HAS NEVER MADE SENSE: Einstein offered a thought experiment!


Isaacson, Nova described it: Way back in 1916, Albert Einstein was trying to make relativity accessible to people who aren't theoretical physicists. 

He described his intentions the following way in the preface to his short, historic book, Relativity: The Special and the General Theory:

The present book is intended, as far as possible, to give an exact insight into the theory of Relativity to those readers who, from a general scientific and philosophical point of view, are interested in the theory, but who are not conversant with the mathematical apparatus of theoretical physics. 

The limiting phrase, "as far as possible," may have served as a bit of a warning. At any rate, as he continued along in his preface, Einstein didn't guarantee that he could make Einstein easy, as we'll see below.

Einstein was one of the greatest theoretical physicists in human history. He wasn't necessarily equally skilled as a popular writer—as someone who could translate "the mathematical apparatus of theoretical physics," which he of course understood, into analogies and images the average person could understand.

At issue today is the way he explained an important concept in the very short Chapter IX of his book for non-specialists, a book which remains in print to this day. 

The chapter in question is only three pages long. (You can see the whole chapter here.) Its title—"The Relativity of Simultaneity"—names the important principle it sought to explain.

As we noted yesterday, Walter Isaacson drew directly upon the presentation made in that chapter in his sweeping biography, Einstein: His Life and Universe (2007). In a perfectly reasonable account of what Einstein wrote in that chapter, he describes Einstein's "key insight" as shown:

[T]he 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.

Two events which appear to be simultaneous to one observer will not appear to be simultaneous to another observer who is moving rapidly! In Isaacson's rendering, that was Einstein's key insight—or, at the very least, it was the first part of that insight.

In our view, that's a perfectly reasonable account of what Einstein presents in Chapter IX of his book. It should also be said that Isaacson, like everyone else, regards this as a major part of Einstein's special theory of relativity, which Einstein formulated in 1905, when he was just 26.

In Isaacson's account, that key insight came to Einstein in a "eureka moment"—in the "eureka moment" in which Einstein "took one of the most elegant imaginative leaps in the history of physics." As such, Isaacson describes that key insight playing a very important role in the creation of modern physics.

The relativity of simultaneity is routinely presented as a major building block in Einstein's paradigm-shattering "special theory." That said, there's one major problem with the presentation Isaacson offers in his well-received book, whose scientific accuracy was fly-specked by at least a dozen major physicists.

In our view, Isaacson's account follows Einstein's presentation in a perfectly reasonable way. Also, and unmistakably, Isaacson's account of that "key insight" just plain doesn't make sense.

AS WE NOTED YESTERDAY, Isaacson describes a "thought experiment" which Einstein presented in Chapter IX of his 1916 book. This thought experiment—this illustration of Einstein's thinking—involved a fast-moving train and a pair of lightning strikes. 

Yesterday, we showed you the way Isaacson introduced this thought experiment in his 2007 book. You can review Einstein's original text, rudimentary drawing included, by just clicking here.

In paraphrased fashion, here's the way Isaacson describes the thought experiment. In 2015, the narrator for an hourlong Nova broadcast on PBS describes the thought experiment in very much the same way:

In Einstein's thought experiment, a very long train is moving along a railroad track at a constant velocity. As it does, lightning bolts strike the embankment alongside the track at two distant places, A and B. 

As it hurtles down the track, the train is moving away from lightning strike A. It's moving toward lightning strike B. At this point, the human element enters:

A person is standing on the railway embankment as the long train hurtles past. He is standing exactly halfway between the two distant lightning strikes. For that reason, light from the two lightning strikes reaches him at the exact same time. 

"For him, the two strikes are simultaneous," the Nova narrator said in 2015, offering Nova's account of this part of Einstein's presentation. In his 2007 book, Isaacson says much the same thing, in a slightly more complex fashion.

So far, largely so good! If the person is standing halfway between the two lightning strikes, light from the two strikes will indeed reach him at the exact same time. For that reason, it will be natural for him to say that the two lightning strikes were simultaneous. 

So far, this makes perfect sense—but this is where Einstein's thought experiment really starts to kick in. Unfortunately, Einstein's presentation led Isaacson to state a conclusion which simply doesn't make sense.

Eight years later, Nova followed suit. In our view, Isaacson and Nova were being reasonably faithful to Einstein's presentation, and yet each stated a triumphant conclusion which doesn't seem to make sense.

THE PERSON STANDING ON THE embankment is halfway between the two lightning strikes. For the reason, light from the two lightning strikes reaches him at the same time. ("For him, the two strikes are simultaneous.")

