Atoms and Programming: Exploring the Unknown

[alxm]

jgm340: You're not talking about science there, IMO you're making a rather confused point about semiotics, not physics.

 

[jgm340]

jgm340: You're not talking about science there, IMO you're making a rather confused point about semiotics, not physics.

No, I am making a point about physics.

If I ask you: (i) "What is force?", you might say: (ii) "It is a quantity which measures the relationship between acceleration and mass, described by the equation F = ma."

Then a similar question to that of the OP's is, (iii) "Can we say that force, as defined above, actually exists?"

It's important to note that "F= ma" is conceptual language just in the same way "relationship between" is conceptual language. Sentence 2 is describing a (supposedly) physical object by the abstract properties it is supposed to have. (Here I use object as a general term for object/phenomenon/whatever)

There is an implicit assumption that there is only one physical thing fitting the above definition. For example, "work" also involves acceleration and mass, but doesn't satisfy the equation "Work = ma".

Thus we can rephrase sentence 3 to be less ambiguous: (iv) "Does there exist a physical object/phenomenon that measures the relationship between acceleration and mass, described by the equation F = ma?"

Already we can see a problem in trying to answer this question. What, exactly, are acceleration and mass? Do we even know these exist?

The idea behind a definition, of course, is to provide an unambiguous way of tracing back to a few concepts which are taken as axioms. We like to think that mass, time, and distance as being so fundamental that we do not define them in terms of other concepts. These are basically our axioms.

Because of the way we have defined force, however, it exists by definition, so long as mass, distance, and time exist as quantities! (This step in my argument is crucial to understand).

In other words, what we can make is a conditional statement (which is definitely true) about the existence of force: (v) "If mass, time, and distance exists as quantities, then the quantity force exists". So, using the definition, question 4 actually is equivalent to this question: (vi) "Do there exist quantities mass, time, and distance?"


Here's where things get tricky. How do we know our axioms are true? How do we know mass, time, and distance exist? We have an intuitive notion of mass as being "how heavy something is", and time as being "how long I have to wait", but these are nowhere near suitable for physics. In physics, time, mass, and distance are abstract quantities. They may as well be called mygork, traujdov, and dastyern, as to not be confused with informal notions we may have about them.

(In modern physics, it turns out that time, distance, and mass are NOT fundamental independent quantities. How so? Well, the speed of light is a constant that posits a relationship between them.)

Assuming for the sake of argument that they are fundamental quantities, however, how would we know they exist? As physics is a science, it comes down to empirical evidence. Basically, we make assumptions in how we interpret our sensory information. We assume that when we put two objects on a balance, that it will balance if and only if they are the same mass. We assume that two sets each of two points are the same distance apart if and only if they measure the same on a piece of metal. We assume that if the same number of ticks of a clock happen during the start and end of two events, then they happened in the same amount of time. Basically, we define mass, time, and distance solely in empirical terms. This is the only way in which physics can claim to make statement about reality; any statement physics makes about reality boils down to a statement about what we would experience if we were to do certain things.

What we can conclude, then, is that the axioms of physics are not that "mass exists", "distance exists", and "time exists", but rather statements about the equivalence of certain things. They are statements like "It doesn't matter which balance I use", and "it doesn't matter how fast the object is moving when I use a stick to measure how long something is" and "two clocks ticking the same will tick the same number of ticks during an event no matter what". We just define mass to be a number describing what happens when we put it on a balance with other objects. We just define time to be the number of ticks that happen on the clock. So we are defining time, distance, and mass in terms of our senses, rather than taking them as axioms.

So the only axioms of physics are statements about our senses. It turns out that some of these statements are wrong! Physicists have chosen the wrong axioms in the past.

But this is precisely what physics is about! Physics is about finding a set of axioms that are actually physically true!

Now we can actually address the issue at hand. How can we say something like "mass" or "force" exists? Well, we say it exists if and only if they are well-defined. In other words, we might define "time" to be "the number of ticks that happen on a clock during the event". In order for time to be a well-defined notion, it must be that it is true regardless of the clock used, regardless of the location of the clock, regardless of the movement of the clock, etc. In other words, there must be a unique number that we can assign to any two points denoting the time between them.

What this boils down to then, is simply the question of "Do all our axioms ALWAYS hold?" If so, then we can claim that "time", "acceleration", etc actually exist as we have defined them! If not, then we cannot.

Does this make sense?

To give a final example, "mass" does not exist in the way most people would define it. Why? Because the usual axioms used to define mass aren't consistent! It is not true that there is conservation of mass!

What is an example of something that we think very strongly does exist? The speed of light. We believe that the speed of lights exists, because is agrees with a set of axioms which people haven't found fault in yet.

If something like "mass" can fail to exist in the way it is defined, then do you see why something like an "atom" could fail to exist in the way it is defined?

 

[The legend]

yes they do!

