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SolusLupus
2005-Oct-22, 04:12 PM
This is a curiosity to me, and I'm more of curious what the surrounding arguments around the idea of Absolute Truth state. I know that, technically, this might not be "against the mainstream", but I felt this might be best to post it here, since it might be... I'm not sure what's surrounding this issue, hence my question.

I had once been in a philosophical debate with a friend. I was talking about the idea of Absolute Truth - that behind everything, there is truth. For instance: I have a table. This table is made of wood. These are facts. It is currently in my living room. Fact.

People can debate about this table across the world. Even though they can't see it, it's still there. Even if 6 billion people don't see it, it still exists. Even if 6 billion people don't acknowledge its existance, it still exists. Nothing changes this fact.

Thus, I was basically explaining that in my view, no matter all the beliefs, the conjecture, and the ideas, the truth is always somewhere in there. And it's not what we make of it, but how we perceive it.

Yet, this idea seemed to emit some resistance from my friend. I couldn't tell why. He can be VERY vague when he disagrees with something, and rarely goes into detail why.

So this is my question - why would anyone contest the idea of Absolute Truth? WHen I say it, am I unknowingly spouting off a different philosophical standpoint? Am I just confused as to the "true meaning" of it? Or what?

Any help is appreciated, thanks in advance.

tbm
2005-Oct-22, 04:56 PM
Greetings.

You say your table is made of wood and that is the truth.

Where is your evidence? I cannot prove your truth either way; I cannot test your truth either way. I am taking you at your word. You say that it is wood. Are you a carpenter? A trained forester?

There are so many ways a truth can be questioned. Testing (proving?) a truth is another matter.

Personally I believe you. I have a "table" made of "wood". But you will have to take my word for it.

And that's the truth.

(Anybody remember Lily Tomlin's characer "Edith Ann"?)

tbm

WaxRubiks
2005-Oct-22, 05:03 PM
why don't you take a picture of this "table" and post it on this thread, that should clear things up.:D

WaxRubiks
2005-Oct-22, 05:15 PM
seriously though, you could also ask the question, if you play a game of chess and keep a record of all the moves made and then halfway through the game destroy the record(piece of paper) then arn't those moves still the moves that got the chess pieces to where they are? Surely nothing can alter those facts.

Bathcat
2005-Oct-22, 05:35 PM
I think the absoluteness (absolutivity?) of truth depends on how fine-grained it is.

You have a table made of wood.

Good, we can agree that that is the truth.

You have a table made of 5X10^10 molecules.

Well, I think we could eventually, after laborious investigation, agree that this is true.

You have a table in which the position of Electron Number 7 around Molecule Number 5,1295,998 is precisely equidistant between the nucleii of the third and fourth carbon atoms.

No, we cannot even in principle agree that this is the absolute truth.

----

We can agree that the Sun will rise at 8:59:33 tomorrow, given a particular city, skyline, and date.

We can agree that the Sun will rise at 8:59:33 on the same date a few years hence.

But we cannot agree that it will rise at an exact time 100,000,000 years in the future because the motions of the solar system are chaotic beyond analysis over very long time periods.

----

So: absolute truth depends on being somewhat coarse-grained: on averaging out quantum indeterminacy, and on summing over the effects of chaos in certain systems.

----

What about maths? What about logic? Is it an absolute truth that 2 + 3 = 5? Why? We might speculate that it's a result of the conservation laws, but why should they be Truth?

I dunno.

nokton
2005-Oct-22, 06:02 PM
Hi Lonewulf, hope your day good for you.
Understand your path wulf, but dwell awhile on concepts.
We all have a different level of understanding of the world
around us, that level is determined by knowledge and experience.
The 'big picture' is determined by ones experience of life and knowledge.
Quantum theory dictates we can be in two places at the same time.
Your table is there for you, in your time. In someone elses, is not.
Hope you understand,
Nokton

tbm
2005-Oct-22, 06:21 PM
"We can agree that the Sun will rise at 8:59:33 tomorrow, given a particular city, skyline, and date."

You and I may agree, but Nancy Lieder would have a problem with that.........


tbm

Disinfo Agent
2005-Oct-22, 06:42 PM
Suggested reading: The problem of induction (Hume's analysis) (http://www.princeton.edu/~grosen/puc/phi203/induction.html), The problem of induction (Karl Popper) (http://dieoff.org/page126.htm).

WaxRubiks
2005-Oct-22, 06:57 PM
there is alway the possibility that we are all in some kind of matrix and then you could say "there is no table". You can't discount this possibility.

NanC
2005-Oct-22, 08:24 PM
Thus, I was basically explaining that in my view, no matter all the beliefs, the conjecture, and the ideas, the truth is always somewhere in there. And it's not what we make of it, but how we perceive it.
I don't understand the part "how we perceive it". Our perception of the truth should also have no effect on it. Whether we perceive it or not or if we perceive it incorrectly the truth doesnt change. Was this misspoken?

SolusLupus
2005-Oct-22, 10:13 PM
No no no, you all got it all wrong! (I think)

Okay, first of all: the truth is STILL IN THERE, and if we cannot claim to know the answer, that doesn't effect the basic truth. The trick is knowing the truth - and it seems to me we're far off from KNOWING every truth, with every expert.

Also, as for how we perceive it, I didn't mean to imply that it affected the truth. The only thing is, our perception of the truth might be different than what that truth is. One can see Lightning and describe the true reason for lightning. Back a few thousand years ago, we'd give a divine reason for it. Well, from the looks of it, that wouldn't be the Truth - just our perception of it. Thus, the perception is wrong, but the truth is not. Still, my point is this:

Hidden under all these blankets of misinterpretations and misperceptions, the truth still lies within. This is common sense - the truth never changes, it isn't altered. Even if something is changed (for instance: My table blows up at 11:00 AM Tuesday...), it doesn't matter for the truth (...my table still had existed at 10:00 AM Tuesday)

The thing is, I'm not claiming that anyone KNOWS the "Absolute Truth". I'm just claiming that it's THERE, that it exists. Some people seem to disagree with that concept, and I'm curious as to why.

Disinfo Agent
2005-Oct-22, 10:19 PM
That is a sensible, common sense assumption, to use Popper's term, and I don't usually challenge it myself.
Still, can you prove it?... :)


'If a tree falls in a forest and nobody hears it, does it make a sound?' :shhh:

SolusLupus
2005-Oct-22, 10:26 PM
Yes, it makes a sound. Sound waves are a documented and proven thing - there is no reason to believe that the tree falling did not make a sound wave. As well, there is nothing changing the fact that the tree fell in the first place. Thus, it's only logical that "sound", as we know it, was made - it just didn't vibrate the eardrums of "anybody" (which applies to just humans, or humans and animals, depending on what you mean by "nobody")

NanC
2005-Oct-22, 10:29 PM
I am interested in the answer. I can't imagine a scientific reason someone would doubt that the absolute truth does exist whether we know what it is or not. Is it not the truth behind an event that causes the event to occur? By truth I think you are referring to actual facts, reality, not the opposite of lies or falsehoods. I require to think that because it doesnt make sense in my phrasing otherwise.

Is there actually a scientific argument that a tree would not make sound in the forest if it were not listened to? I have never understood that question at all.

Disinfo Agent
2005-Oct-22, 10:49 PM
I do not have an answer, myself. I don't think anyone does.


Yes, it makes a sound. Sound waves are a documented and proven thing - there is no reason to believe that the tree falling did not make a sound wave.Perhaps, but how can you prove it did, if no one observed the sound wave?


As well, there is nothing changing the fact that the tree fell in the first place. Thus, it's only logical that "sound", as we know it, was made - it just didn't vibrate the eardrums of "anybody" (which applies to just humans, or humans and animals, depending on what you mean by "nobody")That's logical, but it's not a fact. We assume that the universe is regular, or at least act as though it were regular, but can we be really certain that we live in a logical universe?

TheBlackCat
2005-Oct-22, 11:05 PM
Although there is certainly absolute truth, there is no reason to assume anything we percieve is the absolute truth. Everything we percieve is filtered by our brains. We never really see anything, our brain takes the photons of light to trigger electrical impulses, these impulses are filtered. Then parts of the brain look for certain patterns in the electrical impulses (impulses corresponding to shape, movement, orientation, color). The actual impulse is broken up into a massive number of individual characteristics of individual parts of the image, and these characteristics are processed by a number of completely different sections of the brain. All these pieces are then re-assembled by your consciousness to form an image. There is no reason to assume such processes are perfect. We know the brain misses certain things, we know the processing isn't perfect. In the end all perception is purely subjective. There is no way to prove, for instance, that the human brain is not wired in such a way that although your table is really made of stone, all the sensory input from the table is altered so people percieve it as being wood. You can't disprove that statement. You can't prove that what you are percieving is really how things are. In fact, you can't even prove you are percieving anything, for all you know you could be dreaming. You can't even prove your own existance, you could be the dream of some other entity.

There is actually a game called "The Legend of Zelda: Link's Awakening", where your character is trapped in the dream of a sleeping creature. You are real, but all events in the game, the characters you meet, the monsters you fight, everything is simply the dream of this creature. However, you don't know it. You simply pass out when your boat is destroyed in a storm and find yourself on an island. You set about trying to save people on the island from a group of monsters. In reality you are not on the island, but sleeping as you drift on the wreckage of your boat. The monsters are trying to keep the creature asleep to preserve the world they live in. In the end you kill the monsters and wake up the creature, setting you free but killing everyone in the dream (except for one character, who miraculously gets transformed into a seagull if you manage to beat the game without dying).

SolusLupus
2005-Oct-22, 11:36 PM
Interesting concept. But doesn't that mean that the fact that it was a dream mean that it was the Absolute Truth?

Bathcat
2005-Oct-23, 12:19 AM
Lonewulf: "The thing is, I'm not claiming that anyone KNOWS the 'Absolute Truth'. I'm just claiming that it's THERE, that it exists. Some people seem to disagree with that concept, and I'm curious as to why."

What I'm suggesting is that at the quantum level there is no absolute truth. There are only probabilities that something is or is not true.

It's not common sense, but it appears to be true anyway. You cannot, even in theory, assert that an electron is exactly there and also moving exactly that way because the universe does not allow both things to be absolutely true.

It's not that we can't figure out both things about an electron, it is that the universe is consituted in such a way that certain absolute truths are impossible if you look closely enough.

(Incidentally, quantum physics may in theory allow you as a large, non-microscopic human being to be in two places at once, but quantum physics also says that the chance of this actually happening is so incredibly tiny that we would have to wait billions of years before even one large-sized object -- one in the entire universe! -- to shift its position one meter by means of quantum tunneling.)

----

Now, it also depends on what large-scale absolute truths you want to assert. There are testable, objective truths: The Moon exists. And there are subjective truths: Evil exists, beauty exists.

I'd agree with all those statements. But it would be hard to assert that evil exists in an absolute, objective context. It can be defined in a human context, but perhaps not in the context of the Moon.

----

So: do you mean, Good Sir, that macroscopic, non-quantum, objective truths exist? :)

I would say they do, if only conditionally (because they have not been disproved and we cannot imagine that they would be -- realistically, I can't imagine that someone will prove that the Moon does not actually exist.)

This comes close to the definition of scientific evidence and theory, doesn't it?

I think that's no accident. I think science searches for exactly the kinds of absolutes you imagine: it looks for things that are not disproven by the evidence we have, and which all disinterested parties with proper experimental equipment would agree about.

And for things like quantum indeterminacy we look for mathematical laws which explain the form which the stubborn, uncooperative universe seems to take when it does not allow us absolute knowledge.

----

Long reply. I may have been drinking beer, and therefore departing from absolute sober Truth. ;)

NanC
2005-Oct-23, 12:31 AM
It's not common sense, but it appears to be true anyway. You cannot, even in theory, assert that an electron is exactly there and also moving exactly that way because the universe does not allow both things to be absolutely true.
I do know that this is an accepted scientific statement. I cannot even begin to comprehend it despite my best efforts and reading many books. The cat in the box illustrate also utterly escapes me. To say that the cat in the box is both alive and dead and that the act of discovering its state is what makes it one way or the other seems to be the ultimate in obfuscated logic. There is something that simply refuses to let me accept the concept and this may be simply I have not ever had it properly explained to me. I doubt that. But it is possible. Would you like to take a stab at teaching me?

SolusLupus
2005-Oct-23, 12:32 AM
I'm still finding it hard to buy all this Quantum stuff. :/ From my knowledge, the "cat in the box" thing was only meant as a joke (according to a reliable source)

As for subjective truths, they are subjective. However, that's an example of perception. If a man steals something, then it's a fact that he took an object which was considered a theft within the area he was in. It's a fact that he was considered to have committed a crime, according to enstated laws of the area.

However, calling it "evil", "good", or "acceptable", is dependant on perception of that Truth.

Bathcat
2005-Oct-23, 01:22 AM
NanC: The cat in the box illustrate also utterly escapes me. To say that the cat in the box is both alive and dead and that the act of discovering its state is what makes it one way or the other seems to be the ultimate in obfuscated logic.

Sheesh, Shroedinger's cat is, as Lonewulf mentioned, more of a joke than an actual example. A cat cannot be alive/dead, or up/down, or any other quantum superposition of states because a cat is a MACROSCOPIC OBJECT!

Shroedinger surely knew this perfectly well.

The hammer which breaks the vial is non-quantum, and the Geiger counter is a big honking box of seriously non-quantum size.

----

If we hit a vial of cyanide with a hammer it will break exactly when we hit it. By contrast, though, the exact time a radioactive atom decays is not caused by anything. A given atom may decay in five minutes, or in five days.

Therefore, until we get a macroscopic event that tells us the atom has decayed we cannot know, even in principle, whether it has busted apart or not.

The detection-event in the Geiger counter is essentially that link between the quantum and the macroscopic.

The only use for the cat is to make some joke, nein?

----

Better perhaps to think about a tunnel diode.

In a precise universe an electron cannot cross a particular insulating barrier. (It could if we cranked up the voltage enough to arc across, but never mind that -- we are speaking of the case in which the barrier is classically too great.)

However, suppose the universe is not precise. Suppose that as an electron comes down a wire to the barrier it is not really at any exact point but rather "smeared out" across a range of points, with a mathematically defined probability of being at any real spot at any given time.

We can imagine a situation where the electron approaches the barrier such that 60% of its position-probability-curve is on one side of the barrier, 30% inside the barrier, and 10% of its position-probability-curve is actually on the FAR SIDE of the barrier!

The skinny tail of its possible positions would be over in a place that it could not ever get to in a classically absolute universe.

We would expect that, if there is not really an absolute position for an electron but only probabilities, that one in ten electrons would magically appear on the far side of the barrier.

And that's what the real universe tells us actually happens.

The electron does not have an absolute position AND an absolute velocity.

The darned universe allows tunnel diodes to work, and it appears they work precisely because at the quantum level absolute truths become impossible. (Truths of certain kinds, anyways. Those we describe as linked by Heisenberg uncertainty.)

----

Really, the English language is not suited to explaining this stuff. Everybody talks the kind of language Newton used to describe an absolute reality. For that matter, all we see with our eyes and handle with our hands appear to be things that obey macroscopic, absolutist-type laws.

We are not evolved to intuitively understand quantum reality.

We just aren't! We are evolved to throw macroscopic, Newtonian rocks at bananas, and catch the macroscopic Newtonian bananas when we knock them out of the tree.

So the general wisdom is, you can't intuitively understand quantum indeterminacy the way you can intuitively understand Euclidean geometry.

If you're looking for that kind of understanding, I don't think you'll easily find it. I certainly have no glimmer of it.

ASEI
2005-Oct-23, 01:31 AM
The skinny tail of its possible positions would be over in a place that it could not ever get to in a classically absolute universe.

We would expect that, if there is not really an absolute position for an electron but only probabilities, that one in ten electrons would magically appear on the far side of the barrier.

And that's what the real universe tells us actually happens. Could this possibly still be explained in terms of unknown, but determined properties when we take into account the inexactness of our knowledge of the barrier as well? After all, there may be a small path through the barrier that an electron can make it through? Or not? Is the shape of the electron's probability curve effected by the presence of the barrier in this case?

NanC
2005-Oct-23, 01:35 AM
Sheesh, Shroedinger's cat is, as Lonewulf mentioned, more of a joke than an actual example. A cat cannot be alive/dead, or up/down, or any other quantum superposition of states because a cat is a MACROSCOPIC OBJECT!
I apologize for not knowing this was a joke. I have some more problems with understanding things than most people so I try harder so probably I was too busy trying to understand it to realize it was a joke.

However, suppose the universe is not precise. Suppose that as an electron comes down a wire to the barrier it is not really at any exact point but rather "smeared out" across a range of points, with a mathematically defined probability of being at any real spot at any given time.
So the electron does not actually exist in one place but is just a probibility that it could exist there? I really am trying. Does this mean my TV somehow works with only this probability of electrons moving around if you look at it on the quantum level or does this mean it works on actual electrons or are electrons just probabilities?

