What is Quantum Physics??

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Offline stana

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What is Quantum Physics??
« on: 10/01/2008 19:11:04 »
Hey guys. Im kinda wondering its complicated..so can someone give me a basic explination into what it is please?

Thanks

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Offline neilep

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What is Quantum Physics??
« Reply #1 on: 11/01/2008 16:34:18 »
It's not easy is it ?

I can't help you except to say that it deals with the weird and wonderful science of physics at the atomic level, the behavior of atomic particles at the atomic level.

Ask any physicist about the ' measuring ' problem and it's hair ripping out time.

Something to do with the fact that the very act of a person observing an atomic particle has an affect on it. It's as if the particle knows it's being observed !

See ?...well confusing or what ?

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Offline opus

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What is Quantum Physics??
« Reply #2 on: 11/01/2008 19:41:41 »
I only know that if you think you understand it............you don't!!

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lyner

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What is Quantum Physics??
« Reply #3 on: 11/01/2008 23:24:31 »
There seem to be a lot of people like that!
It's incredible how definite some of the statements are that we read on forums like this one.
I'm always happier to lay down the law when it comes to classical Physics; there are a few things of which we can be pretty sure - within their limits - like Newton's Laws of Motion and Snell's law of refraction.

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Offline lightarrow

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« Reply #4 on: 12/01/2008 11:32:47 »
There seem to be a lot of people like that!
It's incredible how definite some of the statements are that we read on forums like this one.
Especially if Nobel Prize Richard Feynman says this on 1985.

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Offline Soul Surfer

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What is Quantum Physics??
« Reply #5 on: 14/01/2008 00:03:58 »
The simple level answer is that matter and energy have to come in defined lumps and cannot be continuously divided into smaller and smaller pieces.  the detailed rules are complicated and best given in answers t more specific questions or looked up in a text book
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Offline opus

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What is Quantum Physics??
« Reply #6 on: 14/01/2008 23:31:12 »
How does this tie in (sorry ) with string theory then soul surfer?

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Offline Soul Surfer

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What is Quantum Physics??
« Reply #7 on: 15/01/2008 09:24:58 »
A lot of the aspects of quantum physics are similar to classical continuous physics.  This means that there is a sort of underlying classical idea that describes what is going on inside the "quantum box".  The original idea describes point like particles with no physical size.  But this has problems when you get to very high energy events because the mathematics does not make sense because values become infinite.  By allowing the point particles to be slightly extended like little strings or surfaces makes the mathematics much more tractable but makes the possible options for solutions to the equations much greater.
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Offline opus

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« Reply #8 on: 15/01/2008 20:29:44 »
Thanks soul surfer- Is the 'quantum box' the place where tiny protons (?) can leap from 'floor ' to 'floor', thereby dictating the density, and/or size of the particle?

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Offline Soul Surfer

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What is Quantum Physics??
« Reply #9 on: 15/01/2008 23:36:46 »
I have used the term "quantum box" to refer to things that go on inside the limits of observation set by the uncertainty principle.  This defines the limits of position and momentum or energy and time of observation of a particle or group of particles below which it is impossible to know exactly what is going on.  Within this area quantum theory says what is happening is a superimposed mixture of everything that it is possible to happen.
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Offline Eagle333

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What is Quantum Physics??
« Reply #10 on: 16/01/2008 04:23:05 »
After all, Einstein called it the spooky theory...it was hard to define...it is hard to know what's going on when the same particle is in two places at the same time....

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lyner

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What is Quantum Physics??
« Reply #11 on: 16/01/2008 19:34:18 »
You have to avoid carrying your preconceptions with you into Quantum land. The particle isn't in two places at once. It COULD  be in one of two places. Until you have actually detected it in one place or the other, you just don't know. It cannot be measured / detected in both places - so it's not in either before you observe it.
The odd thing is that the probability of it's turning up can be found by treating it as a wave, being diffracted by its surroundings. The probability of it being found somewhere is given by the amplitude of a wave of the appropriate wavelength.
Treat it all as a game with unexpected rules and, after a while, it doesn't won't seem so odd. Remember - the rules that you 'know and love' about the world were not obvious to previous generations.
« Last Edit: 16/01/2008 19:58:38 by sophiecentaur »

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Offline opus

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« Reply #12 on: 16/01/2008 20:03:33 »

It's incredible how definite some of the statements are that we read on forums like this one.
Hmmmmm!
« Last Edit: 16/01/2008 20:06:43 by opus »

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Offline Eagle333

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« Reply #13 on: 17/01/2008 00:58:02 »
Actually, that is true. It is the possibility...

