Questions about Heisenberg's Uncertainty Principle & Vacuum Energy

[zoque999]

hello, registered just to ask this questions and "if possible" i want philosophical, descriptive, or, "made of words" answers since i don't really know much about physics.

1. Heisenberg and his uncertainty principle; i see a problem there. he says, to see where is the electron, you have to use photons, right? and that gives "unnatural" results, as photon affects electrons (tell me if I'm wrong) BUT, then, if I'm right, we are under constant photon bombardment... so, even if we can measure where this electron is without photons, it will be still unnatural it seems to me... or, there's no natural at all to begin with... so, what do you think about this?

2. vacuum energy. can't we put this in the very beginning instead of little big bang thing better? or, can we say, big bang was "in" vacuum energy? since this vacuum energy thing present even in devoid of matter? and then, can't we say, there was never nothingness, as in, big bang and whatever "surrounds" it? cause, if there are quantum fluctations then i say there's something. simply, putting something in the beginning doesn't help. they still ask you what was there before it, who put it there and stuff like that. i need an omnipresent thing like god too. or maybe i don't, why then?

 

[ansgar]

no that is not what Heisenberg uncertainty principle tells us, it is a statistical property of the outcome of measurment of position and momentum. It is quantum resolution, even if we could in principle determine the position and momentum of particles with infinite resolution, the stastical behaviour of many such measurments will lead to the Heisenberg uncertainty relation, that the standard deviation of x times standard deviation of p is larger than h-bar/2

so the answer is really physical, the statement of the uncertainty relation you wrote is false, hence all the derivations from that premise will be false as well.

 

[zoque999]

i don't understand, how can you say that, starting with an "even if" and ending it like "will lead to"... i mean from where this "standart deviation" comes from? if not from our methods of determining position and momentum. don't we use light to measure those things? isn't this formula of yours what we have derived from using light and failing? and if we don't use light to measure those thing, again, how can you say "still".

 

[jtbell]

What he means is this. Prepare a large number of particles (thousands or millions) in the same quantum state. At the same time after preparation, under the same conditions, measure the position of each particle. In general, you get a different result each time, no matter how precise your measuring apparatus is. From these measurements, calculate the
mean and standard deviation. Call the standard deviation \Delta x.

Prepare another collection of particles the same way, and measure their momenta under identical conditions, at the same time after preparation as the first batch. Again, in general you get a different result each time, no matter how precise your measuring apparatus is. From these measurements, calculate the mean and standard deviation. Call the standard deviation \Delta p.

The Heisenberg Uncertainty Principle says that \Delta x \Delta p \ge \hbar / 2 for the ensemble of measurements, regardless of the precision of each individual measurement.

If we know the QM wavefunction for the particles, we can calculate, in advance, \Delta x and \Delta p, and they will always satisfy the HUP; but we cannot calculate in advance the precise position and momentum that we will measure for any single particle.

 

[zoque999]

prepare thousand of particles... you don't need particles, even if they are ants, you will get different results, if you measure their position and momentum less than .5 seconds each time... we are talking about ultra fast electrons here, of course "each time" their position will change. (let alone momentum)

let's say we use a camera, you take a shot, and you pictured electron in this x position. now, even if you take the second shot .00000001 seconds later, i bet electron will spin around protons and stuff 928374 times. so what this "each time" means, i really don't understand.

then, i don't know what's the meaning of putting this as if it's so mysterious, calling it uncertain. tell me our way of measuring electrons simply sucks and i'll understand it. but the principle and you guys talk like as if we have the best apparatus and it's just electron that is acting weird or uncertain or random or fuzzy. and from this "each time" example of yours, i doubt it.

so what i mean is, even if I'm right and even if uncertainity principle says "we just can never take two shots, so close to each other, so we can see electron moving 2 or 3 steps... we will never, reach that technological level"... then, again, i can't see how we are deriving formulas and physics equations, having such neanderthal tools, if you know what i mean.

