Uncertainty

[Resha Caner]

This will probably seem like a silly question, but what would falsify the Uncertainty Principle?

I don't ask because I disagree with the Uncertainty Principle. For me it actually has a nice, intuitive feel to it. This is just a thought experiment on my part. Is there something a physicist could try where a particular result would falsify the Uncertainty Principle?

 

[Tinker Grey]

IANAPhysicist, however, if we discovered a principle/mechanism/method by which we could know both the momentum and position of a quantum particle, then we would have falsified the Uncertainty Principle.

It is hard for me to imagine an experiment that would do this without also have some evidence that suggests the possibility that something else might explain reality better. Once something like that is hinted at, one might imagine a way to test it.

But again, I am not a physicist.

 

[Resha Caner]

IANAPhysicist, however, if we discovered a principle/mechanism/method by which we could know both the momentum and position of a quantum particle, then we would have falsified the Uncertainty Principle.

It is hard for me to imagine an experiment that would do this without also have some evidence that suggests the possibility that something else might explain reality better. Once something like that is hinted at, one might imagine a way to test it.

Yep. Well said. But it seems like there should be a way. That's why I was thinking you couldn't shoot directly for the target. You'd have to go after something that underlies uncertainty (like how the blackbody radiation problem led up to it) or something that follows from it.

 

[DontTreadOnMike]

This doesn't answer your question AT ALL but I just thought that it might interest you. I asked some physicists on reddit about the uncertainty principle and here are a few tidbits that helped me understand it.

"You can't simultaneously know the position and the momentum of a particle with arbitrary precision. You can know that a particle is around-hereish and the momentum is something-like-that all day long."

"Let's say I know that the particle is somewhere in the LHC [Large Hadron Collider]. That means the uncertainty in its position is 28 kilometers. According to the uncertainty principle, the minimum uncertainty in momentum is about 3.5 picoelectron volts/c. That means that I can know the momentum to within a trillionth of a trillionth of the actual value."


"The uncertainty principal doesn't say you can't know the position and speed/direction -- it says that you can't know it past a degree of certainty.
That degree of certainty is enough to hit two protons together."

 

[DontTreadOnMike]

But it seems like there should be a way.

No there is no way. To measure something you have to be able to interact with it. The act of measuring changes the position and momentum of the particle.

 

[Agonaces of Susa]

If it were possible to determine precisely the position and velocity of an electrically charged particle simultaneously, that would falsify it. Or if the more precisely you knew the position of an electrically charged particle and therefore the more precisely you would know it's velocity, if that were true, that would falsify it.

Or if everyone could predict the future 100% of the time, that would falsify it.

 

[Chesterton]

I'll try and make the OP feel less silly by comparison:

Why can't they just get two physicists observing a particle: one measures momentum, the other measures position, then afterwards they compare.

 

[Resha Caner]

I'll try and make the OP feel less silly by comparison:

Why can't they just get two physicists observing a particle: one measures momentum, the other measures position, then afterwards they compare.

Sigh. If I wanted comedy, I wouldn't look for it here.

In an attempt to display a certain amount of competence, I shall answer Chesterton's question. As mentioned above, any "measure" of an object affects that object. It is a constant struggle for we engineers to run a test where we don't affect the outcome by the way we set up our instrumentation. That physicists even try at the quantum level just boggles my mind ... but then they usually have more money for their toys than I have for solving the world's real problems.

So, in one attempt to measure position, the momentum of the particle is changed. Then, in a second attempt to measure momentum (even if "simultaneous" with the first - and that would be a very difficult thing to do), it is different than during the first measurement. (Or vice versa).

I did wonder for a time if one could make a long series of alternating measurements of a particle: position, then momentum, then position, then momentum, etc. where each measurement was designed to push the particle back and forth between the two measurements like a ping pong. And if, from that, one could ascertain the affect the measurements were having on the particle so that they could be subtracted out - much the same way I deal with white noise. Maybe the question is worth asking, but my general thought is this:

There are a lot of smart people in the world. If there were a way to do it, someone would have devised it by now.

So, I'm going in an opposite direction. What phenomena can we measure with confidence that has derived from the uncertainty principle?

 

[Wiccan_Child]

The uncertainty principles are a result of quantum mechanics. Anything that supports QM, supports the principles. Anything that disproves QM, disproves the principles.

But if you want to falsify them directly, try and measure two such observables (position-momentum, energy-time, etc) to arbitrarily large degrees of accuracy.

 

[DontTreadOnMike]

The uncertainty principles are a result of quantum mechanics. Anything that supports QM, supports the principles. Anything that disproves QM, disproves the principles.

But if you want to falsify them directly, try and measure two such observables (position-momentum, energy-time, etc) to arbitrarily large degrees of accuracy.

Right. We can try all we want but we'll never be able to do it. It's not a case of our technology being inadequate. It's just the nature of particles. It's like saying that if you want to falsify pi, try to measure a circle where pi equals 2.6. It can't be done. It is the nature of circles that pi= 3.141...

No matter how advanced our science becomes, it can't change the nature of pi or quantum particles.

 

[metherion]

Just thought I would pipe in, as I just had a bit of this earlier in the spring during physical chemistry II.