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Offline rhade

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What is Quantum Physics??
« Reply #14 on: 30/01/2008 16:40:55 »
Sorry, guys, but if I may say so, I don't think the above is answering the question that was actully asked, and has side tracked into the uncertainty principle, which is a linked, but slightly different issue.
To that end:-
At the turn of the previous century, (19th. to 20th.) Max Plank, a German mathematician, postulated the theory that energy exists as particles (quanta) as well as waves. The equation that detemines the energy of a single quantum is still called Plank's constant in his honour.
« Last Edit: 12/09/2008 17:19:18 by rhade »
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Offline DoctorBeaver

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What is Quantum Physics??
« Reply #15 on: 30/01/2008 17:53:18 »
...there are a few things of which we can be pretty sure - within their limits - like Newton's Laws of Motion ...

Moti Milgrom may disagree with you on that point  [;)]
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Offline lightarrow

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What is Quantum Physics??
« Reply #16 on: 30/01/2008 18:16:14 »
Sorry, guys, but if I may say so, I don't think the above is answering the question that was actully asked, and has side tracked into the uncertainty principle, which is a linked, but slightly different issue.
To that end:-
At the turn of the previous century, (19th. to 20th.) Max Plank, a German mathematician, postulated the theory that energy exists as particles (quanta) as well as waves. The equation that detemines the energy of a single quantum is still called Plank's constant in his honour.

I appreciate your effort and your interest for physics but you have to correct several things in your post.

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Offline DoctorBeaver

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What is Quantum Physics??
« Reply #17 on: 30/01/2008 19:46:46 »
I don't see that the Uncertainty Principle can be called a side-track. It is a fundamental and crucial part of quantum physics. It would be like saying that fluid dynamics or Newton's laws of motion are not really a part of classical physics.

The term Quantum Physics does not simply pertain to quanta of energy; it is an umbrella term that encompasses many fields - Quantum Field Theory, Quantum Electro-Dynamics, Quantum Chromo-Dynamics, Quantum Loop Gravity, etc. The study of all of these is subject to the Uncertainty Principle.
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Offline JP

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What is Quantum Physics??
« Reply #18 on: 31/01/2008 18:15:48 »
The Uncertainty Principle is certainly one of the fundamental features of QM that distinguishes it from classical mechanics.  It's also one of the best ways to demonstrate how counterintuitive quantum mechanics can be.  However, I wouldn't go so far as to say it's "fundamental" to the theory itself, since the Uncertainty Principle is a result of postulates that give rise to the theory, and not the other way around.

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Offline DoctorBeaver

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« Reply #19 on: 31/01/2008 18:25:25 »
The Uncertainty Principle is certainly one of the fundamental features of QM that distinguishes it from classical mechanics.  It's also one of the best ways to demonstrate how counterintuitive quantum mechanics can be.  However, I wouldn't go so far as to say it's "fundamental" to the theory itself, since the Uncertainty Principle is a result of postulates that give rise to the theory, and not the other way around.

I humbly bow to your greater understanding of the subject. But could QM still work without the Uncertainty Principle? Is it not an integral part of the mathematics of QM without which any calculations would give nonsense results?
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Offline JP

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« Reply #20 on: 31/01/2008 21:37:34 »
It's an integral part of the theory because it comes out of the mathematics needed for quantum mechanics automatically.  Its hard to draw a parallel to classical mechanics, but perhaps its similar to elliptic orbits for planets and Newton's theory of gravity.  You wouldn't usually say you were starting from elliptic orbits as a basis for the theory, but it's something that comes naturally out of the math and that is clear evidence the math is right.

In other words, quantum mechanics implies uncertainty principles, but uncertainty principles do not imply quantum mechanics.  In fact, there are uncertainty relations in signal analysis, optics, acoustics, and many other areas.  I do agree completely that it's a good point to bring up in explaining quantum mechanics.  Most people want to know what quantum mechanics predicts that plain old classical mechanics lacks, and the uncertainty principle is a classic example. 

