Definition of a Law?

[lolwatever]

salams ppl, just curious

u know physical laws right... i was readin sumwhere that its defined as:

"A Law of Nature is, by definition, something which holds true in all cases, no matter how hard you look, no matter what precision you use and no matter where in the universe you go. It doesn't mean "It works like this in some cases if you don't look too hard, if you don't look in too many places and if you don't look too closely."


my question is...doesn't that entail that its impossible they're wrong? I mean if it was possible that it was wrong, whats the diff between a law and a theory? :?

Examples of laws that i have in mind for example is law of conservation, laws of thermodynamics, newtons laws of motion etc?

 

[Abdul Fattah]

Well the first important thing here is to look how laws are constructed. In science all laws are based on empirical testing. That means we look at what happens. Take Newton's laws. He studied the way that gravity works, and after carefull examination found that bodies always interact in a certain ratio so then he formed that ratio into an equation. For example Newton's second law of mechanics:
F = dp/dt
That law is part of Newton's theory of gravity. And generally people assume that that law always apply to bodies of mass. However when examining bodies with high speed and high mass then suddenly Newton doesn't cut the mustard and we need Einsteins relativity. So no a theory does not always work. People who claim so forget the empirical research part. In mathemetics we're thought that in order to proof something you need to either construct a general proof that applies to all cases or construct a proof for every single possible variation of that something you want to proof. Now if we form theories without look at all possibilities (like Newton forming a theory of gravity without looking at extreme situations like black holes with high density and low volume) then it's possible that the theory is flawed. So because we base our theories on (limited) empirical tests; to claim a theory is never wrong would thus be very wrong.

Also note that there are different "theories"
For example the theory of gravity is a mainstream physics theory.
The M-theory is a proposed physics theory.
The watchmaker theory is a philosophical theory.
Functionalism is a sociological theory.

Just because they are all named theory doesn't mean they are all equally accepted or strong. A common mistake is pro-evolution theorists claiming that evolution is equally strong a theory as the theory of gravity is. Which for various reasons it is not.

More info here:
http://en.wikipedia.org/wiki/Physical_theory
http://en.wikipedia.org/wiki/Physical_law

 

[sevgi]

Examples of laws that i have in mind for example is law of conservation, laws of thermodynamics, newtons laws of motion etc?

sorry to change the topic but jst have to say that u sure do love ur physics.

 

[lolwatever]

Salams bro steve, jazaks 4 input

Seeing your basing the analysis on newton's law, i think you made a small error,

Newton's second law actually is:



What you're talking about is F=ma which is relationship between mass and acceleration when 'mass is constant'... which was never actually a law. F=dp/dt actually holds on a relativistic scale, hence the law remaining intact.

F = dp/dt seems to fit the definition i gave in my first post, and henc emy question 'doesnt the fact its called a law mean that its impossible it's wrong'


?


Jazaks!!

 

[lolwatever]

btw here's how Newton's 2nd law (i.e. F=dp/dt) holds on a relativistic scale..

http://www.geocities.com/physics_world/sr/force_trans.htm

btw i've never studied relativity, i'm just posing questions based on some reading i done so yeh not tryin 2 pull off an act here that i'm a relativity genius

 

[Abdul Fattah]

Salams bro steve, jazaks 4 input

Seeing your basing the analysis on newton's law, i think you made a small error,

Newton's second law actually is:

Euhm... how is this different from what I wrote?

F = dp/dt seems to fit the definition i gave in my first post, and henc emy question 'doesnt the fact its called a law mean that its impossible it's wrong'

Well like I suggested, try this formula inside a singularity. there the mass is so high that gravity plays an important role but at the same time the volume it takes up is so small that you need quantum mechanics, and using both you get nonsensical results. So it is safe to say at least one of the two laws is inaccurate.

 

[lolwatever]

ohhh oops lol i thought u said F=dp/dt was his theory of gravity when i read the line after it lol.... sorry akhee! :hiding:

Well like I suggested, try this formula inside a black hole and you get nonsensical results. So it is inaccurate at least.

Isn't a black hole case an example of us needing to treat it as a relativity problem? So that F=dp/dt still holds in that situation.

Or is it that you mean 'nonsensical' results because you get thing slike negative mass? in which case dere's this paper i read a while ago that explains it has logical implications.. ill plug it here if i find it.

 

[Abdul Fattah]

Isn't a black hole case an example of us needing to treat it as a relativity problem? So that F=dp/dt still holds in that situation.

