[NT] Someone explain quantum physics (or theortical physics) to me

[6.4]

YTMND - Why Quantum Physics is Cool Pt 1 (Updated with pt 2 URL)

4 parts, i just liek the music tbh

Link to rest = ytmnd - you're the man now dog! | search

 

[Tamske]

The Elegant Universe- Brian Greene
.

This is a very good book, but it's still quite difficult. It's about string theory... the thing that tries (and still fails) to combine quantum mechanics and general relativity.

For quantum mechanics I recommend QED from R. Feynman. Feynman is a master in explaining difficult things in an easy way! QED is easy enough for a layman to understand AND accurate enough for a physicist to look things up.

As you've asked me for more, here is some more: measuring. Please remember my previous post - every time you look, observe, measure or interact in any way with a small particle, the quantum mechanical die will get thrown and the behavior of the particle changes. You can't observe anything without interacting with it. For seeing something, you need light to bounce off it.

Picture two cars colliding. There will be effect on both of the cars. Both will be damaged, both will stop,...
Now picture a car colliding with a mountain. The car will be damaged and stop. The mountain will not move.
The mountain doesn't "feel" the impact of the car that much, because the mountain is very huge compared to the car.

Now back to very small things... Light consists out of particles called photons. If you want to observe a table (or another "big" thing), you can throw as much light particles on it as you want without the table moving. We are used to observe anything without changing the thing. A table stays a table whether you look at it or not.

Probably you can already guess what will come... quantum mechanical particles change their behaviour when you observe them. When a photon collides with an electron, the electron will get knocked away, it's die starts rolling again... the same is true about the photon.

There is nothing magical about this. There has been lots of nonsense been said and written about quantum mechanics and observation... You don't need a conscious person to "observe". It's not something that works from a distance. When you see the electron due to that photon, the photon has already interacted with the electron and knocked it away. You won't know how the electron behaved before the photon knocked it away, but you're able to tell (from the photon's behaviour) how the electron is behaving now.

 

[uumlau]

Well, I did Einstein's Special and General Theory of Relativity in a nutshell in a different thread. Let's see if I can manage quantum physics.

The best book on the topic would probably be Feynman's QED (the layman's version). QED stands for quantum electrodynamics, which is the theory of how light and electromagnetism interact on the quantum level. [EDIT: I see a prior poster also recommended it. I 2nd the recommendation. And 3rd it and 4th it. Also, try Feynman's lectures in Project Tuva (google it): there's a section on really basic quantum mechanics.

The main problem with explaining quantum physics is that it all sounds like a series of counterexamples to Newtonian classical physics. "It works just like normal, except it's probabilities and particle-waves when things get really small." Except that's a fairly bogus explanation, since the main rule of quantum mechanics is "nothing acts like normal once the scale is small enough."

I can't even begin to explain quantum mechanics the same way I can relativity. Relativity is fairly specific, covering specific phenomena. Quantum physics, on the other hand, covers everything. I mean everything.

It explains why the sun doesn't burn out in a single flash (this is the origin of Planck's constant and blackbody radiation. It explains how a black hole is possible. It explains how a black hole disintegrates. It explains why you don't fall through the chair you're sitting on. It makes modern computers possible. It explains how nuclear reactions happen. It lets us know that there is something very very wrong with the current theory of gravity. It lets us run MRIs that detail the insides of a person without cutting one open. It explains how atoms are structured and how they bind into molecules. It explains why certain materials have certain colors. It's essential to how we use atomic clocks to measure time.

The above is not an exhaustive list. Quantum mechanics explains pretty much all material science knowledge we have of the world except things like gravity, biology, evolution, and so on.

 

[Tamske]

The main problem with explaining quantum physics is that it all sounds like a series of counterexamples to Newtonian classical physics. "It works just like normal, except it's probabilities and particle-waves when things get really small." Except that's a fairly bogus explanation, since the main rule of quantum mechanics is "nothing acts like normal once the scale is small enough."

You're absolutely right.
Saying "quantum is classical except..." is the same as saying "an ENTP is an ISFJ except he's not introvert, not sensing, not feeling and not judging" - to use an example that would be well understood on a typology forum

I still want to compare with classical mechanics, because classical mechanics is what we are used to ("just like normal"). Like I would explain the ENTP mind to someone who knows the ISFJ type. You know what "introvert" means? That's like this and that, isn't it? That's how an ISFJ acts, isn't it? Well, now, "extravert" is like this...

You know determinism? Like classical mechanics works? Well, now... this is probabilistic. That's how quantum mechanics works.
You know observing? Just observing, not meddling with something? Like classical mechanics works? Well, now... in quantum mechanics, observing and meddling is one and the same.
I'll tackle quanta next...

 

[entropie]

Another important difference is, dunno if it was mentioned yet, newtonian physics are based on the principle of cause and effect, while in quantum physics it sometimes seems like there is an effect without a cause.

Basically this means, since the most part of quantum physics still deals primarily with running equations, the theory cant be unified with newtonian physics cause in the latter the basic principle demands cause and effect to be real.

As an observer one may ask now, why then deal with equations at all and not just rely on the things I can practically prove. The answer is, we are centuries away of proving anything from quantum physics, cause we do not have the technology. So physics look at the apple and then specualte by drawing similiarities to other fruits they have taken apart how the core of the apple may look like.

Regarding quantum physics, I still think the theory from Stargate is the most plausible, in which quantum physics was considered as one way from the past were mankind went wrong

 

[Fluffywolf]

Although what I'm about to say is symbolic and should in no way be taken as a fact. I see the difference of physics and quantum physics much like the difference in two dimensions. Quantum physics just adds another dimension in which it is measured on different boundaries and rules. And whilest they both sometimes seem to contradict each other. The contradictions are nothing more than lack of perspective understanding.

Anyways, like I said, symbolic. >.> *hurries along*

 

[yenom]

The Elegant Universe- Brian Greene

This will cover all those things you mentioned and is quite accessible as an introduction to general relativity and quantum mechanics as well.

Thank you Jock.