Wolverine
2005-Oct-23, 05:55 AM
Thread moved into General Science -- while the underlying theme perhaps might be more philosophical, I think it's more at home in this section rather than ATM.

FWIW, long as I'm posting: given the dynamic nature of the universe and what we've observed to date, the concept of an "Absolute Truth" strikes me as being somewhat of a chimera. I'm quite comfortable dealing with variables and unknowns, and accept (somewhat reluctantly) that answers to some fundamental questions concerning the cosmos simply aren't within our grasp during our lifespan.

Gillianren
2005-Oct-23, 07:55 AM
(Anybody remember Lily Tomlin's characer "Edith Ann"?)

Yes. She's why that's not my name. (I'm legally Edith. My younger sister's middle name is Ann. Mom likes the name Ann, but--wisely, to me--chose not to saddle me with both names.)

And again, no, we cannot agree that the sun will rise at a certain point. We can agree that the sun will appear to rise at a certain point.

Ken G
2005-Oct-23, 11:50 AM
In my view, Absolute Truth is a scientific theory, like any other. It happens to be the best of all scientific theories, in that every experiment ever conducted under controlled and repeatable conditions has failed to falsify this theory. It is also very simple (Occam's razor), and extremely useful at organizing facts. Voila, a great scientific theory, and one so basic that even non-scientists have come to rely on it daily. But like any scientific theory, we may one day discover a situation or regime in which this concept breaks down. Relativity and quantum mechanics were both blows to the concept, but neither destroyed it because relativity allows you to transform from one person's reality to another (so the broken concept is in effect glued back together by these known transformations), and quantum mechanics allows the microscopic probabilities to congeal into a macroscopic reality when the system is large enough. Still, it took a few hits there! Who's to say some new experiment won't completely shatter it? That's science. But in the regimes where it has already proven itself to be of value, we should continue to use it. That's about all you can say, within a carefully defined mode of thinking.

SolusLupus
2005-Oct-23, 01:31 PM
FWIW, long as I'm posting: given the dynamic nature of the universe and what we've observed to date, the concept of an "Absolute Truth" strikes me as being somewhat of a chimera. I'm quite comfortable dealing with variables and unknowns, and accept (somewhat reluctantly) that answers to some fundamental questions concerning the cosmos simply aren't within our grasp during our lifespan.

You still don't get it :P

The idea isn't "discovering" Absolute Truth, but the possibility of it existing. Unless you mean "We'll never know if there is Absolute Truth", which I would accept.


In my view, Absolute Truth is a scientific theory, like any other. It happens to be the best of all scientific theories, in that every experiment ever conducted under controlled and repeatable conditions has failed to falsify this theory.

Yeah, I'd agree with that. After all, what if the universe is far more chaotic, but we don't know it? I just think that Absolute Truth has a lot of evidence behind it, however - there's the possibility it doesn't really exist, but it seems to exist for almost all things, except for those tricky quantum-level thingies.

I don't know why my friend disagreed with my idea. I'll have to ask him to define the concept of Absolute Truth first, so I can see what he thinks he's disagreeing with. Thanks, all.

BTW: Sorry for posting up at ATM. I wasn't sure where it would fall, really.

Nereid
2005-Oct-23, 03:31 PM
We will all, I'm sure, agree that quantum theory is the most successful of all theories of physics, so far (let me know if you'd like a looooong list of reasons why).

It's also not terribly controversial that things are really, really weird in the quantum world - crunch the math and you get exquisitely accurate descriptions/predictions of what you can observe.

Now what does it all mean? This Wiki page may be a good place to start - interpretations of quantum mechanics (http://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics).

And it didn't get much out of the realm of 'deep thinking' until the experimental tests of Bell theorem (http://en.wikipedia.org/wiki/Bell%27s_theorem) became so strict - you certainly have to 'give up' something in our 'absolute' world - is it (part of) logic? (part of) realism? or perhaps the most creative of scifi writers just haven't had sufficient creative imaginations??

Bathcat
2005-Oct-23, 10:10 PM
ASEI: "Could this [electron tunneling] possibly still be explained in terms of unknown, but determined properties when we take into account the inexactness of our knowledge of the barrier as well?"

Last I read there was a very slim chance that some version of the "hidden variables" theory might be possible. Most easy versions of the "unknown, but determined" properties being responsible for quantum indeterminacy have been ruled out by experiments and mathematical analysis.

I don't really understand the debate, all I can do on that is parrot what I've read. Google on "Bell's Inequality" and "Quantum Theory Hidden Variables" -- there are technical papers online as well as non-technical discussions.

NanC: "So the electron does not actually exist in one place but is just a probibility that it could exist there? ... Does this mean my TV somehow works with only this probability of electrons moving around if you look at it on the quantum level or does this mean it works on actual electrons or are electrons just probabilities?"

(Dont' apologize about the Shroedinger's cat thing, a lot of people take it very seriously indeed. I just can't believe Shroedinger would, or did! My opinion.)

But yeah -- inside the picture tube of your TV the electrons flying from the gun toward the screen have no absolutely defined momentum and position. They are "smeared out."

BUT -- (the cool part) -- when they hit a phospor dot on the back of the glass screen, suddenly they have caused a macroscopic event that reveals exactly where they are! They have a position, and it is well-defined!

Information on their movement, though, is gone. We can know their position OR their momentum, but not both.

Back to your TV: Quantum theory is by and large a theory of probabilities and averages. As you know, if you roll a pair of dice only 10 times it's not hard to get some pretty odd streaks of numbers. But if you roll them 100,000,000 times you will almost certainly come up with a very close approximation of the mathematical probabilities for each number combination.

The electrons in your TV "roll the quantum dice" so many times (because there are so many electrons) that the overhwelming odds are that the TV will behave exactly as the sum of average electron behavior says it will.

----

I once read that undergraduates are sometimes asked to calculate the odds that the Moon will quantum-tunnel to a new position in the sky. After all, an electron can do it, why not the Moon?

It turns out that for an object the size of the Moon to "roll the quantum dice" and come up with a "lucky streak" that would quantum-tunnel it a foot in any direction would, on average, take thousands of times the present lifespan of the Universe.

As the author whose name I can't recall said, the point of the exercise is to bring home to the student that quantum tunneling of macroscopic things is, practically speaking, impossible.

The Moon and your TV obey Newton's and Faraday's laws not because every single electron in them obeys classical physics, but because on average they do. And the probability is overwhelming that this huge number of particles will behave exactly as the probabilities say they will.

And the probabilities end up being identical to classical physics in nearly all large-scale cases like televisions and moons.

----

At least that's my layman's understanding of the situation. Perhaps someone else can put it more clearly.

----

Addition, a minute later: I keep writing things like "nearly all large-scale cases" because there are odd exceptions. A lump of macroscopic Bose-Einstein condensate behaves in some ways as a quantum object, for instance.

ASEI
2005-Oct-23, 10:52 PM
Still, it's hard to believe that absolute reality would vanish as a principle. Everything we see macroscopically, all the way down to quantumn physics, seems to be based on conservation laws and regular descriptions of something there. That it would all go fuzzy for a reason not due to our instruments or knowledge, on a small scale, is hard to wrap my mind around. Why isn't the integration of fuzzy microscopic components into macroscopic components not more fuzzy? How can a well-defined macroscopic realm be composed of ill defined quantum components?

If we can no longer describe position, or momentum as being absolutely there, in terms of particle properties, could we possibly still hold to some absolute properties? After all, the electron is there right? If it cannot have properties such as position or momentum theoretically defined, could you at least hold the various probability fields as absolute properties of the particle?

my current world-model goes something like this:
class entity
{
properties...;
behaviors...;
};
Where's the error in this model?

in my classically specific model:
class entity
{
//properties
vector position, velocity, acceleration, ect...;
double mass, various energies, charge, ...;
};
could this be swapped for:
class entity
{
//properties
giant vecor/scalar fields of position and momentum probability;
double mass, charge, ect...;
};??

north
2005-Oct-24, 02:12 AM
Still, it's hard to believe that absolute reality would vanish as a principle. Everything we see macroscopically, all the way down to quantumn physics, seems to be based on conservation laws and regular descriptions of something there. That it would all go fuzzy for a reason not due to our instruments or knowledge, on a small scale, is hard to wrap my mind around. Why isn't the integration of fuzzy microscopic components into macroscopic components not more fuzzy? How can a well-defined macroscopic realm be composed of ill defined quantum components?

