Quantum physics

[astrocuriousstudent]

Another question, Quantum Physics. how is it that the same particles are governed by two completly different sets of laws of physics? I realize there are attempts to come up with a universal set of physics, at least I think there is. But in the meantime, how can we really rely on the laws we have come up with? That logic seems akin to a student in school that finds out a way to solve a certain set of problems, but not the real way that works for everything in that unit area of study. i also realize that the microcosm is much more governed by the strong and weak nuclear forces than the macrocosm around us is so that might be why, but in anycase, could someone offer me an explanation to the rationality of relying on two different sets of physics to explain the same particles, only on different scales?

[Jay-qu]

Well in general theories are just a good explanation of the world we see around us.

 

If we can predict something through calculation and then show that it works repeatably then its a valid scientific theory. As you have realised not all theories work in every situation we can apply them to. Newtonian mechanics is a great and much simpler explanation than Einsteins Relativity, but it doesnt work when velocities start getting up towards the speed of light. Because of the nature of our everyday experience most of the time it is fine to use the simplified equations because it just doesnt make that much difference.

 

This happens with the quantum world also. One could calculate the probability of being able to spontaneously walk through a wall, but the probability would be so low that you would have to walk into it for longer than the age of the universe to have even a small chance of succeeding. Quantum effects are so small in most everyday experience that we can just ignore them.

 

Currently there is no theory that can be applied to every situation, such a thing is called a Theory of everything (TOE) or a grand unified theory (GUT) and IMO we are a long way off finding one! The main problem is being able to connect the small scale quantum world with the large cosmological scale one. The is loads of literature available on the net, just try googling some of the above terms or even 'quantum gravity' happy hunting :)

[Erasmus00]

Currently there is no theory that can be applied to every situation, such a thing is called a Theory of everything (TOE) or a grand unified theory (GUT) and IMO we are a long way off finding one!

 

It is worth noting we have a completely valid theory of (so far) everything but gravity- the standard model of particle physics.

-Will

[sanctus]

Yes, but if LHC fails to find the higgs-boson also the standard model might be no more completely valid.

[Erasmus00]

Yes, but if LHC fails to find the higgs-boson also the standard model might be no more completely valid.

 

There are higgsless models that accomplish the same thing (providing spontaneous symmetry breaking) via other fields. But its true, this would be a slight modification to the standard model.

-Will

[Little Bang]

I don't think they will find the Higgs but the human race will die still believing the standard model correct.

[Erasmus00]

I don't think they will find the Higgs but the human race will die still believing the standard model correct.

 

Why do you feel that way? Without a Higgs at LHC, some beyond the standard model physics will have to be called into play. This also sounds slightly pejorative(though I may be wrong, attitude is so hard to discern in writing), do you think something is wrong with "believing" the standard model?

-Will

[Michaelangelica]

I don't think there is any logic in quantum physics ("There's life Jim but not as we know it" -ST)

 

I think you have to have an act of faith like religion or learning a fairy tale.

Then once you assume all the crazy bits about dead cats and live cats and all that space in an atom; and an electron being everywhere at once, (sort of); and a nucleus really not being as solid lump but a sort of "bell curve" lump, you can talk knowledgeably about it at BBQs ;) and parties.:weather_snowing:

Everyrone assumes you must be intelligent as they don't understand a word you are saying. :hihi:

 

Quantum physics books like the very popular A Brief History of Time,( which stayed on the British Sunday Times best-seller list for a record-breaking 237 weeks.) by Stephen Hawking; is a bit like Karl Marx- "the most read/quoted but least understood book of all time". anon

[CraigD]

Another question, Quantum Physics. how is it that the same particles are governed by two completly different sets of laws of physics?

The short answer, I think, is that they’re not. Of the two, classical “Newtonian” mechanics and quantum physics, quantum physics is true (with an important shortcoming mentioned previously in this thread, and later in this post), classical mechanics just in approximate agreement for a limited subset of phenomena. Another way of stating this is that classical physics is applicable to special cases of the more general theory of quantum mechanics.

