A basic explanation of Quantum physics needed

[gribbon]

Hi there...

 

I need a basic explanation of quantum physics what does it mean? What is it exactly? Sorry I'm so ignorant.....but I can't really get a grip on this subject....;)

[hallenrm]

Why not first read thae article quantum physics and the ask some more pointed questions.

 

Or if you find it difficult try this article written especially for laypersons.

;)

[Qfwfq]

Don't take the one for laypeople toooooo seriously! I had a brief look through the wiki, it's not perfectly accurate either but at least it's more serious.

 

I could try to give a brief summary but I would have to work on it. Actually, it would make sense to have a tutorial thread for people seriously interested in improving their grasp.

 

Briefly: reality is wierd, really wierd, but that's just the way it is. ;)

[InfiniteNow]

Read up on the Uncertainty Principle a bit. My understanding is that's the heart of QM.

 

 

Briefly: reality is wierd, really wierd, but that's just the way it is. :hyper:

 

That is the best description I've ever read. :)

[Qfwfq]

But insufficient, I'm ever in a hurry lately, shouldda said "really, absolutely freakin' wierd!".

 

:naughty:

[Qfwfq]

Particle or wave?

 

Neither! In past centuries, there was debate amongst natural philosophers over whether light was a wave or a bunch of corpuscles. Experiments in optics made more and more apparent effects that could be explained by considering it to be a wave. Maxwell eventually summed up electromagnetism in a form that predicted electromagnetic waves and there was reason to say that these would be visible light, when the frequency and wavelength were right. Until a little more than a century ago, there was little doubt that the old controversy had been resloved. Meanwhile atomic theory was being confirmed and experiments showed the existence of the electron, a particle carrying a fixed amount of negative electric charge. According to what was already known, electrons were a quite small part of an atom's mass, it was proposed that atoms were a distribution of positive charge, peppered with electrons (Well, not quite peppered in the case of the first few atoms!). Then...

• Rutherford got some surprising results from scattering alpha rays (small atoms stripped of electrons) off a thin gold foil, showing that the positive charge and most of the mass is concentrated into a tiny "kernel", or nucleus in Latin, so it was guessed that the negative electrons might be orbiting the positive nucleus like a tiny solar system. Materials are mostly empty space!!!
   
  This, however, runs into difficulty with the fact that the charge, moving thus around the nucleus, ought to act like a tiny antenna and radiate all it's kinetic energy away...
   
   
  
• Planck found an ingenious explanation of blackbody radiation, which avoids the so-called "ultraviolet catastrophy", by making a bold hypothesis: Electromagnetic radiation (such as light) of a given frequency can be present in a closed system only in multiples of a fixed quantity (called a quantum) proportional to said frequency. As you may have just guessed, that's how the term quantum came in and stuck on.
   
   
  
• Einstein performed expeiments on the photoelectric effect that confirmed the Planck hypothesis of quanta, even matching the proportianality constant that could be gleaned from blackbody spectra at various temperatures. The photon was born!

 

What is a particle?

 

Ha! :hihi: A particle is a mysterious thing, it has odd properties and behaves in mysterious ways.

 

Classically a particle was considered exactly what the word means: a "small part" or corpuscle, "small body", which always has a position and a velocity (whether or not these are known by measurement) and which MAY have an extension, in which case it MIGHT spin like a little top.

 

What is a wave?

 

A wave is the propagation of some kind of oscillation through a spatial distribution of "something" over time. It results from the oscillation at each point being more or less weakly coupled to neighbouring points. The propagation may be described in terms of wavelength and fequency, or distributions of these called spectra. At each position and each time, the oscillation will be at some point of its cycle, this is called the phase which is given by an angle, compared to some reference point of the cycle. Classically at least, that is...

 

So, particle or wave?

 

Models of atoms were developped, more and more complicated, with electrons having orbits with fixed energy and rules and regulations about how they could and couldn't radiate their precious energy, and always there being a "ground state" from which that minimum energy couldn't be radiated away. This began to provide an inkling of why different atoms and molecules will absorb and emit some wavelengths very well and not others. Soon de Broglie made the bold hypothesis that even the electron had a wavelength, like the photon, and this idea eventually took hold for all things bright and beautiful, not just the photon and the electron. This was used to refine and complicate these atomic models which were ever more perfectly describing all observations, from the optical spectra of atoms up through to chemistry and the structure of materials.

 

Well, currently it hardly makes sense to talk about a wave, it is a useful way (up to a point) of describing the behaviour of what are currently called particles although the term isn't meant in the classical sense at all. At least, it is meant hardly in the classical sense but it makes more sense to think of a particle than of a wave. In the formalism which has had vast success in describing things, the state of any system is given in terms of amplitudes that are complex-valued and thus have a phase --even without needing to vary in modulus-- and from this description of the state there's a way of calculation the probability (or density of) for outcomes of measurements. In any state, while the outcome of some mesurements may be certain, it's impossible for the outcome of all measurements to be certain. However, the other way around, it can also be said that observations confirm that any wave should be regarded as Planck regarded the electromagnetic wave.

 

It's like, "If it's a wave, it's really a particle but, if it's a particle, it's also kinda like a wave."

[Jay-qu]

Quantum Phyisics is the physics of the very small, or more appropriately it only produces noticible effects on very small scales.

[Qfwfq]

At large scales it's just less easy for effects to be noticeable, especially at high temperature.