Or is it that you mean 'nonsensical' results because you get thing slike negative mass? in which case dere's this paper i read a while ago that explains it has logical implications.. ill plug it here if i find it.

I didn't mean the relativity problem. I had already edited the previous post before I read your reply. I think now it should be more clear.

 

[lolwatever]

^ oh ok i read the updated post,

fair enough, in that case, how is it that either of the laws must be false?

It's just that the equations of transformation between quantum and relativistic scales havn't been discovered yet.

Just like the lorenz transformations make the link between classical and relativitsitc theory, the mystery now is to find the equations that make the link between quantum and relativity.

At the moment, or atlesat till these equations are discovered, we just treat the problem as either quantum or relativistic, the introduction here explains what im tryin to say in better detail i guess
http://arxiv.org/PS_cache/gr-qc/pdf/0603/0603110.pdf

So point is, just because we don't have the link between the two 'realms', doesnt mean that either of the laws fail.

Allahu alam,

salamz


ps: btw i dont think this is going off topic right? coz it's important to the idea of 'laws being correct no matter wat'

 

[Abdul Fattah]

^ oh ok i read the updated post,

fair enough, in that case, how is it that either of the laws must be false?

It's just that the equations of transformation between quantum and relativistic scales havn't been discovered yet.

Just like the lorenz transformations make the link between classical and relativitsitc theory, the mystery now is to find the equations that make the link between quantum and relativity.

Yeah I know, that's why I used the word innacurate rather then false

 

[lolwatever]

Yeah I know, that's why I used the word innacurate rather then false

oh ok cool! , but then it means they're still laws ?

Like i dont see how we could say that 'either of einsteins relativity or classical theory' are inaccurate because we dont hav the transformation equations (lorenz's equations of transformation)

if you do agree with that bro, so doesn't it mean that a law by definition is correct? Otherwise its just a theory...

Also bro, btw, am i wrong to assume that 'every law is a theory, but not every theory is a law'? :?

jazaks!
tc

 

[Abdul Fattah]

oh ok cool! , but then it means they're still laws ?

Like i dont see how we could say that 'either of einsteins relativity or classical theory' are inaccurate because we dont hav the transformation equations (lorenz's equations of transformation)

Well we can't say, for all we know transformations might not cut it and we might have the revise the theories. For example there could be a part of the formula missing that results into a factor "1" in normal conditions. If such a thing were the case then the formula would work on simple situations but not on the extreme situations were the factor would not be one. Of course that's all hypotecal. Point is, the way it is now it's not good enough.

if you do agree with that bro, so doesn't it mean that a law by definition is correct? Otherwise its just a theory...

A law refers to an equation that describes by what ratio causal events effect one another. A theory usually refers to much more then just the law itself.

Another thing, if the source of that causality, the enforcer of causality no longer enforces that causality then the law is no longer accurate.

Also bro, btw, am i wrong to assume that 'every law is a theory, but not every theory is a law'? :?

If a law is not part of a theory then it is rather pointless. I could tell you qwerty=abcd/efgh and propose it as a law, but without a decent theory explaining that equation it would be rather pointless.

 

[lolwatever]

sorry i'm replying back to front... i understood your post better backwards hehe

A law refers to an equation that describes by what ratio causal events effect one another. A theory usually refers to much more then just the law itself.

Another thing, if the source of that causality, the enforcer of causality no longer enforces that causality then the law is no longer accurate.

So in other words, the law is no longer a law as such ? :?

my question is... has such thing ever happened?

Well we can't say, for all we know transformations might not cut it and we might have the revise the theories. For example there could be a part of the formula missing that results into a factor "1" in normal conditions. If such a thing were the case then the formula would work on simple situations but not on the extreme situations were the factor would not be one. Of course that's all hypotecal. Point is, the way it is now it's not good enough.

hmm but that's too speculative isn't it?

From the little i read, the problem with finding the relationship between quantum and relativistic properties is that there's so many higher order inordinary differential equations to account for (and they are literally hard to solve). As well as other forms of equations (e.g. difference equations.. i dunno wat they mean by difference equations)

The problem is to try account for those differentials... i dont think researchers are even thinking about possibility of there being a factor unaccounted for in F=dp/dt isn't it?

coz keep in mind, it was real easy with regards to the lorenz transformations since lorenz was dealing with ordinary first order equations. not the ugly partial differentails facing new researchers....

