04 May 2026 8 min read

Jokes aside

When I was in High School, my chemistry teacher scared most of our freshman chemistry class with a stunt that made one girl faint. After everyone took their seats, he produced an apple, two 200 mL beakers containing clear fluid, an empty 500 mL beaker, and an eye dropper. He proceeded to cut the apple in half with a butcher’s knife and then placed it back in locked drawer (he didn't trust us!). With the dropper, he squirted some of liquid A onto one half of the apple, and we all saw it eat away at the apple rather quickly. Then, after rinsing the dropper, he squirted some of liquid B onto the remaining half of the apple, which also ate it away. He then poured liquid A and liquid B into the 500 mL beaker, and swirled the mixture for a few moments (about twenty seconds). And then downed the whole thing in one big swallow! As it turned out, liquid A was hydrocloric acid, and liquid B was sodium hydroxide. They were both of the same molarity, and so when mixed, they produced salt water. It was perfectly executed, and might have given people ideas, but I don’t advise you try this yourself. If you do, make sure you know a lot about chemistry and that you get the concentrations right!!!

Jack, my neighbour was in his second year of studying Physics at Victoria University, Wellington when I was still in High School. He chatted with me sometimes about what he was learning at university. And also mentioned there were not many girls studying physics, but he found ways to mingle with them at parties. He said the best way to get them interested in physics and maths was to start with a joke. Since they were sharing travel stories at a party one time, he told them the ‘Sheep in Scotland‘ joke. A mathematician, a physicist, and an engineer are riding a train through Scotland. The engineer looks out the window, sees a black sheep, and exclaims, "Hey! They've got black sheep in Scotland!" The physicist looks out the window and corrects the engineer, "Strictly speaking, all we know is that there's at least one black sheep in Scotland." The mathematician looks out the window and corrects the physicist, " Strictly speaking, all we know is that at least one side of one sheep is black in Scotland."

The girls found this mildly amusing and then the talk turned to mobile phones. Jack got overconfident and began talking about GPS technology and Einstein’s Theory of Relativity. He told me later that he should have quit while he was ahead. I wanted to hear about it, even if it wasn’t popular with the girls at the party. So Jack humoured me with his knowledge. He told me GPS was physical proof that time was relative. What did that mean? Well he explained it like this.

Take two different observers (you vs. a satellite). You’ll find that between the two of you, you won’t agree on how much time has passed. That’s relativity and it’s weird. It happens because time can slow down for an object when it is moving very fast through space (known as time dilation). And gravity ‘curves’ spacetime, meaning that the weaker the gravity, the more time speeds up. These two effects, described as Special Relativity, and General Relativity respectively, have an impact on satellites in orbit around the Earth. GPS satellites travel at speeds of around 14,000km/h, making their clocks effectively, lose about 7 microseconds per day. Likewise, the weaker gravity in space means that their clocks gain about 45 microseconds per day. The net result is a combined gain of 38 microseconds. If we didn’t account for these 38 microseconds, GPS locations would drift roughly 10 kilometers every day, and render Google maps useless.

When the first GPS satellite was launched in 1977, many engineers didn’t believe the clocks would drift by 38 microseconds a day just because of ‘curved spacetime’. But to cover all bets, when the first GPS satellite was launched it was done so with a frequency synthesiser that could be turned on or off. After 20 days in orbit, the clock had drifted exactly as Einstein had predicted. The engineers then flipped the switch to apply the relativistic correction and the system finally worked.

Before Albert Einstein came up with his Special Relativity (in 1905) and General Relativity (in 1915), he made a decision to treat the speed of light as a constant. Treating the speed of light in a vacuum as a universal constant, independent of the motion of the source or the observer, was the key critical decision and fundamental postulate Einstein made to develop his Special Theory of Relativity. Prior to this, scientists believed that the speed of light would change when measured by an observer on Earth, because it was assumed that the Earth was moving through a ‘sea’ of aether as it orbited the Sun. If light were emitted in the opposite direction to the Earth’s motion, scientists expected that the speed of light measured would appear to be moving faster than if the light were emitted in the same direction as the Earth’s orbit.

To understand, you need to look at the “aether wind logic”. Scientists assumed the aether was a stationary, all-pervading substance throughout the universe. Because the Earth orbits the sun at roughly 30 km/s, they believed the Earth was moving through this stationary aether. This motion would create an "aether wind" pushing against the Earth, similar to the wind you feel on your face when riding a bicycle.

If Earth moves through the stationary aether at velocity (v) then this creates an aether wind blowing past the Earth at velocity (v) in the opposite direction. Light always moves through the aether at a constant speed (c). When emitting light in the same direction as the Earth’s orbit, Earth is “chasing” the light beam. The light is trying to move away at speed (c) but the observer on Earth is catching up at speed (v). The result: light appears slower (c-v). On the other hand, emitting light in the opposite direction of Earth’s orbit means the light beam and the Earth are moving away from each other. The light moves one way at (c) and the Earth moves the other way at (v). The result: the light appears faster (c+v).

