Anything that doesn’t matter has no mass.

Hey guys! Today I will be giving you a glimpse inside my favourite course this semester – Modern Physics! While I am enrolled as a Biomedical Engineering student, I have decided to pursue a Minor in Physics. Some of the courses that can be put towards the completion of the Physics Minor include Quantum Physics, Nuclear Physics / Radiation Protection, Fundamentals of Astrophysics, Photonics & Optical Devices, Biophysics, and, of course, Modern Physics. Consider this post a mishmash highlighting some of the really cool physics concepts I’ve learned in the course so far, with a special focus on Einstein’s Theory of Special Relativity.

**Principle of relativity** – Proposed by Einstein, this simple but powerful idea states that the laws of physics are the same in all inertial reference frames. For classical mechanics and situations where objects move at velocities much smaller in magnitude than the speed of light, this isn’t a big deal. It’s when objects start approaching the speed of light when things get interesting…

**Constancy of the speed of light (c)** – Call it the “universal speed limit,” the speed of any object cannot exceed the speed of light (3*10^8 m/s, shortened to ‘c’) and this is true for all inertial reference frames, regardless of how said frames are moving with respect to each other. Imagine I throw a ball at you at 15 m/s while riding a bike at 5 m/s in the same direction. You would say that the ball approached at 20 m/s relative to you and the ground (the velocities are summed up). Now imagine I throw a ball at you at a a speed of 0.9999 c while travelling at a speed of 0.8 c on the same bike. In this case, the velocities are not summed up and the ball would travel at 0.9999 c relative to to my bike AND relative to you and the ground. Its crazy, I know.

**Spacetime event** – Any physical activity which occurs at a defined point in space and time. A spacetime event must be expressed in terms of its spacetime coordinates (x, y, z, t). These coordinates can vary from one inertial frame of reference to another. For example, the same event could occur in frame S and in frame S’ but the spacetime coordinates in S’ would be measured to have different values (x’, y’, z’, t’).

**Time dilation** – The “stretching” of a time interval, characteristics of moving clocks running slow. Time dilation is a consequence of the fact that the time interval between two ticks of a clock is the shortest in the reference frame in which the clock is at rest. For example, the clocks on the constantly orbiting International Space Station need to be synchronized to include the effect of time dilation, as eventually they will run a significant amount behind the clocks on Earth. What does this mean?

**The Twin Paradox** – Imagine you have a twin astronaut who decides to go on an interstellar trip. Your twin’s spaceship moves at approximately 0.95 c to a star that is around 10 light years away from our solar system, and promptly makes a u-turn. When your twin returns from the trip, he/she will be 14 years younger than you! This is a consequence of time flowing differently in two reference frames moving to each other.

That’s all for today! I find the material behind Modern Physics incredibly rich. One of the reasons why I am so passionate about this course is because of the outstanding instructor teaching the course, Dr. Pedro Goldman. He truly is a testament to what academics should strive towards – his excitement and infatuation with physics manifests beautifully in the classroom (sometimes he gets so excited he literally jumps across the room).

Until next time,

-MAZ