I recently read Walter Isaacson’s Einstein: His Life and Universe. This ranks as my favorite book of 2023 - highly recommend reading it. Isaacson’s recent book on Elon Musk, released on September 12th, is also interesting.
Einstein is a great read, for it offers interesting scientific insights on theory and experiments but also interesting detail on how Einstein’s personality and life allowed him to make such discoveries. I usually struggle with biographies that lean too far into seemingly unimportant personal history. But, Isaacson’s book perfectly blends the scientific content with a vivid understanding of Einstein’s life and reconciles the developments in his life with his scientific work.
Rather than summarizing the book, I’ll take ideas from the book as a starting point and expand upon them below.
Gravity and Light Theory
In the first half of Einstein’s life, he relied heavily on thought experiments and relentless imagination to question conventional wisdom / classical physics and ultimately discover new theories. He was rebellious, revolutionary and extremely curious of the world.
For instance, as a young teenager, he pictured what it would be like to ride alongside a light beam. This thought experiment would ultimately lead to groundbreaking discoveries in physics - general relativity and quantum mechanics. In terms of light theory, his discoveries argued that light could be thought of as a wave but also as tiny particles called quanta. We’ll discuss in detail in the next post.
This would lead to a new realm of physics - quantum mechanics - that he would push against for the second half of his life as it destroyed the idea of strict causality found in classical physics.
Quickly on the history of physics. In 1666, Newton developed a theory of gravity that would hold for over 200 years. Newton is also famous for the Laws of Motion:
An object at rest remains at rest, and an object in motion remains in motion at a constant speed and in a straight line unless acted on by an unbalanced force
The acceleration of an object depends on the mass of the object and amount of force applied
Whenever one object exerts a force on another object, the second object exerts an equal and opposite on the first
Newton’s classical physics relied upon strict causality - a universe that is explained by universal laws, whether those laws have been discovered or remain unknowable.
In the early 1900s, Einstein began upending classical physics and Newtonian ideas with his Special Theory of Relativity (1905) and General Theory of Relativity (1915).
The General Theory of Relativity explains Einstein’s new theory of gravity.
In effect, Einstein argued that gravity is a warping of space and time. Imagine rolling a bowling ball across a trampoline. The ball bends the fabric of the trampoline. Now roll ping pong balls across the trampoline, and those that roll near the bowling ball will slope down the fabric towards the ball.
The ping pong balls would move toward the bowling ball due to a mysterious attraction towards the bowling ball. But, observing the fabric of the trampoline, we can observe that the source of this attraction is due to how the bowling balls create “gravity” by bending the fabric of the trampoline (spacetime).
The mass of the bowling ball creates gravity by bending the trampoline. In space, objects like planets, the sun or black holes create gravity by bending the fabric of spacetime.
Similarly, we can infer how gravity bends light. Light travels across space as a wave, from object A to object B. Much like a wave traveling across the ocean.
In our trampoline example, let’s roll the bowling ball to the middle of the trampoline, so it’s bending the middle. Now, let’s get a hose and shoot water across the trampoline. The water represents light waves traveling through space.
As the water runs across the trampoline, it would bend as it runs over the fabric near the bowling ball.
This is how light travels across spacetime. Gravity bends spacetime, which in turn bends the light waves that travel through spacetime. Below, you can see how the Sun bends light from a star as it travels to the Earth.
This was shown experimentally in 1919 by a team of astronomers measuring the light refraction during a solar eclipse, thereby supporting Einstein’s 1915 paper on General Relativity!
The equations in his 1915 paper estimated the degree to which light from a star would be bent by the sun, and the astronomers supported this finding 4 years later during a solar eclipse.
Let’s look at a real-world example.
Notice in this picture, from the James Webb Space Telescope, how some of the galaxies are blurry. That’s because there exist gravity-creating objects, such as black holes, in between the pictured galaxy and the observer on earth that is bending the light as it travels.
Also interestingly, there’s light pictured in this image from 2022 that captures light not long after the Big Bang.
Reflection Example
Let’s look at one more analogy to cement the idea of i) gravity represented as the bending of spacetime and ii) bending of light. Take a look at this picture.
Suppose the houses across the water are a distant galaxy. The photographer is an observer on earth. The water represents the fabric of spacetime.
Looking directly at the house, you see it pictured clearly as the light travels unobstructed from the house to your eyes.
However, notice the house’s reflection in the water. It’s blurry. The water bends the light. Yes, we know this is because the water has ripples. Objects that bend spacetime (thereby create gravity) are what create the ripples in spacetime. So imagine a bunch of black holes in the water as what’s creating each ripple.
That’s a simpler example of why the galaxies in the previous picture appear blurry.
Simultaneity
Another interesting idea is that no two events can be precisely simultaneous. Simultaneous events depend upon the reference point. Here’s an example.
Excuse my elementary drawing and handwriting.
