Does a tree exist if no one is there to observe it?

[srfriggen]

and no one is around to hear it does it make a sound?...

my real question is, does the tree even exist if no one is around? and what qualifies an "observer". do wave functions collapse only in the presence of humans? why can't schroedinger's cat tell if it is dead?

I guess I'm asking for a general overview so that I can contribute CORRECT information the next time conversation of this type starts. Nothing worse than asserting incorrect facts about physics, or anything for that matter.

 

[olgranpappy]

and no one is around to hear it does it make a sound?...

yes

my real question is, does the tree even exist if no one is around?

yes

and what qualifies an "observer". do wave functions collapse only in the presence of humans?

no

why can't schroedinger's cat tell if it is dead?

something dead does not know it is dead since it is dead.

I guess I'm asking for a general overview so that I can contribute CORRECT information the next time conversation of this type starts. Nothing worse than asserting incorrect facts about physics, or anything for that matter.

This thread should probably be moved to the philosophy section since the answers I gave are highly unsatisfactory.

 

[Marcaias]

do wave functions collapse only in the presence of humans?

Of course not!

However, the behaviour of the system is exactly the same as if all the "observations" made by the tree, the grass, the wildlife, and so on were instead made by you when you stumbled into the forest a year later.

 

[srfriggen]

jeez, way to take the question out of context and make it seem ridiculous. maybe someone else can give a less arrogant answer.

it's not a philosophical question, it's a question about wave function collapses and observation.

 

[srfriggen]

Of course not!

However, the behaviour of the system is exactly the same as if all the "observations" made by the tree, the grass, the wildlife, and so on were instead made by you when you stumbled into the forest a year later.

hey, my last comment wasn't aimed at you. I'm having a tough time wrapping my head around your answer. is there a way you can explain it further? I've heard people reply to the question, "if a tree falls in the woods does it make a sound" with "well, actually quantum theory tells us the tree doesn't even exist if we aren't around to observe it, therefore no sound can be made from a non-existent tree". comments on that?

 

[msumm21]

and no one is around to hear it does it make a sound?...

my real question is, does the tree even exist if no one is around?

if the fall leaks information out into the surrounding environment (limbs break, wildlife runs away, ...) then I guess it's real to your mind. couldn't you go measure things afterward and see that it broke?

 

[Marcaias]

hey, my last comment wasn't aimed at you. I'm having a tough time wrapping my head around your answer. is there a way you can explain it further? I've heard people reply to the question, "if a tree falls in the woods does it make a sound" with "well, actually quantum theory tells us the tree doesn't even exist if we aren't around to observe it, therefore no sound can be made from a non-existent tree". comments on that?

If any of the people who told you "the tree doesn't even exist if we aren't around to observe it" are physicists, please smack them for me. :)

To expand on what I meant...

In quantum computing, it's called the "principle of deferred measurement." I believe it to be the fundamental paradox in quantum mechanics, and the root of all the trouble people have in understanding it.

The evolution of a quantum system can be modeled by a series of continuous operations U, interspersed with discontinuous, "jumpy" measurements R of the whole or part of the system R. So you can conceptually think of the evolution of a quantum system as a continuous graph with a bunch of discontinuous jumps. (I take this picture directly out of the Road to Reality by Penrose.)

http://img228.imageshack.us/img228/8575/roadtorealitylx6.png

The principle of deferred measurement states that such an evolution can ALWAYS be replaced by one with a single, continuous U, and a single measurement R performed at the very end.

In computational terms, whenever you want to measure the value of a qubit and perform a routine like, "if I measure a 0, perform operation A; if I measure a 1, perform operation B," you can replace that measurement and procedure by a purely quantum operation.

In other words, you can always push back or defer an observation until the very end of your "computation."

In terms of a tree in the forest, you can reasonably say that the tree was in a "Schrodinger's Tree" state until you entered the forest and peeked at it. But you can just as reasonably say that when the tree fell, the ground measured its position, and so on, and so on, and by the time you finally peaked at it, you simply saw an already collapsed quantum system.

