Help, my brain hurts. Does anything exist?

[freddiy]

Hi there. I have read that quantum particles change when we observe them, Does this mean, nothing in the universe is as it is unless we observe it? If so then how can the planets that give life exist before we observe them? I am sure I sound like an idiot, but I hope you can understand my questions. Thank you.

 

[DennisN]

Hi freddiy! If your brain hurts, you may have been thinking too much.

First a note on terminology; "observation" in science usually means measurement, detection etc. by a human and/or machine. Often this means preparing an experiment, manipulating some things and measuring what happens. That things change (in some respect) when we measure them is perfectly normal; there's no free lunch (see e.g. Observer effect).

"I have read that quantum particles change when we observe them"

Sort of; but I wouldn't say change, their basic properties do not change (e.g. mass, charge). They can however behave differently depending on how we experiment with them. The double-slit experiment is a common example;

• no particle detectors at the slits -> light (photons) will form an interference pattern
• particle detectors at the slits -> the photons will not form an interference pattern

This does not depend on if we observe the experiment or not, it depends on how the experiment is set up, i.e. with or without particle detectors. It might seem strange, but it's not paranormal.

"Does this mean, nothing in the universe is as it is unless we observe it?"

So my answer is obviously no, certainly not. Yesterday I observed the Moon in the evening. Today I observed it again. My conclusion is that the Moon exists in exactly the same way when I'm not observing it.

 

[lostprophets]

if i observed the slits with my eyes close up, would that change them also?
the saying "i can feel his/her eyes piercing through me would suggest we give off a wave of energy through our eyes... i know its a saying but do we?
if so would this energy wave be enough to change things at a sub atomic level.
we could not do this with our eyes to the moon its to massive but with teeny weenies maybe so.

 

[DrChinese]

Hi there. I have read that quantum particles change when we observe them, Does this mean, nothing in the universe is as it is unless we observe it?

It would make more sense to say that the particles themselves exist all of the time, but that some specific properties of those particles do not exist unless observed. Most properties of a system are conserved, such as total energy. So it is not like things are popping into and out of existence.

 

[Mark M]

Hi Freddiy!

First of all, it isn't observation that causes particles to "collapse" to one state, it's interfering with them. It appears as if observation causes this, because to observe something, you must shine light on it it, or set up a detector. This is called decoherance.

Second, when the particles are left by themselves it's not that they don't exist. Instead they are described by what is called a wavefunction. Think of it like a blur between different positions, speeds, charges, etc. so that you cannot tell what it's properties are. Then, when you interfere with it, you cause it to collapse to a much more definite state, an egienstate. But, it still has some uncertainty, you can never fully determine a particle's properties, only make very accurate estimates.

BTW, welcome to the forum!

if i observed the slits with my eyes close up, would that change them also?
the saying "i can feel his/her eyes piercing through me would suggest we give off a wave of energy through our eyes... i know its a saying but do we?
if so would this energy wave be enough to change things at a sub atomic level.
we could not do this with our eyes to the moon its to massive but with teeny weenies maybe so.

It's not the act of observing the experiment that causes decoherance. It's interfering with the experiment. In the case of the DSE, it's the fact that you are bombarding the particles with your detectors. Human consciousness or observation has no effect on this.

 

[Naty1]

I have read that quantum particles change when we observe them, Does this mean, nothing in the universe is as it is unless we observe it?

Hi freddiy! If your brain hurts, you may have been thinking too much.

I disagree...keep on thinking until you reach some conclusions.


See my post #8 for some ideas on wavefunction:

https://www.physicsforums.com/showthread.php?t=579640

All that of post relates to quantum theory.


In fact everything in the universe IS as we observe it. But what we observed is not fixed:
Here are a few examples of how OBSERVATIONS change in relativity:

[1] Unruh effect: an accelerating observer will measure a different local temperature than an inertial [fixed velocity] observer,

[2] Clocks tick at different rates according to observers with different velocities and those in different gravitational potentials...so GPS satellite clocks, for example, tick at different rates than do Earth bound clcoks [Wikipedia has a good article on this.].

[3] While the speed of light appears the same to all observers locally, different observers moving at different velocities relative to the source will observe different colors [different wavelengths]...this is called the Doppler effect.

