Special relativity is beyond weird. Among its many expressions are that moving clocks run slower and moving rulers become smaller. So how do we make sense of this? To understand the physics of relativity, we need to look back. time A little.
in 1865 James Clerk Maxwell We discovered that what we call “light” is actually waves electricity and magnetism. But like all waves, these waves had to pass through something. Sound waves travel through air. Ocean waves move in oceans. So Maxwell believed that light waves traveled through a substance now appropriately known as the “luminescent ether” of ancient times.
This “ether” (or “aether”) was supposed to have some strange properties. You couldn’t feel it, touch it, smell it, or otherwise sense it. So it had to be almost invisible, but it also had to allow light to pass through it, so it had to exist. There was a lot of debate about the nature of the ether in the late 1800s, and it turns out everyone was wrong.
Relating to: Double slit experiment: Is light a wave or a particle?
But they didn’t know they were wrong until 1887 when a pair of scientists decided to measure our movement in the ether. The pair were Albert Michelson of the Case School of Applied Science and Edward Morley of Western Reserve University. An experiment we call the Michelson-Morley experiment at what we call Case Western Reserve University.
The basic idea is that if there is ether, we should be floating in it and notice this movement as a change in the ether. speed of light.
The Michelson-Morley experiment tried to measure this but failed completely. So there was a problem. Light is a wave and it has to pass through something, the ether. But we cannot measure our own movement in the ether. So, what’s going on?
long contractions
Shortly after the Michelson-Morley experiment, physicist Oliver Heaviside noticed something interesting: When electric charges are set in motion, their electric fields compress slightly depending on the direction of that motion.
Then came Hendrik Lorentz, who had the absolutely brilliant idea: If we are all made up of electric charges, and the fields get smaller as we move, then maybe We When we move, we shrink. That is, we cannot measure changes in the speed of light due to length contraction; The speed of light changes as we move through the ether, but so does our measuring device, thus canceling it out.
This was considered a highly successful theory; it worked and explained all the data. Matter gets crushed when it moves due to some physical interaction and ether is there but undetectable.
Later, Einstein appeared and asked a very important question: if this ether is always and forever undetectable, then why do we need it? Why don’t we let things contract on their own? Not to explain some experimental results we don’t like, but simply as an obvious fact of the matter. Universe?
This is Einstein’s great conclusion. Other people were working towards relativity, but no one could make the breakthrough he did. Einstein declared that length contraction was a feature of the universe, not a bug. No more ether, no more attempts to insert a square electromagnetic peg into a round ether hole. Lengths become shorter as they move. Period. End of discussion.
Einstein’s length contraction was slightly different from Lorentz’s. For Lorentz, this was a physical effect, like objects blending together. According to Einstein, this was a feature. space itself is independent of real objects. And this realization allowed Einstein to take another powerful step.
Birth of relativity
For anything to work, Einstein realized there had to be some give and take. You cannot achieve length reduction (reduction by moving the rulers) alone. You also need time dilation; Moving clocks run slowly. These always work together to ensure that all observations and all perspectives are meaningful.
Take, for example, the heavier modest muon. electron. Because the muon is so large, its lifespan is short; only 2.2 microseconds. When energetic particles hit air molecules in the upper atmosphere, they produce muons, which then travel toward the ground.
These muons travel nearly at the speed of light, but that speed is not fast enough for them to reach the ground in their short lifetime. But relativity teaches us that moving clocks run slowly; From our perspective, muons persist much longer, so they have more than enough time to travel.
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But the muon has a different perspective. It does not experience time dilation from the perspective that it will only exist for 2.2 microseconds. So how does the muon have enough time to reach the ground from its perspective? The answer on this side is length contraction; From the perspective of the fast muon, the distance to the ground is much shorter, so it doesn’t have as far to travel.
special relativity It is the mathematical machine we need to change perspectives and keep things organized. The universe may be crazy, but at least it follows rules we can understand.