also means that stars burn through their fuel half as fast, and therefore age half as fast and live twice as long. That would require that most of the stars that we see be twice as old as we assume that they are. First of all, that would require a re-calculation of cosmology to allow the Big Bang to be twice as long ago as we believed, and second of all, it would require that the Earth itself be twice as old as we believed (and all radioactive-dated minerals and fossils--and since this dating method is based on FISSION reactions, it implies that the rules of fission would have to have changed just as much as the rules of fusion).

As such, you can see that assuming that fewer neutrinos are produced pretty much amounts to pulling the rug out from under our understanding of nuclear reactions over the past 75-80 years, whereas saying "they are there but we can't see them" changes things much less and is preferable until we have a theory that would allow fewer neutrinos to be produced without upsetting the reactions.

[J Thomas]

The more elaborate the indirection, the more likely you are to get silly results. So for example, neutrinos are almost undetectable. Every now and then something happens that you can assume would not have happened unless a neutrino intervened at precisely the right moment, so that's your evidence that a neutrino was there. But people calculated the number of neutrinos they expected to see from the sun, and they didn't get that number. They got about half as mny. They could have assumed this meant there was something about the sun they didn't know. But instead they assumed that the sun's neutrinos oscillate between a form that is rarely detectable and a form that is completely undetectable. And the fact that at any given time half of the neutrinos are completely undetectable has profound implications. It's possible that all this is clearly the right way to think about it when you have enough background information. But from where I sit it looks like assumption piled on top of assumption. The observable consequences are too far removed from the hypothetical causes.

To put it in the simplest terms that I am able, it upsets known physics a lot less to assume that half of the neutrinos become undetectable than to assume that they were never created in the first place. Assuming that only half the expected number of neutrinos are produced by the Sun would mean that either 50% of fusion reactions produce zero neutrinos while 50% produce one neutrino (even though the reactions ought to all produce either exactly one or exactly zero), or else there are only 50% as many fusion reactions going on inside the Sun, in which case said reactions release twice as much energy each as we believed while happening only half as frequently, which completely upends our understanding of fusion and the internal processes of stars.

As an aside, let's look at the implications of the "half as many fusion reactions, therefore half as many neutrinos" hypothesis. Not only does this mean that we are getting twice as much energy from each reaction as we thought (which OUGHT to show up in H-bomb tests and fusion reactor tests producing more energy than anticipated), it also means that stars burn through their fuel half as fast, and therefore age half as fast and live twice as long. That would require that most of the stars that we see be twice as old as we assume that they are. First of all, that would require a re-calculation of cosmology to allow the Big Bang to be twice as long ago as we believed, and second of all, it would require that the Earth itself be twice as old as we believed (and all radioactive-dated minerals and fossils--and since this dating method is based on FISSION reactions, it implies that the rules of fission would have to have changed just as much as the rules of fusion).

As such, you can see that assuming that fewer neutrinos are produced pretty much amounts to pulling the rug out from under our understanding of nuclear reactions over the past 75-80 years, whereas saying "they are there but we can't see them" changes things much less and is preferable until we have a theory that would allow fewer neutrinos to be produced without upsetting the reactions.

That all sounds reasonable. But what if the reality is that the law of conservation of energy, momentum, etc are not quite true? Perhaps there is at least one alternate universe, and in these reactions a little bit of conserved things are transferred between ours and some other. And something about doing that means it's more likely than before that another reaction will go the opposite direction somewhere nearby in the near future.... I don't at this time see any reason to prefer that explanation, but it could probably be adjusted to fit just as well as the neutrino story.

In recent generations there's been a prejudice in physics to see particles everywhere. Like, it's been observed that when you have a fixed electric charge, other nearby charges get pulled toward it or pushed away. That's what's observed. But people want to think that only particles can push or pull and only when they're in the same place, so they imagine undetectable particles that stream out from one charge to hit other charges and push them, that then bounce back to the source and push on it. Or particles that somehow stream out and pull when they hit before they bounce back and pull again. Similarly for gravity, light, and anything else that looks like action at a distance. We observe action at a distance and we imagine particles. What's wrong with fields? It looks like sheer prejudice to me, but then physicists do use field ideas whenever they're useful for computation or whatever.