This gives chemistry resoning
http://digilander.libero.it/mfinotes/VEuropeo/Physics/atom.htm

scanning and tunneling microscope
http://en.wikipedia.org/wiki/Scanning_tunneling_microscope

 

[Drakkith]

Whether or not our interpretation/picture of atoms are accurate, they are still atoms. We know that atoms exist through observation and measurement and whatever. If something isn't quite right about our description of it, so what? It's still an atom.

If we believed the moon to be made of cheese, and once we send probes up to scoop up this moon cheese we find out it's actually rock, that doesn't change the fact that it is still the moon. It is just different than we first believed.

 

[sophiecentaur]

A rose, by any other name would smell as sweet.
If we can explain what happens in Chemistry, in an accelerator or under a tunnelling microscope in terms of the existence of atoms then we can treat them as if they exist.

You could also say the same of the negative number concept. It doesn't 'exist', in as far as you can't have less than one cow but it serves, in Maths, as a useful and very valid concept.

If you get too wound up by this sort of thing you can limit what little understanding anyone can hope to gain about any Science.

"What is it really?" and "Does it exist?" are not, actually, very fruitful questions.

Better to ask questions like "How does the model work?". That assumes they do exist and that we can see that things can be explained in terms of their existence and accepted properties. Then, if data from a later observation clashes with what we know already, we can modify our model.

 

[jgm340]

A rose, by any other name would smell as sweet.

Yes, but if you call any flower a rose, then a rose also smells like rotting flesh: http://en.wikipedia.org/wiki/Rafflesia

Better to ask questions like "How does the model work?".

Precisely! And that is what the OP's professor was trying to get across: we're working with a model. If you forget the fact that what you're working with is just a model, then you are more prone to miss opportunities to improve it.

 

[DaveC426913]

Precisely! And that is what the OP's professor was trying to get across: we're working with a model. If you forget the fact that what you're working with is just a model, then you are more prone to miss opportunities to improve it.

Theng kew.

 

[Gokul43201]

I think jtbell answer the question correctly, except he was being polite.

Precisely! And that is what the OP's professor was trying to get across: we're working with a model. If you forget the fact that what you're working with is just a model, then you are more prone to miss opportunities to improve it.

Sure. But our "model" of the atom is no more or less of a model than the models we use to explain anything else, from the forces on a table, to the path of a projectile, to the behavior of an electronic circuit.

This whole singling out of the atom as something that is just a model is just specious talk.

 

[Ivan Seeking]

I think jtbell answer the question correctly, except he was being polite.Sure. But our "model" of the atom is no more or less of a model than the models we use to explain anything else, from the forces on a table, to the path of a projectile, to the behavior of an electronic circuit.

This whole singling out of the atom as something that is just a model is just specious talk.

It's turtles all the way down.

Physics does simply produce models. It says nothing about essence. Even if we accept something as abstract as the notion that energy is really just information, we are still left with a turtle.

I am struggling to remember the scientist who famously argued this point, but isn't this idea intrinsic to the popular "practical" interpretation of QM ~ What matters are the results, not the underlying philosophical paradoxes or implications? Physics answers what?, not why? You folks seem to be directly contradicting the philosophy that emerged in opposition to the Copenhagen Interpretation, and the one that I thought was most popular.

 

[russ_watters]

Precisely! And that is what the OP's professor was trying to get across: we're working with a model. If you forget the fact that what you're working with is just a model, then you are more prone to miss opportunities to improve it.

I agree with Gokul: Why would characterizing it differently imply that we'd be prone to opportunities to miss it? "Just a model" or "just a theory" has a condescending tone to it that is not necessary. It is silly to point out to a scientist that a theory is a theory or a model is a model. It's like saying your car is just a car. It has no point unless you don't understand what a car is, so when you say that a scientist might miss an opportunity to improve a theory/model, you are suggesting they don't know that a theory/model is by definition incomplete.

And none of that has anything whatsoever to do with whether an atom is real. The two questions:

1. Is our understanding of what the atom is complete?
2. Is the atom real?

...have essentially nothing to do with each other. But if the prof referenced in the OP even simply broached either question, it implies an anti-science attitude/misunderstanding of science/scientists. So they can be answered separately but imply the same thing.

And I know I'm just repeating myself now, but:

We do not know that "just a model" was intended as a dismissal per se. That's your interpretation (of a secondhand paraphrasing).

That's the only possible interpretation. There can be no other reason for saying something is "just a model":

Giving both the OP and the prof he's paraphrasing the benefit of the doubt, I think he may simply be saying it's a model because we don't fully understand everything about it yet.

Yes, and since that's redundant and pointlesss as saying a car is just a car, the condescention is evident in the statement.

 

[Ivan Seeking]

I agree with Gokul: Why would characterizing it differently imply that we'd be prone to opportunities to miss it? "Just a model" or "just a theory" has a condescending tone to it that is not necessary. It is silly to point out to a scientist that a theory is a theory or a model is a model. It's like saying your car is just a car. It has no point unless you don't understand what a car is, so when you say that a scientist might miss an opportunity to improve a theory/model, you are suggesting they don't know that a theory/model is by definition incomplete.