 

[pallidin]

... then, again, i can't see how we are deriving formulas and physics equations, having such neanderthal tools, if you know what i mean.

One of the beauties of higher education is understanding the foundation of these formulas.
Not that it's necessary, but, if you desire to challenge them it most definitely is.

 

[zoque999]

i don't really challenge any formulas, i only challenge jtbell's "each time" concept. tell me one thing, can we even measure where's the electron and how we are doing that? i was reading since half an hour, found this; http://en.wikipedia.org/wiki/Heisenberg's_microscope

simply, he says...

If the photon has a long wavelength and low momentum, the collision doesn't disturb the electron's momentum very much, but the scattering will reveal its position only vaguely.

and

If the photon has a short wavelength, and therefore a large momentum, the position can be measured accurately. But the photon scatters in a random direction, transferring a large and uncertain amount of momentum to the electron.

so, as far as i can see, what we use, or "thought" to use to measure electron's position and momentum is a photon just like i said. and i say, just because photon has these effects on electron, it doesn't mean, electron is actually acting weird or has any uncertainty in its nature. it's just our tools that makes the uncertainty.

 

[DaveC426913]

so what i mean is, even if I'm right and even if uncertainity principle says "we just can never take two shots, so close to each other, so we can see electron moving 2 or 3 steps... we will never, reach that technological level"...

it doesn't mean, electron is actually acting weird or has any uncertainty in its nature. it's just our tools that makes the uncertainty.

No.

It is important to note that this in not a "measurement problem"; and it is not an "inadequate technology" problem.

The nature of the universe is such that there is no way, even in principle, of measuring both the position and momentum of a particle simultaneously beyond a certain degree of accuracy. The electron does not have both.

One of the ways of reconciling this is to realize that an electron is not a shiny, rigid ball such that we could determine its exact position; it is smeared out across space (as all matter is). The more precisely we try to pinpoint a specific spot, the less of the "smearing" we are including in our measurement. Conversely, to try to capture all the "smearing" that constitutes the electron, we cannot talk about a pinpoint. Loose and oversimplified, but it might help.

 

[zoque999]

the point is, even if this photon throwing thing works like Heisenberg thought, aren't we under constant photon bombardment and if we are, how can you say electron is not affected?

edit since mr. dave added four more lines: then, did Heisenberg simply tried to do something impossible, pinpointing something can not be pinpointed and just because he failed this impossible mission, saying uncertain and stuff ? what was that microscobe he thought and all, if a smearing thing was the case?

besides, how can you tell something is smearing, has a glow, or it's the glow itself, while you can't even measure it's position and momentum. its dimensions or shape should be even harder to determine. like, can't we be wrong about it, making out smearing things, to rationalize (wrongly) uncertain (in theory) results?

because from what i read at that Heisenberg's microscope page, all i can say is electron is just too fast, photon is too big to throw at it (if you throw strongly it changes electron's momentum)

 

[DaveC426913]

the point is, even if this photon throwing thing works like Heisenberg thought, aren't we under constant photon bombardment and if we are, how can you say electron is not affected?

edit since mr. dave added four more lines: then, did Heisenberg simply tried to do something impossible, pinpointing something can not be pinpointed and just because he failed this impossible mission, saying uncertain and stuff ? what was that microscobe he thought and all, if a smearing thing was the case?

besides, how can you tell something is smearing, has a glow, or it's the glow itself, while you can't even measure it's position and momentum. its dimensions or shape should be even harder to determine. like, can't we be wrong about it, making out smearing things, to rationalize (wrongly) uncertain (in theory) results?

because from what i read at that Heisenberg's microscope page, all i can say is electron is just too fast, photon is too big to throw at it (if you throw strongly it changes electron's momentum)

You cannot learn enough about a subject in so short a time and be able to draw conclusions from it, let alone challenge it. If you're interested in learning why it is the way it is, grab a book and read.

Alternately, ask your questions one or two at a time, and we'll try to answer them. Stream of consciounsess writing is not very constructive.