If we can no longer describe position, or momentum as being absolutely there, in terms of particle properties, could we possibly still hold to some absolute properties? After all, the electron is there right? If it cannot have properties such as position or momentum theoretically defined, could you at least hold the various probability fields as absolute properties of the particle?

my current world-model goes something like this:
class entity
{
properties...;
behaviors...;
};
Where's the error in this model?

in my classically specific model:
class entity
{
//properties
vector position, velocity, acceleration, ect...;
double mass, various energies, charge, ...;
};
could this be swapped for:
class entity
{
//properties
giant vecor/scalar fields of position and momentum probability;
double mass, charge, ect...;
};??

or if i'm on the right track here, macro(world) orders the randomness of the micro(quantum).

Disinfo Agent
2005-Oct-24, 07:39 PM
Lonewulf: "The thing is, I'm not claiming that anyone KNOWS the 'Absolute Truth'. I'm just claiming that it's THERE, that it exists. Some people seem to disagree with that concept, and I'm curious as to why."

What I'm suggesting is that at the quantum level there is no absolute truth. There are only probabilities that something is or is not true.

It's not common sense, but it appears to be true anyway. You cannot, even in theory, assert that an electron is exactly there and also moving exactly that way because the universe does not allow both things to be absolutely true.

It's not that we can't figure out both things about an electron, it is that the universe is consituted in such a way that certain absolute truths are impossible if you look closely enough.I'm a layman in these matters, too, and apparently more than you, but I'm a bit skeptical about the contention that the Schroedinger's Cat thought experiment rules out absolute truth. Where QM does put a nail is in the coffin of determinism: the idea that every effect is well-determined by a certain set of causes, the same set of causes invariably producing the same unique effect.

The statement that the cat is "half living and half dead" before someone opens up the box seems silly (I may be terribly wrong, though). For every particular "cat" in every particular "box", it is either alive or dead. It's just that, when you repeat the experiment a large number of times, with many cats and boxes, you find that half of the time the cat is dead, and half of the time it's dead, and -- here's what's truly mindboggling -- for a particular box and a particular cat, there's no way to predict whether he will survive or be killed before the experiment is performed!

So, at the quantum level, it seems, the same set of causes can lead to different effects! In your example of the diode, I'd say that there are (roughly) 60% atoms in one side of the barrier, 20% inside the barrier, and 10% on the other side of the barrier at all times1. The question is that there is no way to determine which electrons will end up in each place without somehow capturing them. Their distribution when 'free' seems to be completely random. :eek:

1Although... technically, we can't prove this. It's another case of 'Tree-falling-in-a-forest-with-no-one-around-to-see-it'.


Still, it's hard to believe that absolute reality would vanish as a principle. Everything we see macroscopically, all the way down to quantumn physics, seems to be based on conservation laws and regular descriptions of something there. That it would all go fuzzy for a reason not due to our instruments or knowledge, on a small scale, is hard to wrap my mind around. Why isn't the integration of fuzzy microscopic components into macroscopic components not more fuzzy? How can a well-defined macroscopic realm be composed of ill defined quantum components?It's for the reason that Bathcat wrote above:


Back to your TV: Quantum theory is by and large a theory of probabilities and averages. As you know, if you roll a pair of dice only 10 times it's not hard to get some pretty odd streaks of numbers. But if you roll them 100,000,000 times you will almost certainly come up with a very close approximation of the mathematical probabilities for each number combination.

The electrons in your TV "roll the quantum dice" so many times (because there are so many electrons) that the overhwelming odds are that the TV will behave exactly as the sum of average electron behavior says it will.As you make more and more random experiments, the results tend to 'smoothen out', reflecting the general pattern more often than not.

Argos
2005-Oct-25, 05:39 PM
I donīt think the adjective "absolute" is needed to modify the noun "truth".

I would say that in order to recognize the truth one has to have information. We are limited at that (the uncertainty principle, again). We can only approach the truth in an asymptotic fashion, at best.

WaxRubiks
2005-Oct-25, 06:53 PM
of course there is the world of mathematics, you could argue that the truth in maths are indestructable.

SolusLupus
2005-Oct-25, 07:00 PM
Frog March, I will forever love you for having me equate
"Absolute Truth"

With the idea of

"I AM INDESTRUCTIBLE! Mwahahah!"

Sorry, I have a weird mindset. It would've been funnier if you used the word "invincible", or even "inveencible", though.

Argos
2005-Oct-25, 07:18 PM
Karl Popper has an interesting take on the validity of the uncertainty principle, which I think ultimately pertains to this discussion.
Popper´s experiment (PDF) (http://arxiv.org/PS_cache/quant-ph/pdf/0405/0405057.pdf) (a must).

NanC
2005-Oct-25, 10:40 PM
Bathcat, thank you. Your explaining had me thinking "Okay, I undestand. Almost. It works like so. No. But I have the idea. The idea is something. I understand now. Almost" I laughed at myself because your explaining got me closer to getting my mind around this than before but my mind is still not that agile. Thank you for your efforts.

I ask this to see if I understand one part of it. Does quantum theory say the electrons are actually spread out fuzzy so we can not tell where they are and where they are going or does it say we can not tell both things so they are fuzzy? I did not ask that right. If we had a pretend machine that could look at electrons without opening the box would it see where they are and where they are going or would it see them fuzzy? I am still not asking right. I am not perfect with English. Do you understand my question? It is are electrons actually fuzzy or is it just that trying to detect them makes them fuzzy?

SolusLupus
2005-Oct-25, 10:51 PM
I find it funny that this went into Quantum Physics as greatly as it did.

Bathcat
2005-Oct-26, 01:32 AM
I'm going to get in over my pointy little head directly if I'm not careful.

----

NanC, your question is difficult.

We can't detect the position of an electron without losing information about its motion. And we can't detect the motion of an electron without losing information about its position.

Most physcists seem to agree that this is a real aspect of the universe.

If we had a magic machine to look inside a TV tube, if the magic machine obeyed the physics of our universe, then it would be able to either see an electron's location or it would be able to see the electron's motion (kinetic energy).

A magic machine which could detect both properties of the same electron at the same time could not be built in our universe. We can imagine such a machine, but the universe does not allow it to exist.

We can imagine seeing both things about the same electron in the way we can see both a billiard ball's position and its movement. But this is imagination and not physics.

Physicists seem to agree that what we imagine is not a reasonable indicator for the way the universe really is. The experimental reality is a better indicator...and therefore they say that the electron really is smeaned out the way the experiments suggest.

----

On another topic: I'm reluctant to say quantum indeterminacy makes all absolute truth impossible. I think that certain absolute truths are dependent on a degree of coarse-graining...they depend on summing over or averaging out quantum indeterminacy (and, in practice, chaotic behavior).

I would not quarrel with an absolute assertion that the Moon exists. Or that Lonewulf has a table. Or that I am going bald.

And maths are something else again. In our universe math facts may be absolutely true.

SolusLupus
2005-Oct-26, 03:35 AM
*Rubs Bathcat's bald head* Great Buddha, allow me this wish...

Oh, wait, that's the stomach.

and you need to be overweight. Erm, sorry. ^_^;

Nereid
2005-Oct-26, 07:39 AM
also deals with the various interpretations of the experimental results:

EPR paradox (http://en.wikipedia.org/wiki/EPR_paradox) (Einstein, Podolsky and Rosen - if there are no hidden variables, the universe is spooky).

Bell's theorem (http://en.wikipedia.org/wiki/Bell%27s_theorem) (here's a way to test the EPR paradox; yep, the universe IS spooky!)

Interpretations of quantum mechanics (http://en.wikipedia.org/wiki/Interpretation_of_quantum_mechanics) (some people go to extraordinary lengths to try to banish spookiness)

Argos
2005-Oct-26, 12:46 PM
If we had a pretend machine that could look at electrons without opening the box would it see where they are and where they are going or would it see them fuzzy? I am still not asking right. I am not perfect with English. Do you understand my question? It is are electrons actually fuzzy or is it just that trying to detect them makes them fuzzy?

The quantum state of a particle is not only unknown but is actually unknowable. There is no "god´s eye" when it comes to quantum mechanics. The object and the observer are inextricably intertwined. That´s fundamental to QM.

Ilya
2005-Oct-26, 05:39 PM
People can debate about this table across the world. Even though they can't see it, it's still there. Even if 6 billion people don't see it, it still exists. Even if 6 billion people don't acknowledge its existance, it still exists. Nothing changes this fact.

<skip>

Yet, this idea seemed to emit some resistance from my friend. I couldn't tell why. He can be VERY vague when he disagrees with something, and rarely goes into detail why.

So this is my question - why would anyone contest the idea of Absolute Truth? WHen I say it, am I unknowingly spouting off a different philosophical standpoint? Am I just confused as to the "true meaning" of it? Or what?

I don't think anyone here actually answered Lonewolf's question: Why do some people deny the concept of Objective Truth? (I prefer the term "objective," i.e. independent of observer, to "absolute," which itself is a somewhat vague term.)

