In the late 19-teens, Albert Einstein had
a new hammer, and he was in search of nails
to hit.
He had just developed a new and more powerful
mathematical description of gravity , and
was using it to make predictions willy-nilly.
First, Einstein checked that his new description
matched up with the previous state-of-the-art
description of gravity, newton’s law, for
situations where newton’s law agreed with
experiments.
And it did.
So far so good.
Then Einstein plugged in the orbit of Mercury
and got a prediction that correctly matched
the experimental observations of the day;
observations which had an anomaly that couldn’t
be explained with Newton’s law of gravitation.
He plugged in starlight passing by the sun
and got a prediction that it should bend because
of the sun’s gravity; this was later confirmed.
He plugged in starlight leaving large stars
and got a prediction that the spectrum of
the light should be redshifted as it climbs
out of the gravity well; this was later confirmed.
He plugged in empty space and got a prediction
that waves of gravitation should propagate
through it; this, too, was later confirmed.
And he plugged in the universe and got a prediction
that it should be static and unchanging.
Which was wrong.
Now, the general understanding at the time
was that the universe didn’t expand or contract,
and while there were starting to be rumors
that distant nebulas were consistently moving
away from us , Einstein was firmly in the
“static universe” camp.
And it just so happened that when Einstein
did his calculation about the universe, he
made a small but significant technical mistake
that implied that the universe couldn’t
be expanding or contracting.
I suspect Einstein probably didn’t catch
the mistake for two reasons: because tensor
calculus is hard and annoyingly subtle, and
because he agreed with the result so had no
reason to question it.
This is all the more significant because the
mistake ultimately meant that his equations
predicted the universe couldn’t have anything
in it at all, and Einstein had to find a totally
different clever mathematical trick in order
for his equations to describe a universe that
did have stuff in it in spite of his mistaken
calculation.
Anyway a few years later, Russian physicist
Alexander Friedmann plugged the universe into
Einstein’s equations, and he didn’t make
the mistake Einstein did.
He got a prediction that the universe could
either be expanding, or contracting, or static,
depending on how much stuff there was in it
and the balance of matter and energy.
But Einstein still didn’t realize that he
had made a mistake: instead, he published
a criticism of Friedmann’s work, justifying
his critique with the same erroneous calculation
as before.
So Friedmann wrote Einstein a private letter,
graciously (but firmly) explaining to Einstein
the correct calculation, and (again graciously)
asking Einstein to either show him where HE
was wrong, or publish a correction.
And Einstein eventually saw that Friedmann
was right - so he admitted it and published
a retraction of his previous criticism.
Turns out the equations of general relativity
could describe an expanding or contracting
universe after all.
The scientific end to this story is that Friedmann
died before the conclusive experimental data
came in and showed that the universe is expanding,
so he never knew which possible outcome of
his equation was right.
And Einstein died before the conclusive experimental
evidence came in that showed that the mathematical
trick he had used to adjust for his mistake
turned out to be super useful and is now used
to describe dark energy.
So Einstein was famously upset about the whole
episode; the story is typically written to
suggest that he simply regretted being wrong.
And maybe that’s the truth.
But speaking as a physicist - and to be clear,
this is purely my own personal speculation
- I kind of wonder if Einstein also was kicking
himself in the pants because if he hadn’t
made that silly math error, maybe he could
have arrived, years earlier, at the same equations
as Friedmann (and which are now called the
Friedmann equations, and are the foundation
of our modern understanding of the large-scale
structure of the universe).
But I’m not entirely sure he would have
been able to do what Friedmann did - because
all people, even scientists, have biases,
and biases tend to be held so strongly and
so deeply that they not only blind us to alternatives,
they blind us to their existence.
The beauty of keeping an open, rational and
scientific mindset is that when one of your
biases is wrong, you’re more willing to
look at the evidence, see that you’re wrong,
and admit it.
But that’s really hard to do, even - or
maybe especially - for somebody like Einstein.
And I wonder if Einstein would have been able
to see past his bias about the static nature
of the universe without outside help.
Einstein, like all of us, was human after
all.
What we can take from Einstein’s actions
in this story is this : we can understand
that we can be wrong, and when we are, graciously
admit it.
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