ONE HUNDRED YEARS LATER: Isaacson explains Einstein's "key insight!"

FRIDAY, APRIL 15, 2016

Part 4—Woman B banished from Earth:
To what extent was Walter Isaacson able to make Einstein easy?

Let's put that a different way:

To what extent was Isaacson able to explain the "eureka moment" which led Einstein to his special theory of relativity, the revolutionary theory he propounded in 1905? To what extent was Isaacson able to explain the "key insight" which lay at the heart of that theory, Einstein's "great conceptual step?"

One hundred and eleven years later, we'd say he didn't explain it well. In fairness, we'll offer a quick excuse:

It's beginning to seem that explaining Einstein is hard!

Let's reset the scene for our continuing search. In 2007, Isaacson published a lengthy biography, Einstein: His Life and Universe. The book was a major best-seller. Isaacson presents a lucid and engaging portrait of Albert Einstein the person.

Here's the problem. When the science hits the fan, the lucidity quickly breaks down.

In Chapter Six, Isaacson accepts the special relativity challenge. He attempts to explain the revolutionary theory Einstein propounded when he was just 26.

In Wednesday's report, we showed you the passage in which Isaacson sets the stage for that famous breakthrough. In Isaacson's presentation, Einstein is speaking with Michael Besso, a "brilliant but unfocused engineer" friend, when his "eureka moment" occurs.

Within five weeks, Einstein had submitted "his most famous [scientific] paper" for publication. A scientific revolution has begun.

On page 123 of his fascinating book, Isaacson starts trying to explain the "key insight" which produced, or emerged from, that eureka moment. To what extent was Isaacson able to accomplish this task? For today, our analysis starts with this passage, in which Isaacson seems to define the key insight:
ISAACSON (page 123): 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.”

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.
As you can see, we're on our way to the "thought experiment" Nova tried to explain last November, in its hour-long broadcast, Inside Einstein's Mind. That rumination was described by Einstein himself in his 1916 book, Relativity: The Special and The General Theory, a brief book which was aimed at general readers.

Isaacson is on his way to that thought experiment. In his very next paragraph, he starts describing the two lightning strikes and the fast-moving train, just as Nova did last fall, following Einstein's own book.

We're about to encounter that fast-moving train and the light from those two lightning strikes! That said, let's make a few observations about possible problems which have already surfaced in Isaacson's text, in just the two paragraphs we've already posted.

For starters, let's note this possible problem. In this, his first bite at the apple, Isaacson is referring to events which "appear to be" simultaneous. We note that fact because, a few paragraphs later, he seems to switch to ruminations about events which "are" simultaneous, without explaining the switch.

That may or may not be a problem. That said, one apparent problem already does exist. In this, his opening presentation, Isaacson has erased Woman B from the face of the earth! Here's how that atrocity happened:

Isaacson makes a ringing declaration concerning Einstein's "key insight:"

"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."

It sounds like that will always be true. Isaacson doesn't say that these two events may not appear to be simultaneous to another observer who's moving rapidly. He says the two events in question will not appear to be simultaneous to some such observer.

We don't know why he said that. As we've endlessly noted, if Woman B is in the caboose of the fast-moving train, the two events may well appear to be simultaneous to her! And she is moving at very high speed, on a fast-moving train.

Woman B has been wiped from the earth. But then again, so has Man B! As we postulated earlier this week, he's the fellow who is standing at the far end of the railway platform which Isaacson will soon describe.

Man B isn't moving at all. But as we've noted this week, the two events we'll soon be discussing will not appear to be simultaneous to him!

The two events will appear to be simultaneous to the one observer Isaacson will cite, the man who's standing at the midpoint of the railway platform. But those same events will not appear to be simultaneous to Man B, who is standing all the way down at the end of the platform!

These players seem to undermine Isaacson's key declaration. But as Isaacson sets the scene, Woman B and Man B have both been erased from the earth. In that sense, his presentation already seems to have a rather large problem.

There's one more problem with Isaacson's presentation. That problem is lodged in this somewhat puzzling claim:

"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 will soon be talking about Einstein's two lightning strikes. Given the way they'll be described, is it true that "there is no way to declare that the two [lightning strikes] are truly simultaneous?"