[Mohit Pandey]

Einstein played an important role in QP. But he didn't support it.

He gave the theory of relativity which is applicable over large scale.

So at one end, we have QP and at other relativity. Modern physicts are trying to combine the time for solving the problem of creating Theory of Everything.

 

It seems certain that Einstein was doubly wrong when he said "God does not

play dice." Consideration of particle emission from black holes would seem

to suggest that God not only plays dice but also sometimes throws them

where they cannot be seen. -- Dr Stephen W. Hawking, NATURE, 1975 [no

article by Hawking in Nature that year, but mentioned thus: Specifically,

it is in Nature 257 (October 2, 1975), 352, an account of a conference

written by Malcolm MacCallum. The account begins "God not only plays dice.

He also sometimes throws the dice where they cannot be seen" This statement

is made by S. W. Hawking (Cambridge University) in his recent work on black

holes... The reference seems to be to two preprints circulated by Hawking.

[also found in] Hawking concluded by reminding us that Albert Einstein once

said "God does not play dice with the universe." "On the contrary,"

Hawking said, "it appears that not only does God play dice, but also that

he sometimes throws the dice where they cannot be seen." --Jerry

Pournelle, _Galaxy_ magazine article reporting on Hawking lecture at Cal

Tech, October 1975, collected in the book _A Step Farther Out_ by Jerry

Pournelle, cr. 1979

Science Jokes:9. MISCELLANY : 9.2 EINSTEIN QUOTES

 

Do you think this is true that Hawking said so?

[billby]

for someone who just finished highschool and was taught a bit of quantum physics over the last 4 weeks of classes, we finished on the De Broglie wavelength, what would be the next step for someone who wanted to learn more?

[sanctus]

Doing classical mechanics I would say and get a grip of what the Hamiltonian is, afterwards I would start to read any book titled something like "Introduction to QM" give or take a Modern in front of it.

[IDMclean]

I quite like Dr. Quantum's explinations of quantum phenomena. I am unsure as to whether it qualifies as a primer for Quantum Physics but nontheless I find his presentations Fascinating.

 

The Double Slit Experiment http://youtube.com/watch?v=DfPeprQ7oGc

 

Heisenberg's Uncertainty Principle http://youtube.com/watch?v=KT7xJ0tjB4A&feature=related

[Rade]

I would suggest you view the following lectures by Richard Feynman:

The Vega Science Trust - Richard Feynman

 

Feynman gives a very basic explanation of rules of quantum physics. Be sure to start with first lecture then second, etc.

[HydrogenBond]

One way to look at quantum theory, is matter and energy states are not continuous but exist in distinct states, with discontinuities between each state. The easiest to see are atomic spectra of atoms. Rather than be a smooth curve, the energy curves appears as a bunch of lines with spaces between them. The electrons are sort of jumping between very distinct states instead of moving smoothly in a continuous way. These very distinct states are called quanta, which is the basis for quantum theory

 

The wave nature of matter and energy can be understood as a sine wave, more or less, where peaks appear. The peaks are very distinct. The particle nature of matter has its own quanta, which are defined as distinct packets or states of matter. These are both ways to explain quanta observations. Depending on the experiment, one of these two types of quanta is more convenient for explaining that particular type of observation.

 

Quantum physics works between the larger more obvious peaks of nature, to find even smaller and smaller peaks, that are also quanta. Wave type math is often used because when we add or subtract waves, one can get composite waves that will show new peaks and valleys. Based on these composite math wave predictions, physics simulates this in the lab. Very unique wave composites allow brand new quanta states to appear.

 

As an analogy, say you were at the ocean on a smooth beach. The waves crest come in at a certain height, as long waves parallel to the beach. These are the quanta. Next, you move down the beach where the sand is irregular causing the waves to come at you from many directions at once. These overlap and add and can make smaller peaks, like a little mountain. These may not happen exactly this way, at that spot very often, but it too is a type of quanta that is predicted by unique wave situations. Particle matter is like a little boat. As it rides this little mountain, its behavior does so in an unique quantum way, following the unique action of the wave. The quantum physicists is able to set the sand on the beach, so to speak, so very unique wave states can occur, including very unique fast virtual states. As fine and small as we have achieved, the quantum nature is still there.

[Mohit Pandey]

The Double Slit Experiment

From this, I conclude that paticles propagate in the form of waves but observed as particles. Since, it propagates in the form of wave, there are various possiblities where it is observed. At that various possiblities , the particles are observed.

One more thing, energy propagates in the form of waves and matter in the form of particles.

Am I correct?:)

[IDMclean]

Actually, according to the Standard Model matter and energy propagates as wave and particle but only to a certain degree depending on what you measure. The Uncertainty Principle essentially states a corresponding relationship between things like position and rate. When you attempt to observe a body's rate you correspondingly reduce the accuracy observed of the body's position; usually, this is simply stated as "the more you know about the rate the less you know about the position and vice versa."

 

Also, if you look at a body's rate with finer and finer precision, the body begins to act more and more like a wave; if you observe the bodies position with finer and finer precision, the body begins to act more and more like a particle, but it is both at the same time.

[Mohit Pandey]

Re:Am I correct?

From HydrogenBond-----One way to look at quantum theory, is matter and energy states are not continuous but exist in distinct states, with discontinuities between each state.

KickAssClown in his last line--............., but it is both at the same time.

 

Which is correct