Basic Definitions in Physics

[Mister Mister]

Hi I wanted to pose some open questions for those of you who have a good knowledge and understanding of science and physics.  In my opinion, modern physics and cosmology has become a total mess, full of internal contradictions, and unresolved conflicts between different departments competing for grant money, and where most of the funding and energy is put towards exploring concepts which have no tangible relation to concrete reality, such as super-strings, dark matter/energy, virtual particles, black holes, and so on.  But I don't want to argue that for the time being.  I want to start at the foundation of physics, and see if we can parse out this confusion, and determine if my concerns are legitimate or not.

Can anyone tell me what are the proper rational definitions of the following terms:

  Matter
  Energy
  Space
  Light
  Mass
  Charge

As far as I can tell, these concepts form the foundation of physics.  Have I missed any?

[Pepin]

Your impression isn't really accurate. The major issue facing physics today is that it takes more than four years to get a decent introduction into modern physics. This is for many reasons, a major being that there is just a lot of content, the other being that the content is extremely complex and difficult to understand. It is really impossible to explain advanced physics concepts and to really have someone understand it without lots of formal training.

 

I say this because the conversation isn't going to go anywhere without a decent understanding of the subject. I'd advise you look into the subject if you are curious. There are a good number of books, but the link below provides a lot of content in a fast manner.

 

https://www.youtube.com/user/DrPhysicsA

 

These are not easy subjects to understand and often require a lot of time to grasp. It is almost impossible to provide any satisfactory answer without going into the mathematics and experiments.

 

What is important to understand is that the entire science of physics is based around models of measurements. We take something that we can measure, whether it is charge or time, and we find relations between that measurement and others. Like with time, we don't have any clue as to what it is, but we can measure it to extreme degrees.

[TheRobin]

I'm no physicist, but I think I can help you when it comes to the definitions (to a degree at least).

 

The main problem with any definition that concerns a fundamental aspect of reality is that you can't really define it as nicely as you can anything else. If you're familiar with categorical logic, then you know that usually definitions relate the chategory that you want to define to an overarching category and then show how it differs from everything else in that category.

For instance if I want to define human beings I'd first say they're mammals (overarching category) and then show the difference between all other mammals (like ability to think, opposing thumbs, etc.).

However fundamental aspects of reality don't have an overarching category. Matter doesn't share properties with anything else except matter, so the definition will be slightly different.
We know matter excerts force on other matter (gravity), but of course that definition is circular in nature. However because you can't really compare it to anything else, that is all you can do.

As for "exploring concepts with no tangible relation to concrete reality" that's not at all accurate. Dark matter for instance is a result of the difference between observational data and the laws of nature that we know. (i.e. the way the universe expands should be different than it is, given our formulas have been accurate so far, so we need to add more mass/energy to make it work).
And this is nothing new at all. Before we had telescopes good enough to see Saturn we already knew from models that there "must be" some body there that has a gravitaional pull, if the models we used are correct. So scientist plotted the planet's course and mass before we actually could observe it (and ofc this was confirmed once we could observe it).
Dark Matter is the same thing. We add it because we assume our models are correct, so instead of arbitrarily creating new models, we just assume there must be some undiscovered mass that explains the actual observations.
And afaik they're setting up an experiment to proof/disproof the existence of dark matter too, so it's very tangible in that sense.

I'm not sure what your problem is with black holes (especially since you put it in the "non-tangible"-category) and I don't even know of virtual particles.

As for string theory it's "just" a different way to explain the fundamental aspects of physics in a way that should make it possible to get rid of the problems of not being able to combine the General Theory of Relativity with Quantum Mechanics. However I'd agree here, that it doesn't come from any observations and is just a made up thing. And given that so far no predictions from String Theory were accurate, I think that shows that this is not a rational approach to create new models.

[Pepin]

I don't even know of virtual particles.

 

Virtual particles are so very interesting. When you first learn about them, you think that it is a dumb concept because they by definition cannot be measured directly. Then when you start hearing about how they test for them indirectly, it all makes a lot more sense.

 

The main reason why we know they exist is because they made a prediction, and the experiment agreed to one part in a billion, which makes it very easily the most accurate prediction in all of history.

 

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

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

 

 

 

As for string theory it's "just" a different way to explain the fundamental aspects of physics in a way that should make it possible to get rid of the problems of not being able to combine the General Theory of Relativity with Quantum Mechanics. However I'd agree here, that it doesn't come from any observations and is just a made up thing. And given that so far no predictions from String Theory were accurate, I think that shows that this is not a rational approach to create new models.