 

However, any talk of generally and specially true “laws of physics” needs to be preceded by a careful examination of what is really meant by science and scientific laws, and, practically, how they’re best used.

 

A core assumption of science is that anything measurable – star-sized bodies, sub-atomic particles, light, etc. – is orderly, and thus can be explained and predicted using invented formulae. The term “law of nature” or “law of physics” doesn’t mean a rule that nature is somehow compelled to follow by some cosmic police, but an observation about it that appears, within some well-defined area of experience, to be always true, or so nearly always true that it’s still useful.

 

In technical language, the term “law” is actually a weaker one than others, such as “principle” or “prediction of ____ theory”. Calling a formula a law implies a lack of understanding of why it works – accurately describes a natural phenomena – rendering a mere observed coincidence. For example, Kepler’s Laws appear to accurately describe the motion of the planets, though Kepler and his contemporaries weren’t sure why (Kepler himself had some strange notion, including some involving nesting the platonic solids, which turned out not to be mathematically fun, but not even vaguely useful physics). Newton's law of universal gravitation explain, with the help of the Calculus, why Kepler’s Laws work, but don’t explain the fundamental mechanism by which gravity work. General Relativity allows calculations more closely matching observed reality than those possible with Kepler and Newton’s laws, but doesn’t address how they work, either.

 

Newton’s laws of motion do a superb job of describing the motion of everyday objects like cars and canon balls, but have serious problems when applied to very small objects, such as atoms, and phenomena such as diffraction patterns of light. Quantum physics (referring to the general discipline also called particle physics or the Standard Model) does a superb job of describing these places where classical mechanics fail, and further, don’t contradict the predictions of classical mechanics where it works well. This last trait is very important, as calculating the behavior of everyday phenomena like cars and cannon balls, while in principle possible using quantum mechanical formulae, is terribly difficult, beyond the planning and mathematical ability of nearly all human beings, and the calculating ability of any computer. That quantum mechanics assures us we can trust classical physics for most tasks is critical.

 

While quantum mechanics is, like Kepler’s laws, really just a well-organized collection of explanations and predictions of how measurable reality appears to happen, it introduces a major twist in precisely describing how well we can possibly measure anything – it’s uncertainty principle. Because the physical “size” of the particles of the Standard Model are (speaking very roughly) below these limits, an argument can be made that it’s “gone as far as it needs to or can”, and that it’s laws are for all intents and purposes the same thing as reality. Speculation in this direction is, however, more on of philosophy than practical science, so I’ll say no more of it here.

 

Despite it’s great success as a theory, the Standard Model of particle physics has a glaring shortcoming – to date, no one has been successful (as judged by the scientific community) is expanding the model to explain and predict the effects of gravity – the big, though slightly flawed success of Kepler’s laws. Where the model has been able to well-describe every other observed force by introducing a “boson” particle, the boson for gravity (name the graviton, even though it’s not accepted) hasn’t allowed anyone to write formulas that agree with observed reality

… could someone offer me an explanation to the rationality of relying on two different sets of physics to explain the same particles, only on different scales?

Again, the short answer: you shouldn’t. Use quantum physics for describing individual subatomic particles, such as protons and electrons, and classical physics for describing huge collection of these and other Standard Model particles, such as cars.

 

Science if full of situations where slightly inaccurate formulae are preferable to more accurate but more computationally difficult ones, so practical skill in science can’t be developed by learning a single “everything” theory. Much of this skill involves systematically deciding what discipline and theory to apply to a given problem.

[coldcreation]

I don't think they will find the Higgs but the human race will die still believing the standard model correct.