And none of that has anything whatsoever to do with whether an atom is real. The two questions:

1. Is our understanding of what the atom is complete?
2. Is the atom real?

...have essentially nothing to do with each other.

And I know I'm just repeating myself now, but: That's the only possible interpretation. There can be no other reason for saying something is "just a model": Yes, and since that's redundant and pointlesss as saying a car is just a car, the condescention is evident in the statement.

I agree that the title of the thread is not the same question as that implied in the post. "Are atoms real" is not the same as asking if we understand the model. But you are missing the essential point: Physics is limited. It doesn't tell us about the essence of that studied. That is why we have philosophy. And that is why the most interesting sections in my ud QM book were the philosophical epilogues.

You can't avoid philosophical questions while claiming to offer a complete understanding of existence.

 

[russ_watters]

But you are missing the essential point: Physics is limited. It doesn't tell us about the essence of that studied. That is why we have philosophy.

And that is why the most interesting sections in my ud QM book were the philosophical epilogues.

I don't recognize that philosophy has anything relevant to say in response to those two qestions unless it wants to argue definitions (which is ultimately a useless thing to do). What you are saying might be true, but it is irrelevant to the issues being discussed here.

It's fine that you like such conundrums as 'is a photon in two places at once' - I do too. But I'm not sure if that's really within the scope of the theory. As long as the math works out and the experiments match the predictions, the interaction that makes that happen is "real". What is "the essence"? (whatever that even is) doesn't factor into the answer.

Ie, 'what is the essence of the gravitational force?' doesn't have anything to do with whether gravity is real: gravity is real. Whether it is a force carried by a particle or a biproduct of the curvature of space; either way, it is still real.

You can't avoid philosophical questions while claiming to offer a complete understanding of existence.

Science makes no such claim.

 

[sophiecentaur]

Using the words "just a model" does not necessarily belittle the Science involved. More likely, the words were used to get things in proportion and to discourage the pointless notion that we can ever get truly to the bottom of things.
If two people observe the same phenomenon they need a shared term to communicate about it. We use the term 'atom' as a single word which describes the sum total of all our experiences of things that we find inside molecules (another of those terms) which make up substances (yet another term). Yes - it's turtles all the way down -and up. Is there anything better?
Why lose any sleep about it?

 

[DaveC426913]

You can't avoid philosophical questions while claiming to offer a complete understanding of existence.

Science makes no such claim.

And frankly, I think this is the very point the professor was trying to make. To remind the students that reality is not a bunch of billiard balls bouncing off each other in well-behaved fashion.

 

[sophiecentaur]

I agree that the title of the thread is not the same question as that implied in the post. "Are atoms real" is not the same as asking if we understand the model. But you are missing the essential point: Physics is limited. It doesn't tell us about the essence of that studied. That is why we have philosophy. And that is why the most interesting sections in my ud QM book were the philosophical epilogues.

You can't avoid philosophical questions while claiming to offer a complete understanding of existence.

Don't get me started about Philosophers; they are fighting a losing battle against the Brain Scientist.
Any Philosopher who actually thinks that real Science claims to offer complete understanding should read a bit more actual Science (not a Journalist's view). The much mis-quoted Charles Darwin started his major work with the words "I think" and that represents the humble approach that all proper Scientists follow.

It's only Philosophy and Religion that offer complete answers because they are, basically axiomatic and then change the axioms to suit changing circumstances.

 

[G037H3]

>axiomatic+change axioms to suit changing circumstances

sounds like science as well.

 

[sophiecentaur]

Hypotheses + changing hypotheses - not axioms- leading to theories, or working rules.
There is a difference. The point is that Scientific theories are falsifiable. That's the basis of the system. Axioms are just axioms and not falsifiable because you can't test an axiom.
Individual Scientists are only human and they may fight tooth and nail to maintain their ideas but the basis of Science is that it allows for change - it is a continuing search with no ultimate goal because it doesn't expect to 'arrive'.
The Others all believe that someone or something can and will supply all the answers or has supplied them already. Very cosy but a bit of a cop out afaiac.

 

[G037H3]

measurements=/= perspectives



i don't see how that could be misconstrued as difficult

 

[sophiecentaur]

What am I construing as difficult?
I am just pointing out the essential between the ideal Scientific approach and that of Philosophy (and Religions) which start with axioms. And an axiom is not a hypothesis because it does not need to be tested - you just state it and work from there. Natch, they don't all lead very far but some of them (like those used in Logic) have a good track record.
Or are you answering a different post? :)

 

[Gokul43201]

To remind the students that reality is not a bunch of billiard balls bouncing off each other in well-behaved fashion.

I guess this would be just as true if you were actually talking about billiard balls. Heck, in some ways an atom behaves more like the idealized billiard ball than a real billiard ball does!