 

I understand there is a lot of criticism of string theory, but I think for the wrong reasons. There is plenty of empirical proof for string theory, all of QM and GR back it up, it is just that QM and GR also explain phenomena just as well.

 

To provide a thought experiment, if for some reason physicists first came up with string theory as the model as opposed to QM or GR,  then when someone came up with QM and GR, it would be seen as explaining less. Though breaking it up would make the math a lot easier, it would be argued that QM and GR not only don't have any more predictive value, but that it has less predictive value because it breaks up something that has been unified.

 

With that said, the main issue with string theory is of course that many forms of it do make predictions and those predictions aren't verifiable. There are also the obvious issues of QM and GR perhaps being distinct things.

 

Please understand that I'm not really supporting string theory per se, but rather I am making the case that if it models QM and GR in accurately, that although it may break down at certain points where it hasn't been tested, it is a useful and valid theory that has a high relation with reality. I say this because there are certain version of string theory (technically M-theory) which are designed just to model QM and GR and do so very well, and it makes little sense to call them wrong.

[TheRobin]

From what I understand about String theory, I think you're incorrect when you say that GR and QM back it up. String Theory was designed to come to the same conclusions as GR and QR, because physicists already know the validity of those theories. But it's more like knowing the eliptic curve of the Earth and then deciding to describe it with circles within circles. Of course, given enough time, you can make the circles-model be accurate with what you already know, but because there's no deduction of prinicples that give you any new insight it won't be reasonable to expect that it can then solve other problems that you haven't already solved.

Might be dead wrong here of course. It's been a while since I read aynthing about string theory, but that's how I always understood it.

[Pepin]

From what I understand about String theory, I think you're incorrect when you say that GR and QM back it up. String Theory was designed to come to the same conclusions as GR and QR, because physicists already know the validity of those theories. But it's more like knowing the eliptic curve of the Earth and then deciding to describe it with circles within circles. Of course, given enough time, you can make the circles-model be accurate with what you already know, but because there's no deduction of prinicples that give you any new insight it won't be reasonable to expect that it can then solve other problems that you haven't already solved.

 

Might be dead wrong here of course. It's been a while since I read aynthing about string theory, but that's how I always understood it.

 

The validity of a model is dependant upon how well it can describe the empirical data. If planetary positions can be described to high accuracy with circles within circles, then the model is accurate and valid.

 

People focus a little too much on the interpretation of the model. Like with the above example, they might retort that the mechanics of the motion are not founded in circles within circles, therefore it is coming to the wrong conclusion about what it is describing. But math doesn't imply anything about what it is describing, it is always up to the physicists to interpret the math.

 

What is interesting about the Ptolemaic model is that even after they found out that their model was incorrect, it was still more accurate than the more modern models. Despite the Ptolemaic system being quite convoluted and not being capable of describing everything accurately, it was still quite accurate. It wasn't until better mathematics came about that the Ptolemaic system became useless.

 

Now of course a false premise can only get you so far when it comes to modeling. In the case of the Ptolemaic system, the premise is that the earth is the center of the universe doesn't work. There are also obvious issues with the implications as the system, such as the sun being close enough to kill everyone on earth. But that is again interpreting the data. It is important to ask what the model is measuring: positions of bodies in space with respect to earth, and if the model describes it.

 

When it comes to string theory, my argument is much the same. Understand that when I say string theory, I mean the particular theories that successfully model QM and GR. These theories are built on the premise that strings are fundamental particles, but that can actually be ignored. Mathematically, the question is "can we model QM and GR with string like objects". The answer is yes.

 

The idea that there is no usefulness of formulating different ways of describing the same data isn't really backed up. A lot of the history of physics has been reworking formulas and figuring out new things from it. For instance, the wave function in QM has been formulated in numerous ways, each with their own insights and uses.

 

There may be obvious breakdowns with string theory if the premise is false, but there are already lots of breakdowns with QM and GR. There are also many premises which go unquestioned. QM treats electrons like they are point particles. There is no real validation for this besides that the point particle model describes the data with high precision. It may be true that electrons are point particles, but they may also have an internal structure. Nobody knows because we are just going off a model.

 

To conclude, again I am not supporting string theory, rather I am supporting mathematical modeling. Models are easy to understand when the interpretation is more built in, but this becomes less and less possible as we get away from everyday experience. With many the many models of QM, physicists really only understand what is happening on a mathematical level. There tend to be interpretations of the math, but there is no agreed interpretation, and with stuff like entanglement, nobody knows what that is.

