Part 1—This week's dramatis personae: What did Albert Einstein say in 1916, in Chapter 9 of a short, famous book?
The famous book bears this title: Relativity: The Special and the General Theory. It was Einstein's attempt to explain relativity to non-specialist readers.
Einstein had propounded the special theory of relativity in 1905, when he was 26. In 1915, he presented the general theory of relativity.
One year later, he tried to explain this scientific revolution in his brief, famous book. To peruse that book, click here.
Last November, Nova presented an hour-long broadcast, Inside Einstein's Mind. The broadcast was timed to mark the hundredth anniversary of general relativity.
About ten minutes into the program, Nova presented an explanation of the "thought experiment" which led Einstein to the special theory of relativity in 1905. To watch that broadcast, click this.
To our eye and ear, Nova's presentation made and makes no apparent clear sense. Before the week is done, we're going to look at the part of Einstein's brief book from which the PBS program was working, almost one hundred years later.
One hundred years later, we ourselves are going to make a strange suggestion. Einstein's own explanation of his historic thought experiment is muddy, clouded, unclear.
One hundred years later, our professors and journalists don't seem to have noticed. But so it goes inside our society's ubiquitous "culture of incoherence."
Is it possible? Is it possible that Einstein's explanation of his own work didn't and doesn't exactly make sense? Is it possible that, one hundred years later, our most famous professors haven't yet noticed this fact?
It may seem hard to imagine such a state of affairs. That said, Einstein's own revolution started with his rejection of the professors of his own day.
Are our professors sharper than his? We'll explore that question this week.
For today, let's start by reviewing the problem which arose in Nova's broadcast. More specifically, let's produce a dramatic personae to which we'll refer all week.
To get started, let's list the characters of the "brilliant thought experiment" the PBS program tried to describe and explain. As described by Nova, there were two players in Einstein's thought experiment. The thought experiment involved two people along with two lightning strikes:
NARRATOR: In a brilliant thought experiment, [Einstein] questions what "simultaneous" actually means, and sees that the flow of time is different for an observer that is moving versus one that is standing still.In Nova's treatment, we have a man standing on a railway platform and a woman passing by on a fast-moving train. If we restrict ourselves to Nova's treatment, our cast of characters will therefore look like this:
He imagines a man standing on a railway platform. Two bolts of lightning strike on either side of him.
The man is standing exactly halfway between them, and the light from each strike reaches his eyes at exactly the same moment. For him, the two strikes are simultaneous.
Then, Einstein imagines a woman on a fast-moving train traveling at close to the speed of light. What would she see?
As the light travels out from the strikes, the train is moving towards one and away from the other. Light from the front strike reaches her eyes first.
For the woman on the train, time elapses between the two strikes. For the man on the platform, there is no time between the strikes.
This simple thought has mind-blowing significance. Simultaneity, and the flow of time itself, depends on how you're moving.
Dramatis personae, Einstein's thought experiment:If we restrict ourselves to Nova's account, that's our complete cast of characters. From the story as Nova tells it, Einstein deduced this "mind-blowing" conclusion:
The man on the railway platform: This man is standing at the midpoint of a very long railway platform.
The woman on the train: The woman is riding in the middle car of a very long fast-moving train. She's passing the man on the railway platform at a high rate of speed.
"Simultaneity...depends on how you're moving." At first glance, that conclusion may appear to be sound.
(Warning! In street cons, the "mark" is always sure he knows under which shell the marble is hiding.)
At first glance, Nova's conclusion may appear to be sound. As described by Nova, the lightning strikes will at least seem to be simultaneous to the man on the platform. But the lightning strikes won't seem to be simultaneous to the woman on the train. And she is moving very fast, while the man is standing still!
Case closed, Nova has said! Simultaneity depends on how you're moving. If we leave the matter there, we can exit the Nova program with the sense that we've mastered some "mind-blowing" physics.
Unfortunately, Nova's limited, two-person presentation doesn't quite seem to make sense. When we watched the program last fall, we thought that presentation was one of the worst non-explanation explanations we had ever seen.
A few weeks ago, we began explaining that claim by introducing two more characters. Let's recall who they were:
First, we introduced Man B. This man is standing all the way down at the end of the very long railway platform.
