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flyinghippos101
09-05-2009, 10:48 AM
I've been wrapping my head around this for the past few days, anyone help me shed some light on this?

Claudius
09-05-2009, 11:01 AM
That is an intriguing question. Why don't you ask it on the physics forum?

canadave
09-05-2009, 11:03 AM
ahhh, finally a topic I know something about :)

In a very over-simplified explanation:

Classical physics is based on the idea that the universe is a "Great Machine"....that it is composed of "things" (like particles) that behave in predictable ways. For instance, in classical physics, you can predict the outcome of a system at any given point in time (such as the exact position of particles in a container) if you know all the initial variables (such as the initial speed of the particles, how big they are, and so on).

Quantum physics is based on the fact that nature does NOT seem to be organized in this way. For instance, take what we perceive as light. Is it a particle (a photon), or a wave (as in a light wave)? In classical physics, it was a light wave. But quantum physics shows it is BOTH, in a sense; light has particle-like characteristics and wave-like characteristics.

In addition, quantum physics has shown that individual events cannot be predicted; there is some uncertainty built in to events, based on the measurements we make of that event. We can predict probabilities of multiple events, but not the outcome of individual events.

For instance, particles that collide at high energies will decay into other particles. Two protons, for example, may collide and decay into a neutron and a photon. Or, they might decay into a tau particle and a photon. Or something else.

Each possibility will occur a certain percentage of the time, which can be calculated with great certainty. The neutron/photon may appear 63.2346% of the time, the tau/photon may occur 25.4566% of the time, and so on. But it's impossible to know which one will happen for a SINGLE collision. We know the probabilities, but that's it.

This is a very short and necessarily abbreviated explanation. If you want a really good layman's book that talks about these things, read "The Dancing Wu Li Masters" by Gary Zukav. THE best layman's explanation of the differences between classical and quantum physics I've ever read.

flyinghippos101
09-05-2009, 11:05 AM
Wow that's awesome, thank you so much.

canadave
09-05-2009, 11:06 AM
More differences:

Classical physics holds that mass and energy are two different concepts. Einstein's "E=mc2" equation and quantum physics show that they are both two version of the same thing--each can be changed into the other. What that "thing" is, is one of the big questions of all time ;)

A quantum, by the way, is a "packet of energy/mass". Classical physics has no corresponding concept.

35ft6
09-05-2009, 11:07 AM
What is Quantum Physics?

Quantum physics is a branch of science that deals with discrete, indivisible units of energy called quanta as described by the Quantum Theory. There are five main ideas represented in Quantum Theory:

Energy is not continuous, but comes in small but discrete units. 1
The elementary particles behave both like particles and like waves. 2
The movement of these particles is inherently random. 3
It is physically impossible to know both the position and the momentum of a particle at the same time. The more precisely one is known, the less precise the measurement of the other is.4
The atomic world is nothing like the world we live in. 5You know, you don't have to pose this kind of question at a tennis message board.

canadave
09-05-2009, 11:08 AM
Wow that's awesome, thank you so much.

You're welcome. If you have any specific questions I can try to answer here, I'll be happy to give it a go. Quantum physics really is a fascinating topic and not at all as hard to understand at its basic levels as it sounds.

canadave
09-05-2009, 11:10 AM
You know, you don't have to pose this kind of question at a tennis message board.

I disagree. That's what the Odds and Ends forum is for. And good on him for having an inquiring mind.

It's at least as deserving as the "yo mama" joke thread going on here.

David_Is_Right
09-05-2009, 11:34 AM
Classical (Einsteinian and Newtonian) physics relates to the world of the large, such as everyday objects and galaxies. Quantum physics relates to the world of the very small, like particles, atoms and molecules.

Both of these theoretical systems work great and have amazing predictive power. However, physicists have infamous problems using them together because they describe the world in completely different ways. However, they both seem to be right, and have been tested to astoninging degrees of accuracy.