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Offline DoctorBeaver

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« Reply #21 on: 31/01/2008 21:52:26 »
OK, I get that. Thanks.
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Offline rhade

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« Reply #22 on: 07/02/2008 16:20:16 »
Yeah, guys, but with all due respect, I think you are missing the semantics of the question, which was, "basically, what is it?" So I was trying to give a BASIC answer. I know the uncertainty principle and all those other wider issues are tied in, and I wasn't suggesting that they are not, but the guy asked for the basics. I think if you plunge into all the complexities without explaining what I did above, you're trying to walk before you can run, so to speak. Do you see where I'm coming from?
« Last Edit: 12/09/2008 17:19:42 by rhade »
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Offline JP

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What is Quantum Physics??
« Reply #23 on: 07/02/2008 17:48:45 »
Good point, rhade.  This forum tends to dive into complexities quickly.  Your statements about Planck are on the right track, but you got a few details wrong.  Planck postulated a theory that correctly explained the light emitted by a black body (a perfect absorber/emitter of electromagnetic radiation).  In order to do so, he had to model the energy as being emitted by little radiation-generators (harmonic oscillators), which each only emitted one particular energy (which was the frequency of the light multiplied by Planck's constant).  However, Planck thought of this as a mathematical trick that gave the right answer, and didn't know about quantum mechanical particles. 

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Offline DoctorBeaver

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« Reply #24 on: 07/02/2008 18:54:27 »
Wasn't it Einstein who proved that light can be treated as particles? Was it something to do with pollen? Or was that something else? [???]
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Offline JP

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What is Quantum Physics??
« Reply #25 on: 07/02/2008 22:45:59 »
Planck (1901) came up just short of treating light as particles.  He assumed that the wave sources in the cavity could be well-modeled by harmonic oscillators.  The result was that the energy (E) from each harmonic oscillator was E=hf (where f was the oscillation frequency and h is Planck's constant).  By summing up the energies from all oscillators, Planck accurately modeled black body radiation.  However, Planck never thought of the light itself as coming in packets of energy E=hf.  He just thought his model of oscillating sources was a good one to get the black body spectrum right. 

Einstein (1905) came up with the idea that light energy itself came in discrete packets of E=hf.  This was independent of the source it came from.  In hindsight, it seems obvious, but at the time, people were far more ready to accept Planck's model of oscillating (but still classical) sources, whereas Einstein's idea that the light itself was divided into energy packets was shocking.

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Offline DoctorBeaver

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« Reply #26 on: 08/02/2008 16:46:39 »
And, if I remember correctly, Einstein got the Nobel for that.
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Offline McQueen

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What is Quantum Physics??
« Reply #27 on: 09/02/2008 10:29:17 »
QM is the most wonderful , fantastic development in physics!!! It opens up and expands minds like never before!!  Unfortunately it comes with some pre-concieved litter carried over from classical physics. Take for instance the phenomena of electricity which was formulated before ever photons were discovered, which has resulted in one hell of a humongous bollocks up!
« Last Edit: 09/02/2008 10:38:40 by McQueen »
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Offline DoctorBeaver

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« Reply #28 on: 09/02/2008 12:03:15 »
QM is the most wonderful , fantastic development in physics!!! It opens up and expands minds like never before!!  Unfortunately it comes with some pre-concieved litter carried over from classical physics. Take for instance the phenomena of electricity which was formulated before ever photons were discovered, which has resulted in one hell of a humongous bollocks up!

How can you say that? QM turned conventional physics upside-down, inside-out, and every which way. The "pre-conceived litter" was put through the mincer.
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Offline rhade

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« Reply #29 on: 12/02/2008 16:22:20 »
I just read my last post and realised I said "walk before you can run," and not "run before you can walk." Whoops! I was up against the clock when I was typing that.
Thanks, jpetrucelli, for the above responce. I certainly don't claim any great expertise on the subject, and was pretty much quoting the brief explanation given in Brockhampton's Dictionary of Science (which is a useful little book) in my "back to basics" comment.
Of course, contemporary thinking tends to see energy as either particles or waves, depending on your point of view, just as where (or indeed, when) the energy is depends on your point of view.
Hopefully, if we all throw in what we think we know about the subject, this question will eventually get answered. Say, where's stana, the guy who posted the question in the first place. Is any of this helping, stana?
« Last Edit: 12/09/2008 17:20:31 by rhade »
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Offline rhade

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What is Quantum Physics??
« Reply #30 on: 12/02/2008 16:26:03 »
Oh, and thanks, mcqueen for the phrase "humungous bollocks up." That's one of the technical terms scientists use, right?
« Last Edit: 12/09/2008 17:20:49 by rhade »
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Offline DoctorBeaver

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« Reply #31 on: 12/02/2008 22:07:36 »
Oh, and thanks, mcqueen for the phrase "humungous bollocks up." That's one of the technical terms scientists use, right?

I can well imagine that it actually is!
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