 

[ansgar]

I thought philosophers were quite aware and found of "in principle arguments"...

I agree with DaveC426913, now you just seems nervous

https://www.physicsforums.com/showthread.php?t=394171

 

[zoque999]

okay then, one simple question each time: how do we measure electron's position? (only position) do we still "have" only Heisenberg's microscobe? do we still throw photons at it or did scientists found a better way since Heisenberg?

simple enough i guess.

 

[ansgar]

okay then, one simple question each time: how do we measure electron's position? (only position) do we still "have" only Heisenberg's microscobe? do we still throw photons at it or did scientists found a better way since Heisenberg?

simple enough i guess.

But that measurments distrub the system also occur in the "classical" world, it is nothing special with quantum physics in that sense. So why one should be intersted in that issue when it comes to QM is not clear to me.

 

[zoque999]

i can tell you the same thing now, you just seem nervous. how can you even compare thermometer's effect on my body to photon's effect on electron! do i change the momentum of this car when i take two pictures of it?

if electron is not a rigid ball, how to say, even after throwing a photon at it and calculating its deviation from its original route, that electron was here or there?

like, if you throw a billiards ball to another, you both know their weight, what they are made of and stuff... but throwing a photon to a pretty much dreamy glowing/smearing/energy packet...

i'm just trying to understand, i guess you people think I'm attacking quantum mechanics though, no.

 

[ansgar]

i can tell you the same thing now, you just seem nervous. how can you even compare thermometer's effect on my body to photon's effect on electron! do i change the momentum of this car when i take two pictures of it?

if electron is not a rigid ball, how to say, even after throwing a photon at it and calculating its deviation from its original route, that electron was here or there?

like, if you throw a billiards ball to another, you both know their weight, what they are made of and stuff... but throwing a photon to a pretty much dreamy glowing/smearing/energy packet...

i'm just trying to understand, i guess you people think I'm attacking quantum mechanics though, no.

I am not the one who is nervous, I am PHD in theoretical particle physics..

Yes photons change the momentum of the car when they hit it... but very very very small. You are also too quick to go to systems which you think you can handle. What if I gave you a tiny ball with mass = electron mass and radius 1 fm, and put it on a surface with no friction. Strike this ball with photons and it will move due linear momentum conservation. But let us now switch on quantum physics, then one additional source of uncertainty appears, due to the INTRINSIC wave nature of this "ball". THAT is where Heisenberg uncertainty relation comes in, it gives the INTRINSIC QUANTUM uncertainty of measurements. Thus even if one IN PRINCIPLE could measure position and momentum with infinite good precision, one will still have this quantum uncertainty - THIS is what you must understand and accept.

The thing is that you are approaching quantum mechanics from an intuitive everyday life way, this is not what one should do - QM is contraintuitive, one must "do the math" to understand why and how quantum phenomomena occurs.

Of course the effect of the photon striking the electron will have greater effect, but still the effect on the car is there (put the car in vacuum and on a surface with no friction and you will see this)

And in physics, it is perfectly fine to have collisions/scattering of objects with no finite extension, since the logical language of physics is MATH not "plain words" as in philosophy.

 

[zoque999]

well, it was you who said what I'm talking about also happens in classical world. yet, now you are removing friction out of that world. even though i understand what you mean, you have to spend rest of your life typing "very" and then when you die, i can add "small". and still, that won't be close to describe how very small is photon's effect on car. you went compared that to quantum particles and now saying i have phd shut up, or so it seems to me...

consider this dart i have is a photon. and consider electron is the dart board (in fact, it's only the bullseye of dart board, but it moves or waves so fast it kind of makes the rest of the dart board) also, i have a robot to throw the dart and it's throwing it always at this constant speed. and finally, dart has no needle.

i crack open this robot's skull and i enter in what angle it should throw the dart. dart goes and hits bullseye then bounces 2 meters away with x angle and y momentum and whatever... this is my first data. then i open its skull again and entering new angle. dart hits the board again, but not bullseye, bounces back, gives different results.

is it like this?