DISCLAIMER: *im not underestimating the effort put in2 figuring out the lorenze transforms... but u get wat i mean lol* :hiding:



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Getting back to the point, my question is, based on that wiki definition u gave of a law:

• True. By definition, there have never been repeatable contradicting observations.
• Universal. They appear to apply everywhere in the universe. (Davies)
• Simple. They are typically expressed in terms of a single mathematical equation. (Davies)
• Absolute. Nothing in the universe appears to affect them. (Davies)
• Stable. Unchanged since first discovered (although they may have been shown to be approximations of more accurate laws—see "Laws as approximations" below),

Meaning that they can never be disproven if declared to be a law? right?''


jazaks so much bro 4 ur patience with me!

 

[Abdul Fattah]

Meaning that they can never be disproven if declared to be a law? right?''

Well who knows. We don't know the reason behind the laws (why is F=dp/dt?)
So far every time that we tried teh formula worked. So that means that the reason behind the formula (the reason why F= dp/dt) remains present. But we have no gaurantee that it always will. In philosophy we say: just because the sun came up every morning so far is no guarantee that it will come up tomorrow.

 

[lolwatever]

The reason is actually mentioned here (screenshot from one of my lec slides):



In wiki, newton further goes on to say:

If a force generates a motion, a double force will generate double the motion, a triple force triple the motion, whether that force be impressed altogether and at once, or gradually and successively. And this motion (being always directed the same way with the generating force), if the body moved before, is added to or subtracted from the former motion, according as they directly conspire with or are directly contrary to each other; or obliquely joined, when they are oblique, so as to produce a new motion compounded from the determination of both.

so infact the "reason behidn the law" is actually the law, F= d(mv)/dt = dp/dt was derived as a consequence of that reason. Wiki makes an interesting point that if we wanna be raelly picky.... the above quote is the law, F=dp/dt is just mathematical interpretation of it.

But we have no gaurantee that it always will. In philosophy we say: just because the sun came up every morning so far is no guarantee that it will come up tomorrow.

That's coz we simply can't predict teh future according to another law, Heinbergs Uncertainty Principle* innit :? Doesnt necessarily mean that the laws are false.



Allahu alam... but i really got a strong feeling from the wiki definition and others that laws are laws, will hold as long as everythign else is constant




* After a lil more thinking, it's not, it's more to do with teh definition of the term 'to know'. You don't know that something will happen unless you can prove the event exists in spacetime. Which is impossible unless you're time independent.

 

[Abdul Fattah]

The reason is actually mentioned here (screenshot from one of my lec slides)
In wiki, newton further goes on to say:

so infact the "reason behidn the law" is actually the law, F= d(mv)/dt = dp/dt was derived as a consequence of that reason. Wiki makes an interesting point that if we wanna be raelly picky.... the above quote is the law, F=dp/dt is just mathematical interpretation of it.

That is not a reason. Newton, found that bodys with mass attract one another in a certain ratio and found the formula that describes this. But he didn't know why bodies with mass attract one another (and neither do we). Find out the why, and you will know wheter or not the law can be broken.

That's coz we simply can't predict teh future according to another law, Heinbergs Uncertainty Principle innit :? Doesnt necessarily mean that the laws are false.

Well that also means we cannot predict that the law will still be applicable in the future.

 

[lolwatever]

That is not a reason. Newton, found that bodys with mass attract one another in a certain ratio and found the formula that describes this. But he didn't know why bodies with mass attract one another (and neither do we). Find out the why, and you will know wheter or not the law can be broken.

salams bro!

Ok i done a bit of reading b4 because it was a thought-provoking question mashalah... my question is:

Are you sure we need to know 'why' in order to knwo whether it can be broken? :?

I read a couple sources, the bset seems to be this (source), its straigh tto the point and xplained that the validity of the law rested upon the ability to measure "previously undetected masses in the solar system".

The continual success in the application of Newton's law of gravitation led to the theory becoming so indisputable that any observed deviations were seen as evidence for previously undetected masses.

which seems to make sense if it was going to be labelled a law right?

Well that also means we cannot predict that the law will still be applicable in the future.

That's my question, if what you said is true, why is a law then defined as being 'true' and 'universal' and 'absolute'?

jazaks!
tc

ps: after thinkin a lil more about the sun example u gave me, it's not to do with heisenbergs principle coz that's at quantum level, it's more to do with the simple fact you do not "know" (in the true sense of the meaning) that something will happen unless it did and you're aware of it. I can throw a rock and predict it's going to fall on the ground, but i don't know it will till it does. It's more of a philosophical point rather than physical one.