That's where the wrinkle enters Einstein's thought experiment. In Isaacson's slightly stylized rendering, a second person now appears:

In Isaacson's slightly stylized rendering, a person on the very fast train is directly adjacent to the person standing on the embankment when the strikes occur. If the train was standing still, light from the two strikes would reach this second person at the exact same time, just as it does for the person standing on the embankment. 

That said, the train is moving ahead very fast. It's moving away from lightning strike A and in the direction of lightning strike B. 

Uh-oh! In the time it takes for the light from the two lightning strikes to arrive, the person in the train will have moved closer to lightning strike B and farther away from lightning strike A. Unlike the stationary person on the embankment, this second person is no longer halfway between the two lightning strikes.

Because the train has moved down the track, light from the two lightning strikes won't reach the person on the train at the exact same time. For this reason, the two lightning strikes won't seem to be simultaneous to the person on the train. 

For the man standing on the embankment, the lightning strikes will seem to be simultaneous. For the person in the fast-moving train, the strikes won't seem to have been simultaneous.

This is the way Isaacson understands Einstein's thought experiment. Unfortunately, this leads him to voice a sweeping conclusion which just plain doesn't make sense.

AS WE NOTED ABOVE, Isaacson describes the key insight emerging from this rumination in the following way:

[T]he 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.

It's clear that Nova understood Einstein's presentation in the same way, except even more simplistically, We'll examine the simplistic language from Nova's transcript in our next report.

For now, back to Isaacson. That's the way he understood the key insight which came to Einstein during his eureka moment. Unfortunately, he starts with a sweeping statement which doesn't seem to make any sense:

Two events that appear to be simultaneous to one observer will not appear to be simultaneous to another observer who is moving rapidly! 

In Isaacson's rendering, this is, or is part of, "the key insight" at the heart of Einstein's thought experiment. Unfortunately, this statement doesn't seem to make sense, a point we'll detail in our next report.

In closing today, we'll cite two major figures as we apologize for the delay in reaching our major points. One of these figures is the later Wittgenstein, who lamented the difficulty involved in untangling certain types of conceptual confusion.

"We feel as if we had to repair a torn spider's web with our fingers," Wittgenstein says at one point in Philosophical Investigations. Wittgenstein was never able to offer a simple account of what he was doing in his later work, but he was eloquent in this description of the tangled webs our highest intellectual elites have frequently managed to weave.

The second person to whom we refer is Einstein himself. In the preface to his 1916 book, he explicitly said that he wouldn't necessarily be able to make Einstein easy.

"I make no pretence of having withheld from the reader difficulties which are inherent to the subject," Einstein said in his preface. So too here, as we struggle with a remarkable set of facts:

By any normal standard, Walter Isaacson is very smart. Also, the scientific portions of his book were reviewed by at least a dozen major physicists.

Despite those facts, his explanation of the basic principle at issue here doesn't make any sense. So it can go, even today, at the top of our academic and literary elites, as they pretend to make Einstein easy and we pretend that we get it.

Tomorrow or Friday: Nova made it even simpler—and it doesn't make any sense. (To review Nova's transcript, you can just click this.


  1. Hello Mao, Cecelia. Look forward to your comments.

    1. Anonymouse 9:41am, I don’t have any overwrought statements suggesting that the bee in Bob’s bonnet is an attack on the entire concept of professional expertise and that his statements on age-related mental decline are an affront to cognitive science. You know…silly claims such as saying Bob doesn’t believe that racism exists and Bob is against the concept of public schools.

      I wouldn’t dream of suggesting that I personally do or do not find the Easier- Einstein books relatable. If I didn’t find them that then I would know that this is due to the point at which I, myself, am starting, and if I said that I did understand, I’d be a liar.

      I give credence to any doubts expressed about this book genre being able to live up to the sort of glowing endorsements found in the reviews that Bob has excerpted. I don’t find a damn thing wrong with any blogger being skeptical and derisive about that industry, or of human pretentious, or of bloggers being absolutely outraged over the modern day dumbing-down of once scrumptious fast food (ok, the latter is my thing). Bloggers write on what interests THEM.

      I also don’t find it unthinkable when Bob says that some of Einstein’s own attempts at describing complex concepts don’t make sense. He has repeatedly wondered if we have gotten to the point in the field of physics where language cannot relate what we know, or of what we think we know.

      Lord knows Bob is not saying that (or anything else on this subject) for the first time.

      I’m glad you missed me. Hope this post helps. The daily churning out of long-winded, chiding, and specious posts are the stuff of Anonymices with political (and psychological) axes to grind.

