The speed of light being a constant sounds like a simple statement. But there is more to it, quite a bit more. Let’s look at what this constancy really means. At first glance, it says that if you are standing somewhere, and there is a ray of light going from your right to left, it has a speed c. And another ray of light going from left to right also has a speed c. So far, so good. Now let’s say you are in a rocket ship, as shown in the figure below, moving from right to left.
Special Theory of Relativity
When we hear about Einstein and the special relativity (or the special theory of relativity, to use the real name), we think of the famous 
equation, and weird things like the twin paradox. While those things are all true and important, the problem SR tries to solve is a completely different one. It is an attempt to defend a basic principle in physics.
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Quantum Mechanics – Interpretations
Whenever we talk about Quantum Mechanics, one of the first questions would be, “What about the cat?” This question, really, is about the interpretations of Quantum Mechanics. The standard interpretation, the so-called Copenhagen interpretation, leads to the famous Schrodinger’s cat.
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Quantum Field Theory
In this post on Quantum Mechanics (QM), we will go a bit beyond it and touch upon Quantum Field Theory – the way it is used in particle physics. In the last couple of posts, I outlined a philosophical introduction to QM, as well as its historical origin – how it came about as an ad-hoc explanation of the blackbody radiation, and a brilliant description of the photoelectric effect.
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Historical Origin of Quantum Mechanics
In this section, we will try to look at the historical origin of Quantum Mechanics, which is usually presented succinctly using scary looking mathematical formulas. The role of mathematics in physics, as Richard Feynman explains (in his lectures on QED given in Auckland, New Zealand in 1979, available on YouTube, but as poor quality recordings) is purely utilitarian.
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Quantum Mechanics
Quantum Mechanics (QM) is the physics of small things. How do they behave and how do they interact with each other? Conspicuously absent from this framework of QM is why. Why small things do what they do is a question QM leaves alone. And, if you are to make any headway into this subject, your best bet is to curb your urge to ask why. Nature is what she is. Our job is to understand the rules by which she plays the game of reality, and do our best to make use of those rules to our advantage in experiments and technologies. Ours is not to reason why. Really.
Classical Physics
The main difficulty in describing particle physics to general public is the fact that it is built on modern physics. Even if you are physics aficionado and did extremely well in your high school physics, what you have learned and loved is classical physics. The difference between classical physics and modern physics is not just more physics, but a completely new way of looking at the reality around us.
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Reductionism
In all our scientific endeavors, we use similar high-level techniques to understand and study things. The most common technique is reductionism. It is based on the belief that the behavior, properties and structure of large and complex objects can be understood in terms of their simpler constituents. In other words, we try to understand the whole (the universe, for instance) in terms of smaller, reduced constituents (such as particles).
Particles and Interactions
Recently, I gave a talk on particles and interactions to my daughter’s classmates who were planning on a trip to DESY, Germany and wanted to have an idea of what it was all about. As my first talk of this kind, I was a bit nervous because I didn’t know what level, and background, I should peg the talk at. I didn’t want to make it too basic, which I thought would be a waste of time. Nor did I want to make it too technical, which also would make it useless in a different way.
Sensory and Physical Worlds
Animals have different sensory capabilities compared to us humans. Cats, for instance, can hear up to 60kHz, while the highest note we have ever heard was about 20kHz. Apparently, we could hear that high a note only in our childhood. So, if we are trying to pull a fast one on a cat with the best hifi multi-channel, Dolby-whatever recording of a mouse, we will fail pathetically. It won’t be fooled because it lives in a different sensory world, while sharing the same physical world as ours. There is a humongous difference between the sensory and physical worlds.