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  1. Quantum Mechanics


    #654752013-11-05 10:21:28 *Rune said:

    Hi all, I was thinking that with the recent lack of a decent discussion threads lately, I feel that maybe we could try and discuss something that is pretty confusing for a change. Honestly though, the reason why I created this thread is because I feel genuinely interested in the subject but I can't really fathom the concept because it requires a lot of math to comprehend and most of the videos explaining it are mostly designed to mind-boggle you. And even when they've gone past that, then you have these things called 'paradoxes' which is... just...

    Anyway, this thread here is probably more of a resource bank as well as a discussion thread. Feel free to comment or share resources explaining how quantum mechanics work here and any concepts pertaining to it. I know it's rather 'general' and a bit cluttery at this point but hopefully this would get better as time goes on..

    Now then, let's get on our first concept.


    Table of Contents


    History of Quantum Mechanics

    Note: The following paragraphs are just a transcription of the video slightly rephrased. You can either just watch the video or watch it and read it or just read it; whatever you want. It mostly explains about how Quantum Mechanics came to be with experiments about the Electromagnetic spectrum, Black body radiation, and then the Plank relation before finally getting to Einstein's theory of how shining a light upon a metal plate can release electron within certain wavelength.

    This video gives out the brief history of Quantum mechanics which explains color and electromagnetic radiation. It begins with the experiment in 1750s where scientists burned different substances in flames and then put the resultant light through a prism. This experiment showed how different hot gases given off by the burning materials emitted different colors of light, or spectra.

    Furthermore, The experiment also showed how not every color in the spectrum appeared, as there were dark gaps in between the colors. This led to the discovery of how spectra could be used to detect and identify small quantities of elements within a powder that is put into a flame.

    In 1802, the white light of the sun was discovered to have little gaps in its spectrum just like it was with the substance burning experiment. However, the reason for this phenomenon and the relationship to each substance within it, remained a mystery.

    Past forward to a little over 100 years ago, scientists examined lights given off by solid heated objects. They discovered that these solid objects gave a continuous spectra and the color of the light. revealed the temperature of the object. This was important because then scientists realized that they could measure the temperature of an object from a distance like, the sun for instance.

    In addition, they also noticed that some objects also absorbed light extremely well, almost perfectly in fact. These were called *black bodies' because they virtually absorbed all the white that were shown on their surfaces. They also radiated perfectly and just as how the temperature also determined what colors were admitted through.


    http://i.imgur.com/7M6YZvA.png

    At 2:30 in the video, you can see how much light is admitted in a heated back body object in relation to its temperature in graph form.

    Basically, in cold temperature objects, there isn't that much light at all and most lights are at the end of the red spectrum. This spectrum of weaker than red is called the infrared spectrum and it is not visible to the naked eye. Right now, only red light is visible.

    With medium temperature object, most light admitted are in the yellow, orange, and green wavelengths. With the increase in wavelength, more lights also becomes more visible. Combining with the previous red, the resultant visible light from this now looks yellow.

    With really hot objects, most of the light are admitted through the blue spectrum and more light would be visible. When all the visible colors are combined, the resulting visible light will be white. This is the color path that a heated black body follows as the temperature rises, and this is shown in the video with the example of the heat inside a kiln.

    For more information on this, you can visit this link

    http://www.physicsclassroom.com/Class/light/u12l2a.cfm


    Now, with that explanation, we are brought into the theory of the color spectrum and electromagnetic waves just like what was taught during HS physics class. This is how we can see colors, which exist in the form of standing waves, or waves in which like guitar strings, do not move as if they are attached at both ends. The different wavelengths would then give out different colors like red, orange, yellow, and so forth.

    But then, once you get into higher wavelengths, past when all the colors have been admitted, you might expect more light to appear beyond the blue range right? After all, so far, the higher the wavelength means more color admitted in as we have seen with how every color would then produce a visible white light. But if you look at the chart here:

    http://i.imgur.com/PpkI4C9.gif

    And you have gotten X-Ray scans for example, you should know that at the higher end of the spectrum, the lights aren't visible to human eyes! This means that rather than admitting more light with the increase of wavelength, it actually admits less and less light once you go further the high-end of the scale (or the UV range). This was called the Ultraviolet catastrophe.

    But then, as the story goes, a great scientist called Max Planck, figured out an explanation to this phenomenon. He concluded that the energy contained in the standing waves, did not and could not contain just any, and all different amounts of energy. Instead, the quantity of energy possessed had to be limited to a few specific discrete values of energy for each color!

    So, the blue light for example, can only have energy equal to: 0 ev (electron volts), or 3 ev, or 6 ev, or 9 ev, and so on. In general, Energy equals, any whole number, or 'n', times Planck's constant, or 'h', times the frequency of light 'ν' (Nu), or in formula form:

    E = nhv

    But notice how blue light standing waves cannot be equal to 1 ev, 2 ev, or 4 ev (that would be a different light entirely). Realizing how energy could have only discrete values was the beginning of quantum mechanics as we know it (and all of the ARRGGHHH!!! and table flipping that ensues in many a high school classrooms). The 'n' from the equation above would came to be called a 'quantum number'.


    Alright, coffee break here or whatever but that was a whole lot of material to sink in for just about 7 and a half minutes of video... Anyway, so far we've just covered the basics that you guys have (or will have) likely learned in highschool and stuff (if you'd pay attention). From here on, it's gonna get weirder as we bring in Albert Einstein into the equation...

    Why weirder? Well, for one, now we're going to get into the real quantum mechanics stuff. Stuff that will go into the electron realm and stuff that is really, really small. Because of this, there will be lots of ideas that are really really strange, almost as strange as theological debates only with electrons instead of God...

    Oh yeah also, there will be theological debates as well and I really couldn't blame them for going back to faith because some of these stuffs are really really weird. Even Einstein had to go the God part with the "God does not play dice with the universe" quote and then contradicting that statement afterwards and... ARGGGHHH

    But yeah, Let me know what you think of this so far. Now if you haven't realized yet, I pretty much kind of have an idea on all of these concepts... in a way... perhaps...

    But unfortunately, besides being good at physics in highschool, I have no further knowledge of these things other than reading about it a lot as well as watching Youtube videos like this one a lot. If any of you is a theoretical physicist or something, then please if you would, post any resources or explanations regarding Quantum mechanics in this thread. Thank you.


    Credits and Links

    The videos in this thread so far, have been from The Cassiopeia Project, an effort to make science education videos free to anyone who wants them. I will use their videos that they have uploaded to youtube to explain quantum mechanics concepts which will consist of six chapters in total.

    However for now, here are some other videos regarding Quantum Mechanics that are available on Youtube:

    Other Links: