Classical vs Quantum Mechanics

In summary, The speed of light is always 1 Planck length per Planck time, and this value is dependent on the units of length and time that we have chosen to use. These units are based on ratios between different physical quantities, and if these ratios were to change, our perception of the speed of light would also change. Therefore, the speed of light is not determined by any specific force, but rather by the units of measurement that we have chosen.
  • #1
NutriGrainKiller
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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 (calc-based), 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!
 
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  • #2
NutriGrainKiller said:
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,

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

the answer isn't complicated, but there is some insight required. i might suggest that you look at the Wikipedia article on Planck units: http://en.wikipedia.org/wiki/Planck_units . that speed of propagation (of either E&M or gravity) of 299,792,458 m/s is a number that is totally dependent on the units (meter and second) that it is expressed it. but when we measure anything, we ultimately only measure dimensionless numbers. (When one commonly measures a length with a ruler or tape-measure, that person is actually counting tick marks on a given standard or is measuring the length relative to that given standard, which is a dimensionless value. It is no different for physical experiments, as all physical quantities are measured relative to some other like dimensioned values.) that numerical value of 299,792,458 is only a consequence of the units of length and time we humans have decided use.

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.
 
  • #3


I understand your curiosity and interest in classical and quantum mechanics. Both of these theories play a crucial role in understanding the physical world around us. However, they are fundamentally different in their approach and principles.

Classical mechanics, based on Newton's laws, describes the motion of macroscopic objects like planets, cars, and even our own bodies. It is a deterministic theory, meaning that given the initial conditions of a system, we can predict its future behavior with certainty. However, when we look at the microscopic world, things start to behave differently and classical mechanics fails to explain their behavior.

This is where quantum mechanics comes in. It is a probabilistic theory, meaning that it can only predict the probability of a particle's position or velocity, not its precise values. At the subatomic level, particles behave like waves and have properties of both particles and waves. This is known as wave-particle duality. The force that drives subatomic particles is described by the wave function, which is a mathematical expression that determines the probability of finding a particle in a particular location.

Now, to address your questions:

Q1: In classical mechanics, the force that drives objects is caused by the interactions between them, such as gravity, electromagnetic force, or contact forces. In the quantum world, these forces are described by the exchange of particles called bosons. For example, the electromagnetic force is carried by photons, and the strong force is carried by gluons. These forces act on particles at the quantum level and determine their behavior.

Q2: Light does not have mass, but it does have energy and momentum. In Einstein's theory of relativity, mass and energy are equivalent, and this is why we talk about the mass of light. The speed of light, 299,792,458 m/s, is a fundamental constant of nature and is the maximum speed at which anything can travel in the universe. Light is always traveling at this speed, and nothing can change it. The force that propels light is the energy it carries. When light interacts with matter, it can transfer its energy and momentum, causing the matter to move.

In summary, the concepts of force and mass are different in classical and quantum mechanics. While classical mechanics explains the behavior of macroscopic objects, quantum mechanics is needed to understand the behavior of subatomic particles. I hope this helps to clarify your questions and provides a glimpse into the fascinating world of quantum mechanics. Keep exploring and asking questions,
 

1. What is the main difference between classical and quantum mechanics?

The main difference between classical and quantum mechanics is the scale at which they operate. Classical mechanics describes the behavior of large objects, while quantum mechanics describes the behavior of very small objects, such as atoms and subatomic particles.

2. How do classical and quantum mechanics explain the behavior of particles?

Classical mechanics explains the behavior of particles by using the laws of motion and gravity, while quantum mechanics explains the behavior of particles through the use of wave functions and probability calculations.

3. Can classical and quantum mechanics coexist?

Yes, classical and quantum mechanics can coexist. Classical mechanics provides a good approximation for the behavior of large objects, while quantum mechanics accurately describes the behavior of small objects. Both theories are used in different contexts and complement each other.

4. What are some real-life applications of classical and quantum mechanics?

Classical mechanics has applications in fields such as engineering, mechanics, and astronomy. Quantum mechanics has applications in fields such as electronics, computing, and quantum chemistry.

5. Are there any unresolved issues between classical and quantum mechanics?

Yes, there are still some unresolved issues between classical and quantum mechanics. One example is the incompatibility between the two theories in explaining the behavior of particles at the quantum level. This is known as the measurement problem and is a topic of ongoing research and debate.

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