None of these are quantum effects..all are relativistic effects.

So in our two greatest theoretical constructs of all time, GR and QM, we learn that things are not so simple as they appear. That's likely because evolution so far has not prepared us, not developed senses, for them as it has, say, to detect a predator heading right at us

 

[Naty1]

It would make more sense to say that the particles themselves exist all of the time, but that some specific properties of those particles do not exist unless observed.

Another 'expert' here, has said something quite different, like...'Particles are rare and only exist when we observe them'...suggesting most things are in a wave form most of the time...the views are complementary...not necessarily mutally exclusive...

For example, what does an electron 'look' like??
It looks one way when confined in an atomic orbital,in a cloud around a nucleus; it is stuck in different size and shape clouds in different nucleii; it looks bigger when confined in a box...it changes wavefunction depending on how it is 'confined'...which means how it's degrees of freedom and energy are constrained. And shoot electrons [or photons, quanta of light] through a pair of slits, the 'double slit' experiment and 'unexpected' patterns emerge [unexpected from our usual experience, not un expected to scientists].
Yet as Dr Chinese says, electrons follow energy conservation laws too...they are not free to do anything they wish!

"Don't doubt me." as Limbaugh says[ lol] ...look here for neat illustrations of what 'electrons look like' in different orbitals in THE SAME ATOM!:

http://en.wikipedia.org/wiki/Atomic_orbital#Orbitals_table

 

[Naty1]

one more idea freddiy:

" Who do you think you are?"

Do you realize you cells replace themselves completely every so often...I forget about how long it takes, but unlike a rock, for example, you actively replace every cell in your body periodically whether you or anyone else observes it or not...talk about change!

 

[jeffmoor]

Second, when the particles are left by themselves it's not that they don't exist. Instead they are described by what is called a wavefunction. Think of it like a blur between different positions, speeds, charges, etc. so that you cannot tell what it's properties are. Then, when you interfere with it, you cause it to collapse to a much more definite state, an egienstate. But, it still has some uncertainty, you can never fully determine a particle's properties, only make very accurate estimates.

So, tell me if I understand... A particle, when left alone, does exist, and has a specific position, charge, and momentum at each instantaneous moment in time. Because of uncertainty (our inability to measure it without interfering with it) we can't know these all at once, so describe the particle's properties with a wave function. It's not that, in all reality, the particle doesn't have specific values for these properties, it's just that we can't measure them. The wave function is our probabalistic descriptor of the particle. Is this true?

 

[Demystifier]

Hi there. I have read that quantum particles change when we observe them, Does this mean, nothing in the universe is as it is unless we observe it? If so then how can the planets that give life exist before we observe them? I am sure I sound like an idiot, but I hope you can understand my questions. Thank you.

It's not really that observation per se changes the world, it's the interaction with the environment that changes it.

 

[bugatti79]

Hi Freddiy!

Second, when the particles are left by themselves it's not that they don't exist. Instead they are described by what is called a wavefunction. Think of it like a blur between different positions, speeds, charges, etc. so that you cannot tell what it's properties are. Then, when you interfere with it, you cause it to collapse to a much more definite state, an egienstate. But, it still has some uncertainty, you can never fully determine a particle's properties, only make very accurate estimates.

But why do we need a wave function to describe that the properties are so called 'blurred' when we know that the particles have distinct properties even when we are not 'measuring/interacting with them with our machines?

In other words, why do we describe something as 'blurred' or the 'particle is in many positions at once' just because we can't measure it with 100% certainty?

 

[DrChinese]

So, tell me if I understand... A particle, when left alone, does exist, and has a specific position, charge, and momentum at each instantaneous moment in time. Because of uncertainty (our inability to measure it without interfering with it) we can't know these all at once, so describe the particle's properties with a wave function. It's not that, in all reality, the particle doesn't have specific values for these properties, it's just that we can't measure them. The wave function is our probabalistic descriptor of the particle. Is this true?

Welcome to PhysicsForums, jeffmoor!

No, your assessment is not quite accurate from the perspective of the standard model. The particle exists, yes. It has elements such as mass and charge and momentum, which are conserved. However, these do not all have specific values at all times. Some, such as momentum, take on discrete values only when observed. And when they take on a discrete value, some other properties (those called non-commuting) take on an uncertain character. This has nothing to do with our inability to measure it without changing it. Note that commuting properties do not have this restriction. I can measure spin without changing momentum, yet any spin measurement effectively erases all prior spin values. Go figure!