We're not sure why Isaacson would say that. In the relevant part of his brief 1916 book, Einstein presents "the most natural definition of simultaneity"—the "most natural definition" of what it means to say that two events are simultaneous. (Click here, see chapters 8 and 9.)

According to that definition, the two lightning strikes in our thought experiment actually are simultaneous. They don't simply appear to be simultaneous. According to Einstein's most natural definition, we would say that they actually are!

In our view, Isaacson is already in a world of hurt even before he starts describing Einstein's famous "thought experiment." But as his presentation continues, that's what he does next:

As he continues, Isaacson describes the famous "thought experiment" with which Nova struggled last fall. Essentially, that's all he does in the following passage.

Below, you see Isaacson's text, in which he describes the railway platform, the fast-moving train and the two lightning strikes. He doesn't refer to the man on the platform and the woman on the train; they were inventions of Nova.

Instead, Isaacson simply refers to two "observers," just as Einstein did. To see the "drawing" to which Isaacson refers, click here for Einstein's own book and scroll to page 30:
ISAACSON (continuing directly): Einstein later explained this concept using a thought experiment involving moving trains. Suppose lightning bolts strike the train track’s embankment at two distant places, A and B. If we declare that they struck simultaneously, what does that mean?

Einstein realized that we need an operational definition, one we can actually apply, and that would require taking into account the speed of light. His answer was that we would define the two strikes as simultaneous if we were standing exactly halfway between them and the light from each reached us at the exact same time.

But now let us imagine how the event looks to a train passenger who is moving rapidly along the track.
In a 1916 book written to explain this to nonscientists, he used the following drawing, in which the long train is the line on the top:


Suppose that at the exact instant (from the viewpoint of the person on the embankment) when lightning strikes at points A and B, there is a passenger at the midpoint of the train, Mt, just passing the observer who is at the midpoint alongside the tracks, M. If the train was motionless relative to the embankment, the passenger inside would see the lightning flashes simultaneously, just as the observer on the embankment would.

But if the train is moving to the right relative to the embankment, the observer inside will be rushing closer toward place B while the light signals are traveling. Thus he will be positioned slightly to the right by the time the light arrives; as a result, he will see the light from the strike at place B before he will see the light from the strike at place A. So he will assert that lightning hit at B before it did so at A, and the strikes were not simultaneous.
As on Nova, so too here. To the observer who's standing on the railway platform, the lightning strikes will "appear to be simultaneous." To the observer on the fast-moving train, the light from one strike will arrive before the light from the other strike.

In that sense, the strikes will not "appear to be simultaneous" to that observer, who is indeed "moving rapidly."

Of course, if another observer is in the caboose of that fast-moving train, he might be passing the observer on the platform just as the light from the two strikes arrives. That observer is also "moving rapidly."

But uh-oh! To that rapidly moving observer—to Rapidly Moving Observer B—the two lightning strikes will "appear to be simultaneous," in the language of our parable. Isaacson's original declaration has started breaking down.

That said, Isaacson's account has banished Rapidly Moving Observer B from the face of the earth. Ninety-one years after Einstein's own book appeared, it still hadn't occurred to Isaacson that the lightning strikes actually might "appear to be simultaneous" to "another observer who is moving rapidly."

Isaacson's original declaration has already broken down. That said, toward what point is Isaacson heading? What exactly is the "key insight" derived from this thought experiment?

As he continues, Isaacson tries to explain—and he produces a muddle. Einstein said "embankment" instead of "railway platform:"
ISAACSON (continuing directly): “We thus arrive at the important result: Events that are simultaneous with reference to the embankment are not simultaneous with respect to the train,” said Einstein. The principle of relativity says that there is no way to decree that the embankment is “at rest” and the train “in motion.” We can say only that they are in motion relative to each other. So there is no “real” or “right” answer. There is no way to say that any two events are “absolutely” or “really” simultaneous.

