Part 2—Isaacson sets the scene: Just this once, just tell us the truth.
Do you understand—if necessary, could you explain—the "mind-blowing" nugget conclusion from Nova's presentation of Albert Einstein's "brilliant thought experiment?"
Tell the truth. We all know how to repeat script and cant, formulaics we may have received from academic authority figures.
We can all learn how to recite standard bumper stickers. But in the case of the Nova broadcast, could you really explain this conclusion:
"Simultaneity, and the flow of time itself, depends on how you're moving."
Let's simplify that a tad: "Simultaneity depend on how you're moving." Based on Nova's depiction of Einstein's thought experiment, could you really explain what that means?
Do you have a clear idea of what that statement actually means? Would you know how to explain it, especially if questions were allowed?
Bravely, we'll go first:
Based on Nova's presentation, we don't know how to explain that "mind-blowing" concept. Based on Nova's account of Einstein's thought experiment, we don't know how to invest that nostrum with something resembling clear meaning.
Quickly, let's review. Nova presented two characters—a man standing on a railway platform and a woman passing by on a fast-moving train.
In that sense, "how they're moving" is different. And Nova showed us something else—the light from a pair of lightning strikes would reach these two observers in a different sequence.
(For more detail, see yesterday's report.)
In Nova's example, the light from the two atrikes would reach the man at the same time. But for the woman, time would elapse between the arrival of the light from the two strikes.
"For him, the two strikes are simultaneous," Nova declared, using some shaky language. By implication, Nova also seemed to say that, for the woman, the lightning strikes weren't simultaneous.
The woman is moving, the man is not. "For him," the strikes "are simultaneous." For her, we're basically told that they aren't!
It seemed that things were moving along, until we imagined two more people. Man B was standing at the end of the railway platform. But uh-oh! Even though he's standing still, "for him, the strikes are not simultaneous."
Woman B is in the caboose of the train. But uh-oh! Even though she's moving as fast as the other woman, "for her, the two strikes are simultaneous."
"Simultaneity depends on how you're moving?" With the addition of these players, do you still feel sure you know what Nova means?
For ourselves, we don't know what Nova means. We don't know how to explain the "mind-blowing" conclusion offered by the PBS org.
If we might borrow from our Frost, something someone is withholding seems to have made us weak! And this is intriguing, because Nova really was describing the "thought experiment" which led Einstein to his special theory of relativity in 1905, when he was just 26.
Nova didn't invent its example. Einstein describes the same thought experiment in the book he published in 1916—a book intended to explain relativity to general readers.
That historic book bears the following title: Relativity: The Special and the General Theory. You can peruse the short book here. Nova was working from chapters 8 and 9 (pages 30-35).
Nova didn't imagine that thought experiment; it comes from Einstein's own account of his work. That thought experiment has long been considered to be quite central to Einstein's revolution.
How central to Einstein's work is that thought experiment? For today, let's review the way Walter Isaacson introduces that thought experiment in his best-selling biography, Einstein: His Life and Universe.
Isaacson's book appeared in 2007. As we noted a few weeks ago, it carried blurbs from an array of ranking professors, praising Isaacson for the way he'd managed to make Einstein easy.
Except when the science hits the fan, Isaacson is an extremely lucid writer. In Chapter Six, "Special Relativity," he starts us toward that thought experiment in the passage shown below.
In Isaacson's account, Einstein experiences a "eureka moment." Within five weeks, Einstein, then just 26, has written and submitted "his most famous [scientific] paper:"
ISAACSON (page 122): It was a beautiful day in Bern, Einstein later remembered, when he went to visit his best friend Michele Besso, the brilliant but unfocused engineer he had met while studying in Zurich and then recruited to join him at the Swiss Patent Office. Many days they would walk to work together, and on this occasion Einstein told Besso about the dilemma that was dogging him.Quickly, note a small hint of a possible problem.
“I’m going to give it up,” Einstein said at one point. But as they discussed it, Einstein recalled, “I suddenly understood the key to the problem.” The next day, when he saw Besso, Einstein was in a state of great excitement. He skipped any greeting and immediately declared, “Thank you. I’ve completely solved the problem.”
Only five weeks elapsed between that eureka moment and the day that Einstein sent off his most famous paper, “On the Electrodynamics of Moving Bodies.” It contained no citations of other literature, no mention of anyone else’s work, and no acknowledgments except for the charming one in the last sentence: “Let me note that my friend and colleague M. Besso steadfastly stood by me in my work on the problem discussed here, and that I am indebted to him for several valuable suggestions.”
So what was the insight that struck him while talking to Besso? “An analysis of the concept of time was my solution,” Einstein said. “Time cannot be absolutely defined, and there is an inseparable relation between time and signal velocity.”
Isaacson is about to start describing the thought experiment involving that fast-moving train. As he does, he offers this quote from Einstein: “Time cannot be absolutely defined, and there is an inseparable relation between time and signal velocity."
Isaacson hasn't tried explaining those statements yet, but he's already introduced an element of confusion. How many readers will have any idea what "signal velocity" means?
Because he's writing for general readers, the answer is "very few." But as he continues, Isaacson doesn't try to define this technical term. As best we can tell, the term appears nowhere else in his 551-page book—a book which is extremely lucid until the science starts.
We offer this as a minor point. Einstein actually used the term. There's no hard and fast rule which says it mustn't be quoted.
But just like that, a possible bit of confusion has wormed its way into Isaacson's text. For the general reader, the lucidity of this passage has already perhaps been eroded.
At any rate, Isaacson proceeds as shown below. As you can see, we're on our way to a seat on that fast-moving train:
ISAACSON (continuing directly): More specifically, the key insight was that two events that appear to be simultaneous to one observer will not appear to be simultaneous to another observer who is moving rapidly. And there is no way to declare that one of the observers is really correct. In other words, there is no way to declare that the two events are truly simultaneous.Isaacson goes on to describe and discuss the same "thought experiment" Nova discussed in last November's program. Like Nova, Isaacson is working straight out of Einstein's book.
Tomorrow, we'll see if Isaacson was able to craft a clearer account of that material. In our view, Nova tried and failed. Isaacson, a very clear writer, had a chance to do better.
For today, let's only note this:
Essentially, Isaacson says that the fast-moving train is part of Einstein's "eureka moment." After a few short weeks, he says this eureka moment led to Einstein's most famous scientific paper.
In his next paragraph, Isaacson starts describing the two lightning strikes. It's now his turn to try to explain the experiment's "mind-blowing significance."
How well was Isaacson able to do that? We'll leave you today with a minor warning:
You'll note he says that two events may not appear to be simultaneous to each of two observers. Is that the language Einstein used? We ask that question because, truth to tell, that isn't the language from Nova.
Einstein's work is hard to explain. Truth to tell, we don't know if anyone has ever done it.
That said, no one made Nova and Isaacson say that they could do it. It's up to them to accomplish the task they chose to undertake.
Can you explain what Nova and Isaacson are saying about that thought experiment? Remember—it's up to them to explain the science to you. It isn't your job to nod your head, like Einstein's niece, and cover for these journalistic authorities.
According to Isaacson, Einstein always refused to blindly affirm his professors, to recite what he saw as their cant. We think you'd be well advised to trundle along in his shoes.
Tomorrow: Isaacson's attempt