[Carl Green]

I get the impression with modern science that there's too much trying to fit a model into a theory.

[TheRobin]

Not quite sure what you mean with that, Carl. Can you expand a bit on that?

[Carl Green]

Maybe I'm only getting that impression about modern science because it's the only one I've experienced, but what I'm talking about is when someone gets an idea of how they think it is, they test to see if they're right.

 

"___ phenomenon has occurred. it was probably because of _____. I'll run experiments to see if I'm right"

 

Now I understand it's pretty naive think it's possible to not do this in all situations and still be able to do certain science and such. Of course you have to have an idea of what you think is going on in order to design experiments to test out what's going on.

 

I'm probably way off and projecting a lot but I get the sense that we're currently trying what they were doing with the geocentric astronomical chart. It was wickedly complex and hard to figure out and only got harder the more you tried to figure it out. Then along came the heliocentric model and it simplified everything. I have a feeling that this is currently what's going on in quantum theory and the like but I'm well ignorant of the subject so a feeling is all I have to go on.

[Pepin]

I have a feeling that this is currently what's going on in quantum theory and the like but I'm well ignorant of the subject so a feeling is all I have to go on.

 

Likely not. It isn't that thinking there is more to QM isn't a bad thought, Einstein set out to prove that and figured out that according to QM, you ought to be able to entangle particles and get spooky action at a distance. He argued that this meant QM was false as it just seemed silly. After his death, quantum entanglement was finally able to be tested, and it actually happened. By trying to disprove the theory, Einstein actually uncovered a very unexpected aspect of it many years in advanced actual testing.

 

This is partly why QM is so confusing, as all of the experiments meant to disprove it end up confirming it. Even worse, everything at the subatomic scale is highly mathematical, which has allowed for predictions to be made far before the technology required to test them exist. This has caused some stir in regard to epistemology, as so much is being derived without the need for experiment, yet the predictions are almost always spot on.

 

There is actually a set of experiments which are designed to figure out if QM is purely statistic, or if there are hidden variables. Though there are still a few experiments that need to be done to ensure there aren't hidden variables, so far it looks like QM is purely statistical.

 

Because of this, I am very skeptical of there being a theory which could make sense of it all. Once all of the tests are performed, it is most likely that any new theory which explains something more will have to contain QM.

 

http://en.wikipedia.org/wiki/Bell%27s_theorem

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

 

With that said, QM doesn't really make sense to our human minds because we didn't evolve that capacity. Classical mechanics makes plenty of sense because it deals with a lot of concepts that we evolved to understand. Scientifically, all that matters is that QM makes sense on a mathematical level, which it does completely.

[Matthew Ed Moran]

With that said, QM doesn't really make sense to our human minds because we didn't evolve that capacity. Classical mechanics makes plenty of sense because it deals with a lot of concepts that we evolved to understand. Scientifically, all that matters is that QM makes sense on a mathematical level, which it does completely.

 

What specifically do you mean QM does not make sense to us? Are you saying that logical laws such as the law of identity "break down" at the quantum level? I have heard this phrase used before, and I have a problem with the epistemology I think it implies.

 

As I understand it, the purpose of science is to attempt to form true theories of cause and effect about the external world. A theory contains premises, and deductions from those premises.

 

A theory is true when it is both internally consistent (valid) and has true premises. A theory can be proven false when it is shown to be internally inconsistent (all invalid theories are false), or when any premise which is not the result of prior deductions is contradicted by empirical evidence. Therefore, any valid theory whose conclusions are false must contain one or more false premises. I am guessing you know this, but I just wanted to lay it out.

 

My logic says that if the mathematics of QM are valid, and if a conclusion of QM is that the law of identity is false, then one ore more premises of QM must be false. Because the law of identity is a necessary premise of all valid scientific inquiry, for any theory to conclude that that the law of identity were false would prove that theory internally inconsistent. It would have a conclusion which is inconsistent with a premise of the theory.

 

Does that make sense? I am not a physicist, but I am curious how a theory could "prove" the law of identity false (even if it were just in the instance of the observations of that particular theory) without self-detonating, since all scientific inquiry necessarily relies on the law of identity for its validity and therefore its truth content as an explanation of empirical reality.

 

Since you said that "scientifically, all that matters is that QM makes sense on a mathematical level" I am not sure you are aware of the difference between validity and truth in this instance, because the math of a theory could very well be valid, but if a premise of the theory were untrue or in contradiction with another premise or the conclusion, then the theory would still be false.