For further reading, try the excellent The Elegant Universe or The Fabric of the Cosmos by Brian Greene or In Search of Schrödinger's Cat by John Gribbin.

aphex
09-05-2009, 11:43 AM
I've been wrapping my head around this for the past few days, anyone help me shed some light on this?

if by "classical", you mean newtonian, there is always cause and effect in classical physics.

in quantum physics, it is all a matter of probabilities. the most important expression of quantum physics is heisenberg's uncertainty principle http://en.wikipedia.org/wiki/Uncertainty_principle

if you're interested, read up on it a bit. it is the pinnacle of human scientific thought in the 20th century (even more so than the theory of relativity imo...)

canadave
09-05-2009, 11:44 AM
Both of these theoretical systems work great and have amazing predictive power. However, physicists have infamous problems using them together because they describe the world in completely different ways. However, they both seem to be right, and have been tested to astoninging degrees of accuracy.

Just to clarify that a bit--classical physics is "accurate" and "right" only in a rough sense, in what we'd call "the macroscopic world" of cars, people, and so on. It is useful for predicting, say, how long it takes to get from NYC to Los Angeles in a car at a certain speed...but for high speeds and small objects, classical physics "breaks down."

David_Is_Right
09-05-2009, 11:47 AM
Yep, I already stated that classical physics applies to the world of large and everyday objects. It's accurate in a very real, precise calculative sense for large objects and high speeds.

35ft6
09-05-2009, 12:55 PM
I disagree. That's what the Odds and Ends forum is for. And good on him for having an inquiring mind.Really? I always find it interesting when people ask incredibly technical questions on message boards like TW. The YoMama thread is relevant, because that's the kind of people he's asking. I mean not everybody, but the internet is an incredible resource, with 30 seconds of googling he can find places much more useful to him than TW with our yomama threads. If I wanted to install aftermarket exhaust on my car, I wouldn't ask about it here, and quantum physics is way more complex than that. I'm not saying he doesn't have the right to post anything he wants here, just questioning the utility of this board as a source of information on quantum physics. But hey, to each their own...

David_Is_Right
09-06-2009, 04:37 AM
It wasn't a technical question, he just wanted a summary. A forum allows for feedback and further, specific questions to be asked.

35ft6
09-06-2009, 01:08 PM
^ I also post a lot at a pop culture magazine board. One dude posts a lot of threads like "how does gravity work?" Maybe I underestimate the TW boards but I wouldn't come here first for answers to anything meaningful outside the realm of tennis. Opinions? Sure, I'd ask for those. And then there are the kids who come here asking us to practically research an essay for them. Nice try, but I don't care about the ethics of it, just the fact that they can get their answers quicker simply by googling. Okay, maybe it's a pet peeve. Just seems inefficient.

SystemicAnomaly
09-06-2009, 02:54 PM
...

For further reading, try the excellent The Elegant Universe or The Fabric of the Cosmos by Brian Greene or In Search of Schrödinger's Cat by John Gribbin.

PBS has a great presentation of The Elegant Universe in their NOVA series. It is available online & is well worth watching. Even tho' the entire program is 3 hrs long it is presented in manageable chunks that are about 4 to 10 minutes in length:

www.pbs.org/wgbh/nova/elegant/program.html (http://www.pbs.org/wgbh/nova/elegant/program.html)


For more about this kind of stuff, check out these pages as well:

www.pbs.org/wgbh/nova/elegant/everything.html (http://www.pbs.org/wgbh/nova/elegant/everything.html)

www.pbs.org/wgbh/nova/elegant (http://www.pbs.org/wgbh/nova/elegant/)
.

dennis10is
09-06-2009, 07:34 PM
You shoot one photo of light, exactly in between two slit. If the photon goes on the slit on the right, Nadal becomes number 1 and eventually GOAT, the US goes bankrupt but is saved by aliens from Alpha Centauri. However, if the photon goes thru the slit on the left, Fed wins the USO, becomes GOAT, the US buys China and India, the aliens who built the pyramids comes back and ask for the planet back, turns out we rented from them and now we have to leave because they want to some planet remodeling.