Register to reply 
Classical vs Quantum Mechanics 
Share this thread: 
#1
Sep2505, 11:34 PM

P: 61

I'll get straight to the point  my knowledge is based on Newtonian physics, I have not been introduced to quantum stuff in a classroom setting, only in casual conversation. I am in physics 111 at a university (calcbased), so keep in mind that I have not been introduced to most of the topics I’m delving in to. Still, I am very interested (and intrigued) by this sort of physics, and have a few elementary questions that are way above my head.
I have two questions that relate to each other; Q1: According to Newton's laws, perpetual motion is impossible. However, what I do not understand is the force that drives subatomic particles. What force is exerted on electrons to make them move about the nucleus? I understand things work differently at this level (where quantum mechanics comes in), however to me it just doesn't make sense. Q2: I remember always being told that light has mass  this is why light cannot escape a black hole. Einstein said that light accelerates instantaneously to 299,792,458 m/s. He also said that if you were to hop on a bike and petal to 9/10ths the speed of light, the light will still travel away from you at the speed of light. This makes sense, but what I don't understand is what determines that speed, and also what force is expended on light to propel it to that speed in any situation? Obviously, Newton’s laws no longer apply at this level. I would like to at least understand the vague concept behind my questions. But then again, I ask a complicated question, I should get a complicated answer….so me asking to put this in layman’s terms is like telling you to convert apples to oranges. Replies are greatly appreciated Thanks! 


#2
Sep2605, 12:58 AM

P: 2,251

In Planck units the speed of light is always 1 Planck length per Planck time. if some God somehow changes [tex] c [/tex], it's still 1 Planck length per Planck time. so the question is: "why is there 5.39121 x 10^{44} seconds in a Planck Times and why is there 1.61624 x 10^{35} meters in a Planck length? in other words, why did we choose our unit time and unit length to have the reciprocals of those two numbers  to have that many Planck times in a second and to have that many Planck lengths in a meter? now, i don't know why an atom's size is approximately [tex] 10^{25} l_P \ [/tex], but it is, or why biological cells are about [tex] 10^{5} \ [/tex] bigger than an atom, but they are, or why we are about [tex] 10^{5} \ [/tex] bigger than the cells, but we are and if any of those dimensionless ratios changed, life would be different. but if none of those ratios changed, nor any other ratio of like dimensioned physical quantity, we would still be about as big as [tex] 10^{35} l_P \ [/tex], our clocks would tick about once every [tex] 10^{44} t_P \ [/tex], and, by definition, we would always perceive the speed of light to be [tex] c = \frac{1 l_P}{1 t_P} \ [/tex] which is the same as how we do now, no matter if it could conceptually be changed to another speed. 


Register to reply 
Related Discussions  
Fundamental difference between classical and quantum mechanics  Introductory Physics Homework  2  
Quantum analogue of classical mechanics  General Physics  3  
Quantum analogue of classical mechanics  General Physics  3  
Quantum mechanics and classical physics  Quantum Physics  13  
Classical and quantum mechanics  General Physics  6 