Suppose you have two people sitting across from one another in a train car, person A and person B. They want to sign papers at exactly the same time to consummate a deal. To do this, they agree to sign immediately when a light turns on, which is situated at the middle of the table. Observer C is on the train and agrees to ensure both participants sign at the same time (i.e., when the light turns on).
So, the light turns on and both A and B sign at the same time. Observer C agrees. Ok, great. These events were simultaneous…right? Not necessarily.
Let’s now put a person on the train platform, observer D.
Now, let’s suppose the train is moving very fast across the platform. Person A is facing the direction in which the train is moving while person B has their back towards the train’s moving direction.
Let’s re-run the thought experiment. The light turns on, both A and B sign. Observer C will still say that they signed at the same time. But, observer D will say that they did not.
Observer D will witness person A sign before person B although observer C witnessed them signing at the same time. Why is this?
Because the light reaches person A before it reaches person B, so person A signs before B.
Since the train is in motion, when the light turns on, person A is moving towards the light, while person B is moving away from the light.
The speed of light does not change - this is a constant. It’s only that the light reaches person A first, and takes longer to reach person B.
We learn that simultaneity is relative - it depends on the reference point… in our example, the observer.
Think about this in another way. Suppose Observer D watches lighting strike both ends of the train car at exactly the same time, according to their perspective.
Although, that is not what Observer C witnesses. While the light is traveling from each end of the train to Observer C, Observer C is moving. At the moment that Observer D sees both flashes, Observer C has already moved past Observer D’s position (towards the front of the train / the front bolt), so he’s sees the front flash first, and then the back flash.
So what does this mean? That two events that appear to be simultaneous to one observer will not appear to be simultaneous to another observer who is moving rapidly, or vice versa.
And, we don’t know which observer is correct. There is no way to declare that the two events are truly simultaneous. And since there is no way to declare two events truly simultaneous, there is no such thing as real or absolute time.
The examples above indicate that there is no absolute time. Rather, all moving reference frames have their own relative time.
This idea that time is relative is in direct contrast to Newtonian physics. Newton believed in absolute time - thinking that there exists an underlying time independent of any observations. A tick-tock for the universe that is absolute.
Newton believed the same for absolute space and distance. In turn, Newton believed in a state of absolute rest, which was later abandoned for Einstein’s theory of relativity.
If you are sitting down right now, you might think that you are at rest. But you’re not. Sure, you are at rest relative to, say, the wall in front of you.
But what if we change the reference point? If a “at rest” person is at the equator, then they are spinning with the earth’s rotation at 1,040 miles per hour and orbiting the earth around the sun at 67,000 miles per hour. So relative to your wall, you are at rest. But relative to the sun, you’re moving incredibly fast!
It all depends on your reference point… so it’s all relative.
Time Dilation
Another interesting concept is time dilation.
Imagine shooting a light beam from the top of a ship to the deck. To an observer on the ship, the light will travel the exact length of the mast.
However, to an observer on land, the light beam will travel at a diagonal formed by the distance of the mast plus the distance that the ship has traveled forward from the time the light beam was shot to the time that it hits the deck.
The speed of light is the same to both observers. The land observer will see the light traveling farther before it hits the deck.
So, the exact same event (a light beam shot from the top of the mast to the deck) took longer when viewed by a person on land than by a person on the ship.
The distance the light must travel is the distance of the mast (10m) + the distance that the ship moved (x).
Noise Cancelling Headphones
Here is an interesting explanation of noise cancelling headphones that I discovered as I was researching wave theory.
Noise cancelling headphones is all about interference. The headphones record the waves and plays it back to you, but flipped!
When the original soundwave peaks the new one dips, and when the original dips the new one peaks.
Instead of being twice as loud, the waves interfere and cancel each other out.
Let’s visualize it.
So the waves cancel one another out and collapse into a flat baseline…meaning a reduced sound wave / less noise.
That’s all - just found that to be interesting.
Conclusion
Reading the Einstein book led me to further explore many of the interesting physics ideas presented here. This post is not all encompassing by any means and will deserve many follow up articles to further explore the ideas of gravity, time dilation, special and general relativity, black holes, the ether, the Doppler Effect, etc.
I wanted to keep this post from running on endlessly, so we’ll explore these ideas in more detail in future posts, as well as introduce other interesting topics.
For one, a discussion on classical physics vs quantum mechanics is warranted. In other words, General Relativity vs Quantum Mechanics. These two approaches collide and cannot reconcile into a Unified Field Theory to understand Everything.
Einstein spent the second half of his life trying to reconcile General Relativity with Quantum Mechanics but failed as the world became increasing more complex with discoveries of more particles and forces.
String Theory is an attempt to reconcile the two. We can explore that and the “spooky” nature of quantum mechanics next.
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Until next time.
John Galt
Very interesting and great lesson on physics for someone who knows nothing about physics (me). Fascinated to read more! I’d also love to hear your thoughts about Einstein’s role in the movie Oppenheimer/his public perception throughout his life, especially at the end. Did people give him the respect he deserved or was he laughed at for being crazy and questioning such long standing theories? What a brilliant mind!