If somebody came up with an alternative explanation for the things neutrinos explain that predicted exactly the same things, it wouldn't really be an alternative explanation at all, right? If two theories provide the same results then they're the same theory. Right? And yet the extra ideas we put into our theories do affect our thinking even when they don't affect the results. The belief that neutrinos are particles and not "probability waves" or something else might affect which hypotheses about them that you think of to test.

[gmalivuk]

But what if the reality is that the law of conservation of energy, momentum, etc are not quite true?

Then the laws of physics depend on your location, and we can't reliably do science any more.

[J Thomas]

But what if the reality is that the law of conservation of energy, momentum, etc are not quite true?

Then the laws of physics depend on your location, and we can't reliably do science any more.

Then we can reliably do science as well as physical reality lets us. The conservation laws will be reliably true as far as they are reliably true, and we can study the small exceptions and look at how they work. Which is in fact what we have done, except that we have assumed that each time a violation occurs an undetectable particle is created or consumed.

[gmalivuk]

But what if the reality is that the law of conservation of energy, momentum, etc are not quite true?

Then the laws of physics depend on your location, and we can't reliably do science any more.

Then we can reliably do science as well as physical reality lets us.

Which isn't very, if the laws aren't the same everywhere.

[J Thomas]

But what if the reality is that the law of conservation of energy, momentum, etc are not quite true?

Then the laws of physics depend on your location, and we can't reliably do science any more.

Then we can reliably do science as well as physical reality lets us.

Which isn't very, if the laws aren't the same everywhere.

Whatever. We must do physics with the physical world we actually have, whatever that is, and not whatever world we wished we had.

When you do alternate theoretical physics, shouldn't it be a form of pure math?

[gmalivuk]

Well yeah, but in an inconsistent universe we can't make predictions or useful discoveries, so we might as well assume it is consistent unless/until proven otherwise.

[Pfhorrest]

In recent generations there's been a prejudice in physics to see particles everywhere. Like, it's been observed that when you have a fixed electric charge, other nearby charges get pulled toward it or pushed away. That's what's observed. But people want to think that only particles can push or pull and only when they're in the same place, so they imagine undetectable particles that stream out from one charge to hit other charges and push them, that then bounce back to the source and push on it. Or particles that somehow stream out and pull when they hit before they bounce back and pull again. Similarly for gravity, light, and anything else that looks like action at a distance. We observe action at a distance and we imagine particles. What's wrong with fields? It looks like sheer prejudice to me, but then physicists do use field ideas whenever they're useful for computation or whatever.

As far as I understand, in contemporary physics all particles are considered to be nothing more than perturbations in underlying fields. It's just that interactions between those fields are quantized, so it makes sense to track the packets of discrete quantities of energy exchanged in those interactions, and each of those -- each quanta -- is mathematically the same thing as a particle.

Well yeah, but in an inconsistent universe we can't make predictions or useful discoveries, so we might as well assume it is consistent unless/until proven otherwise.

What could even count as conclusive proof otherwise, rather than "there is this really weird phenomenon we don't understand at all yet"? How can we tell the difference between something being contingently not understood and something being necessarily incomprehensible? And if we can't, why should we ever be defeatists and assume it is an insurmountable problem rather than just an unsolved one?

[J Thomas]

Well yeah, but in an inconsistent universe we can't make predictions or useful discoveries, so we might as well assume it is consistent unless/until proven otherwise.

What could even count as conclusive proof otherwise, rather than "there is this really weird phenomenon we don't understand at all yet"? How can we tell the difference between something being contingently not understood and something being necessarily incomprehensible? And if we can't, why should we ever be defeatists and assume it is an insurmountable problem rather than just an unsolved one?