This is a simple insight, but also a radical one. It means that there is no absolute time.
Instead, all moving reference frames have their own relative time. Although Einstein refrained from saying that this leap was as truly “revolutionary” as the one he made about light quanta, it did in fact transform science. (Isaacson's italics)
In fairness, Isaacson constructs a more sophisticated muddle than Nova does. In this case, he starts constructing his muddle by directly quoting Einstein himself, in a passage from Chapter 9 of Einstein's brief book.

We'll look at Einstein's book in our next block of reports. For today, let's restrict ourselves to these basic questions about Isaacson's work:

Do we really understand what Isaacson has said in this passage? Would we be able to explain his account of Einstein's "key insight," which "did in fact transform science?"

Would we know how to answer basic questions about this "radical" insight? Remember, it's Isaacson's burden to explain this revolution to us. As readers, we aren't required to pretend that Isaacson has made the science clear, that it must be our fault if we remain confused.

Uh-oh! According to Isaacson, this is Einstein's key insight:
There is no way to say that any two events are “absolutely” or “really” simultaneous...there is no absolute time. (Isaacson's italics)
We'll go first! We have no idea what that is supposed to mean. Just for starters, here's why:

Applying Einstein's "most natural definition," it's easy to say that the two lightning strikes in that thought experiment are "really" simultaneous.

According to Einstein's "most natural definition," two events are simultaneous if light from the two events reaches an observer midway between them at the exact same time. And that's what happened in this event, as described by Einstein himself!

Applying his "most natural definition," the two lightning strikes really "are" simultaneous, however they may "appear" to various observers. This isn't a complex observation. Isaacson has constructed a muddle around this rather elementary point.

In fairness, Isaacson emerges with a deep-sounding claim: "There is no absolute time." It's the kind of "mind-blowing" claim (we're quoting Nova) college freshmen will gasp about at two in the morning, especially if they're stoned.

That said, could you explain what that Zen-sounding statement actually means? Are you sure it means anything at all? For a bit of perspective, consider a simple thought experiment concerning the physics of sound:
Simple thought experiment:
John Smith has parked his brand new red convertible by the side of the road. The top is down. He has the car radio on, turned to highest volume.

Observer A is standing next to the car. Her eardrums are ready to burst, the radio is so loud.

Observer B is a quarter mile down the street. He can see the bright red car, but he can barely hear the radio.
It's easy to imagine some such set of events happening in the real world. Here's what wouldn't happen:

Based on the different experiences of those observers, no one would be mystified, or even surprised, by the fact that the car radio "seemed quite loud" to Observer A but not to Observer B.

No one would think we should try to discern how loud the car radio "really" is. No one would think that even made sense.

Most important, no one would conclude from these events that there is no absolute car radio volume. No one would be inclined to form some such metaphysical-sounding statement. No one on earth would take that route, not even a gang of stoned freshmen.

We all understand the basic physics of sound. More precisely, we all know that a source of sound may "appear to be very loud" if you're positioned right next to it, but not if you're farther away.

Similarly, people in the world of fast-moving trains would understand the basic physics of light and vision. They would understand that light from some event will reach you sooner if you're close to the event, but that additional time will elapse if someone else is farther away.

Many people already do understand this basic fact about light. Truthfully, that's all that's involved in that thought experiment, as least as it's been described.

Do you really have any idea what Einstein's "key insight" was? (A few pages later, Isaacson describes it as his "great conceptual step.")

We'll go first! We don't.

By banishing Woman B from the earth, Isaacson's book and the Nova broadcast created a vastly simplified picture, from which they drew some simple-minded conclusions. One hundred years after Einstein's brief book, this remains the best they can give us!

Those simple-minded, muddled constructions are part of our fascinating "culture of incoherence." In our next set of reports, we'll be asking an awkward question about these muddled constructions:

Is it possible that Einstein did a poor job explaining his own revolutionary work?

Is it possible that Einstein did that? Answer: Of course it is!

Albert Einstein didn't get famous as a skilled popular writer. Indeed, when he wrote his book for general readers, Einstein used his 16-year-old niece as his focus group. She was "baffled" by Einstein's text, Isaacson amusingly writes, but she wasn't willing to say so to her world-famous uncle.