(The same principle made it so difficult for me to understand entanglement! The trouble with entanglement goes away if all the interactions are purely quantum ones until the two entangled particles "meet" and get measured, but it's incredible that any number of local measurements before the meeting, when the particles are miles apart, can be replaced by quantum operations. It seems as though a local measurement has an effect on the pair particle, but this effect is in a sense virtual.)

You might instead ask, what if I never observe the tree, and in fact no one ever goes inside it and no one observes whether the tree fell over or not?

It's in the answer to that question that you may be tempted to say, it simply doesn't exist, in the sense that it is a completely isolated system, and so anything that happens in it has no effect on us. However, completely isolated systems don't exist in reality. The universe is one, big quantum system where everything is connected on some level.

You can ask the same question outside of any quantum theory, if, say, you're trying to calculate the acceleration of a falling object on earth. The force of gravity exerted by the moon is so negligible that we can consider the Earth an isolated system. But it's absurd to say the moon doesn't exist because of this.

 

[Dmitry67]

Sorry for repeating it again
There is no such thing as wavefunction collapse.
There is no R process.
http://en.wikipedia.org/wiki/Quantum_decoherence

Can we finally put Copenhagen interpretation to a place where it belongs - ether etc.

 

[Ivan Seeking]

From the wiki link

Environmental decoherence, that is the effects of an external agent on a quantum system, does not claim to offer answers to the main interpretational questions about quantum mechanics. Two points are essentially unanswered by this approach:

Environmental decoherence does not produce a collapse of the wavefunction, it simply provides an explanation for the appearance of wavefunction collapse.
Does an isolated quantum system ever collapse to a classical state? This could be an irrelevant question, since decoherence demonstrates that we can regard empirically the wavefunction as having collapsed; whether it actually has collapsed or not is not a meaningful question since collapse is not empirically determinable. Regarding the appearance of collapse: if the isolated system has sufficient complexity to support thermal, internal degrees of freedom then observers embedded with the isolated system would observe collapse.
The first point is easily understood in the following way. As said above, einselection removes interfering terms due to the external environment. The obtained state gives just independent probabilities for each selected state to be seen by a measurement apparatus. Collapse of a wavefuntion implies that just a possible state is singled out by measurement. The passage from independent probabilities for the states to a single one is not understood yet and this is a dark area that is still under hot discussion.

The second point appears just a scientific question to be answered by experiments and underlies a more subtle question as an effect could be at work for an isolated system becoming classical. A lot of work has been done about and several proposals have been put forward [17]. Some experimental results were also obtained. The problem implicated here is the irreversibility of time evolution and more technically, the understanding of Boltzmann's hypothesis of molecular chaos or Stosszahlansatz. This was the answer due to Boltzmann to the Loschmidt's paradox. Environmental decoherence does not give a satisfactory answer to this question, rather closed quantum systems are expected to keep on being quantum forever.

Finally, but not less important, is the cosmological problem. Universe is an isolated system and so how did it become classical? This extends to the more general problem of cosmological perturbations that appear to be strictly classical.

Currently it appears as the idea of environmental decoherence, surely correct, should be complemented with some other mechanism for isolated quantum systems. Anyhow, this is an open research problem and more results are to be expected in the future.

Why Decoherence has not Solved the Measurement Problem: A Response to P.W. Anderson
Stephen L. Adler
Institute for Advanced Study, Princeton

It has lately become fashionable to claim that decoherence has solved the quantum measurement problem by eliminating the necessity for Von Neumann’s wave function collapse postulate. For example…

These striking statements to the contrary, I do not believe that either detailed theoretical calculations or recent experimental results show that decoherence has resolved the difficulties associated with quantum measurement theory.[continued]

http://arxiv.org/abs/quant-ph/0112095

The Role of Decoherence in Quantum Mechanics
http://plato.stanford.edu/entries/qm-decoherence/

 

[Dmitry67]

Decoherence solves all problems only when coupled with the Multi-world interpretation of course. Multi-world is a consequence of quantum decoherence, not an axiom like in early theories.

The passage from independent probabilities for the states to a single one is not understood yet and this is a dark area that is still under hot discussion.