 

[ansgar]

If you remove friction of the car, then you would notice the effect much easier, the issue here is "in principle"

 

[zoque999]

"So why one should be intersted in that issue when it comes to QM is not clear to me."

because there's no friction in qm, because stuff "in principle" doesn't really affect classical world and because of all this, photon's effect on electron is an issue, unlike photon's effect on car, because there's friction and removing it saying in principle doesn't change the facts.

 

[ansgar]

"So why one should be intersted in that issue when it comes to QM is not clear to me."

because there's no friction in qm, because stuff "in principle" doesn't really affect classical world and because of all this, photon's effect on electron is an issue, unlike photon's effect on car, because there's friction and removing it saying in principle doesn't change the facts.

so the car put on a frictionless surface is NOT a classical situation?

 

[DrChinese]

...

Yes, it is true that you measure an electron with photons. But the uncertainty imparted by the photon is not the cause of the Heisenberg relations. You can measure the position of an electron as precisely as you like. So where is the issue, you may ask?

The answer is that the electron behaves as a point particle when you consider its position. But it behaves as something more akin to a wave when you consider its momentum. For example, it can exhibit interference effects that do not appear when you consider its position.

You may find it easier to understand if you consider entangled particle pairs. Entangled electrons obey the HUP too, even when separated. Research the exploits of Alice and Bob and I think that may help put you in the ballpark.

 

[zoque999]

can you say this is correct?

 

[Sillyboy]

My comprehension is that, no matter how preicise the measurement is, we connot get the exact value of position and momentum simutaniously. From the formula delta_x*delta_p>=p_bar/2, if we measure one of them(say x), which is that delta_x=0. Then delta_p=infinite. We can measure them simutaniously in the macroscopic world because we can make delta_x and delta_p little simutaniously, which is far under our current precision!
If my comprehesion is wrong, please point out and tell me!

 

[DaveC426913]

My comprehension is that, no matter how preicise the measurement is, we connot get the exact value of position and momentum simutaniously. From the formula delta_x*delta_p>=p_bar/2, if we measure one of them(say x), which is that delta_x=0. Then delta_p=infinite. We can measure them simutaniously in the macroscopic world because we can make delta_x and delta_p little simutaniously, which is far under our current precision!
If my comprehesion is wrong, please point out and tell me!

Yes. You've described what happens, but not how it is so.

 

[DrChinese]

can you say this is correct?

This model is good for junior high school and little more. For purposes of PhysicsForums, I would say it is completely incorrect. For example: an electron does not exhibit any size at all when you press it in that respect. It acts like a point particle. On the other hand, when allowed to roam freely (within an atom) it seems to occupy a shell according to certain rules and acts accordingly.

The same is true of all fundamental particles. Because they all follow the HUP.

 

[DrChinese]

can you say this is correct?

By the way, this is sometimes called a classical model. By 1913, physicists were aware that the classical model had significant problems. The reason people tend to like the classical model is that it is very similar to the model of the solar system.

But the problems with the above are very serious if you want to do anything useful. For example, you cannot explain things like spin, orbitals, Pauli exclusion, or just about anything that you might verify experimentally. In other words, it is ruled out based on evidence. There is almost nothing that you could predict from this model that could be verified using any technology from the past 100+ years.

 

[zoque999]

well, my dart and dart board example in the other page didn't work so i tried to show what i mean with the classical model. point is, whether electron exhibits any size or not, it has wave nature (tried to symbolize it with outer circle) and THIS IS IMPORTANT when a photon hits that outer circle, that's not "exactly" where electron is.

or does qm consider outer circle as electron itself?

 

[DrChinese]

well, my dart and dart board example in the other page didn't work so i tried to show what i mean with the classical model. point is, whether electron exhibits any size or not, it has wave nature (tried to symbolize it with outer circle) and THIS IS IMPORTANT when a photon hits that outer circle, that's not "exactly" where electron is.

or does qm consider outer circle as electron itself?