Out of that wonderfully comical process emerged a book which is now one hundred years old. One hundred years later, our former Rhodes scholars and our PBS shows still can't begin to explain, or critique, what that famous book says.

Much like Einstein's teen-aged niece, we all agree not to notice. According to Isaacson, this is precisely the type of behavior Einstein always refused to engage in.

Coming attractions: What did Einstein say in his book? After that, it's on to Wittgenstein!


  1. It looks like Isaacson didn't understand Einstein's thought experiment. Do not read Isaacson! Do not watch the Nova episode! Read Einstein's book.

    Two events can be in the same place for one observer and not for another. Suppose lightning strikes the middle of the platform as the woman is passing. She'll say, "It was right next to me." Suppose lightning strikes again, as the caboose is passing the middle of the platform. She'll say, "It was behind me, next to the caboose." But the man will say, "They were both right here, next to me." For her, the events happened in different places, for him, in the same place.

    In the same way, one observer can say, correctly, that two events were simultaneous, and another can say, just as correctly, that one event preceded the other.

    Study the Lorentz transformation, derived in an appendix to Einstein's book.

    1. "For her, the events happened in different places, for him, in the same place."

      For her the events happened in the same place, but since she was moving past the event location, the second event happened behind her yet in the same location.

    2. I'll try to make it clearer. Suppose lightening strikes the engine just as the engine is passing the man on the platform. Then it strikes the caboose just as the caboose is passing the man. The woman says, "Lightening struck the train in two places." The man says, "Lightening struck twice right in front of me."

      The events occurred in the same place for him, but different places for her. Einstein's insight was that events can happen at the same TIME for one observer but different TIMES for another observer.

  2. Study? What kind of advice is that?

  3. This post seemed to go on forever. Was I standing in the wrong place?
    Bob Gardner
    Randolph, MA

  4. This comment has been removed by the author.

    1. Bob Somerby says:

      We don't know why he said that. As we've endlessly noted, if Woman B is in the caboose of the fast-moving train, the two events may well appear to be simultaneous to her! And she is moving at very high speed, on a fast-moving train.

      The two events will not appear simultaneous to her. The two events are not the light from the bolts reaching her. The two events are the bolts striking the ground and generating the light that reached her.

      Like Somerby, Woman B knows the light originating from a more distant event takes a longer time to reach her than light from a nearer event. Therefore she realizes that without knowing where each bolt struck she could not know when each bolt struck based only on the fact that the light from both bolts reached her at the same time. By the same token, Man B at the end of the railroad platform would not or, at least, should not assume the bolts struck at different times because the light from the bolts reached him at different times.

      If Woman B wants to determine if the bolts struck simultaneously or at different times she must know both when the light from each reached her AND where the bolts struck. Because Woman B knows the light from one bolt struck the ground next to the engine at the other end of the train and the light from a second bolt struck next to the caboose where she is sitting and the light from both bolts got to her at the same time, that's how she knows the bolts struck the ground at different times.

      Here's what Somerby's not getting. Light leaving the vicinity of the engine cannot get from the engine to the caboose any faster than the speed of light can travel the length of the train regardless of what speed or direction the caboose is moving.

      Someone on the ground shoots a bullet from a rifle at the caboose while next to the engine of a speeding train. The bullet is going 1000 mph, the train 200 mph. The relative velocity of the bullet to the train is 1200 mph.

      A bolt of lightning strikes the ground next to a locomotive and sends photons at the caboose. The photons are traveling at 186,000 miles per second, the train is traveling at .9 times that speed or at 167,000 miles per second. The relative velocity of the photons to the train is 186,000 miles per second.

      Man B will tell you the same thing about the speed of the photons which reached him from both strikes.

    2. Bob is getting two things right: Isaacson's explanation is wrong, and the Nova explanation is wrong. When Bob goes on to say Einstein's explanation is inadequate, I disagree. I think Einstein got it right, and he warned the reader it would take some effort.

      Relativity cannot be made easy.

    3. That's quite fair of you, impCaesarAvg.

    4. Mike, it's bad enough to exploit a woman almost struck by lightning. But to exploit a falling child -- truly, that's beyond the pale.

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