And yes, there ARE people who deny there is sush thing as Objective Truth. They are called Postmodernists. Here is a critique of postmodernist thought (http://www.leaderu.com/critical/istruth.html).


According to postmodernists, words do not have a definite objective meaning. Rather, meaning is only a matter of interpretation. People interpret words in different ways; therefore, words are incapable of communicating any kind of objective truth, as such. In practice, this "deconstruction" of language means that such texts as the Constitution and the Bible do not have fixed meanings, but are open to unlimited interpretation.


Here is a more neutral (and long) description of postmodernism (http://www.as.ua.edu/ant/Faculty/murphy/436/pomo.htm)

And here is an article which touches upon why people would follow such a wooly philosophy (http://www.ctlibrary.com/le/1997/winter/7l1052.html)

SolusLupus
2005-Oct-26, 05:47 PM
I love you, Ilya. I'll read over those when I have enough time (about to go to dentist soon. Yay.)

And it's Lonewulf, not Lonewolf :)

Disinfo Agent
2005-Oct-26, 05:52 PM
I don't think anyone here actually answered Lonewolf's question: Why do some people deny the concept of Objective Truth?Hold on a minute... The concept of objective truth, or the existence of objective truth?
I thought Lonewolf's question was about whether one could question the existence of an absolute truth. If so, then I believe the answer is 'yes'. As for the concept of absolute truth, denying a concept seems kind of silly. If you can think about it, it's there to think about.

SolusLupus
2005-Oct-26, 05:57 PM
I believe I did, indirectly, in the previous page: because they can.
Ur? I recall you saying something about how you can never be sure if a tree makes a sound if it falls in a forest even if no one hears it. Though that argument is VERY silly, to me, personally. Maybe I'm just arrogant, but I say that I'm very sure that it makes a sound.

Here's a better question:

If a tree is launched into space and hits a space station, does it not make a sound? If you aren't there, how can you be sure?

Disinfo Agent
2005-Oct-26, 05:58 PM
Nevermind that, Lonewulf. I've edited my post. I think there's something else that we need to clarify.

SolusLupus
2005-Oct-26, 06:04 PM
Well, I was more of talking about the concept of AT. Someone seemed weirded out that I could believe in such a thing. He was more like, "Well, if that's what you want to believe, hey, why not?". He never explained to me what HE thought, and I haven't talked to him in a long while (This is another one of those "Shower Incidents" - I remember the conversation in a shower and I need to know an answer :P )

However, I AM curious about questioning the existence of AT. I find it rather interesting that people can't think that you cannot be sure that there is a truth behind everything.

I mean, it doesn't matter how you perceive it, if you hear it, or not. For instance: About the tree falling in the woods.

It doesn't matter if you hear the sound or not. If it didn't make a sound, then it didn't make the sound. That's the truth. If it did make a sound, then it made a sound. That's the truth. The truth is there, whether you perceive it or not, understand it or not, or can determine it or measure it or not.

Science, as a whole, is about understanding the fundamental truths about all that surrounds us - whether we like it or not. Even if what we discover flies in the face of all we believe, then it's still a fundamental truth (unless our perception of it is faulty, but we can argue about that until the cows come home)

Disinfo Agent
2005-Oct-26, 06:19 PM
However, I AM curious about questioning the existence of AT. I find it rather interesting that people can't think that you cannot be sure that there is a truth behind everything.But I do think so... ;)


I mean, it doesn't matter how you perceive it, if you hear it, or not. For instance: About the tree falling in the woods.

It doesn't matter if you hear the sound or not. If it didn't make a sound, then it didn't make the sound. That's the truth. If it did make a sound, then it made a sound. That's the truth. The truth is there, whether you perceive it or not, understand it or not, or can determine it or measure it or not.How do you know that?


Science, as a whole, is about understanding the fundamental truths about all that surrounds us - whether we like it or not. Even if what we discover flies in the face of all we believe, then it's still a fundamental truth (unless our perception of it is faulty, but we can argue about that until the cows come home)Exactly my point: we can argue about the existence, and the nature, of absolute truth until the cows come home, because everything we "know" is questionable.

I don't know if this is what the person who spoke to you meant, but it is how I see it.

Grey
2005-Oct-26, 06:39 PM
Last I read there was a very slim chance that some version of the "hidden variables" theory might be possible. Most easy versions of the "unknown, but determined" properties being responsible for quantum indeterminacy have been ruled out by experiments and mathematical analysis.A hidden variables model could underlie quantum mechanics as long as you're willing to throw out locality (locality says that information has to be physically transmitted by something to get from one place to another, which limits the speed of information to the speed of light, since that's as fast as anything can go; Einstein referred disparagingly to hypothetical nonlocal interactions as "spooky action at a distance"). For a while, physicists dismissed the possibility of hidden variables because they were convinced that locality held. However, Bell's Theorem shows that quantum mechanics isn't consistent with locality no matter what, and there are even experimental results that support this, so any replacement theory for quantum mechanics would also have to allow nonlocal interactions to be consistent with observation. So it turns out that particles definitely can pass information to each other faster than light, though it also appears that they do so in a manner which doesn't ever allow us to use this to communicate faster than light. A grand joke the universe has played on us, perhaps. So, as long as you have to throw out locality anyway, the idea of hidden variables underlying quantum mechanics isn't out of the question, though this isn't the most popular view.


(Dont' apologize about the Shroedinger's cat thing, a lot of people take it very seriously indeed. I just can't believe Shroedinger would, or did! My opinion.)Not quite a joke. More an attempt to show that there must be some deeper description of reality than quantum mechanics, to describe how things went from a mixture of states at the quantum level to one or the other at the macroscopic level. Many of the brilliant physicists who developed quantum mechanics nevertheless felt that there would be some more complete theory that would avoid all the weirdness of quantum theory and the strange probabilistic nature of reality that it seemed to imply. Of course, decades of research since then has led us to believe that, if anything, the universe is even weirder than they supposed. ;)

WaxRubiks
2005-Oct-26, 06:45 PM
truth is a matter of perception.

you don't really know how anyone else perceives things.

WaxRubiks
2005-Oct-26, 06:52 PM
Doesn't locality only really makes sense when you are talking about the transmission of information?
So if entanglement can't transmit information then there is no spooky action at a distance, I would have thought.
To say that there is an objective truth that has been transmitted seems a bit ridiculous and vague.

Ken G
2005-Oct-26, 07:25 PM
This has become a very interesting thread! Here's my take:



So it turns out that particles definitely can pass information to each other faster than light, though it also appears that they do so in a manner which doesn't ever allow us to use this to communicate faster than light.

I'm not sure there is a way to define information passed by particles to each other, only information that we can interpret, which would represent communication, so I agree with Frog March there. But I also agree with Grey that entanglement does represent some sort of spooky nonlocality. [Edit: see Grey's next posting for clarification.]



Dont' apologize about the Shroedinger's cat thing, a lot of people take it very seriously indeed.

In my view, the cat business is not so mysterious. The point is, there is no way to only couple the life of the cat to the quantum mechanical event in question, the decay of the particle. You have to have some way to kill the cat! This will involve a bulky macroscopic apparatus, and the apparatus will come complete with lots of "white noise". White noise destroys the fragile quantum mechanical correlations needed to be able to say that the cat is in a superposition state of being dead and alive. What you end up with instead is called a "mixed state" (rather than a "superposition"), which is no different from the state a pair of dice are in between the time when you roll them and when you look at the result. Nothing quantum mechanical about the cat at all. Indeed, there's enough noise within the cat's own body to destroy any quantum mechanical correlations that apply to the whole cat, like being alive or dead. A cat is simply not a quantum system.



Truth is a matter of perception.

If that statement were true for you, logically, then it would have to be the way you perceive truth to be. So, do you perceive truth as a matter of perception? I mean, when you get out of bed in the morning, do you make good and sure to open your eyes and look at the floor so you can perceive it before stepping on it, or do you just stumble out bleary-eyed, firm in the belief that the floor is actually there without looking?

Grey
2005-Oct-26, 07:27 PM
Doesn't locality only really makes sense when you are talking about the transmission of information?
So if entanglement can't transmit information then there is no spooky action at a distance, I would have thought.It depends on what you mean by "information". Entangled particles do communicate nonlocally with each other, and that communication influences the results of experiments performed on them. However, since the results of those experiments are themselves probabilistic, it's not possible to see that there must have been nonlocal communication unless you compare the results on both sides to look for correlations. Separately, any experiments on just one of the two entangled particles look perfectly normal, which is what prevents us from sending a message using this connection.

publiusr
2005-Oct-26, 07:42 PM
Instead of Aboslute truth, how about we just list levels of proof.