I think he's kind of agreeing with you. But he has gone from "conservation laws may not always be completely upheld" to "the universe is inconsistent". As if any universe where conservation laws sometimes fail must be inconsistent. And then he figures it's defeatist to suppose that conservation laws might ever fail, so we should accept that all known conservation laws are true until we get conclusive proof they are not.

And it would be extremely hard to prove that a conservation law fails. Look at the neutrino example. What is observed is conservation law failure. But this is taken as evidence for completely undetectable particles instead. Can I say that any plainer?

The only possible way to detect a neutrino is to detect an example of a conservation law failing. That is what it means to detect a neutrino. When conservation laws are observed to fail, that is taken as evidence for undetectable particles that make up the difference so the conservation law does not fail after all. Either an undetectable particle is created on the spot and zooms off at approximately lightspeed, carrying away whatever is missing. Or an undetectable particle just happens to be onhand to supply whatever surplus stuff otherwise could not be explained.

It's is a case of the Emperor's New Particle.

[gmalivuk]

As if any universe where conservation laws sometimes fail must be inconsistent.

If a universe has time- and location-invariant rules, it has conservation laws that don't fail. Ergo, if conservation laws sometimes fail, the universe must not have time- and location-invariant rules. Sure, this doesn't quite mean it's inconsistent, but it still makes science pretty hard if we're forced to admit that the laws of the universe today might not be the same as yesterday, and that they may also be different on the Moon.

[J Thomas]

As if any universe where conservation laws sometimes fail must be inconsistent.

If a universe has time- and location-invariant rules, it has conservation laws that don't fail. Ergo, if conservation laws sometimes fail, the universe must not have time- and location-invariant rules. Sure, this doesn't quite mean it's inconsistent, but it still makes science pretty hard if we're forced to admit that the laws of the universe today might not be the same as yesterday, and that they may also be different on the Moon.

You might easily be right about this, but I am ignorant about it and I don't see it immediately.

You seem to be saying that the particular conservation laws we have assumed -- conservation of energy, conservation of momentum, conservation of angular momentum etc -- must be true everywhere all the time, or else no other conservation laws can be consistent in different places or different times. I don't see that at all.

Why couldn't our preferred assumed conservation laws be partly right everywhere in the same ways? Why can't they be consistently broken the same ways everywhere?

[gmalivuk]

You might easily be right about this, but I am ignorant about it and I don't see it immediately.

It may not be intuitive, but it's true nonetheless. Noether's theorem states that, in particular, a physical system that behaves the same regardless of spatial orientation conserves angular momentum, one that behaves the same regardless of time conserves energy, and one that behaves the same regardless of position conserves (linear) momentum. Therefore, a physical system in which e.g. energy is not conserved is a physical system that behaves differently at different times.

[J Thomas]

You might easily be right about this, but I am ignorant about it and I don't see it immediately.

It may not be intuitive, but it's true nonetheless. Noether's theorem states that, in particular, a physical system that behaves the same regardless of spatial orientation conserves angular momentum, one that behaves the same regardless of time conserves energy, and one that behaves the same regardless of position conserves (linear) momentum. Therefore, a physical system in which e.g. energy is not conserved is a physical system that behaves differently at different times.

Oh, I see. But first, that does not say that nothing is conserved. We have observed that energy, momentum, and angular momentum are not conserved, but that does not mean there are no conservation laws -- just not those particular ones.

And second, they can still be conserved on average, most of the time. As far as I've heard, all of the exceptions found so far happen at atomic nuclei -- which are very rare locations!

Also when there is a violation, there is some tendency to get an opposite violation at some time and distance away that tends somewhat to balance the first. So even though the real physical universe does violate our proposed conservation laws in some ways, and doesn't behave exactly the same everywhere (since some nuclei occasionally gain energy etc, while others occasionally lose it), still there is enough order available that physicists can soldier on.