      If not a monetary one— per word.

    2. Somerby hasn’t made any statements on age-related mental decline.

    3. Somerb has never said he was against the concept of public schools. I don’t recall any anon saying he did.

    4. It is true that bloggers can write about whatever they want. That doesn't mean they can lie or dishonestly present quotes out of context or truncated to distort the meaning. They still need to be logical and reason well, especially when criticizing others for being illogical or not reasoning well. The internet has enough disinformation without bad bloggers spreading more. And of course, commenters have as much right to speak their minds as bloggers have to speak theirs.

      Mathematics is the language of physics.

    5. Anonymouse 9:20pm. actually bloggers can relevantly have a different interpretation of quotes than you. Actually, the burden of proof that anyone is lying is on whoever makes the accusation.

      Actually, just because you say so, Somerby isn’t to be automatically deemed unreasonable via his take on the latest movie version of Little Women to an Einstein Made Incredibly Easy review.

      We can and do ascertainthe context of the commentariat at this blog and yes, mathematics is the language of physics— book reviewers be damned…

    6. No, Cecelia be damned. You are the one saying that Somerby found language inadequate to explain Einstein’s theories. Not Somerby. He is finding the authors inadequate, not language.

    7. No, Somerby argues that language is inadequate in the midst of the industry congratulating itself for its clarity.

      You all be damned.

    8. Somerby,like his attendant fanboys, offers a confused mess of misguided logical positivism and right wing talking points; assertions are made that pointedly "contain nothing but sophistry and illusion." Somerby et al are coy about their agenda, due to a lack of coherency: relativity, lying, and racism aren't verifiable; context is abhorrent. So racism and inequality grows, misery finds increasing purchase, and while the left tries to help, the right smirks and shrugs.

      Righteousness is the "tell" of the guilty.

  2. "Einstein didn't guarantee that he could make Einstein easy"

    Einstein's theories of general and special relativity are not about Einstein. They are about the universe. Einstein didn't disover Einstein, he discovered how nature works. So, he was never trying to "make Einstein easier" but he was trying to explain how the physical world works.

    Somerby's use of language here is telling. He doesn't seem to have much of a conception of what scientists, including Einstein, are trying to do. That would impair his ability to learn from a science textbook, since his focus appears to be on Einstein and not on learning more about our physical world. That is perhaps why he glosses the distinction between a physicist writing about Einstein's ideas (such as Hawking) and a biographer, who is writing about the man himself (such as Isaacson).

    At least Somerby has stopped calling this Einstein's universe, which it has never been, any more than our universe belongs to any of us individually.

    How you look at things can influence what you find out. This is true whether you are Einstein or Somerby trying to read a physics book without thinking about physics. Is Somerby trying to play gotcha with Einstein? That depends on how big a fool he is.

  3. "It's clear that Nova understood Einstein's presentation in the same way, except even more simplistically,"

    If a show such as Nova explains something simplistically, that doesn't necessarily mean they understood it simplistically.

  4. "Two events that appear to be simultaneous to one observer will not appear to be simultaneous to another observer who is moving rapidly! "

    Why doesn't this sentence make sense to Somerby? It makes sense to me. There are many aspects of physics that are counter-intuitive. That is part of the fun of scientific discovery -- finding things that were not obvious using common sense or conventional wisdom.

  5. Somerby seems to understand that Godel at the end of his life was not the same as his younger self. Somerby calls Godel crazy in his old age. Why cannot Somerby understand that Wittgenstein, at the end of his life, may have been less of a philosopher and more of a crank too?

    Wittgenstein emphasized that language takes meaning from context and that because language is a shared endeavor, meanings cannot be purely personal, but derive from shared meaning. Current psychologists study "meaning spaces" arising from shared meaning and common experience across human beings. The current study of language bears no resemblance to that of the philosophers that Wittgenstein was criticizing. Somerby appears to have no notion of what is going on in linguistics, psycholinguistics, semantics, semiotics and cognitive science today.

    Instead, Somerby uses Wittgenstein as an excuse to complain that Einstein couldn't possibly have communicated anything to other people. Somerby doesn't explain why Einstein and Isaacson make no sense, because Somerby doesn't understand Wittgenstein well enough to apply his ideas to that context. That is Somerby's failure, not Einstein's and not Wittgenstein's either.

    There are methods for studying how meaning is created and shared among people. I used those methods in my own dissertation research, and I developed a methodology for comparing meaning across domains without having to define one in terms of the other. I have published numerous papers and was an expert on categorization, reference and naming, before retiring.