 

My points would be true regardless of the predictive power of QM, because a false theory could still have predictive power (and this would likely mean there is something useful about the theory).

 

Last thing:

 

"Classical mechanics makes plenty of sense because it deals with a lot of concepts that we evolved to understand"

 

What do you mean by this? It sounds as if you think there are some set of concepts which are "out there" in a platonic sense, which we evolve to understand, when it would seem concepts are a product of our mind, not external reality.

 

Thanks for taking the time to read my post.

[Carl Green]

Thanks Pepin, you covered it beautifully.

 

This is partly why QM is so confusing, as all of the experiments meant to disprove it end up confirming it.

 

This is pretty much what I was talking about. Since we can't just 'see' what's going on down there, we have to do experiments to find out what's not going on, and like you're saying, it's done by finding out what it isn't. (which when there are unkowns it means the possibilities of what IS going on, are practically infinite so how can you finally know what it actually is, and not just what it's not)

[Susana]

Have you guys seen all the articles coming out about Black holes and CERN? thoughts?

[Romulox]

Have you guys seen all the articles coming out about Black holes and CERN? thoughts?

 

The last time I heard that issue come up, the consensus was that any black holes formed by CERN would be a fraction of the size of a proton, in which case it would evaporate almost instantly.  Though there were a few outliers who thought CERN would form a black hole that would sink to the center of the earth, slowly growing in size until it gobbled up the entire earth a few years later. 

 

Since that theory was fairly well known a few years ago, I can only assume the black hole has finally reached its critical size and the apocalypse is nigh

 

Do you have some links to any good articles on the subject?  Hopefully something that will relieve my fears of impending doom...

[Pepin]

What specifically do you mean QM does not make sense to us? Are you saying that logical laws such as the law of identity "break down" at the quantum level? I have heard this phrase used before, and I have a problem with the epistemology I think it implies.

 

As I understand it, the purpose of science is to attempt to form true theories of cause and effect about the external world. A theory contains premises, and deductions from those premises.

 

A theory is true when it is both internally consistent (valid) and has true premises. A theory can be proven false when it is shown to be internally inconsistent (all invalid theories are false), or when any premise which is not the result of prior deductions is contradicted by empirical evidence. Therefore, any valid theory whose conclusions are false must contain one or more false premises. I am guessing you know this, but I just wanted to lay it out.

 

My logic says that if the mathematics of QM are valid, and if a conclusion of QM is that the law of identity is false, then one ore more premises of QM must be false. Because the law of identity is a necessary premise of all valid scientific inquiry, for any theory to conclude that that the law of identity were false would prove that theory internally inconsistent. It would have a conclusion which is inconsistent with a premise of the theory.

 

Does that make sense? I am not a physicist, but I am curious how a theory could "prove" the law of identity false (even if it were just in the instance of the observations of that particular theory) without self-detonating, since all scientific inquiry necessarily relies on the law of identity for its validity and therefore its truth content as an explanation of empirical reality.

 

Thanks for putting in the time with your post.

 

Nothing in QM proves the law of identity to be false, it is just that describing the results in non-mathematical terms give the impression that it is being violated. To put it this way, QM is a purely mathematical theory, meaning that everything is described by equations, and mathematics is in many ways based on the laws of identity.

 

Where it gets confusing is that the math is a little complex and you need to understand a decent amount about knowledge about classical physics and especially waves. Statements like "the spin is up and down at the same time until the electron is measured" sounds wrong on the offset, but if you actually go through the math it follows.

 

I had a decent understanding of QM from the layman's point of view and was looking for something more in depth. I ended up finding the video series linked below, and I was really surprised because so many of the odd statements that people made about QM actually come from the formulas and make complete sense to say. If you have any mathematical experience, I'd advise watching it. The first couple of videos is explaining how the math works because QM uses mathematics that aren't very common in other areas, but eventually you get into the areas of interest, and so long as you understood the previous sections, it makes sense. Of course not on a intuitional level, but on a logical/mathematical level.

 

[Pepin]

Since you said that "scientifically, all that matters is that QM makes sense on a mathematical level" I am not sure you are aware of the difference between validity and truth in this instance, because the math of a theory could very well be valid, but if a premise of the theory were untrue or in contradiction with another premise or the conclusion, then the theory would still be false.

 

My points would be true regardless of the predictive power of QM, because a false theory could still have predictive power (and this would likely mean there is something useful about the theory).