Preponderance of evidence -------------50%+1
Clear and Convincing--------------------70%
Beyond reasonable doubt----------------90%?
Scientific proof
Mathematical proof (highest)

Ken G
2005-Oct-26, 07:49 PM
Beyond reasonable doubt----------------90%?

I'd argue that "beyond reasonable doubt" should be much better than 90%, or else 10% of the people you have in your prisons are actually innocent!

WaxRubiks
2005-Oct-26, 10:21 PM
I wouldn't have thought that entangled particles "communicate".
As an example I thought it was like- a woman has three pairs of shoes, red,green and blue. She wears the red ones but packs her suitcase early in the morning with one of the other pairs, in the dark(so she doesn't wake her husband). She then gets on the plane in London and flys to NewYork perhaps you could say that the pair of shoes in the woman's suitcase and the pair she left back in London are entangled but neither she or her husband know what shoes are where. The husband comes home later that day and discovers the green shoes in the cupboard- the uncertainty has collapsed and he knows that when his wife opens her suitcase in NewYork she will find the blue shoes.

If there are many universes all branching off from each other, while there is some uncertainty,there is also some uncertainty as to which universe they are in. Collapsing uncertainty just resolves which universe they were in all along.

at least that's my theory.

Nereid
2005-Oct-26, 10:35 PM
I wouldn't have thought that entangled particles "communicate".
As an example I thought it was like- a woman has three pairs of shoes, red,green and blue. She wears the red ones but packs her suitcase early in the morning with one of the other pairs, in the dark(so she doesn't wake her husband). She then gets on the plane in London and flys to NewYork perhaps you could say that the pair of shoes in the woman's suitcase and the pair she left back in London are entangled but neither she or her husband know what shoes are where. The husband comes home later that day and discovers the green shoes in the cupboard- the uncertainty has collapsed and he knows that when his wife opens her suitcase in NewYork she will find the blue shoes.

If there are many universes all branching off from each other, while there is some uncertainty,there is also some uncertainty as to which universe they are in. Collapsing uncertainty just resolves which universe they were in all along.

at least that's my theory.Hey everyone - all of these, and more, are explored (with considerably more rigour) in the links I provided! :)

As has already been said - several times - in this thread, hundreds (thousands?) of brilliant minds (physicists, philosophers) have wrestled with the 'interpretive' challenges the unambiguous experimental results have caused us Homo Sap. minds to ponder.

Spooky? Yep, in spades.

Discomforting? Yep, flies in the face of a great deal of the 'intuitive' notions we poor Homo Sap's bring to the table to deal with it.

Throws a giant monkey wrench into our neat conceptual categories ('reality', 'absolute', 'truth', 'communication', 'logic', ...)? Yep, sure does.

Sets philosophers back on their heels (aka makes them realise they really don't have a clue)? Roll up ladies and gentlemen! Take a number!! The Great Wheel of Quantum 'mess with your minds' is about to be spun!!

Of course, mathematicians have been there, done that; 'truth' and 'proof' have been 'done and dusted' a good century now (though Georg Cantor, a founding father of the 'way' suffered a nervous breakdown, and lived the last 33 years of his life in a mental institution - you have been warned).

WaxRubiks
2005-Oct-26, 10:48 PM
If that statement were true for you, logically, then it would have to be the way you perceive truth to be. So, do you perceive truth as a matter of perception? I mean, when you get out of bed in the morning, do you make good and sure to open your eyes and look at the floor so you can perceive it before stepping on it, or do you just stumble out bleary-eyed, firm in the belief that the floor is actually there without looking?

your body and its senses are part of the perception process not just the eyes. If I woke up and was just a brain in a jar then that would be a matter of someone elses perception, I wouldn't know where I was. layers of perception.

SolusLupus
2005-Oct-26, 11:55 PM
How do you know that?

I'm really feeling like throttling you while insulting you. Okay, I'm going to try this one more time

It doesn't matter if I know. It doesn't matter if you know. It doesn't matter if the all the people in the world know or not.

Whether or not the tree makes a sound, it either does or doesn't make that sound. That's the truth.

It doesn't matter if you perceive it or not.

It happens.

See?

Everyone seems to assume that it doesn't happen if people don't perceive it. Do the animals perceive it? Or do you mean if every instinct or animal doesn't perceive it?

Bathcat
2005-Oct-27, 01:06 AM
Perhaps what Lonewulf is speaking of is the existence of an external reality, not any standard of perceived truth.

Perhaps, like Parmenides, he's asking whether our imperfect senses reflect an external, absolute reality.

If that's the case, Lonewulf, you've got friends in high places...Parmenides thought that we can't prove that any such thing as an absolute external reality exists. Zeno's paradoxes seem to have been created by Zeno in order to show that "reality" is illogical, and therefore his teacher Parmenides was correct. Socrates' "I know only one thing, and that is that I know nothing" was probably a song on the same fiddle -- admitting that all he really knew was that "reality" was unknowable.

On the other hand, everybody behaves like reality really is real. Science assumes that there is something out there to measure. That assumption is that when a tree falls in the forest, something has happened and we can infer from logic and physics that a noise was produced.

Parmenides might smile knowingly, but there's a lot to be said for the assumption that reality is real.

SolusLupus
2005-Oct-27, 01:39 AM
Yeap, I'll agree with that. To be honest, you've all got me confused on what I really mean. I'll post tomorrow when I'm more lucid :D

WaxRubiks
2005-Oct-27, 07:27 AM
trees make sounds in the same way as fast food is fattening, food is just food until it is eaten.

Disinfo Agent
2005-Oct-27, 12:02 PM
To be honest, you've all got me confused on what I really mean.I'm starting to think the same. Make up your mind about what you want to discuss, and then maybe then it will be worth discussing.

SolusLupus
2005-Oct-27, 01:57 PM
To be honest, there's not much for me to discuss now. Ilya pretty much answered my question, so I don't have much to say overall. I now know there are people that don't believe in objective truth, I know what they call themselves, and I know the links that further explain them.

Though I don't regret being vague, I learned a few minor tidbits and provoked some discussion. I don't regret that.

Disinfo Agent
2005-Oct-27, 02:21 PM
Next time you decide to be vague, try not to complain about being misunderstood (http://www.bautforum.com/showpost.php?p=587773&postcount=60).

Grey
2005-Oct-27, 03:21 PM
I wouldn't have thought that entangled particles "communicate".
As an example I thought it was like- a woman has three pairs of shoes, red,green and blue. She wears the red ones but packs her suitcase early in the morning with one of the other pairs, in the dark(so she doesn't wake her husband). She then gets on the plane in London and flys to NewYork perhaps you could say that the pair of shoes in the woman's suitcase and the pair she left back in London are entangled but neither she or her husband know what shoes are where. The husband comes home later that day and discovers the green shoes in the cupboard- the uncertainty has collapsed and he knows that when his wife opens her suitcase in NewYork she will find the blue shoes.

If there are many universes all branching off from each other, while there is some uncertainty,there is also some uncertainty as to which universe they are in. Collapsing uncertainty just resolves which universe they were in all along.

at least that's my theory.
It's not actually that simple, and depends on the limits of quantum information. Quantum entanglement and measurement is much more complex than your example with the shoes, where the question is just one of lack of classical knowledge. This is going to be fairly lengthy, and in some sense is a digression. But in another sense, it gets at the very heart of what quantum mechanics has to say about the nature of reality that underlies what we see. Let me lay some important groundwork.

Suppose I have a photon, and I'm measuring it's spin. Now, it turns out that if I measure the spin in any given direction, call it x, I'll find the photon to be either aligned with that direction (call it x+), or aligned in the opposite direction (call it x-). Now, it turns out that the spins measured for any orthogonal directions are incompatible observables, just like position and momentum for single particle. If I measure the spin in the x direction, I have no idea what the spin in the y or z direction are. We can actually test this. If I take a stream of photons, and set up a filter that strictly removes any photons that are x-, I'll have a stream of photons that are all x+. If I pass them through the same kind of filter, all of them will pass through, since only the x+ ones are left. If I pass them through the same kind of filter rotated 90 degrees, to instead allow only spin y+ photons through I'll find that half of them will make it, and the other half will be blocked. The thing is, that you might think that the photons left after this second filter are all x+, y+ photons, but it turns out that measuring the spin in the y direction completely destroys any information I had about the x direction. If I measure the x spin again, I'll find that half of the photons are x+ and half are x-. Presumably, the act of measuring the spin in one direction, no matter how carefully done, destroys the information about the spin in the other direction. What if I redefine my axes, and tilt them 45 degrees (let's call this direction x') instead of 90? Quantum mechanics predicts, and experiment bears out, that there will be some amount of correlation (I won't get just half and half like I did when I rotated the filter 90 degrees), but it won't be complete. In fact, I can work out exactly what the probability that a photon I know is x+ will be aligned with any other direction, given the angle between the two directions.