The above is definitely written by the person who does not believe in many-worlds, so he talks about a 'single one' - not even leaving a room for 2 cats and 2 observers asking 'how the wavefuctions had collapsed into an alive/dead cat?'. These 2 copies of the same observer also claim that QM is random because they can not tell in advance if cat is alive while in fact QM is deterministic

 

[mgb_phys]

There was once a man who said `God
Must think it exceedingly odd
If he finds that this tree
Continues to be
When there's no one about in the Quad.'

Sir, Your astonishment's odd:
I am always about in the Quad.
And that's why the tree
Will continue to be,
Since observed by Yours faithfully, God.

 

[DrChinese]

my real question is, does the tree even exist if no one is around?

Welcome to PhysicsForums!

It is generally agreed that the tree exists independently of the act of observation.

However, some observable attributes of the tree - say its color, shape, location - are dependent on the act of observation. This view is not shared by all, but is certainly consistent with experimental evidence. In this view, those attributes are said to be contextual (or non-realistic).

 

[mn4j]

If a tree falls in the woods...
and no one is around to hear it does it make a sound?...
my real question is, does the tree even exist if no one is around?

Looking at it philosophically:

Let us put your questions in more formal terms. It can therefore be summarized as follows:

1. There exists a tree (T) in the woods
2. The tree (T) falls
3. There is no human around to hear it (T)

Q1. Does T it make a sound?
Q2. Does T exist?

As you can see, The answer of Q2 is obvious, it is one of your premises (1). The tree must exist for your question to make sense.

Now the answer to Q1 is also obvious. It is implied by your third premise. If the tree does not make a sound, then the act of "hearing it" is a logical impossibility which would imply that your third premise is false. Therefore for your question to make sense, the tree must exist and must make a sound when it falls.

Looking at it physically, a falling tree produces vibrations in air molecules and ground molecules within 1000 and 6000Hz, the range of frequencies detectable by human ears (ie sound). So long as molecules are present, they will vibrate. Humans ears hear sound, they do not create sound. The sound must exist for ears to be able to hear them not the reverse. In other words, vibrating air molecules transfer energy to the molecules of the ear-drum which start vibrating as well so the vibrating air molecules must be vibrating BEFORE ear molecules start vibrating.

 

[Dmitry67]

I am an adept of Multi-Worlds+Quantum Decoherence

When tree falls and you don't know about it, the state of your consciousness is the same no matter if a tree fell or not. So different branches of reality (tree fell or not) can interfere before decoherencing finally in your mind.

 

[Marcaias]

I am an adept of Multi-Worlds+Quantum Decoherence

When tree falls and you don't know about it, the state of your consciousness is the same no matter if a tree fell or not. So different branches of reality (tree fell or not) can interfere before decoherencing finally in your mind.

If you intend your interpretation to be predictive in the slightest, you still need to apply the usual probabilistic Rules of Quantum Mechanics at some point or you end up simply engaging in philosophical onanism.

And the fact will remain that what you call Nature probabilistically choosing a universe for us to travel down will look exactly like what I call a measurement resulting in collapse.

The latter is also useful. But if practical use is not your concern, there are plenty of string theorists who are all-ears to such ideas.

 

[olgranpappy]

jeez, way to take the question out of context and make it seem ridiculous. maybe someone else can give a less arrogant answer.

yes

it's not a philosophical question, it's a question about wave function collapses and observation.

no. maybe.

 

[Renge Ishyo]

This question can easily be run around in circles depending on how "sound" is defined, but in general you can say that a falling tree on Earth will produce "sound waves" upon falling even if these waves do not carry to a humans ear for a human to become aware that they were made. Note that this assumes the tree is in an environment/earth where "sound" is produced...if you placed the tree on the moon and it fell it would not make a sound even if an observer was five feet away watching it fall (because there is no medium in space to carry the sound). Some people define "sound" as the sensation we experience only when those sound waves interact with the receptors in our ear drums. In this case, "sound" is not produced if a human is not around because there are no ear drums to receive the waves. And so on. Like much of philosophy these arguments boil down to how sound is defined. Once that is sorted out, you can answer the question reasonably enough.