 

Last thing:

 

"Classical mechanics makes plenty of sense because it deals with a lot of concepts that we evolved to understand"

 

What do you mean by this? It sounds as if you think there are some set of concepts which are "out there" in a platonic sense, which we evolve to understand, when it would seem concepts are a product of our mind, not external reality.

 

Thanks for taking the time to read my post.

 

My first post is awaiting approval due to length.

 

When I say that all that matters is that it makes sense on a mathematical level, I mean that we need to judge the theory based on math and not words. The math describes particles being in many places at once, which when said in words makes little to no sense as it contradicts our everyday experience, but you don't want to judge the statement in terms of words and instead want to delve into the math.

 

I kind of discussed this in a previous post, but given that a model describes reality to some degree, it cannot be considered false. The truth or falsehood of a theory is determined by the relation of the theory to reality. A false theory will have little to no relation, while a true theory will have a decent relation. A theory is not expected to model all circumstances to be true, it just needs to model some circumstances within some known margin of error.

 

For instance, classical mechanics has a high relation to reality, but it is not entirely accurate. As you approach light speed, the theory begins to diverge by quite a lot. Though the theory lacks predictive power at these speeds, it does not mean that it is false, rather it means that it is less accurate in those ranges or that it isn't applicable in those ranges. Special relativity is a theory which can account for this discrepancy in classical mechanics, making it more accurate, but that wouldn't imply any falsehood on classical mechanics. Special relativity is just an improvement.

 

As far as the last part, I mean that cosmology and QM had no role in the evolutionary development of humans. Classical mechanics did. When throw an object, we are using basic Newtonian physics to calculate how to throw it. On a more basic level, our genes produce brains that can deal with a 3 dimensional world. Our genes do not condition us to live in a 4 dimensional world despite it being more accurate because the 4th dimension plays almost no role in survival. Understand that I do not mean any of this in a conceptual manner, dogs for instance use classical mechanics to catch balls, but they have ideas what they are doing. Many mammals when born will travel to the nipple and begin sucking despite having no understanding of what is happening.

Have you guys seen all the articles coming out about Black holes and CERN? thoughts?

 

Anything particular?

[TheRobin]

 

The math describes particles being in many places at once, which when said in words makes little to no sense as it contradicts our everyday experience

 Maybe I'm just arrogant and daft here, but it makes quite a lot of sense to me actually.

 

To use Stef's example with the invisible spider. If you claim that a spider is sitting on your hand, but no instrument can measure it's existence, then we must conclude that the spider is actually identical to not existing at all (as it has all the characteristics of non-existence (well, mainly, a lack of characteristics ofc)).

 

And similarly, since the Heisenberg Uncertainty Principle tells us that we can't know location and impulse of things more precisely than a specific given number then, for all intents and purposes, statistical probabilities of stuff being in more than one location is effectively how things are at that level.

 

It would be similar to putting 10 tennis balls into a black box that doesn't allow for any information or radation to pass through and then put the box on a spinning wheel to keep it in constant motion. Since we no longer have access (can't measure) to the location and impulse of the tennis balls, then for all intents and purposes they become a purely statistical phenomenon without any clear impulse and location that we could define accurately at any single point and it would stop makng any sense to still treat them as everyday objects so to speak, because we can't apply the characteristics of everyday object (i.e. precise knowledge of location and impulse) to them anymore.

[FriendlyHacker]

Matter = Any particle not traveling at the speed of light
Light = A specific wavelength in the electrophotomagnetic spectrum, usually reffered to as the visible light spectrum

And similarly, since the Heisenberg Uncertainty Principle tells us that we can't know location and impulse of things more precisely than a specific given number then, for all intents and purposes, statistical probabilities of stuff being in more than one location is effectively how things are at that level.

The uncertanty principle is not a description of how the Universe works, is a description of the limitations in quantum mechanics to properly describe the Universe, there are other explanations for the cat problem that do not require many worlds.

Maybe I'm only getting that impression about modern science because it's the only one I've experienced, but what I'm talking about is when someone gets an idea of how they think it is, they test to see if they're right.

 

Major breakthroughs happen by accident, and the reason they are breakthroughs is because nobody thought whatever happened could be possible. A lot of theoretical physics seems like guessing, because it is guessing. The difference is that it only becomes science after the guess has been shown to be a good description of how the world actually works

[TheRobin]

 

The uncertanty principle is not a description of how the Universe works, is a description of the limitations in quantum mechanics to properly describe the Universe, there are other explanations for the cat problem that do not require many worlds.