The uncertainty is equal to or greater than (Plack's constant)/(4 times pi).

So you CAN know it, as long as (uncertainty in position) times (uncertainty in momentum) is greater than or equal to h/(4*pi).

Metherion

 

[Resha Caner]

Right. We can try all we want but we'll never be able to do it. It's not a case of our technology being inadequate. It's just the nature of particles. It's like saying that if you want to falsify pi, try to measure a circle where pi equals 2.6. It can't be done. It is the nature of circles that pi= 3.141...

It's not quite the same thing. Pi results from definitions. I define a circle to be a certain thing and I define the radius to be a certain thing. Pi then becomes a tautology - the only possible relation between a circle and its radius.

We didn't define the behavior of particles. We observed it.

So, let me try to draw this out a bit. Uncertainty is based on Planck's constant. Planck's constant originally came from an attempt to explain blackbody radiation. So, suppose I found a body that emitted more radiation at ultraviolet wavelengths than is predicted by Planck's law. I suspect that would throw things into a tizzy.

But, just creating a standard blackbody furnace isn't going to get us there. It's been done. I'm digging at the assumptions behind this all. Is there a "parallel postulate" type assumption - however trivial - that if changed, would change the result?

 

[DontTreadOnMike]

It's not quite the same thing. Pi results from definitions. I define a circle to be a certain thing and I define the radius to be a certain thing. Pi then becomes a tautology - the only possible relation between a circle and its radius.

We didn't define the behavior of particles. We observed it.

So, let me try to draw this out a bit. Uncertainty is based on Planck's constant. Planck's constant originally came from an attempt to explain blackbody radiation. So, suppose I found a body that emitted more radiation at ultraviolet wavelengths than is predicted by Planck's law. I suspect that would throw things into a tizzy.

But, just creating a standard blackbody furnace isn't going to get us there. It's been done. I'm digging at the assumptions behind this all. Is there a "parallel postulate" type assumption - however trivial - that if changed, would change the result?

Hey man, I was an art major. I'm doing the best I can alright?

 

[Wiccan_Child]

It's not quite the same thing. Pi results from definitions. I define a circle to be a certain thing and I define the radius to be a certain thing. Pi then becomes a tautology - the only possible relation between a circle and its radius.

We didn't define the behavior of particles. We observed it.

So, let me try to draw this out a bit. Uncertainty is based on Planck's constant. Planck's constant originally came from an attempt to explain blackbody radiation. So, suppose I found a body that emitted more radiation at ultraviolet wavelengths than is predicted by Planck's law. I suspect that would throw things into a tizzy.

But, just creating a standard blackbody furnace isn't going to get us there. It's been done. I'm digging at the assumptions behind this all. Is there a "parallel postulate" type assumption - however trivial - that if changed, would change the result?

The foundational postulates of quantum mechanics, I'd imagine.

 

[Chesterton]

As mentioned above, any "measure" of an object affects that object.

Why is that?

It is a constant struggle for we engineers to run a test where we don't affect the outcome by the way we set up our instrumentation. That physicists even try at the quantum level just boggles my mind ... but then they usually have more money for their toys than I have for solving the world's real problems.

So, in one attempt to measure position, the momentum of the particle is changed. Then, in a second attempt to measure momentum (even if "simultaneous" with the first - and that would be a very difficult thing to do), it is different than during the first measurement. (Or vice versa).

I did wonder for a time if one could make a long series of alternating measurements of a particle: position, then momentum, then position, then momentum, etc. where each measurement was designed to push the particle back and forth between the two measurements like a ping pong. And if, from that, one could ascertain the affect the measurements were having on the particle so that they could be subtracted out - much the same way I deal with white noise. Maybe the question is worth asking, but my general thought is this:

There are a lot of smart people in the world. If there were a way to do it, someone would have devised it by now.

So, I'm going in an opposite direction. What phenomena can we measure with confidence that has derived from the uncertainty principle?

You're saying that what I suggested is too difficult or too expensive, or what?

 

[Wiccan_Child]

Why is that?

I think he's referring to active measurements. Passive measurements don't affect the object, inasmuch as the change has already occurred. We can passively scan nebulae by measuring their spectra, for instance, and that doesn't change the object.

 

[DontTreadOnMike]

Why is that?



You're saying that what I suggested is too difficult or too expensive, or what?

Well a couple things, how do you measure something without interacting with it? And interacting with something as small as a particle will change it a lot. How do you measure where a particle is? Do you shoot a laser at it? A laser is just a stream of particles. That'd be like measuring where a drop of water is by pouring a bucket on it haha.

And second, you couldn't even really measure where particles anyway because they behave like waves in some instances. You can predict the probability of it being in a certain spot but you can't know for sure. They're not little marbles that you can just point to and say "oh there it is", they actually have a probability of being in lots of places all at once.

 

[Maxwell511]

What phenomena can we measure with confidence that has derived from the uncertainty principle?

Computers. We as engineers can confidentially say that we can derive computers from the uncertainty principle and some other things.

Or at least I think we can, am I imagining the internet?

 

[Wiccan_Child]

Computers. We as engineers can confidentially say that we can derive computers from the uncertainty principle and some other things.

Or at least I think we can, am I imagining the internet?

It's uncertain