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EDDINGTON’S ECLIPSE EXPEDITION
Outline
Albert Einstein’s Conjecture Sir Arthur Eddington’s Test Popper’s Account
Einstein’s Conjecture
Einstein’s Conjecture
In 1915, Albert Einstein publishes his General Theory of Relativity (GTR).
His Special Theory of Relativity (STR) had already been published in 1905.
Einstein’s Conjecture
STR is based on two postulates. (Roughly…) The laws of physics
are invariant with respect to frame of reference.
The speed of light is constant in all inertial frames of reference.
Einstein’s Conjecture
STR was special—it did not address gravity.
GTR was intended to unite STR with Newton’s law of universal gravitation.
Einstein’s Conjecture
GTR, like STR, was considered philosophically compelling because it unified separate theories and observations in a simple, elegant way.
But neither had been empirically tested.
Einstein’s Conjecture
Many people thought GTR (which included the idea that “time is relative”) was a wild idea, on par with Marxism and Freudianism.
But the distinction, as Karl Popper sees it, is that GTR is falsifiable, for GTR predicted that the path of light would be measurably curved by massive objects.
Einstein’s Conjecture
Another way of looking at it: GTR was informative in the sense that it ruled out many possible observations, saying in effect that we will never observe certain things x, y, z.
GTR is thus a bold conjecture since if we ever do observe x, y, or z, then we can refute it.
As Godfrey-Smith and others have put it, GTR “sticks its neck out”.
GTR is precise. It is easier to refute a precise theory than a vague one.
Eddingtion’s Test
Eddington’s Test
GTR predicts that light paths (or the space through which light propagates) are curved by massive objects.
In those days, we had no easy way to test this.
Predicted curvature in most cases was too small to measure.
And in the one case in which it would be large enough to measure, there was a problem.
Eddington’s Test
The Sun is large enough to measurably curve light from distant stars.
However, the Sun is also very bright. We cannot normally see or otherwise detect stars in daylight.
Eddington’s Test
The one thing massive and local enough to test GTR is also the thing that keeps us from testing it!
If only we could blot out the sun’s light in a way that allowed us to look at distant stars which appeared to be next to it.
Eddington’s Test
The one thing massive and local enough to test GTR is also the thing that keeps us from testing it!
If only we could blot out the sun’s light in a way that allowed us to look at distant stars which appeared to be next to it.
Fortunately, we have a moon. And it sometimes passes in front of the sun, making it dark enough to detect the starlight coming from distant stars.
Eddington’s Test
GTR is falsifiable because it predicts that during an eclipse, the paths of starlight which pass near the Sun will be detectably curved.
Thus it will appear to us that the stars are in different locations.
Eddington’s Test
GTR is falsifiable because it predicts that during an eclipse, the paths of starlight which pass near the Sun will be detectably curved.
Thus it will appear to us that the stars are in different locations.
If this does not occur, GTR is refuted.
Eddington’s Test
In 1919, Eddington goes to the island of Principe to critically test GTR by measuring the apparent positions of stars during the eclipse…
GTR passes the test!
Popper’s Account
GTR passes the test.
Does this mean GTR was confirmed?
GTR passes the test.
Does this mean GTR was confirmed?
Not according to Karl Popper.
GTR survived an attempted refutation, which means it might be true.
Indeed, any theory which predicted the stars would appear just where they were was falsified.
But this does not mean we have confirmed GTR.
GTR has survived an attempted refutation.
GTR has survived an attempted refutation.
Its distinction lies in its being falsifiable, bold/risky, having been critically tested in an attempted refutation, and having survived that attempted refutation.
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