 

But if you can't get a more precise description, then what's the difference?

 

Also from what I understand, "particles" do get an increase in momentum if the location where they could be is limited. Like, electrons don't stick to the atomic core, cause the less possible locations it could be as it gets there means that its momentum will just increase, hence it will never stick to the protons, despite if EM forces dragging it there.

 

Also not sure how this requires the many worlds interpretation to be valid.

[Guest Gee]

Hi guys.

I'm rounding of a degree in physics, perhaps I can help.

 

With regards to the uncertainty principle, it is not fundamentally a quantum effect, it is a wave phenomenon as applies to all wave motion (such as waves in an ocean, or the wave of a hand).

 

Schrodinger's equation is a wave equation. It describes the behavior of particles as a wave. This is not to be confused as meaning that the particles are waves, just that their behavior can be described as waves.

 

Returning to the uncertainty principle, it basically says there are paired variables of a particle, position with momentum and energy with time, and that there are limits to what can be known about one given knowledge of the other.

 

For example..............Position-Momentum

 

Position (a point in space) contains no information about direction or speed.

Momentum (direction and speed) contains no information about position.

 

The more known about the position, the less known about speed and direction and visa-versa.

 

Consider a picture of a car perfectly in focus. 

Given that it is perfectly in focus we can say with great certainty where the car was at the time the picture was taken (position), but next to nothing about its speed or its direction, it could be not moving or driving forward or back but we could not know.

Now consider the same picture but the car has come out a blur, we can now say the car is moving and in which direction (momentum) but we can say a lot less about exactly where the car was when the picture was taken (position).

 

Given this limitation does it mean that the car has more momentum in one picture than the other? The short answer is no, what is limited is our ability to describe the car given the information available to use through measurement (the picture).

 

 

As for particles being everywhere.............

 

We really don't know where anything is until we measure where it is (silly i know). 

Because QM particles move around in space in order to describe their behavior we have to measure them over and over and over again and then create a mathematical description of their behavior in said space.

When they are measured repeatedly the particles are found to be in different places with varying probabilities.

So to describe their behavior it is most appropriate to use a probabilistic description.

Consider an particle in a box.

Using a probabilistic description of the particles behavior within the box leads to the following conclusion (after measurement), there is a non zero probability of the particle being at any point within the box, or, when we measure the position of the particle it may be anywhere within the box, which is different to saying it is everywhere within the box.

As QM particle motion is described by wave equations, we then say that upon measurement the particle collapsed from a wave which could be anywhere to a particle which can only be in one place.

 

 

With regards to the cat.....

 

Schrodinger's cat is a thought experiment to describe a property of a class of quantum particles called spin.

Spin may have two values, up or down (dead or alive).

It may not be both.

When experiments measure spin it turns out there is a 50/50 chance of spin being up or down and this spin state of the particle changes in a non predictable manner (it is not a persistent characteristic like charge or mass).

Of course this reallllllly confused physicists.

Schrodinger's cat is an analogy of spin.

Though we may not know the state of the cat (spin), the cat certainly is either alive or dead (up or down), it can not be both.

 

 

Both string theory and the many worlds theory (of which there are many) are lacking any experimental verification and I agree with pipen, the state of scientific education is awful. 

[TheRobin]

Hey gSmtih, First of all. I'm really happy to hear someone with an actual physics degree participating in the conversation

So maybe you can explain me this then, cause form a physics lecture (link below) I had it explained to me that the uncertainty principle actually does generate a force if the possible location was small enough. This was given as the reason why in a hydrogen atom the electron doesn't just stick to the proton for example.
(see this

(don't let the title of the lecture confuse you though, the first point he makes is about eh uncertainty principle)ç

In general I found the whole Phyiscs-x series quite intersting, as it tries to show the concepts without much of the (heavy) math, while still giving some clear experimental setups and all.

 

[Guest Gee]

No Worries theRobin.

 

I can see the confusion, he is wrong.

 

To clarify, the uncertainty principle relates to the limits of knowledge about a system, not the characteristics of the system. It more formally states the product of position and momentum must be greater than or equal to the reduced phlank constant divided by two. This limit is due to the characteristics of the system, not due to the uncertainty principle being a fundamental law.

 

The reason electrons do not merge with atomic nuclei  results from the angular momentum of the orbiting electron, at a basic level the same reason satellites can orbit the earth.

