Thread: People who know about Quantum Mechanics/Physics/Thoery Please come here

Originally Posted by Dog Biscuits

Do you think thats because of a fundamental limit on our logic? Like we can only go so far with logic and after that its "beyond" us? I know you mentioned "string" theory but that isnt an accecpted theory yet.

That great big Hadron accelerator in Switzerland that some fear may "KILL US ALL" will hopefully move us a step closer to achieving that goal. Unfortunately, even after they repair it and even after it starts up again, it will be quite a while before they bring it up to full power and even longer before we see any serious analysis of the massive amounts of data that will be collected.

Originally Posted by Dog Biscuits

Do you think thats because of a fundamental limit on our logic? Like we can only go so far with logic and after that its "beyond" us? I know you mentioned "string" theory but that isnt an accecpted theory yet.

Consider the difference with the unknown and the unknowable. As long as we are able to ask a question, we should be able to find an answer. The unknowable is when when we can't even ask the right questions.

But in this case, I think we just have something wrong somewhere.

Does anybody know any of the weird stuff that happens in Quantum Mechanics?

Originally Posted by WhiteWolf

Does anybody know any of the weird stuff that happens in Quantum Mechanics?

Off the top of my head, here are a few that have been supported by experimentation.

Casimir Effect

Superfluidity

Vacuum Energy

Quantum Tunnelling

Originally Posted by WhiteWolf

Does anybody know any of the weird stuff that happens in Quantum Mechanics?

There's tons of weird stuff that happens in QM.

For instance, it allows for people to walk through walls! If you chuck something at a brick wall, tiny pieces of the thrown object will break off, randomly borrow energy from the particles of the wall, allowing it to pass right through.

If you had an infinite amount of time to attempt walking through a brick wall an infinite number of times, then eventually, you would borrow enough energy to pass right through.

That's an example from the book The Elegant Universe. But it seems to be the only explanation for how pieces of straw can become embedded in concrete or steel during hurricanes.

Quantum computing for me is my favorite "here and now, you can touch it and feel it" quantum topic. Bits on and off at the same
time .. the actual computer OFF and still able to work (according to a recent news story which may just be a little to overly optimistic). Observation however is still a problem so quantum computing is still moving at a slow pace but they do exist now .. multi-threading (the concept at least) taken to the n'th level thanks to Mr S's cat. How can a light (Qbit) be on and off at the same time and all states in between simultaneously? QM.

@ The Cusp I'am still trying to get a hold of that book "The Elegant Universe"... But any how I find QM very amusing. But still hope to get a nice understanding of it, If thats possible .

Yaaa I finally got a hold of the book. Thanks to any one who recommended it. But I just quickly read it and I find that the book is mostly about String theory. Am I right?... And is there anything else in the book perhaps some stuff on relativity?

Originally Posted by The Cusp

The problem facing modern physics is that we have two sets of rules to describe the universe. We have relativity for the very large and very fast, and quantum mechanics for the very minute.

Since we know the atomic make up and behavior of stars and such, we should be able to predict their behavior at a macroscopic level using quantum mechanics. Likewise we should be able to deduce the quantum specifics of large scale objects from our knowledge of the behavior on the macroscopic level. But in either case, it just doesn't work.

Really, we should only have one set of rules to describe the universe, and the inability of the two theories to mesh really screws things up. That's why String or M-Theory is considered a "unified theory", and a working unified theory is the holy grail of modern physics.

What you seem to be saying here is that the quantum model of the universe fails at a macroscopic level. That statement is wrong - the quantum model is actually a revised addition of classical physics. There are a number of formulae which perfectly describe phenomena at both a microscopic and macroscopic level, they include terms which become more significant as the scale of the problem becomes smaller.

I would like to see some proof of your second paragraph as I have yet to see a quantum model that fails at the macroscopic level. This comes from studying quantum mechanics and thermodynamics at university; I haven't continued in that field and would be interested in seeing its shortcomings.

Which quantum model explains gravity then?

I like this video. Quantum Physics explained simply.

http://www.youtube.com/watch?v=XEZtw1yt8Kc

Originally Posted by Xei

Which quantum model explains gravity then?

Oh snap! Forgot about that one.

However, that's not enough to say that the QM model fails at a macroscopic level, it simply doesn't have the scope of the classical model yet.

"I don't understand it, therefore it's wrong and I'll be here to say it was wrong when I'm proven right in the next few decades".

I'm sure you're aware this is an argument from ignorance.

The first 10 weeks of a first year university chemistry degree deals exclusively with quantum physics to allow you to understand wave particle duality, and properties of electrons. I've learned more about QM in the last 5 weeks than I have in the last 5 years of armchair physics via wikipedia and youtube.

Watch some videos over at TED.com by Brian Cox. He's the closest thing the world of physics has to a rock star.

Here, I even found it for you: http://www.ted.com/index.php/talks/b...rcollider.html

If we 'got it wrong' in QM, we got something MAJOR wrong at the very heart and core of the science. Given all of the experimental data and knowledge we have amassed, that is unfathomably unlikely. It all fits too well together right now to just turf it all out and start again from scratch. You don't throw the baby out with the bathwater, and you don't ditch a jigsaw puzzle when you realise you're missing some pieces.

You look for the damn pieces.

Originally Posted by Alextanium

"I don't understand it, therefore it's wrong and I'll be here to say it was wrong when I'm proven right in the next few decades".