The aether argument existed because at the time, every known wave required a physical medium to move. Sound needed air or water, ocean waves needed water, seismic waves needed the Earth. Since light was proven to be a wave, physicists assumed it needed a medium. They described aether as: weightless and invisible - it filled the “emptiness“ between stars and planet. Perfectly elastic - it allowed light to vibrate at incredibly high speed. Stationary - it acted as an absolute “frame of reference“ for the entire universe.

The "common sense" math of the day was Galilean Invariance. This principle stated that velocities were additive and the framework suggested that there was no universal speed limit. If you measure the speed of anything from a moving platform, you simply add or subtract your platform's speed to get the result.

Scientists in the 19th century thought this was correct and wanted to use the changes in light speed to calculate the Earth’s absolute velocity. By measuring how much the speed of light drifted from its theoretical constant, they hoped to prove exactly how fast the Earth was “drifting“ through the static universe.

However, when the Michelson-Morley experiment was performed to test the Earth’s absolute velocity relative to the stationary aether, they found that the speed of light was exactly the same in every direction. This created a massive crisis in physics because it showed absolute motion did not exist. For 200 years, Newtonian physics had successfully explained everything from falling apples to orbiting planets, and this experiment proved its core assumptions about space and time were wrong. The problem was that if there was no aether, there was no “stationary” centre of the universe. Without a fixed background, scientists could not define what “absolute rest” or “absolute motion“ even meant.

By the late 1800s, there were two "kings" of physics whose laws contradicted each other:

Newton: Said speeds should always add up (c+v).
Maxwell: His equations for electromagnetism showed light had one set speed (c), with no mention of a medium or observer motion.
The Crisis: The experiment proved Maxwell was right and Newton—the father of modern physics—was wrong about how motion works at high speeds.

The experiment was so precise that the "null result" couldn't be ignored as an error.

The Logic Gap: If Earth is moving, and light is a wave, the math demanded a shift in the light patterns.
The Crisis: The fact that no shift occurred suggested that either the Earth wasn't moving (which they knew was false) or the very laws of motion were broken.

Before Einstein, scientists tried to "save" the aether with increasingly strange theories:

Aether Drag: Maybe Earth drags a "bubble" of aether with it? (Disproved by star observations).
Length Contraction: Maybe objects physically shrink when they move through aether? (This was a "math trick" that didn't have a physical explanation yet).

The crisis lasted until 1905, when Albert Einstein published his Special Theory of Relativity. He suggested we stop trying to "fix" the aether and simply accept that the speed of light is constant for everyone, everywhere—even if it meant rewriting our understanding of time and space.

By making this decision, Einstein forced a complete overhaul of classical physics:

Abandonment of Absolute Simultaneity: Dictated that it is impossible to say in an absolute sense whether two distinct, spatially separated events occur at the same time. While in classical (Newtonian) physics, time is considered universal—meaning everyone agrees on which events happen simultaneously—relativity shows that the timing of events depends entirely on the observer's frame of reference, particularly when they are in motion relative to one another
Abandonment of the Aether: It made the theoretical "aether" (a medium supposed to carry light) unnecessary and redundant.
Relativity of Time & Space: This led directly to time dilation (time slowing down) and length contraction.
E=mc² The constancy of the speed of light is central to the derivation of mass-energy equivalence.

Down the road, the consequences of Einstein’s Special Relativity meant a lot of stranger than fiction concepts.

Time Dilation: Time passes slower for an object in motion compared to one at rest. At near-light speeds, years could pass on Earth while only hours pass for a pilot. Length Contraction: Objects physically shorten in the direction of their travel as they approach the speed of light. Mass-Energy Equivalence (E=mc²): Mass and energy are two versions of the same thing. A tiny amount of matter can be converted into a massive amount of energy (the secret behind stars and nuclear power). The Universal Speed Limit: Nothing with mass can reach the speed of light. As you speed up, your kinetic energy adds to your "effective" mass, making it harder and harder to accelerate further. Relativity of Simultaneity: Two events that happen at the "same time" for you might happen at different times for someone moving past you.

And the consequences of General Relativity included:

Gravitational Time Dilation: Time runs slower in stronger gravitational fields. Your feet actually age slightly slower than your head because they are closer to Earth's center. Light Bending (Lensing): Gravity warps space, so light traveling near a heavy object (like a sun or galaxy) follows a curved path rather than a straight line. Black Holes: If enough mass is packed into a small enough space, the curvature of spacetime becomes so intense that not even light can escape. Gravitational Waves: Huge cosmic events, like colliding black holes, create "ripples" in the fabric of spacetime that travel across the universe. The Expanding Universe: The theory showed that the universe cannot be static; it must be either expanding or contracting (leading to the Big Bang theory).

Jack had done me a great favour in sharing some of what he was learning at University with me. His enthusiasm was contagious and the ideas were jaw dropping! I took new interest in science classes at school and poked around in books to find out more.

See you in the next post!