Well, there are a couple of basic issues here that affect this answer:

a) The size of an electron can appear to be a point, or actually any size (theoretically as big as the universe). This is a function of the HUP. It is not limited to its wavelength.

b) When any particle interacts with any other particle, there is also a field effect. Without the field effect, most everything would be invisible to everything else. In other words, to use your example, light would "miss" the electron and would travel into space before it could interact with anything. This effect is not just theoretical, it is quite real. You are probably aware that neutrinos from the sun pass right through you. So would light, if not for the electromagnetic field induced by electrons in your body.

So there is no "outer" sphere as you imagine. In fact, a captured electron (one which is part of an atom) can also have a spherical shell around a nucleus. But none of these is considered well-defined in the traditional sense. It is more like smeared "probabilities" rather than a distinct object with a distinct boundary.

 

[zoque999]

... but that gives me nothing :)

nothing at all!

shoot a photon towards an electron which can be as big as the universe?

"But none of these is considered well-defined in the traditional sense. It is more like smeared "probabilities" rather than a distinct object with a distinct boundary"

-----------

i don't want to nitpick every word. just tell me, how in this circumstances photon throwing thing "works"... then you will contradict yourself "it seems" to me.

 

[DrChinese]

... but that gives me nothing :)

nothing at all!

shoot a photon towards an electron which can be as big as the universe?

"But none of these is considered well-defined in the traditional sense. It is more like smeared "probabilities" rather than a distinct object with a distinct boundary"

-----------

i don't want to nitpick every word. just tell me, how in this circumstances photon throwing thing "works"... then you will contradict yourself "it seems" to me.

The problem is that quantum mechanics is more oriented around mathematical descriptions - things that help you make predictions for experiments. It is somewhat poorly suited for traditional descriptions.

The fact is that the wavefunction for every atom in your body is constantly expanding all over the place, even to the moon. You don't notice this because the likelihood is vanishingly low. But it is a relevant factor. An electron's charge induces a field around it. The electron - when the field is considered - is called a "dressed" particle. When light interacts with an electron, the dressed field is relevant. And electrons sit in "shells" which have discrete values according to some rules. If they didn't chemical interactions would not be possible. They do not circle in orbits in any sense.

So the contradictions are really yours. Your model cannot possibly account for these phenomena. You can nitpick my words but I am simply trying to describe - in reasonable terms - a better way to understand quantum particles. They do not act at all as you are trying to imagine. Not sure what else to say but there are literally tens of thousands of experiments that show this to be the case. I can throw some voodoo terms in if that will help, but I am actually being as straightforward as possible. Please re-read what I am saying and look at some additional introductory texts.

 

[zoque999]

okay, let's turn back to stoneage! no, that's too much i guess. let's turn back to aristotle or descartes. whoever you chose, really !

2 plus 2 equals to 4. under what conditions? do we have any real 2 to represent in this world? no! 2 is equals to ankh symbol or a crescent. it's nothing but a symbol. it doesn't mean anything... linguistics, this language we are condemned to use. it ruins everything. if it was 2 plus 2 equals to 5, five with the "meaning" of 4. that would be true as well.

then, math is not another dimension. it still comes from our own universe. numbers and operators nothing but what we have symbolized to calculate things easier.

now, you are telling me, there's no explanation other than maths. how is that happened? when math became more real (even though its very roots lies in neanderthal brains) than the fact and effect?

what can 94325435435, this number, can express all by itself?

i'm asking you how to shoot a photon towards an electron which can be as big as universe, and you are replying me like a priest. god is everywhere, god is omnipresent, god is electron, it's here, it's there, it's everywhere. and even so, when you shoot a photon at god, you can measure its position. that's what you said... what the hell? how to believe any crazy maths supposed to prove this. my conscience tells me, either you speak without knowing anything or quantum theory is completely a joke.

probably former.