It is better to say that from what I understand of it, a lot of it will probably be disproven because it is apparently illogical.

Originally Posted by Universal Mind

It is better to say that from what I understand of it, a lot of it will probably be disproven because it is apparently illogical.

It's only illogical because our brains weren't evolved to think about matter on such small scales as the picometer and the Angstrom. All matter in the universe has a wave function, even your body. But just like when you get to the quantum level gravity becomes a pathetically weak force, when you scale up to the macroscopic (or cosmic) level, the waveform of an object is just as insignificant as gravity in the quantum realm. The reason that electrons and photons can act as both particles and waves is due to their minuscule nature - they are small enough that they are of a significant portion of the size of their own wavelengths that said waveforms can affect their interaction with other matter.

To us in the macro realm, that seems completely weird and ridiculous. But the models work, predictions can and have been made that work and tests verify (most) of the theory, and there we have the Standard Model.

Other theories such as string theory are in a realm of their own. They operate on distances so small they make the Planck length look huge. String theory has a fantastic internal mathematical symmetry, but is currently (and may be for hundreds of years) beyond our technology to prove or disprove.

Concepts and principles such as wave-particle duality and Uncertainty aren't the kind of things that may be disproved in the future. And since the rest of the field sort of rests on their shoulders, you're not left with much to radically redesign the wheel.

I'm not saying it can't happen. Just that it's very unlikely. Ridiculous upsets, upheavals and turn arounds in scientific knowledge just don't happen any more because there are too many checks and balances in place against bad science making it into the books in the first place.

I dont know anything......but this guy does









and there is a shit load more on his channel website.

Wow he talks fast. But he definitely knows his physics.

Originally Posted by Alextanium

It's only illogical because our brains weren't evolved to think about matter on such small scales as the picometer and the Angstrom. All matter in the universe has a wave function, even your body. But just like when you get to the quantum level gravity becomes a pathetically weak force, when you scale up to the macroscopic (or cosmic) level, the waveform of an object is just as insignificant as gravity in the quantum realm. The reason that electrons and photons can act as both particles and waves is due to their minuscule nature - they are small enough that they are of a significant portion of the size of their own wavelengths that said waveforms can affect their interaction with other matter.

To us in the macro realm, that seems completely weird and ridiculous. But the models work, predictions can and have been made that work and tests verify (most) of the theory, and there we have the Standard Model.

Other theories such as string theory are in a realm of their own. They operate on distances so small they make the Planck length look huge. String theory has a fantastic internal mathematical symmetry, but is currently (and may be for hundreds of years) beyond our technology to prove or disprove.

Concepts and principles such as wave-particle duality and Uncertainty aren't the kind of things that may be disproved in the future. And since the rest of the field sort of rests on their shoulders, you're not left with much to radically redesign the wheel.

I'm not saying it can't happen. Just that it's very unlikely. Ridiculous upsets, upheavals and turn arounds in scientific knowledge just don't happen any more because there are too many checks and balances in place against bad science making it into the books in the first place.

That is not what seems illogical to me. What raises my skepticism are quantum physics' rejection of determinism and its emphasis on the supposedly subjective nature of physical events.

I hold pretty much exactly the same views as Alextanium, especially about our perception of what is 'logical' only being based on our brains, which are themselves only based upon local experience - which is never microscopic. There are many other instances of this happening through science, often resulting in an initial rejection of the hypothesis; but evidence will always win out in the end. The twin paradox, for example; it is totally counterintuitive that if I travelled at a large velocity for a period of time, time will pass more slowly for me than my twin, with the result that when we meet up again, I could be a year older and my twin could have lived out the entire course of his natural life. However, time dilation has been proven beyond any doubt by empirical evidence.

Although, regarding the determinism of the quantum world, things are still quite inconclusive; we really need to wait for a unified theory (if that ever happens), but I read in the New Scientist that some physicist thinks it could be achieved by a deterministic fractal... it's really too uncertain to say either way. And that's without even going into what the philosophical consequences would be.

Originally Posted by Universal Mind

That is not what seems illogical to me. What raises my skepticism are quantum physics' rejection of determinism and its emphasis on the supposedly subjective nature of physical events.

Quick note:
The emphasis is on the subjective nature of the observation of physical events.
I haven't yet seen any mention of actual events being subjective. If you could clarify this point further, I'd be happy to discuss it.

Originally Posted by WhiteWolf

Yaaa I finally got a hold of the book. Thanks to any one who recommended it. But I just quickly read it and I find that the book is mostly about String theory. Am I right?... And is there anything else in the book perhaps some stuff on relativity?

If I'm not mistaken I believe the first 80 or so pages is mostly explaining the ideas behind special and general relativity. The thought experiments are trippy You are right though the backbone of "the elegant universe" is largely based on string and M theory but in order to begin understanding those theories one must understand the theories that contradict it and that's why the first 1/3 of the book is on relativity and QM.

...The whole point of string theory is that it doesn't contradict relativity or quantum mechanics. :l

Anyone interested in QM (and which also has a bit of mathematical knowledge) should check out the "Particle in a box" example

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

(wikipedia might not be the best source...)

It is a bit hard to understand, but gives a very good example of how QM really works how it differs from classical physics and so on.

I hope I get to study this stuff next year in school.