 

[Dmitry67]

And the fact will remain that what you call Nature probabilistically choosing a universe for us to travel down will look exactly like what I call a measurement resulting in collapse.

You are misunderstandig the multi-world.
There are many 'us', so we are traveling in all possible paths
But as we remember only the Past, we perceive Time as linear, not like a tree.

If some interpretations include Collapse and others do not, shouldn't we cut the Collapse using occams razor?

Also, if you believe in collapse you need to answer all sorts of questions like 'what exactly makes a measurement apparatus so magical that it causes a collapse while other collections of QM particles do not, deal with a dead/alive cat and Wigners'friend etc.

 

[mn4j]

If some interpretations include Collapse and others do not, shouldn't we cut the Collapse using occams razor?

"Multi-world" is by itself an extreme violation of Ockham's Razor.

Also, if you believe in collapse you need to answer all sorts of questions like 'what exactly makes a measurement apparatus so magical that it causes a collapse while other collections of QM particles do not, deal with a dead/alive cat and Wigners'friend etc.

Same questions apply to multi-world, What exactly makes a particular decomposition preferred over others in a measurement? In other words, if the cat is alive in one world and dead in another, what causes the observer to perceive one state and not the other on opening the box?

 

[Dmitry67]

1
"Multi-world" is by itself an extreme violation of Ockham's Razor.

2
Same questions apply to multi-world, What exactly makes a particular decomposition preferred over others in a measurement? In other words, if the cat is alive in one world and dead in another, what causes the observer to perceive one state and not the other on opening the box?

1 Why?
At first, it is not an axiom but a consequence of Quantum Decoherence
I understand that for some reasons it is easy to imagine and to believe into an infinite time or infinite space. But for the infinite number of parralel options is 'weird'.
For some reason, some infinities are much easier to imagine then others.

2 If I understood your question correctly,
As soon as box is opened the observer is decoherenced with a cat. So it splits into 2 copies: one copy observing dead cat, another copy observing a live one. Both copies are asking the same question "what causes me to perceive one state and not the other on opening the box?" :) So the full picture is deterministic.

There are some questions which in fact are not addressed by the Multi-world, but you don't ask them :)

 

[OrbitalPower]

I think this is something related to Locke's "Primary and Secondary qualities," that the sound is dependent upon the observer. I think physics has incidentally discredited these beliefs.

What if a tree falls and makes a sound and scares some animals? The animals then run toward you in a place where you were unable to hear the sound and thus affecting you in somewhat of an indirect way. We often see animals who are frightened and wonder if maybe they've seen or heard something we didn't notice.

Looking at it physically, a falling tree produces vibrations in air molecules and ground molecules within 1000 and 6000Hz, the range of frequencies detectable by human ears (ie sound). So long as molecules are present, they will vibrate. Humans ears hear sound, they do not create sound. The sound must exist for ears to be able to hear them not the reverse. In other words, vibrating air molecules transfer energy to the molecules of the ear-drum which start vibrating as well so the vibrating air molecules must be vibrating BEFORE ear molecules start vibrating.

I agree completely.

Couldn't you also apply the same logic to color and so on, though?

 

[Pythagorean]

I think this is something related to Locke's "Primary and Secondary qualities," that the sound is dependent upon the observer. I think physics has incidentally discredited these beliefs.

What if a tree falls and makes a sound and scares some animals? The animals then run toward you in a place where you were unable to hear the sound and thus affecting you in somewhat of an indirect way. We often see animals who are frightened and wonder if maybe they've seen or heard something we didn't notice.
I agree completely.

Couldn't you also apply the same logic to color and so on, though?

somewhat, if you mean in terms of wavelength, but qualitatively what you experience as "red" is mostly something your brain does to interpret, store, and label the information it's getting.

To make the idea more clear, consider tonality and music. As humans we are pretty good at telling tones apart, and whether you're going up a tone, down a tone. You'd be surprised how many people can recognize an octave a short time after hearing their first example of one. Our sense of smell, however is not organized like that (it's not ordered like consecutively ascending tones).