 

This is an interesting way to visualize what is a Higgs bozon, the Higgs mechanism: A quasi-political Explanation of the Higgs Boson; for Mr Waldegrave, UK Science Minister 1993

 

CC

[Little Bang]

CC, I must guess at the spelling, Tolamay came up with a theory to explain how the planets orbit the earth. The loops that he put in their orbits allowed him to predict the positions of the planets. As far as he knew his theory was correct because it worked. How do we know that we have not made a similar error with the standard model? His theory worked just fine until they found that the earth was not the center of the universe.

[Erasmus00]

CC, I must guess at the spelling, Tolamay came up with a theory to explain how the planets orbit the earth.

 

Ptolemy. And the difference with Ptolemy's theory and the standard model is one of prediction. Ptolemy could not predict how a new planet would move, he had to fit his epicycles to that planet. The standard model, on the other hand, predicts a great number of things. I would also argue that the standard model is (by comparison) very elegant.

-Will

[questor]

This may not seem to belong in this thread, but since we supposedly have good mathematical explanations or theories on physical occurences and quatum mechanics, can someone offer information about the condition called life? At what particulate level does life exist? And how can it be described? It has to be mechanical because the enzymatic reactions that cause it consist of atoms and particles and electrons-the same building blocks of the earth.

What is a thought? There is no weight, there is no known particle or mass,

there is some electricity involved ,but what engenders it? How does it occur and where does it go? How is it stored so it can be retreived? I would think the solutions to these questions should be a very important part of the

Theory of Everything.

[Little Bang]

Your right Eras, how stupid of me to suggest that the elegant standard model could have any possible errors.

[Erasmus00]

Your right Eras, how stupid of me to suggest that the elegant standard model could have any possible errors.

 

I wasn't saying it was stupid, simply suggesting that the comparison to Ptolemy isn't all that solid. You also haven't suggested errors, your actual statement was that "the human race will die still believing the standard model," even though a higgs won't be found. I'm merely asking for clarification on what you mean.

-Will

[CraigD]

CC, I must guess at the spelling, Tolamay came up with a theory to explain how the planets orbit the earth.

Ptolemy. And the difference with Ptolemy's theory and the standard model is one of prediction. Ptolemy could not predict how a new planet would move, he had to fit his epicycles to that planet.

Another problem with Apollonius of Perga’s “deferent and epicycle” model (Until wikiing it just now, I hadn’t realized that the scheme was not originated by Ptolemy or one of his students, but 300 years earlier by AofP) is that the more precisely one measured the motion of celestial bodies, the less they agreed with the model. This lead subsequent astronomer/geometers to add “epicycles of epicycles” to it to correct the discrepancies, only to require additional epicycles of epicycles. By the 13th century, documentation indicates that “40 to 60” nested epicycles were needed for each planet.

 

A neat bit of science trivia is that Copernicus was still using epicycles in the 16th century when he wrote “De revolutionibus”. By his switch to a heliocentric model, he is said to have been able to reduce the number of nested epicycles per planet from 80 to 34. So, though Copernicus’s Sun-centered model matches modern models, it still used the old-fashioned circles-within-circles orbit model, not the modern elliptical model Kepler’s famous for.

 

IMHO, a sign of a good model is that you don’t have to keep adding complexity to it to explain increasingly precise observations. I agree with Erasmus that the Standard Model exhibits this sign.

 

The major flaw with the current Standard Model, I think most physicists would agree, is not that it requires constant “redesigning” (except for certain predefined "tuning constant", it doesn’t), but that it’s mute on the whole subject of gravity.

[Qfwfq]

Due to more insistence on something off the point of this thread, I moved recent posts to a new thread:

 

http://hypography.com/forums/physics-mathematics/13399-newton-standard-model.html

 

I don't think there is any logic in quantum physics

It is actually constructed on solid logic and mathematics. There is a fundamental difference between logical and intuitive and there are many things which, although not intuitive, are logically alright. You can say QM is highly counterintuitive and everybody agrees. Einstein, who strongly disagreed with Born's opinions, didn't find them illogical.