Your last statement (wave function being probabilistic descriptor) is correct. However, we don't really know where the line is as to the source of the apparently random variations that are seen.

 

[JamesOrland]

First of all, it isn't observation that causes particles to "collapse" to one state, it's interfering with them. It appears as if observation causes this, because to observe something, you must shine light on it it, or set up a detector. This is called decoherance.

From what I understand, that's not quite it. Instead, it's more like the particles are interfering with us. Decoherence isn't that the environment has leaked into the system, but rather the system has leaked into the environment.

What I mean? I mean that decoherence is what happens when the environment suddenly depends on the system being observed. That is, when you measure the particle, there is suddenly a LOT of cells in your brain that change to reflect what you measured, so now your state of being depends on the state of the system being observed.

So, tell me if I understand... A particle, when left alone, does exist, and has a specific position, charge, and momentum at each instantaneous moment in time. Because of uncertainty (our inability to measure it without interfering with it) we can't know these all at once, so describe the particle's properties with a wave function. It's not that, in all reality, the particle doesn't have specific values for these properties, it's just that we can't measure them. The wave function is our probabalistic descriptor of the particle. Is this true?

That is somehow what is explained at many textbooks, but it's not quite true. Uncertainty isn't on the map, it's in the territory; that is, it's a part of the world, it's not a part of how we understand it. It has been explained above that there are properties which cannot be known simultaneously. That has nothing to do with our ability to measure it, we can measure either property (momentum or position) with a high degree of accuracy without affecting it too much. But talking for instance about momentum and position, once the wavefunction describing a single electron's position has been confined to a narrow area (that is, its position is known with some accuracy), the momentum becomes indefinite, and it can take any value.

But why do we need a wave function to describe that the properties are so called 'blurred' when we know that the particles have distinct properties even when we are not 'measuring/interacting with them with our machines?

In other words, why do we describe something as 'blurred' or the 'particle is in many positions at once' just because we can't measure it with 100% certainty?

As I said, it's not about measuring. It really is blurred. An electron really is in many places at the same time, and furthermore, those places can even interact! (That is, one electron can interact with itself.) The particles have some distinct properties that are fixed, like mass, but there are others that are not fixed.

Your last statement (wave function being probabilistic descriptor) is correct. However, we don't really know where the line is as to the source of the apparently random variations that are seen.

The idea that a wavefunction describes a probability is called the non-realistic view of the wavefunction. There's another idea that claims that the wavefunction is an actual part of the universe, something physically real, instead of just a description of "randomness".

 

[DrChinese]

There's another idea that claims that the wavefunction is an actual part of the universe, something physically real, instead of just a description of "randomness".

That tends to be my view, and the following paper will likely make this a more accepted viewpoint:

The quantum state cannot be interpreted statistically
http://arxiv.org/abs/1111.3328

 

[bugatti79]

As I said, it's not about measuring. It really is blurred. An electron really is in many places at the same time, and furthermore, those places can even interact! (That is, one electron can interact with itself.) The particles have some distinct properties that are fixed, like mass, but there are others that are not fixed.

Forgive my ignorance, but how do we know the electron is in many places at one time. Is this verified from the double slit experiment?

 

[Mark M]

So, tell me if I understand... A particle, when left alone, does exist, and has a specific position, charge, and momentum at each instantaneous moment in time. Because of uncertainty (our inability to measure it without interfering with it) we can't know these all at once, so describe the particle's properties with a wave function. It's not that, in all reality, the particle doesn't have specific values for these properties, it's just that we can't measure them. The wave function is our probabalistic descriptor of the particle. Is this true?

Actually, no. The uncertainty is a built in characteristic of particles, not an experimental limit. A particle at any time occupies several positions, and literally exists as a wavefunction. The view that you are expressing was that of Albert Einstein, but today we know (from John Bell) that wavefunctions are very much real, not just probabilistic descriptions.

But why do we need a wave function to describe that the properties are so called 'blurred' when we know that the particles have distinct properties even when we are not 'measuring/interacting with them with our machines?