Now, Einstein, Podolsky, and Rosen used this, along with the notion of entanglement, to try to show that quantum mechanics was not wrong, but incomplete. It's possible for two photons to be emitted by a source in such a way that they are spin correlated. That is, if one is down in the x direction, the other must be up in the x direction, and vice versa. Now, you take such a pair of photons, and wait until they're a long way away from each other, so there's no chance that they can interact. You measure the spin in the x direction for one of them, and find that it's (say) x+. You measure the spin in the y direction for the other one, and find that it's y+. But you know that the second photon has to also be x-, since it has to be opposite the spin of the first one in the x direction, and "obviously" that first measurement can't have affected the spin of the second one in any way (you could have waited until the photons were light years apart before making the measurements). So now you know the spin in two different directions for these photons (one is x+, y- and the other is x-, y+), more information than quantum mechanics says you can have. EPR claimed this showed that quantum mechanics was incomplete. Each photon must "really know" which way its spin is aligned in each direction. And actually, my choices of x, y, and z were arbitrary; I could have chosen different axes, so technically each photon knows which way it will respond to a measurement of spin in any direction at all. These photons would then be like the shoes: they have specific attributes, we just don't know what they are.

So let's follow this assumption, that photons are ordinary objects with real (though possibly unknown) attributes, and see where it leads us. Bell's equality says that, for any collection of objects with any three attributes, A, B, and C, N(A, not B) + N(B, not C) >= N(A, not C), where N(A, not B) is the number of objects that have trait A but not trait B, N(B, not C) is the number of objects that have trait B but not trait C, and so forth. The attributes can be linked or not, but the inequality holds so long as these are real attributes. Let's see why. First, we know that

N(A, not B, C) + N(not A, B, not C) >= 0

This is just the statement that either there are no objects that would satisfy one of these conditions or there are some that do. I can move from there to here, just by adding the same thing to both sides of the equation.

N(A, not B, C) + N(not A, B, not C) + N(A, not B, not C) + N(A, B, not C) >= N(A, not B, not C) + N(A, B, not C)

Now, if these are real attributes, then an object either has some trait, or doesn't have some trait. So N(A, not B, C) + N(A, not B, not C) is just the same as N(A, not B). That is, if you count the objects that have trait A but not trait B, that will be the same as adding up the objects that have trait A, do not have trait B, and have trait C along with those that have trait A, do not have trait B, and do not have trait C. All objects either have trait C or not. Similarly, N(not A, B, not C) + N(A, B, not C) can be replaced by N(B, not C) and N(A, not B, not C) + N(A, B, not C) is just the same as N(A, not C). This gives us Bell's inequality:

N(A, not B) + N(B, not C) >= N(A, not C)

I'd suggest you go back over that and convince yourself that I haven't made any mistakes here. If you're still not convinced, you might come up with a concrete example (say, a classroom of people, with your traits as being female, having blue eyes, and having dark hair), and check yourself that, however many members of the set there are and which ones have or do not have various traits, this inequality holds.

Done with that? Good. :)

So, now we go try to measure this on some photons. We're going to test whether N(x+, x'-) + N(x'+, y-) >= N(x+, y-). We run into a problem, though. We can't measure the spin in two directions for a single photon, because we know that the measurement in the first direction will mess up the measurement in the second direction. But we can use the trick EPR suggested for using entangled photons to find this out. We measure the spin in the x direction on one of them, and in the x' direction (this was tipped at some angle less than 90 degrees, remember) on the other one, and then we must know both spins for each particle. If we perform the experiment, though, we find out that the inequality is broken. The right side is actually greater than the left. This is also exactly what quantum mechanics predicts, but the fact that experimental results also seem to bear out the result means that even if someday quantum theory is superseded by some deeper theory (as EPR imagined it might), that theory will have the same problem.

How can this be? Well, we really only made a few assumptions in our work above. One is that we used basic rules of logic. It's hard to imagine that those are flawed. Another is that we assumed that these photons actually had definite real attributes, we just didn't know what they were. Another is the assumption that our measurements on the photons (separated possibly by light years) did not affect each other. It turns out that, regardless of whether we assume the attributes were real before we measured them, we can't get around the influence question. That is, to explain the results we see, one photon has to "tell" the other one, instantaneously regardless of distance, what it's results were, and the results of the measurements on the second one will be affected by this.

Let's revisit the woman and her shoes, with a slight change. Let's say she owns hundreds of shoes, all red, green, or blue, in equal proportion. She always packs one at random. If she does this many times, there will be a 1 in 3 chance for each color. Her husband always picks one of the boxes that she left behind at random and looks at the color. There's always a 1 in 3 chance for him to find each color. But, if they both open their boxes with them oriented the same way (either both vertically or both horizontally), there's a 1 in 2 chance that they picked the same color, whatever it was, while if they open their boxes holding them oriented differently, there's only a 1 in 6 chance that the colors match. The only way for that kind of correlation is if the act of opening the box is instantly communicated to the other pair of shoes somehow, and it has the possibility of changing its color in response. But also note that, since each measurement alone just gives a straight 1 in 3 chance for each color, just as we'd expect, there's no way to see this correlation, or to know which way the other person was holding the box (or even if they've opened it yet), until the woman comes back and they compare the results.

Bathcat
2005-Oct-27, 04:41 PM
Best layman-level explanation of Bell's inequality I have ever read, Grey.

It would appear that quantum properties like photon spin are not "real" properties in the classical sense that the color of a billiard ball is. They can change simply because a linked property is measured. When we measure whether a quantum billiard ball has a stripe or not, we suddenly no longer know what color it is until we re-measure that...and then we don't know anymore if it has a stripe or not!

Hehe!

So to get back to NanC's questions, at a quantum level there are inevitable unknowns -- aspects of reality that are unavoidably "smeared out" into uncertainty.

We can measure a real, classical billiard ball and know for sure that it is purple and has a black stripe. But we cannot know both things about a quantum one.

If we know one property, the other really does become uncertain. And we are absolutely sure of that because if we measure the color of a bunch of quantum balls and select all purple ones, then measure whether or not they have stripes, and then measure the color again...we find that the color of our selected group is no longer all purple.

----

We can imagine knowing both the x spin and the y spin simultaneously, and we can imagine a magical machine which knows both, but such a machine is "non-physical" -- it is impossible in our universe.

Our excellent ape imaginations, operating on the classical-physics logic which applies to virtually everything we have observed in our long evolutionary history before the twentieth century, persists in visualizing absolute, discrete properties for electrons and quarks.

Intuitively.

The Universe, however, is laughing up its sleeve. It isn't constrained to behave the way we Earth-apes intuitively believe it does.

----

So the fun part is understanding that in this case our wonderful, useful, and very often accurate commonsense intuition about the universe really really is wrong!

How wonderful that is! What great views open up before us if we accept that our intuition is not always right, and we can stretch our imaginations and our calculations beyond it, into new landscapes and new discoveries!

One can only say, with Galileo, YAY!

SolusLupus
2005-Oct-27, 04:45 PM
Next time you decide to be vague, try not to complain about being misunderstood.

Sorry. v.v

publiusr
2005-Oct-27, 06:58 PM
I'd argue that "beyond reasonable doubt" should be much better than 90%, or else 10% of the people you have in your prisons are actually innocent!

That just might be the case...

Ken G
2005-Oct-27, 08:50 PM
I hope not, that's an awful lot. I always imagined a good murder mystery would be one in which two people were gambling against a dealer, who was spinning a roulette wheel. One of the gamblers bet all his money that a given number would come up, with probability 1/38 (if you know roulette). The other bet all his money that it wouldn't. This much is agreed by both men. The dealer spun the wheel and as a result, one of the men became so angered he grabbed a knife and killed the dealer. Both say the other did it, and the result of the wheel was lost in the melee. Can you convict the guy who bet on the single 1/38 chance based on this evidence? Can't you say that there is more than a 97% chance he is guilty, and that's beyond a reasonable doubt? Meanwhile, he claims that what he thought was his luckiest day ever just ended up getting him in prison...

