by Special relativity is beyond weird. Among his many statements are that moving clocks go slow and moving rulers slow down. But how are we going to make sense of this? To understand the physics of relativity, we need to go back inside time a little.
In 1865, James Clerk Maxwell he discovered that what we call “light” is actually waves of it electricity and magnetism. But like all waves, these waves needed to be waved through something. Sound waves move through the air. Ocean waves move through the oceans. So Maxwell believed that light waves traveled through a substance known today as the proper ancient luminous ether.
This “aether” (or “ether”) had certain strange properties. You couldn’t feel it, touch it, smell it or feel it. So it had to be almost invisible but it had to let the light through, so it had to be there. In the late 1800s, there were many debates about the nature of the aether, and it turns out, everyone was wrong.
Related: The double-slit experiment: Is light a wave or a particle?
But they didn’t know they were wrong until a pair of scientists determined our movement by measuring the aether in 1887. It was Albert Michelson, of the Case School of Applied Science, and Edward Morley, of Western Reserve University, who invented the those two. an experiment we now call the Michelson-Morley experiment at what we now call Case Western Reserve University.
The basic idea is that if the aether exists, we should be swimming through it and we should notice this movement as a change in the speed of light.
The Michelson-Morley experiment attempted to measure this and failed miserably. So there was a problem. Light is a wave, and it has to move through something – the ether. But we can’t seem to measure our own movement through the aether. So what’s going on?
Long contractions
Shortly after the Michelson-Morley experiment, the physicist Oliver Heaviside noticed something exciting: When electric charges are set in motion, their electric fields move slightly in the direction of that motion.
Then came Hendrik Lorentz, who had a great idea: If we are all made of electric charges and the fields shrink when they move, then maybe we Reduce when we move. So we can’t measure changes in the speed of light due to distance contraction – as we move through the aether, the speed of light changes, but so does our measuring apparatus, which cancels it out.
This was considered a fairly successful theory; he worked and explained all the details. Matter arises when it moves from some physical interactions, and the ether exists but cannot be detected.
Then, Einstein he showed up and asked a very important question: If this aether is always and forever invisible, then why do we need it? Why don’t we just let things stand on their own — not as some experimental result we don’t like to explain, but as a bare fact the universe?
This is Einstein’s great result. Others were working towards relativity, but no one made the leap he did. Einstein declared that distance contraction is a feature, not a bug, in the universe. No more aether, don’t try to fit electromagnetic square pegs into a round hole of aether. Length of contract when they move. Period. End of discussion.
The Einstein distance contraction was slightly different from the Lorentz contraction. For Lorentz, it was a physical effect, things smoothing together. For Einstein, it was a feature space itself, independent of the actual objects. And this realization allowed Einstein to take another mighty leap.
The birth of relativity
For it all to work, Einstein realized that some give and take was necessary. You can’t have length contraction – rulers shrink in motion – by itself. You also need time dilation – moving clocks run slowly. These always work together to allow every observation and every point of view to make sense.
For example, take the humble muon, heavier sibling the electron. Because the muon is massive, it has a short lifetime – only 2.2 microseconds. When energetic particles hit air molecules in the upper atmosphere, they generate muons which then streak down towards the ground.
These moons travel at nearly the speed of light, but not yet fast enough to reach the ground in their short lifetimes. But relativity teaches us that clocks move slowly – from our perspective, the muons continue much longer, so they have more than enough time to make the trip.
Related stories:
—The ‘twin paradox’ shows us what it really means for time to be relative
—Distortions in space-time could end Einstein’s theory of relativity
—Is time travel possible?
But the muon has a different view. He does not experience time dilation from his own perspective, from which he only exists for 2.2 microseconds. So how does the muon have enough time to get the ground from his perspective? The answer on this side is length contraction – from a fast muon point of view, the distance to the ground is much shorter, so it’s not that far to go.
Special relativity it is the mathematical machinery we need to change perspectives and keep everything organized. The universe may be crazy, but at least it follows rules we can understand.