In other words, why do we describe something as 'blurred' or the 'particle is in many positions at once' just because we can't measure it with 100% certainty?

Like I said at the beginning of this post, particles do not have distinct properties. It's not just an experimental limit, it is a fact of quantum mechanics that the best you can do is predict the probability of a specific outcome.

From what I understand, that's not quite it. Instead, it's more like the particles are interfering with us. Decoherence isn't that the environment has leaked into the system, but rather the system has leaked into the environment.

What I mean? I mean that decoherence is what happens when the environment suddenly depends on the system being observed. That is, when you measure the particle, there is suddenly a LOT of cells in your brain that change to reflect what you measured, so now your state of being depends on the state of the system being observed.

Thanks for posting a more in depth definition! I was just trying to keep it simple for the OP.

 

[JamesOrland]

That tends to be my view, and the following paper will likely make this a more accepted viewpoint:

The quantum state cannot be interpreted statistically
http://arxiv.org/abs/1111.3328

Yeah, it tends to be mine, too :) I just got home, but I'll read the article you mentioned.

Forgive my ignorance, but how do we know the electron is in many places at one time. Is this verified from the double slit experiment?

Yes, among other stuff. The effect observed in the double slit experiment is exactly what one would expect if suddenly the electron became two electrons, one coming from each slit, and then interacting with itself, to a T. I mean, truly, if you make your calculations assuming there's actually two waves, one coming from each slit, and that they interact, you will get the same interference pattern observed. That is not the only experiment that confirms this fact, but it's the most well known and the simplest to picture and explain.

 

[jeffmoor]

Actually, no. The uncertainty is a built in characteristic of particles, not an experimental limit. A particle at any time occupies several positions, and literally exists as a wavefunction. The view that you are expressing was that of Albert Einstein, but today we know (from John Bell) that wavefunctions are very much real, not just probabilistic descriptions.

Well, heck, if my understanding of quantum mechanics has caught up to Einstein, I shouldn't feel too badly! :-)

So the wavefunction really exists. Particles really are smeared, and in several places at once. They look like they are in one place when we observe them, but only because our observation "kills their buzz."

So, here's my really big question: How does one go about gaining some sense of intuitive comfort with this part of reality. I'm past the feeling that it must all be some form of dark magic at work... but only just.

 

[JamesOrland]

Well, heck, if my understanding of quantum mechanics has caught up to Einstein, I shouldn't feel too badly! :-)

In very deed a quite motivational thought!

So the wavefunction really exists. Particles really are smeared, and in several places at once. They look like they are in one place when we observe them, but only because our observation "kills their buzz."

Yes, that's pretty much it. The Many Worlds Interpretation says that this "buzzkill" of sorts is actually an epiphenomenon of the fact that when you observe them, you become part of the wavefunction. That is, while the electrons do still keep a superposition of a bazillion states, you too enter a superposition of a bazillion yous, each you having seen the electron at one different position. Sort of.

So, here's my really big question: How does one go about gaining some sense of intuitive comfort with this part of reality. I'm past the feeling that it must all be some form of dark magic at work... but only just.

Well, intuitive doesn't work very well. It's common knowledge already that physics doesn't agree with our merely human intuitions.

On the other hand, I will borrow one of the wisest sayings of Yudkowsky: it all adds up to normalcy. That is, no matter how weird stuff is down there, everything you see is the direct result of everything that happens there. The world didn't get any weirder. It's just that now you know how it works a little better.

And I also just realized how often I use the expression 'that is.' Man...

 

[jeffmoor]

Well, intuitive doesn't work very well. It's common knowledge already that physics doesn't agree with our merely human intuitions.

True. "Intuitive" was a poor choice of words. I suppose what I really desire is just some intellectual comfort with what a wave function is. Energy? Matter? Dark magic? An extremely surprising new structural form of carbon?

I don't doubt my ability to understand the mathematics of the wave function, were I to someday study it in depth. Sadly, my introduction to eigenvectors was a long time ago. For now, that math is far beyond me.

Even if I did understand it, I very much doubt it would make me feel nearly as warm and fuzzy as picturing a tiny, spherical electron, mechanically orbiting a somewhat solar atomic nucleus. Deep, deep down inside, I want a wave function to be something simple and tangible, like an infinitesimally small, smooth piece of stone in just 3 or 4 dimensions. Even if it vibrates, I can wrap my mind around that sort of thing.