SolusLupus
2005-Oct-27, 09:03 PM
I hope not, that's an awful lot. I always imagined a good murder mystery would be one in which two people were gambling against a dealer, who was spinning a roulette wheel. One of the gamblers bet all his money that a given number would come up, with probability 1/38 (if you know roulette). The other bet all his money that it wouldn't. This much is agreed by both men. The dealer spun the wheel and as a result, one of the men became so angered he grabbed a knife and killed the dealer. Both say the other did it, and the result of the wheel was lost in the melee. Can you convict the guy who bet on the single 1/38 chance based on this evidence? Can't you say that there is more than a 97% chance he is guilty, and that's beyond a reasonable doubt? Meanwhile, he claims that what he thought was his luckiest day ever just ended up getting him in prison...

*applauds* VERY well put, good sir.

Ken G
2005-Oct-27, 09:15 PM
The Bell inequality stuff is quite interesting, but I would have thought that in the EPR setup, the act of measuring would have imparted the necessary spin, why would they assert that the total spin added up to zero? Or put differently, if you measure the spin of something in a superposition state and get a definite result, does that not impart angular momentum to the measuring device? In principle I mean, of course it would be tough to measure it.

Nereid
2005-Oct-27, 10:46 PM
The Bell inequality stuff is quite interesting, but I would have thought that in the EPR setup, the act of measuring would have imparted the necessary spin, why would they assert that the total spin added up to zero? Or put differently, if you measure the spin of something in a superposition state and get a definite result, does that not impart angular momentum to the measuring device? In principle I mean, of course it would be tough to measure it.I think the most certain way to address this question is to go through the original papers. Fortunately "Dr Chinese" has collected them all together on a single webpage (http://www.drchinese.com/David/EPR_Bell_Aspect.htm)!

If you're interested in digging deeper, I can give you a link to a discussion forum where experts who love this stuff will be both very patient in walking you through the maze and very knowledgable about the issues (HINT: they're the folk who you see referenced in the 'discussion' pages of the relevant wiki entries).

Ken G
2005-Oct-28, 01:35 AM
Thanks for the webpage, though I tried to load the Bell paper and my computer crashed! In any event, I think my question is simpler than the one addressed in that paper, though no doubt there would be insight there. But does anyone know the answer to this simpler QM question:
If you prepare a particle in a pure state of known spin +1/2 in the z direction, and then measure its spin in the x direction and get +1/2, doesn't the measuring instrument have to soak up the +1/2 angular momentum in the z direction and the -1/2 in the x direction? In other words, won't it get an angular momentum of hbar/root(2) in a direction 45 degrees between the z and -x axis? If so, then clearly the measuring instrument gave the particle its angular momentum, and I don't see why EPR would have expected to be able to know both the z and x spin in Grey's very detailed explanation of the EPR paradox in this thread. I do still see the idea of "entangled" wave functions, however, but I'm missing the point of rotating the angle of the spin measurement.

WaxRubiks
2005-Oct-28, 08:51 AM
I didn't really understand the EPR paradox but I think that if no actual information is being sent between the two then it is just some property of the situation rather than a paradox.

John_Charles_Webb
2005-Oct-30, 01:25 AM
The "truth" of your table is only a temporary truth and not an "absolute truth".
Perhaps, "absolute truth" is timeless and never subject to change.
If absolute truth is timeless, then there are no absolute truths about material things (or that IS the only absolute truth regarding temporal items, that there is no materially based absolute [everlasting] truth). 5 years from now you may not have that table. The fact that you have that table now is absolutely truthFULL but not absolute truth.

There is a difference between "true meaning" and "absolute truth". The difference is temporal (time based).

and that is absolutely true http://www.bautforum.com/images/icons/icon7.gif

ASEI
2005-Oct-30, 08:06 AM
I think what we mean by "absolute truth" is that there is something with some properties (even if we cannot know them exactly) which we are attempting to observe. That something is objectively there with some objective property. That it isn't some sort of show put on for our senses, or some other slippery philosophical hall of mirrors which we're observing.

nokton
2005-Oct-30, 03:49 PM
Lonewulf, you undersand not? absolute truth in the mind of a believer
dwells, never a seeker of knowledge, but blind faith, more important,
you of science, as am I, Have faith in what your learning tells you.
Nokton

Grey
2005-Oct-30, 09:11 PM
But does anyone know the answer to this simpler QM question:
If you prepare a particle in a pure state of known spin +1/2 in the z direction, and then measure its spin in the x direction and get +1/2, doesn't the measuring instrument have to soak up the +1/2 angular momentum in the z direction and the -1/2 in the x direction? In other words, won't it get an angular momentum of hbar/root(2) in a direction 45 degrees between the z and -x axis?No, that's not necessarily the case, as far as I know. You're thinking about the situation classically. There's no such thing as a real spin in a specific direction (whether of the particle or of the measuring apparatus) when it's not being measured. One of the important later realizations of quantum mechanics is that a disturbance model (where measuring a parameter inevitably affects the properties of the things you're measuring) is not sufficient to explain quantum behavior. It's not just that we can't measure incompatible observables at the same time. It's that particles really don't have both properties at the same time.


I didn't really understand the EPR paradox but I think that if no actual information is being sent between the two then it is just some property of the situation rather than a paradox.Certainly. But it's important to realize just what that property of the situation is. The assumption that led to a conflict was that quantum objects have real properties that don't "spookily" change instantaneously in response to things happening arbitrarily far away. That turns out not to be the case.

In that sense, ASEI's suggestion that there's something underlying our reality that has conventional properties is probably not the case, at least not in the sense we might expect. There might be objective objects, and they might have properites, but not in the way that macroscopic objects do.

Nereid
2005-Oct-30, 11:04 PM
Thanks for the webpage, though I tried to load the Bell paper and my computer crashed! In any event, I think my question is simpler than the one addressed in that paper, though no doubt there would be insight there. But does anyone know the answer to this simpler QM question:
If you prepare a particle in a pure state of known spin +1/2 in the z direction, and then measure its spin in the x direction and get +1/2, doesn't the measuring instrument have to soak up the +1/2 angular momentum in the z direction and the -1/2 in the x direction? In other words, won't it get an angular momentum of hbar/root(2) in a direction 45 degrees between the z and -x axis? If so, then clearly the measuring instrument gave the particle its angular momentum, and I don't see why EPR would have expected to be able to know both the z and x spin in Grey's very detailed explanation of the EPR paradox in this thread. I do still see the idea of "entangled" wave functions, however, but I'm missing the point of rotating the angle of the spin measurement.Grey already answered this, but to repeat: I think you have misunderstood the subtleties, and the best advice I can give you is to keep trying that webpage. If, after you've read the material, you still have questions, I'll gladly point you to an internet forum where Dr Chinese himself will be pleased to answer your questions, at whatever depth you ask, and to whatever level you think you need.

At the risk of sounding like a broken record, this stuff is exceedingly counter-intuitive, it is astonishingly easy to (unknowingly) make the ellision from sound physics to nonsense, and the effort required to 'get your mind around it' (let alone attempt to explain it to others) is far, far greater than you can imagine. :surprised

SolusLupus
2005-Oct-31, 03:52 PM
The "truth" of your table is only a temporary truth and not an "absolute truth".
Perhaps, "absolute truth" is timeless and never subject to change.
If absolute truth is timeless, then there are no absolute truths about material things (or that IS the only absolute truth regarding temporal items, that there is no materially based absolute [everlasting] truth). 5 years from now you may not have that table. The fact that you have that table now is absolutely truthFULL but not absolute truth.

Semantics, good sir. The table still was there. You can list the time the table existed should the table be destroyed. If the table gets scratched, you can list when it wasn't scratched. Alternatively, when a river dries up, there's still a riverbed scored within the rocks -- the absence of the river does not change this fact.


Lonewulf, you undersand not? absolute truth in the mind of a believer
dwells, never a seeker of knowledge, but blind faith, more important,
you of science, as am I, Have faith in what your learning tells you.
Nokton

I'm not quite sure if I understand this. It seems you're proclaiming that "Absolute Truth" only exists for the Believer, not a seeker of knowledge.

I disagree. I see Science as wanting to find what the truths are. They don't invent the truth, or consider truth subjective, but instead tries to test Life, the Universe, and Everything, and attempts to put figures to them, make laws on them (see the Laws of Physics, and Laws of Conservation, or Laws of Thermodynamics)... please, no Douglas Adams jokes, those get old after a while.

Anyhow, a seeker of knowledge has to be sure that the knowledge is True. This does require a modicum of faith, but the same amount of faith as one needs for anything in life. Such as the faith that your bed will be there when you wake up, the sun will have risen in the morning, that the forecast is something to go off of (if not always accurate), that your electrical power will be there, and that you will be alive for a while more. The same thing is required of a seeker of knowledge - they have faith that the knowledge they learn is Truth. That the evidence of Theory keeps them closer and closer to the Truth.

Thus, I don't really feel comfortable with either of these responces, personally.