(In his 1916 book, Einstein specifies that we're talking about "a very long train." He further specifies that the two lightning strikes occur "at two places A and B far distant from each other.")
Uh-oh! Even though Man B is standing still, he will experience those lightning strikes much as the woman on the train does. She will be directly adjacent to Man B's position when light arrives from the nearer strike. She is in motion, he is not. But in terms of simultaneity, they will experience the two lightning in much the same way.
For Man B, "time elapses between the two strikes," in the language used by Nova. For Man B, "the two strikes are [not] simultaneous," again using Nova's construction.
Man B introduced confusion into Nova's story-line. To him, the two strikes won't seem simultaneous, even though he's standing still, like the original man on the platform.
Man B introduced confusion into this story. Woman B made things even worse.
We said that Woman B was in the caboose of that fast-moving train. She's moving at the same high rate of speed as the original "woman on the train." But because she's at the rear of their train, she's directly adjacent to the original "man on the platform" when the light arrives from the two lightning strikes.
In terms of simultaneity, we'll allege that Woman B will experience the lightning strikes exactly as the original "man of the platform" does. As with him, so with her—the light from the two lightning strikes will reach her at the exact same time.
For Woman B, as for the original man on the platform, "the two strikes are simultaneous...there is no time between the strikes." But she's moving at a high rate of speed, and he is standing still.
We now have a more complex thought experiment, with a longer list of characters. For better or worse, our cast of characters will now look like this:
Dramatis personae, Einstein's (expanded) thought experiment:For us, Nova's presentation broke down when we imagined Man B. Like the original woman on the train, he won't experience the two lightning strikes as simultaneous. But she is moving at a very high speed, and he is standing stock still.
The man on the railway platform: This man is standing at the midpoint of a very long railway platform.
The woman on the train: The woman is riding in the middle car of a very long, fast-moving train. She's passing the man on the railway platform at a high rate of speed.
Man B: This man is standing at the end of the railway platform. He is directly adjacent to the woman on the train when the first light arrives from one of the lightning strikes.
Woman B: This woman is in the caboose of the fast-moving train. She is directly adjacent to the man on the platform when the first light from the two strikes arrives.
Presumably, he won't experiences the two lightning strikes in exactly the same way as the original woman. Because she's moving away from the more distant strike, it will take longer for the light from that strike to reach her eyes.
On the other hand, it seems that Woman B will experience the two lightning strikes in exactly the same way as the original man on the platform. Because he's midway between the two strikes, the light from the two strikes will reach him at the same time. Why wouldn't she have the same experience?
Back in November, we instantly pictured Man B down at the end of the platform. For him, "time elapses between the two strikes," as is the case for the original woman on the train.
What then, exactly, was the point of Nova's formulation? What becomes of Nova's "mind-blowing" take-away:
"Simultaneity...depends on how you're moving."
What becomes of that nugget formulation when we introduce Man B and Woman B?
In our new cast of characters, both of our men are standing still. But in the language of Nova, the strikes "are simultaneous" for the original man on the platform, but not for Man B.
Beyond that, though, a second problem is swimming around in Nova's presentation. The program makes no attempt to separate seeming from being. To wit:
The original woman on the train may initially judge that the two strikes were sequential, not simultaneous. That may be her first impression, based on the way the light reaches her from the two strikes.
That said, she will likely change her assessment when she's told that one of the strikes occurred closer to her position. We humans adjust our judgments in such ways about a wide array of phenomena involving light, sound and other sensory experience. We my such adjustments of judgement all the time.
(You experience two earthquake shocks. One shock rattles your dishes more; you judge that it was stronger. But you later learn the other shock occurred much farther away. You accept the claim you hear on the news—the shock which rattled your dishes less was in fact much stronger.)
Citizens, can we talk? To this day, we can't explain the point the Nova broadcast was making in the passage under review. Almost surely, you can't explain it either.
Tomorrow, we'll review the way Walter Isaacson described this same thought experiment in his best-selling biography, Einstein: His Life and Universe. His book appeared in 2007, ninety-one years after Einstein published his brief book.
On Thursday, we'll go to the ultimate source. How did Einstein explain and describe this important thought experiment?
One hundred years later, is Einstein's explanation clear? If not, riddle us this:
They've had a hundred years to do it. One hundred years later, can our professors explain this part of his book?
Tomorrow: Einstein's "eureka moment"