 

Electron orbits are a tou

ch more complicated though, Niels Bohr demonstrated that electron angular momentum are quantised and therefore electron orbitals are also quantised (the Bohr radius).

 

Being that the angular momentum and orbitals are quantised, minimal uncertainty of both may be related by Heisenberg's principle.

 

It's a touch mathematical, but here is a derivation by Kahn academy (i'm not sure if the embedded worked).

 

https://www.youtube.com/watch?v=7Zin8hG9Nhw

[TheRobin]

In a way that's not really helpful at all, though I appreciate the answer. But given that the guy is a Prof at a university and giving a lecture on the topic, simply saying "he's wrong" isn't really adding much.

 

But okay, let me ask you this then, if it's just limits of knowledge, then you could easily get around that with certain setups in experiment, by letting an electron without angular momentum get to the proton (and then  stick to it), then you'd know the exact momentum and have a really small delta on the location too, which accoridng to the prininciple shouldn't be possible, as that would give you a zero value, where the principle demands something greater than zero.

So, is the Uncertainty principle therefore only valid for certain experimental setups then?

[FriendlyHacker]

The way I see in the uncertainty principle, is not of a limit of how much it can be known about a system, but a limit of what can be known with our current technology. The interference problem is a solvable problem, and the way to approach it is to actually try to solve it, instead of assuming that nothing more can be known about the system.

[Guest Gee]

The way I see in the uncertainty principle, is not of a limit of how much it can be known about a system, but a limit of what can be known with our current technology. The interference problem is a solvable problem, and the way to approach it is to actually try to solve it, instead of assuming that nothing more can be known about the system.

 

Uncertainty in physical systems of interest? Absolutely, better measurement techniques yield would be fantastic.

 

Heisenberg's principle of uncertainty is a physical limit because of the physical limits of the quantum system. Given the quantised nature of reality, there are limits to information on complimentary variables yielded by simultaneous measure because of the limits of nature, not of measurement.

 

What I would like to convey, is that this limit is set by the system, not set by Heisenberg's principle.

When one states that Heisenberg's principle has been violated or would be violated by a proposition, it is really a short hand way to say that the proposition violates the fundamental properties of nature and the proposition is therefor unphysical. 

 

 

In a way that's not really helpful at all, though I appreciate the answer. But given that the guy is a Prof at a university and giving a lecture on the topic, simply saying "he's wrong" isn't really adding much.

 

But okay, let me ask you this then, if it's just limits of knowledge, then you could easily get around that with certain setups in experiment, by letting an electron without angular momentum get to the proton (and then  stick to it), then you'd know the exact momentum and have a really small delta on the location too, which accoridng to the prininciple shouldn't be possible, as that would give you a zero value, where the principle demands something greater than zero.

 

So, is the Uncertainty principle therefore only valid for certain experimental setups then?

 

I would like to point out that I did not simply say he is wrong. I said he is wrong about his statement of the principle of uncertainty, I explained that electrons do not spiral into the nucleus because of the angular momentum of the electron and I linked the least intensive mathematical derivation of why this is so, which, is a mathematical proof. 

 

To briefly go through the history of the atomic model.....

 

Thomson's plum pudding model.

Electrons should stick to the protons like a plum pudding.

Experimentally disproved, electrons orbit the nucleus.

 

Rutherford model of the atom:

Electrons do not spin into the nucleus because electrons have angular momentum analogous to that of the earth as it orbits the sun.

This explains why electrons do not spiral into the nucleus BUT predicts that electrons may orbit at any distance from the nucleus at any velocity permissible by such an orbit.

Experimentally disproved, elections do not orbit anywhere they want too but are constrained to certain regions.

 

Rutherford-Bohr model of the atom:

Electrons do not spin into the nucleus because electrons have angular momentum analogous to that of the earth as it orbits the sun.

Electron angular momentum is quantised THEREFORE only certain orbits are physically permissible because of this quantisation of angular momentum.

 

Given that electrons behave as waves, they may be described by wave mechanics (mathematics to describe wave motion).

Given that they may be described by wave mechanics, the uncertainty principle of complimentary variables applies (as it does in all wave motion).

Given that momentum is quantised there is a physical limit on permissible momentum values (discovered by Niels Bohr).

This physical limit due to the quantised nature of momentum sets the limit expressed by the uncertainty principle.

This limit in uncertainty is called Heisenberg's uncertainty principle.

 

So Heisenberg's principle of uncertainty constrains the information knowable about complimentary variables when those variables are measured simultaneously because those variable may not take any value.