I despise thinking that something at the heart of my reality might be so foreign to my experience - even worse, beyond my brain's ability to map its intricacies - that I might never feel quite comfortable explaining it to my kids.

 

[Maui]

It's not really that observation per se changes the world, it's the interaction with the environment that changes it.

So, because all 'particles' are constantly interacting with the environment, there should exist no wave-like behavior? Wave-like behavior is crucial for the stability of atoms in molecules(e.g. covalent bonds http://en.wikipedia.org/wiki/File:Covalent_bond_hydrogen.svg , a molecule of two H atoms, each with just one electron shared between the atoms). From this i conclude that the H20 molecule would fall apart if it weren't for the delocalized wave-like behavior. This point also goes against decoherence, at least the version that is sometimes pushed as an explanation for the measurement problem.

 

[Maui]

Hi there. I have read that quantum particles change when we observe them, Does this mean, nothing in the universe is as it is unless we observe it?

If by 'observe' you mean information about the system can potentially be extracted, i'd say yes, the system behaves classical-like(this doesn't state if it were real or not before information about it was available).

BTW, there are no experts on this question, make up your mind only after you have enough information on this contentious issue.

 

[JamesOrland]

True. "Intuitive" was a poor choice of words. I suppose what I really desire is just some intellectual comfort with what a wave function is. Energy? Matter? Dark magic? An extremely surprising new structural form of carbon?

What the wavefunction really is depends on your interpretation, it's really an open question in physics nowadays. I myself subscribe to the idea that the wavefunction is what the particles really are about. That is, they're not waves, and they're not round little things, they're wavefunctions. That's what they really are. So wavefunction is, basically, everything.

So, because all 'particles' are constantly interacting with the environment, there should exist no wave-like behavior?

No. That is incorrect. Wave-like behaviour is not destroyed by that interaction at all. The impression that we have when there is thermodinamically irreversible interaction between the wavefunction-described system and the environment is that the wavefunction is no longer passive to being described by ψ₁ + ψ₂ and is only described by one of those.

That is, according to the differential equations that govern Quantum Mechanics, every solution is real and possible, and the final system is a superposition of all of them. On the other hand, each element of the superposition (each particular solution to the equations) is a wave in and of itself. So when we observe the system, when it interacts in a thermodinamically irreversible way with the environment, the wave-like behaviour does not disappear, it's just reduced from a bazillion interacting waves to a single one.

If by 'observe' you mean information about the system can potentially be extracted, i'd say yes, the system behaves classical-like(this doesn't state if it were real or not before information about it was available).

Not quite true. 'Observation' in Quantum Mechanics really only means interaction with the environment in a thermodinamically irreversible way, which happens regardless of the presence of conscious observers.

 

[Maui]

So when we observe the system, when it interacts in a thermodinamically irreversible way with the environment, the wave-like behaviour does not disappear, it's just reduced from a bazillion interacting waves to a single one.

How does your theory of single waves explain the photoelectric effect? I think wave-particle duality is a well established aspect of qm, so it would be a rather bold claim to say/imply it doesn't exist.

Not quite true. 'Observation' in Quantum Mechanics really only means interaction with the environment in a thermodinamically irreversible way, which happens regardless of the presence of conscious observers.

Which textbook says that? (your certainty implies you have read that in a textbook, not as conjecture in a paper)

 

[JamesOrland]

How does your theory of single waves explain the photoelectric effect? I think wave-particle duality is a well established aspect of qm, so it would be a rather bold claim to say/imply it doesn't exist.

Uh... I never said that. You said that when there was interaction the wave-like behaviour was destroyed, and I said it was not. When there is interaction, what is destroyed is the superposition of states, not the wave-like behaviour.

Furthermore, it is generally accepted that 'wave-particle duality' is not quite correct, because the structures at atomic and subatomic level do not behave either as waves or as particles, but as something else entirely, which we describe by the wavefunction. In this case I can cite one source that says exactly that, off the top of my head, that being Richard Feynman.