    It offends me that Somerby, instead of studying these aspects of human cognition, uses Wittgenstein (in isolation from subsequent philosophy and research) as a battering ram to attack science and accumulated wisdom and replace it with his own brand of nihilism.

    1. When Goedel got old, he wasn't the same as his younger self. When Wittgenstein got old, he wasn't the same as his younger self. When Somerby got old, ... .

  6. Einstein carefully defined simultaneity. Two events are simultaneous if an observer midway between them sees them both at the same time. The events don't just seem simultaneous, they are simultaneous, by definition.

    But simultaneity is not a property of the two events, it is a property of the two events and the observer. Simultaneity is thus relative to the observer.

    Einstein's train thought-experiment shows that the same two events are not simultaneous to another observer who is also midway between them. That's the "relativity of simultaneity."

    The two events don't "seem" to be simultaneous or not. They ARE simultaneous or not, relative to the observers. Einstein explained this clearly, and Isaacson did not.

    Here's an analogy. Two astronauts in interstellar space fly by each other. One guy snaps his fingers twice. To him, these two events occur in the same place -- in his space ship. To the other guy, the two events may be thousands of meters apart. Same-place is thus relative to the observer.

    Relativity of same-place isn't so hard to grasp. Relativity of simultaneity is very hard for the human brain to grasp. So it wasn't discovered until 1905 CE.

    1. First, humans had to notice that the speed of light in a vacuum is absolute while time and simultaneity cannot therefore be absolute. The guy on the train cannot make light travel faster by shining his flashlight in the direction of the train’s travel, nor slow light by shining his flaslight to the rear. That is the thing that is not intuitive for a person used to reasoning thru a Euclidean coordinate system where parallel lines never meet.

  7. I've lost track of the many recent entries of Daily Howler which promise to explain why Isaacson's account of Einstein's Special relativity does not make sense. All of them start by saying that, then repeat what was said the proviso time, and promise to reveal the nub of the question next time. Then, in the following entry, I read the same damn thing, all over again: the same lead-in, in the same words, the same failure to state exactly what's ununderstandable, and the same promise to provide it next time. This has long left the stage of self-parody.

    1. mmeo, my perception is that TDH's point (a pointless one at that) isn't so much that Einstein's theory doesn't make sense - it's a stranger one: that Einstein himself, and others who have tried to explain the theory so that ordinary people can understand it, have failed, they haven't explained the theory at all. And he also seems to have a fly up his ass because reviewers of popularizers, like Isaacson, have falsely claimed that the popularizers have actually explained the theory in an adequate manner to non-experts.

    2. A general rule of thumb is that when Bob uses the word “we” it is in the context of denigrating everyone else in the group that he claims to belong to. It’s his perverse version of that Groucho Marx quip, only in this case he doesn’t want to belong to a group in which he claims to be a member. As in “we”, “our town”, “our tribe” etc. etc. etc…. Here , Bob would like to draw us in to the shaded part of the Venn diagram that includes himself and Einstein’s teenage niece. And for all we know, the niece may well have ultimately grown into an adult with enough intellect to understand her uncle’s work. She’s now too dead to defend herself here. That would leave Bob and anyone else volunteering to join him in his little “we” circle of un-understanders to complain about this issue. The repetitiveness and beating around the bush writing noted by mmeo is likely because it is hard to describe in detail what you cannot grasp. If you read Dr. Seuss to Lucy the chimp she might be able to sign to you her confusion but not in any detail what she was confused about. That’s where Bob finds himself here, as he tries to enlist dead philosophers in his quest to convince himself and anybody listening that the word “I” means “we”.

  8. The US really has no choice other than to send President Trump to jail. Bob, apparently, simply is not up to the subject.

    1. The "US" obviously has lots of choices, many of which would not be good ones. I suppose whether the "US" should send Trump to jail is a "subject" which TDH is not currently opining on (instead he has some odd, but harmless, type of fetish about whether Einstein's theories have been adequately explained by popularizers to the general public) whether the "US" should send Trump to jail, there are myriads of other topics he isn't opining on. Maybe you could set up a blog about how the "US" should send Trump to jail, and there are probably other sites you could go to and enjoy discussion of that topic.

    2. The U.S. has been a banana republic for 4 decades (thanks Reagan).

  9. Did Einstein really come up with special relativity because he was thinking about very long trains? This is hard to believe - a train that is long enough or moves fast enough to illustrate the principle is really fantastic. More likely he started with Maxwell's equations and then the demonstration by Michelson-Morley that there was no medium carrying the waves, that is no fixed frame of reference. Then he started thinking about trains as hypothetical illustrations.