 

With regards to your example, position and momentum have not be measured simultaneously therefore H.U.P. does not apply.

[A4E]

I see that black holes have been mentioned so I thought I would share what I have come across on them.

If it does not fit in here then tell me to delete it or something.

 

This guy says that black holes do not exist.

And a google search brings up more interesting sources on challenging the black hole.

 

What is your take on this?

[SigmaTau]

"...The way I see in the uncertainty principle, is not of a limit of how much it can be known about a system,.."

 

There is a misconception (although lightly) about "uncertainty". It is used in 2 concepts

 

1) for QM At the time of measurement all properties will be EXACTLY known (speed and position) , its called "the collapse of the wavefunction"  ,

BUT where the particle will "choose" the exist is not exactly predictable , it is only known through probability. 

 

2) This is the biggest misconception,  it says that position vs impulse (velocity)  or  (energy vs exitation-time) cannot be exactly known at the same time.. this wording is false as it has nothing to do with (1).  It means that with repeated measurements (ensemble) the PRODUCT "variance" (the statistical property variance) of "position" and variance of  "momentum"  are a constant.

A lot of layman confuse 1 with 2. On the other hand i don't know if I explained it well enough without using mathematics. 

[hannahbanana]

Hi I wanted to pose some open questions for those of you who have a good knowledge and understanding of science and physics.  In my opinion, modern physics and cosmology has become a total mess, full of internal contradictions, and unresolved conflicts between different departments competing for grant money, and where most of the funding and energy is put towards exploring concepts which have no tangible relation to concrete reality, such as super-strings, dark matter/energy, virtual particles, black holes, and so on.  But I don't want to argue that for the time being.  I want to start at the foundation of physics, and see if we can parse out this confusion, and determine if my concerns are legitimate or not.

 

Can anyone tell me what are the proper rational definitions of the following terms:

  Matter

  Energy

  Space

  Light

  Mass

  Charge

 

As far as I can tell, these concepts form the foundation of physics.  Have I missed any?

I might also recommend that on top of learning the basic concepts used in physics, also look at the Laws of Physics, which are the real useful things that basically all mathematics of physics is built upon by applying further assumptions or simplifications. This would include Newton's Laws of Motion, the Laws of Thermodynamics, Coulomb's and Gauss' Laws of Electrostatics, and also Einstein's theory of relativity (all of which we can find by googling "laws of physics"). These all basically apply universally, except when you're talking about things that are close to the speed of light or things that are very very small. Now, it's been about a year and a half since I've finished my Physics classes so I may have forgotten some things, but I'm pretty sure I'm correct on this and would love to know if I'm not

[Guest Gee]

I see that black holes have been mentioned so I thought I would share what I have come across on them.

If it does not fit in here then tell me to delete it or something.

 

This guy says that black holes do not exist.

And a google search brings up more interesting sources on challenging the black hole.

 

What is your take on this?

 

Really interesting video, thanks for the link.

 

The guy is right, the physics of black holes is incomplete and the current theories of black holes is incompatible with existing physics, notably existing thermodynamics (if Hawking is to ever receive a Nobel, he would have to demonstrate his theories are consistent with thermodynamics).

 

Also the chap raises some interesting points about "Einstein's" theories, something wonderfully expounded upon a book I happened to find in my university library (incredible referencing in the book).

http://www.amazon.co.uk/Albert-Einstein-The-Incorrigible-Plagiarist/dp/0971962987

[SigmaTau]

Khan academy is nice)) various subjects,. I believe Khan is a physicist himself.

[Guest Gee]

SigmaTau is absolutely right, Khan academy is fantastic.

 

If you realllllllllly want to know about physics might I sugest the following?

 

 

Physics for scientists and engineers:

http://www.amazon.co.uk/Physics-Scientists-Engineers-Modern/dp/1292020768/ref=sr_1_2?ie=UTF8&qid=1435256023&sr=8-2&keywords=physics+for+scientists+and+engineers

 

Physics for scientists and engineers, a student work book:

http://www.amazon.co.uk/Physics-Scientists-Engineers-Student-Workbook/dp/1447971353/ref=sr_1_2?ie=UTF8&qid=1435256048&sr=8-2&keywords=physics+for+scientists+and+engineers+workbook

 

These two books would set you back maybe £100 ($160?) and would cover all the broad physics you would student in the first two years of university! And there really accessible. Supplement that with Khan academy and this forum and in no time you'd have a fantastic knowledge of physics!