On the other hand, neurologists are finding that canines interpret smells the same way we interpret tones. If we add a hydrogen atom to some arbitrary aromatic, the dog will detect the new molecule as being as some "tone interval" higher (maybe an octave? I don't know the specifics, but the point is they organize the information in the way we organize sound in our brain).

So yeah, there's a buffer between us and reality. Traditionally, we consider wavelength/frequency to be the reality, and "color" to be our interpretation of the reality based on how our brain chooses to codify, recognize, and store information pertaining to visual stimulation.

Conclusive Response to this Thread:

When threads like this come up, it's common to show how we realize that there is a buffer between us and reality that makes it confusing and difficult to understand reality, but it doesn't mean reality only exists when we're around. It's more like our own, personal, skewed versions of reality only exist when we're in the presence of the reality we're skewing.

 

[epkid08]

and no one is around to hear it does it make a sound?...

my real question is, does the tree even exist if no one is around? and what qualifies an "observer". do wave functions collapse only in the presence of humans? why can't schroedinger's cat tell if it is dead?

I guess I'm asking for a general overview so that I can contribute CORRECT information the next time conversation of this type starts. Nothing worse than asserting incorrect facts about physics, or anything for that matter.

There is a simple answer to this question. It depends on how you define sound. If you define sound as the literal interpretation of sound waves, then no, it doesn't make a sound. If you define sound as literal sound waves, a tangible thing, then yes it does make a sound.

 

[a2tha3]

Quantum physics suggests that when you aren't looking at an object it doesn't exist, or exists in a vague and undetermined state.

When something falls (yet it doesn't exist) does the nonexistent object make a nonexistent sound?

No.

But if we postulate that the tree does exist, then as the person above me says it depends on how you define sound. It still makes the same frequency, but no one is around for the frequency to interpret it...

 

[Monaco]

I am an adept of Multi-Worlds+Quantum Decoherence

When tree falls and you don't know about it, the state of your consciousness is the same no matter if a tree fell or not. So different branches of reality (tree fell or not) can interfere before decoherencing finally in your mind.

Ah, but I DO know about these trees falling...

I don't know exactly where they are, what time they fell or what they look like- but I am aware of the theory of trees falling or not falling and my imagination (or whatever it's called) took that into account, recreated and played back that sound in my head! What is the explanation of this phenomena and how is it realative to trees falling or not? Ok, so the ear drum translates sound waves to the brain and we call this hearing. That's great, but I bypassed the middle man and I can still hear it. How in the world is that possible? (If it helps, there were little yellow birds chirping in the background.)

So if a tree falls in my head, bypasses my ears, but I still perceive it, does it make a sound? It would be interesting to know where the sound goes after resonating the ear drum and on what medium they are recorded on. There's also the absense of sound, which sounds to me like a sound all in itself. It sounds like a lot of trees are falling and only hippies can hear them. (btw, I'm not a physician, I'm a musician)

 

[Monaco]

Quantum physics suggests that when you aren't looking at an object it doesn't exist, or exists in a vague and undetermined state.

Quantum physics sounds retarded.
If I'm not looking at a tree, it's not there? That's about as absurd as looking at a nothing and seeing a tree.

Quantum physics puts a lot of weight on sight = existence. I think it's bull. Bats scream at things and paint pictures in their head of where they are. The bat can't see the tree, but it still exists.

 

[disregardthat]

This philosophical riddle has nothing to do with sound, the question could more generally be asked as "If a tree falls in the forest, and no one is around to sense it, did it fall?". This question is about the nature of existence versus the nature of experience and observation. I.e. how these are concepts are connected. To come with a scientific explanation of sound waves and sound in our brains is completely dodging the point.

 

[disregardthat]

Quantum physics sounds retarded.
If I'm not looking at a tree, it's not there? That's about as absurd as looking at a nothing and seeing a tree.

There are many aspects of existence which many have illusions of. Such a view as you present is philosophically banal, and modern science no longer supports it (which it never really did. The interpretations of science did however).

 

[tauon]

my real question is, does the tree even exist if no one is around?

I don't know, go take a look!

 

[Entropee]

So if a creature with absolutely no self awareness is secluded to an area of relativly empty space, does it exist? Hopefully it does