Which textbook says that? (your certainty implies you have read that in a textbook, not as conjecture in a paper)

I don't know of any textbooks. Indeed, I should have been clearer in my statement: that is the position held by the Many-Worlds interpretation. Other interpretations may or may not agree with that. But it is also a general consensus that conscious observers do not have any special role in the Universe.

 

[Maui]

Uh... I never said that. You said that when there was interaction the wave-like behaviour was destroyed, and I said it was not. When there is interaction, what is destroyed is the superposition of states, not the wave-like behaviour.

Furthermore, it is generally accepted that 'wave-particle duality' is not quite correct, because the structures at atomic and subatomic level do not behave either as waves or as particles, but as something else entirely, which we describe by the wavefunction. In this case I can cite one source that says exactly that, off the top of my head, that being Richard Feynman.

So you have no explanation for the photoelectric effect? If so, i don't think i can accept the proposition that wave-like behavior is preserved.

Further,

Compton scattering -

"The effect is important because it demonstrates that light cannot be explained purely as a wave phenomenon. Thomson scattering, the classical theory of an electromagnetic wave scattered by charged particles, cannot explain low intensity shifts in wavelength. (Classically, light of sufficient intensity for the electric field to accelerate a charged particle to a relativistic speed will cause radiation-pressure recoil and an associated Doppler shift of the scattered light,[2] but the effect would become arbitrarily small at sufficiently low light intensities regardless of wavelength.) Light must behave as if it consists of particles to explain the low-intensity Compton scattering. Compton's experiment convinced physicists that light can behave as a stream of particle-like objects (quanta) whose energy is proportional to the frequency."

http://en.wikipedia.org/wiki/Compton_scattering

 

[JamesOrland]

So you have no explanation for the photoelectric effect? If so, i don't think i can accept the proposition that wave-like behavior is not destroyed.

I'm sorry, could you please be more specific about your doubt? I don't quite understand why the photoelectric effect would be affected at all by collapse and observation considerations.

 

[Maui]

I'm sorry, could you please be more specific about your doubt? I don't quite understand why the photoelectric effect would be affected at all by collapse and observation considerations.

Because it cannot be explained purely as a wave-like phenomenon, same as with

Compton scattering -

"The effect is important because it demonstrates that light cannot be explained purely as a wave phenomenon. Thomson scattering, the classical theory of an electromagnetic wave scattered by charged particles, cannot explain low intensity shifts in wavelength. (Classically, light of sufficient intensity for the electric field to accelerate a charged particle to a relativistic speed will cause radiation-pressure recoil and an associated Doppler shift of the scattered light,[2] but the effect would become arbitrarily small at sufficiently low light intensities regardless of wavelength.) Light must behave as if it consists of particles to explain the low-intensity Compton scattering. Compton's experiment convinced physicists that light can behave as a stream of particle-like objects (quanta) whose energy is proportional to the frequency."

http://en.wikipedia.org/wiki/Compton_scattering

 

[JamesOrland]

Because it cannot be explained purely as a wave-like phenomenon, same as with

Compton scattering -

"The effect is important because it demonstrates that light cannot be explained purely as a wave phenomenon. Thomson scattering, the classical theory of an electromagnetic wave scattered by charged particles, cannot explain low intensity shifts in wavelength. (Classically, light of sufficient intensity for the electric field to accelerate a charged particle to a relativistic speed will cause radiation-pressure recoil and an associated Doppler shift of the scattered light,[2] but the effect would become arbitrarily small at sufficiently low light intensities regardless of wavelength.) Light must behave as if it consists of particles to explain the low-intensity Compton scattering. Compton's experiment convinced physicists that light can behave as a stream of particle-like objects (quanta) whose energy is proportional to the frequency."

http://en.wikipedia.org/wiki/Compton_scattering

I think you are stuck in thinking that light (or anything else) has an 'either/or' mode suggested by the notion of wave-particle duality. It's not quite like that. It's more of a 'neither/nor'. The behaviour of light, in this case, can be approximated by the behaviour of a particle-like object; in other cases, it can be approximated by the behaviour of a wave-like object; in reality it is neither, and those are just that, approximations. One must abandon classical ideas such as particles and waves to deal with the very very tiny.

I am not denying that light's behaviour in this experiment is typical of a particle-like energy carrying structure. I am just saying that it's more complicated than that.